Explore the vast range of titles available.

The closely related inhibitory killer-cell immunoglobulin-like receptors (KIR), KIR2DL2 and KIR2DL3, regulate the activation of natural killer cells (NK) by interacting with the human leukocyte antigen-C1 (HLA-C1) group of molecules. KIR2DL2, KIR2DL3 and HLA-C1 are highly polymorphic, with this variation being associated with differences in the onset and progression of some human diseases. However, the molecular bases underlying these associations remain unresolved. Here, we determined the crystal structures of KIR2DL2 and KIR2DL3 in complex with HLA-C*07:02 presenting a self-epitope. KIR2DL2 differed from KIR2DL3 in docking modality over HLA-C*07:02 that correlates with variabilty of recognition of HLA-C1 allotypes. Mutagenesis assays indicated differences in the mechanism of HLA-C1 allotype recognition by KIR2DL2 and KIR2DL3. Similarly, HLA-C1 allotypes differed markedly in their capacity to inhibit activation of primary NK cells. These functional differences derive, in part, from KIR2DS2 suggesting KIR2DL2 and KIR2DL3 binding geometries combine with other factors to distinguish HLA-C1 functional recognition. KIR2DL2 and KIR2DL3 are two inhibitory members of the killer-cell immunoglobulin-like receptors (KIR) family that share a common HLA-I preference in binding HLA from the C1 group. However, it is still unclear to what extent binding and function is equivalent between KIR2DL2 and 2DL3. Here, the authors present the crystal structures of KIR2DL2 and 2DL3 in complex with HLA-C*07:02 and observe differences in HLA-C recognition between KIR2DL2 and 2DL3, which correlates with differences in HLA-C binding preference as they show with mutagenesis and binding studies.

Structural determination and analysis of HLA-I that presents an HIV-derived peptide to an NK cell receptor reveal that N-terminal extended epitope conformations contribute to immune recognition and mechanisms of HIV immune escape. Major histocompatibility complex class I (MHC-I) molecules play a crucial role in immunity by capturing peptides for presentation to T cells and natural killer (NK) cells. The peptide termini are tethered within the MHC-I antigen-binding groove, but it is unknown whether other presentation modes occur. Here we show that 20% of the HLA-B*57:01 peptide repertoire comprises N-terminally extended sets characterized by a common motif at position 1 (P1) to P2. Structures of HLA-B*57:01 presenting N-terminally extended peptides, including the immunodominant HIV-1 Gag epitope TW10 (TSTLQEQIGW), showed that the N terminus protrudes from the peptide-binding groove. The common escape mutant TS N LQEQIGW bound HLA-B*57:01 canonically, adopting a dramatically different conformation than the TW10 peptide. This affected recognition by killer cell immunoglobulin-like receptor (KIR) 3DL1 expressed on NK cells. We thus define a previously uncharacterized feature of the human leukocyte antigen class I (HLA-I) immunopeptidome that has implications for viral immune escape. We further suggest that recognition of the HLA-B*57:01-TW10 epitope is governed by a 'molecular tension' between the adaptive and innate immune systems.

Immunophenotypic differences between closely related human leukocyte antigen (HLA) alleles have been associated with divergent clinical outcomes in infection, autoimmunity, transplantation and drug hypersensitivity. Here we explore the impact of micropolymorphism on peptide antigen presentation by three closely related HLA molecules, HLA-B*57:01, HLA-B*57:03 and HLA-B*58:01, that are differentially associated with the HIV elite controller phenotype and adverse drug reactions. For each allotype, we mine HLA ligand data sets derived from the same parental cell proteome to define qualitative differences in peptide presentation using classical peptide binding motifs and an unbiased statistical approach. The peptide repertoires show marked qualitative overlap, with 982 peptides presented by all allomorphs. However, differences in peptide abundance, HLA-peptide stability, and HLA-bound conformation demonstrate that HLA micropolymorphism impacts more than simply the range of peptide ligands. These differences provide grounds for distinct immune reactivity and insights into the capacity of micropolymorphism to diversify immune outcomes. Human leukocyte antigens (HLA) are multi-allelic and polymorphic genes that present antigens to immune cells for inducing protective immunity. Here, using systems biology and structural approaches, the authors show that micropolymorphism of three HLA has effects beyond the modulation of antigen diversity.

Joining a function-enhanced Fc-portion of human IgG to the SARS-CoV-2 entry receptor ACE2 produces an antiviral decoy with strain transcending virus neutralizing activity. SARS-CoV-2 neutralization and Fc-effector functions of ACE2-Fc decoy proteins, formatted with or without the ACE2 collectrin domain, were optimized by Fc-modification. The different Fc-modifications resulted in distinct effects on neutralization and effector functions. H429Y, a point mutation outside the binding sites for FcγRs or complement caused non-covalent oligomerization of the ACE2-Fc decoy proteins, abrogated FcγR interaction and enhanced SARS-CoV-2 neutralization. Another Fc mutation, H429F did not improve virus neutralization but resulted in increased C5b-C9 fixation and transformed ACE2-Fc to a potent mediator of complement-dependent cytotoxicity (CDC) against SARS-CoV-2 spike (S) expressing cells. Furthermore, modification of the Fc-glycan enhanced cell activation via FcγRIIIa. These different immune profiles demonstrate the capacity of Fc-based agents to be engineered to optimize different mechanisms of protection for SARS-CoV-2 and potentially other viral pathogens.

The SARS-CoV-2 spike receptor binding domain (RBD) is the major target for neutralising antibodies. However, subdomains like RBD may constrain the availability of CD4 T follicular helper (TFH) cells and impact immunogenicity. We engineered a chimeric trimeric RBD (CTR) glycoprotein, replacing the RBD of HKU-1 spike with SARS-CoV-2 RBD (ancestral WT/Omicron BA.2). This maintains trimerised RBD, while providing CD4 help via the HKU-1 scaffold. In C57BL/6 mice, CTR-BA.2 elicited high anti-BA.2-RBD IgG and neutralising titres, matching native spike responses. Germinal centre B cells were predominantly WT + /BA.2 + cross-reactive, and TFH predominantly recognised HKU-1 epitopes, demonstrating scaffold-directed help. In macaques, CTR-WT elicited comparable anti-RBD IgG, anti-spike IgG and neutralising responses to native spike, with elevated RBD-specific GC B cells in draining lymph nodes. Macaque TFH responses targeted RBD, NTD/S2 or HKU-1 peptides. This chimeric design overcomes poor RBD immunogenicity by engaging CD4 TFH, maintaining neutralising responses that is non-inferior to native spike.

NL63 is an alphacoronavirus that uses the same ACE2 receptor as SARS-CoV and SARS-CoV-2, but generally causes mild respiratory illness. In a cohort of healthy adults, we characterised humoral responses against NL63 spike and isolated a panel of human monoclonal antibodies (mAbs), including five with potent viral neutralising activity. Four neutralising mAbs blocked ACE2 receptor engagement and were found to target the receptor binding motif. A single mAb targeting the S2 subunit displayed potent neutralisation activity comparable to those directly blocking receptor engagement. The S2 mAb targets a membrane proximal heptad repeat 2 (HR2) region in spike that is absent in betacoronaviruses, potentially revealing a site of vulnerability unique to alphacoronaviruses. For all neutralising mAbs, putative epitopes were highly conserved in over 200 NL63 sequences, including recent clinical isolates. A deeper understanding of the recognition of alphacoronavirus spike by human antibodies will guide vaccine and therapeutic development against alphacoronavirus threats.

The SARS-CoV-2 receptor binding domain (RBD) is both the principal target of neutralizing antibodies and one of the most rapidly evolving domains, which can result in the emergence of immune escape mutations, limiting the effectiveness of vaccines and antibody therapeutics. To facilitate surveillance, we developed a rapid, high-throughput, multiplex assay able to assess the inhibitory response of antibodies to 24 RBD natural variants simultaneously. We demonstrate how this assay can be implemented as a rapid surrogate assay for functional cell-based serological methods to measure the SARS-CoV-2 neutralizing capacity of antibodies at the angiotensin-converting enzyme 2–RBD (ACE2-RBD) interface. We describe the enhanced affinity of RBD variants N439K, S477N, Q493L, S494P, and N501Y to the ACE2 receptor and demonstrate the ability of this assay to bridge a major gap for SARS-CoV-2 research, informing selection of complementary monoclonal antibody candidates and the rapid identification of immune escape to emerging RBD variants following vaccination or natural infection.

[This corrects the article .].

Objectives Following infection with SARS‐CoV‐2, virus‐specific antibodies are generated, which can both neutralise virions and clear infection via Fc effector functions. The importance of IgG antibodies for protection and control of SARS‐CoV‐2 has been extensively reported. By comparison, other antibody isotypes including IgA have been poorly characterised. Methods Here, we characterised plasma IgA from 41 early convalescent COVID‐19 subjects for neutralisation and Fc effector functions. Results Convalescent plasma IgA from > 60% of the cohort had the capacity to inhibit the interaction between wild‐type RBD and ACE2. Furthermore, a third of the cohort induced stronger IgA‐mediated ACE2 inhibition than matched IgG when tested at equivalent concentrations. Plasma IgA and IgG from this cohort broadly recognised similar RBD epitopes and had similar capacities to inhibit ACE2 from binding to 22 of the 23 prevalent RBD mutations assessed. However, plasma IgA was largely incapable of mediating antibody‐dependent phagocytosis in comparison with plasma IgG. Conclusion Overall, convalescent plasma IgA contributed to the neutralising antibody response of wild‐type SARS‐CoV‐2 RBD and various RBD mutations. However, this response displayed large heterogeneity and was less potent than IgG. Following infection with SARS‐CoV‐2, virus‐specific antibodies are generated, which can both neutralise virions and clear infection via Fc effector functions. Here, we demonstrate that convalescent plasma IgA was largely incapable of mediating antibody‐dependent phagocytosis in comparison with plasma IgG. However, IgA from > 60% of the cohort had the capacity to neutralise SARS‐CoV2 wild‐type and numerous RBD variants, although this response was heterogeneous and less potent than IgG.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has dramatically expedited global vaccine development efforts 1 , 2 – 3 , most targeting the viral ‘spike’ glycoprotein (S). S localizes on the virion surface and mediates recognition of cellular receptor angiotensin-converting enzyme 2 (ACE2) 4 , 5 – 6 . Eliciting neutralizing antibodies that block S–ACE2 interaction 7 , 8 – 9 , or indirectly prevent membrane fusion 10 , constitute an attractive modality for vaccine-elicited protection 11 . However, although prototypic S-based vaccines show promise in animal models 12 , 13 – 14 , the immunogenic properties of S in humans are poorly resolved. In this study, we characterized humoral and circulating follicular helper T cell (cTFH) immunity against spike in recovered patients with coronavirus disease 2019 (COVID-19). We found that S-specific antibodies, memory B cells and cTFH are consistently elicited after SARS-CoV-2 infection, demarking robust humoral immunity and positively associated with plasma neutralizing activity. Comparatively low frequencies of B cells or cTFH specific for the receptor binding domain of S were elicited. Notably, the phenotype of S-specific cTFH differentiated subjects with potent neutralizing responses, providing a potential biomarker of potency for S-based vaccines entering the clinic. Overall, although patients who recovered from COVID-19 displayed multiple hallmarks of effective immune recognition of S, the wide spectrum of neutralizing activity observed suggests that vaccines might require strategies to selectively target the most potent neutralizing epitopes. In a cohort of recovered patients with COVID-19, virus spike-specific antibodies were consistently elicited, but neutralizing activity was highly variable and inversely correlated with the proportion of CCR6 + CXCR3 − spike-specific circulating follicular helper T cells.