A T lymphoid cell line responds to a thymic stromal cell line by expression of Thy-1 and CD4

We have cloned both T lymphoid and stromal lines from a single murine thymic tumor that was induced by a retrovirus carrying the v-myc oncogene (M-MuLV(myc]. The T lymphoid line, L4, was cloned by growth in agar. L4 cells were initially negative for Thy-1.2 and CD4 (although they contained rearranged TCR-beta genes), and they remained so if passaged in medium alone. However, cocultivation of these Thy-1.2- CD4- cells with the cloned stromal cell line, St3, resulted in sequential expression of Thy-1.2 and CD4 in subpopulations of cells. Thy-1.2+ CD4- and Thy-1.2+ CD4+ L4 subclones were obtained from the cocultures by subsequent cloning in agar. Derivation of these subclones from the starting Thy-1.2- CD4- clone was verified by Southern blot analyses specific for TCR-beta gene rearrangements and for M-MuLV(myc) proviral integration sites. Continuous cocultivation of Thy-1.2+ CD4+ L4 subclones with the St3 stromal cells was necessary for maintenance of CD4 on the cell surface. Furthermore, CD4 expression which was lost when CD4+ L4 cells were removed from the stroma could be reinduced if they were again cultured on St3 stroma. These cells may provide a model system for studying thymocyte-stromal cell interactions in induction and maintenance of expression of Thy-1 and CD4 molecules.