Biology subjects

Gachard, N.

Publications and source records attributed to Gachard, N..

3 recordsLinked to original sources

bioRxiv2022

Increased frequencies of IgH locus suicide recombination points on Chronic Lymphocytic Leukemia with low rate of AID related somatic mutations, cMYC overexpression and short telomeres

In normal activated B-cells, Activation Induced-cytidine deaminase (AID) is absolutely required for immunoglobulin (Ig) class switch recombination (CSR) and IGHV somatic hypermutation (SHM). AID is also implicated in the Locus Suicide Recombination (LSR) of the Ig heavy (IgH) locus, resulting in the deletion of the IgH constant part. Chronic lymphocytic leukemia (CLL) is an indolent non-Hodgkin B-cell lymphoma characterized by tumor CLL B-cells that weakly express a B cell receptor (BCR) on their surface. The great majority of CLL tumor B-cells are non class-switched. Searching for abnormalities of IgH locus recombination in CLL, we investigated CSR and LSR in samples from CLL patients (N=47) with high blood tumor cell infiltration (>98%) and in healthy volunteers (HV) as controls (N=9). LSR was detectable at comparable levels in both HV and CLL groups. CSR counts were decreased in CLL samples as expected. As distribution of LSR counts was bimodal, we separated CLL patients in two groups so called LSRHigh and LSRLow. LSRHigh CLLs exhibited very weak AID expression and low mutation rate of IgHV region and of the AID off-target PIM1 gene. LSR junction diversity, evaluated using the Shannon index, was increased in LSRHigh CLLs suggesting that LSR was on-going in these cells. Also, shorter telomeres were observed in LSRHigh CLLs suggesting an increased number of past mitosis. Consistently, increased levels of cMYC expression were detected in LSRHigh CLLs and treatment free survival of these cases was markedly decreased. We hypothesized that LSR in LSRHigh CLLs is AID independent and could be due to DNA lesion and inaccurate DSB repair within the IgH locus, which could be accessible to recombination machinery due to increased IgH locus transcription. Altogether, our results indicate the accessibility of IgH locus and the proliferation increase LSR rate in LSRHigh CLLs could be related to cMYC resulting in shorter treatment free survival of patients and point on an AID independent mechanism of IgH recombination.

cancer biology↗

bioRxiv2019

Full-length immunoglobulin high-throughput sequencing reveals specific novel mutational patterns in POEMS syndrome

POEMS syndrome is a rare multisystem disease due to an underlying plasma cell (PC) dyscrasia. The pathophysiology of the disease remains unclear but the role of the monoclonal immunoglobulin (Ig) light chain (LC) is strongly suspected, due to the highly restrictive usage of two {lambda} variable (V) domains (IGLV1-40 and IGLV1-44) and the general improvement of clinical manifestations following PC clone-targeted treatment. However, the diagnostic value of Ig LC sequencing, especially in case of incomplete forms of the disease, remains to be determined. Using a sensitive high-throughput Ig repertoire sequencing on RNA (RACE-RepSeq), we detected a {lambda} LC monoclonal expansion in the bone marrow (BM) of 85% of patients with POEMS syndrome, including some in whom bone marrow tests routinely performed to diagnose plasma cell dyscrasia failed to detect {lambda}+ monoclonal PCs. Twenty-four of the 30 LC clonal sequences found (80%) were derived from the IGLV1-40 and IGLV1-44 germline genes, two from the closely related IGLV1-36 gene, and all were associated with an IGLJ3*02 junction (J) gene, confirming the high restriction of VJ region usage in POEMS syndrome. RACE-RepSeq VJ full-length sequencing additionally revealed original mutational patterns, the strong specificity of which might crucially help establish or eliminate the diagnosis of POEMS syndrome in uncertain cases. Thus, RACE-RepSeq appears as a sensitive, rapid and specific tool to detect low-abundance PC clones in BM, and assign them to POEMS syndrome, with all the consequences for therapeutic options hereby.

immunology↗

bioRxiv2019

B-cell enforced expression of the mouse ortholog of MYD88L265P is responsible for Waldenstrom-like B-cell lymphoma.

Here, we created a conditional transgenic mouse model with insertion of a sequence coding for both MYD88L252P and the Yellow Fluorescent Protein (YFP) into the rosa26-locus. B-cell specific induction of the transgene constantly led to spleen enlargement with expansion of YFP positive B-cells in 8-12 month-old mice, with a moderate B-cell proliferation increase. Being clonal or oligoclonal, these B-cells exhibited a marked morphological and immunophenotypic lymphoplasmocytic aspect with a plasma cell transcriptomic signature and a serum immunoglobulin M peak. Therefore, continuous activation of MYD88 in mice can lead on its own to a lymphoma close to Waldenstrom Macroglobulinemia.\n\nKey pointB-cell specific enforced expression of MYD88L252P leads to a clonal indolent lymphoplasmocytic B-cell lymphoma with a serum IgM peak.

cancer biology↗