SAT0232 Reactivation of immune checkpoints by an epitope-specific vaccine reinstates tolerogenic pathways and induces clinical amelioration in patients with rheumatoid arthritis

Abstract

Background: Immune checkpoints like PD-1 that govern immune tolerance are attractive therapeutic targets in diseases driven by the dysregulation of tolerogenic pathways. We have previously reported that the induction of immune tolerance by epitope-specific immunotherapy with dnaJP1, a peptide sharing sequence homology to the HLA alleles implicated in the pathogenesis of rheumatoid arthritis (RA), results in clinical improvement in RA and represents a promising therapeutic intervention. Objective(s): In the present work, we adopt a holistic approach in deciphering the tolerogenic immune mechanisms underlying the efficacy of epitope-specific immunotherapy with dnaJP1 in a fully human context. We hypothesize that clinical amelioration of RA by dnaJP1 immunotherapy is attributed to the reactivation of immune checkpoints that triggers immune mechanisms modulating immune tolerance and clinical control. Method(s): Peripheral Blood Mononuclear Cells (PMBCs) were obtained at the end of the Phase II trial (Day168), from clinical responders treated with dnaJP1 (n=6) and clinical non-responders treated with placebo (n=10). Gene expression analysis was performed by quantitative PCR. The T cell compartment was studied by multi-coloured flow cytometry using specifically designed antibody panels. Flow cytometry results were then analysed by clustering with Multi-Dimensional Automated Reduction and Visualization (MARVis). Result(s): Analysis of the T cell immunomes of dnaJP1 responders and placebo non-responders revealed a subset of CD4+FoxP3+ regulatory T (Treg) cells exclusively in dnaJP1 responders that displayed a higher expression of the inhibitory immune checkpoint receptor, PD-1. The expression of PD-1 contributes to an enhancement of the tolerogencity of this Treg cell subset by upregulating the production of signature anti-inflammatory cytokines such as TGFbeta. In addition, we observed a corresponding reshaping of the effector T (Teff) cell compartment in which the expression of pro-inflammatory cytokines such as IL-17A and IFNgamma was downregulated. Importantly, epitope-specific immunotherapy also induced a subset of active antigen-experienced memory T cells (CD4+CD45RO+CD69+) which sustains the tolerogenic immune response by secreting TGFbeta. Lastly, our preliminary findings demonstrate that the concurrent use of Hydroxychloroquine (HCQ) exerts a synergistic effect in reinstating immune homeostasis by promoting the immunomodulatory capacity of antigen-presenting cells (APCs). The switch to a tolerogenic DC phenotype in the presence of HCQ in turn skews effector T cells towards a functionally protective phenotype by upregulating the expression of PD-1. Conclusion(s): Our data exemplifies that the toggle between inflammation and tolerance is delicately controlled by a unique subset of Treg cells in which the immune checkpoint protein, PD-1 is switched on. We have also provided mechanistic knowledge on the synergistic relationship between HCQ and the clinical effectiveness of dnaJP1. Taken together, we demonstrate a vaccine-like therapeutic strategy that modifies the multitudinous perturbations in the auto-reactive immune system by reactivating immune checkpoints governing tolerogenic pathways.