Ability of thymosin to decrease in vivo and in vitro suppressor cell activity in tumor bearing mice and cancer patients.

We have demonstrated that splenic lymphocytes from normal syngeneic animals can stimulate tumor growth. This effect is T-cell dependent. Preincubation of these lymphocytes with thymosin not only blocks facilitated tumor growth but can induce a significant reduction of local tumor growth and number of pulmonary metastases. Furthermore, thymosin can also block the expression of suppressor activity of lymphocytes either stimulated by Con A or originating from various advanced solid tumor bearing patients. These results therefore suggest that thymosin is able to modulate, directly or indirectly, functional expression of suppressor cells.