Effects of Thymosin Fraction 5 in Cancer Patients: In Vitro Studies and Correlations with Clinical Course in Patients Receiving Thymosin

Abstract

Previous studies assessing the immunological effects of thymosin fraction 5 indicate that its major immunologic effect is reconstitution of immune defects rather than augmentation of relatively normal levels of cell-mediated immunity to significantly higher levels. Paralleling these observations, in studies of the effect of thymosin on T-cell levels in vitro among normal and cancer patients we found that, in general, T-cell levels increased after incubation with thymosin in populations with low initial T-cell levels and decreased in populations with high initial T-cell levels. We also studied blood specimens from patients with small cell carcinoma of the lung receiving intensive chemotherapy who were randomized to receive no further therapy (C), thymosin 20 mg/m2 (T20), or thymosin 60 mg/m2 (T60) twice weekly during the first six weeks of therapy, and among whom increased survival occurred in patients receiving T60. In this treatment group there was a significant correlation between complete tumor remission and low CEA levels. Furthermore, the patient group with low pretreatment T-cell or α2HS-glycoprotein levels receiving T60 had significantly prolonged survival compared to a similar group of patients receiving chemotherapy alone. In contrast, patients receiving T60 with high pretreatment T-cell or α2HS-glycoprotein levels did not achieve significantly enhanced survival compared to a similar group of patients receiving chemotherapy alone. These observations suggest that cancer patients most likely to benefit from adjuvant treatment with thymosin are those with relatively low parameters of cellular immunity. The in vitro correlations with clinical course illustrate the potential usefulness of certain serum glycoproteins in identifying such patient groups.