Biology subjects

Demengeot, J.

Publications and source records attributed to Demengeot, J..

4 recordsLinked to original sources

bioRxiv2026

Widespread cryptic RAG-mediated recombination in developing T lymphocytes

V(D)J recombination generates antigen receptor diversity through the targeted activity of the RAG1/2 recombinase, but the extent to which RAG also engages cryptic genomic targets during normal lymphocyte development remains poorly defined. Here, we developed a targeted PCR-sequencing approach to detect and quantify rare RAG-mediated rearrangements in mouse thymocytes. We first examined the TCRb locus and found that four of its twelve pseudogenes undergo detectable rearrangement in vivo, despite being considered non-functional components of the repertoire. Extending this analysis across the locus revealed 33 previously uncharacterized cryptic recombination sites involved in non-functional rearrangements with DJb segments. These events occurred across both the Vb region and the largely inaccessible Vb30-Db1 intergenic region, with individual cryptic sites spanning a broad range of recombination frequencies. Cryptic sites were highly heterogeneous in sequence and chromatin context: neither RSS resemblance, predicted Z-DNA formation, local epigenetic features, nor chromosomal interactions reliably distinguished sites with detectable recombination from those at which recombination was not detected. We further identified additional cryptic RAG-mediated rearrangements at the Bcl11b locus, demonstrating that such events are not restricted to antigen receptor loci. Together, these findings reveal an unexpectedly broad landscape of low-frequency RAG-mediated DNA rearrangement in developing T lymphocytes and suggest that cryptic target selection cannot be explained solely by the local genetic and epigenetic features examined here.

immunology↗

bioRxiv2021

Amino acids 484 and 494 of SARS-CoV-2 spike are hotspots of immune evasion affecting antibody but not ACE2 binding

Understanding SARS-CoV-2 evolution and host immunity is critical to control COVID-19 pandemics. At the core is an arms-race between SARS-CoV-2 antibody and angiotensin-converting enzyme 2 (ACE2) recognition, a function of the viral protein spike. Mutations in spike impacting antibody and/or ACE2 binding are appearing worldwide, with the effect of mutation synergy still incompletely understood. We engineered 25 spike-pseudotyped lentiviruses containing individual and combined mutations, and confirmed that E484K evades antibody neutralization elicited by infection or vaccination, a capacity augmented when complemented by K417N and N501Y mutations. In silico analysis provided an explanation for E484K immune evasion. E484 frequently engages in interactions with antibodies but not with ACE2. Importantly, we identified a novel amino acid of concern, S494, which shares a similar pattern. Using the already circulating mutation S494P, we found that it reduces antibody neutralization of convalescent and post-immunization sera, particularly when combined with E484K and N501Y. Our analysis of synergic mutations provides a landscape for hotspots for immune evasion and for targets for therapies, vaccines and diagnostics. One-Sentence SummaryAmino acids in SARS-CoV-2 spike protein implicated in immune evasion are biased for binding to neutralizing antibodies but dispensable for binding the host receptor angiotensin-converting enzyme

immunology↗

bioRxiv2020

Interruption of thymic activity in adults improves responses to tumor immunotherapy

The thymus produces precursors of both effectors and regulatory T cells (Tconv and Treg, respectively) whose interactions prevents autoimmunity while allowing efficient protective immune responses. Tumors express a composite of self- and tumor-specific antigens and engage both Tconv and Treg cells. Along the aging process, the thymus involutes, and tumor incidence increases, a correlation proposed previously to be causal and the result of effector cell decline. In this work, we directly tested whether interruption of thymic activity in adult mice affects Foxp3 expressing Treg composition and function, and alters tumor immune surveillance. Young adult mice, on two different genetic backgrounds, were surgically thymectomized (TxT) and analyzed or challenged 2 months later. Cellular analysis revealed a 10-fold decrease in both Tconv and Treg numbers and a bias for activated cells. The persisting Treg displayed reduced stability of Foxp3 expression and, as a population, showed compromised return to homeostasis upon induced perturbations. We next tested the growth of three tumor models from different origin and presenting distinct degrees of spontaneous immunogenicity. In none of these conditions adult TxT facilitated tumor growth. Rather TxT enhanced the efficacy of anti-tumor immunotherapies targeting Treg and/or the checkpoint CTLA4, as evidenced by increased frequency of responder mice and decreased intra-tumoral Treg to CD8+IFN{gamma}+ cell ratio. Together, our findings point to a scenario where abrogation of thymic activities affects preferentially the regulatory over the ridding arm of the immune activities elicited by tumors, and argues that higher incidence of tumors with age cannot be solely attributed to thymic output decline.

immunology↗

bioRxiv2019

A weak Foxp3 hypomorph enhances spontaneous and therapeutic immune surveillance of cancer in mice

It is well established that therapeutic impairment of Foxp3+ regulatory T cells (Treg) in mice and humans favors immune rejection of solid tumors. Less explored are the genetic associations between Foxp3 allelic variants and tumor incidence, only sporadically reported in human studies. In this work, we tested and demonstrate that Foxp3fGFP, an allele classified as hypomorphic in Th1 inflammatory contexts but not affecting health at steady state, confers increased anti-tumor immunity. Our conclusions stem out of the analysis of three tumor models of different tissue origin, in two murine genetic backgrounds. When compared to wild type animals, mice carrying the Foxp3fGFP allele spontaneously delay, reduce or prevent primary tumor growth, decrease metastasis growth and potentiate the response to anti-CTLA4 monotherapy. These findings suggest that allelic variance at the Foxp3 locus may have significant impact on cancer incidence and/or the success of cancer-immunotherapies in humans.

cancer biology↗