ImmYOUnology

More than just vaccines


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A risk worth taking–And one your immune system is prepared to take.

When was the last time you made an important decision with 100% certainty?

Most, if not all, decisions in life come with risks, consequences or trade-offs. Healthcare is no different from anything else. Every surgery, pill, shot, even every new diet or exercise routine has its risks. And vaccines are not exempt. It’s true, vaccines have risks (probably the most common one for most vaccines is soreness at the injection site). And it’s no secret either—check out this list on the Center for Disease Control’s (CDC) website. They even list extremely rare reported events that they can’t prove were related to vaccination, but occurred around the same time.

Early recipients of vaccines understood side effects all too well. In the 1700’s, vaccination against smallpox, which entailed rubbing pus from an afflicted person into a small cut, was known to cause a mild form of disease, and in 1-2% of cases, death. But to those who saw what real smallpox could do firsthand, the risk was worth it, because even if they didn’t yet know how it worked, they knew that vaccination saved lives.

These days, vaccines are far safer, but the fear of potential side effects often overshadows the fear of disease. Perhaps the most notorious of these fears is the alleged and debunked link between autism and the measles, mumps and rubella (MMR) vaccine.  Many researchers have taken an honest and thorough look at this and the question has been settled from a scientific standpoint.

As is the case with everything, though, people factor things besides scientific evidence into their decisions. For example, a sense of social responsibility may influence your decision to get the flu shot each year. You may also factor in anecdotes about a co-worker’s friend getting the flu after being vaccinated. Though rejecting one piece of information and blindly accepting another is everyone’s right, making an informed decision requires consideration of all types of information.

Many take the reasonable route of deferring to their doctors who have hopefully kept abreast of the scientific evidence and have likely seen the anecdotal evidence first hand. A doctor may defer to the recommendations of an organization like the Advisory Committee on Immunization Practices (ACIP), a rotating group of doctors and scientists who painstakingly study the science and side effects of every vaccine that goes onto the market. You can learn more about ACIP here and even attend their meetings if you want.

Then there are some who would like to have a couple of questions answered and to feel more involved and informed about their own, or their children’s health care. And then some who are just plain scared of the potential side effects. These lingering questions and fears surrounding vaccination are worth addressing (not to mention scientifically fascinating). For a thorough list of such questions, I recommend this site (and of course, it’s always wise to speak with a trusted healthcare professional about your concerns). Over the next couple of posts, I plan to explore some recent research that sheds light on a just couple of these questions:

First, can a vaccine make you sick? And second, why do vaccinated people still catch disease?

One way to explore the first question is look at the differences between the altered form of a virus found in a vaccine and the real deal. For something like the flu shot, which contains dead virus, the difference is obvious. If the virus is not alive, it can’t get into cells and replicate. It can, and should, activate immune cells, which could bring along soreness or a headache.


You may have heard about people getting the flu, or flu symptoms from the flu shot itself. There is some evidence that the act of getting the flu shot can put you at risk for the flu. One study published last year concluded that just going to the doctor slightly increased the probability of experiencing flu-like symptoms within the following two weeks (read this for more). If you get the vaccine at a clinic or doctor’s office, you could increase your chance of contact with people who have the flu or surfaces they have recently touched. It takes about a week for your body to generate antibodies good enough to protect you from the virus, so it’s definitely possible to get sick just after being vaccinated. For more flu myths, check out this list.


For some diseases, like measles, the immune system really needs to see a live vaccine to generate long-term immunity. The reason for this is not completely clear, but we do know that it takes a while for our bodies to generate the “best and brightest” long-lived immune cells and a dead vaccine may be cleared too quickly for this to happen. So, we’re stuck with live vaccines, at least until researchers come up with something better.

Do live vaccines have more risks than dead ones? Well, for some people, yes. There are a handful of case reports of kids with rare genetic immunodeficiency disorders getting polio from the vaccine, and live vaccines could make someone with uncontrolled AIDs sick. However, there have been very few reports of HIV+ people getting sick after receiving a live viral vaccine (Summarized here).  And just to be safe, the CDC recommends pregnant women and those on immune-depleting chemotherapy avoid most live vaccines, though there is not a lot of data for or against them in those cases.

Measles pneumonia - Histopathology

Lung cells fusing together into one, measles-infected “giant cell.”

But what about in the average healthy person? What happens after a live virus vaccine enters your body, and how is it different from a live, natural, infectious virus? Let’s take a closer look at the recently popular measles vaccine. The virus used in for measles vaccine is “weakened” because it’s been grown, harvested, and grown again and again in human or chicken cells in culture dishes. The virus adapted to its environment in a culture dish, and lost its potency in the human body. On a molecular scale, scientists are still collecting information about exactly how this “weakening” happens. One thing they know is that the vaccine version of the virus infects different kinds of cells than the natural version of the virus does.

One researcher working toward a better understanding of this question is W. Paul Duprex, at the Boston University School of Medicine. His lab engineered measles viruses to glow by giving them the gene for the jellyfish green fluorescent protein (GFP). Then they infected macaques monkeys with either the infectious natural measles virus or the vaccine strain and looked for the glowing viruses in different parts of the animals’ bodies. When they looked for the virus in blood or throat swabs, they found much less—orders of magnitudes less—of the vaccine strain compared to how much natural virus was growing in the monkeys. The researchers also examined slices of lymph nodes with a microscope and measured GFP in immune cells using a laser and detected very little, if any, of the vaccine virus strain inside immune cells. The infectious version, on the other hand, seemed to love infecting and dividing inside of immune cells.

Both viruses were able to infect one type of innate immune cell, but only in the lungs. And, it’s important to note that the scientists delivered both types of virus straight into the animals’ airways, so both strains had ample opportunity to infect. Just this month, though they published a study that mimicked the actual vaccine route, which is an injection into a muscle, and saw that the vaccine virus also only infected innate immune cells in the muscle. To see pictures of Duprex’s “glowing” virus infecting these cells, check out this recent National Geographic blog post.

When these innate immune cells, called dendritic cells and macrophages, get infected, they display little bits of the virus to other immune cells in nearby lymph nodes. For this reason, they are called professional antigen presenting cells. Other immune cells in the lymph nodes will generate a response, clear the present virus, and remember it well enough to prevent infection with the natural version in the future.

If innate immune cells brought the natural virus to the lymph nodes, cells in the lymph node would become infected and the virus would continue to spread throughout the body. This research is just getting started, but so far it looks like the vaccine version of the virus is well contained by dendritic cells and macrophages. They are professionals after all, and they do this kind of thing all day every day.

So, should you fear live viral vaccines? Well, do you fear the live bacteria, viruses and fungi living all over your body? Your immune system has done a good job at keeping them in check so far. If you’re generally healthy, a live viral vaccine is like a blip on your immune system’s radar.

I think of it like going on a roller coaster. You can stand in line and mull over all of the things that have a one in a million chances of going wrong, or consider the actual data–the hundreds of people who rode it without any incident just during the time you were in line.

In the case of live vaccines, millions of people have had them with no incident just in the past year. And unlike a roller coaster ride, the marginal risks of measles vaccination are exchanged for a major, life-long benefit.

Please note:

I am not a medical professional and the opinions within this blog are not intended to be used as medical advice.

Sources:

Gerber J. (2009). Vaccines and Autism: A Tale of Shifting Hypotheses, Clinical Infectious Diseases, 48 (4) 456-461. DOI: http://dx.doi.org/10.1086/596476

Simmering J.E., Joseph E. Cavanaugh & Philip M. Polgreen (2014). Are Well-Child Visits a Risk Factor for Subsequent Influenza-Like Illness Visits?, Infection Control and Hospital Epidemiology, 35 (3) 251-256. DOI: http://dx.doi.org/10.1086/675281

Angel J. (1998). Vaccine-Associated Measles Pneumonitis in an Adult with AIDS, Annals of Internal Medicine, 129 (2) 104-106. DOI: 10.7326/0003-4819-129-2-199807150-00007

de Vries R.D., Lemon K., Ludlow M., McQuaid S., Yüksel S., van Amerongen G., Rennick L.J., Rima B.K., Osterhaus A.D.M.E. & de Swart R.L. & (2010). In vivo tropism of attenuated and pathogenic measles virus expressing green fluorescent protein in macaques., Journal of virology, PMID: http://www.ncbi.nlm.nih.gov/pubmed/20181691

Rennick L.J., Thomas J. Carsillo, Ken Lemon, Geert van Amerongen, Martin Ludlow, D. Tien Nguyen, Selma Yüksel, R. Joyce Verburgh, Paula Haddock & Stephen McQuaid & (2014). Live-Attenuated Measles Virus Vaccine Targets Dendritic Cells and Macrophages in Muscle of Nonhuman Primates, Journal of Virology, 89 (4) 2192-2200. DOI: http://dx.doi.org/10.1128/jvi.02924-14

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The most promising treatments for ebola are based on basic immunology-part 2

One of the more peculiar, historic and almost cinematic treatments being discussed in the midst of the ebola crises is the use of blood transfusions. In movies, the blood of a survivor or someone special is often supposed to have some sort of mystical effect on the (usually villainous) recipient. It turns out, blood transfusions from people who have survived ebola are nearly as mystical.

It seemed obvious to me at first that the active components in blood transfusions from ebola survivors must be anti-ebola antibodies. Such antibodies would neutralize the virus and help the immune system clear it out. And in fact, a 1999 study reported that seven patients who survived the 1995 outbreak in the Democratic Republic of the Congo after receiving transfusions from survivors had anti-ebola antibodies circulating in their blood. One kind of antibody, called IgM, was absent in another patient who received a transfusion and died. This very small study seemed to indicate that transfusions could work against ebola and that antibodies are key to making them work. (You may be wondering why, if the transfusions worked, more patients weren’t treated this way during the 1995 outbreak. One important reason is that that blood cannot be transfused unless the donor and recipient blood types are compatible.  So the treatment is limited by the number of willing survivors and their blood types.)

This idea was challenged by a 2007 study done in a nonhuman primate species, rhesus macaques. For this study, researchers drew blood from a rare few monkeys who had survived an ebola infection four or five years earlier and a second “boost” infection 30 days earlier. They transferred the blood into other, recently-infected animals, and none of them survived…even those that made a lot of antibody. There are, of course, caveats. Monkeys are not humans, after all. It is possible that they fight the virus differently. And in the discussion of the paper, the researchers admit the experiments that had successfully transferred antibody-mediated immunity in guinea pigs had not worked in rhesus macaques.

There are also caveats to the human study though. The main one being that it can’t account for the better treatment transfusion patients received compared to other patients. The seven may have survived simply because they received better care in the clinics. The boost of cells, fluids, proteins and electrolytes that come along with blood transfusions may also have helped.

Scanning electron micrograph of red and white blood cells (National Cancer Institute)

Scanning electron micrograph of red and white blood cells (National Cancer Institute)

In spite of it all, the World Health Organization is behind blood transfusions and transfer of plasma from ebola survivors.  Plasma is the liquid part of blood that contains proteins like antibodies, along with other things like electrolytes and hormones. The first of the eight original transfusion patients, a 27 year-old nurse, was originally supposed to receive plasma and not whole blood. This was because, in 1978, a researcher who received plasma survived an ebola infection brought on by a finger prick in the lab. The nurses’ doctors settled for blood because they didn’t have the right tools to separate the plasma (a process called plasmapheresis).

The seven transfusion patients who followed the nurse ranged from a 54 year-old woman to a 12 year-old girl who caught the virus by kissing her newborn niece just days before the infant died. Antibodies seem to be the most likely explanation for the high rate of survival, but it is still not clear whether they were. Well-controlled human trials to determine whether blood transfusions work for ebola will probably never be possible. But, more and more people may be receiving them, so there may soon be more information about whether and how they work.


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The most promising ebola treatments are based on basic immunology

Though for many of us, the ebola crises is oceans away, the epidemic still weighs heavily on the hearts and minds of people all over the world. For some researchers, public health officials and drug developers, it is the driving force of all daily activity. Right now, there are two vaccines and eight treatments being developed or tested for their effectiveness against controlling infection or stopping the  virus’ spread. The most encouraging results have come from treatments that rely on a very basic aspect of immunology: antibodies neutralize viruses.

Antibodies are proteins made by immune cells called B cells. Each one of your millions of B cells is capable of producing antibodies specific for one thing, and when a B cell comes into contact with that one thing, it secretes lots of antibodies. The antibodies then tag invading pathogens, like viruses, to make other immune cells aware of the invader’s presence. If enough antibodies stick to a virus, they can cover it up, or neutralize it, and prevent it from infecting cells.

Ebola infection does trigger an antibody response, but for reasons that are still being studied, those antibodies are not usually enough to stop the virus before it spreads throughout the body. The concept behind ebola treatments like Zmapp, blood transfusions, vaccines and even supportive care, is to help the immune system outpace the growing virus.

 

Zmapp

Over the summer, this product was on headlines everywhere. Zmapp sparked a controversy over who should get the most cutting-edge treatments when it was given to two missionary doctors who flown to Atlanta for care.  Zmapp is not really a drug; it’s a combination of three kinds of antibodies that bind to the surface of ebola virus particles. Because each type was originally produced by one individual B cell they are called monoclonal antibodies. Monoclonal antibodies are used for treating cancer, autoimmune diseases and other infections.

Identifying the right monoclonal antibodies can be a painstaking and years-long process. Researchers collect B cells from a person or animal in the midst of an active immune response, in this case, against ebola. Then they seed individual antibody-making B cells into tiny wells on a cell culture dish. Later they test the culture media from each well for the presence of antibodies and select the cells making the best antibody to be “immortalized.” Cells are immortalized by altering their genes or fusing them with cancer cells that are already immortal. Usually the cells are frozen and stored for later use. They can be thawed anytime and grown to large quantities to make antibody.

Forget cigarettes...tobacco plants have lots of potential for "pharming" biological drugs like the monoclonal antibodies in Zmapp (From Wikemedia Commons)

Forget cigarettes…tobacco plants have lots of potential for “pharming” biological drugs like the monoclonal antibodies in Zmapp (From Wikemedia Commons)

It seems simple, but getting the process right can take years. The monoclonal antibodies in Zmapp were originally derived in mice back in 2000.

From there, the antibodies have to be purified. It can take liters and liters of cell media to purify enough antibody to treat one person one time. As a therapeutic, monoclonal antibodies are typically dosed over multiple treatments. In a recently published study showing the effectiveness of Zmapp against ebola infected monkeys, the animals were treated three to five times a day.

There are alternative ways to do this, however. Because antibodies are proteins they are coded by specific genes. So instead of fusing selected B cells with cancer cells, researchers could copy the gene coding for the cell’s antibody and put it into something else, like bacteria or, in the case of Zmapp, tobacco plants. Many biological products, like insulin have been produced in bacteria since the 1980s. Plant production of human proteins is a bit more recent.  The first human protein produced in plants in 2012 for a medical purpose was an enzyme injected into patients who can’t make it themselves. Some insulin is also now produced in plants.

Unlike cell-based or bacteria-based approaches, plants don’t have to be genetically manipulated and then grown up and harvested. Instead, adult plants are infected with viruses engineered to express the antibody-coding genes. The viruses introduce the genes, and the plants make the antibody. For some proteins, this results in much higher yields than cell-based methods. The monoclonal antibodies in Zmapp are being made by three different companies using a variety of these methods.

But there is a catch. When any kind of cell (plant, animal, bacteria) produces a protein, it adds little sugar labels to keep track of it during each stage of production. This process is called glycosylation. These glyo-labels vary by species and they can affect the way a protein functions. Because of this, the plants being used to grow Zmapp are not your run-of-mill tobacco. They are genetically modified so that they can give the anti-ebola antibodies more human-looking labels. That adds another layer of complexity to be addressed as these companies start to make large quantities of Zmapp.

It’s fascinating how this technology was developed step by step—often in obscurity—over the course of many decades.  Hopefully, it will be scaled up successfully in the coming months to provide more much-needed doses.

Next time…Blood transfusions.


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Banking on baby: all about umbilical cord blood stem cell transplants

Over the summer, my then-pregnant friend asked for my opinion about umbilical cord blood banking, naturally sending me into a world of fascinating biology, cutting edge medicine and some ethical quandaries.

If you can afford the $1000-2000 processing fee and at least $100 a year to store the blood, banking seems like a no-brainer. “You never know,” rings in the backs of many expecting parents’ minds as the one-time opportunity approaches. But there is more to consider than price. The biology behind the technique and the currently available applications of frozen cord blood may influence one’s decision about whether to bank, and also how and where to do it.

Cord blood contains a high frequency of hematopoietic stem cells, which can differentiate into any kind of blood cell. They can mature into megakaryocytes that make platelets, red blood cells, or immune cells like B cells or eosinophils. We all carry these stem cells throughout our lives, mainly in our bone marrow, and they produce cells that periodically replace blood cell populations.

Blood cells arising from hematopoietic stem cells. (Wikimedia commons, based on original by A. Rad)

Blood cells arising from hematopoietic stem cells. (Wikimedia commons, based on original by A. Rad)

Cancers rising from white blood cells (like lymphoma or leukemia) and genetic defects interfering with the production of any kind of blood cell can conceivably be addressed by resetting the whole system with a bone marrow (or stem cell) transplant.  Transplants using donated bone marrow have been used to do just this for about 50 years. In the late 1980s, it became clear that cord blood stem cells could do the same with some distinct advantages.

For one thing, collecting cord blood is much less difficult and invasive compared to harvesting bone marrow. Bone marrow donation involves anesthesia and a very large needle stuck directly into the bone. Stem or progenitor cells can also be separated from adult blood through a process called apheresis, but it is no cakewalk, especially compared to harvesting cord blood, which simply involves injecting a needle into the cord after it’s been cut.

Donor matching is also more flexible for cord blood. To avoid graft rejection, stem cell (and all organ) donors and recipients are matched for proteins expressed on the surface of immune cells. If they don’t match, the T cells in the donated transplant may attack the tissues of the recipient. T cells found in cord blood respond with less gusto and there are higher frequencies of T cell subsets that control the immune response called T regulatory cells. This means there’s a lower chance of the donor immune system harming the recipient.

Given these advantages, is banking worthwhile? It depends on what you hope to get out of it. When you think about storing a baby’s cord blood, you may think it’s for the sake of that particular child. The truth is, the stem cells in that kid’s blood are more likely to be useful for someone else. That was the case of the first ever cord blood transplant performed in 1988. A five year-old boy with a rare genetic disease called Fanconi Anemia received cord blood cells from his newborn sister. At the time, the boy’s white blood cell counts were dropping because inherited defects in a DNA repair pathway made it impossible for his bone marrow to produce healthy blood cells quickly enough. His own cord blood, of course, would have been useless because the same genetic defect would manifest again. Today, that patient is a grown man, but he has a female blood and immune system thanks to his sister.

Cases covered in the news about cancer patients cured because of cord blood transplants are usually about patients who received donated cord blood from public banks. In fact, their own stem cells would not have worked. In such cases, the transplant is an imperfect match on purpose so that the new immune system will attack cancer cells that the old immune system was blind to. This is typically done for blood cancers like leukemia. A transplant of a close or perfect match is desirable for patients whose bone marrow is depleted as a side effect of chemotherapy and/or irradiation for other types of cancer. However, stem cells for this kind of transplant can also be harvested from one’s own bone marrow or blood before beginning treatment.

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photo credit: Banc de Sang i Teixits via photopin

Even if the chances of using one’s own cord blood are remote, it may be desirable to store it in case a family member could use it. There are a couple of caveats to consider, however, before committing to private banking. First, it’s been estimated that at least 70% of adult recipients need two units of cord blood to successfully reinstate a new blood and immune systems That means it’s likely that even if you do save your baby’s cord blood, it may not be enough if he or she needs it as an adult. This may change in the future; a study published last week in Science found that a drug compound called UM171 kept human cord blood stem cells “immature” while allowing them to expand. There are also several clinical trials underway that will test whether expanding cord blood progenitors through other means can reduce the number of units needed and increase transplant success.

The second caveat is a little bit more about logistics and politics than science. Right now, only 10% of collected cord blood meets the standards required for transplantation. These standards included how many cells are present, how many cells survived and whether the blood was collected, shipped and frozen properly. (For an interesting glimpse at what could go wrong, check out this Wall Street Journal article).  And the way cord blood units are handled and stored is only regulated by the Food and Drug Administration if they are stored in public banks. That is not to say that there are no good and reputable private banks. It is, however, important to recognize that private banking requires lots of research and care when choosing a company.

I mentioned that the chances of performing a cord blood transplant on the original donor are not very high given the current uses of cord blood stem cells—mainly to replace blood stem cells in the bone marrow. That is not the whole story though. There are clinical trials going on to test the therapeutic effects of cord blood stem cells for things like cerebral palsy, type I diabetes and even hearing loss. These studies are based on observations suggesting stem cells found in cord blood can reduce brain damage after injury, but it’s not yet clear how. There are also other kinds of stem cells in cord blood that can differentiate into cells other than blood cells (pancreatic cells for example). There may still be a lot of untapped potential for cord blood. For many parents, that is enough reason to put their kids’ blood “on ice” and wait it out.

Sources:

Metheny L., Caimi P. & de Lima M. (2013). Cord Blood Transplantation: Can We Make it Better?, Frontiers in oncology, PMID: http://www.ncbi.nlm.nih.gov/pubmed/24062989

Gluckman E., Arleen D. Auerbach, Henry S. Friedman, Gordon W. Douglas, Agnès Devergie, Hélène Esperou, Dominique Thierry, Gérard Socie, Pierre Lehn & Scott Cooper & (1989). Hematopoietic Reconstitution in a Patient with Fanconi’s Anemia by Means of Umbilical-Cord Blood from an HLA-Identical Sibling, New England Journal of Medicine, 321 (17) 1174-1178. DOI: http://dx.doi.org/10.1056/nejm198910263211707

Wagner J.E. Should double cord blood transplants be the preferred choice when a sibling donor is unavailable?, Best practice & research. Clinical haematology, PMID: http://www.ncbi.nlm.nih.gov/pubmed/19959107

Fares I., Chagraoui J., Gareau Y., Gingras S., Ruel R., Mayotte N., Csaszar E., Knapp D.J.H.F., Miller P. & Ngom M. & Cord blood expansion. Pyrimidoindole derivatives are agonists of human hematopoietic stem cell self-renewal., Science (New York, N.Y.), PMID: http://www.ncbi.nlm.nih.gov/pubmed/25237102

Petrini C. (2014). Umbilical cord blood banking: from personal donation to international public registries to global bioeconomy., Journal of blood medicine, PMID: http://www.ncbi.nlm.nih.gov/pubmed/24971040


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Allergies are no fun…but the biology behind them is!

Spring is nearly upon us and along with trees and flowers, seasonal allergies will bloom once again.  Even though allergies can be annoying, debilitating and even life-threatening, the science behind them is fascinating.  Science published a timely paper at the end of February describing some of the ways different kinds of allergens work.  Allergens are small parts—individual proteins or molecules—of things that cause allergic responses.

The group who published the study worked with cells called mast cells, one of the common types of the immune cells that respond to allergens and make you itchy, sneezy and swollen.  Before they can activate mast cells, allergens have to be recognized by a particular type of antibody, or immunoglobulin, called immunoglobulin E, or IgE.  On one end, IgE binds an allergen, and on the other it interacts with a protein receptor on mast cell surface.

By connecting the mast cell to the allergen, IgE gives the mast cell permission to do its thing, and its thing is called degranulation.  Mast cells are brimming with packets, or granules, of histamine and heparin and other proteins that damage microbes as well as tissue.  When the cells degranulate, they open up and release their contents into whatever tissue they happen to be in—the skin, the lungs or the gut for example.  Many of the contents released make blood vessels leaky and attract lots of immune cells, causing inflammation.  Antihistamines prevent the released histamine from binding its receptors on blood vessel cells.  Another treatment option currently under investigation is a drug that blocks the interaction between IgE and the receptor on mast cells to prevent this process from even getting started.  

The recent Science paper took a close look at the mast cell response to IgE-bound allergen and showed just how fine-tuned it can be. The researchers activated mast cells with allergens that bound tightly or weakly to IgE and found that the strength of the interaction, also called affinity, changed the way that mast cells responded.

http://commons.wikimedia.org/wiki/File%3ASMCpolyhydroxysmall.jpg

Skin mast cells stained with Toluidine blue

The researchers could study mouse mast cells in culture dishes, because mast cells grow up from stem cells inside bone marrow.  So they grew up mast cells from mouse bone marrow and then gave them the strongly binding allergen (high affinity) or the weakly binding one (low affinity). They could get the mast cells to respond and degranulate with both, but it took 100 times more of the weak binding allergen to get the same response caused by the strong one.

To understand how allergic reactions work in living creatures, researchers often sensitize mouse ears by exposing them to an allergen and later re-introduce the allergen through the bloodstream. Then they can measure how inflamed the ears get and how many and what kinds of immune cells travel to the ear after injecting the allergen.  In this study, the strong binding allergen caused more intense and more sudden ear inflammation and immune cell infiltration than the weaker binding allergen.

So how does this fascinating mechanism actually relate to human allergies, which for some people is a life-threatening condition.  Although some allergies go away with age, there is currently no permanent cure for those that don’t.  Treatment of serious allergies is centered around desensitization immunotherapy, which is just repeated exposure to small doses of allergen over time.  The treatment may last anywhere from months to a lifetime and there are no biomarkers, or biological tests, that tell doctors when the treatment is working.  Instead, they simply test allergens on patients, which could mean pricking the skin or making them eat peanuts one at a time until they do or don’t get sick.  

A clinical study that came out in January helped me understand how knowledge of allergen binding strength could be helpful in treatment.  In this study, children with milk allergies were undergoing oral immunotherapy, which in this case simply meant they had to drink small amounts of milk that were increased over time.  The researchers collected serum samples from the kids in the study and measured levels of IgE as well as the affinity of IgE for proteins found in cow’s milk to see if either would change as kids became more tolerant to milk.

In some cases, the immunotherapy had to be discontinued because the reactions to milk were too severe.  The researchers found that the IgE from the kids whose treatment was discontinued bound more tightly to milk proteins compared to kids who responded well to the treatment.  So the strength of the interaction between IgE and allergens does matter, at least in the case of cow’s milk allergies. This study didn’t look at mast cells, but it does indicate that the molecular details of how IgE connects allergens to mast cells are worth studying.  Those details can provide clues about what is going on inside a person with allergies and how well they may respond to immunotherapy.

Sources:

Mastcellaware.com (A whole website about Mast Cells)

Suzuki R., Leach S., Liu W., Ralston E., Scheffel J., Zhang W., Lowell C.A. & Rivera J. (2014). Molecular Editing of Cellular Responses by the High-Affinity Receptor for IgE, Science, 343 (6174) 1021-1025. DOI:

Savilahti E.M., Kuitunen M., Valori M., Rantanen V., Bardina L., Gimenez G., Mäkelä M.J., Hautaniemi S., Savilahti E. & Sampson H.A. & (2014). Changes in IgE and IgG4 epitope binding profiles associated with the outcome of oral immunotherapy in cow’s milk allergy, Pediatric Allergy and Immunology, n/a-n/a. DOI:

Moran T.P., Vickery B.P. & Burks A.W. (2013). Oral and sublingual immunotherapy for food allergy: current progress and future directions, Current Opinion in Immunology, 25 (6) 781-787. DOI:


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Tuning down the immune system could improve the flu vaccine

This post is based on an article I recently wrote for an internship application, so it’s more formal than a typical post, but I think it’s a cool story that helps explain how the flu vaccine works. Enjoy! And stay healthy!

After more than 2,000 confirmed cases and over twenty deaths, the 2013-14 flu season is still approaching its peak.  Vaccination remains the best prevention despite the flu vaccine’s hit-or-miss reputation.   Each year the U.S. Food and Drug Administration recommends three strains of influenza that the World Health Organization believes are worth targeting, and six months later the season’s new vaccine is distributed.

influenza-virus-labels

This nasty viral particle is trying to get inside a cell. It’s covered in NA (red) and HA (blue) proteins.

One of the flu vaccine’s biggest problems is its inability to induce immunity against multiple viral subtypes.  Subtypes of the influenza A virus, like H1N1 or H5N1 are distinguished by the surface proteins hemagglutinin (HA) and neuraminidase (NA).  The vaccine can protect against a few subtypes at a time, but if a subtype not included in the shot makes a strong appearance one season, not much can be done to prevent it from spreading.  This year, the vaccine is pretty spot on. It includes H1N1 which has been making a comeback this year.

This problem has driven researchers to pursue a universal vaccine that could protect against multiple subtypes.  This type of protection is called heterotypic immunity.  One group of scientists from St. Jude Children’s Research Hospital hit on an unexpected way to expand the reach of one flu vaccine to multiple subtypes.  Dr. Maureen McGargill and her group published their study in Nature Immunology in December.  They studied how a common immunosuppressive drug called rapamycin influenced the ability of vaccinated mice to generate heterotypic immunity.  They vaccinated mice with one viral subtype and infected them with three other lethal subtypes.  Surprisingly, the mice who got rapamycin were better able to resist infection by all the subtypes, including an altered H5N1 strain, commonly known as the avian flu.

Rapamycin is commonly used to dampen the immune system to prevent organ transplant rejection.  It blocks an immune system regulating protein called mTOR.  Three other animal vaccine studies previously found that rapamycin enhanced generation of memory T cells, cells that can remember a virus and kill infected cells when they detect viral proteins.  None of these studies linked higher numbers of memory T cells to protection from infection.  McGargill’s group observed both higher memory T cell numbers and better protection, but could not link the two. Rather, they found that protection was related to changes in the kinds of antibodies that the vaccine induced.

The flu vaccine contains pieces of viral proteins called antigens and mice and humans make antibodies that specifically bind these antigens on the viruses and neutralize them.  The more specific the antibodies are though, the more they drive those proteins to mutate so the virus can escape detection.  This shape-shifting tactic is called antigenic drift, and it is part of the reason it is so difficult to predict which vaccine formulation will be most effective each year.    

The coveted universal vaccine would induce antibodies that recognize parts of the virus that are shared, or conserved, by many subtypes and unlikely to mutate.  But B cells, the cells that make antibodies, tend to make more and more specific antibodies over time.  Over several weeks, B cells go from making weak, broadly binding antibodies that can cross-react with many subtypes, to strong and specific ones.   McGargill and her colleagues found that rapamycin interrupted this process and caused the mice to make more of the broadly binding antibodies.  The antibodies also targeted different parts of the hemagglutinin protein.

The group could not determine exactly how the altered antibodies contributed to protection from infection.  They concluded that the antibodies produced after rapamycin treatment were less specific and therefore able to cross-react with several viral subtypes.   As a result, the treated mice were less susceptible to the three different influenza subtypes.

These findings could be useful for quickly designing broadly protective vaccines in the face of a new subtype outbreak or epidemic.  It currently takes about six months to manufacture the annually recommended formulation.  A heterotypic vaccine would not be as dependent on the World Health Organization’s laborious surveillance and data analysis, and could be stored and used for many flu seasons.

Sources:

Bridges CB et al. Effectiveness and cost-benefit of influenza vaccinations on healthy working adults: A randomized controlled trial. JAMA (2000) 284:1655-63.

Keating R. et al. The kinase mTOR modulates the antibody response to provide cross-protective immunity to lethal infection from influenza virus.  Nature Immunology (2013) 14:1266-76.

McMichael A and Haynes B. Influenza vaccines: mTOR inhibition surprisingly leads to protection. Nature Immunology (2013) 14:1205-07.

Pica N and Palese P. Toward a universal influenza virus vaccine: Prospects and challenges. Ann. Rev. Med. (2013) 64:189-202.

http://www.cdc.gov/flu


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Norovirus! (AKA the 24 hour stomach bug) Can it be avoided?

The other day I found myself in the break room near my lab eyeing a container of chocolate-covered nuts left over from the Christmas holiday.  Someone left them out as a treat for foraging graduate students and post-docs.  I stood for a moment holding a single piece in my fingers and as I was about to put it into my mouth, I remembered—Norovirus!

I had no reason to think the nuts could be a reservoir of norovirus, but I did have good reason to avoid shared uncooked food with an unknown history.   A good chunk of my family had just had their holiday ruined by the virus, sometimes known as the 24-hour bug or stomach flu.  It causes gastroenteritis, or inflammation of the gut, complete with diarrhea, vomiting and overall exhaustion.  It can only be transmitted via stool or vomit, and though there was certainly none of that visible in the bin of delicious looking nuts, I began to think of all the hands that may have been inside. If it came from a family holiday party, some of those hands may have belonged to kids who haven’t yet learned to wash them for a full 30 seconds after using the bathroom. I threw the candy away, closed the container and left the break room.

I may have avoided norovirus that day by a judicious food choice, but not everyone has that moment of doubt before sharing a drink, holding a child’s hand or ordering a deli sandwich.  It is sometimes just unavoidable, especially because it’s contagious for up to two weeks after the first horrible 24 hours. The center for disease control estimates that 19-21 million people are infected with norovirus each year and it’s actually responsible for somewhere between 600 and 800 deaths per year. Those most vulnerable are either over 65 or under 5 years old.

These figures are driving researchers to search for a vaccine, even if just for those most vulnerable or during outbreaks.  But norovirus, or I should say noroviruses are particularly complicated. They are split into 5 groups (I-V) based on how similar their DNA sequences are. Those groups, called genogroups, are split into anywhere between 8 and 30 genotypes and those can be further divided into variants.  The classification is complicated enough to require the use of a software program that compares genome sequences.

Only three of the genotypes can infect humans and the strain GII.4 has been the most common cause of outbreaks since the early 2000s.  For decades before that, a different strain dominated, and the power structure may shift again.  The abundance of genotypes and variants and their changing frequencies in communities make vaccine design a daunting task.  On top of that, researchers are still discovering new genotypes and variants.  In 2012 a strain called GII.4-Sydney was identified in Australia and made its way to the UK and the US within a year.

Norovirus 4

Up close scanning electron microscopic image of norovirus particles

There is evidence that infection with norovirus can generate immunity in some people, meaning that once they get infected, they are protected from re-infection for some weeks or months. However, no one knows how all of the viral subgroups and variants might affect immunity and vaccine design. In a study published in September, researchers from the University of Florida infected mice with one of two closely related norovirus strains and found major differences in the immune responses.

One of the two strains was much better at activating a class of immune cells called antigen presenting cells. These include dendritic cells and macrophages, and they are experts at displaying pieces of virus and training B and T cells to respond to the infection and turn into memory cells. As a result of the enhanced response, infected mice were protected from a reinfection six weeks later.

{Researchers determine “protection” by measuring how much virus shows up in an animal’s organs after infection. In this case, they measured norovirus in the small and large intestines and in the lymph nodes attached to the intestines.}

Oddly enough, the researchers narrowed down the cause of these changes down to a group of structural proteins whose sequences only varied by about 10% between the two strains.

A key finding in this study was that the protective norovirus strain protected mice from re-infection with both strains.  This is important since any vaccine against norovirus would have to protect against several strains and genotypes. It also points out specific characteristics of the immune response that make all the difference between becoming immune or getting re-infected, for example, robust antigen presentation and B and T cell memory.  A vaccine that could foster those characteristics could potentially protect people from several norovirus strains.  It may take a while to get there. In the meantime I will keep my hands clean and out of community candy dishes.

prevent-norovirus

*A reader noted that the poster above says norovirus is contagious for 2-3 days, whereas I wrote above that it can be contagious for 2 weeks.  To clarify, the virus is most contagious for 2-3 days, but it can continue to be shed in stool for 2 weeks. See http://www.cdc.gov/norovirus/preventing-infection.html for more.

Sources:

The CDC

Zhu S., Regev D., Watanabe M., Hickman D., Moussatche N., Jesus D.M., Kahan S.M., Napthine S., Brierley I. & Hunter R.N. & (2013). Identification of Immune and Viral Correlates of Norovirus Protective Immunity through Comparative Study of Intra-Cluster Norovirus Strains, PLoS Pathogens, 9 (9) e1003592. DOI:

Hoa Tran T.N., Trainor E., Nakagomi T., Cunliffe N.A. & Nakagomi O. (2013). Molecular epidemiology of noroviruses associated with acute sporadic gastroenteritis in children: Global distribution of genogroups, genotypes and GII.4 variants, Journal of Clinical Virology, 56 (3) 269-277. DOI: