Highlights•HIV neutralizing antibodies were isolated from rabbits immunized with BG505 SOSIP.664•These antibodies target a hole in the glycan shield of BG505•Serum neutralization specificity maps to the same immunodominant glycan hole•Most HIV strains lack a conserved glycan site that could be a neutralization targetSummaryA major advance in the search for an HIV vaccine has been the development of a near-native Envelope trimer (BG505 SOSIP.664) that can induce robust autologous Tier 2 neutralization. Here, potently neutralizing monoclonal antibodies (nAbs) from rabbits immunized with BG505 SOSIP.664 are shown to recognize an immunodominant region of gp120 centered on residue 241. Residue 241 occupies a hole in the glycan defenses of the BG505 isolate, with fewer than 3% of global isolates lacking a glycan site at this position. However, at least one conserved glycan site is missing in 89% of viruses, suggesting the presence of glycan holes in most HIV isolates. Serum evidence is consistent with targeting of holes in natural infection. The immunogenic nature of breaches in the glycan shield has been under-appreciated in previous attempts to understand autologous neutralizing antibody responses and has important potential consequences for HIV vaccine design.Graphical abstract
Countermeasures to prevent and treat coronavirus disease 2019 (COVID-19) are a global health priority. We enrolled a cohort of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-recovered participants, developed neutralization assays to investigate antibody responses, adapted our high-throughput antibody generation pipeline to rapidly screen more than 1800 antibodies, and established an animal model to test protection. We isolated potent neutralizing antibodies (nAbs) to two epitopes on the receptor binding domain (RBD) and to distinct non-RBD epitopes on the spike (S) protein. As indicated by maintained weight and low lung viral titers in treated animals, the passive transfer of a nAb provides protection against disease in high-dose SARS-CoV-2 challenge in Syrian hamsters. The study suggests a role for nAbs in prophylaxis, and potentially therapy, of COVID-19. The nAbs also define protective epitopes to guide vaccine design.
Extensive studies with subtype A BG505-derived HIV Env immunogens have revealed that the dominant autologous neutralizing epitope in rabbits is located in an exposed region of the heavily glycosylated trimer that lacks potential N-linked glycosylation sites at positions 230, 241, and 289. The Env derived from B41, a subtype B virus, shares a glycan hole centered on positions 230 and 289. To test whether broader neutralization to the common glycan hole can be achieved, we immunized rabbits with B41 SOSIP alone, as well as B41 and BG505 co-immunization. We isolated autologous neutralizing antibodies (nAbs) and described their structure in complex with the B41 Env. Our data suggest that distinct autologous nAb lineages are induced by BG505 and B41 immunogens, even when both were administered together. In contrast to previously described BG505 glycan hole antibodies, the B41-specific nAbs accommodate the >97% conserved N241 glycan, which is present in B41. Single particle cryo-electron microscopy studies confirmed that B41 and BG505-specific nAbs bind to overlapping glycan hole epitopes. We then used our high-resolution data to guide mutations in the BG505 glycan hole epitope in an attempt to broaden the reactivity of a B41-specific nAb, but only recovered partial binding. Our data demonstrate that lack of cross-reactivity in glycan hole antibodies is due to amino acid differences within the epitope and our attempts to rationally design cross-reactive trimers resulted in only limited success. Thus, even for the immunodominant glycan hole shared between BG505 and B41 the prospect of designing prime-boost immunogens remains difficult.
Dengue virus (DENV) causes the major arboviral disease of the tropics, characterized in its severe forms by signs of hemorrhage and plasma leakage. DENV encodes a nonstructural glycoprotein, NS1, that associates with intracellular membranes and the cell surface. NS1 is eventually secreted as a soluble hexamer from DENV-infected cells and circulates in the bloodstream of infected patients. Extracellular NS1 has been shown to modulate the complement system and to enhance DENV infection, yet its structure and function remain essentially unknown. By combining cryoelectron microscopy analysis with a characterization of NS1 amphipathic properties, we show that the secreted NS1 hexamer forms a lipoprotein particle with an open-barrel protein shell and a prominent central channel rich in lipids. Biochemical and NMR analyses of the NS1 lipid cargo reveal the presence of triglycerides, bound at an equimolar ratio to the NS1 protomer, as well as cholesteryl esters and phospholipids, a composition evocative of the plasma lipoproteins involved in vascular homeostasis. This study suggests that DENV NS1, by mimicking or hijacking lipid metabolic pathways, contributes to endothelium dysfunction, a key feature of severe dengue disease.
Significance Rational development of successful vaccines requires utilization of predictive models of vaccination. One approach for development of an HIV vaccine has been to study broadly neutralizing antibodies (bnAbs) and revert the mutations back to germline. However, there are limitations to such models. Therefore, we generated three knockin mice expressing B cell receptors (BCRs) from authentic naive VRC01-class B cells from healthy human donors (“HuGL” mice). This approach revealed that human VRC01-class naive B cell BCRs are indeed competent for antigen-specific responses in vivo. Additionally, a series of experiments shows the importance of precursor frequency and affinity on B cell responses to vaccine antigens. Overall, these HuGL mouse models validate a central tenet of the germline-targeting approach to vaccine design.
(Cell Reports 21, 222–235; October 3, 2017) In the originally published version of this article, a statement in the discussion was not updated to reflect the data finally presented in Figure 1. The original publication contained the following statement: (3) “Differing V2-apex iP reactivity. The most effective immunogens, C108 and CRF250, bind all of the PG9, CH01, and CAP256 prototype iPs, while WITO and MGRM8 are neutralized by only two of these antibodies. Further, WITO and MGRM8 SOSIPs showed the poorest binding to iP/UCA antibodies by BLI, suggesting there are potentially fewer ways for them to trigger naive BCRs.” This statement has now been replaced by the following revision: (3) “Differing V2-apex iP reactivity. One of the more effective immunogens, CRF250, binds all of the PG9, CH01, and CAP256 precursor antibodies, suggesting there are potentially multiple ways for this trimer specifically to engage V2-apex-directed naive BCRs and giving it a potential advantage with regard to nAb elicitation.” The authors apologize for this error. Elicitation of Neutralizing Antibodies Targeting the V2 Apex of the HIV Envelope Trimer in a Wild-Type Animal ModelVoss et al.Cell ReportsOctober 03, 2017In BriefVoss et al. show that select V2-apex-focusing immunogens derived from bnAb precursor neutralization-sensitive HIV isolates can reproducibly elicit autologous neutralizing responses to components of the bnAb epitope, including K169/K171 and N156, in a wild-type animal model. Full-Text PDF Open Access
Targeting sarbecoviruses As we continue to battle the COVID-19 pandemic, we must confront the possibility of new pathogenic coronaviruses emerging in humans in the future. With this in mind, Rappazzo et al. isolated antibodies from a survivor of the 2003 severe acute respiratory syndrome coronavirus (SARS-CoV), used yeast display libraries to introduce diversity into these antibodies, and then screened for binding to SARS-CoV-2. One of the affinity-matured progeny strongly neutralized SARS-CoV-2, SARS-CoV, and two SARS-related viruses from bats. In addition, this antibody bound to the receptor-binding domains from a panel of sarbecoviruses, suggesting broader activity, and provided protection against SARS-CoV and SARS-CoV-2 in mouse models. Science , this issue p. 823
