Signal-transducing adaptor protein-2 promotes generation of functional long-term memory CD8+ T cells by preventing terminal effector differentiation.

Long-surviving memory CD8+ T cells generated by stimulation with appropriate tumor-associated antigens are the most aggressive and persistent tumoricidal effectors. In this event of memory CD8+ T cell development, the signal transducer and activator of transcription (STAT) proteins function as the crucial intracellular signaling molecules, but the regulatory mechanism of STATs in CD8+ T cells is not fully understood. In this study, we report for the first time, by using murine vaccination models, that signal-transducing adaptor protein-2 (STAP2) maintains the cytotoxicity of long-lived memory CD8+ T cells by controlling a STAT3/suppressor of cytokine signaling 3 (SOCS3) cascade. Following T cell activation, STAP2 expression was transiently reduced but was subsequently recovered and augmented. Analysis using small-interfering RNA (siRNA) demonstrated that restored STAP2 expression was associated with the activation of STAT3/SOCS3 signals and maintenance of cytotoxic T lymphocytes (CTLs) secondary responses by preventing their differentiation into terminal effector cells. Notably, this STAP2-dependent memory differentiation was observed in the spleen, but not in the lymph nodes (LNs). These findings indicate an essential role for STAP2 in the generation of a high-quality memory CD8+ CTLs periphery, and suggest the therapeutic potential of STAP2 in cancer patients.

Stimulation through very late antigen-4 and -5 improves the multifunctionality and memory formation of CD8⁺ T cells.

T cells express multiple integrin molecules. The significance of signaling through these molecules on acquisition of T-cell effector functions and memory formation capacity remains largely unknown. Moreover, the impact of stimulation through these signals on the generation of T cells for adoptive immunotherapy has not been elucidated. In this study, using a recombinant fragment of fibronectin, CH-296, we demonstrated that stimulation via very late Ag (VLA)-4 and VLA-5 in human and BALB/c mouse CD8(+) T cells, in combination with TCR stimulation, enhances effector multifunctionality and in vivo memory formation. Using TCR-transgenic mouse-derived CD8(+) T cells expressing TCR specific for the syngeneic CMS5 fibrosarcoma-derived tumor Ag, we showed that stimulation by CH-296 improved the ability of tumor-specific CD8(+) T cells to inhibit CMS5 tumor growth when adoptively transferred into hosts with progressing tumors. Improved antitumor effects were associated with decreased infiltration of Foxp3(+) CD4(+) Treg cells in tumors. These results suggest that stimulation via VLA-4 and VLA-5 modulates the qualities of effector T cells and could potentially increase the efficacy of adoptive therapy against cancer.

T-cell receptor gene therapy targeting melanoma-associated antigen-A4 inhibits human tumor growth in non-obese diabetic/SCID/γcnull mice.

Adoptive cell therapy with lymphocytes that have been genetically engineered to express tumor-reactive T-cell receptors (TCR) is a promising approach for cancer immunotherapy. We have been exploring the development of TCR gene therapy targeting cancer/testis antigens, including melanoma-associated antigen (MAGE) family antigens, that are ideal targets for adoptive T-cell therapy. The efficacy of TCR gene therapy targeting MAGE family antigens, however, has not yet been evaluated in vivo. Here, we demonstrate the in vivo antitumor activity in immunodeficient non-obese diabetic/SCID/γc(null) (NOG) mice of human lymphocytes genetically engineered to express TCR specific for the MAGE-A4 antigen. Polyclonal T cells derived from human peripheral blood mononuclear cells were transduced with the αß TCR genes specific for MAGE-A4, then adoptively transferred into NOG mice inoculated with MAGE-A4 expressing human tumor cell lines. The transferred T cells maintained their effector function in vivo, infiltrated into tumors, and inhibited tumor growth in an antigen-specific manner. The combination of adoptive cell therapy with antigen peptide vaccination enhanced antitumor activity, with improved multifunctionality of the transferred cells. These data suggest that TCR gene therapy with MAGE-A4-specific TCR is a promising strategy to treat patients with MAGE-A4-expressing tumors; in addition, the acquisition of multifunctionality in vivo is an important factor to predict the quality of the T-cell response during adoptive therapy with human lymphocytes.