A number of oncogene-containing retroviruses will be examined for their ability to infect fetal thymocytes. The infected cells will be introduced into lymphocyte-depleted fetal thymus rudiments which are known to supply all of the factors necessary for thymocyte proliferation and differentiation. Infection will be assayed by the ability of virus-infected cells to induce foci or drug-resistant colonies in NIH 3T3 cells. The criterion for successful infection will be the establishment of persistently infected lymphocyte populations which can proliferate within rudiments and which have the phenotypic properties known to be associated with thymocyte progenitors. This strategy will identify candidate oncogene-containing retroviruses which can be used in attempts to establish temperature-sensitive progenitor cell lines. T-lymphocytes are one of the major cell lineages that comprise the cells of the imune system. There are two major difficulties that currently impede study of T-lymphocyte differentiation: 1) the relevant progenitors are minor constituents of a heterogeneous population of cells, and 2) there is no simple in vitro system that permits the clonal expression of thymocyte progenitors in quantity. This project, if successful, will develop a cell culture system that would permit isolation of cloned populations of thymocyte progenitors in quantity and the study of their differentiation into mature thymocytes. Although at present this research must be regarded as "high risk", the potential for the use of such a system in basic studies of T-cell development is very great.
