GVHD-like reactions are doubtful when the TCR repertoire is limited. (A,B). C57BL/6–pmel-1 (H-2^b/b) cells were stimulated with the relevant peptide and cultured for 1 week in IL-2 and subsequently challenged in overnight cocultures against irradiated splenocytes derived from different inbred mouse strains (SJL, H-2^s/s and DBA, H-2^d/d) and F1 mice (B6-A F1, H-2^b/a; B6-C3H F1, H-2^b/k; and B6-BALB/c F1, H-2^b/d) displaying different allogeneic MHC haplotypes in the presence or the absence of the relevant peptide gp100_25-33 (+ pep). Syngeneic C57BL/6 H-2^b/b irradiated splenocytes in the presence or the absence of the relevant gp100_25-33 peptide were used as positive and negative controls, respectively. Panels A and B are representative of 2 independent experiments. (C) pmel-1 cells were generated on a B6-C3H F1 background (H-2^b/k) and used in combination with vaccinia virus encoding hgp100 and exogenous rhIL-2 to treat B16 tumors established for 10 days in either B6-C3H F1 (SynPVI) or in B6-DBA F1 mice (H-2^d/b) (AlloPVI). All groups were irradiated with 9 Gy TBI and given autologous BMT. Some groups also received different doses (10⁴ or 10⁵) of open repertoire B6-C3H F1 CD8⁺ naive T cells in conjunction with pmel-1 cells, vaccine, and rhIL-2 (AlloPVI + 10⁵ CD8 and AlloPVI + 10⁴ CD8). Results of tumor area are the mean of measurements of at least 5 mice per group (± SEM). Data are representative of 2 independent experiments. (D) Percentage of initial weight of mouse groups is shown.