Sorted CFSE^bright cells after MLR have reduced ability to mediate GVHD. Purified murine CD4⁺ T cells were stimulated with T-cell- and NK cell-depleted MHC class II disparate splenocytes. After 8 days of culture, viable cells were analyzed. (A) MLR cultured cells were analyzed for intensity of CFSE staining; 65% of the cells were blasts, and a precursor frequency of approximately 3% was calculated. The CFSE^bright gate was the sole parameter for sorting. Postsort evaluation reveals cells are markedly depleted of primed CFSE^dim cells. Results were typically more than 98% purity. (B) Sorted CFSE^bright T cells have much reduced GVHD-causing potential. After culture, the CFSE^bright or CFSE^dim cells were sorted, and 3 × 10⁵ were transplanted. Results are from 2 pooled experiments. Mean survival times were as follows: sorted control, 20 days; CFSE^dim cells, 21 days; and CFSE^bright cells, more than 60 days (not reached). Comparison of CFSE^bright versus sort control was very significant (P < .0003).