Deletion-deficient chimera-derived T cells proliferate in response to host type APC. A total of 5 × 10⁵ Splenocytes or 10⁶ thymocytes were stimulated with titrated numbers of T-cell–depleted, irradiated splenocytes. Origin of effectors and APC was as indicated in the figure. Exogenous IL-2 was added to thymocyte and splenocyte cultures unless indicated otherwise.³H-thymidine incorporation was assessed 3 to 4 days later.