Cytotoxic function of perforin expressed in murine P14/Prf1^−/− splenocytes. Murine splenocytes expressing human perforins were coincubated with gp33-loaded EL4 target cells in a standard chromium release assay. Cytotoxicity was measured by the percentage of chromium released from targets. The negative control cells were transduced with vector alone (no perforin). WT indicates wild-type human perforin. The top panel is a single representative assay. Each E/T coincubation is performed in quadruplicate to generate a mean plus or minus SE. The bottom panel is the data summarized from 3 independent retroviral transductions followed by cytotoxicity assays, graphed as a percentage of WT function for each assay. Only the T435M and vector alone were different from WT. *Statistical significance (2-tailed Student t test, P < .01).