Biology subjects

Marchalot, A.

Publications and source records attributed to Marchalot, A..

5 recordsLinked to original sources

bioRxiv2026

High-resolution single-cell atlas of the human B cell compartment and immune microenvironment across tissues

The immune system is a dynamic network of diverse cell types distributed across tissues. While mouse studies have highlighted the importance of tissue-localized B-cell responses in infection and tissue repair, research on human B cells has remained largely confined to peripheral blood. Here, we specifically investigated the human B-cell compartment and its interactions with the immune microenvironment across 10 tissues, using single-cell RNA sequencing and paired B-cell receptor sequencing. We mapped the full spectrum of B-cell populations and revealed diverse differentiation trajectories spanning naive, memory, and plasma cell types. Germinal center B cells and plasma cells showed tissue-specific adaptations in transcriptional states, isotype usage, and functional profiles. Plasma cell isotypes influenced both effector functions and predicted interactions with T cells. Finally, we defined tissue-specific residency gene modules that outperformed existing memory B-cell signatures. Together, this dataset serves as a foundation for systematically studying tissue-localized B cells and reveals how local microenvironments shape humoral immunity.

immunology↗

bioRxiv2026

MAIT cell responses to S. aureus and sensitivity to HlgAB are modulated by activation and tissue-dependent virulence effects

Mucosa-associated invariant T (MAIT) cells are unconventional T cells with innate-like rapid antimicrobial effector functions and serve as resident sentinels at mucosal and non-mucosal barriers. However, their role in immune defense against Staphylococcus aureus and the impact of bacterial immune evasion mechanisms are incompletely understood. Here, we have investigated MAIT cell responses to S. aureus and the impact of its broadly expressed leukocidin toxin HlgAB on MAIT cell responses in different human tissue sites. MAIT cells respond to S. aureus with a complex polyfunctional profile spanning pro-inflammatory IL-17, TNF, and IFN{gamma}, anti-inflammatory IL-10, plus granzymes A, B, and K, perforin, and granulysin. The quality of responses was influenced by microbial dose and time of exposure and was dependent on both MR1-presented antigen and cytokine co-activation. CD56 MAIT cells displayed stronger effector responses and higher HlgAB sensitivity compared to CD56- cells. MAIT cells were partially resistant to HlgAB-toxicity compared to monocytes; blood-derived MAIT cells remained susceptible, whereas tonsillar MAIT cells showed minimal sensitivity. Notably, activation reduced the MAIT cell susceptibility to HlgAB, and such activation also afforded indirect protection to monocytes in co-cultures. The reduced susceptibility of tonsillar MAIT cells correlated with lower CCR2 and CXCR1 expression, a pattern shared with barrier tissues such as the lung and intestines. In conclusion, these findings indicate that MAIT cells exhibit tissue- and context-dependent responses to S. aureus and sensitivity to HlgAB-mediated immune evasion. ImportanceMAIT cells are an evolutionarily conserved unconventional T cell subset that responds to riboflavin pathway-derived antigens from a range of microbes. Here, we found that the human MAIT cell response to the pathogen S. aureus is robust with a polyfunctional complexity influenced by bacterial concentration and response kinetics. The ubiquitously expressed S. aureus immune-evasive toxin HlgAB attacks MAIT cells via CCR2. However, the sensitivity of MAIT cells to HlgAB varies depending on tissue localization, where in particular tissue-resident MAIT cells in tonsils are resistant. Antigen-specific activation of MAIT cells reduces HlgAB sensitivity, with protection also afforded to monocytes in the vicinity. These findings uncover the complex and dynamic interaction between an evolutionarily conserved arm of immunity, and immune evasion mechanisms of the important pathogen S. aureus.

immunology↗

bioRxiv2024

Selective killing of plasma cell clones using splice-switching oligonucleotides targeting immunoglobulin variable exons.

Deregulated proliferation of a plasma cell (PC) clone is accompanied by an excess production of a monoclonal immunoglobulin (mo-Ig) component with unique V(D)J rearrangement features. In systemic Ig light chain (AL) amyloidosis, organ dysfunction is due to the deposition of amyloid fibrils composed of mo-Ig light chains in target tissues. Recent advances in exon skipping therapy using splice-switching antisense oligonucleotides (ASO) prompted us to examine a new antisense strategy targeting the variable (V) exon in myeloma cells. Indeed, we previously observed that the production of truncated Ig light chains, encoded by alternatively spliced mRNAs lacking V exon, heightened endoplasmic reticulum (ER) stress and triggered apoptosis of antibody-secreting plasma cells. We designed ASO hybridizing donor or acceptor V exon splice sites on mo-Ig pre-mRNAs. These compounds were very potent alternative splicing inducers and increased the production of V-domain-less truncated Ig chains. Remarkably, in vitro experiments and tumor xenograft models revealed that myeloma cells were highly sensitive to specific ASO treatment, compared to an irrelevant control-ASO. RNA-seq experiments further confirmed that the production of truncated Ig induced upon ASO treatment provoked a massive myeloma cell death through ER stress-associated apoptosis. In addition, high throughput sequencing of Ig repertoire demonstrated that ASO targeting JH2 or J{kappa}1 donor splice site induced massive elimination of VDJH2- or VJ{kappa}1-rearranged clones respectively, while sparing the others. Collectively, these data provide evidence that ASO targeting V exon on mo-Ig pre-mRNAs can emerge as new weapons to induce selective killing of plasma cell clones.

immunology↗

bioRxiv2020

Splice switching oligonucleotide mediated gene knockdown in B cells and plasma cells

The need to identify new therapeutic approaches to the treatment of cancers of the B lymphoid lineage is crucial. Unlike CRISPR/Cas technology, antisense strategies result in transient modifications of gene expression and lack mutagenic effects at the DNA level. Here, we provide evidence for efficient knockdown of c-REL and RELA expression after treatment with splice switching antisense oligonucleotides (SSO) inducing exon skipping and reading frameshifts. We also developed a tool to facilitate the choice of exons for on purpose inhibition of mouse and human gene expression. Interestingly, treatments with morpholino SSO targeting the c-REL exon 2 donor splice site or RELA exon 5 acceptor splice site elicited very efficient knockdown in diffuse large B cell lymphoma (DLBCL) cell lines and antibody-secreting cells derived from primary human B cells. Consistent with the clinical relevance of c-REL activation in DLBCLs, treatment with c-REL SSO induced major alterations in NF-{kappa}B and TNF signalling pathways and strongly decreased cell viability. Altogether, SSO-mediated knockdown is a powerful approach to transiently inhibit the expression of given genes in B-lineage cells that should pave the way for cancer treatments, provided optimized ligand-conjugations for in vivo delivery. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=169 SRC="FIGDIR/small/302984v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@170de4forg.highwire.dtl.DTLVardef@113229corg.highwire.dtl.DTLVardef@145377forg.highwire.dtl.DTLVardef@13e8c1e_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2019

Uncoupling splicing from transcription using antisense oligonucleotides reveals a dual role for I exon donor splice sites in antibody class switching

Class switch recombination (CSR) changes antibody isotype by replacing C constant exons with different constant exons located downstream on the immunoglobulin heavy (IgH) locus. During CSR, transcription through specific switch (S) regions and processing of noncoding germline transcripts (GLTs) are essential for the targeting of Activation-Induced cytidine Deaminase (AID). While CSR to IgG1 is abolished in mice lacking I{gamma}1 exon donor splice site (dss), many questions remain regarding the importance of I exon dss recognition in CSR. To further clarify the role of I exon dss in CSR, we first evaluated RNA polymerase II (RNA pol II) loading and chromatin accessibility in S regions after activation of mouse B cells lacking I{gamma}1 dss. We found that deletion of I{gamma}1 dss markedly reduced RNA pol II pausing and active chromatin marks in the S{gamma}1 region. We then challenged the post-transcriptional function of I exon dss in CSR by using antisense oligonucleotides (ASO) masking I exon dss on GLTs. Treatment of stimulated B cells with an ASO targeting I{gamma}1 dss, in the acceptor S{gamma}1 region, or I dss, in the donor S region, did not decrease germline transcription but strongly inhibited constitutive splicing and CSR to IgG1. Altogether, this study reveals that the recognition of I exon dss first supports RNA pol II pausing and the opening of chromatin in targeted S regions and that GLTs splicing events using constitutive I exon dss appear mandatory for the later steps of CSR, most likely by guiding AID to S regions.

immunology↗