Transgene IL-21-Engineered T Cell-Based Vaccine Potently Converts CTL Exhaustion via the Activation of the mTORC1 Pathway in Chronic Infection

CD8+ cytotoxic T lymphocyte (CTL) exhaustion is one of the major obstacles for the effectiveness of virus control in chronic infectious diseases. We previously generated novel ovalbumin (OVA)-specific 41BBL-expressing OVA-TEXO and human immunodeficiency virus (HIV-1) Gag-specific Gag-TEXO vaccines, inducing therapeutic immunity in wild-type C57BL/6 (B6) mice, and converting CTL exhaustion in recombinant OVA-specific adenovirus AdVOVA-infected B6 (AdVOVA-B6) mice with chronic infection. IL-21 cytokine plays an important role in controlling chronic infections. Therefore, in this study, we constructed recombinant transgene IL-21-expressing AdVIL-21, and generated IL-21-expressing OVA-TEXO/IL-21 and Gag-TEXO/IL21 vaccines, or control vaccines (OVA-TEXO/Null and Gag-TEXO/Null) by infecting OVA-TEXO and Gag-TEXO cells with AdVIL-21 or the control AdVNull, lacking transgene, and assessed their effects in B6 or AdVOVA-B6 mice. We demonstrate that both OVA-TEXO/IL-21 and control OVA-TEXO/Null vaccines are capable of converting CTL exhaustion in chronic infection. However, the OVA-TEXO/IL-21 vaccine more efficiently rescues exhausted CTLs by increasing stronger CTL proliferation and effector cytokine IFN-γ expression than the control OVA-TEXO/Null vaccine in AdVOVA-B6 mice with chronic infection, though both vaccines stimulated comparable OVA-specific CTL responses and protective immunity against OVA-expressing BL6-10OVA melanoma lung metastasis in wild-type B6 mice. In vivo, the OVA-TEXO/IL-21-stimulated CTLs more efficiently up-regulate phosphorylation of mTORC1-controlled EIF4E and expression of mTORC1- regulated T-bet molecule than the control OVA-TEXO/Null-stimulated ones. Importantly, the Gag-TEXO/IL21 vaccine induces stronger Gag-specific therapeutic immunity against established Gag-expressing BL6-10Gag melanoma lung metastases than the control Gag-TEXO/Null vaccine in chronic infection. Therefore, this study should have a strong impact on developing new therapeutic vaccines for patients with chronic infections.