Human B Cell Epitope Map of the Lyme Disease Vaccine Antigen, OspA

Abstract

The Lyme disease (LD) vaccine formerly approved for use in the United States consisted of recombinant outer surface protein A (OspA) from Borrelia burgdorferi sensu stricto (ss), the bacterial genospecies responsible for the vast majority of LD in North America. OspA is an ∼30 kDa lipoprotein made up of 21 antiparallel β-strands and a C-terminal α-helix. In clinical trials, protection against LD following vaccination correlated with serum antibody titers against a single epitope near the C-terminus of OspA, as defined by the mouse monoclonal antibody (MAb), LA-2. However, the breadth of the human antibody response to OspA following vaccination remains undefined even as next-generation multivalent OspA-based vaccines are under development. In this report, we employed hydrogen exchange–mass spectrometry (HX-MS) to localize the epitopes recognized by a unique panel of OspA human MAbs, including four shown to passively protect mice against experimental B. burgdorferi infection and one isolated from a patient with antibiotic refractory Lyme arthritis. The epitopes grouped into three spatially distinct bins that, together, encompass more than half the surface-exposed area of OspA. The bins corresponded to OspA β-strands 8–10 (bin 1), 11–13 (bin 2), and 16–20 plus the C-terminal α-helix (bin 3). Bin 3 was further divided into sub-bins relative to LA-2’s epitope. MAbs with complement-dependent borreliacidal activity, as well as B. burgdorferi transmission-blocking activity in the mouse model were found within each bin. Therefore, the resulting B cell epitope map encompasses functionally important targets on OspA that likely contribute to immunity to B. burgdorferi.

Structural Elucidation of a Protective B cell Epitope on Outer Surface Protein C (OspC) of the Lyme disease spirochete,Borreliella burgdorferi

“…HX-MS provides peptide level resolution of antibody-antigen interactions in solution based on differential hydrogen-deuterium exchange rates between unbound and bound targets (Angalakurthi et al, 2018; Brier et al, 2021; Chen et al, 2019; Grauslund et al, 2021; Hodge et al, 2022; Malito et al, 2013; Seow et al, 2022; Vinciauskaite and Masson, 2022). We recently used HX-MS to localize a dozen human B cell epitopes the B. burgdorferi antigen, OspA (Haque et al, 2022). In the case of OspC, we first generated a peptidic map of OspC A , which yielded 87 peptides that covered the entire length of the molecule ( Figure S3 ).…”

“…OspC A and B5 MAb were buffer exchanged and assayed by our previous protocol (Haque et al ., 2022). Previously flash frozen OspC A (19μM) was thawed at room temperature.…”

“…Bound state (OspC A +B5) was prepared by three strokes mixing and adjusted to a final concentration of 9 μM. HX-MS labeling conditions, robot methods, maximally deuterated experiment (OspA paper) protocol, data analysis was done as recently reported (Haque et al ., 2022).…”

High-Throughput Epitope Mapping by Hydrogen Exchange-Mass Spectrometry

“…The accuracy of the HEXITOPE algorithm vs X-ray crystallography has previously been established (Toth et al., manuscript in preparation), including with the antibody–antigen systems used in this study . The goal of this work is to establish the accuracy of the screening HX protocol vs complete HX.…”

“…In our previous study, we reported epitope mapping of OspA with a range of mAbs by complete HX. In the present study we have selected two mAbs (212-55 and 3-24) to validate our screening HX method.…”