Age-related and thymus-dependent rejection of adenovirus 2-transformed cell tumors in the Syrian hamster

Adenovirus type 2-transformed hamster cell-induced newborn tumor lines were usually rejected when transplanted s.c. into 21-day-old syngeneic, weanling hamsters. The tumor-inducing capacity of two of these lines (Ad2HTL3 and Ad2HTL6) was tested in intact and neonatally thymectomized hosts. After s.c. injection of suspensions prepared from these lines, none of the weaning hamsters developed tumors while 100% of the newborns and 35.2% of neonatally thymectomized, weanling hamsters developed progressively enlarging neoplasms. The susceptibility of neonatally thymectomized hamsters to tumor challenge was directly related to the degree of immunosuppression observed following thymectomy as indicated by the amplitude of the in vitro response of blood leukocytes to concanavalin A. Pretreatment of thymectomized weanlings with syngeneic adult lymphoid cells (i.p.) resulted in a significant reduction in tumor susceptibility (p = 0.03). These findings suggest that acquisition of resistance to adenovirus type 2-transformed cells during the first 21 days of life may be a thymus-dependent cellular immune process.