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Novel HIV-1 Gag-specific Exosome-targeted CD8+ T cell-Based Therapeutic Vaccine Capable of Converting CTL Exhaustion in Chronic Infection



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Human immunodeficiency virus type 1 (HIV-1) is the cause of acquired immune deficiency syndrome (AIDS). HIV-1 is a worldwide epidemic that currently affects over 35 million people worldwide, and continues to spread at an appalling rate. A universal HIV-1 preventive vaccine is considered to be the optimal solution in achieving the ultimate goal of AIDS eradication. Regretfully, most endeavors thus far of developing a prophylactic vaccine have been largely disappointing. Highly Active Anti-Retroviral Therapy (HAART) has been shown to reduce the plasma HIV-1 RNA level to below the detection limit of clinical assays (50 copies/ml); it combines three or more antiretroviral drugs which belong to at least two different classes – targeting distinct steps in the viral life cycle, and inhibiting viral replication. However, unless the infection is eradicated, strict adherence to a lifelong treatment regimen is required. HAART is limited by its high cost, drug availability, complicated administration schedules, serious side effects, and the potential that the virus will ultimately develop drug resistance. A more plausible approach lies in therapeutic vaccines that provide immunity to partially control viral replication postinfection – delaying or minimizing ART, and offering “drug holidays”. The primary goal of a therapeutic vaccine is to effectively induce HIV-1 specific cytotoxic T lymphocyte (CTL) responses, which plays a critical role in control of viral proliferation. Dendritic cells (DCs)-based therapeutic vaccines have been showing the most promising results. However, the therapeutic efficacy of DCs based vaccines is limited. This is partially due to the fact that DCs induced CD8+ T cell responses are largely CD4+ T cell dependent, while HIV-1 infection usually renders the immune system very “helpless” from CD4+ T cells. In addition, infection, impaired function, and physical depletion of DCs are often reported during the early stage. Furthermore, DCs are often found to be inflammatory and immunosuppressive, which is mainly mediated by the interaction between HIV-1 Env gp120 and DC receptors. Thus, the search for a novel therapeutic vaccine strategy is warranted. Using T-APC (T cells-antigen-presenting cells) as a novel T cell-based vaccine has emerged as a potential candidate for a HIV-1 therapeutic vaccine, which aims at boosting HIV-specific CTL responses. Our previous work demonstrated that CD4+ and CD8+ T cells derived from ovalbumin (OVA)-specific T cell receptor (TCR) transgenic OT II and OT I mice via co-culture with OVA-pulsed DCs (DCOVA) can be activated, acquiring pMHC I, pMHC II, and costimulatory molecules, thus act as CD4+ T helper-antigen-presenting cells (Th-APCs) and CD8+ cytotoxic T-antigen-presenting cells (Tc-APCs). We also elucidated that DC-derived exosomes (EXO), which are 50- to 90-nm diameter vesicles containing antigen-presenting, tetraspan, adhesion, and costimulatory molecules, can transfer the antigen-presenting activity of DCs to activated CD4+T cells through EXO uptake. EXOOVA-targeted activated CD4+T (aTexo) cells can (1) stimulate more efficient central memory CD8+ CTL responses and T cell memory than EXOOVA or DCOVA, (2) activate CD8+ CTL responses independent of CD4+Th cells, and (3) counteract CD4+25+regulatory T (Tr) cell-mediated immune suppression. These results formed the new concept of novel EXO-targeted CD4+ T cell vaccines. In this study, we tailored EXO-targeted T cells vaccine by using polyclonal activated CD8+ T cells instead of CD4+ T cells, as CD4+ T cells served as the primary target for HIV-1 infection. We showed that (1) OVA-specific exosome-targeted CD8+ T cell-based vaccine (OVA-Texo) can stimulate efficient OVA-specific CD8+ CTL and memory responses, inducing sufficient antitumor immunity against OVA-expressing tumor cells in mouse models. (2) This exosome-targeted CD8+ T cell-based vaccine strategy could be applied to HIV-1-Gag protein, provoking effective Gag-specific CD8+ CTL, T cell memory, and antitumor immunity against Gag-expressing tumor cells. (3) Engineering Gag-Texo with up-regulated 4-1BBL (APC derived costimulatory molecule) expression could improve the performance of Gag-Texo vaccine. (4) OVA-Texo is able to evoke a successful immune response in bystander chronic infection, converting CD8+ T cell exhaustion, restoring effector functions of exhausted CD8+ T cells. Moreover, combination of OVA-Texo vaccine with PD-L1 blockage in a dual treatment could result in a synergistic effect in rescuing CTLs exhaustion in chronic infection. Those desired features make EXO-targeted CD8+ T cells vaccine an appealing novel strategy in HIV-1 infection. The EXO-targeted CD8+ T cells vaccine may be applicable to therapeutic HIV treatment through the use of autologous T cells with uptake of EXOs derived from engineered DCs.



HIV-1, exosome, T-cell vaccine, therapeutic, chronic infection, CTLs exhaustion.



Doctor of Philosophy (Ph.D.)


School of Public Health


Vaccinology and Immunotherapeutics



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