Comprehensive knowledge of immunoglobulin genetics is required to advance our understanding of B cell biology. Validated immunoglobulin variable (V) gene databases are close to completion only for human and mouse. We present a novel computational approach, IgDiscover, that identifies germline V genes from expressed repertoires to a specificity of 100%. IgDiscover uses a cluster identification process to produce candidate sequences that, once filtered, results in individualized germline V gene databases. IgDiscover was tested in multiple species, validated by genomic cloning and cross library comparisons and produces comprehensive gene databases even where limited genomic sequence is available. IgDiscover analysis of the allelic content of the Indian and Chinese-origin rhesus macaques reveals high levels of immunoglobulin gene diversity in this species. Further, we describe a novel human IGHV3-21 allele and confirm significant gene differences between Balb/c and C57BL6 mouse strains, demonstrating the power of IgDiscover as a germline V gene discovery tool.
Summary The development of soluble envelope glycoprotein (Env) mimetics displaying ordered trimeric symmetry has ushered in a new era in HIV-1 vaccination. The recently reported native, flexibly linked (NFL) design allows the generation of native-like trimers from clinical isolates at high yields and homogeneity. As the majority of infections world-wide are of the clade C subtype, we examined responses in non-human primates to well-ordered subtype C 16055 trimers administered in soluble or high-density liposomal formats. We detected superior germinal center formation and enhanced autologous neutralizing antibodies against the neutralization-resistant (tier 2) 16055 virus following inoculation of liposome-arrayed trimers. Epitope-mapping of the neutralizing monoclonal antibodies (mAbs) indicated major contacts with the V2 apex and 3D electron microscopy reconstructions of Fab-trimer complexes revealed a horizontal binding angle to the Env spike. These vaccine-elicited mAbs target the V2 cap, demonstrating a means to accomplish tier 2 virus neutralization by penetrating the dense N-glycan shield.
The non-human primate (NHP) model is important for pre-clinical evaluation of prophylactic and therapeutic intervention strategies. The recent description of the rhesus macaque germline immunoglobulin loci and establishment of a database of germline gene segments offer improved opportunities to delineate Ig gene usage in the overall B cell repertoire as well as in response to vaccination. We applied 454-pyrosequencing and single-cell RT-PCR of bulk and sorted memory B cells respectively to investigate Ig heavy chain variable gene segment expression in rhesus macaques. The two methods gave remarkably concordant results and identified groups of gene segments that are frequently or rarely used. We further examined the VH repertoire of antigen-specific memory B cells induced by immunization with recombinant HIV-1 envelope glycoproteins (Env), an important vaccine component. We demonstrate that Env immunization activates a highly polyclonal response composed of most of the expressed VH gene segments illustrating the considerable genetic diversity of responding B cells following vaccination.
Klein et al. find that frequently arising antibodies that normally fail to control HIV-1 infection can synergize with passively transferred bNAbs to prevent the emergence of bNAb viral escape variants.
Due to the genetic variability of the HIV-1 envelope glycoproteins (Env), the elicitation of neutralizing antibodies to conserved neutralization determinants including the primary receptor binding site, CD4 binding site (CD4bs), is a major focus of vaccine development. To gain insight into the evolution of Env-elicited antibody responses, we utilized single B cell analysis to interrogate the memory B cell Ig repertoires from two rhesus macaques following five serial immunizations with Env/adjuvant. We observed that the CD4bs-specific repertoire displayed unique features in the third complementarity determining region (CDR3) of Ig heavy chains with minor alterations along the immunization course. Progressive affinity maturation occurred as evidenced by elevated levels of somatic hypermutation (SHM) in antibody sequences isolated at late immunization time point compared to the early time point. Antibodies with higher SHM were associated with increased binding affinity and virus neutralization capacity. Moreover, a notable portion of the CD4bs-specific repertoire was maintained between early and late immunization time points, suggesting that persistent clonal lineages were induced by Env vaccination. Furthermore, we found that the predominant persistent CD4bs-specific clonal lineages had larger population sizes and higher affinities than that from the rest of the repertoires, underscoring the critical role of antigen affinity selection in antibody maturation and clonal expansion. Genetic and functional analyses revealed that the accumulation of SHM in both framework regions and CDRs contributed to the clonal affinity and antigenicity evolution. Our longitudinal study provides high resolution understanding of the dynamically evolving CD4bs-specific B cell response following Env immunization in primates.
Next generation sequencing (NGS) of immunoglobulin (Ig) repertoires (Rep-seq) enables examination of the adaptive immune system at an unprecedented level. Applications include studies of expressed repertoires, gene usage, somatic hypermutation levels, Ig lineage tracing and identification of genetic variation within the Ig loci through inference methods. All these applications require starting libraries that allow the generation of sequence data with low error rate and optimal representation of the expressed repertoire. Here, we provide detailed protocols for the production of libraries suitable for human Ig germline gene inference and Ig repertoire studies. Various parameters used in the process were tested in order to demonstrate factors that are critical to obtain high quality libraries. We demonstrate an improved 5′RACE technique that reduces the length constraints of Illumina MiSeq based Rep-seq analysis but allows for the acquisition of sequences upstream of Ig V genes, useful for primer design. We then describe a 5′ multiplex method for library preparation, which yields full length V(D)J sequences suitable for genotype identification and novel gene inference. We provide comprehensive sets of primers targeting IGHV, IGKV, and IGLV genes. Using the optimized protocol, we produced IgM, IgG, IgK, and IgL libraries and analyzed them using the germline inference tool IgDiscover to identify expressed germline V alleles. This process additionally uncovered three IGHV, one IGKV, and six IGLV novel alleles in a single individual, which are absent from the IMGT reference database, highlighting the need for further study of Ig genetic variation. The library generation protocols presented here enable a robust means of analyzing expressed Ig repertoires, identifying novel alleles and producing individualized germline gene databases from humans.
The human immunodeficiency virus (HIV-1) envelope glycoproteins (Env) mediate virus entry through a series of complex conformational changes triggered by binding to the receptors CD4 and CCR5/CXCR4. Broadly neutralizing antibodies that recognize conserved Env epitopes are thought to be an important component of a protective immune response. However, to date, HIV-1 Env immunogens that elicit broadly neutralizing antibodies have not been identified, creating hurdles for vaccine development. Small-molecule CD4-mimetic compounds engage the CD4-binding pocket on the gp120 exterior Env and induce Env conformations that are highly sensitive to neutralization by antibodies, including antibodies directed against the conserved Env region that interacts with CCR5/CXCR4. Here, we show that CD4-mimetic compounds sensitize primary HIV-1 to neutralization by antibodies that can be elicited in monkeys and humans within 6 months by several Env vaccine candidates, including gp120 monomers. Monoclonal antibodies directed against the gp120 V2 and V3 variable regions were isolated from the immunized monkeys and humans; these monoclonal antibodies neutralized a primary HIV-1 only when the virus was sensitized by a CD4-mimetic compound. Thus, in addition to their direct antiviral effect, CD4-mimetic compounds dramatically enhance the HIV-1-neutralizing activity of antibodies that can be elicited with currently available immunogens. Used as components of microbicides, the CD4-mimetic compounds might increase the protective efficacy of HIV-1 vaccines. IMPORTANCEPreventing HIV-1 transmission is a high priority for global health. Eliciting antibodies that can neutralize transmitted strains of HIV-1 is difficult, creating problems for the development of an effective vaccine. We found that small-molecule CD4-mimetic compounds sensitize HIV-1 to antibodies that can be elicited in vaccinated humans and monkeys. These results suggest an approach to prevent HIV-1 sexual transmission in which a virus-sensitizing microbicide is combined with a vaccine.
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