Cells of chemically induced tumors differentially express major histocompatibility complex class I antigens

Several recent studies have indicated that alterations in expression of major histocompatibility complex (MHC) antigens by tumor cells affects the ability of the host to mount an effective antitumor immune response. To investigate whether newly induced tumors frequently exhibit altered MHC antigen expression, we used methylcholanthrene to induce a series of tumors and elevated MHC antigen expression by these cells. The tumors exhibited a variety of MHC phenotypes in vitro. The nature of their phenotypes suggested that these cells were, in fact, capable of independent and abnormal regulation of MHC class 1 genes. However, when maintained in vivo, these same tumor cells expressed measurable levels of all of the appropriate MHC class I antigens. Thus, newly induced tumor cells are capable of abnormal MHC class I antigen expression. However, there was no obvious correlation between the phenotypes exhibited by these tumor cells in vitro and either their phenotype or their tumorigenic potential in vivo.