Characterization of the Syngeneic Anti‐tumour Response Against the Gr9

Isoantisera and syngeneic monoclonal antibodies have been produced against A7, a clone derived from a BALB/c methylcholanthrene-induced tumour named GR9. The antigens defined by the isoantisera and mAbs are widely distributed in a large number of GR9 clones as well as in other tumour cell lines of different aetiology and origin. Two GR9 clones with marked differences in H-2 expression and syngeneic in vivo growth (A7, which is H-2d-positive and highly immunogenic and B-9, which is H-2d-negative and highly malignant) were selected to further analyse the presence or absence of the antigens recognized by the syngeneic anti-tumour antibodies. Immunoprecipitation data with two different isoantisera revealed a group of proteins with a molecular weight of Mr 65-70,000 present in both clones. Furthermore, immunoprecipitation with the A7-1 mAb again showed a single Mr 65K band present in A7 and B9 clones. We conclude that the marked differences observed in the syngeneic growth of the two clones are not due to differences in tumour associated antigens (TAA), defined by syngeneic antibodies, and emphasize the role that class I H-2 antigens could play in tumour rejection.