HIV-1 treatment timing shapes the human intestinal memory B-cell repertoire to commensal bacteria.

HIV-1 infection causes severe alterations of gut mucosa, microbiota and immune system, which can be curbed by early antiretroviral therapy. Here, we investigate how treatment timing affects intestinal memory B-cell and plasmablast repertoires of HIV-1-infected humans. We show that only class-switched memory B cells markedly differ between subjects treated during the acute and chronic phases of infection. Intestinal memory B-cell monoclonal antibodies show more prevalent polyreactive and commensal bacteria-reactive clones in late- compared to early-treated individuals. Mirroring this, serum IgA polyreactivity and commensal-reactivity are strongly increased in late-treated individuals and correlate with intestinal permeability and systemic inflammatory markers. Polyreactive blood IgA memory B cells, many of which egressed from the gut, are also substantially enriched in late-treated individuals. Our data establish gut and systemic B-cell polyreactivity to commensal bacteria as hallmarks of chronic HIV-1 infection and suggest that initiating treatment early may limit intestinal B-cell abnormalities compromising HIV-1 humoral response.

Potent human broadly SARS-CoV-2-neutralizing IgA and IgG antibodies effective against Omicron BA.1 and BA.2.

Memory B-cell and antibody responses to the SARS-CoV-2 spike protein contribute to long-term immune protection against severe COVID-19, which can also be prevented by antibody-based interventions. Here, wide SARS-CoV-2 immunoprofiling in Wuhan COVID-19 convalescents combining serological, cellular, and monoclonal antibody explorations revealed humoral immunity coordination. Detailed characterization of a hundred SARS-CoV-2 spike memory B-cell monoclonal antibodies uncovered diversity in their repertoire and antiviral functions. The latter were influenced by the targeted spike region with strong Fc-dependent effectors to the S2 subunit and potent neutralizers to the receptor-binding domain. Amongst those, Cv2.1169 and Cv2.3194 antibodies cross-neutralized SARS-CoV-2 variants of concern, including Omicron BA.1 and BA.2. Cv2.1169, isolated from a mucosa-derived IgA memory B cell demonstrated potency boost as IgA dimers and therapeutic efficacy as IgG antibodies in animal models. Structural data provided mechanistic clues to Cv2.1169 potency and breadth. Thus, potent broadly neutralizing IgA antibodies elicited in mucosal tissues can stem SARS-CoV-2 infection, and Cv2.1169 and Cv2.3194 are prime candidates for COVID-19 prevention and treatment.

Epitope convergence of broadly HIV-1 neutralizing IgA and IgG antibody lineages in a viremic controller.

Decrypting the B cell ontogeny of HIV-1 broadly neutralizing antibodies (bNAbs) is paramount for vaccine design. Here, we characterized IgA and IgG bNAbs of three distinct B cell lineages in a viremic controller, two of which comprised only IgG+ or IgA+ blood memory B cells; the third combined both IgG and IgA clonal variants. 7-269 bNAb in the IgA-only lineage displayed the highest neutralizing capacity despite limited somatic mutation, and delayed viral rebound in humanized mice. bNAbs in all three lineages targeted the N332 glycan supersite. The 2.8-Å resolution cryo-EM structure of 7-269-BG505 SOSIP.664 complex showed a similar pose as 2G12, on an epitope mainly composed of sugar residues comprising the N332 and N295 glycans. Binding and cryo-EM structural analyses showed that antibodies from the two other lineages interact mostly with glycans N332 and N386. Hence, multiple B cell lineages of IgG and IgA bNAbs focused on a unique HIV-1 site of vulnerability can codevelop in HIV-1 viremic controllers.

Potent human broadly neutralizing antibodies to hepatitis B virus from natural controllers.

Rare individuals can naturally clear chronic hepatitis B virus (HBV) infection and acquire protection from reinfection as conferred by vaccination. To examine the protective humoral response against HBV, we cloned and characterized human antibodies specific to the viral surface glycoproteins (HBsAg) from memory B cells of HBV vaccinees and controllers. We found that human HBV antibodies are encoded by a diverse set of immunoglobulin genes and recognize various conformational HBsAg epitopes. Strikingly, HBsAg-specific memory B cells from natural controllers mainly produced neutralizing antibodies able to cross-react with several viral genotypes. Furthermore, monotherapy with the potent broadly neutralizing antibody Bc1.187 suppressed viremia in vivo in HBV mouse models and led to post-therapy control of the infection in a fraction of animals. Thus, human neutralizing HBsAg antibodies appear to play a key role in the spontaneous control of HBV and represent promising immunotherapeutic tools for achieving HBV functional cure in chronically infected humans.

TLR9 signalling in HCV-associated atypical memory B cells triggers Th1 and rheumatoid factor autoantibody responses.

BACKGROUND & AIMS: Hepatitis C virus (HCV) infection contributes to the development of autoimmune disorders such as cryoglobulinaemia vasculitis (CV). However, it remains unclear why only some individuals with HCV develop HCV-associated CV (HCV-CV). HCV-CV is characterized by the expansion of anergic CD19+CD27+CD21low/- atypical memory B cells (AtMs). Herein, we report the mechanisms by which AtMs participate in HCV-associated autoimmunity. METHODS: The phenotype and function of peripheral AtMs were studied by multicolour flow cytometry and co-culture assays with effector T cells and regulatory T cells in 20 patients with HCV-CV, 10 chronicallyHCV-infected patients without CV and 8 healthy donors. We performed gene expression profile analysis of AtMs stimulated or not by TLR9. Immunoglobulin gene repertoire and antibody reactivity profiles of AtM-expressing IgM antibodies were analysed following single B cell FACS sorting and expression-cloning of monoclonal antibodies. RESULTS: The Tbet+CD11c+CD27+CD21- AtM population is expanded in patients with HCV-CV compared to HCV controls without CV. TLR9 activation of AtMs induces a specific transcriptional signature centred on TNFα overexpression, and an enhanced secretion of TNFα and rheumatoid factor-type IgMs in patients with HCV-CV. AtMs stimulated through TLR9 promote type 1 effector T cell activation and reduce the proliferation of CD4+CD25hiCD127-/lowFoxP3+ regulatory T cells. AtM expansions display intraclonal diversity with immunoglobulin features of antigen-driven maturation. AtM-derived IgM monoclonal antibodies do not react against ubiquitous autoantigens or HCV antigens including NS3 and E2 proteins. Rather, AtM-derived antibodies possess rheumatoid factor activity and target unique epitopes on the human IgG-Fc region. CONCLUSION: Our data strongly suggest a central role for TLR9 activation of AtMs in driving HCV-CV autoimmunity through rheumatoid factor production and type 1 T cell responses. LAY SUMMARY: B cells are best known for their capacity to produce antibodies, which often play a deleterious role in the development of autoimmune diseases. During chronic hepatitis C, self-reactive B cells proliferate and can be responsible for autoimmune symptoms (arthritis, purpura, neuropathy, renal disease) and/or lymphoma. Direct-acting antiviral therapy clears the hepatitis C virus and eliminates deleterious B cells.

HIV-1 Envelope Recognition by Polyreactive and Cross-Reactive Intestinal B Cells.

Mucosal immune responses to HIV-1 involve the recognition of the viral envelope glycoprotein (gp)160 by tissue-resident B cells and subsequent secretion of antibodies. To characterize the B cells "sensing" HIV-1 in the gut of infected individuals, we probed monoclonal antibodies produced from single intestinal B cells binding to recombinant gp140 trimers. A large fraction of mucosal B cell antibodies were polyreactive and showed only low affinity to HIV-1 envelope glycoproteins, particularly the gp41 moiety. A few high-affinity gp140 antibodies were isolated but lacked neutralizing, potent ADCC, and transcytosis-blocking capacities. Instead, they displayed cross-reactivity with defined self-antigens. Specifically, intestinal HIV-1 gp41 antibodies targeting the heptad repeat 2 region (HR2) cluster II cross-reacted with the p38α mitogen-activated protein kinase 14 (MAPK14). Hence, physiologic polyreactivity of intestinal B cells and molecular mimicry-based self-reactivity of HIV-1 antibodies are two independent phenomena, possibly diverting and/or impairing mucosal humoral immunity to HIV-1.

A human immune system mouse model with robust lymph node development.

Lymph nodes (LNs) facilitate the cellular interactions that orchestrate immune responses. Human immune system (HIS) mice are powerful tools for interrogation of human immunity but lack secondary lymphoid tissue (SLT) as a result of a deficiency in Il2rg-dependent lymphoid tissue inducer cells. To restore LN development, we induced expression of thymic-stromal-cell-derived lymphopoietin (TSLP) in a Balb/c Rag2-/-Il2rg-/-SirpaNOD (BRGS) HIS mouse model. The resulting BRGST HIS mice developed a full array of LNs with compartmentalized human B and T cells. Compared with BRGS HIS mice, BRGST HIS mice have a larger thymus, more mature B cells, and abundant IL-21-producing follicular helper T (TFH) cells, and show enhanced antigen-specific responses. Using BRGST HIS mice, we demonstrated that LN TFH cells are targets of acute HIV infection and represent a reservoir for latent HIV. In summary, BRGST HIS mice reflect the effects of SLT development on human immune responses and provide a model for visualization and interrogation of regulators of immunity.

Scarcity of autoreactive human blood IgA+ memory B cells.

Class-switched memory B cells are key components of the "reactive" humoral immunity, which ensures a fast and massive secretion of high-affinity antigen-specific antibodies upon antigenic challenge. In humans, IgA class-switched (IgA+ ) memory B cells and IgA antibodies are abundant in the blood. Although circulating IgA+ memory B cells and their corresponding secreted immunoglobulins likely possess major protective and/or regulatory immune roles, little is known about their specificity and function. Here, we show that IgA+ and IgG+ memory B-cell antibodies cloned from the same healthy humans share common immunoglobulin gene features. IgA and IgG memory antibodies have comparable lack of reactivity to vaccines, common mucosa-tropic viruses and commensal bacteria. However, the IgA+ memory B-cell compartment contains fewer polyreactive clones and importantly, only rare self-reactive clones compared to IgG+ memory B cells. Self-reactivity of IgAs is acquired following B-cell affinity maturation but not antibody class switching. Together, our data suggest the existence of different regulatory mechanisms for removing autoreactive clones from the IgG+ and IgA+ memory B-cell repertoires, and/or different maturation pathways potentially reflecting the distinct nature and localization of the cognate antigens recognized by individual B-cell populations.

Mutations in endothelin 1 cause recessive auriculocondylar syndrome and dominant isolated question-mark ears.

Auriculocondylar syndrome (ACS) is a rare craniofacial disorder with mandibular hypoplasia and question-mark ears (QMEs) as major features. QMEs, consisting of a specific defect at the lobe-helix junction, can also occur as an isolated anomaly. Studies in animal models have indicated the essential role of endothelin 1 (EDN1) signaling through the endothelin receptor type A (EDNRA) in patterning the mandibular portion of the first pharyngeal arch. Mutations in the genes coding for phospholipase C, beta 4 (PLCB4) and guanine nucleotide binding protein (G protein), alpha inhibiting activity polypeptide 3 (GNAI3), predicted to function as signal transducers downstream of EDNRA, have recently been reported in ACS. By whole-exome sequencing (WES), we identified a homozygous substitution in a furin cleavage site of the EDN1 proprotein in ACS-affected siblings born to consanguineous parents. WES of two cases with vertical transmission of isolated QMEs revealed a stop mutation in EDN1 in one family and a missense substitution of a highly conserved residue in the mature EDN1 peptide in the other. Targeted sequencing of EDN1 in an ACS individual with related parents identified a fourth, homozygous mutation falling close to the site of cleavage by endothelin-converting enzyme. The different modes of inheritance suggest that the degree of residual EDN1 activity differs depending on the mutation. These findings provide further support for the hypothesis that ACS and QMEs are uniquely caused by disruption of the EDN1-EDNRA signaling pathway.

Mutations in TUBG1, DYNC1H1, KIF5C and KIF2A cause malformations of cortical development and microcephaly.

The genetic causes of malformations of cortical development (MCD) remain largely unknown. Here we report the discovery of multiple pathogenic missense mutations in TUBG1, DYNC1H1 and KIF2A, as well as a single germline mosaic mutation in KIF5C, in subjects with MCD. We found a frequent recurrence of mutations in DYNC1H1, implying that this gene is a major locus for unexplained MCD. We further show that the mutations in KIF5C, KIF2A and DYNC1H1 affect ATP hydrolysis, productive protein folding and microtubule binding, respectively. In addition, we show that suppression of mouse Tubg1 expression in vivo interferes with proper neuronal migration, whereas expression of altered γ-tubulin proteins in Saccharomyces cerevisiae disrupts normal microtubule behavior. Our data reinforce the importance of centrosomal and microtubule-related proteins in cortical development and strongly suggest that microtubule-dependent mitotic and postmitotic processes are major contributors to the pathogenesis of MCD.