Anti-influenza H7 human antibody targets antigenic site in hemagglutinin head domain interface

Although broadly protective, stem-targeted Abs against the influenza A virus hemagglutinin (HA) have been well studied, very limited information is available on Abs that broadly recognize the head domain. We determined the crystal structure of the HA protein of the avian H7N9 influenza virus in complex with a pan-H7, non-neutralizing, protective human Ab. The structure revealed a B cell epitope in the HA head domain trimer interface (TI). This discovery of a second major protective TI epitope supports a model in which uncleaved HA trimers exist on the surface of infected cells in a highly dynamic state that exposes hidden HA head domain features.

Identification of Structurally Related Antibodies in Antibody Sequence Databases Using Rosetta-Derived Position-Specific Scoring

The amount of antibody (Ab) variable gene sequence information is expanding rapidly, but our ability to predict the function of Abs from sequence alone is limited. Here, we describe a sequence-to-function prediction method that couples structural data for a single Ab/antigen (Ag) complex with repertoire data. We used a position-specific structure-scoring matrix (P3SM) incorporating structure-prediction scores from Rosetta to identify Ab variable loops that have predicted structural similarity to the influenza virus-specific human Ab CH65. The P3SM approach identified new members of this Ab class. Recombinant Ab expression, crystallography, and virus inhibition assays showed that the HCDR3 loops of the newly identified Abs possessed similar structure and antiviral activity as the comparator CH65. This approach enables discovery of new human Abs with desired structure and function using cDNA repertoires that are obtained readily with current amplicon sequencing techniques.

A Site of Vulnerability on the Influenza Virus Hemagglutinin Head Domain Trimer Interface

Here, we describe the discovery of a naturally occurring human antibody (Ab), FluA-20, that recognizes a new site of vulnerability on the hemagglutinin (HA) head domain and reacts with most influenza A viruses. Structural characterization of FluA-20 with H1 and H3 head domains revealed a novel epitope in the HA trimer interface, suggesting previously unrecognized dynamic features of the trimeric HA protein. The critical HA residues recognized by FluA-20 remain conserved across most subtypes of influenza A viruses, which explains the Ab's extraordinary breadth. The Ab rapidly disrupted the integrity of HA protein trimers, inhibited cell-to-cell spread of virus in culture, and protected mice against challenge with viruses of H1N1, H3N2, H5N1, or H7N9 subtypes when used as prophylaxis or therapy. The FluA-20 Ab has uncovered an exceedingly conserved protective determinant in the influenza HA head domain trimer interface that is an unexpected new target for anti-influenza therapeutics and vaccines.

Cross-Neutralizing and Protective Human Antibody Specificities to Poxvirus Infections

Monkeypox (MPXV) and cowpox (CPXV) are emerging agents that cause severe human infections on an intermittent basis, and variola virus (VARV) has potential for use as an agent of bioterror. Vaccinia immune globulin (VIG) has been used therapeutically to treat severe orthopoxvirus infections but is in short supply. We generated a large panel of orthopoxvirus-specific human monoclonal antibodies (Abs) from immune subjects to investigate the molecular basis of broadly neutralizing antibody responses for diverse orthopoxviruses. Detailed analysis revealed the principal neutralizing antibody specificities that are cross-reactive for VACV, CPXV, MPXV, and VARV and that are determinants of protection in murine challenge models. Optimal protection following respiratory or systemic infection required a mixture of Abs that targeted several membrane proteins, including proteins on enveloped and mature virion forms of virus. This work reveals orthopoxvirus targets for human Abs that mediate cross-protective immunity and identifies new candidate Ab therapeutic mixtures to replace VIG.

Human antibody specificities that confer protective immunity to poxvirus infections (VAC11P.1109)

Immunization with vaccinia virus (VACV) induces cross-protective immunity to variola, the causative agent of smallpox, and other clinically important poxviral species, such as cowpox and monkeypox viruses. Vaccine-mediated protection has been correlated with elicitation of broad neutralizing antibodies (Abs). However, the specificity and breadth of protective human Abs to poxviruses are largely unknown. We used a highly-optimized human hybridoma technology to generate a panel of 90 anti-VACV monoclonal Abs from vaccinia-immunized subjects or from subjects who had a history of naturally-acquired monkeypox infection. Then, we assessed the neutralizing and protective capabilities of the Abs in vitro and in a lethal respiratory VACV challenge in a mouse model. A large fraction of Abs from the panel (>40%) possessed neutralizing activity against VACV, cowpox and/or monkeypox viruses. Antibodies to a variety of envelope proteins in VACV extracellular virions (A33, B5) or mature virions (L1, A27, D8, H3) contributed substantially to neutralizing activity in vitro. For protective immunity in vivo, L1, A27, A33 and B5 antibodies conferred levels of protection that were comparable to those induced by live viral vaccination, especially when used in combination. Such antibody cocktails have promise for use in as immunotherapeutics in humans.

Poxviral infection elicits human neutralizing antibodies recognizing diverse epitopes of the major vaccinia virus surface protein D8 (VIR4P.1016)

Immunization with vaccinia virus (VACV) confers cross-protective immunity to variola, the causative agent of smallpox, and other clinically important poxviral species, such as cowpox and monkeypox viruses. Vaccine-mediated protection has been correlated with elicitation of broad neutralizing antibody (Ab) responses, however the specificity of human neutralizing antibodies to poxviruses is poorly understood. We used a highly-optimized human hybridoma technology to generate large panels of anti-VACV monoclonal Abs (mAbs) from vaccinia-immunized subjects or from subjects who had naturally acquired monkeypox infection. Immunologic characterization and DNA sequencing of the panel revealed 16 individual mAbs that recognized the immunodominant surface protein antigen D8. Several of anti-D8 mAbs possessed neutralizing activity against VACV, cowpox and monkeypox viruses. These Abs exhibited mainly a complement-dependent pattern of neutralization and they formed at least four cross-blocking groups, suggesting the existence of several non-overlapping neutralizing epitopes for D8. The results suggest that D8 is an important target for human neutralizing Abs generated following poxviral infection or vaccination, and suggest the existence of novel epitopes targeted by anti-D8 Abs that contribute to cross-protective immunity following smallpox vaccination.