Question

. Would you expect a good clinical outcome from a bone marrow transplant that used only CD150 negative cells? (Yes/No).

Explain your answer providing details about the way these cells would perform in a bone marrow transplant.

Answer 1

CD150 or signaling lymphocyte activation family member 1 (Slam F1) is expressed by long term hematopoietic stem cells (HSC). These co-receptors signal via SAP, a small adapter protein and are involved in T lymphocyte adhesion, cytotoxicity, cytokine production and survival of immune cells.

When bone marrow rich in CD150 HSC cells are transplanted, there is a higher chance of the bone marrow transplant to be successful. This is because CD150High HSC has higher self –renewal property as compared to CD150neg HSC. They, thus regenerate the primitive stem cell compartment faster than CD150neg HSC. CD150 distinguishes long term HSC (LT-HSC) from multipotent progenitors (MPPs). MPPs lack CD150 marker on cell surface. Both LT-HSC and MPPs can give rise to all types of blood cells. However, MPPs are not able to sustain this production of blood cells for a long time. The CD150neg HSCs are mostly MPPs.

It is known that CD150high HSC cells can self-renew to form CD150highHSC cells. They can also divide to form CD150low HSC cells and CD150neg HSC cells. However, CD150neg HSC cannot form CD150highHSC. LT-HSC expresses both CD150 and CD34 markers. They form short term progenitors cells which can then differentiate into CD150 neg MPPs or CD34+ MPPs. The CD34+ MPP can form mostly myeloid lineage while the CD150neg MPPs can form mostly lymphoid lineage.

Thus, CD150neg HSC cells can divide to form lymphoid blood cells lineages, but because of their slow self-renewal properties, they cannot maintain the blood population for a long time. The bone marrow transplant should replace all HSC in the individual. Hence, there should be maintenance of long term blood population. This would not be possible with CD150neg HSC bone marrow transplants.

These CD150neg HSC cells can however reconstitute the lymphoid system, which the first step for lymphocyte differentiation. They are highly lymphoid and faint myeloid progenitors. Thus, they will be beneficial for secondary transplantation.

Right choice: No.