Loss of Transplantation Antigen in Primary Simian Virus 40-Induced Tumors and Their Metastases

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Abstract
Cell suspensions, prepared from primary tumors induced by simian vacuolating virus (SV40) in 22 hamsters, and 17 lung metastases of these tumors were inoculated into adult normal hamsters and hamsters immunized with SV 40. The presence of specific tumor cell antigen responsible for immunity was studied. Some of the primary tumors were obtained from animals immunized by reinfection with SV 40 at the end of the latent period. All the tumors studied soon after their appearance in nonimmunized hamsters contained the transplantation antigen. However, the gradual loss of transplantation antigen, apparently due to the autoimmunization of the host, took place during the growth of the tumor. A direct correlation between the loss of specific antigen and the duration of tumor growth in immune organism confirms this point. The disappearance of antigen from the metastases is detected earlier than from the original tumor node. Immunization of hamsters at the latent period hastens the process of antigen loss, so that at the time the tumor appears, or soon after, the antigen is absent from some tumors. Preliminary data on the possible role of humoral Factors of immunity in the antigen loss are presented. The incidence of metastases in hamsters immunized during the latent period was the same as that for nonimmunized hamsters. Data on the tumor cell accumulation in macroscopically normal lung tissues of tumor-bearing immunized and non immunized hamsters are included.