Thymic hormonal activity on human peripheral blood lymphocytes, in vitro. IV. Proliferative response to allogeneic tumor cells in healthy adults and cancer patients.

A mixed lymphocyte tumor culture (MLTC) assay was used in order to assess thymic hormonal activity on human T-lymphocyte function. Peripheral blood mononuclear cells (PBMC) from 55 healthy subjects and 54 immunodeficient cancer patients were incubated with the thymic extract TP-1, cultured with allogeneic tumor cells (Raji lymphoma or IgR3 melanoma cells) under limiting stimulation conditions and their proliferative response measured by 3H-thymidine incorporation. Mean proliferative response in the cancer group was lower than in the healthy group. TP-1 caused a significant enhancement of mean proliferative response, comparable in the healthy and cancer groups, under all the conditions tested. Analysis of response in the individual cases disclosed a wide scatter of TP-1 effects, including some cases of TP-1 induced suppression. A significant negative correlation between TP-1 effect and level of proliferative response in control was found: enhancement of proliferative response by TP-1 became progressively greater as control proliferative response became progressively lower. A similar pattern was noticed in the cases of TP-1 induced suppression. The negative correlation was similar for the healthy and cancer groups. These results cannot be interpreted in terms of restoration of deficient immune functions, but are compatible with an indirect, regulatory effect of TP-1 on proliferative response, exerted to a comparable degree in the healthy and immunodeficient situations. The possibility that thymic factors regulate normal immune functions, not merely restore deficient functions to normal, may have interesting clinical implications.