LYMPHOCYTE DIFFERENTIATION FROM PRECURSOR CELLS IN VITRO *

Much of the recent work in our laboratory has centered about an induction assay developed by Komuro and Boyse in which one of the early maturational steps in the T-cell development, the differentiation from prothymocyte to early thymocyte, can be induced in vitro within two hours. This assay is based on a decade of work concerned with the characterization of cell-surface markers, especially the cytotypic differentiation alloantigens of murine T-cells. As a result of this work on the cell-surface composition of murine lymphocytes, we can summarize the antigenic phenotype of the cortical thymocyte as shown in FIGURE 1. The maturational step in the pathway of T-cell differentiation that can be induced in vitro involves the appearance of this characteristic antigen profile on the surface of the precursor cell; it can be seen that in this differentiation event the products of at least six unlinked genes are expressed. This rapid in vitro T-cell induction assay clearly had potential as a possible bioassay for the identification of the thymic hormone responsible for inducing T-cell differentiation in vivo. Our further studies were designed to answer pertinent questions with respect to this possible application of the assay.