Inefficient Tax-specific T-cell responses in mice after syngeneic transplantation with tax -transgenic mouse-derived adult T-cell leukemia cells

Adult T-cell leukemia (ATL) is induced by chronic latent infection of human T-cell leukemia virus type 1 (HTLV-1). HTLV-1 Tax is an oncogenic factor and can be a target for host T-cell responses. However, Tax expression in vivo is little in ATL cells and the impact of Tax-specific T-cell responses on ATL progression remains unclear. In the present study, we examined Tax-specific T-cell responses in C57BL/6 mice after syngeneic transplantation with tax-transgenic mouse-derived ATL (mATL) cells. We first confirmed that cellular tax cDNAs are mostly maintained and detectable in the spleen three weeks after mATL cell transplantation. The mATL cell transplantation did not induce significant Tax-specific T-cell responses. Mice immunized with DNA and adenovirus vectors expressing Tax elicited Tax-specific CD4(+) T-cell responses but showed no enhancement of the responses or reduction in cellular tax cDNA levels after mATL cell transplantation. This study provides an animal model for analyzing the interaction between ATL cells and host immune responses and indicates limited impact of Tax-specific T-cell responses on ATL cell proliferation.