The effect of T lymphocyte deficiency on tumor induction and growth

Severe reduction in the numbers of T lymphocytes as occurs in thymectomized, X-irradiated, bone marrow reconstituted mice or nude mice did not increase the animals susceptibility to chemical carcinogenesis. However, once established, many tumors grew distinctly slower in the T cell deficient animals. This was demonstrated to be due to lack of normal T cell function since tumors arising in TXB hosts progressed much faster in normal secondary hosts than in secondary TXB hosts. In most instances, established tumor cell lines from tissue culture also grew more slowly in T deficient hosts. The suggestion was made that T cells may not be required for immune surveillance while the immune mechanism(s) that promote subsequent tumor growth are T cell dependent. Alternative possibilities are discussed.