Understanding the reconstitution of the B‐cell compartment in bone marrow and blood after treatment for B‐cell precursor acute lymphoblastic leukaemia

Summary A better understanding of the reconstitution of the B‐cell compartment during and after treatment in B‐cell precursor acute lymphoblastic leukaemia ( BCP ‐ ALL ) will help to assess the immunological status and needs of post‐treatment BCP ‐ ALL patients. Using 8‐colour flow cytometry and proliferation‐assays, we studied the composition and proliferation of both the B‐cell precursor ( BCP ) population in the bone marrow ( BM ) and mature B‐cell population in peripheral blood ( PB ) during and after BCP ‐ ALL therapy. We found a normal BCP differentiation pattern and a delayed formation of classical CD 38 dim ‐naive mature B‐cells, natural effector B‐cells and memory B‐cells in patients after chemotherapy. This B‐cell differentiation/maturation pattern was strikingly similar to that during initial B‐cell development in healthy infants. Tissue‐resident plasma cells appeared to be partly protected from chemotherapy. Also, we found that the fast recovery of naive mature B‐cell numbers after chemotherapy was the result of increased de novo BCP generation, rather than enhanced B‐cell proliferation in BM or PB . These results indicate that post‐treatment BCP ‐ ALL patients will eventually re‐establish a B‐cell compartment with a composition and B‐cell receptor repertoire similar to that in healthy children. Additionally, the formation of a new memory B‐cell compartment suggests that revaccination might be beneficial after BCP ‐ ALL therapy.