CHEMICALLY-INDUCED SARCOMAS FROM NUDE-MICE ARE MORE IMMUNOGENIC THAN SIMILAR SARCOMAS FROM CONGENIC NORMAL MICE

To detect possible differences in immunogenicity between tumors induce d in T cell-deficient mice and phenotypically normal congenic mice, 16 sarcomas, 8 having developed in nude BALB/c mice and 8 having develop ed in congenic normal (nu/+) mice, were transplanted to normal BALB/c recipients and the rates of rejection or acceptance were registered. T he 16 tumors were chosen randomly from a panel of 39 sarcomas induced with 0.5 % or 0.1% 3-methylcholanthrene and maintained as cell lines i n culture. Out of the tumors originating from nude mice, 66% were reje cted by the normal BALB/c recipients, while only 30% of the tumors ori ginating from normal mice were rejected. Tumors with short induction t imes from normal mice were more readily accepted than tumors with long induction times. Tumors originating from nude mice had significantly longer mean latency times after transplantation to both normal and nud e recipients than tumors originating from normal mice. Contrary to wha t has been reported by others, there was no correlation between the re jection rates of the individual tumors and their K-d, D-d or L(d) majo r histocompatibility complex (MHC) class I surface expression as measu red by flow cytometric analysis of cultured tumor cells. The K-d, D-d and L(d) proteins of the transplanted tumor lines were analyzed by iso electric focusing for the occurrence of mutations resulting in altered charge of the MHC protein. No such mutations were found, ruling out M HC mutations of that kind as the source of immunogenicity in the cell lines used in these experiments. Our results suggest the existence of a T cell-mediated selection in the original tumor cell mass of tumors induced in normal mice, adapting the tumor to growth in a host with a functional T cell system, but apparently there is no connection betwee n this loss of immunogenicity and loss of MHC class I expression.