Biology subjects

Ghebremichael, M.

Publications and source records attributed to Ghebremichael, M..

5 recordsLinked to original sources

bioRxiv2026

Duration of Initial Viremia Modulates Functional Properties of HIV-specific T Cell Receptors

Virus-specific CD8+ T cells are crucial in controlling chronic human viral infections such as HIV-1, but the effect of persistent antigen exposure on T cell repertoire formation is not well understood. In this study, we examined epitope-specific CD8+ T cell repertoires in people living with HIV-1, where duration of viremia following hyperacute infection was modulated by the time of initiation of continuous suppressive antiretroviral therapy (ART). After ART-induced undetectable viremia in persons expressing the same HLA class I allele, we analyzed the impact of early (n=6) versus delayed (n=6) ART initiation on the clonotypic composition, clonotypic cross-reactivity, functional avidity and memory differentiation profile of the HIV-specific T cell repertoire restricted by HLA-B*58:01. Using a panel of barcoded tetramers, we mapped T cell receptor (TCR) clonotypes specific for three dominant epitopes and their variants. Both groups exhibited polyclonal TCR repertoires with evidence of cross-reactivity, which was significantly enriched in donors with prolonged antigen exposure. Within this cohort, broadly cross-reactive clonotypes capable of recognizing all autologous variants were identified, but these were rare (<1%). Early ART initiation preserved repertoires characterized by higher-avidity TCRs and a relative enrichment of transitional memory CD8+ T cell subsets. These functional differences were not associated with differences in TRBV gene sharing, indicating that ART timing shapes repertoire quality and memory differentiation without altering TRBV gene bias. These findings demonstrate how antigen suppression dynamics differentially shape the breadth, functional sensitivity, and memory composition of the HIV-specific TCR repertoire, with implications for T cell-directed immunotherapies and HIV cure strategies. One Sentence SummaryThe duration of viral antigen exposure during early HIV infection shapes the functional quality, breadth, and memory composition of virus-specific CD8 T cell receptor repertoires. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/702605v1_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@9a5a6dorg.highwire.dtl.DTLVardef@1a6bbdaorg.highwire.dtl.DTLVardef@17707e8org.highwire.dtl.DTLVardef@1a84d9e_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2025

Loss of B cell tolerance at the T2/T3a B cell transition is a convergent pathogenic mechanism in common variable immunodeficiency

Many patients with common variable immunodeficiency (CVID), including those with CTLA4 deficiency, NFKB1 variants and activated PI3K-delta syndrome (APDS), develop autoimmunity that is refractory to treatment. Despite this shared clinical phenotype, a unifying mechanism for the breakdown of B cell tolerance across monogenic forms of CVID has not been established. Here, we demonstrate that patients with loss-of-function NFKB1 variants, like those with CTLA4 variants and APDS, exhibit dysregulated CD4+ T cell expansion, accumulation of transitional B cells, and a relative lack of follicular B cells. In patients with monogenic CVID and clinical autoimmunity, we observed a relative expansion of transitional and activated naive (aN: CD21loCD11chi) B cells in peripheral blood accompanied by a marked increase in the frequency of VH4-34 expressing autoreactive 9G4+ B cells, which expanded between T2 and T3a transitional B cell stages. Single-cell transcriptomic and B cell receptor analysis further revealed a marked expansion of activated T1/2, T3 and extrafollicular activated naive and double negative (DN: IgD-CD27-) B cell subsets in APDS patients. Notably, one B cell subset appeared exclusively in the APDS disease state, characterized by high oxidative phosphorylation in transitional B cells, specifically. In APDS patients, we also observed a clonal expansion of specific extrafollicular class-switched DN B cells, which were clonally derived from activated transitional B cells. DN B cells were also identified in APDS lung tissue, consistent with the contribution of activated, extrafollicularly-derived B cells to tissue inflammation. Together, these findings suggest that in many patients with CVID and autoimmune features, premature activation of autoreactive transitional T2 and T3a B cells induces the survival and expansion, rather than the tolerization and elimination, of self-reactive B cells. This process leads to extrafollicular expansion of autoreactive B cells capable of tissue infiltration. One Sentence SummaryLoss of transitional B cell tolerance and extrafollicular expansion of autoreactive B cells drive autoimmunity in monogenic causes of CVID.

immunology↗

bioRxiv2024

PPARγ downregulation in colonic CD8+ T cells results in epithelial barrier disruption in people with HIV on antiretroviral therapy

A hallmark of HIV infection is disruption of intestinal barrier integrity that persists in people with HIV (PWH) despite treatment with antiretroviral therapy (ART). This disruption is central to HIV disease progression, yet the causes remain incompletely understood. We report a novel mechanism by which immunometabolic defects in colon resident CD8+ T cells in PWH lead to intestinal epithelial apoptosis and disruption of intestinal barrier integrity. We show that in PWH, these cells downregulate the lipid sensor peroxisome proliferator-activated receptor-{gamma} (PPAR{gamma}), which results in reduced intracellular lipid droplets, impaired fatty acid oxidation, and acquisition of lipids by CD8+ T cells from intestinal epithelial cells, which then contributes to epithelial cell death. Our findings indicate that HIV-associated immunometabolic dysregulation of colon CD8+ T cell leads to loss of intestinal epithelial homeostasis. These results identify potential new strategies to reduce comorbidities in PWH and other disorders with disrupted intestinal barrier integrity.

immunology↗

bioRxiv2024

Congenital T cell activation impairs transitional to follicular B cell maturation in humans

CTLA4-deficient patients exhibit profound humoral immune dysfunction, yet the basis for the B cell defect is not known. We observed a marked reduction in transitional to follicular B cell development in CTLA4-deficient patients, correlating with decreased CTLA4 function in regulatory T cells and increased mTORC1 signaling in transitional B cells. Treatment of transitional B cells with CD40L was sufficient to induce mTORC1 signaling and inhibit follicular B cell maturation in vitro. Frequent cell-cell contacts between CD40L+ T cells and naive IgD+CD27- B cells were observed in patient lymph nodes. Follicular B cell maturation in CTLA-deficient patients was partially rescued following CTLA4 replacement therapy in vivo. We conclude that functional regulatory T cells and the containment of excessive T cell activation are required for follicular B cells to mature and attain metabolic quiescence and thus acquire a state of immunological self-tolerance. One Sentence SummaryCongenital T cell activation in CTLA4-deficient patients impairs transitional to follicular B cell maturation and can be rescued by CTLA4 replacement therapy in vivo.

immunology↗

bioRxiv2020

Profound Treg perturbations correlate with COVID-19 severity

The hallmark of severe COVID-19 disease has been an uncontrolled inflammatory response, resulting from poorly understood immunological dysfunction. We explored the hypothesis that perturbations in FoxP3+ T regulatory cells (Treg), key enforcers of immune homeostasis, contribute to COVID-19 pathology. Cytometric and transcriptomic profiling revealed a distinct Treg phenotype in severe COVID-19 patients, with an increase in both Treg proportions and intracellular levels of the lineage-defining transcription factor FoxP3, which correlated with poor outcomes. Accordingly, these Tregs over-expressed a range of suppressive effectors, but also pro-inflammatory molecules like IL32. Most strikingly, they acquired similarity to tumor-infiltrating Tregs, known to suppress local anti-tumor responses. These traits were most marked in acute patients with severe disease, but persisted somewhat in convalescent patients. These results suggest that Tregs may play nefarious roles in COVID-19, via suppressing anti-viral T cell responses during the severe phase of the disease, and/or via a direct pro-inflammatory role.

immunology↗