Development of a highly effective vaccine or antibodies for prevention and ultimately elimination of malaria is urgently needed. Here, we report the isolation of a number of human monoclonal antibodies (mAbs) directed against the Plasmodium falciparum (Pf) circumsporozoite protein (CSP) from several subjects immunized with an attenuated whole sporozoite (SPZ) vaccine (Sanaria® PfSPZ Vaccine). Passive transfer of one of these antibodies, mAb CIS43, conferred high-level, sterile protection in two different mouse models of malaria infection. Stoichiometry and affinity of mAb CIS43 for PfCSP indicate two sequential multivalent binding events to six sites: the first 7-fold higher affinity binding event is to a unique “junctional” epitope positioned between the N-terminus and the central repeat domain of PfCSP. Moreover, mAb CIS43 prevented proteolytic cleavage of PfCSP on PfSPZ. Crystal structures of the CIS43 fragment antigen binding (Fab) in complex with the junctional epitope determined the molecular interactions of binding, revealed the epitope’s conformational flexibility, and defined NPN as the structural repeat motif. The demonstration that mAb CIS43 is highly effective for passive prevention of malaria has potential application for use in travelers, military personnel and elimination campaigns and identifies a new and conserved site of vulnerability on PfCSP for next generation rational vaccine design.

Epstein-Barr virus (EBV) is a causative agent of infectious mononucleosis and is associated with 200,000 new cases of cancer and 140,000 deaths annually. Subunit vaccines against this pathogen have focused on the gp350 glycoprotein and remain unsuccessful. We isolated human antibodies recognizing the EBV fusion machinery (gH/gL and gB) from rare memory B cells. One anti-gH/gL antibody, AMMO1, potently neutralized infection of B cells and epithelial cells, the two major cell types targeted by EBV. We determined a cryo-electron microscopy reconstruction of the gH/gL-gp42-AMMO1 complex and demonstrated that AMMO1 bound to a discontinuous epitope formed by both gH and gL at the Domain-I/Domain-II interface. Integrating structural, biochemical, and infectivity data, we propose that AMMO1 inhibits fusion of the viral and cellular membranes. This work identifies a crucial epitope that may aid in the design of next-generation subunit vaccines against this major public health burden.

SUMMARY Broadly HIV-1 neutralizing VRC01 class antibodies target the CD4-binding site of Env. They are derived from VH1–2*02 antibody heavy chains paired with rare light chains expressing 5-amino acid-long CDRL3s. They have been isolated from infected subjects but have not yet been elicited by immunization. Env-derived immunogens capable of binding the germline forms of VRC01 B cell receptors on naive B cells have been designed and evaluated in knockin mice. However, the elicited antibodies cannot bypass glycans present on the conserved position N276 of Env, which restricts access to the CD4-binding site. Efforts to guide the appropriate maturation of these antibodies by sequential immunization have not yet been successful. Here, we report on a two-step immunization scheme that leads to the maturation of VRC01-like antibodies capable of accommodating the N276 glycan and displaying autologous tier 2 neutralizing activities. Our results are relevant to clinical trials aiming to elicit VRC01 antibodies.

Highlights d An epitope present on different immunogens selects for different targeted B cells d Each selected subpopulation comprises B cells with diverse affinities d The relative affinity dictates the fate of B cells following the initial selection d Developed 426cOD, a novel VRC01-class germline targeting immunogen

VRC01 broadly neutralizing antibodies (bnAbs) target the CD4-binding site (CD4BS) of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein (Env). Unlike mature antibodies, corresponding VRC01 germline precursors poorly bind to Env. Immunogen design has mostly relied on glycan removal from trimeric Env constructs and has had limited success in eliciting mature VRC01 bnAbs. To better understand elicitation of such bnAbs, we characterized the inferred germline precursor of VRC01 in complex with a modified trimeric 426c Env by cryo-electron microscopy and a 426c gp120 core by X-ray crystallography, biolayer interferometry, immunoprecipitation, and glycoproteomics. Our results show VRC01 germline antibodies interacted with a wild-type 426c core lacking variable loops 1–3 in the presence and absence of a glycan at position Asn276, with the latter form binding with higher affinity than the former. Interactions in the presence of an Asn276 oligosaccharide could be enhanced upon carbohydrate shortening, which should be considered for immunogen design.