HIV-1 promotes loss of CD4+ T cell stemness and enrichment of effector-like states via Vpr-mediated TCF7 degradation

Allograft Inflammatory Factor 1 expression in cDC1 is required to direct Tbet—driven T cell immunity to defend against intracellular pathogens in vivo 2256292

Allograft Inflammatory Factor‑1 (AIF1) is a calcium‑binding protein enriched in conventional dendritic cells, with selective expression in cDC1. We hypothesized that AIF1 programs cDC1 immunity to intracellular pathogens by sustaining their activation and T cell‑priming capacity. To directly address, AIF1 was selectively deleted in CD11c+ cells prior to infection with the intracellular or extracellular pathogens in vivo. DC and T cell subsets were then analyzed by multiparametric flow cytometry. Additionally Single-cell RNA sequencing (scRNA-seq) under steady-state conditions was analyzed by differential expression and gene set enrichment (GSEA). Conditional deletion of AIF1 in DCs resulted in a modest (∼20%) reduction of cDC1, without affecting cDC2 populations, indicating a partial lineage dependency. During infection with intracellular pathogens Listeria monocytogenes and LCMV, AIF1‑deficient cDC1 showed impaired activation and defective pathogen control, leading to markedly reduced CD4+ T cell activation, loss of Th1 polarization (CD4+T‑bet+), and diminished CD8+CD54+GranzymeB+ cytotoxic responses. In contrast, infection with extracellular pathogens Helicobacter pylori and Nippostrongylus brasiliensis, eliciting Th2-biased immunity, induced no observable impairment in T cell responses. This aligns with AIF1’s unique expression within cDC1, but not cDC2. These findings identify AIF1 as a critical regulator of cDC1 immunogenic identity and protective T cell immunity to intracellular infection, defining a pathway where AIF1 loss reprograms DC—T cell communication toward a regulatory, non-protective outcome. National Institutes of Health (NIH) Classical and Non-Classical Antigen Presenting Cells (APC)

Immune checkpoint blockade enhances CD4 effector function to control persistent viral infection 2267612

T cell exhaustion, a defining hallmark of chronic viral infections and cancer, is characterized by the progressive loss of effector function and sustained expression of inhibitory receptors on T cells. Although immune checkpoint blockade (ICB) therapies, such as PD-1 inhibition, can transiently reinvigorate subsets of exhausted CD8+ T cells, their efficacy remains constrained by the limited pool of self-renewing, progenitor-like TCF1+ CXCR5+ CD8+ T cells. We have previously demonstrated that B cell—derived IL-27 signaling is necessary for the expansion and maintenance of this progenitor-like population during chronic infection. Using an IL-27 receptor deficient mouse model, we reveal a previously unrecognized mechanism by which PD-1 blockade mediates viral clearance. We demonstrate that PD-1 inhibition enhances CD4+ T cell function, specifically through increased IL-21 production from T follicular helper (Tfh) cells which promotes both humoral and cytotoxic antiviral responses. Our findings identify a novel IL-27 independent CD4+ T cell axis through which checkpoint blockade controls persistent viremia. To determine the impact of checkpoint inhibition on persistent viral infection, IL-27 receptor—deficient mice were infected with chronic lymphocytic choriomeningitis virus (LCMV clone 13) and treated with PD-1 blocking antibodies. We used flow cytometry and viral titers to evaluate CD4+ and CD8+ T cell subsets, the importance of IL-21, and persistent viral clearance. PD-1 blockade restored antiviral immunity in IL-27 receptor—deficient mice and resulted in enhanced CD4+ T cell function. We saw increased IL-21 production from T follicular helper cells that led to higher cytotoxic and humoral antiviral responses. Our studies reveal that PD-1 blockade can drive persistent viral clearance through an IL-27—independent mechanism that involves IL-21—producing CD4+ T cells. N/A Viral Immunology (VIR)

RORα governs CD8+ T cell memory subset specification and offers a therapeutic node for antiviral immunity 2259080

The establishment of immunological memory is crucial for durable antiviral immunity and underlies effective vaccine design in enhancing memory responses. The retinoic acid receptor—related orphan receptor α(RORα), a ligand-regulated transcription factor of the nuclear receptor superfamily, has been implicated in CD8+ T cell immunity, yet its role remains poorly defined. To investigate this, we integrated genomic approaches with both genetic and pharmacologic perturbations of RORα to examine its role in CD8+ T cell development during antiviral responses. RORα-deficient mice infected with acute lymphocytic choriomeningitis virus (LCMV) exhibited fewer virus-specific CD8+ T cells and higher splenic viral titers at day 5 post-infection than wild-type controls. Despite reduced numbers, RORα-deficient CD8+ T cells showed enhanced cytotoxic potential, indicating that RORα modulates effector programming rather than overall functional capacity. RORα deficiency also led to increased migration and redistribution of CD8+ T cells into non-lymphoid compartments, particularly the liver and adipose tissues, and promoted the development of memory precursors (MP), peripheral memory (TPM), and tissue-resident memory (TRM) populations. Single-cell RNA-seq and ATAC-seq revealed enrichment of transcriptional and chromatin programs linked to MP and TRM gene signatures, including elevated expression of Tcf7 and Runx family members, alongside reduced accessibility at loci governing terminal effector differentiation. Pharmacologic inhibition of RORα with the RORα-selective inverse agonist, SR3335, recapitulated the knockout phenotype, favoring memory CD8+ T cell differentiation over terminal effectors. Collectively, our data reveal distinct programming of CD8 T effector versus memory populations attributable to RORα activity. As a ligand-regulated transcription factor, RORα may be a promising target to enhance CD8+ T cell memory responses for improved vaccines and cell-based immunotherapies. N/A Immune Response Regulation: Molecular Mechanisms (IRM)

CD96 marks a phenotypically distinct checkpoint-associated HCV-specific CD8+ T-cell subset featuring memory-associated states

Introduction Hepatitis C virus (HCV) infection frequently progresses to chronicity, where persistent antigen exposure drives differentiation of virus-specific CD8+ T cells toward an exhausted phenotype. This state is defined by progressive upregulation of inhibitory receptors and functional impairment of antigen-specific T cells. Because patients span distinct clinical stages from acute infection to spontaneous resolution or therapy induced sustained virological response, HCV provides a unique model to study how T-cell exhaustion is established, maintained, and potentially reversed. While PD1 and TIGIT are well established in this context, CD96 (TACTILE) is a less-characterized receptor that shares its ligand CD155 with TIGIT and DNAM-1 and may modulate CD8+ T-cell differentiation and function. Methods To evaluate the role of CD96 across infection stages, we used HCV-specific MHC class I tetramers combined with high-dimensional flow cytometry to phenotypically profile virus-specific CD8+ T-cells ex vivo in 32 patients spanning acute, subacute, chronic, spontaneously resolved infection, and post-treatment sustained virological response. We assessed CD96 co-expression with PD1/TIGIT, transcription factors (TCF1, TOX, IRF4, T-bet, NR2F6), and relevant differentiation and exhaustion markers. Results CD96+ HCV-specific CD8+ T cells consistently increased relative to bulk across all stages of HCV infection, with approximately four-fold higher frequencies than bulk CD96+ CD8+ T cells (p<0.0001), and highest frequencies of 51,13% observed in the chronic group. Because CD96 expression was predominantly distributed continuously rather than strictly bimodal, we also report CD96 MFI as a continuous measurement alongside CD96+ frequencies. Phenotypically, HCV-specific and bulk CD96+ CD8+ T cells were enriched for IRF4+, TOX+ and TCF1+ subsets, suggesting possible reduced effector features and increased memory-associated characteristics. Notably, the CD96+ PD1+ TIGIT+ subset was about five times higher in HCV-specific than in bulk CD8+ T-cell populations (p<0.0001). In cross-sectional comparison, frequencies of CD96+ PD1+ TIGIT+ HCV-specific CD8+ T cells decreased, while the CD96- PD1- TIGIT- counterparts expanded. Discussion These findings identify CD96 as a marker of a phenotypically distinct checkpoint-associated HCV-specific CD8+ T-cell subset featuring memory-associated rather than terminally exhausted states. Whether this phenotypic association has functional or therapeutic significance for combination immune therapy will require future studies, including direct functional assays of sorted CD96+ versus CD96- HCV-specific CD8+ T cells.

Experimental Evidence for HIV-Associated Phenotypic Reprogramming of CD4□ T Cells: An Exploratory Immunological Study

Sp1 links CD46 to CD4 T cell metabolic fitness, survival, and retroviral control.

CD46, a human-specific complement receptor, regulates gene programs essential for T helper 1 (TH1) cell differentiation, yet how it exerts direct transcriptional control remains unclear. We show that the CD46 signaling domain cytoplasmic tail 1 (CYT-1) engages the transcription factor Sp1 in human CD4 T cells to dynamically modulate Sp1-DNA interactions. Beyond promoting TH1 cell induction, CD46-Sp1-controlled programs support naive CD4 T cell survival by maintaining nutrient transporter expression and suppressing the intrinsic caspase 9-caspase 3 apoptotic pathway. The CD46-Sp1 axis also restrains HIV transcription in infected CD4 T cells in vitro. Disruption of CYT-1-Sp1-regulated programs identifies T cells from individuals with HIV who exhibit incomplete viral suppression during antiretroviral therapy. Together, these findings define a human-specific transcriptional mechanism linking complement signaling to metabolic adaptation, apoptosis regulation, and antiviral defense, highlighting an unexpected role for CD46 in coordinating T cell homeostasis and host protection.