Vaccine responses after allogeneic BMT are significantly decreased to both class I and class II H-Y antigens in both thymus-bearing and thymectomized recipients but can be restored using T cells tolerized in a separate thymus-bearing host. None indicates no DLI was given; Low, a DLI dose of 10⁶ cells; Moderate, 5 × 10⁶ cells; and High, 10 or 20 × 10⁶ cells, which produce equivalent results. All DLIs were given on days 14 and 28. (A) ELISPOT analysis of CD8⁺ and CD4⁺ T cells to the H-Y antigens was assessed in thymus-bearing recipients on day 42 after BMT, 7 to 11 mice/group, *P < .05. (B) ELISPOT analysis of CD8⁺ and CD4⁺ T cells to the H-Y antigens were assessed in thymectomized recipients on day 42 after BMT, 8 to 11 mice/group. *P < .05, **P < .01, ***P < .001.