TLR5 Agonist Recombinant Flagellin, CBLB502 Increases Anti-CMV Immunity By Increasing T-Bet and Eomes Expressing T Cells after MCMV Infection

We have previously shown that highly purified cGMP grade recombinant flagellin, CBLB502, a TLR5 agonist, protected allo-HSCT recipients from GvHD without compromising anti-CMV immunity of donor T cells in vivo. A single prophylactic dose (25mg/mouse i.p) of CBLB502 in wild type C57BL/6 (B6) mice also enhanced anti-CMV immunity of NK cells against CMV. CMV is a potential opportunistic infectious agent and most often causes severe life-threatening clinical complications in immunocompromized patients, particularly in cancer patients treated with allogenic bone marrow transplantation (allo-BMT). A mechanism by which CBLB502 protected host against CMV infection has not been well investigated. Transcription factors ROR gammaT, T-bet and EOMES are known to control immune responses of innate and adaptive immunity in vivo. In this study, we have explored the transcription factors ROR gammaT, T-bet and EOMES expressing NK and T cells in CBLB502-treated and MCMV-infected B6 mice. Total numbers of spleen cells increased by 1.7-fold within 48 hours of CBLB502 treatment (day 0 MCMV infection) and by 2.3-fold on day 3 after MCMV infection compared with PBS-treated MCMV-infected mice. T-bet expressing CD8+ T cells (not CD4+ T cells) increased significantly on day 0 of mCMV infection, 48hrs after CBLB502 treatment (CD4, p=0.1; CD8, p<0.001) and both CD4+ and CD8+ T cells increased significantly on day 3 (CD4, p<0.001; CD8, p<0.01) after MCMV infection. CBLB502 treatment had no effect on the ROR gammaT expression on T cells.  Interestingly, although EOMES expressing CD4+ and CD8+ T cells increased significantly on day 0 (48 hrs after CBLB502 treatment) (CD4, p<0.01; CD8, p<0.01) and day 3 (CD4, p<0.001; CD8, p<0.001) in the spleens of CBLB502-treated mice compared with the PBS-treated mice, EOMES expression on CMV-specific tetramer+ CD8+ T cells rapidly decreased by day 10 after infection in both CBLB502 and PBS treated mice. However, >90% of CMV-specific CD8+ T cells had persistent expression of T-bet even after 30 days post CMV infection. In contrast, CBLB502 treatment did not have a significant effect on the numbers of ROR gammaT, T-bet and EOMES expressing NK cells compared with PBS-treated mice. These data suggest that 1) CBLB502-induced anti-CMV immunity of T cells is persistently maintained through increased T-bet expression but not by EOMES expression; and 2) CBLB502-induced anti-viral immune regulation is not maintained through transcription factor ROR gammaT. 3) CBLB502-induced increased anti-CMV immunity of NK cells is independent of transcription factors ROR gammaT, T-bet and EOMES. Taken together, these data support the early peri-transplant use of TLR5 agonists as a novel method to enhance antigen-specific anti-viral immunity in recipients of allo-BMT.