Short‐term cultured autologous peripheral blood mononuclear cells as a potential immunogen to activate Tax‐specific CTL response in adult T‐cell leukemia patients

Activation of CD8(+) Tax‐specific CTL is a new therapeutic concept for adult T‐cell leukemia (ATL) caused by HTLV‐1. A recent clinical study of the dendritic cell vaccine pulsed with Tax peptides corresponding to CTL epitopes showed promising outcomes in ATL patients possessing limited human leukocyte antigen (HLA) alleles. In this study, we aimed to develop another immunotherapy to activate Tax‐specific CTL without HLA limitation by using patients’ own HTLV‐1‐infected cells as a vaccine. To examine the potential of HTLV‐1‐infected T‐cells to activate CTL via antigen presenting cells, we established a unique co–culture system. We demonstrated that mitomycin C‐treated HLA‐A2‐negative HTLV‐1‐infected T‐cell lines or short‐term cultured peripheral blood mononuclear cells (PBMC) derived from ATL patients induced cross–presentation of Tax antigen in co–cultured HLA‐A2‐positive antigen presenting cells, resulting in activation of HLA‐A2‐restricted CD8(+) Tax‐specific CTL. This effect was not inhibited by a reverse transcriptase inhibitor. IL‐12 production and CD86 expression were also induced in antigen presenting cells co–cultured with HTLV‐1‐infected cells at various levels, which were improved by pre–treatment of the infected cells with histone deacetylase inhibitors. Furthermore, monocyte‐derived dendritic cells induced from PBMC of a chronic ATL patient produced IL‐12 and expressed enhanced levels of CD86 when co–cultured with autologous lymphocytes that had been isolated from the same PBMC and cultured for several days. These findings suggest that short‐term cultured autologous PBMC from ATL patients could potentially serve as a vaccine to evoke Tax‐specific CTL responses.