ImmYOUnology

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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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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:

Cancer immunotherapy named Science breakthrough of the year for 2013

It was exciting to see today that Science Magazine called cancer immunotherapy the breakthrough of 2013. The author Jennifer Couzin-Frankel calls it a “breakthrough strategy” and though she admits the approach is not yet widespread, she highlights promising clinical trials that have stacked up this year. “Immunotherapy marks an entirely different way of treating cancer-by targeting the immune system, not the tumor itself,” she wrote. The article deals mainly with experiments focused on activating T cells by blocking surface proteins that shut T cells down. To learn more about other approaches, see my post about cancer vaccines.  


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A closer look at the immune response to DTaP may explain why it wears off

In my last post, I wrote about how the vaccine against whooping cough or pertussis (the “p” in DTaP) may be wearing off.  Scientists are hard at work characterizing the basics of the immune response to the current acelluar vaccine (DTaP) and the formerly prevalent whole bacteria vaccine (DTP).

What exactly does it mean for a vaccine to “wear off”?  Effectiveness is generally measured by how many vaccinated people get sick.  To follow the immune response to a vaccine, scientists measure immunoglobulin (Ig) levels in the blood.  Ig is made by B cells when these cells detect components either made by bacteria or viruses or engineered into vaccines. Among other things, Ig tags bacteria and viruses as a signal for other cells to attack. As the initial immune response downgrades, B cells that make the strongest-binding Ig are stored as memory B cells or as a different form of B cell called a plasma cell.

Memory B cells wait quietly until they see the same microbe and quickly divide and make large amounts of Ig when they do. Plasma cells wait inside bone marrow and constantly release Ig into the blood as an early defense against any re-exposure to a microbe. Measuring Ig over a long period of time is essentially measuring the health and activity of the plasma cells in the bone marrow.  Ig from both types of B cells help neutralize a re-invading pathogen.

Vaccine protection could wane if the vaccine didn’t produce enough memory B cells or plasma cells, or if cells formed but then quickly died off.  So Ig levels, memory B cells and plasma cells have been common benchmarks to study after vaccination.

Kids enrolled in a Dutch study published in September experienced major drops in pertussis-specific Ig two years after their last booster shots.  But this was true for both the whole bacteria and acellular vaccines.

These results are difficult to interpret because the researchers measured Ig responses to the very three proteins engineered into the acellular vaccine.  The whole bacteria vaccine has a lot more than three proteins that B cells can respond to. So even if Ig levels to the three proteins in the study may be lower, the whole cell vaccine could be inducing an overall higher amount of Ig that is just spread over a larger number of proteins and that information could be missed.

By counting memory B cells from in blood samples the scientist also found that kids given either type of vaccine produced some memory B cells that expanded during the first month after booster but dropped back down by the two year time point. Measuring plasma cells in bone marrow is a bit more challenging in human volunteers, but a study published in 2010 tried to compare these cells in mice after giving them DTaP or DTP.

This group actually found more plasma cells in the bone marrow of the DTaP -vaccinated animals. (Again, the issue of only testing the three antigens found in the DTaP may have skewed these results.) They also found poor memory B cell survival and responsiveness to both forms of the vaccine.

The B cells don’t seem to be acting differently in response to the two vaccines. In fact, the current data suggest that B cells do better after the DTaP, so poor B cell responses are unlikely the main culprit behind the vaccine’s waning protection.

Memory T cells are another force to be reckoned with for infectious bacteria like B. pertussis. The same Dutch study that found better long-term pertussis-specific Ig after the acellular vaccine also saw better T cell responses a year after boost with the whole bacteria vaccine.

An in-depth look at the pertussis-specific memory T cells suggested the whole bacteria vaccine may be better at making memory T cells. Instead of making Ig like memory B cells, memory T cells respond to re-exposure to bacteria or viruses by making immune-stimulating proteins called cytokines.  A group of researchers cultured T cells from kids given the acellular or whole cell vaccine with pertussis proteins (again the same three found in the acelluar vaccine).  The T cells made after whole bacteria vaccine responded by making more cytokines than the ones made in response to the acellular vaccine.  These T cells also divided after detecting the pertussis proteins and were twice as likely to make cytokines and divide at the same time.

These are early studies, but it seems that the T cells may be what differentiate the two vaccines.  None of these basic immunology studies followed kids over time to see whether they became infected.  Hopefully this last study will encourage researchers to look for any relationships between T cell responses and long term pertussis immunity.

Sources:

Differential T- and B-cell responses to pertussis in acellular vaccine-primed versus whole-cell vaccine-primed children 2 years after preschool acellular booster vaccination. SchureRM, et. al. Clin. Vaccin Immunol. Sept, 2013

Impaired long-term maintenance and function of Bordetella pertussis specific B cell memory. Stenger RM, et al. Vaccine. Sept 2010

Different T cell memory in preadolexcents after whole-cell or acellular pertussis vaccination. Smits K, et. al. Vaccine. Oct 2013