XCR1+ DCs are critical for T cell-mediated immunotherapy of chronic viral infections

The XCL1-XCR1 axis supports intestinal tissue residency and antitumor immunity

Tissue-resident memory T cells (TRM) provide frontline protection against pathogens and emerging malignancies. Tumor-infiltrating lymphocytes (TIL) with TRM features are associated with improved clinical outcomes. However, the cellular interactions that program TRM differentiation and function are not well understood. Using murine genetic models and targeted spatial transcriptomics, we found that the CD8+ T cell-derived chemokine XCL1 is critical for TRM formation and conventional DC1 (cDC1) supported the positioning of intestinal CD8+ T cells during acute viral infection. In tumors, enforced Xcl1 expression by antigen-specific CD8+ T cells promoted intratumoral cDC1 accumulation and T cell persistence, leading to improved overall survival. Notably, analysis of human TIL and TRM revealed conserved expression of XCL1 and XCL2. Thus, we have shown that the XCL1-XCR1 axis plays a non-cell autonomous role in guiding intestinal CD8+ TRM spatial differentiation and tumor control.

RUNX2 Phase Separation Mediates Long-Range Regulation Between Osteoporosis-Susceptibility Variant and XCR1 to Promote Osteoblast Differentiation

GWASs have identified many loci associated with osteoporosis, but the underlying genetic regulatory mechanisms and the potential drug target need to be explored. Here, a new regulatory mechanism is found that a GWAS intergenic SNP (rs4683184) functions as an enhancer to influence the binding affinity of transcription factor RUNX2, whose phase separation can mediate the long-range chromatin interaction between enhancer and target gene XCR1 (a member of the GPCR family), leading to changes of XCR1 expression and osteoblast differentiation. Bone-targeting AAV of Xcr1 can improve bone formation in osteoporosis mice, suggesting that XCR1 can be a new susceptibility gene for osteoporosis. This study is the first to link non-coding SNP with phase separation, providing a new insight into long-range chromatin regulation mechanisms with susceptibility to complex diseases, and finding a potential target for the development of osteoporosis drugs and corresponding translational research.

Anti-PD-L1 Immunotherapy of Chronic Virus Infection Improves Virus Control without Augmenting Tissue Damage by Fibrosis

Immunotherapy with checkpoint inhibitors, albeit commonly used against tumors, is still at its infancy against chronic virus infections. It relies on the reinvigoration of exhausted T lymphocytes to eliminate virus-infected cells. Since T cell exhaustion is a physiological process to reduce immunopathology, the reinvigoration of these cells might be associated with an augmentation of pathological changes. To test this possibility, we here analyzed in the model system of chronic lymphocytic choriomeningitis virus (LCMV)-infected mice whether treatment with the checkpoint inhibitor anti-PD-L1 antibody would increase CD8 T cell-dependent fibrosis. We show that pre-existing spleen fibrosis did not worsen under conditions that increase CD8 T cell functionality and reduce virus loads suggesting that the CD8 T cell functionality increase remained below its pathogenicity threshold. These promising findings should further encourage immunotherapeutic trials against chronic virus infections.

Differential kinetics of splenic CD169+ macrophage death is one underlying cause of virus infection fate regulation

Acute infection and chronic infection are the two most common fates of pathogenic virus infections. While several factors that contribute to these fates are described, the critical control points and the mechanisms that underlie infection fate regulation are incompletely understood. Using the acute and chronic lymphocytic choriomeningitis virus (LCMV) infection model of mice, we find that the early dynamic pattern of the IFN-I response is a differentiating trait between both infection fates. Acute-infected mice generate a 2-wave IFN-I response while chronic-infected mice generate only a 1-wave response. The underlying cause is a temporal difference in CD8 T cell-mediated killing of splenic marginal zone CD169+ macrophages. It occurs later in acute infection and thus enables CD169+ marginal zone macrophages to produce the 2nd IFN-I wave. This is required for subsequent immune events including induction of inflammatory macrophages, generation of effector CD8+ T cells and virus clearance. Importantly, these benefits come at a cost for the host in the form of spleen fibrosis. Due to an earlier marginal zone destruction, these ordered immune events are deregulated in chronic infection. Our findings demonstrate the critical importance of kinetically well-coordinated sequential immune events for acute infection control and highlights that it may come at a cost for the host organism.