Functional hybrids between human cytotoxic T and mouse myeloma cells

The establishment of functional human cytotoxic T lymphocyte (CTL) hybrids was investigated. Human CTL, generated in a seven-day, one-way mixed lymphocyte-tumor cell interaction (MLTI) against an allogeneic melanoma cell line (DW) in the presence of a third-party helper cell line and crude interleukin 2 (IL2), were fused with a mouse myeloma cell line (P3-X63 Ag8). Following fusion in polyethylene glycol, the hybrids were examined for cytotoxic potential against the sensitizing target cells DW. Hybrids with detectable levels of cytotoxicity were cloned in soft agar. Two clones demonstrating stable activity were selected for analysis of lineage and specificity of cytotoxicity. Both clones expressed cytotoxicity in a reasonable stable manner without dependence on IL2 for growth or function. Interferon had no effect on the cytotoxicity of the hybrids against the natural killer (NK)-sensitive target cells K562 or the DW cells. The cytotoxic activities of the hybrids against the sensitizing target cells DW, however, could be markedly facilitated in the presence of IL2-containing supernatants in the assay medium and less so in the presence of lectin. The range of the cytotoxic activities of the two clones was identical and restricted to the DW cells and another melanoma cell line, suggesting the possibility of a shared target molecule(s) between these two target cells for these cytotoxic hybrids. These observations indicate that the hybrids might require a mediator present in IL2 supernatant for optimum expression of cytotoxicity and suggest that the hybrids express the cytotoxic specificity of the hybridized CTL. These hybrids offer unique opportunities for critical examination of the molecular mechanisms of cellular cytotoxicity and specificities exhibited by activated human CTL.