Due to their central role in controlling immunity, dendritic cells are logical targets for priming naive cytotoxic T lymphocytes against tumour cells. In a strictly autologous system, we fused dendritic cells with melanoma cells, both of which were derived from patients with metastatic malignant melanoma. Hybridomas were positive for major histocompatibility complex (MHC) class II, CD40, CD54, CD83, CD86, and the pro-inflammatory cytokine interleukin-12. Autologous T lymphocytes were co-incubated with hybridomas. After 6 days, in-vitro-primed T lymphocytes revealed a strong proliferation activity and released Th-1-associated, but not Th-2-associated, cytokines. Furthermore they showed effective anti-melanoma activity, resulting in death of 70 +/- 9% of autologous melanoma cells. After depletion of CD4+ cells from the mixed population of primed T lymphocytes, the remaining CD8+ cells were able to kill 63+/-8% of autologous melanoma cells. Following depletion of CD8+ cells, however, the cytotoxic capacity of the remaining T lymphocytes caused death in only 32+/-6% of autologous melanoma cells. Blocking of MHC class I, but not class II, molecules on hybridomas impaired T cell proliferation, secretion of Th-1-associated cytokines, as well as the cytotoxic activity of primed T cells. These findings strongly suggest that hybridomas deliver melanoma-associated antigens via MHC class I molecules to T lymphocytes, resulting in the generation of CD8+ cytotoxic T lymphocytes with effective anti-melanoma activity in vitro. The data may serve as a basis for the use of hybridomas in the immunotherapy of malignant melanoma in vivo.