Outbreak or not, vaccine immunology is still exciting

The recent US measles outbreak ended just over a week ago. But with an even larger outbreak ongoing in Sudan, and rising concerns over the possibility of one in Nepal, measles vaccination is still a hot topic globally. (Though for me, viruses and vaccines are always hot topics).

I saw a graph a couple of months ago that shows a huge plunge in measles cases and deaths in the few years leading up to the 1968 licensure of the measles vaccine. The graph actually comes up quickly if you do an image search for “measles graph.” I’ve seen it used to support the argument that the measles vaccine just doesn’t work and is therefore not worth the trouble.

I dug up the primary data used for this graph and made my own (below). It shows that measles cases dropped before introduction of the 1968 vaccine (measles deaths follows the same pattern). But you’ll also see that this plunge occurred two years after the first version of the measles vaccine was licensed in 1963.  I am not a public health expert, but it’s pretty clear that the drop in cases and deaths from measles came after licensure of the initial measles vaccine.

I did this research to both appease my curiosity and demonstrate that the question of whether the vaccine works on a population scale has been settled for a long time.  That doesn’t mean that on an individual level it’s impossible to get sick even if being vaccinated against measles.

There are many potential reasons one may not respond to a vaccine. These range from very basic reasons, like the vaccine being stored at the wrong temperature or being injected incorrectly, to complex biological reasons that are active areas of ongoing research.  For example, we know that mothers’ antibodies (or immunoglobulins) circulate in newborns for about 12 months. Although these antibodies can protect a newborn from pretty much anything its mom is immune to, they also prevent the child’s own immune system from generating memory responses to the same diseases. Mom’s antibodies can actually cover up viruses and bacteria and hide them from baby’s immune cells. They can also form complexes with bits of virus or bacteria that bind a receptor that shuts down B cells, the cell responsible for making new antibodies. This receptor, called FcγRIIb, is part of a negative feedback system that tells B cells when they’ve made enough antibodies.

All of these possibilities are part of why the CDC recommends two shots separated by at least a month; statistically, getting two shots means you’re covered because the chance that your immune system would miss out twice in a row is very low. Still, the only way to be 100% sure an individual responded to the vaccine is to measure the level of antibodies in the blood that can bind to and neutralize the measles virus. For different viruses, there are different thresholds for the concentration of antibodies needed to protect a person from getting sick. When a vaccine is first tested, antibody levels are monitored to make sure it actually works. After that, it would be too expensive and unnecessary to measure antibodies in every person who receives the vaccine. So, even though two shots should do the trick statistically, there’s always a remote chance the vaccine just didn’t induce a good immune response, and most of the time, no one would be the wiser.

There was such case in New York City back in 2011, in which a woman who had gotten both requisite vaccinations still managed to get sick. The researchers who did this study measured measles-neutralizing antibodies in the woman’s blood and found that she was making a kind of antibody that the body mainly produces the very first time it sees a pathogen. That kind of antibody is called immunoglobulin M (IgM), and it’s a sort of knee-jerk, immature antibody response that keeps the virus at bay as the immune system generates the more mature, “stickier” IgG. So her body was acting as though it had never seen the measles before, even though she was vaccinated twice.  This is not a huge surprise; even after two shots, the failure rate for the measles vaccine is 3%.

What was unique was that she also ended up spreading measles to 4 other people who were also vaccinated (that’s 4 out of a total of 88 contacts).  All of these people made strong IgG responses and none of them spread the virus to anyone else. And, unlike the first case, none of them were hospitalized—even one who was on immunosuppressive drugs. So this study shows that yes, it is possible to get measles and even spread it to others if you’ve been fully vaccinated. It’s an anomaly, but it’s possible. In fact, that’s what made this case so interesting—the fact that it was so unlikely.

With all the variables of human life, it’s a wonder that the measles vaccine works 97% of the time. This study shows that even when it doesn’t work, the measles virus can’t go far if enough people are vaccinated. The strong secondary immune responses of those 4 cases made their illness less severe and reduced their chances of spreading the disease any further.

Sources

Committee to Review Adverse Effects of Vaccines; Institute of Medicine; Stratton K, Ford A, Rusch E, et al., editors. Adverse Effects of Vaccines: Evidence and Causality. Washington (DC): National Academies Press (US); 2011 Aug 25. 4, Measles, Mumps, and Rubella Vaccine. Available from: http://www.ncbi.nlm.nih.gov/books/NBK190025/

Niewiesk S. (2014). Maternal Antibodies: Clinical Significance, Mechanism of Interference with Immune Responses, and Possible Vaccination Strategies, Frontiers in Immunology, 5 DOI: http://dx.doi.org/10.3389/fimmu.2014.00446

Rosen J.B., C. J. Hickman, S. B. Sowers, S. Mercader, P. A. Rota, W. J. Bellini, A. J. Huang, M. K. Doll, J. R. Zucker & C. M. Zimmerman & (2014). Outbreak of Measles Among Persons With Prior Evidence of Immunity, New York City, 2011, Clinical Infectious Diseases, 58 (9) 1205-1210. DOI: http://dx.doi.org/10.1093/cid/ciu105

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.

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

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.

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.

*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: 10.1371/journal.ppat.1003592.s001

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: 10.1016/j.jcv.2012.11.011

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.

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