A cloned lymphoid Thy1+ tumor line derived from murine yolk sac cells maintained in long-term cell culture in the absence of a thymic microenvironment expresses an unusual cell surface phenotype.

We have previously established conditions under which murine yolk sac cells can be maintained in vitro in the absence of thymus, and we reported that a spontaneously transformed Thy1.2+ yolk sac cell line was obtained after long term culture in vitro. We now provide further phenotypic characterization of a clone, YSA1, of this Thy1.2+ cell line showing that it expresses Thy1.2, CD3/TCR V beta 8, IL-2 receptor (IL2R), and heat stable antigen (HSAg), but does not express CD4/CD8 or TCR gamma delta. The YSA1 clone is an immature cell as indicated by the expression of IL2R and HSAg and by nonproduction of IL-2 upon stimulation by anti-CD3 antibody. The data show that yolk sac stem cells can differentiate into CD3/TCR expressing cells in the absence of thymus, but do not progress in vitro paralleling observations made on freshly-isolated yolk sac stem cells.