Biology subjects

Megret, J.

Publications and source records attributed to Megret, J..

7 recordsLinked to original sources

bioRxiv2026

Variant-specific spike conformational dynamics shape memory B cell selection during recall

Immune imprinting profoundly shapes antibody responses to breakthrough infections and vaccination against evolving endemic viruses. Current vaccine design primarily focuses on antigen sequence and variant mutations but rarely consider the structural context in which these antigens are being recognized. In this study, we make use of the longitudinal analysis of memory B cell (MBC) responses in boosted individuals enrolled in the COVIBOOST clinical trial to provide a proof of principle that variant-specific conformational dynamics can impact MBC recruitment and protective antibody responses, independently of epitope conservation. Combining functional characterization of MBC-derived monoclonal antibodies, repertoire analysis, epitope mapping and in silico structural modeling of epitope accessibility, we found that the adjuvanted B.1.351 spike vaccine preferentially recalled MBCs targeting exposed receptor-binding domain neutralizing epitopes. This preferential recruitment arises from the more restricted conformational dynamics of the B.1.351 spike compared to the ancestral Hu-1 spike, leading to increased masking of class 4 and 5 cryptic RBD epitopes. These findings demonstrate that antigen conformational dynamics can be leveraged to redirect pre-existing immunity toward neutralizing epitopes upon boost immunization.

immunology↗

bioRxiv2025

AXL mediates mast cell survival and resistance to tyrosine kinase inhibitors in mastocytosis

Mastocytosis is a clonal disorder driven by KIT mutations, but resistance to tyrosine kinase inhibitors (TKIs) remains a major challenge. Following the discovery of an AXL L197M mutation in a patient with congenital aggressive mastocytosis, we demonstrated unexpected wild-type AXL expression in neoplastic mast cells (MCs) across mastocytosis subtypes, challenging current views concerning mastocytosis pathophysiology. AXL was undetectable in steady-state MCs but several factors, including IFN- and IFN-{beta}, induced its expression, consistent with the inflammatory nature of mastocytosis and the high interferon levels in patient plasma. Ectopic expression of WT or L197M AXL in the ROSA KIT D816V cell line enhanced proliferation and survival by upregulating pSTAT5, pSTAT3, pFAK, p-p38, survivin and BCL2. Both AXL forms conferred resistance to the KIT inhibitor PKC412/midostaurin by sustaining BCL2, MCL1, and BCL-XL expression while reducing caspase-3 activation. L197M AXL induced slightly stronger resistance to apoptosis than WT, but this difference was not significant. Combined KIT and AXL targeting (PKC412+R428) restored TKI sensitivity by downregulating BCL-XL, Livin and cIAP1, and activating caspase-3, highlighting the therapeutic potential of dual KIT/AXL pathway inhibition. Importantly, neoplastic MCs from a mast cell leukemia patient harboring the KIT F522C mutation and unresponsive to PKC412 strongly expressed AXL and displayed marked in vitro sensitivity to R428 alone, highlighting AXL as a potential therapeutic target in aggressive mastocytosis not driven by KIT D816V. These findings identify AXL as a previously unrecognized driver of malignant MC survival and TKI resistance, and support AXL inhibition as a promising therapeutic strategy in aggressive mastocytosis. Key Points- AXL is aberrantly expressed in neoplastic mast cells, driving survival and resistance to KIT inhibition in mastocytosis. - Dual KIT and AXL inhibition restores TKI sensitivity in KIT-mutant mastocytosis. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=182 SRC="FIGDIR/small/686205v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@1569c9eorg.highwire.dtl.DTLVardef@1445b32org.highwire.dtl.DTLVardef@bf3565org.highwire.dtl.DTLVardef@14a94f0_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2023

Omicron BA.1 breakthrough infection drives long-term remodeling of the memory B cell repertoire in vaccinated individuals.

How infection by a viral variant showing antigenic drift impacts a preformed mature human memory B cell (MBC) repertoire remains an open question. Here, we studied the MBC response up to 6 months after Omicron BA.1 breakthrough infection in individuals previously vaccinated with three doses of mRNA vaccine. Longitudinal analysis, using single-cell multi-omics and functional analysis of monoclonal antibodies from RBD-specific MBCs, revealed that a BA.1 breakthrough infection mostly recruited pre-existing cross-reactive MBCs with limited de novo response against BA.1-restricted epitopes. Reorganization of clonal hierarchy and new rounds of germinal center reaction, however, combined to maintain diversity and induce progressive maturation of the MBC repertoire against common Hu-1 and BA.1, but not BA.5-restricted, SARS-CoV-2 Spike RBD epitopes. Such remodeling was further associated with marked improvement in overall neutralizing breadth and potency. These findings have fundamental implications for the design of future vaccination booster strategies.

immunology↗

bioRxiv2021

Immune escape of SARS-CoV-2 Omicron variant from mRNA vaccination-elicited RBD-specific memory B cells.

Memory B cells (MBCs) represent a second layer of immune protection against SARS-CoV-2. Whether MBCs elicited by mRNA vaccines can recognize the Omicron variant is of major concern. We used bio-layer interferometry to assess the affinity against the receptor-binding-domain (RBD) of Omicron spike of 313 naturally expressed monoclonal IgG that were previously tested for affinity and neutralization against VOC prior to Omicron. We report here that Omicron evades recognition from a larger fraction of these antibodies than any of the previous VOCs. Additionally, whereas 30% of these antibodies retained high affinity against Omicron-RBD, our analysis suggest that Omicron specifically evades antibodies displaying potent neutralizing activity against the D614G and Beta variant viruses. Further studies are warranted to understand the consequences of a lower memory B cell potency on the overall protection associated with current vaccines.

immunology↗

bioRxiv2021

Memory B cells control SARS-CoV-2 variants upon mRNA vaccination of naive and COVID-19 recovered individuals.

How a previous SARS-CoV-2 infection may amplify and model the memory B cell (MBC) response elicited by mRNA vaccines was addressed by a comparative longitudinal study of two cohorts, naive individuals and disease-recovered patients, up to 2 months after vaccination. The quality of the memory response was assessed by analysis of the VDJ repertoire, affinity and neutralization against variants of concerns (VOC), using unbiased cultures of 2452 MBCs. Upon boost, the MBC pool of recovered patients selectively expanded, further matured and harbored potent neutralizers against VOC. Maturation of the MBC response in naive individuals was much less pronounced. Nevertheless, and as opposed to their weaker neutralizing serum response, half of their RBD-specific MBCs displayed high affinity towards multiple VOC and one-third retained neutralizing potency against B.1.351. Thus, repeated vaccine challenges could reduce these differences by recall of affinity-matured MBCs and allow naive vaccinees to cope efficiently with VOC.

immunology↗

bioRxiv2020

Maturation and persistence of the anti-SARS-CoV-2 memory B cell response.

Memory B cells play a fundamental role in host defenses against viruses, but to date, their role have been relatively unsettled in the context of SARS-CoV-2. We report here a longitudinal single-cell and repertoire profiling of the B cell response up to 6 months in mild and severe COVID-19 patients. Distinct SARS-CoV-2 Spike-specific activated B cell clones fueled an early antibody-secreting cell burst as well as a durable synchronous germinal center response. While highly mutated memory B cells, including preexisting cross-reactive seasonal Betacoronavirus-specific clones, were recruited early in the response, neutralizing SARS-CoV-2 RBD-specific clones accumulated with time and largely contributed to the late remarkably stable memory B-cell pool. Highlighting germinal center maturation, these cells displayed clear accumulation of somatic mutations in their variable region genes over time. Overall, these findings demonstrate that an antigen-driven activation persisted and matured up to 6 months after SARS-CoV-2 infection and may provide long-term protection.

immunology↗

bioRxiv2020

Direct contribution of skeletal muscle mesenchymal progenitors to bone repair

Tissue regeneration relies on the activation of tissue resident stem cells concomitant with a transient fibrous tissue deposition to allow functional tissue recovery. Bone regeneration involves skeletal stem/progenitors from periosteum and bone marrow, the formation of a fibrous callus followed by the deposition of cartilage and bone to consolidate the fracture. Here, we show that mesenchymal progenitors residing in skeletal muscle adjacent to the bone fracture play a crucial role in mediating the initial fibrotic response to bone injury and also participate in cartilage and bone formation in the fracture callus. Combined lineage and scRNAseq analyses reveal that skeletal muscle mesenchymal progenitors adopt a fibrogenic fate before they engage in a chondrogenic fate after fracture. In polytrauma, where bone and skeletal muscle are injured, skeletal muscle mesenchymal progenitors fail to undergo fibrogenesis and chondrogenesis. This leads to impaired healing and persistent callus fibrosis originating from skeletal muscle. Thus, essential bone-muscle interactions govern bone regeneration through the direct contribution of skeletal muscle as a source of mesenchymal progenitors driving the fibrotic response and fibrotic remodeling, and supporting cartilage and bone formation.

physiology↗