The effects of x-irradiation and anti-lymphocyte serum on the responses to tumour allografts.

The growth of a CBA mammary adenocarcinoma has been studied following transplantation to syngeneic and allogeneic recipients, with particular reference to the susceptibilities of the primary and secondary responses elicited by the tumour allografts, to impairment by whole-body X-irradiation and by treatment with rabbit-anti-mouse lymphocyte serum. In syngeneic recipients, the diameter of tumour implants increases linearly with time and there is no difference in the growth curves in females and in males. Later tumour generations grow faster than earlier generations. In allogeneic recipients, there is a relationship between the tumour diameter on day 21 (T) and the dose of X-irradiation (D) administered before implantation:T = 0.028 D - 9.17for early tumour generations (SMT4) but this is obscured for later generations (SMT21). The primary response to tumour allografts was radiosensitive whereas the secondary response was radioresistant. This radioresistance of the secondary response persisted for at least 5 months after primary sensitization. Unlike whole-body X-irradiation, treatment with rabbit-anti-mouse lymphocyte serum suppresses both the primary and secondary responses to tumour allografts. The possibility is considered that after exposure to antigenic stimulation, an immunologically reactive cell population is formed which is radioresistant but sensitive to ALS, unlike the precursor cells from which this population is derived, which are radiosensitive and sensitive to ALS.