Unfractionated lymph node cells and purified CD4+ cells were sufficient to reject cardiac xenografts in B6 rag1−/− recipients (11.4 +\− 1.7 days, n=5 and 13.0 +/− 2.6 days, n=4 respectively). Column purified CD4+ cells were incapable of rejecting xenografts when adoptively transferred to C2D rag1−/− mice (>100 days, n=5, p<0.005). Unreconstituted C2D rag1−/− mouse recipients cannot reject rat cardiac grafts (>100 days, n=3). They are still incapable of rejecting rat hearts after reconstitution with column purified B6 CD4+ LNCs. Although we did not expect an antibody involvement in our rag−/− recipients, we did perform flow cytometry for IgG, IgG1 and IgG2a to confirm that our column purified T-cell preparations were not contaminated. These immunoglobulins were all evident in wild type mice that had rejected rat grafts, but totally absent in B6rag−/− and C2Drag−/− recipients (data not shown).