MSOE > CBM > Student Programs > Science Olympiad > The Molecular Story of XIAP > Transplant

What / Where is your Immune System?

Science Olympiad Participant Your immune system – or more specifically, your adaptive immune system – is composed of a collection of hematopoietic (blood) cells that originate in your bone marrow. These blood cells can be broadly categorized as either red blood cells, white blood cells, or platelets. Lymphocytes are specific types of white blood cells that recognize foreign invaders (pathogens) and produce antibodies, or activated, cytotoxic T-cells that fight infection.

 

MHC Proteins

Because your immune system can mount a cytotoxic attack on foreign cells and pathogens, it is important that it can distinguish between "self" and "non-self". "Self" is recognized by your characteristic family of proteins that make up your Major Histocompatibility Complex (MHCs). Your specific collection of MHC proteins are displayed on the surface of your cells – – – and your immune system has evolved to recognize these MHC's as meaning "self".

The structure of a Class I MHC protein is shown in the Jmol image below. This protein will be featured in the 2012 Science Olympiad Protein Modeling event at the National Tournament.

 

Transplanting Immune Systems

The cells of your adaptive immune system have relatively short half–lives – they last only several days to weeks – compared with other cells in your body. Because they are short–lived and they circulate throughout your body, it is possible to transplant a healthy immune system from a donor into a patient whose immune system is defective in some way.

Healthy Nic Volker

In order to successfully transplant a new immune system into a patient, a donor must be identified whose cells are closely "matched" to the recipient's cells with respect to the MHC proteins that are exposed on their surface. Once the matched donor cells are in hand, the patient's defective immune cells are destroyed using toxic chemoradiotherapy that targets these rapidly dividing cells. The patient is then "rescued" by transfusing the donor immune cells – which re–populate the patient's bone marrow, where they take up residence and proliferate.

This transplant process is not without risk. After the patient's own immune system has been destroyed, and before the transplanted system has "engrafted", the patient is at risk for developing an infection from a variety of common microbes and/or viruses.

In Nic's case, the transplant was successful. And now, one year following his transplant, he is enjoying life, doing all the things little boys are supposed to do – just with a little more enthusiasm than most boys his age.

 

Uncommonly Amazing

Nic's story is one of uncommon resiliency of a family looking for help for their critically ill little boy – and the intersection of that search with the timely development of individualized genomic medicine. And while this story has a happy ending, we must be careful not to create an unrealistic expectation for this new genomic medicine. In Nic's case, once a molecular diagnosis had been made his physicians could recommend an appropriate treatment, in the form of a hematopoietic progenitor cell transplant. Unfortunately, this will not be case for many future patients whose molecular disease is diagnosed by genomic sequencing. Therefore, we must continue to support the efforts of basic and translational scientists who are working to understand the molecular details of how our bodies work, so that the development of new therapies can keep pace with our rapidly expanding ability to diagnose molecular defects at the level of the patient's DNA sequence.