A long-term culture system for the expansion of hematopoietic stem cells from embryonic yolk sac with the capacity to seed erythroid and lymphoid development in vitro and to reconstitute the lymphoid compartment in severe combined immunodeficient mice.

We have established a long-term culture system under which hematopoietic stem cells derived from the embryonic yolk sac may be maintained for long periods. Evidence for the persistence of stem cells in this culture is provided by three experimental observations. First, erythroid progenitors, as evidenced by morphological, functional, and phenotypical analysis, may be generated from these yolk sac cultures after more than 7 months in culture. The yolk sac derived erythroid progenitors are distinct from those of bone marrow derived cells both qualitatively and quantitatively. This is evidenced by the high colony plating efficiency, large colony size, different growth factor requirements, increased sensitivity to Epo and other cytokines, as well as significant and prolonged expansion capability, suggesting that the yolk sac derived progenitors are both more proliferative and more primitive than their bone marrow derived analogs. Second, under different conditions, lymphoid progenitors may also be derived from these long term yolk sac cultures in the presence of the appropriate cytokines. Third, preliminary data suggest the engraftment of these yolk sac cells and reconstitution of at least some compartments of the hematopoietic system of host animals. This long-term culture system will provide a useful model for the study of early embryonic hematopoiesis, and the cells derived from this culture system may also have the potential of serving as donor cells for hematopoietic cell transplantation.