To evaluate whether the rectal route of immunization may be used to provide appropriate protection against enteric pathogens such as rotaviruses (RV), we studied the antibody response and the protection induced by rectal immunization of mice with RV virus-like particles (VLP). For this purpose, 6-week-old BALBc mice were rectally immunized twice with RV 8-2/6/7-VLP derived from the bovine RV RF81 strain either alone or combined with various adjuvants including four toxins [cholera toxin (CT) and three attenuated Escherichia coli -derived heat-labile toxins (LTs), LT(R192G), LT(R72), and LT(K63)] and two Toll-like receptor-targeting adjuvants (CpG and resiquimod). Six weeks after the second immunization, mice were challenged with murine RV strain ECw. RV VLP administered alone were not immunogenic and did not protect mice against RV challenge. By contrast, RV VLP combined with any of the toxin adjuvants were immunogenic (mice developed significant titers of anti-RV immunoglobulin A [IgA] in both serum and feces and of anti-RV IgG in serum) and either efficiently induced complete protection of the mice (no detectable fecal virus shedding) or, for LT(K63), reduced the amount of fecal virus shedding after RV challenge. When combined with RV VLP, CpG and resiquimod failed to achieve protection, although CpG efficiently induced an antibody response to RV. These results support the consideration of the rectal route for the development of new immunization strategies against RV infection. Rectal delivery of a VLP-based vaccine might allow the use of adjuvants less toxic than, but as efficient as, CT.

Tumors exploit numerous immune checkpoints, including those deployed by myeloid cells to curtail antitumor immunity. Here, we show that the C-type lectin receptor CLEC-1 expressed by myeloid cells senses dead cells killed by programmed necrosis. Moreover, we identified Tripartite Motif Containing 21 (TRIM21) as an endogenous ligand overexpressed in various cancers. We observed that the combination of CLEC-1 blockade with chemotherapy prolonged mouse survival in tumor models. Loss of CLEC-1 reduced the accumulation of immunosuppressive myeloid cells in tumors and invigorated the activation state of dendritic cells (DCs), thereby increasing T cell responses. Mechanistically, we found that the absence of CLEC-1 increased the cross-presentation of dead cell–associated antigens by conventional type-1 DCs. We identified antihuman CLEC-1 antagonist antibodies able to enhance antitumor immunity in CLEC-1 humanized mice. Together, our results demonstrate that CLEC-1 acts as an immune checkpoint in myeloid cells and support CLEC-1 as a novel target for cancer immunotherapy.

Autoimmune liver diseases (AILD) involve dysregulated CD4 T cell responses against liver self-antigens, but how these autoreactive T cells relate to liver tissue pathology remains unclear. Here we perform single-cell transcriptomic and T cell receptor analyses of circulating, self-antigen-specific CD4 T cells from patients with AILD and identify a subset of liver-autoreactive CD4 T cells with a distinct B-helper transcriptional profile characterized by PD-1, TIGIT and HLA-DR expression. These cells share clonal relationships with expanded intrahepatic T cells and exhibit transcriptional signatures overlapping with tissue-resident T cells in chronically inflamed environments. Using a mouse model, we demonstrate that, following antigen recognition in the liver, CD4 T cells acquire an exhausted phenotype, play a crucial role in liver damage, and are controlled by immune checkpoint pathways. Our findings thus suggest that circulating autoreactive CD4 T cells in AILD are imprinted by chronic antigen exposure to promote liver inflammation, thereby serving as a potential target for developing biomarkers and therapies for AILD.

Intracellular ion fluxes emerge as critical actors of immunoregulation but still remain poorly explored. In this study, we investigated the role of the redundant cation channels TMEM176A and TMEM176B (TMEM176A/B) in retinoic acid–related orphan receptor γt⁺ cells and conventional dendritic cells (DCs) using germline and conditional double knockout mice. Although Tmem176a/b appeared surprisingly dispensable for the protective function of Th17 and group 3 innate lymphoid cells in the intestinal mucosa, we found that they were required in conventional DCs for optimal Ag processing and presentation to CD4⁺ T cells. Using a real-time imaging method, we show that TMEM176A/B accumulate in dynamic post-Golgi vesicles preferentially linked to the late endolysosomal system and strongly colocalize with HLA-DM. Taken together, our results suggest that TMEM176A/B ion channels play a direct role in the MHC class II compartment of DCs for the fine regulation of Ag presentation and naive CD4⁺ T cell priming. Key Points Germline and conditional double KO mice target Tmem176a and Tmem176b. Tmem176a/b appear dispensable in RORγt⁺ cells. Tmem176a/b are required in DCs for optimal MHC class II–mediated antigen presentation.

The aim of our study was to determine whether granzyme B-expressing regulatory B cells (GZMB⁺ B cells) are enriched in the blood of transplant patients with renal graft tolerance. To achieve this goal, we analysed two single-cell RNA sequencing (scRNAseq) datasets: (1) peripheral blood mononuclear cells (PBMCs), including GZMB⁺ B cells from renal transplant patients, i.e., patients with stable graft function on conventional immunosuppressive treatment (STA, n = 3), drug-free tolerant patients (TOL, n = 3), and patients with antibody-mediated rejection (ABMR, n = 3), and (2) ex-vivo-induced GZMB⁺ B cells from these groups. In the patient PBMCs, we first showed that natural GZMB⁺ B cells were enriched in genes specific to Natural Killer (NK) cells (such as NKG7 and KLRD1) and regulatory B cells (such as GZMB, IL10, and CCL4). We performed a pseudotemporal trajectory analysis of natural GZMB⁺ B cells and showed that they were highly differentiated B cells with a trajectory that is very different from that of conventional memory B cells and linked to the transcription factor KLF13. By specifically analysing GZMB⁺ natural B cells in TOLs, we found that these cells had a very specific transcriptomic profile associated with a reduction in the expression of HLA molecules, apoptosis, and the inflammatory response (in general) in the blood and that this signature was conserved after ex vivo induction, with the induction of genes associated with migration processes, such as CCR7, CCL3, or CCL4. An analysis of receptor/ligand interactions between these GZMB^+/− natural B cells and all of the immune cells present in PBMCs also demonstrated that GZMB⁺ B cells were the B cells that carried the most ligands and had the most interactions with other immune cells, particularly in tolerant patients. Finally, we showed that these GZMB⁺ B cells were able to infiltrate the graft under inflammatory conditions, thus suggesting that they can act in locations where immune events occur.