Increase in immunogenicity of a pulmonary squamous-cell carcinoma, propagated in vitro.

The chemically induced, non-immunogenic lung squamous-cell carcinoma (MSC-10) propagated in vitro gradually loses tumorigenicity in immunocompetent hosts with increasing in vitro passage. This was found to be related to an increase in antigenicity, since immunosuppressed hosts (thymectomy plus 600 rads whole body X-irradiation) supported the growth of tumor cells, whereas immunocompetent recipients did not. The antigens involved in rejection are not heterologous serum proteins present in culture media since the cell line grown in isologous serum is also rejected. Immunization with the in vitro tumor line partially protected against the parental in vivo line, therefore the antigens involved must be present on both tumor lines. Inoculation of the cultured cell line into normal or immunosuppressed hosts produced tumors with the same histological characteristics as those of the in vivo tumor line. We concluded that by in vitro culture the weakly antigenic carcinoma becomes more immunogenic and thereby capable of inducing transplantation resistance. The cultured tumor cells retain their antigenic specificity and histologic characteristics while increasing their antigenic potency.