Immunity

An effective HIV-1 vaccine will likely require broadly neutralizing antibodies (bnAbs) targeting multiple complementary epitopes on the Envelope (Env) glycoprotein. Donor-derived bnAbs targeting the conserved silent face (SF) epitope complement established bnAb classes, but the maturation pathways underlying SF bnAb development and their inducibility via vaccination remain poorly understood. Here, we elicit SF-like bnAbs by vaccination and define pathways by which these responses can be guided toward breadth. Structural analysis of the donor-derived bnAb SF10 revealed that broad neutralization depends on a minimal set of heavy chain mutations despite extensive overall somatic hypermutation. We leveraged these insights to engineer Env immunogens that engage an SF10 precursor and selectively favor breadth-associated mutations during sequential immunization in a new immunoglobulin knock-in mouse model. Vaccination reproducibly elicited heterologous neutralizing serum responses and monoclonal antibodies that acquired key SF-like improbable mutations and broad neutralizing activity. Notably, elicited antibodies combined features of distinct human SF bnAbs, demonstrating that vaccination can access alternative mutational solutions rather than precisely recapitulating a donor-derived maturation pathway. These findings establish the silent face as a tractable vaccine target and expand the bnAb specificities available for multi-epitope HIV-1 vaccine strategies.

Ectopic lymphoid structures are typically associated with chronic tissue inflammation in autoimmunity and cancer, where they can amplify local immune responses. Similar structures arise spontaneously with age, yet their origin and function remain unclear. Here we identify tissue retention of mature migratory conventional dendritic cells (cDCs) as a driver of age-associated lymphoid organization. Mature cDCs accumulated within lymphoid structures in aged human and mouse tissues. We demonstrate that impaired cDC egress or pharmacological cDC expansion induced de novo structures in mice across multiple otherwise homeostatic organs without associated pathology. Strikingly, senescence-associated tissue cues, which promoted a distinct cDC maturation state, were required for lymphoid niche initiation. Unlike inflammatory structures described in disease, these cDC-driven structures preferentially accumulated tissue-adapted regulatory T cells and protected against inflammatory injury, revealing a previously unrecognized regulatory dimension of age-associated lymphoid organization.

Despite the success of immune checkpoint blockade in cancer therapy, overcoming the immunosuppressive tumor microenvironment remains a major barrier to durable responses. Here, we introduce cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4)-targeting chimeras (cTACs), a class of synthetic molecules that harness CTLA-4-mediated trans-endocytosis (TE) for targeted protein degradation across cellular boundaries. The lead candidate, cTAC4.0, is composed of the extracellular domain of CD80 fused to an anti-programmed death-ligand 1 (PD-L1) fragment via a human immunoglobulin G4 (IgG4) heavy chain. Unlike existing protein degraders that function within cancer cells via house-keeping pathways, cTAC4.0 operates in trans between immune and tumor cells. It redirects the natural CD80-CTLA-4 internalization to capture and degrade PD-L1 from tumor cells into T cells, while simultaneously converting PD-L1-mediated suppression into CD28-driven co-stimulation, depending on the relative availability of CTLA-4 or CD28. Mechanistically, we demonstrate that cTAC4.0 promotes CTLA-4-dependent internalization and lysosomal degradation of both membrane-bound and soluble PD-L1, reduces surface PD-L1 levels on target cells, and activates T cells in a CD28-dependent manner. Functionally, cTAC4.0 enhances the cytotoxicity of both bispecific T cell engagers and T cell receptor (TCR)-engineered T cells in vitro, and when combined with these engineered T cells, it suppresses tumor growth in vivo in a glioblastoma xenograft model. By coupling immune checkpoint degradation with T cell activation in an immune synapse-enriched manner, cTACs establish a paradigm for intercellular protein degradation systems that simultaneously deplete suppressive ligands and enhance T cell function to overcome resistance in cancer immunotherapy.

Vaccination generates heterogenous B cell responses that collectively provide protective immunity, yet how this diversity is established remains poorly understood. Here, we identify the draining lymphatic network as a spatial organizer of humoral immunity. Vaccine dispersal across interconnected draining lymph nodes (dLNs) establishes gradients of antigen and inflammation that create distinct B cell differentiation and selection environments. dLNs proximal to the vaccination site preferentially support antibody-secreting cells and clonally diverse germinal center (GC) responses. In contrast, distal dLNs impose more stringent selection, favoring clonally restricted GCs enriched for high-affinity B cells. Spatially distinct inflammatory environments further determine antibody isotype, linking LN position to antibody effector class. These spatial biases persist upon recall and can be reprogrammed through vaccine design, including nanoparticle properties and LN-directed targeting. Thus, lymphatic networks diversify B cell fate, repertoire and affinity selection, and antibody isotype, revealing a programmable axis for tuning humoral immunity through vaccine design.

During respiratory virus infection, CD8 T cells kill infected cells and establish antigen-specific memory, but mechanisms regulating these functions remain incompletely understood. Here, we identify mitochondrial transcription factor A (TFAM)-dependent mitochondrial fitness as a regulator of CD8 T cell function during influenza infection. Human CD8 T cells exhibited an age-associated decline in TFAM expression and mitochondrial function. To model this physiologically relevant decline and determine its consequences for antiviral immunity, we generated CD8 T cell-specific TFAM-haploinsufficient mice. TFAM insufficiency disrupted mitochondrial integrity and bioenergetics and increased mitochondrial DNA and oxidative stress. During influenza infection, TFAM-insufficient CD8 T cells exhibited increased cytotoxic and inflammatory activity associated with lung immunopathology without improved viral control. This early phenotype was followed by loss of effector function, diminished antigen-specific responses, reduced protection following adoptive transfer, and impaired heterosubtypic recall immunity. Thus, TFAM-dependent mitochondrial fitness is a cell-intrinsic regulator that limits immunopathology while sustaining recall immunity.

Despite decades of HIV-1 vaccine development, the clonal and cellular determinants of durable vaccine-induced T cell memory remain incompletely understood. Here, we combined antigen-specific T cell receptor (TCR) identification, longitudinal TCR sequencing, and single-cell multi-omics to characterize Env- and Gag-specific memory precursor T cells elicited by the HIV Vaccine Trials Network (HVTN) 505 DNA prime-recombinant adenovirus serotype 5 (rAd5) boost (DNA/rAd5) vaccine regimen. We developed a generalizable high-throughput approach to identify HIV-1 Env- and Gag-specific TCRs and found distinct patterns of clonal expansion, persistence, and contribution to memory between Env- and Gag-specific CD8 T cell responses. The DNA prime and rAd5 boost differentially shaped these repertoires, with rAd5-induced clones contributing proportionally more to the Gag-specific than to the Env-specific memory precursor compartment. Single-cell immune profiling further revealed distinct memory precursor states, with Env-specific responses enriched for GZMBPRF1 cytotoxic effector-memory (EM) CD8 T cells and Gag-specific responses containing a larger cycling/proliferative population. Together, these findings demonstrate that heterologous DNA/rAd5 vaccination generates antigen-specific CD8 T cell memory with distinct clonal trajectories and cellular programs, providing new insights into how vaccine platform and antigen-specificity shape the durability and functional properties of HIV-1 specific cellular immunity.

T and B cell-mediated immunosurveillance of the central nervous system (CNS) can become maladaptive in multiple sclerosis (MS). Epstein-Barr virus (EBV) is a likely driver of MS, yet how exactly EBV-specific T cells contribute remains unclear. We generated an antigen-resolved atlas of blood and cerebrospinal fluid (CSF) T cells from untreated MS patients and controls. T cell clones carrying a GZMK effector-memory program in blood were CSF-biased, particularly in MS, and associated with EBV reactivity. In CSF, EBV-reactive GZMK CD8 T cells engaged B lineage cells. Activated CD8 T cells promoted atypical B cell and plasmablast formation, whereas GZMK-enriched effector-memory cells induced IL-6 and IL-8 release from myeloid cells. Together, these findings identify an infection-imprinted, CNS-biased state and support a model in which EBV-specific CD8 T cells contribute to inflammation through a non-canonical mode of B cell and myeloid cell activation.

Malaria is a leading cause of childhood mortality, yet infant immune responses to vaccination remain poorly understood. Here, we characterize 88 monoclonal antibodies (mAbs) directed against the Plasmodium falciparum circumsporozoite protein cloned from African infants immunized with the RTS,S/AS01E malaria vaccine, identifying potent antiparasitic mAbs exhibiting molecular features resembling those observed in adults and minimal somatic hypermutation. Importantly, germline-reverted variants of four mAbs inducing sterile protection in vivo maintained high binding affinity and Fab-dependent parasite killing. Structural analyses revealed that a few amino acid replacements drive homotypic helical assemblies, fine-tuning parasite inhibition and protective efficacy. Thus, despite maturational constraints of early life, infants can generate potent antimalarial antibodies in a near-germline configuration, informing next-generation vaccine development for this vulnerable group.

Natural killer (NK) cells and type 1 innate lymphoid cells (ILC1s), collectively known as group 1 innate lymphoid cells (ILCs), are critical mediators of anti-tumor immunity, yet their role in brain metastasis remains poorly defined. Using single-cell RNA sequencing and functional depletion models, we show that group 1 ILCs fail to provide adequate tumor control in breast cancer brain metastasis (BCBM). In contrast to the liver, where diverse, functionally competent group 1 ILC populations facilitate excellent metastatic control, group 1 ILCs in BCBM show limited diversity and profound tissue-specific dysfunction such that their depletion had no effect on tumor burden despite modest parenchymal infiltration. We attribute this group 1 ILC dysfunction to severely restricted IL-15 availability, with IL-15R protein detected at 500-fold lower concentration in the brain than in the liver. Local IL-15 complex administration restored group 1 ILC accumulation, cytotoxicity, and tissue residency, significantly reducing brain metastatic burden independent of T cells. Intracranial delivery of IL-15-secreting induced pluripotent stem-cell-derived (iPSC)-NK cells, already in clinical testing for non-small cell lung cancer, significantly reduced tumor burden. Collectively, these findings reveal how tissue-specific differences in cytokine availability shape group 1 ILC population diversity and disease response, establishing localized IL-15 signaling as a compelling strategy to unlock innate immunity against intracranial malignancies.

The generation of appropriate responses to the intestinal microbiota is an essential aspect of immune homeostasis. Studies of microbes that elicit stereotyped, antigen-specific CD4 T cell responses support the view that immune recognition of the microbiota is specific, relatively limited, and largely skewed toward Tregs, but recent profiling efforts have suggested that recognition of the microbiota may be broader and less regulatory. Such studies have mostly tracked responses to single antigens or used mice that acquire their microbiota after weaning, which has made it difficult to generalize the rules that govern microbiota-mediated T cell responses. Here we comprehensively profile, for the first time, the T cell response to the microbiota at homeostasis, and develop a panel of tools to track multiple, endogenous microbiota-reactive CD4 T cell populations in vivo. Our profiling reveals a broad microbiota-reactive T cell response that is Treg-biased but that also contains non-Treg responses to specific microbes. We find that certain microbiota-reactive T cells require priming during early-life to efficiently establish their Treg identity, while others do not. Our findings illustrate an unappreciated antigen-specific complexity in programming of microbiota-reactive T cells and underscore the importance of studying responses to the microbiota under homeostatic conditions.

Mitochondrial DNA (mtDNA) instability is an emerging feature of cancer, yet its biological effects on the tumor microenvironment (TME) and tumor progression remain incompletely defined. Using melanocyte-specific conditional silencing of mitochondrial transcription factor A (TFAM) in an autochthonous BrafV600E/Pten-/- melanoma model, we demonstrate that tumor cell-intrinsic mtDNA instability accelerates melanoma growth and metastatic dissemination in a cGAS-dependent manner. Transcriptomic profiling of early and late tumor stages revealed that mtDNA instability drives temporal remodeling of the tumor microenvironment (TME), characterized by an early type I interferon (IFN)-rich inflammatory state that licenses immunoregulatory programs as tumors progress. Tumor-associated macrophages emerged as the principal immune cell type reshaped by tumor cell-intrinsic mtDNA stress signaling, with early enrichment of inflammatory states and a shift toward efferocytosis-associated, tissue-adaptive states. The early mtDNA instability-associated macrophage signatures mapped to human melanoma states associated with favorable survival and therapy response, whereas the late signatures mapped to states associated with poor prognosis and therapy resistance across independent cohorts. Anti-PD-1 treatment delayed progression of mtDNA-instable tumors, consistent with a therapeutic sensitivity window associated with the early IFN-rich immune state. These findings establish tumor cell-intrinsic mtDNA instability as a driver of temporal immune-stromal remodeling that promotes melanoma progression and shapes therapeutic response.

Aging is characterized by hallmarks whose mechanistic interdependencies remain poorly defined. Here, we investigate the bi-directional communication between gut microbiota and host mitochondria in the context of immune regulation, healthspan and lifespan. Using a mitochondrial dysfunction PolgAmut mouse model of accelerated aging, we tested the role of mitochondrial dysfunction in modulating microbial homeostasis and aging. We find that impairment of mitochondrial function hastens the decline of microbiota structure over time and induces immune dysregulation and inflammation through metabolic reprogramming of the myeloid immune subset. Further, we find that gut microbiota drives a paradoxical energy state by reducing mitochondrial function systemically while simultaneously driving energy-intensive programs including immune remodelling and protein synthesis, through mTOR signaling. Thus, aging emerges from the progressive imbalance between microbiota-driven energetic demand and declining mitochondrial energy supply. We postulate that microbiota promote host early-life fitness, at the cost of amplifying metabolic stress and inflammation later in life.

Adoptive T cell therapies have revolutionized the treatment of hematological malignancies, however, their efficacy against solid tumors often remains limited. Lack of activation and overabundance of immune checkpoint-mediated inhibitory signals from cancer cells drive T cell dysfunction and limit persistence. To circumvent this imbalance towards inhibitory factors, we engineered a chimeric switch receptor (CSR) that repurposes the immunosuppressive TIGIT extracellular domain by fusing it to a CD28-derived stimulatory signaling tail. Here we show that while the prototype CSR design enhances immediate cytolytic activity, it also induces premature proliferative arrest and terminal differentiation due to excessive tonic signaling. By introducing a strategic point mutation within the CD28 cytoplasmic domain, we "fine-tuned" the activation threshold of the CSR for optimal functional properties. Engineered T cells with 'fine-tuned' CSR exhibit superior mitochondrial bioenergetics and sustained metabolic flux in an in vitro system of chronic antigen exposure. In preclinical xenograft models, fine-tuned CSR-expressing T cells demonstrated robust expansion and durable persistence, leading to complete tumor eradication. These findings provide a scalable strategy to rewire inhibitory checkpoints into tailored costimulatory signals, offering a potent approach to enhance the metabolic fitness and persistence of therapeutic T cells, in suppressive tumor microenvironments, in particular.

Systemic iron sequestration occurs frequently in cancer due to inflammation-driven expression of the iron-regulatory hormone hepcidin. The impact of systemic iron availability on tumoral immunity is unclear. Here, we show that elevated serum hepcidin is associated with reduced survival and decreased intratumoral CD8+ T cells in patients with pancreas cancer. While hepcidin is not induced in murine tumor models, administration of a hepcidin mimetic phenocopies the T-cell-depleted tumor microenvironment seen in patients. Mechanistically, chronic antigen-driven mitochondrial dysfunction disrupts iron metabolism and selectively depletes high avidity CD8+ T cells during iron restriction. These findings establish a direct link between hepcidin-mediated iron sequestration and tumoral immunity and nominate systemic iron dysregulation as a therapeutic target to enhance anti-tumoral CD8+ T cell responses.

Chronic or persistent T cell activation is widely thought to culminate in T cell exhaustion, yet how autoreactive CD8+ T cells remain functionally intact despite sustained self-antigen exposure is poorly understood. In chronic infection and cancer this durability is attributed to stem-like, TCF1+ PD-1+ progenitor-exhausted (Tpex) cells that reside in lymphoid tissue and continuously replenish functional effectors; whether such a reservoir operates within a chronically inflamed peripheral organ during sterile autoimmunity is unknown. Here we show that mice lacking the lysosomal nuclease DNase2a together with the type I interferon receptor Ifnar1 (Dnase2a-/- Ifnar1-/-) develop spontaneous, progressive hepatic inflammation. This hepatitis was dependent on the endosomal DNA sensor TLR9, identifying self-DNA as the initiating ligand. Inflammation was marked by expansion of inflammatory macrophages and accumulation of CD8+ T cells co-expressing PD-1 and TOX that retained, rather than lost, effector function. Paired single-cell TCR and transcriptomic analysis revealed progenitor-exhausted T cells within the liver itself that shared clonotypes with clonally expanded PD-1+ TOX+ T cells, defining a locally operating progenitor-to-effector pipeline. Spatial transcriptomics positioned these intrahepatic T cell clusters adjacent to IL-27-expressing inflammatory macrophages, and disruption of IL-27 or its receptor in bone marrow-derived cells reduced PD-1+ CD8+ T cells and their effector functions. These findings define a novel mechanism for sustaining autoreactive T cells in the liver via TLR9-driven macrophage-induced IL-27 circuit that sustains a functional, self-renewing autoreactive PD-1+ CD8+ T cell program in situ.

Antiretroviral therapy suppresses HIV-1 replication but cannot eliminate the latent viral reservoir persisting in memory CD4 T cells. Existing latency reversal candidates have yet to achieve robust viral reactivation at tolerable doses. We engineered T4IL15{triangleup}, a bispecific biologic that selectively delivers IL-15 signaling to memory CD4 T cells, with minimal off-target stimulation. T4IL15{triangleup} reactivated latent virus in 94% (48/51) of clinical samples ex vivo, 75% (15/20) of administrations in HIV-1-infected and ART-suppressed humanized mice, and 100% (6/6) of SIV-infected and ART-suppressed rhesus macaques at doses well tolerated. We also found that off-target stimulation of non-CD4 cells hindered HIV-1 reactivation ex vivo. T4IL15{triangleup} provides a robust reactivation platform that could complement other reservoir-elimination strategies toward an HIV-1 cure.

Tumor-associated macrophages (TAMs) promote tumor growth, inhibit effector lymphocytes, and induce resistance to immune checkpoint inhibitors (ICI). Therapies designed to deplete TAMs have had little success in the clinic, and strategies aimed to repolarize immunosuppressive TAMs to pro-inflammatory states have struggled with systemic toxicity. We have identified that the combination of low folate in the tumor microenvironment and TAM dependency on the high affinity folate receptor beta (FR{beta}) for folate uptake results in a unique metabolic dependency of TAMs necessary for their immunosuppressive function. FR{beta} (encoded by Folr2) is uniquely expressed on myeloid cells and upregulated on TAMs. FR{beta}+ TAMs exhibit an immunosuppressive phenotype in melanoma and are associated with worse clinical outcomes and resistance to ICI in melanoma patients. We generated a novel Folr2-/- mouse model to study why TAMs express a unique folate receptor and showed that tumor growth was slowed in the absence of Folr2 in a T-cell dependent manner. We observed a dramatic repolarization of Folr2-/- TAMs in vivo to pro-inflammatory states, resulting in increased cytotoxic T cell and NK cell infiltration into tumors. Importantly, we show that folate is low in the tumor microenvironment by performing metabolomics on melanoma tumors and adjacent normal tissue from warm autopsy patient specimens, and that we could increase tumor growth in Folr2-/- mice by increasing serum folate to supraphysiologic concentrations with a high folate diet. Integrated metabolomics and transcriptomic analysis demonstrated that Folr2-/- macrophages have impaired folate uptake and 1C metabolism-based reduction of oxidized glutathione in low folate conditions, resulting in increased mitochondrial reactive oxygen species (ROS) in Folr2-/- cells. Excess ROS results in leakage of mitochondrial DNA into the cytoplasm, activating cGAS-STING signaling and promoting pro-inflammatory macrophage polarization through TBK1 and NF-kB. Together, our data demonstrate that TAM expression of FR{beta} promotes their immunosuppressive functions by maintaining folate uptake in the low folate tumor microenvironment, suggesting that FR{beta} is a novel metabolic checkpoint on TAMs.

CD4+ T-cell recovery is widely used to assess immune reconstitution in people with HIV, but its relationship to virus-specific humoral immunity across pathogens remains unclear. We characterized neutralizing activity against SARS-CoV-2, HIV-1, and influenza viruses in ART-treated, virologically suppressed individuals spanning distinct CD4+ T-cell levels. BA.5 was the dominant SARS-CoV-2 neutralization target across CD4 strata, whereas D614G neutralization increased with greater immune reconstitution. This gradient was largely absent for the antigenically divergent NB.1.8.1 and XFG variants. HIV-1 neutralization was inversely associated with CD4+ T-cell count, while influenza showed strain-dependent patterns. Neutralization-to-protection bridging preserved a CD4-associated gradient for D614G but not for highly immune-evasive variants. These findings show that immune reconstitution does not translate uniformly into antiviral humoral function. Instead, antibody profiles reflect host immune status, prior antigenic exposure, and viral antigenic evolution, supporting pathogen-specific functional assessment alongside conventional immune monitoring.

Partially preserved function of recombination-activating genes (RAG) 1 and 2 can be linked to divergent and hard-to-predict clinical and immunological phenotypes, even among close relatives. It is unclear how intrinsic RAG hypomorphism interacts with extrinsic environmental pressures to shape clinical trajectory. We dissect this phenomenon in a unique cohort of 18 Old Order Mennonite individuals with a novel missense founder RAG1 variant (p.C176F) with 25.8% recombinase activity of wild-type protein. After studying a myriad of markers, we demonstrate varying severity and progression of clinical disease (predominantly in females) that paralleled decline in CMV-specific immune competence, break in tolerance with hallmark presence of antibodies to IFN, a TH1/IFN{gamma}-driven inflammatory milieu with elevated serum markers (CXCL9/10), expansion of follicular helper T cells and clonal B cells enriched for autoreactive-prone VH4.34 B cell receptor. BCR and TCR repertoires carry the fingerprints of both extrinsic and RAG-driven intrinsic changes. Through this experiment of nature, our cohort demonstrated that partial RAG deficiency (pRD) is not a monolithic disease but the result of compounded RAG intrinsic and extrinsic events. Overall, this study uses multi-omics approaches to dissect the contribution of a hypomorphic RAG variant to variable severity of clinical disease and immunological dysregulation at cellular and molecular level. Emerging biomarkers of a multi-omic roadmap should allow monitoring of progression of clinical disease and guide who and when to treat with hematopoietic stem cell transplant in pRD.

Tertiary lymphoid structures (TLS) predict response to checkpoint inhibition, and conventional dendritic cells (cDC) are required to build and maintain them. What renders a niche permissive for their assembly is unknown: chemokines recruit the cellular constituents but do not specify how they organize. Here we show that the organizing signal is a matrix fragment. Proteolysis of the proteoglycan versican (VCAN) releases the matrikine versikine, constitutively in germinal center light zones and inducibly in tumor stroma. Versikine activates CD11b+ cDC and expands cDC1 to assemble TLS-archetypal triads, apposed DC: CD4+ T: CD8+ T units. Versikine-conditioned DC engage progenitor-exhausted CD8+ T cells (Tpex) and Th1-polarized follicular helper CD4+ T cells. Excess unproteolyzed VCAN inverts this toward DC-Treg crosstalk and Tpex loss. Versikine supplied as mRNA or recombinant protein sensitizes refractory tumors to PD-L1 blockade. VCAN proteolysis prospectively predicted outcomes after PD-1 blockade in metastatic colorectal cancer. Matrikines organize chemokine-recruited cells into functional immune niches.