ImmYOUnology

More than just vaccines


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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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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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Training the immune system to kill cancer

Have you ever heard the term “cancer vaccine?”  Are there really vaccines to prevent cancer, and do they really work? The truth is, it’s kind of a misnomer. The vaccine against herpes papilloma virus (HPV) is often called a cancer vaccine, but it’s actually a vaccine to prevent an infection that can lead to cancer.  In other cases, the term “cancer vaccine” describes a treatment that trains immune cells to attack cancer cells.  There is one FDA-approved vaccine treatment for prostate cancer, but there are ongoing clinical trials for many other types of cancers. 

One recent clinical trial for patients with glioblastoma found that a cancer vaccine approach significantly extended the patients’ lives. Glioblastoma is the most common and most aggressive type of tumor that originates in the brain, and the average survival after treatment is about a year. This vaccine approach tested at Cedars-Sinai Medical Center in LA was so significant is because it gave half of the patients about five years.  The results of the study were reported at a meeting, but the details of the trial and initial findings were published in January.

Researchers collected large numbers of white blood cells (immune cells) from the volunteers through a process called leukapheresis, which separates immune cells and returns red blood cells and other blood components back to the donor.  They were after a rare cell type called monocytes that can morph into different cell types depending on their environment. Monocytes originally come from the bone marrow and remain round and smooth as they roll through the blood. Given the right signals, they can leave the blood for other tissues and change into macrophages or dendritic cells, both rugged spindly cells that poke out tiny arms to sense their environment.  

If you put white blood cells in a culture dish, as the scientists at Cedars-Sinai did,  the monocytes will stick to the bottom of the dish in just a couple of hours. Then you can wash away all of the other cells and keep just the monocytes. After about a week, they will morph on their own into macrophages—cells that eat up pathogens or other dead cells.  But if you add a couple of signaling proteins called cytokines, the monocytes will become dendritic cells.

Dendritic cells also eat up foreign material, but they are somewhat more refined at it. They break down everything that they eat and then present little pieces of it to educate other immune cells about what is going on in the body. T cells are their main pupils, and have receptors that sense what the dendritic cells are displaying.  Then both types of cells can make proteins to attack the foreign material (bacteria, cancer cells, infected cells) and signal other cells to start a cascading immune response.

Our bodies use this process to fight infection and to prevent cancers from developing. But once a tumor is formed, tumor cells are very effective at re-educating T cells and other immune cells.  Tumor cells can make proteins that lull and calm immune cells so that they can’t respond or don’t recognize the tumor cells as foreign. Technically, cancer cells aren’t foreign, but mutated and rebellious.  Proteins displayed on cancer cells can be distorted or can be made in excess, distinguishing them from normal cells.

File:Dendritic cell therapy.png

By Simon Caulton. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

The idea behind cancer vaccines is to prepare dendritic cells outside of the body and put them back in where they can push immune system toward actively attacking tumors. The researchers at Cedars-Sinai coaxed monocytes into becoming active dendritic cells in culture. Then they gave the cells peptides, or pieces of proteins, that resembled the ones made in high abundance on glioblastoma cells.  Years of research went into simply identifying exactly which proteins were overproduced by these cancer cells and which would best activate the dendritic cells.  This study used six peptides to activate and train the dendritic cells.  Then the cells were sent back into the patients near their lymph nodes, which are full of T cells awaiting instructions.

Variations on this method are being tested for breast cancer, melanoma, leukemia and many other cancers. The outcomes will depend on which peptides are used, which peptides are made by each person’s tumor, how well one’s cells grow in culture and respond to activation and other variables. It’s a simple idea—to use the body’s own defenses to fight cancer—but there is a lot more to learn about this fascinating and promising treatment.

Sources:

The National Cancer Institute 

Vaccine promises longer survival for brain tumor patients, Belinda Weber Medical News Today, Nov 2013

Phase I trial of a multi-epitope-pulsed dendritic cell vaccine for patients with newly diagnosed glioblastoma, Phuphanich S, Wheeler CJ, et al. Cancer Immunol Immunother. Jan 2013