In mice with a fast‑growing blood cancer, giving thymosin‑alpha‑1 together with tiny amounts of IL‑2 or interferon and a low dose of the chemo drug cyclophosphamide made the tumors disappear and helped the animals live longer. The effect only happened when the three were combined and relied on immune cells like CD4, CD8 and NK cells.

We investigated the effects of the systemic administration of thymosin alpha 1 plus relatively low doses of human recombinant interleukin-2 or very low doses of interferon alpha,beta in untreated and cyclophosphamide (CY)-treated DBA/2 mice challenged either subcutaneously or intravenously (i.v.) with Friend erythroleukemia cells (FLC). Both treatments resulted in the complete regression of subcutaneous tumor and cured a significative percentage of mice. They also increased the survival time of mice i.v. injected with large numbers of FLC. Neither immunotherapy alone nor CY, alone or in combination with single cytokines, produced similar effects. The antitumor action of these combined chemoimmunotherapy protocols seems to involve activation of the immune response since (a) a synergistic increase of the cytotoxicity of spleen cells was demonstrated in treated mice; (b) selective in vivo depletion of asialo-GM1, CD4, or CD8-positive cells abrogated this antitumor activity; and (c) a high lymphoid cell infiltration was found at the tumor site and in the livers of treated mice.