Some HIV-infected individuals develop broadly neutralizing antibodies (bNAbs), whereas most develop antibodies that neutralize only a narrow range of viruses (nNAbs). bNAbs, but not nNAbs, protect animals from experimental infection and are likely a key component of an effective vaccine. nNAbs and bNAbs target the same regions of the viral envelope glycoprotein (Env), but for reasons that remain unclear only nNAbs are elicited by Env immunization. We show that in contrast to germline-reverted (gl) bNAbs, glnNAbs recognized diverse recombinant Envs. Moreover, owing to binding affinity differences, nNAb B cell progenitors had an advantage in becoming activated and internalizing Env compared with bNAb B cell progenitors. We then identified an Env modification strategy that minimized the activation of nNAb B cells targeting epitopes that overlap those of bNAbs.

Delineating the key early events that lead to the development of broadly neutralizing anti-HIV-1 antibodies during natural infection may help guide the development of immunogens and vaccine regimens to prevent HIV-1 infection. In this study, we monitored two HIV-1-positive subjects, VC20013 and VC10014, over the course of infection from before they developed broadly neutralizing antibody (bNAb) activity until several years after neutralizing breadth was detected in plasma. Both subjects developed bNAb activity after approximately 1 year postinfection, which ultimately mapped to the membrane-proximal external region (MPER) in VC20013 and an epitope that overlaps the CD4 receptor binding site in VC10014. In subject VC20013, we were able to identify anti-MPER activity in the earliest plasma sample that exhibited no bNAb activity, indicating that this epitope specificity was acquired very early on, but that it was initially not able to mediate neutralization. Escape mutations within the bNAb epitopes did not arise in the circulating envelopes until bNAb activity was detectable in plasma, indicating that this early response was not sufficient to drive viral escape. As bNAb activity began to emerge in both subjects, we observed a simultaneous increase in autologous antienvelope antibody binding affinity, indicating that antibody maturation was occurring as breadth was developing. Our findings illustrate one potential mechanism by which bNAbs develop during natural infection in which an epitope target is acquired very early on during the course of infection but require time and maturation to develop into broadly neutralizing activity. IMPORTANCEOne major goal of HIV-1 vaccine research is the development of a vaccine that can elicit broadly neutralizing antibodies (bNAbs). Although no such vaccine exists, bNAbs develop in approximately 20% of HIV-1-infected subjects, providing a prototype of the bNAbs that must be reelicited by vaccine. Thus, there is significant interest in understanding the mechanisms by which bNAbs develop during the course of infection. We studied the timing, epitope specificity, and evolution of the bNAb responses in two HIV-1-positive patients who developed bNAb activity within the first several years after infection. In one subject, antibodies to a broadly neutralizing epitope developed very early but were nonneutralizing. After several months, neutralizing activity developed, and the virus mutated to escape their activity. Our study highlights one mechanism for the development of bNAbs where early epitope acquisition followed by sufficient time for antibody maturation drives the epitope-specific antibody response toward broadly neutralizing activity.

Myeloid dendritic cells (DCs) have the innate capacity to sense pathogens and orchestrate immune responses. However, DCs do not mount efficient immune responses to HIV-1, primarily due to restriction of virus reverse transcription, which prevents accumulation of viral cDNA and limits its detection through the cGAS-STING pathway. By allowing reverse transcription to proceed, we find that DCs detect HIV-1 in distinct phases, before and after virus integration. Blocking integration suppresses, but does not abolish, activation of the transcription factor IRF3, downstream interferon (IFN) responses, and DC maturation. Consistent with two stages of detection, HIV-1 "primes" chromatin accessibility of innate immune genes before and after integration. Once primed, robust IFN responses can be unmasked by agonists of the innate adaptor protein, MyD88, through a process that requires cGAS, STING, IRF3, and nuclear factor κB. Thus, HIV-1 replication increases material available for sensing, and discrete inflammatory inputs tune cGAS signaling to drive DC maturation.

Rhesus macaques (RMs) are a widely used model system for the study of vaccines, infectious diseases and microbial pathogenesis. Their value as a model lies in their close evolutionary relationship to humans, which, in theory, allows them to serve as a close approximation of the human immune system. However, despite their prominence as a human surrogate model system, many aspects of the RM immune system remain ill characterized. In particular, B cell-mediated immunity in macaques has not been sufficiently characterized, and the B-cell receptor-encoding loci have not been thoroughly annotated. To address these gaps, we analyzed the circulating heavy- and light-chain repertoires in humans and RMs by next-generation sequencing. By comparing V gene segment usage, J-segment usage and CDR3 lengths between the two species, we identified several important similarities and differences. These differences were especially notable in the IgM+ B-cell repertoire. However, the class-switched, antigen-educated B-cell populations converged on a set of similar characteristics, implying similarities in how each species responds to antigen. Our study provides the first comprehensive overview of the circulating repertoires of the heavy- and light-chain sequences in RMs, and provides insight into how they may perform as a model system for B cell-mediated immunity in humans.

Monoclonal antibody technologies have enabled dramatic advances in immunology, the study of infectious disease, and modern medicine over the past 40 years. However, many monoclonal antibody discovery procedures are labor- and time-intensive, low efficiency, and expensive. Here we describe an optimized mAb discovery platform for the rapid and efficient isolation, cloning and characterization of monoclonal antibodies in murine systems. In this platform, antigen-binding splenic B cells from immunized mice are isolated by FACS and cocultured with CD40L positive cells to induce proliferation and mAb production. After 12 days of coculture, cell culture supernatants are screened for antigen, and IgG positivity and RNA is isolated for reverse-transcription. Positive-well cDNA is then amplified by PCR and the resulting amplicons can be cloned into ligation-independent expression vectors, which are then used directly to transfect HEK293 cells for recombinant antibody production. After 4 days of growth, conditioned medium can be screened using biolayer interferometry for antigen binding and affinity measurements. Using this method, we were able to isolate six unique, functional monoclonal antibodies against an antigen of the human malaria parasite Plasmodium falciparum. Importantly, this method incorporates several important advances that circumvent the need for single-cell PCR, restriction cloning, and large scale protein production, and can be applied to a wide array of protein antigens.

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BackgroundPlasmodium vivax is the most geographically widespread of the human malaria parasites, causing 50,000 to 100,000 deaths annually. Plasmodium vivax parasites have the unique feature of forming dormant liver stages (hypnozoites) that can reactivate weeks or months after a parasite-infected mosquito bite, leading to new symptomatic blood stage infections. Efforts to eliminate P. vivax malaria likely will need to target the persistent hypnozoites in the liver. Therefore, research on P. vivax liver stages necessitates a marker for clearly distinguishing between actively replicating parasites and dormant hypnozoites. Hypnozoites possess a densely fluorescent prominence in the parasitophorous vacuole membrane (PVM) when stained with antibodies against the PVM-resident protein Upregulated in Infectious Sporozoites 4 (PvUIS4), resulting in a key feature recognizable for quantification of hypnozoites. Thus, PvUIS4 staining, in combination with the characteristic small size of the parasite, is currently the only hypnozoite-specific morphological marker available.ResultsHere, the generation and validation of a recombinant monoclonal antibody against PvUIS4 (α-rUIS4 mAb) is described. The variable heavy and light chain domains of an α-PvUIS4 hybridoma were cloned into murine IgG1 and IgK expression vectors. These expression plasmids were co-transfected into HEK293 cells and mature IgG was purified from culture supernatants. It is shown that the α-rUIS4 mAb binds to its target with high affinity. It reliably stains the schizont PVM and the hypnozoite-specific PVM prominence, enabling the visual differentiation of hypnozoites from replicating liver stages by immunofluorescence assays in different in vitro settings, as well as in liver sections from P. vivax infected liver-chimeric mice. The antibody functions reliably against all four parasite isolates tested and will be an important tool in the identification of the elusive hypnozoite.ConclusionsThe α-rUIS4 mAb is a versatile tool for distinguishing replicating P. vivax liver stages from dormant hypnozoites, making it a valuable resource that can be deployed throughout laboratories worldwide.

Highlights d We isolate a non-neutralizing antibody from PyCSPimmunized BALB/cJ mice d A non-neutralizing Ab, RAM1, abrogates the blocking capacity of an aCSP NAb d A non-neutralizing Ab, RAM1, reduces the vaccine efficacy in mice in vivo d Further exploration for the role of pre-existing nNAbs in the field is warranted