Cytokine requirement for the development of T-lymphoid lineage potential in clonal lymphohaematopoietic progenitors in vitro

The early process of T-cell development prior to thymic colonization has be en poorly investigated because of the lack of a sensitive assay, We have de veloped a two-step in vitro culture system by combining a clonal culture wi th a fetal thymus organ culture (FTOC) and analysed the early development o f T cells from lymphohaematopoietic progenitors. Cells of immature colonies derived from bone marrow cells of 5-fluorouracil (5FU)-treated mice using various combinations of early acting cytokines were transferred into a FTOC . All the combinations of stem cell factor (SCF), interleukin (IL)-3 and IL -6 capable of inducing colony formation supported T-cell generation. IL-11 and the Flt3 ligand possessed T-lineage promotional effects similar to IL-6 and SCF respectively However, there were some quantitative differences in the final T-cell yield among cytokine combinations. Thus, the commitment to wards T lineage in lymphohaematopoietic progenitors may be an event determi ned intrinsically rather than induced by specific stimuli, but there map be a hierarchy between the activity of cytokines in further development. Furt hermore. we examined the T-lineage potential of individual colonies derived from Lin(-)c-Kit(+)Sca-1(+) cells clone-sorted from post-5FU marrow cells. No colonies that contained only myelocytic progenitors showed T-lineage po tential, but 23.3% of colonies with a haematopoietic multipotentiality did. Therefore, the divergence of the T lineage from other lineages such as mye loid potential may occur at an early stage of the hierarchy of haematopoies is. The proposed method should prove valuable for exploring the molecular a nd cellular changes that occur during early T-cell development before thymi c colonization.