Using Human Induced Pluripotent Stem Cells to Study Diamond Blackfan Anemia

Diamond-Blackfan Anemia or DBA results from mutations in a gene on chromosome 19 (in most cases). Mutations in the ribosomal protein S19 affects the ability of blood cells to make protein and causes low numbers of red blood cells. DBA patients are dependent on blood transfusions, but some are cured, to some extent at least, by bone marrow transplants. Unfortunately, some DBA patients have severe side effects from bone marrow transplants, which means that bone marrow transplants are not a panacea for all DBA patients.

Fortunately, Michell J. Weiss and his colleagues at the Children’s Hospital of the Philadelphia (CHOP) have used human induced pluripotent stem cells (iPSCs) to study DBA at the molecular level and even develop the beginnings of a cure for DBA patients. Weiss collaborated with Monica Bessler, Philip Mason, and Deborah French, all of whom work at CHOP.

Remember that red blood cells are made inside the bone marrow of the patient by hematopoietic stem cells (HSCs). HSCs divide to renew themselves, and to produce a daughter cell that will differentiate into one of several different types of blood cells. As a kind of gee-wiz number, a healthy adult person will produce approximately 10[11]–10[12] (100 billion to 1 trillion) new blood cells are produced daily in order to maintain steady state levels in the peripheral circulation.

In DBA patients, the bone marrow is empty of red blood cells. In order to get a better idea why, Weiss and his team isolated fibroblasts from the skin of DBA patients, and used genetic engineering techniques to convert them into iPSCs. When Weiss and his group tried to differentiate these iPSCs derived from DBA patients into red blood cells, they were not able to make normal red blood cells. However, Weiss and his colleagues used different genetic engineering techniques to fix the mutation in these iPSCs. After fixing the mutation, these cells could be differentiated into red blood cells. This experiment showed that it is possible to repair a patient’s defective cells.

This is a proof-of-principle experiment and there are many hurdles to overcome before this type of experiment can be done in the clinic to DBA patients. However, these iPSCs can play a vital role in deciphering some of the mysteries surrounding this disease. For example, two family members may have exactly the same mutation, but only one of them shows the disease whereas the other does not. Since iPSCs are specific to the patient from whom they were made, Weiss and his group hope to compare the molecular differences between them and understand the difference in expression of this disease.

Also, these cells offer a long-lasting model system for testing new drugs or gene modifications that may offer new treatments that are personalized to individual patients.

Weiss and his research group used this same technology to test drugs for the often aggressive childhood leukemia, JMML or Juvenile Myelomonocytic Leukemia. Once again, iPSCs were made from JMML patients and differentiated into myeloid cells, which divided uncontrollably just as the original myeloid cells from JMML patients.

Weiss and his colleagues used these cells to test two drugs, both of which are active against JMML. One of them is an inhibitor of the MEK kinase that was quite active against these cells. This illustrates how iPSCs can be used to test personalized treatment regimes for patients.

The stem cell core facility at CHOP is also in the process of making iPCS lines for several inherited diseases: dyskeratosis congenita, congenital dyserythropoietic anemia, thrombocytopenia absent radii, Glanzmann’s thrombasthenia, and Hermansku-Pudlak syndrome.

The even longer term goal is the use these lines to specifically study the behavior of such cells in culture and under certain conditions, test various drugs on them, and to develop treatment strategies on them as well.

Allergy-Relevant Stem Cell Affected by Smoking

A research team at the Helmholtz Center for Environmental Research (UFZ) led by Drs. Irina Lehmann and Kristin Weiβe has found evidence for a link between a particular stem cell population and environmental toxins.  These results could have significant implications for allergy sufferers.

All the blood cells are made by hematopoietic stem cells in the bone marrow.  These bone marrow stem cells divide to renew themselves and generate progenitor cells that can divide a little and differentiate into specific types of blood cells.  The progenitor cells spend some time in the bone marrow, but are released into the peripheral bloodstream to replenish lost blood cells.

One particular progenitor cell is called the eosinophil/basophil progenitor, and this multipotent stem cells can either differentiate into an eosinophil or a basophil.  Eosinophils help fight parasite infections, but they also play an important role in allergies.  Basophils can fight infections, but they also become stationary in tissue and are known as mast cells where they can release chemicals that cause allergies in response to allergen, which are substances that cause allergies.

Several previous studies have shown that allergy sufferers, be they children or adults, have higher levels of eosinophil/basophil progenitor cells circulating in their blood, and that those individuals whose umbilical blood has higher levels of circulating eosinophil/basophil progenitor cells are at higher risk for allergies later in life.

The UFZ team wanted to clarify the relationship between allergies and the presence of eosinophil/basophil progenitor cells.  Since environmental toxins are known to stimulate allergies in younger people, they hypothesized that environmental toxins might increase the quantity of circulating eosinophil/basophil progenitor cells in young children.

Lehmann and Weiβe examined blood samples from 60 one-year old children and used skin tests to measure the tendency of these children to form rashes after exposure to allergens (substances that cause allergies).  The skin tests are a measure of the sensitivity of the children to allergies.  They also measured the levels of environmental toxins  to which the children’s families were exposed.

The results from this study were remarkable.  Children whose families were exposed to higher levels of volatile organic compounds or VOCs, which are quite prevalent in cigarette smoke, showed higher levels of circulating eosinophil/basophil progenitor cells and were more sensitive to allergens.  Thus the environmental influences seemed to influence the levels of those stem cells known to sensitize people to allergies.

Lehmann noted:  “That VOCs, large amounts of which are released with cigarette smoke, have the greatest effect on stem cells was not entirely unexpected.”

Adding to this, Weiβe said:  “Just as important, however, is that we can show that alterations in the number of stem cells as a result of harmful substances that place only in children who have been afflicted with skin manifestations.”  Thus there is a direct relationship between someone’s genetic predisposition for a disease and the environmental influences to which they are exposed.  Another way to say this would be that there are environmental and lifestyle factors which determine whether a genetic predisposition to have allergies results in actually suffering from allergies.  The environmental effects influence the levels of a circulating stem cell known to play a role in allergies.