Immunosuppressor T cells in tumor bearing host.

Thymus or spleen cells of tumor bearing animals (TBA) (methylcholanthrene induced sarcoma bearing A/Jax mice) were shown to possess immunosuppressor cells regulating the immune response to the tumor in syngeneic animals. The immunosuppressive activity of these cells of TBA was totally abolished by the in vitro treatment of anti-theta serum and complement. Soluble factor(s) with identical suppressive activity was isolated from the thymus cells of TBA and its molecular size was estimated to be lower than that of serum albumin in terms of its elution behaviour on gel filtration through a Sephadex G-200 column. These immunosuppressor T cells or their soluble factor(s) may be largely responsible for the growth of antigenic tumors.