The over all objectives of this project is to establish a hemopoietic stem cell model which can be tested to study and understand the mechanism of self renewal and/or commitment to differentiated cell types by a primitive cell. A high incidence of lineage, undifferentiated cells was identified in the spleens of female NZB mice. Phenotyic, morphological, histochemical, genomic and functional characterization of the purified population suggested that these may be very primitive cells of the hemopoietic system. In Vitro, these cells were found to differentiate in reponse to a few early-acting lymphokines and a bone marrow stromal cell conditioned medium. In that, both myeloid (adherent mac-1+), and lymphoid (CD3+, surface Ig+), cell type were detectable. In vivo, these cells were found to differentiate and reconstitute immunodeficient SCID mice. Circulating immunoglobulines of both IgM and IgG class were detectable by ELISA in the seara of reconstituted mice 6, 8 and 12 week post transfer. Mac-1+, CD3+, and sIG+ cells were detectable in the spleens of these reconstituted mice. During the present reporting period (October 1991 through September 1992), the in vivo reconstitutability of splenic stem cells were further investigated in comparison with the stem cells from bone marrow, mature splenic cells originating from the same donors. In parallel, similar cell types from BALB/c mice were also investigated. By 12 weeks post transfer, both bone marrow cells and splenic stem cells but not splenic mature cells) from both NZB and BALB/c mice were found to be completely reconstituted. In that, B220+ were detectable in the peritoneal cavity. The reconstituted mice were found to mount immune response when challenged with SRBC.
