No abstract

Active T cells release bioactive exosomes (EXOs). However, its potential modulation in immune responses is elusive. In this study, we in vitro generated active OVA-specific CD8+ T cells by cultivation of OVA-pulsed dendritic cells (DCOVA) with naive CD8+ T cells derived from OVA-specific TCR transgenic OTI mice and purified EXOs from CD8+ T cell culture supernatant by differential ultracentrifugation. We then investigated the suppressive effect of T cell EXOs on DCOVA-mediated CD8+ CTL responses and antitumor immunity. We found that DCOVA uptake OTI T cell EXOs expressing OVA-specific TCRs and Fas ligand via peptide/MHC Ag I–TCR and CD54–LFA-1 interactions leading to downregulation of peptide/MHC Ag I expression and induction of apoptosis of DCOVA via Fas/Fas ligand pathway. We demonstrated that OVA-specific OTI T cell EXOs, but not lymphocytic choriomeningitis virus-specific TCR transgenic mouse CD8+ T cell EXOs, can inhibit DCOVA-stimulated CD8+ CTL responses and antitumor immunity against OVA-expressing B16 melanoma. In addition, these T cell EXOs can also inhibit DCOVA-mediated CD8+ CTL-induced diabetes in transgenic rat insulin promoter-mOVA mice. Interestingly, the anti–LFA-1 Ab treatment significantly reduces T cell EXO-induced inhibition of CD8+ CTL responses in both antitumor immunity and autoimmunity. EXOs released from T cell hybridoma RF3370 cells expressing OTI CD8+ TCRs have a similar inhibitory effect as T cell EXOs in DCOVA-stimulated CTL responses and antitumor immunity. Therefore, our data indicate that Ag-specific CD8+ T cells can modulate immune responses via T cell-released EXOs, and T cell EXOs may be useful for treatment of autoimmune diseases.

CD4(+) Th17 cells induce antitumor immunity leading to the eradication of established tumors. However, the mechanism of antitumour immunity and CTL activation by Th17 cells and the distinct role of Th17 and Th17-activated CTLs in antitumor immunity are still elusive. In this study, we generated ovalbumin (OVA)-specific Th17 cells by cultivating OVA-pulsed dendritic cells with CD4(+) T cells derived from transgenic OTII mice in the presence of IL-6, IL-23, TGF-β, and anti-IFN-γ antibody. We demonstrated that Th17 cells acquired major histocompatibility complex/peptide (pMHC)-I and expressed RORγt, IL-17, and IL-2. Th17 cells did not have any direct in vitro tumor cell-killing activity. However, Th17 cells were able to stimulate CD8(+) CTL responses via IL-2 and pMHC I, but not IL-17 signaling, which play a major role in Th17-induced preventive immunity against OVA-expressing B16 melanoma. Th17 cells stimulated the expression of CCL2 and CCL20 in lung tumor microenvironments promoting the recruitment of various inflammatory leukocytes (DCs, CD4(+), and CD8(+) T cells) stimulating more pronounced therapeutic immunity for early-stage (5-day lung metastases or 3 mm, s.c.) tumor than for well-established (6 mm, s.c.) tumor. The therapeutic effect of Th17 cells is associated with IL-17 and is mediated by Th17-stimulated CD8(+) CTLs and other inflammatory leukocytes recruited into B16 melanoma via Th17-stimulated CCL20 chemoattraction. Taken together, our data elucidate a distinct role of Th17 and Th17-stimulated CD8(+) CTLs in the induction of preventive and therapeutic antitumor immunity, which may greatly impact the development of Th17-based cancer immunotherapy.