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Why don't stem cell therapies use a virus to deliver gene editing sequences to stem cells instead of the harvesting-transformation-transplant route.
I thought it might be because of a lack of specificity on the part of the viruses, but then I saw phage display techniques that would seem to make that a non-issue.
I thought it might be trans-cytosis or getting the phages out of the blood-stream and into contact with the stem cells. I haven't found an easy solution to this hurdle, but it doesn't seem to be insurmountable.
I think the main issue is regulatory? Perhaps a lack of precedents in this area. What do you think of my analysis? Is this idea even feasible?
Stem cell therapies do in fact utilise viruses. In the examples cited, the stem cells were infected by viruses in vitro, genetically modified, and then reintroduced into the target as autologous transplants. The main issue at hand is that live viruses introduced directly would be targeted and destroyed by the immune system, which greatly reduces their efficacy in causing transformation of cells.
In a recent Nature paper, zinc finger nucleases were used to target and disrupt the CCR5 or CXCR4 gene, which greatly reduces the efficiency of HIV binding to CD4+ T cells. The zinc finger nucleases were introduced into the cells using an adenovirus vector.
Generation of cxcr4 ZFN adenovirus and CGW-siX4s lentiviral vectors. The CXCR4 targeting locations of siX4s and ZFN are shown in Supplementary Figure S1.
This technique was then used in a number of clinical trials to modify hematopoietic stem cells using zinc finger nucleases, as summarised in this review paper. The recent advent of CRISPR-Cas systems will probably lead to an increase in similar techniques, due to the higher specificity and ease of engineering of Cas9-based nucleases.
Thanks to you guys I googled, "stem cell virus animals" and found some promising links! I appreciate you guys emphasizing immunological response. I was hoping that the virus would be effective enough to work on the first shot and thereby avoid most of the immunological complications. However it seems that the second generation of adenovirus vectors in animal models was abandoned for just that reason: source - NCBI.
Here is a nice excerpt regarding animal models:
“third-generation adenovirus vectors”: This research focuses on the development of improved production systems for gutless adenovirus vectors and their use for the efficient introduction of large or multiple transgenes into human progenitor and stem cells with minimal vector-related toxicity. In addition to the use of regular third-generation adenovirus vectors for the transient genetic modification of target cells, we have embarked on the generation of new vector types for stable transgene expression in transduced target cells using locus/site-specific transgene integration or homologous recombination. For example, we have generated new adenovirus/adeno-associated virus vectors. These vectors stably integrate into a specific locus on human chromosome 19 and are capable of genetically complementing dystrophin-deficient human myoblasts.
-Leeds Universitair (NZ)
Why are there so many drugs to kill bacteria, but so few to tackle viruses?
Rachel Roper works for East Carolina University on virus vaccines. This article supports scientific research and I do scientific research. Like most scientists, I have received external funding for my research, government and industry funds.
Christine Carson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
University of Western Australia provides funding as a founding partner of The Conversation AU.
The Conversation UK receives funding from these organisations
As the end of the second world war neared, mass production of the newly developed antibiotic penicillin enabled life-saving treatment of bacterial infections in wounded soldiers. Since then, penicillin and many other antibiotics have successfully treated a wide variety of bacterial infections.
But antibiotics don’t work against viruses antivirals do. Since the outbreak of the coronavirus pandemic, researchers and drug companies have struggled to find an antiviral that can treat SARS-CoV-2, the virus that causes COVID-19.
Why are there so few antivirals? The answer boils down to biology, and specifically the fact viruses use our own cells to multiply. This makes it hard to kill viruses without killing our own cells in the process.Remdesivir is one antiviral researchers are investigating to treat COVID-19, but it has shown mixed results in clinical trials. Ulrich Perrey/Pool/Reuters
Growing hope: New organs? Not yet, but stem cell research is getting closer
Kidney (Image by Lori O'Brien/Andy McMahon Lab, illustration by Mira Nameth)
If you lose a limb, it’s lost for life. If you damage a kidney, you won’t grow a new one. And if you have a heart attack, the scars are there to stay.
But regenerative medicine is poised to change all of this. Building new tissue is within sight, and USC scientists are among the field’s pioneers.
More than 100 scientists, engineers and doctors are united under what’s called the USC Stem Cell initiative. They’re already moving stem cells out of the lab and toward patient care. The potential is exciting: USC researchers have contributed to clinical trials of stem cell approaches to treating colorectal cancer, spinal cord injury, vision problems, HIV/AIDS and Alzheimer’s disease. They’ve also used stem cells to uncover important insights about kidney disease, ALS, arthritis, Zika virus, birth defects and a wide variety of injuries.
Major funders and USC donors have provided hundreds of millions of dollars to support the work. That investment and vote of confidence enables USC Stem Cell scientists to collaborate with other leading universities, biotech companies and key partners to translate their laboratory discoveries into patient cures.
It hasn’t been easy. Scientists are evaluating some stem cell-based therapies through clinical trials, but so far, few treatments have made it to patients. Beyond scientific inspiration, taking treatments from lab bench to patient bedside requires immense amounts of time, money and, sometimes, a bit of luck. It also means working together with other scientists across boundaries.
“Regenerative medicine is still a relatively young field, and it’s still early days,” says Andy McMahon, director of the Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at USC. “When it comes to that final phase of translating stem cell discoveries into clinical therapies for patients, it won’t be individual universities working in isolation. It will be multi-institutional collaborations with our neighbors that will transform medicine over the course of the 21st century.”
The Kidney in Miniature
So far, scientists haven’t been able to create complete adult human kidneys—they’re too complex.
At USC, though, McMahon’s lab is coaxing stem cells to organize themselves into simplified, mini versions of this elaborate organ.
Each healthy human kidney is made up of a million cellular filters called nephrons, which pull wastes out of blood, among other responsibilities. McMahon and his colleagues are making tiny organs (scientists dub them “organoids”) composed of a single nephron—a convenient size for testing potential drugs.
With help from USC’s Chang Stem Cell Engineering Facility, McMahon’s lab has successfully produced organoids carrying the same genetic mutation that causes polycystic kidney disease, the most common genetic cause for kidney failure. Because kidney organoids develop cysts similar to those seen in the disease, scientists can observe how the disease progresses and develop therapies that may halt or reverse symptoms.
Zhongwei Li, an assistant professor of medicine, and stem cell biology and regenerative medicine, is also hard at work growing kidney organoids. There are only 18,000 donor kidneys available each year for more than 400,000 patients who need them, Li explains. He ultimately wants to create organs for transplantation using special stem cellsprogenitor cells that could develop and organize themselves into kidney tissue.
“USC is a perfect place to study the kidney,” says Li, an assistant professor of medicine, and stem cell biology and regenerative medicine.
Healing Hearts/>Heart tissue (Image by Megan McCain, illustration by Mira Nameth)
If you worry about dying in an earthquake, shark attack or lightning strike, don’t waste your energy. You’re far more likely to die of heart disease. Every year, about 610,000 people in the U.S. die of heart disease. That’s one in four deaths. And heart disease is the leading cause of death worldwide.
Cardiac tissue that has died after a heart attack doesn’t come back—it just forms a scar. Studies have shown that doctors can safely inject stem cells into damaged heart tissue, but there’s no clear sign that these injections restore the heart.
At USC, two stem cell researchers are tackling heart repair from other directions.
In the lab of Henry Sucov, researchers aim to harness the heart’s innate ability to heal. They’re studying a regenerative type of heart muscle cell called a mononuclear diploid cardiomyocyte. Newborns have large numbers of these cells, but adults have relatively few, so the adult body has trouble regenerating heart tissue after injury.
When they looked for these cells in mice, they found that some mice had more of these cells than other mice did. They traced that variation to a gene called Tnni3k. Their research suggests that blocking the gene might boost numbers of regenerative cells.
If scientists can create prescription drugs to modulate the activity of the gene, these medications could encourage more regenerative cells to develop in the heart, says Sucov, a professor of stem cell biology and regenerative medicine, integrative anatomical sciences, and biochemistry and molecular biology. “This could improve the potential for regeneration in adult hearts, as a preventive strategy for those who may be at risk for heart failure.”
In Megan McCain’s lab at the USC Viterbi School of Engineering, researchers are building human heart tissue. They not only study how the heart tissue works, but also use it to test how it responds to potential drugs.
The work poses problems that call for the mindset of an engineer. It turns out that heart muscle cells don’t fully mature in the typical laboratory environment for growing cells—a petri dish filled with warm, nutritious liquid. To develop properly, heart muscle cells need to get some exercise by contracting in the rhythm of a beating heart. To do this, they need structure and resistance, which the lab’s researchers provide in the form of a tiny scaffold called a chip.
This “heart on a chip” reproduces natural human heart tissue on a small scale in the lab.
Ultimately, McCain hopes the technology contributes to precision medicine. Scientists could test medications on a patient’s own heart tissue on a chip. Eventually, this could enable doctors to customize dosing and choose drugs that pose the fewest side effects to each patient.
Stronger Bones/>Mouse ribs (Image by Francesca Mariani, illustration by Mira Nameth)
According to common wisdom, bones heal. In reality, every year about 5 million people in the U.S. sustain fractures that fail to mend. From elderly people undergoing total hip or knee replacements to soldiers injured by explosions or gunshots, many patients have bone defects that are too severe to repair. To complicate matters, everything from diabetes to the normal aging process can undermine bone’s ability to heal.
USC researchers hope to one day use stem cells to build new bone in patients with severe or non-healing injuries. Jay R. Lieberman, who chairs the Department of Orthopaedic Surgery at the Keck School, teamed up with Gage Crump and Francesca Mariani, two faculty members from the Department of Stem Cell Biology and Regenerative Medicine, to advance the science.
The team has made a promising start in the lab. They discovered that healing bone requires a special type of repair cell, which they named an ossifying chondrocyte. Now the researchers are studying a substance that stimulates these repair cells to fix bone.
Unlocking Genetic Diabetes
Nearly 10 percent of Americans, or 30 million people, have a form of diabetes. Diabetes happens when glucose levels rise in the blood. Insulin, a hormone made by the pancreas, helps the body pull glucose from blood and into the cells where it’s needed. But sometimes the pancreas doesn’t make enough insulin or the body can’t use insulin well.
Oftentimes, in diabetes, the special cells in the pancreas that make insulin—called beta cells—are attacked by the immune system or wear out. Researchers worldwide are looking at ways to rebuild them.
At Children’s Hospital Los Angeles (CHLA), researcher Senta Georgia aims to use stem cells to help patients with genetic forms of diabetes.
Her lab is focusing on a young CHLA patient with a rare genetic disease known as enteric anendocrinosis. The disease causes chronic diarrhea because patients lack certain gastrointestinal cells that produce hormones, and they eventually lose their beta cells as well, causing diabetes.
With the help of USC’s Chang Stem Cell Engineering Facility, Georgia’s team took stem cells derived from the patient’s skin and edited the cells’ genome to fix the genetic mutation behind the problem. They then used these genetically corrected stem cells to generate new insulin-producing cells.
The goal is to eventually transplant these insulin-producing cells back into the patient to reverse the diabetes—providing a tailor-made cell replacement therapy.
“We hope that this study can create a precedent for how to generate new insulin cells for patients with genetic forms of diabetes,” says Georgia, assistant professor of pediatrics and stem cell biology and regenerative medicine at the Keck School of Medicine of USC.
“Our faces are our identities, and the first thing you see when you look at someone is his or her face,” says Yang Chai, director of the Center for Craniofacial Molecular Biology at the Herman Ostrow School of Dentistry of USC. But when someone has a cleft lip or other facial deformity or trauma, it can be devastating.
Chai aims to find treatments for some of the most common craniofacial birth defects and injuries. To do that, he has tapped into a rich source of stem cells: the pulpy interior of the teeth.
Fueled by a $12 million grant from the National Institutes of Health (NIH), he’s working with researchers from the Keck School of Medicine and institutions from Stanford to City of Hope on the project.
They’ve already used these stem cells to generate the unique, high-density bone that makes up the skull. If these stem cells can effectively repair four-centimeter holes in the skulls of animals, the research project will advance the treatment into a clinical trial for patients with bone deficiencies due to injuries, dental problems or birth defects.
One birth defect USC scientists are tackling is called craniosynostosis. The rare-but-serious problem occurs when sections of a baby’s skull fuse together at joints called sutures, restricting the developing brain and disrupting vision, sleep, eating and IQ. To treat this condition, growing children must undergo repeated skull-expanding surgeries—which are as dangerous and painful as they sound.
Chai is one of at least a dozen USC stem cell researchers working to help these children. His lab has already identified a critical stem cell population that normally resides in the skull sutures, and discovered how to manipulate these stem cells to form new sutures in mice.
“This is something that truly has to be done through a collaborative effort,” Chai says. “USC provides the best environment for collaborative research, which has led to NIH funding and publications as the result of these collaborations. These collaborative studies will fundamentally change the way to provide health care to our patients.”
Vaccines and Anti-viral Drugs for Treatment
In some cases, vaccines can be used to treat an active viral infection. The concept behind this is that by giving the vaccine, immunity is boosted without adding more disease-causing virus. In the case of rabies, a fatal neurological disease transmitted via the saliva of rabies virus-infected animals, the progression of the disease from the time of the animal bite to the time it enters the central nervous system may be 2 weeks or longer. This is enough time to vaccinate an individual who suspects that they have been bitten by a rabid animal, and their boosted immune response is sufficient to prevent the virus from entering nervous tissue. Thus, the potentially fatal neurological consequences of the disease are averted, and the individual only has to recover from the infected bite. This approach is also being used for the treatment of Ebola, one of the fastest and most deadly viruses on earth. Transmitted by bats and great apes, this disease can cause death in 70–90 percent of infected humans within 2 weeks. Using newly developed vaccines that boost the immune response in this way, there is hope that affected individuals will be better able to control the virus, potentially saving a greater percentage of infected persons from a rapid and very painful death.
Another way of treating viral infections is the use of antiviral drugs. These drugs often have limited success in curing viral disease, but in many cases, they have been used to control and reduce symptoms for a wide variety of viral diseases. For most viruses, these drugs can inhibit the virus by blocking the actions of one or more of its proteins. It is important that the targeted proteins be encoded by viral genes and that these molecules are not present in a healthy host cell. In this way, viral growth is inhibited without damaging the host. There are large numbers of antiviral drugs available to treat infections, some specific for a particular virus and others that can affect multiple viruses.
Antivirals have been developed to treat genital herpes (herpes simplex II) and influenza. For genital herpes, drugs such as acyclovir can reduce the number and duration of episodes of active viral disease, during which patients develop viral lesions in their skin cells. As the virus remains latent in nervous tissue of the body for life, this drug is not curative but can make the symptoms of the disease more manageable. For influenza, drugs like Tamiflu (oseltamivir) (Figure 3) can reduce the duration of “flu” symptoms by 1 or 2 days, but the drug does not prevent symptoms entirely. Tamiflu works by inhibiting an enzyme (viral neuraminidase) that allows new virions to leave their infected cells. Thus, Tamiflu inhibits the spread of virus from infected to uninfected cells. Other antiviral drugs, such as Ribavirin, have been used to treat a variety of viral infections, although its mechanism of action against certain viruses remains unclear.
Figure 3. (a) Tamiflu inhibits a viral enzyme called neuraminidase (NA) found in the influenza viral envelope. (b) Neuraminidase cleaves the connection between viral hemagglutinin (HA), also found in the viral envelope, and glycoproteins on the host cell surface. Inhibition of neuraminidase prevents the virus from detaching from the host cell, thereby blocking further infection. (credit a: modification of work by M. Eickmann)
By far, the most successful use of antivirals has been in the treatment of the retrovirus HIV, which causes a disease that, if untreated, is usually fatal within 10–12 years after infection. Anti-HIV drugs have been able to control viral replication to the point that individuals receiving these drugs survive for a significantly longer time than the untreated.
Anti-HIV drugs inhibit viral replication at many different phases of the HIV replicative cycle (Figure 4). Drugs have been developed that inhibit the fusion of the HIV viral envelope with the plasma membrane of the host cell (fusion inhibitors), the conversion of its RNA genome into double-stranded DNA (reverse transcriptase inhibitors), the integration of the viral DNA into the host genome (integrase inhibitors), and the processing of viral proteins (protease inhibitors).
Figure 4. HIV, an enveloped, icosahedral virus, attaches to the CD4 receptor of an immune cell and fuses with the cell membrane. Viral contents are released into the cell, where viral enzymes convert the single-stranded RNA genome into DNA and incorporate it into the host genome. (credit: NIAID, NIH)
When any of these drugs are used individually, the high mutation rate of the virus allows it to easily and rapidly develop resistance to the drug, limiting the drug’s effectiveness. The breakthrough in the treatment of HIV was the development of HAART, highly active anti-retroviral therapy, which involves a mixture of different drugs, sometimes called a drug “cocktail.” By attacking the virus at different stages of its replicative cycle, it is much more difficult for the virus to develop resistance to multiple drugs at the same time. Still, even with the use of combination HAART therapy, there is concern that, over time, the virus will develop resistance to this therapy. Thus, new anti-HIV drugs are constantly being developed with the hope of continuing the battle against this highly fatal virus.
The study of viruses has led to the development of a variety of new ways to treat non-viral diseases. Viruses have been used in gene therapy. Gene therapy is used to treat genetic diseases such as severe combined immunodeficiency (SCID), a heritable, recessive disease in which children are born with severely compromised immune systems. One common type of SCID is due to the lack of an enzyme, adenosine deaminase (ADA), which breaks down purine bases. To treat this disease by gene therapy, bone marrow cells are taken from a SCID patient and the ADA gene is inserted. This is where viruses come in, and their use relies on their ability to penetrate living cells and bring genes in with them. Viruses such as adenovirus, an upper respiratory human virus, are modified by the addition of the ADA gene, and the virus then transports this gene into the cell. The modified cells, now capable of making ADA, are then given back to the patients in the hope of curing them. Gene therapy using viruses as carrier of genes (viral vectors), although still experimental, holds promise for the treatment of many genetic diseases. Still, many technological problems need to be solved for this approach to be a viable method for treating genetic disease.
Another medical use for viruses relies on their specificity and ability to kill the cells they infect. Oncolytic viruses are engineered in the laboratory specifically to attack and kill cancer cells. A genetically modified adenovirus known as H101 has been used since 2005 in clinical trials in China to treat head and neck cancers. The results have been promising, with a greater short-term response rate to the combination of chemotherapy and viral therapy than to chemotherapy treatment alone. This ongoing research may herald the beginning of a new age of cancer therapy, where viruses are engineered to find and specifically kill cancer cells, regardless of where in the body they may have spread.
A third use of viruses in medicine relies on their specificity and involves using bacteriophages in the treatment of bacterial infections. Bacterial diseases have been treated with antibiotics since the 1940s. However, over time, many bacteria have developed resistance to antibiotics. A good example is methicillin-resistant Staphylococcus aureus (MRSA, pronounced “mersa”), an infection commonly acquired in hospitals. This bacterium is resistant to a variety of antibiotics, making it difficult to treat. The use of bacteriophages specific for such bacteria would bypass their resistance to antibiotics and specifically kill them. Although phage therapy is in use in the Republic of Georgia to treat antibiotic-resistant bacteria, its use to treat human diseases has not been approved in most countries. However, the safety of the treatment was confirmed in the United States when the U.S. Food and Drug Administration approved spraying meats with bacteriophages to destroy the food pathogen Listeria. As more and more antibiotic-resistant strains of bacteria evolve, the use of bacteriophages might be a potential solution to the problem, and the development of phage therapy is of much interest to researchers worldwide.
What is Gene Therapy
Gene therapy is the insertion of normal DNA directly into a cell in order to correct genetic defects. The two main approaches to gene therapy are either introducing a gene that encodes for a functional protein or transferring of an entity that alters the expression of a gene in the genome.
- During the introduction of a functional gene into a genome, relatively large pieces of genes (>1kb) are introduced into the cell along with promoter sequences that initiate gene expression. Signaling sequences that direct RNA processing must also be introduced along with the protein-coding region.
- In order to alter the gene expression of an endogenous gene in the genome, relatively short parts of genetic material (20-50 bp) that are complementary to the mRNA of the defective gene are introduced. The alteration of gene expression can be achieved by blocking mRNA processing, translational initiation or leading to the destruction of mRNA.
Efficient delivery methods such as vectors facilitate gene transfer into the cells during gene therapy. Two types of vectors are used in gene therapy: viral vectors and non-viral vectors. The nonviral-based delivery systems can be plasmids or chemically-synthesized oligonucleotides. Optimal vector selection is based on several parameters:
- Type of the target cell and its characteristics
- The longevity of expression required
- The size of the genetic material transferred
After replication, viral RNA can't continue an infection until it is packaged up into a mature virus and gets outside of the host cell. This requires special packaging proteins. (In coronavirus, these proteins do double duty by also helping the viral RNA link up with its copying enzymes.) This packaging step would seem to provide a great opportunity for targeted therapy, as disrupting it should limit the amount of functional virus that gets made and exported from any particular cell.
But drugs that try to block viral packaging are rare—Racaniello can only think of one, a treatment for Hepatitis B that causes the mature virus particles to form without any genetic material inside. "That's been a very unusual antiviral," Racaniello said. "There's no other like it." Part of the problem, he said, is that structural proteins like this are present in high numbers, since they're part of every single virus particle that's produced. And you have to interfere with all these copies to be effective.
Another problem is that the interactions among proteins and genetic material during packaging of a virus tend to involve extensive contacts between multiple molecules. These are a bit harder to disrupt specifically, and doing so may require large molecules that don't diffuse in and out of cells well. So, while we know which protein binds to the RNA and helps package it inside the virus particle, this protein is not an obvious target for therapies.
It's also hard to disrupt newly packaged viruses as they are moved out of the cell. Once packaged, coronaviruses leave their host cell via an export system that's normally used to send material to the cell's surface (a process called exocytosis). This process is fairly generic—it works with a huge variety of proteins in addition to those encoded by coronaviruses—making it vital for cell survival. As a result, there are not many places where we can intervene without shutting down exocytosis in healthy cells as well.
The Good That Viruses Do
It is astonishing that with our more than thirty-five combined years of working in the field of virology, we continue to read on a regular basis about novel emerging viruses infecting species from all three domains of life. The focus of our research is on single-stranded DNA viruses. Even for this apparently small group of viruses, many new members are identified each year that need to be characterized, providing seemingly endless opportunities for new research directions. Indeed, studying these new viruses does not end with characterization of their physical properties or disease-causing phenotypes, because many have the potential to be developed into useful biologics with therapeutic benefits to humans. Our experience as virologists suggests that the use of “good” viruses is common practice. If a survey were to ask nonvirologists for their opinions about viruses, the word “good” would be unlikely to arise. Instead, words such as “disease,” “infection,” “suffering,” or “life-threatening” would likely dominate, as people primarily think of viruses such as HIV, Ebola virus, Zika virus, influenza virus, or whatever new outbreak is in the news. However, as we are now finding out, not all viruses are detrimental to human health. In fact, some viruses have beneficial properties for their hosts in a symbiotic relationship (1), while other natural and laboratory-modified viruses can be used to target and kill cancer cells, to treat a variety of genetic diseases as gene and cell therapy tools, or to serve as vaccines or vaccine delivery agents. The ability to treat diseases using viruses, often referred to as virotherapy, has become the subject of intensive research in recent years.
Cancer is one of the leading causes of death worldwide. According to the World Health Organization, about 8.8 million people died from cancer in 2015. Conventional treatment of cancer is based primarily on chemotherapy, radiation therapy, and surgery. Although these therapies have increased patient survival rates, their efficacy is often limited depending on the type of cancer being treated. In addition, significant side effects occur because noncancerous cells are also targeted by these treatment modalities. Recurrence after successful treatment is also of concern. An emerging field in cancer therapy comprises alternative therapies that use viruses to kill cancer cells selectively. The idea for this approach came through early observations of cancer regression in patients suffering from unrelated viral infections (2). In the past two decades, viruses from a variety of different families (e.g., Adenoviridae, Herpesviridae, Rhabdoviridae, Parvoviridae, Picornaviridae, Reoviridae, and Poxviridae) have been studied for their potential use as anticancer agents (3). Due to their tropism for tumors and their ability to replicate selectively in and eventually lyse cancer cells without harming noncancerous cells, they are referred to as oncolytic viruses. Currently, multiple phase I to phase III clinical trials are ongoing for the treatment of various cancer types, including hepatocellular carcinoma, glioblastoma multiforme, colorectal cancer, and cancers of the lung, breast, prostate, pancreas, bladder, and ovaries (4). In 2015, the first oncolytic virus therapy based on a herpesvirus was approved by the US Food and Drug Administration and European Medicines Agency for the treatment of melanoma lesions in the skin and lymph nodes (5). In the near future we expect to see that the successful completion of several clinical trials will lead to the approval of additional oncolytic virus therapies.
In contrast to oncolytic virus therapies, where the treatment is based on virus replication and cell death, nonreplicating viruses are being utilized as vectors for corrective gene delivery. The goal of virus-mediated gene therapy is the delivery and expression of therapeutic genes to desired target cells to restore the function of a defective gene for the treatment of monogenetic disorders. Viral gene therapy uses the natural capacity of virus particles to protect the encapsidated nucleic acid from degradation and to deliver the DNA to the nucleus. For the ideal gene therapy vector the viral wild-type genome is almost entirely substituted with a recombinant transgene expression cassette. This aspect is a major difference compared with the oncolytic viruses used in anticancer therapies, which encode many viral genes. In hundreds of ongoing clinical trials, the most commonly used vectors for gene therapy are adenoviruses, retroviruses/lentiviruses, and adeno-associated viruses (AAVs) (6). Each system has its pros and cons that must be considered prior to use to ensure efficient gene delivery and expression for clinical success. Recent successes in various clinical trials have been achieved especially using lentiviral and AAV vectors (6). Lentiviral vectors are primarily used for ex vivo hematopoietic gene delivery, where patient cells are removed and transduced with the viral vector, resulting in modified cells that can be transplanted back to the patient after thorough screening of the transplant. The pre-administration screening allows the identification of mutagenic integration sites of proviral genomes in the cellular genome of the transplant. These screenings were incorporated into clinical trial design after the discovery of insertional oncogenesis leading to T cell leukemia in patients undergoing retroviral gene therapy. In contrast, AAV vectors are used mainly for in vivo gene therapy applications, where viral vector particles are injected intravenously, intramuscularly, intracranially, intravitreally, or subretinally, depending on the desired target cells. Notably, an AAV1 vector for the treatment of lipoprotein lipase deficiency was approved as the first viral gene therapy medical product in the Western world by the European Medicines Agency in 2012 (7). This approval led to a massive surge of industry interest and the growth of the AAV biotechnology field, including the raising of $2 billion by just ten companies in 2015 for the development of AAV gene therapies. Another example of a successfully completed AAV vector clinical trial involves an AAV8 vector expressing human factor IX for the treatment of hemophilia B. A single injection of these AAV particles resulted in a more than 90% reduction in the number of bleeding episodes in study participants over a period of more than three years, with no toxic effects (8). One downside is that AAV gene therapy is currently the most expensive therapeutic, at ∼$1 million per treatment. Certainly, continued effort is required to make it affordable. Another problem with AAV gene therapy is the potential for immune responses against the virus capsid as well as the therapeutic gene products that are produced. Ten to fifteen years ago, it was believed that AAVs did not elicit an immune response. However, applications in large animals, nonhuman primates, and humans have since proved that this is untrue. Thus, in order to maintain the expression of the therapeutic protein, different strategies have been developed to avoid or suppress these immune responses (9).
In gene therapy scenarios, it is important to avoid immune responses to the virus capsid and transgene product. In contrast, for viral vaccines, elicitation of immune responses, including the generation of neutralizing antibodies, is the goal. To induce a protective immune response, patients are injected with an attenuated or inactivated virus or with specific viral antigens. For patients with an immune deficiency disorder, passive immunization by direct administration of antibodies can be done. However, this immunity is temporary, lasting only for a few weeks or months. Therefore, gene therapy vectors have been developed that express broadly neutralizing antibodies that can be used for the long-term treatment of HIV and influenza as well as for cancer therapy (10).
Some of the viruses infecting humans are indeed capable of causing severe and often lethal diseases, but other viruses can be manipulated to be beneficial to human health. These viruses offer the potential to cure cancer, correct genetic disorders, or fight pathogenic viral infections. In addition, viruses are used in many genetic studies to determine molecular mechanisms, are used as insecticides, and have been reported to increase drought tolerance in some plants. Virologists must strive to downplay the “bad” reputation of viruses and promote dialogue on the many “good” things that they can do.
There is a lot of research on investigating how stem cells can be used to treat diseases. It is expected that, in the future, stem cell therapies will be developed for many types of diseases for which there are no effective treatments at the moment.
Embryonic stem cells: ↑ Cell that can form all different cell types present in the body.
Ectodermal stem cells: ↑ Cell that forms ectodermal cells, such as skin cells, neurons (brain cells).
Endodermal stem cells: ↑ Cell that forms endodermal cells, such as lung cells, thyroid cells, and cells of the pancreas.
Mesodermal stem cells: ↑ Cell that forms mesodermal stem cells (mesenchymal stem cells and hematopoietic stem cells).
Hematopoietic stem cells: ↑ Cell that forms red blood cells and different types of white blood cells.
Autoimmune diseases: ↑ Disease in which the immune system attacks the own body.
Mesenchymal stem cells: ↑ Cell that forms fat cells, bone cells, cartilage cells, and muscle cells.
In vitro fertilization: ↑ A technique that is used to fertilize egg cells with sperm outside the body.
Culture dish: ↑ Plastic dishes that are used for growing cells in the laboratory.
Why don't stem cell therapies use viruses? - Biology
People hospitalized with severe symptoms from the coronavirus are given medicine to bring down the fever and fluids to keep them hydrated, generally by intravenous tube. Some patients are connected to a ventilator: a mechanical device that helps them breathe.
This menu of treatments is called supportive care, and despite the lukewarm-sounding name, there is no question that it saves lives.
But as for waging a direct attack against this virus, and most other viruses, there are no drugs. The human immune system is on its own.
The reasons involve biology and, to a lesser extent, money. Drug companies have developed treatments for a handful of viruses in the last few decades, such as HIV and the flu, but the arsenal is minimal when compared with all the antibiotics we have for treating bacteria. Remember that viruses are not bacteria, so antibiotics are no help.
The main difficulty is that viruses are technically not alive, instead depending on the “machinery” inside human cells to reproduce, said Zachary A. Klase, associate professor of biology at the University of the Sciences. So a drug that targets any part of that parasitic cycle could harm the patient in the process.
“You want something that targets the sickness and not you,” he said. “You need to look for the special things that only the virus is doing."
A few of the enzymes used by various viruses are distinct enough from their human counterparts that they can be targeted without harming the patient, said Megan Culler Freeman, a fellow in the pediatrics department at the University of Pittsburgh. That is how antiviral drugs work against HIV, for example. But even then, such drugs do not eliminate the virus, but instead keep it under control, she said.
Another reason viruses are so hard to treat with drugs is their wide variety, Klase said.
Like cars and boats
Bacteria all are related to each other, at least distantly, and share some common characteristics, such as having a cell wall. So a drug that works against one kind of bacteria, say, by disrupting that cell wall, often works against another. (That is what is meant by “broad-spectrum” antibiotics, though lately, those tried-and-true weapons have been overused, leading certain bacteria to develop resistance.)
Certain classes of viruses, on the other hand, are fundamentally different from each other. Some use RNA as their genetic code, for example, while others use DNA. Some are surrounded by an envelope, others not.
A good analogy is to imagine that bacteria are about as similar to each other as various kinds of cars, Klase said. Various classes of viruses, on the other hand, can be as distinct from each other as cars and boats.
That’s where the money issue comes in. Developing a new drug for each unrelated virus requires a fresh commitment of time and resources.
“A drug company would rather have one drug that’ll cure everything than to have to have 100 drugs that they’re going to have to sell a bit of at a time for each different problem," Klase said.
That has not kept pharmaceutical companies from testing drugs for one virus to see whether they work against another. With the new coronavirus, for example, scientists have been testing a drug called remdesivir, which was originally developed to treat Ebola. But it did not work very well against Ebola, and results so far against the coronavirus are unclear.
The interest in a coronavirus treatment is so keen that misinformation has a way of spreading much like the microbe itself. Earlier this week, Johnson & Johnson issued a statement to dispel rumors that one of its antiviral drugs showed promise. The company said that it was screening a variety of antiviral compounds against the coronavirus, but that so far there is “no evidence” that darunavir, the drug that sparked the rumors, has any effect.
In fairness to the scientists, they have not been at this problem for very long.
Bacteria were first observed under a microscope in 1683. The existence of viruses, which can be less than one-tenth the size of bacteria, was not verified until more than 200 years later.
And even then, scientists could not see them. In 1892, Russian scientist Dmitri Ivanovsky reported he had extracted fluid from a diseased tobacco plant and run it through a type of filter that was known to remove bacteria. He then demonstrated that the filtered fluid could be used to infect healthy plants. Some invisible agent — which would not be seen until the advent of electron microscopes a few decades later — was somehow transmitting disease.
The ‘care cure’
Effective antibiotics have been around for close to a century. Antiviral drugs have come along only in the last few decades, and only for a handful of serious threats.
And they do not always help. Timing is important. Antiviral drugs can lessen the duration of the flu, for example, but only if given early in the course of the disease. By the time a person develops severe symptoms, antiviral drugs are of little use, said Freeman, the Pitt physician.
That might also hold true for the new coronavirus, but more research is sorely needed, said Freeman, who studied the biology of a different coronavirus, SARS, while a Ph.D. student at Vanderbilt.
“It’s important to be able to learn these things ahead of a disaster so we’ll have tools in our toolbox,” Freeman said.
Multiple teams of researchers also are at work on vaccines for the new coronavirus, teaching the human immune system to make its own medicine: antibodies. The first stages of safety testing already are underway, but it will be at least a year before such a vaccine is approved for widespread use, experts predict.
For now, that leaves supportive care. But as University of Pennsylvania medical historian David Barnes has found, nurses and doctors have been making that concept work for a long time.
At the Lazaretto Quarantine Station, a hospital on the Delaware River used to treat immigrants with yellow fever in the early 19th century, patients were more likely to survive the illness than were many in the general population, he said. The regimen was straightforward: clean bedding, rest, adequate food and drink, and palliative medicines to ease the worst symptoms, said Barnes, who is writing a book on the topic.
“There are actually plenty of cures for viral illnesses," he said. “We just don’t think of them as cures. We’re still kind of myopically fixated on finding a cure, when what we really should be doing is getting adequate basic nursing care for all patients.”
That may yet prove to be a challenge in the coronavirus outbreak. The nation’s hospitals have fewer than 70,000 adult intensive-care beds, while epidemiologists say the number of U.S. coronavirus patients with severe symptoms could reach the hundreds of thousands.
If they all get sick during a short period of time, then even what Barnes calls the “care cure” may be in short supply.
Why Don’t Antibiotics Kill Viruses?
one of my favorite rides at Disneyland (other than the Matterhorn) was Monsanto’s Adventures Thru Inner Space. In it, you boarded a vehicle which pretended to gradually shrink you down to the size of molecules. I’m not the only one who remembers it fondly some guy on the Internet has actually re-created the ride using computer animation and sells it as a download.
Update: Did you know that is article is one of the most common reasons worldwide why people come to our site? I have updated the content for all you far-flung web visitors.
My Internet research also informed me that since the ride was free, most of the people on it were teenagers looking for a place to make out. Well, that and the occasional science nerd like me.
An adventure through biological inner space would be a great ride. My idea is to take a TV talking head news person, and go up his nose. This might explain, on a molecular level, why antibiotics don’t kill viruses.
As we shrink in size, the droning sound of our talking head interviewing a guest will become louder, but earplugs can take care of that. When we are about 1/8 th of an inch, we can easily fit up his nose and see those huge nostril hairs. As we shrink down further, we see the tissue on the inside of the nose is not a smooth uniform sheet but is actually made up of thousands of cells in tight approximation. Continuing to shrink, we find ourselves the size of one of these cells lining his nose. This cell is the target for common cold viruses.
At this level of magnification, we can see bacteria sitting on the cells as well. There are dozens of bacteria, sitting on the outside of the cell, but they are mostly innocent bystanders. Some swim around in the nasal mucous with a whip-like tail, others just wriggle in place. Some are friendly, and by being present they prevent bad bacteria from living up there.
The good bacteria in our talking head’s nose are alive. They move, they divide in two. They eat sugar and give off gas. If you spray them with an antibiotic, they might just keel over and die.
As we shrink, we notice something interesting about the cells lining the nose. Although some look perfectly normal, some look abnormal. One appears broken open. We can’t yet see why, but it has definitely split apart.
Once we shrink down small enough to get inside the cell we see why. There are thousands of tiny particles streaming out of the cell. These are viruses.
Scientists sometimes debate the question of whether viruses are alive or not. Well, they are not alive. This is plainly obvious as we shrink down to the size of a virus. Cells are a hundred times bigger than a bacterium (bacterium = one bacteria), and a bacterium is a thousand times bigger than a virus. If you are down to that size, you are not alive. Why?
If we could feel the signs of life coming from a human cell or a bacterium, if biochemical processes made a humming noise like the engines on space ships in science fiction movies, then human cells would be humming, as would bacteria. There are all sorts of chemical reactions going on inside. Energy is being consumed, things are happening. But the viruses would appear as cold, dead, inactive objects. They don’t move, they don’t show any signs of life. They are not eating or breathing. There are no chemical reactions taking place.
Antibiotics kill bacteria by targeting their life processes. The goal in developing antibiotics is to find substances which disrupt the chemical reactions of life for bacteria but don’t harm human cells. For example, penicillin blocks the formation of bacteria cell walls, but does not affect human cells because we have cell membranes, not cell walls. Ciprofloxacin makes it impossible for bacterial DNA to divide, but it has no effect on human DNA.
But if no life is going on, if no chemical processes are underway, then an antibiotic cannot do anything.
Human viruses, like their computer cousins, are simply a set of instructions written in DNA or RNA instead of computer code, surrounded by a protective protein covering. A virus is engineered to attach to a cell and then squirt a short strand of DNA or RNA into the cell. Sometimes, a virus is packaged with one or two chemicals to help it get in and out of cells or to make copies of its DNA.
Being inside the cell is like making it past airport security. In theory, everyone has been screened and everyone should be a good guy, so the human cell does not really have much in the way of immunity to protect itself against foreign and evil DNA. It assumes any DNA it sees is its own. The human body is very good at attacking things which are outside cells, but not so good once they get inside a single cell.
The human cell takes the DNA from the virus and starts following the instructions on it. Instead of making nose mucous, which might be your job if you are a cell lining a nose, you stop doing that and start following the new instructions given to you by the virus. Those new instructions, not surprisingly, tell the cell to start making more copies of the virus. So the cell now devotes all its energy to making viruses. Soon, the cell is full of hundreds, if not thousands of virus particles and it bursts open. These viruses, in turn, go to attack other cells.
You can’t kill a virus because it is already dead
When viruses are out in the open, the body’s immune system soon recognizes them and will destroy them. Viruses are pretty defenseless just floating out there. They are inert, inactive, and can’t run away. If we want to get rid of a viral infection, antibiotics don’t do anything because antibiotics target biological processes in living organisms and viruses are not living.
A better approach is a vaccine. This is a shot form of millions of killed virus particles (or parts of them). The body sees this and gears up the immune system. When the real virus comes along, we know what it looks like and are ready to destroy it before it can start infecting cells.
Another method to combat viruses are drugs which target the virus directly. We call these drugs “antiviral” drugs to distinguish them from the antibiotics that work on bacteria. For example, the flu virus is good at getting inside cells and forcing the cell to make lots of copies of the virus, but the flu virus particles have a hard time breaking out of the cell. Instead of filling up the cell and bursting it open, each flu virus forms a tiny bud and pushes through the cell membrane, one at a time. In order to accomplish this task, it carries a special enzyme called neuraminidase, which sits on the outside of the virus. The job of this enzyme is to punch a hole in the human cell membrane. Tamiflu is an anti-viral drug which blocks neuraminidase. By latching on to the neuraminidase molecule, the smaller Tamiflu molecule prevents the virus from detaching itself from the cell it has infected. This is how it works against influenza. Obviously, you need a virus with this exact biological behavior to be a target for Tamiflu. That is why Tamiflu won’t work against a cold or stomach flu—these viruses don’t bud out of cells and they don’t have neuraminidase molecules on their surface.
Flu viruses are named by the type of neuraminidase they have, they are numbered N1 to N9, and also by one other enzyme they carry, called hemagglutinin. Hemagglutinin also sits on the outside of the virus and allows it to attach to new cells. The first 3 of the 16 types of hemagglutinin easily infect humans. So one virus might be named H1N1, and another H5N1. The “H5” indicates the fifth type of hemagglutinin, and also, by being numbered greater than 3, is a type that does not (yet) easily infect humans. H5N1 is bird flu.
Anyway, back on our ride through our talking head’s nose. We see that many of the cells lining his nose are infected with rhinovirus, the most frequent cause of the common cold. An azithromycin (Z-Pak) molecule floats by, prescribed unnecessarily by a doctor. Azithromycin is a specialized molecule which gets inside a bacteria and finds the spot where the bacteria makes protein. Azithromycin needs an active, living, metabolizing bacterium to do its job. Once inside, azithromycin binds to the protein-making machinery of the bacteria (which is sufficiently different from our own that the drug is not harmful to our cells) and it kills the bacterium by preventing protein production. The bacteria cannot make anything, it cannot do anything new, and gradually dies. The azithromycin molecules are busy killing off innocent bacteria that normally live in the nose. “I’m innocent!” they scream, but the azithromycin does not know good from evil. It kills all bacteria in its path. Meanwhile, the viral infection goes on unimpeded. The virus makes no protein on its own and cannot be harmed by the Z-Pak. Of course, we kill off a few people every year with a Z-pack prescription, a point I try to make when patients are demanding unnecessary antibiotics. (Don’t trust me, Google it: “Do Z-Paks kill people?”)
We see that the nose has lost thousands of cells. They’ve all been converted to common cold virus production houses. When the cell is full of copies of this virus, it explodes, alien-like, and thousands of new virus particles burst forth. When our patient sneezes, many virus particles shoot out his nose and into the atmosphere.
Soon, his immune system begins to recognize that these virus particles are a foreign invader and they gobble them up. Then new healthy cells need to grow back to line his nose. This takes a few days and accounts for the long recovery period from many viral infections. Long after we are no longer contagious, we feel lousy because new cells must be made to replace those lost in the viral infection.
Why do doctors so commonly prescribe antibiotics for viruses when they do absolutely nothing and might make people worse? It’s all about doctors being busy, making patients happy, and not getting sued. A typical primary care physician is so rushed during his day that his main goal is to see people as quickly as possible. If a patient has an expectation of receiving an antibiotic, it takes much longer to explain why an antibiotic is not necessary than to just write the prescription. If insurance companies paid doctors an extra $100 for not prescribing antibiotics for viral infections, then the practice would drop off sharply. However, a visit for bronchitis generally pays the same—antibiotics or not—and an extra 10 minutes of discussion generates no added revenue.
The second problem is patient satisfaction. Every physician on the planet has seen the angry, arms folded, sour-faced posture of a patient who hears that he or she is not going to get an antibiotic. Patients feel they are not being taken seriously. They think that somehow a bacterial infection means something is “really wrong” but a viral one means “the doctor said there was nothing wrong with me.” Tell that to a guy hospitalized with viral pneumonia! And by the way, AIDS, hepatitis, bird flu, chicken pox, Ebola, and SARS are all viruses. Influenza kills more old people than strep throat.
But in any event, doctors want their patients to be happy. You can turn a frown into a smile with antibiotics. Every doctor has done this, even the purists among us.
The third reason for unnecessary antibiotic prescribing is lawsuits. The fact is that it can be hard to tell the difference between bronchitis and an early pneumonia. Should we get a chest X-ray on everyone with a cough? Clearly, that is not good medicine. Anyway, the x-ray sometimes lags behind clinical symptoms. Most sinusitis is not bacterial, but sometimes it is. Should we do a needle aspiration of the sinus on all patients? The doctor who prescribes an antibiotic unnecessarily, when there is at least some plausible reason for doing so, is unlikely to be sued successfully if the patient does poorly. But Heaven help the doctor who, using his best judgment, does the right thing and avoids an antibiotic. One in a hundred will turn out to have a bacterial infection. No legal harm in writing 100 or 200 unnecessary antibiotic prescriptions, but many physicians feel they will be crucified for missing that one person who might’ve benefited from an antibiotic a day or two earlier.
If you are seeing a physician who wants to prescribe an antibiotic, you can get much better care by saying, “Doc, do I really need this? I don’t want to take antibiotics unless it’s really necessary. Would you take this antibiotic if this were you?” If patients did this, who knows, doctors might reply by saying, “I actually think this is likely to be a virus. Why don’t we wait a day or two and see.” Or a physician might say, “Sir, the red streaks going up your arm and the fever of 104 tells me this is bacterial!”
In my practice, I treat patients how I would treat myself or my own family. I personally would never take an antibiotic for the various types of viral crud that goes around all winter. It will just give me diarrhea and make me prone to a real bacterial infection. However, my mother demands an antibiotic, and so if patients are adamant, I offer my best opinion, but I won’t withhold antibiotics if patients insist and there is at least some plausible rationale for prescribing.