Cellular & Molecular Immunology

UNC93B1 is a crucial chaperone protein for the trafficking of TLRs and regulates antigen presentation in dendritic cells (DCs), which activates downstream immune responses. Here, we identified a novel homozygous gain-of-function (GOF) UNC93B1 variant in an early-onset lupus patient. The patient presented with elevated level of inflammation and auto-antibody, and organ damage. The Unc93b1R95L/R95L transgenic mice also exhibited with autoimmune and autoinflammatory phenotypes. The transcriptional analysis revealed increased inflammation and elevated activation of DCs in the patients PBMCs and bone marrow-derived DCs (BMDCs) from Unc93b1R95L/R95L mice. In addition to the selected TLR7/8 activation in previously reported UNC93B1 GOF variants, the single-cell transcriptome and flow cytometry of splenocytes from Unc93b1R95L/R95L mice demonstrated increased phagocytosis activity and T helper cell differentiation with altered ICAM and MHC signaling in DCs and T cells, respectively. These results suggest UNC93B1 GOF variant enhances antigen presentation from DCs to T cells in the pathogenesis of immune dysregulation. Our study expands the pathogenic variants spectrum of UNC93B1 and offers insight into the underlying mechanism of antigen presentation in immune dysregulation caused by UNC93B1 beyond its trafficking function of TLRs.

Lymph nodes (LN) are key secondary lymphoid organs (SLO) for a coordinated immune response. They have been extensively characterized by numerous investigative techniques chiefly as single cell suspensions because they are composed of vagile yet crowded hematolymphoid elements, unfriendly to spatial tissue organization-saving techniques. We comprehensively classify in situ all cells of 19 human LN free of pathology with a 78-marker antibody panel, an hyperplexed cyclic staining method, MILAN, and an analytical bioinformatic pipeline, BRAQUE. A total of 77 cell types were classified, encompassing T, B, innate immune and stromal cells. CD4 and CD8 T-cells were classified into 27 unique subsets by leveraging the expression profiles of TCF7, the presence of co-inhibitory receptors and the spatial distribution. CD5 and TCF7 expression defined novel B-cell types. CD27+ mature B-cells occupied previously unrecognized nodal spaces non-overlapping with the cortex and the plasma-cell rich medullary cords. Type 2 conventional dendritic cells were located in nodular paracortical aggregates. Statistically controlled pairwise neighborhood analysis showed sparse cell-cell interactions, known and new neighbors, established and novel LN landscape niches. A high-dimensional proteomic interrogation of the normal human LN provides spatial allocation of known cell types, novel interactions and the landscape organization.

Immunoglobulin M (IgM) is the most ancient and conserved antibody class in jawed vertebrates and is typically encoded by a single gene. In contrast, geckos and related lizards (infraorder Gekkota) possess multiple IgM genes within the immunoglobulin heavy chain locus. Here, we analyze 52 IgM constant-region sequences from 13 Gekkota species to clarify the evolutionary origin and functional consequences of this expansion. Phylogenetic reconstruction showed that IgM1 (the canonical form) is nearly monophyletic (86.7% clade purity), whereas internal-locus IgM2-6 variants display complex, lineage-specific duplication patterns. We identified 53 diagnostic amino acid positions distinguishing IgM1 from other variants, concentrated in CH1 (19 positions) and CH2 (25 positions). These differences are accompanied by a pronounced physicochemical shift in CH2: IgM1 carries a net positive charge (+2.01) while other IgMs are negatively charged (-2.13), a {Delta} of +4.14 charge units. Conservation analyses indicate stronger constraint on IgM1 in CH1/CH2, while internal-locus IgMs are more conserved in CH4, consistent with maintained polymerization function. Three-dimensional structural comparison of IgM1 and IgM4 supports functional divergence in assembly: IgM4 adopts an "open mouth" CH1-CH2 conformation with increased heavy-light chain contacts and a more electrostatically enriched interface, suggesting compensatory stabilization mechanisms. Together, these results support specialization of internal-locus IgMs through combined sequence and structural divergence.

Vaccination frequently elicits suboptimal immunogenicity in organ transplant recipients, particularly those on long-term immunosuppressive therapy, highlighting the need for improved understanding of immunosuppression mechanisms and optimized vaccination strategies. This study enrolled a cohort of 132 individuals and observed significantly lower antibody levels in kidney transplant recipients (KTRs) compared to non-transplant controls (non-KTRs). Antibody levels were inversely associated with both the dosage and duration of immunosuppressive therapy. Complementary small animal studies demonstrated that immunosuppressive treatment dosage-dependently and reversibly impaired antibody production, primarily by depleting immune cells, notably B cells. A single shot of adenoviral vector-based vaccines demonstrated enhanced immunogenicity relative to two shots of alum-adjuvanted protein vaccines, inducing potent neutralizing antibodies (NAbs) and a Th1-biased T-cell response even under continuous immunosuppression. The enhanced response was driven by reduced interference from pre-existing antibodies, sustained transgene expression, and the reprogramming of lipid metabolism to activate T and B cells. Our findings advocate for tailored vaccination strategies, positioning adenoviral vectors as a candidate modality for this vulnerable population.

Autoimmunity is emerging as a new etiology for early-onset gastric cancer (GC). However, it remains unclear what molecular pathways drive the initiation and progression of autoimmune tumorigenesis. Given that Major Histocompatibility Complex Class II (MHCII) is the strongest genetic risk factor for many autoimmune diseases, we hypothesized that MHCII-mediated autoantigen presentation drives tumorigenic differentiation of epithelial cells. Here we show that epithelial MHCII, rather than MHCII from immune cells, plays an essential role in the initiation of autoimmunity-driven tumorigenic differentiation of gastric epithelial cells, which was characterized by increased expression of cancer-associated markers with immune-evasive and stem-like features that potentiate premalignant progression. In addition, we show that early gastric premalignancy is reversible upon the removal of epithelial MHCII. This study reveals that epithelial MHCII antigen presentation is essential in the early stages of autoimmune-driven gastric tumorigenesis and highlight epithelial MHCII as a potential biomarker or therapeutic target in early interventions of autoimmunity-driven cancer development.

Immunoglobulin Y (IgY) represents the major serum antibody in reptiles and birds, serving as the evolutionary precursor to mammalian IgG and IgE. While IgY diversification has been documented in several reptilian lineages, the structural basis underlying subclass divergence remains poorly understood. Here, we present a comprehensive phylogenetic and structural analysis of IgY sequences from 20 snake species, revealing two distinct evolutionary lineages (A and B) that arose through gene duplication. Structural modeling of the constant regions from Arizona elegans identified a fundamental difference in the light chain-heavy chain (CL-CH1) disulfide bond architecture between lineages. Lineage B utilizes CYS16 in the CH1 domain (alignment position 13) for the inter-chain disulfide bond with the light chain CYS98, whereas Lineage A employs CYS136 (alignment position 99), representing N-terminal versus C-terminal positioning within the CH1 domain. Analysis of 50 diagnostic amino acid positions between lineages revealed that changes are distributed across all constant domains (CH1-CH4), with 13 positions showing radical substitutions affecting charge or polarity. Sliding window dN/dS analysis demonstrated purifying selection ({omega} < 1) across both lineages, consistent with functional constraint following duplication. These findings provide structural evidence for subfunctionalization of snake IgY genes and suggest that alternative disulfide bond configurations may confer distinct biophysical or functional properties to each antibody subclass. This work advances our understanding of immunoglobulin evolution in reptiles and highlights the structural plasticity of antibody architecture.

The establishment of mixed hematopoietic chimerism is a promising way to induce immune tolerance for islet replacement therapy and to treat the underlying autoimmunity in Type 1 diabetes (T1D). Mixed chimerism not only promotes effective thymic negative selection of autoreactive cells but also restores regulatory T cell (Treg) function and peripheral tolerance. In the current study, we determined that a novel class of donor-derived CD8+CD44+CD122+ Tregs (d-CD8+CD122+ Tregs) plays a crucial role in controlling autoimmunity in non-obese diabetic (NOD) mice with induced mixed chimerism. Using adoptive T cell transfer experiments, we showed that d-CD8+CD122+ Tregs abrogate autoimmunity by selectively depleting the exogenously injected diabetogenic T cells in Recombination-Activating Gene deficient NOD mice. These d-CD8+CD122+ Tregs from NOD chimeras show upregulation of Helios, Programmed cell death protein 1, perforin, granzyme-B, CD39, Folate receptor 4, and downregulation of proinflammatory markers like Scart1 and Scart2. Using in vitro assays, we show that d-CD8+CD122+ Tregs respond specifically to a Complementarity-Determining Region-3 peptide sequence derived from T cell receptors of islet antigen-specific autoreactive T cells. Thus, mixed chimerism might be a method to revitalize CD8+CD122+ Tregs which are decreased in number and functionality in NOD mice. Similarly, we found that individuals with T1D have a deficiency in CD8+CD122+ Tregs, suggesting a potential loss of regulatory function accompanies disease onset. Revitalizing CD8+CD122+ Tregs may offer a new therapeutic strategy of restoring immune tolerance in autoimmune diabetes. One sentence summary Inducing mixed donor chimerism in NOD mice generates donor-derived CD8+CD122+ Tregs that suppress autoimmunity and restore immune tolerance by selectively eliminating autoreactive T cells.

African swine fever (ASF) is a highly pathogenic disease caused by the African swine fever virus (ASFV) infection, which can affect pigs of all ages and breeds, posing significant threat to the global pig farming industry. The ASFV p30 protein is an early-expressed viral structural protein; however, its function is not fully understood. In this study, the interaction of viral p30 with host TRIM21 was identified. The ectopic TRIM21 inhibited ASFV replication, while knockdown or knockout of TRIM21 promoted ASFV replication. Further, p30 was found to interact with RIG-I-like receptor (RLR) signaling adaptor MAVS, and during ASFV infection, p30-TRIM21-MAVS interacted with each other. Mechanistically, TRIM21 activated the K27 polyubiquitination of MAVS to induce IRF3 mediated type I interferon (IFN) production, whereas p30 counteracted TRIM21 activated MAVS K27 polyubiquitination to evade RLR signaling mediated antiviral IFN induction. In summary, our study revealed a novel function of ASFV p30, and provided new insights into the immune evasion of ASFV.

Maladaptive repair of acute kidney injury (AKI) may lead to the development of chronic kidney disease (CKD) characterized by renal fibrosis. Macrophages play roles in AKI-to-CKD progression; however, the interplay between inflammation and fibrosis after AKI remains controversial and the precise role of the distinct macrophage subsets remains elusive. In the present study we identified a unique population of Trem2hi macrophages derived from the bone marrow as a mediator bridging inflammation resolution and fibrosis establishment after kidney injury. Trem2 deficient mice exhibited mitigated renal fibrosis after ischemia-reperfusion injury (IRI) while the renal injury and inflammation persisted. Mechanistically, Trem2 promoted renal inflammation resolution by facilitating macrophage efferocytosis to remove apoptotic tubule cells and reshaping the macrophage cytokine production profile. Loss of Trem2 expression led to excessive cholesterol accumulation in macrophages via Lxr-Abca1/Abcg1 axis and thus sustained pro-inflammatory cytokines production. Moreover, Trem2hi macrophages orchestrated the pro-fibrotic tubular epithelial cells and the activation of myofibroblasts through SPP1 to promote the establishment of renal fibrotic niche. Based on our findings, Trem2hi macrophages may serve as a potential therapeutic target for AKI-to-CKD in combination with anti-inflammatory remedies.

Human Cytomegalovirus (HCMV) is an omnipresent pathogen that is associated with increased morbidity and mortality of immunocompromised individuals. Studies of T-cell immunity to HCMV primarily reflect anti-CMV pp65 or immediate early antigen 1 (IE-1) activity. Recent evidence highlights the importance of the major immediate-early 2 (IE2) protein, which is expressed early after HCMV infection and reactivation, for regulating the lytic HCMV replication cycle. In this study, we designed a comprehensive screening approach to assess T cell responses against the IE2 HCMV protein in the peripheral blood of 15 HCMV-seropositive and 6 HCMV-seronegative healthy adults using IE2 synthetic long peptide (SLP) pools and cytokine flow cytometry. The T cell response against the IE2 protein was dominated by CD4+ T cells whereas IE2-specific CD8+ T-cell reactivity was measured in only 3 donors. Most of the donors recognized chiefly the IE2351-434 residues, revealing a remarkably immunogenic area of the protein. Numerous novel HLA class I- and II-restricted IE2 T-cell epitopes were identified. Functional characterization of the IE2 CD4+ and CD8+ T cell responses uncovered 5 highly antigenic SLPs, which induced polyfunctional Th1 cytokine (IFN-{gamma}+/ TNF+/ IL-2+) response and could serve as candidate vaccine antigens. Evaluation of these 5 highly antigenic IE2 SLPs in T cell-inducing vaccines aiming to inhibit HCMV infection by targeting the expression of immediate-early genes is warranted.

To understand the molecular and cellular mechanisms beyond B-cell depletion with the anti-CD20 monoclonal antibody ocrelizumab, we used comprehensive muti-modal flow cytometry and functional assays in a prospective longitudinal multiple sclerosis (MS) cohort. Ocrelizumab depleted the vast majority of B cells and showed selective effects on different B cells subsets. Analysis of residual/replenished B cells revealed relative enrichment of regulatory B cells like CD27+CD43+ B1 and CD24hiCD38hi transitional B cells, and reduction of CD27+ memory B cell subsets and CD19+IgD+CD27-naive B cells at early time points (1-3 month) and before subsequent infusions at 4-7 months, 11-14 months, and >18 months. CD20+ T cells and peripheral helper T-cells (Tph) were also reduced. RNA sequencing analysis showed B1 cells have significantly higher expression of LGALS1, KCNN4, ITGB1, and IL2RB. Compared to transitional B cells, B1 cells also displayed significantly higher expression of tissue homing molecules ITGAX (CD11c), S100A4, ITGB1, and CXCR3. IL10 signaling pathway is increased in these B cells. Ex vivo B cell functional assays indicated the residual/replenishing B cells were anergic following ocrelizumab, with increased IL10/TNF and IL10/IL6 ratios under BCR stimulation. Ocrelizumab treatment may create a self-reinforcing regulatory circuit: the reduction of Tph cells could alleviate suppression of regulatory B cells, which subsequently expand and further promote regulatory T cell networks via IL2RB, LGALS1, and an increased IL-10 signaling pathway.

AO_SCPLOWBSTRACTC_SCPLOWVaccines comprising peptide antigens for inducing T cell immunity are being developed for a broad range of therapeutic applications including prevention and treatment of cancer, autoimmunity, and infectious diseases. However, many peptide antigens contain cysteine and/or methionine, which are prone to form oxidation products that can present challenges to manufacturing and reduce biological activity. To address this challenge, we introduced oxidation resistant (OXR) antigens wherein the cysteine and methionine residues of naturally occurring, wild type (WT) peptide antigens are substituted with isosteric residues that are structurally related but omit the oxidation-prone sulfur atom. Our results showed that vaccination with OXR antigens substituting cysteine and methionine with isosteres alpha-aminobutyric acid and norleucine, respectively, induced immune responses to the WT antigen that were equivalent or higher than those induced by vaccination with WT antigens. T cell responses were not affected by the position of the amino acid substitutions indicating that the isosteres do not negatively impact major histocompatibility complex (MHC) binding or T cell recognition. The T cells induced were high quality and associated with anti-tumor efficacy in vivo. Interestingly, substitution of cysteine with serine, which replaces the sulfur for an oxygen, did not yield cross-reactive T cell responses, highlighting the high degree of molecular discernment of peptide-MHC processing and presentation. In sum, OXR antigens provide a generalizable strategy for eliminating sulfur oxidation products and improving the manufacturability and shelf-life of peptide-based vaccines without affecting desired biologic activity.

Human parainfluenza viruses (PIVs) are a leading cause of respiratory illness, particularly in vulnerable populations where infection can lead to severe disease. Despite their clinical impact, there are currently no licensed vaccines or effective antiviral treatments available. PIVs have two large surface proteins, the fusion and hemagglutinin-neuraminidase (HN) proteins, both of which are targets of neutralizing antibodies. In this study, we identified and characterized two human monoclonal antibodies (mAbs), 5217-2 and 5217-9, which bind recombinant PIV3 HN protein, bind PIV3-infected cells, and are neutralizing in vitro. We determined the binding epitopes of the PIV3 HN-specific mAbs via biolayer interferometry and found mAb 5217-9 targets a previously defined neutralizing epitope while mAb 5217-2 binds a unique epitope, enabling a more complete understanding of the antigenic landscape. To further understand the newly defined epitope, we determined a cryo-electron microscopy (cryo-EM) structure of mAb 5217-2, which revealed an epitope adjacent to the PIV3 HN protein active site. We also determined the structure of the previously discovered anti-PIV3 HN mAb PIV3HN-09, which was previously shown to be partially protective in vivo. In a hamster challenge model of PIV3, mAb 5217-2 was determined to significantly reduce lung viral titers, demonstrating its protective capacity. Furthermore, as the site 2-directed mAb PIV3HN-05 was previously shown to cross-neutralize PIV1, we evaluated its protective efficacy in an animal challenge model with PIV1, which demonstrated a reduction in lung viral titers. Overall, these findings provide new insights into the antigenic epitopes on the PIV3 HN protein to support structure-based vaccine design efforts and demonstrate new protective mAbs for both PIV3 and PIV1.

The SARS-CoV-2 mRNA vaccine provides effective protection against viral infection and severe disease by inducing efficient adaptive immunity. However, vaccine efficacy is decreased against emerging variants, and immune memory is relatively short-lived. Here, we added new T cell epitopes to the RBD (receptor-binding domain) mRNA vaccine and identified a SARS-CoV-2 membrane epitope that significantly improved vaccine-induced immunity and protection in vivo. That new vaccine, designated G1-C, induced 8.2-fold higher levels of RBD-specific antibodies than did RBD and enhanced spike-specific T cell and B cell responses. Remarkably, the G1-C modulated hematopoietic stem cell (HSC) differentiation and increased levels of B and NK cells by regulating multiple signaling pathways in bone marrow potentially via Fos, Klf4, and Klf6 transcription factors. Altogether, these findings identify a new vaccine candidate to control viral infection by affecting the lymphoid-myeloid lineage bias and suggest the potential role of T cell epitopes in vaccine design and development.

The gastrointestinal pathogen Clostridioides difficile, is a major burden for health systems due to high rates of recurrence. C. difficile pathogenesis is mediated by two virulence factors, toxin A (TcdA) and Toxin B (TcdB). Antibodies specific for TcdA and TcdB are correlated with protection from symptomatic recurrence, however, the role for CD4+ T cells is poorly understood in part due to the lack of tools to study the toxin-specific CD4+ T cell response. Our group recently demonstrated the antibody and CD4+ T cell response to C. difficile toxins is impaired via the glucosyltransferase activity of the toxins; however, tools do not exist to study the protective capacity and the phenotype of toxin-specific CD4+ T cells. Therefore, we developed an MHC-II tetramer to identify TcdB-specific CD4+ T cells via flow cytometry. Herein, we identified an immunodominant epitope (TcdB1961-1975) in the CROPs region of TcdB and optimized an MHC-II tetramer for use in tracking and phenotyping TcdB-specific CD4+ T cell responses following multiple different immunization strategies in mice. Utilizing the tetramer, TcdB-specific T follicular helper (Tfh) cells were detected following TcdB-CROPs mRNA-LNP vaccination validating the advantage of the tetramer. Furthermore, using a modular mRNA vector expressing the TcdB1961 peptide covalently bound to the beta chain of MHC-II (MHC-II{beta}) we were able to generate a robust population of TcdB-specific CD4+ T cells. These data outline the generation of new tools for the C. difficile field and lay the groundwork for future studies of toxin-specific CD4+ T cell responses.

Viral infections are one of the main environmental factors triggering type 1 diabetes (T1D). Pancreatic alpha cells are more resistant than beta cells to diabetogenic viruses, partially explaining their survival in T1D. Similarly, bats have enhanced viral resistance, suggesting putative convergent evolution in antiviral mechanisms. Herein, we compared global gene expression in bat fibroblasts under basal conditions or exposed to double-stranded RNA to human alpha and beta cells and found that alpha cells exhibit greater similarity than beta cells to the antiviral responses of bat cells, as well as stronger intrinsic resistance to viral infection. Interferon-stimulated gene 15 (ISG15), a key regulator of antiviral responses in humans and bats, has higher expression in alpha compared to beta cells in five single-cell RNASeq datasets from human islet cells and in human induced pluripotent stem cell (hiPSC)-derived alpha-like cells. ISG15 knockdown in human insulin-producing EndoC-{beta}H1 cells and human islets increases apoptosis under basal conditions and after IFN exposure, exacerbates IFN responses and increases cell death and viral production after infection with the diabetogenic virus coxsackievirus B1, while its overexpression protects EndoC-{beta}H1 cells from the virus. Collectively, the present results demonstrate that alpha cells but not beta cells have similarities with the virus resistance gene program present in bats and identify ISG15 as an important factor for islet cells to cope with viral and diabetogenic stresses.

Cytotoxic T cells (CTL) are crucial for adaptive immunity that leads to prolonged survival and potential cures for cancer. Recent clinical data has shown that pharmacological inhibition of SUMOylation (SUMOi) profoundly modifies tumor microenvironment (TME) and activates CTL, although the mechanism is not well described. In this study, we found that T cell specific knock out (KO) of the most dominant SUMO paralog, Sumo2/SUMO2, in both mouse and human CD8+ T cells significantly enhanced CD8+ T cell activation that is independent of the known mechanism - inducing type I IFN (IFN-I) expression by myeloid cells. Sumo2/SUMO2 KO in CD8+ T cells increased chromatin accessibility for transcription factors BATF, JunB, ATF3, FRA1, FRA2, and AP1 that are known to promote T cell activation and proliferation. Using antigen-specific T cell models, OT1 and Chimeric Antigen Receptor (CAR)-T cells, we found that Sumo2 KO CD8+ T cells had significantly higher tumor infiltration as revealed by flow cytometry, immuno-fluorescence (IF) staining, and single nuclei RNA-sequencing (snRNA-seq) and conferred greater tumor growth inhibition than wildtype (WT) control T cells. snRNA-seq also revealed Sumo2 KO CD8+ T cells increased the expression of Tumor Necrosis Factor-Related Apoptosis-inducing Ligand (TRAIL), induced apoptosis genes in tumor cells and activated IFN-I and IFN-{gamma} responsive genes in all cell types in the TME. These findings elucidate a novel mechanism regarding how SUMOylation can directly control CTL activation and tumor infiltration that activate anti-tumor immunity in the TME. SUMO2 KO can also be a potential strategy to enhance adoptive T cell therapies of solid tumors by enhancing their activity, tumor infiltration and their ability to after the TME.

The IRE1-XBP1 axis is the most conserved of three major unfolded protein response (UPR) branches that are triggered by the endoplasmic reticulum (ER) stress. Although the transcription factor XBP1 is involved in the development and function of several hematopoietic lineages, the role of XBP1 in the activation of mast cells (MCs) that play key role in allergic response remains largely unknown. Because we have identified salicylaldehyde (SA), which inhibits IRE1 nuclease activity that is essential for production of XBP1, as an inhibitor of MC activation in our previous screening, we investigated the effects of additional IRE1 inhibitors, 3-methyl-6-bromo-salichylaldehyde (MBSA) and KIRA6, targeting nuclease domain and kinase domain, respectively, on MC activation. MBSA and KIRA6 suppressed IgE-dependent degranulation and cytokine release of bone marrow-derived MCs (BMMCs), whereas these inhibitors did not suppress the Ca2+ ionophore- or compound48/80-induced degranulation. Treatment with inhibitors against two other branches of UPR, the PERK and the ATF6 pathways, did not affect IgE-induced activation of BMMCs. Intraperitoneal administration of MBSA or KIRA6 significantly suppressed IgE-induced passive anaphylaxis in mice. Furthermore, to evaluate the effect of XBP1, siRNA-mediated knockdown was performed. It was confirmed that Xbp1 siRNA introduction reduced IgE-dependent degranulation of BMMCs in parallel with the knockdown level of Xbp1 mRNA. Taken together, the IRE1-XBP1 axis plays a significant role in IgE-dependent and MC-mediated allergic response, which is considered to be therapeutic target of allergic diseases.

T-cell senescence is a hallmark of immune dysfunction in persistent viral infections, characterized by DNA damage accumulation and telomere erosion. However, the mechanisms driving CD4 T-cell senescence in the context of chronic hepatitis B virus (HBV) infection remain poorly defined. In this study, we demonstrated that people with chronic HBV infection exhibited CD4 T-cell senescence, marked by elevated KLRG1, along with increased DNA damage and telomere shortening, compared to HS. Notably, activation of the MRN-ATM (MRE11/RAD50/NBS1-Ataxia Telangiectasia Mutated Protein) pathway was prominent in CD4 T cells from HBV patients. Importantly, suppression of MRN attenuated ATM phosphorylation and its downstream signaling molecules, and inhibition of ATM reduced the production of proinflammatory cytokines in CD4 T cells derived from both HBV patients and HS. These results suggest that in chronic HBV infection, the virus induced CD4 T-cell senescence, telomere erosion, and DNA damage, while concurrent activation of the MRN-ATM pathway may serve as a compensatory mechanism to preserve CD4 T-cell function. Elucidating this relationship between T-cell senescence and DNA damage repair helps to understanding the mechanisms underlying HBV persistence and providing potential therapeutic targets against chronic HBV infection.

Clonal expansion of memory lymphocytes after each antigen encounter is the primary mechanism for amplifying immunity. For most vaccines, boosters are common practice and are expected to stimulate proliferation of pre-existing memory B cells (Bmem), thereby expanding the antigen-specific Bmem pool, along with driving their differentiation into antibody-producing plasma cells that replenish antibody titers. It is widely assumed that the number of Bmem present in the body prior to administration of a booster vaccination will define the magnitude of the ensuing response. However, due to technical limitations hampering reliable detection of rare antigen-specific Bmem in human subjects, the extent to which Bmem numbers are actually modulated following a booster vaccination remains unclear. By comparing Bmem frequencies and antibody titers in the same individuals after primary and secondary vaccination with SARS-CoV-2 Spike (S-antigen)-encoding mRNA we found that expansion of Bmem and the magnitude of the secondary antibody response were not determined by the number of Bmem measured before the second vaccine inoculation. Instead, both were inversely correlated with levels of S-antigen-specific serum IgG prior to the secondary antigen exposure. Collectively, the data suggest that secondary B cell responses are constrained by antibody feedback inhibition of Bmem, rather than their paucity.