A syngeneic anti tumor serum recognizing a complex H-2 alloantigen.

A methylcholanthrene induced tumor of BALBc (H-2d) origin had a high rate of spontaneous regression when transplanted into syngeneic animals. The tumor induced in BALB/c mice iso-antibodies with high anti-tumor cytotoxic activity. A specificity analysis of such BALB/c anti MCG4 sera revealed that the antibodies were directed against a tumor antigen which is very similar to H-2- alloantigens (e.g. H-2.5) expressed on normal cells of certain foreign mouse strains. The sera also reacted with nine out of ten B10.W congenic strains bearing H-2wi haplotypes derived from wild mice. Whether the tumor antigen is identical with foreign H-2 antigens or only cross-reactive cannot be decided at present.