Immunoprotective capability of somatic hybrid cells in comparison with parental tumor cells maintained in vitro.

The immunogenicity of X-irradiated hybrid cells derived from fusion of ASL-1 leukemia (A origin) and LM (TK-) fibroblasts (C3H origin) was compared to X-irradiated parental ASL-1 leukemia cells maintained in vivo (V-ASL-1) and to X-irradiated ASL-1 leukemia cells maintained in vitro (C-ASL-1). Immunization with hybrid cells induced transplantation resistance against tumor rechallenge with V-ASL-1 more effectively than did immunization with V-ASL-1 tumor cells. Immunization with X-irradiated C-ASL-1 cells produced the same, or slightly stronger level of transplantation resistance than that with X-irradiated hybrid cells. These findings were observed both in A/J and in (C3H/HeJ X A/J)F1 mice. These results raise a question about whether the apparent increased immunogenicity of hybrid cells is due to a result of cell fusion or a result of their growth in vitro.