Rejection of A20HA B-cell lymphoma in the absence of cross-presentation mediated by BM-derived APCs. H-2^dxb F1 mice were lethally irradiated (10 Gy [1000 rad]), and each received a graft consisting of 4 × 10⁶ bone marrow cells from either BALB/c SCID (H-2^d) or C57BL/6 SCID (H-2^b) donors. Three months after bone marrow reconstitution, either group of chimeras intravenously received 1 × 10⁶ in vitro activated CD4⁺ TCR-transgenic T cells (H2^dxb) specific for HA/IE^d. Four weeks later, all the mice were challenged intravenously with 1 × 10⁶ A20HA cells, and they were inspected twice weekly for the development of tumors. Six mice were included in each group (P < .01). Data are representative of 3 experiments with similar results.