Thymostimulin increases natural cytotoxic activity in patients with breast cancer

The effect of thymostimulin on the Natural Killer (NK) cytotoxic activity of peripheral blood mononuclear cells (PBMC) was investigated in 15 patients with breast cancer after finishing or during chemotherapy (CAF) and in 10 healthy controls. PBMC from these subjects were incubated in the presence of thymostimulin for varying periods of time (18 h or 5 days), and then used as effector cells against 51Cr-radiolabeled NK-sensitive (K-562) and NK-resistant (JY) target cells in cytotoxicity assays. No significant differences were observed between the NK-activity from breast cancer patients and healthy controls. Thymostimulin induced a dose- and time-dependent cytotoxic enhancing effect on the cytotoxic activity of PBMC from these patients against NK-sensitive K562 target cells. The thymostimulin (1000 ng/ml) significantly enhanced cytotoxic activity in PBMC from breast cancer patients who had previously received chemotherapy (p = 0.0277) against NK-sensitive cells. This increase was not statistically significant neither in PBMC from patients receiving chemotherapy nor in healthy controls (p > 0.05 in both cases). The incubation of PBMC from patients with breast cancer was not associated to a significant enhancement of the cytotoxic activity against NK-resistant target cells (p > 0.05). We also found that thymostimulin could synergize with interleukin-2 in inducing NK cytotoxic activity in PBMC after 18 h of culture (p = 0.0277). In conclusion, we have demonstrated that thymostimulin enhances the natural killer cytotoxic activity of PBMC from patients with breast cancer who have previously received chemotherapy.