HTLV-1 Tax-specific memory cytotoxic T lymphocytes in long-term survivors of aggressive-type adult T-cell leukemia/lymphoma

Purpose Adult T-cell leukemia/lymphoma (ATLL) is a relatively refractory peripheral T-cell lymphoma caused by human T-cell lymphotropic virus type 1 (HTLV-1). The objective of this study was to investigate the characteristics of long-term survivors with ATLL. Methods We conducted an observational study of 75 aggressive-type ATLL patients. Flow cytometry was conducted to analyze HTLV-1 Tax-specific cytotoxic T-lymphocytes (CTLs) and T-cell receptor V beta gene repertoire. Results We first evaluated six long-term survivors among 37 patients who were newly diagnosed with ATLL and then treated with intensive chemotherapy without mogamulizumab, a monoclonal antibody for C-C chemokine receptor four antigen. Reversal of the CD4-to-CD8 ratio (CD4/CD8) in peripheral mononuclear cells was observed in all six patients. Three of these six patients showed reversed CD4/CD8 immediately after herpes virus infection. Four of these six patients who could be examined demonstrated long-term maintenance of HTLV-1 Tax-specific CTLs. We subsequently identified four long-term survivors among 38 patients who were newly diagnosed with ATLL and then treated with intensive chemotherapy plus mogamulizumab. All four patients showed reversed CD4/CD8, and three of the four patients contracted herpes virus infection during immunochemotherapy. Six of the total 10 patients were subjected to CTL analyses. Tax-specific CTLs were observed, and the CTLs that were almost entirely composed of memory CTLs in all patients were recorded. HTLV-1 provirus was also detected in all six patients. Conclusions These data suggest that Tax-specific memory CTLs probably, together with anticancer agents, eradicate ATLL cells and exhibit long-term preventive effects from relapse ATLL. Thus, the strong activation of cellular immunity, such as herpes virus infection, seems to be necessary to induce such a potent number of Tax-specific CTLs.