Immune Autoregulatory CD8 T Cells Require IFN-γ Responsiveness to Optimally Suppress Central Nervous System Autoimmunity

Disruption of IFNγ, GZMB, PRF1, or LYST Results in Reduced Suppressive Function in Human CD8+ T Cells

An imbalance between proinflammatory and regulatory processes underlies autoimmune disease pathogenesis. We have shown that acute relapses of multiple sclerosis are characterized by a deficit in the immune suppressive ability of CD8+ T cells. These cells play an important immune regulatory role, mediated in part through cytotoxicity (perforin [PRF]/granzyme [GZM]) and IFNγ secretion. In this study, we further investigated the importance of IFNγ-, GZMB-, PRF1-, and LYST-associated pathways in CD8+ T cell-mediated suppression. Using the CRISPR-Cas9 ribonucleoprotein transfection system, we first optimized efficient gene knockout while maintaining high viability in primary bulk human CD8+ T cells. Knockout was confirmed through quantitative real-time PCR assays in all cases, combined with flow cytometry where appropriate, as well as confirmation of insertions and/or deletions at genomic target sites. We observed that the knockout of IFNγ, GZMB, PRF1, or LYST, but not the knockout of IL4 or IL5, resulted in significantly diminished in vitro suppressive ability in these cells. Collectively, these results reveal a pivotal role for these pathways in CD8+ T cell-mediated immune suppression and provide important insights into the biology of human CD8+ T cell-mediated suppression that could be targeted for immunotherapeutic intervention.

Proteolipid Protein-Induced Mouse Model of Multiple Sclerosis Requires B Cell-Mediated Antigen Presentation

The pathogenic role B cells play in multiple sclerosis is underscored by the success of B cell depletion therapies. Yet, it remains unclear how B cells contribute to disease, although it is increasingly accepted that mechanisms beyond Ab production are involved. Better understanding of pathogenic interactions between B cells and autoreactive CD4 T cells will be critical for novel therapeutics. To focus the investigation on B cell:CD4 T cell interactions in vivo and in vitro, we previously developed a B cell-dependent, Ab-independent experimental autoimmune encephalomyelitis (EAE) mouse model driven by a peptide encompassing the extracellular domains of myelin proteolipid protein (PLPECD). In this study, we demonstrate that B cell depletion significantly inhibited PLPECD-induced EAE disease, blunted PLPECD-elicited delayed-type hypersensitivity reactions in vivo, and reduced CD4 T cell activation, proliferation, and proinflammatory cytokine production. Further, PLPECD-reactive CD4 T cells sourced from B cell-depleted donor mice failed to transfer EAE to naive recipients. Importantly, we identified B cell-mediated Ag presentation as the critical mechanism explaining B cell dependence in PLPECD-induced EAE, where bone marrow chimeric mice harboring a B cell-restricted MHC class II deficiency failed to develop EAE. B cells were ultimately observed to restimulate significantly higher Ag-specific proliferation from PLP178-191-reactive CD4 T cells compared with dendritic cells when provided PLPECD peptide in head-to-head cultures. We therefore conclude that PLPECD-induced EAE features a required pathogenic B cell-mediated Ag presentation function, providing for investigable B cell:CD4 T cell interactions in the context of autoimmune demyelinating disease.

Tolerance Induced by Antigen-Loaded PLG Nanoparticles Affects the Phenotype and Trafficking of Transgenic CD4+ and CD8+ T Cells

We have shown that PLG nanoparticles loaded with peptide antigen can reduce disease in animal models of autoimmunity and in a phase 1/2a clinical trial in celiac patients. Clarifying the mechanisms by which antigen-loaded nanoparticles establish tolerance is key to further adapting them to clinical use. The mechanisms underlying tolerance induction include the expansion of antigen-specific CD4+ regulatory T cells and sequestration of autoreactive cells in the spleen. In this study, we employed nanoparticles loaded with two model peptides, GP33-41 (a CD8 T cell epitope derived from lymphocytic choriomeningitis virus) and OVA323-339 (a CD4 T cell epitope derived from ovalbumin), to modulate the CD8+ and CD4+ T cells from two transgenic mouse strains, P14 and DO11.10, respectively. Firstly, it was found that the injection of P14 mice with particles bearing the MHC I-restricted GP33-41 peptide resulted in the expansion of CD8+ T cells with a regulatory cell phenotype. This correlated with reduced CD4+ T cell viability in ex vivo co-cultures. Secondly, both nanoparticle types were able to sequester transgenic T cells in secondary lymphoid tissue. Flow cytometric analyses showed a reduction in the surface expression of chemokine receptors. Such an effect was more prominently observed in the CD4+ cells rather than the CD8+ cells.

A Functionally Distinct CXCR3+/IFN-γ+/IL-10+ Subset Defines Disease-Suppressive Myelin-Specific CD8 T Cells

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the CNS. We have previously demonstrated that CNS-specific CD8 T cells possess a disease-suppressive function in MS and variations of its animal model, experimental autoimmune encephalomyelitis (EAE), including the highly clinically relevant relapsing-remitting EAE disease course. Regulatory CD8 T cell subsets have been identified in EAE and other autoimmune diseases, but studies vary in defining phenotypic properties of these cells. In relapsing-remitting EAE, PLP_178-191 CD8 T cells suppress disease, whereas PLP_139-151 CD8 T cells lack this function. In this study, we used this model to delineate the unique phenotypic properties of CNS-specific regulatory PLP_178-191 CD8 T cells versus nonregulatory PLP_139-151 or OVA_323-339 CD8 T cells. Using multiparametric flow cytometric analyses of phenotypic marker expression, we identified a CXCR3⁺ subpopulation among activated regulatory CD8 T cells, relative to nonregulatory counterparts. This subset exhibited increased degranulation and IFN-γ and IL-10 coproduction. A similar subset was also identified in C57BL/6 mice within autoregulatory PLP_178-191 CD8 T cells but not within nonregulatory OVA_323-339 CD8 T cells. This disease-suppressing CD8 T cell subpopulation provides better insights into functional regulatory mechanisms, and targeted enhancement of this subset could represent a novel immunotherapeutic approach for MS.