Lymphoid development from hematopoietic stem cells

Mechanisms and pathways for commitment to the lymphoid lineage from hematop oietic stem cells (HSC) remain controversial. The interleukin-7 receptor (I L-7R) transduces nonredundant signals for both T- and B-cell development. R ecently, we identified a clonogenic common lymphoid progenitor population i n mouse bone marrow that can give rise to T,B, and natural killer (NK) cell s, but lacks myeloid differentiation capacity. These cells are not self-ren ewing stem cells, but progenitors that have a limited life span. HSC do not express IL-7R, and the upregulation of the IL-7R occurs at the stage of co mmon lymphoid progenitors. The IL-7R mediates nonredundant signals to reinf orce the survival of developing T cells, and to promote rearrangement of im munoglobulin heavy chain genes in B-cell progenitors. Thus, common lymphoid progenitors exist in early hematopoiesis, and expression of the IL-7R is a critical step in the initiation of lymphoid development from HSC. (C) 1999 The Japanese Society of Hematology.