In mice whose immune systems were knocked down by a chemotherapy drug, a synthetic peptide called thymosin‑alpha‑1 quickly restored immune function, especially T‑cells and macrophages, at very low doses (5‑50 µg per kg). This shows the peptide can help rebuild blood‑forming cells after severe damage, but the work was done in animals, not people.

We found that both thymosin from calf thymus and its constituent peptide alpha 1 prepared by chemical synthesis restore cell-mediated immunity following its suppression in mice by injection of 5-FU. Conditions suitable for assessing the thymosin activity by means of footpad reaction were established in such immunosuppressed mice. In this new animal model, thymosin alpha 1-peptide showed activity at a low dose of 5-50 micrograms/kg, which was 100-1,000 times less than that required for thymosin F-5 preparations. Further studies utilizing the adoptive transfer technique showed that alpha 1-peptide corrects the 5-FU-induced suppression of mature T cells, transferring the DTH response as well as that of macrophage function responsible for the expression of footpad reaction. Furthermore, regeneration of lymph node and bone marrow cells as well as CFU-c (progenitor cells of macrophages and granulocytes) was enhanced by thymosin alpha 1 in the 5-FU-treated mice. All these results indicate that thymosin alpha 1 accelerates the replenishment and maturation of haematopoietic cells, including not only T cells but also macrophages, when they have been severely damaged by the 5-FU treatment.