Absence of IFN-γ signaling on donor bone marrow abrogates GVHD but maintains vaccine responses. (A) Weights were recorded on mice that received either wild-type or IFN-γR1^−/− allogeneic DLI at a dose of 20 × 10⁶ cells given on days 14 and 28 after reconstitution with wild-type bone marrow. Other recipients received wild-type or IFN-γR1^−/− allogeneic bone marrow followed by a normal, alloreactive DLI at a dose of 20 × 10⁶ cells on days 14 and 28; 7 mice/group. (B) Spleens harvested on day 42 were analyzed by flow cytometry for enumeration of lymphocyte subsets. The percentage of the lymphocyte subset was multiplied by the splenocyte count to obtain an absolute number of cells. *P < .05; **P < .01. (C) ELISPOT analysis of CD8⁺ and CD4⁺ T cells to the H-Y antigens were performed on day 42 comparing 4 groups of thymus-bearing mice: mice who received allogeneic bone marrow (BM) without DLI, allogeneic BM with an alloreactive DLI, allogeneic BM with IFN-γR1^−/− allogeneic DLI, and IFN-γR1^−/− BM with an alloreactive DLI. All DLIs used 5 × 10⁶ cells and were given on day 14 and 28, 8 mice/group. *P < .05, **P < .01, ***P < .001.