Impact of the immunomodulating peptide thymosin alpha 1 on multiple myeloma and immune recovery after hematopoietic stem cell transplantation

Multiple myeloma (MM) is characterized by the accumulation of monoclonal plasma cells in the bone marrow and causes several immune alterations in patients. Thymosin alpha 1 (T alpha 1) is a thymic peptide that has been associated with immuno-stimulating properties. In addition, this peptide exerts anti-tumor effects in several cancer types. Beneficial effects of T alpha 1 administration have also been shown on immune reconstitution after hematopoietic stem cell transplantation (HSCT), a current treatment modality in hematological malignancies including MM. In this study, we observed a slight reduction in the proliferation of murine and human MM cell lines in the presence of T alpha 1 in vitro. However, using two immunocompetent murine MM models (5TGM1 and MOPC315.BM), we did not observe any impact of T alpha 1 administration on MM development in vivo. Furthermore, no beneficial effects of T alpha 1 treatment were observed on lymphocyte immune reconstitution after transfusion of human hematopoietic stem cells into immunodeficient mice. In conclusion, despite direct effects of T alpha 1 on human MM cell line proliferation in vitro, T alpha 1 did not exert anti-myeloma effects in vivo in the two murine models tested. Moreover, T alpha 1 failed to improve immune recovery in a xenogeneic HSCT model.