SP37A3 cells stimulate alloantigen-specific cytotoxic T cells in vivo. Mature SP37A3 cells (1 × 10⁶) were transferred intravenously into BALB/c mice. After 7 days, equal numbers (1 × 10⁷) of syngeneic CFSE^low-labeled BALB/c spleen cells and allogeneic CFSE^high-labeled spleen cells from C57BL/6 and FVB/N mice, respectively, were mixed and injected intravenously into recipient mice or naive mice as control. In vivo cytotoxicity against the allogeneic target cells was assessed after 12 hours. Spleen cells (SCs) and lymph node cells (LNCs) were collected, and the proportion of CFSE^high target cells as a percentage of total CFSE⁺ cells was determined by flow cytometry. Histograms show representative data from individual mice; bars represent mean ± SEM of 6 mice per group, obtained in 2 independent experiments. ***P < .001 compared with naive mice receiving CFSE^high C57BL/6 target cells.