Tumor immunization of BMT recipients increases GVT activity against preexisting leukemia.

One month after BMT, SW→ B6 recipients were challenged intravenously with 1.5 × 10⁴ C1498 cells to induce preexisting leukemia. Recipients were then either not immunized (no vaccine; solid line) or immunized 4 times with 10 × 10⁶ irradiated C1498 leukemia cells at a 1-week interval starting 3 days (day 3 vaccine; thick dashed line) or 7 days (day 7 vaccine; thin dashed line) after tumor challenge. Although immunization beginning on day 7 did not improve survival, immunization beginning on day 3 significantly enhanced survival (P = .0351) compared to the nonimmune controls.