Abstract
Although ropeginterferon alfa-2b has recently been clinically applied to myeloproliferative neoplasms with promising results, its antitumor mechanism has not been thoroughly investigated. Using a leukemia model developed in immunocompetent mice, we evaluated the direct cytotoxic effects and indirect effects induced by ropeginterferon alfa-2b in tumor cells. Ropeginterferon alfa-2b therapy significantly prolonged the survival of mice bearing leukemia cells and led to long-term remission in some mice. Alternatively, conventional interferon-alpha treatment slightly extended the survival and all mice died. When ropeginterferon alfa-2b was administered to interferon-alpha receptor 1-knockout mice after the development of leukemia to verify the direct effect on the tumor, the survival of these mice was slightly prolonged; nevertheless, all of them died. In vivo CD4(+) or CD8(+) T-cell depletion resulted in a significant loss of therapeutic efficacy in mice. These results indicate that the host adoptive immunostimulatory effect of ropeginterferon alfa-2b is the dominant mechanism through which tumor cells are suppressed. Moreover, mice in long-term remission did not develop leukemia, even after tumor rechallenge. Rejection of rechallenge tumors was canceled only when both CD4(+) and CD8(+) T cells were removed in vivo, which indicates that each T-cell group functions independently in immunological memory. We show that ropeginterferon alfa-2b induces excellent antitumor immunomodulation in hosts. Our finding serves in devising therapeutic strategies with ropeginterferon alfa-2b.