We studied, in vitro, the stimulating effects of a commercial preparation of low molecular thymic peptides (TP) on the immunocytotoxicity of peripheral blood lymphocytes and monocytes from patients with breast tumors, melanoma and colorectal tumors. On average, tumor patients showed a lower natural killer (NK), lymphokine (IL-2) activated killer (LAK) cell and basic tumoristatic activity of monocytes, compared with healthy donors. There was no correlation between the NK-cell number and the NK-cell activity of the tumor patients. The TP showed no effects on the NK-cell activity in any group, yet elevated the deficient LAK-cell activity of tumor patients and that of healthy donors. On monocytes, TP enhanced the deranged tumoristatic activity only in tumor patients, while being slightly inhibitory on control monocytes. Dividing the donors on the basis of the TP effects on cytotoxicity of the mononuclear cells into TP-nonresponders and TP-responders, a higher number of TP-responders was found among tumor patients, compared with healthy donors. Moreover, a higher number of TP-nonresponders were observed with lymphocytes from colorectal tumor patients at advanced tumor stage. Therefore, on the basis of the applied immunocytotoxic assays, these results may provide a basis for selecting tumor patients, who may respond to TP in immunotherapy protocols.

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