ES cells have only a limited lymphopoietic potential after adoptive transfer into mouse recipients.

While hematopoietic stem cells from adult and fetal stages of murine development are capable of long term reconstitution of all mature blood lineages in vivo, embryonic hematopoietic stem cell repopulation in vivo has proved difficult. It is thought that there are many fewer hematopoietic stem cells in the embryo than in the fetal/adult stages of mouse development and that these cells possess a different developmental potential. One source of such cells are embryonic stem (ES) cells which can differentiate into most mature blood lineages in vitro. We have therefore used transplantation of differentiated ES cells to assess the hematopoietic potential of embryonic hematopoietic cells in vivo. We demonstrate here that precursors obtained from in vitro cultures of normal ES cells can contribute only to restricted and limited hematopoiesis in a mouse without leading to tumour formation. Repopulation occurs for greater than 6.5 months at levels ranging from 0.1% to 6% in B and T cell lineages in peripheral blood. In contrast to in vitro colony data demonstrating the myeloid lineage developmental potential of ES cells, no donor-derived myeloid repopulation was observed in CFU-S assays and no macrophage and mast cells were found in long term repopulated recipients. Thus, the hematopoietic potential of ES cells in vivo is limited to low levels of repopulation and is restricted to the lymphoid lineage.