Cellular immune response to virus‐specific antigen in hamsters bearing isografts of cytomegalovirus‐transformed cells

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Abstract
The immune response of hamsters to syngeneic transplants of hamster embryo fibroblasts (HEF) transformed by cytomegalovirus (CMV) was investigated. Using the microcytotoxicity assay it was found that spleen cells from tumor‐bearing hosts consistently killed both homologous tumor cells and CMV‐infected human embryonic lung (HEL) cells. No significant cytotoxicity was observed when uninfected HEL, normal HEF, or HEF transformed by herpes simplex virus type 1 (HSV‐1) or PARA‐(defective SV40)‐adenovirus 7 (PARA‐7) served as the target cells. Spleen cells from animals bearing isografts of HSV‐1‐ and PARA‐7‐transformed cells were cytotoxic for their respective tumor cells but not for CMV‐transformed cells. Further studies showed that spleen cells from CMV or CMV‐infected HEL immunized hamsters were specifically cytotoxic for CMV‐transformed hamster cells. No antibody cytotoxic for CMV‐transformed cells was detected in the sera of CMV or CMV‐infected HEL‐immunized hosts, or in sera from tumor‐bearing animals. The results corroborate previous serological data that hamster cells transformed by CMV express virus‐related membrane antigen (s), and demonstrate that such antigen (s) can induce a cell‐mediated immune response in the tumor‐bearing host.