Biology subjects

Freeman-Gallant, G.

Publications and source records attributed to Freeman-Gallant, G..

4 recordsLinked to original sources

bioRxiv2025

A Broadly Conserved Protective Epitope on the Lyme Disease Vaccine Antigen, OspA

Lyme disease, caused by the spirochete, Borreliella burgdorferi sensu latu (Bbsl), is a debilitating tickborne infection of increasing incidence in North America, Europe and Asia. While vaccines based on Outer surface protein A (OspA) have proven highly efficacious at blocking Bbsl tick-to-human transmission, the high degree of antigenic variability among the major OspA serotypes (ST) has made the development of a broadly cross protective vaccine difficult. Recent profiling of protective human monoclonal antibodies (mAbs) has suggested the existence of conserved epitopes situated within OspAs central {beta}-sheet (CBS), although direct comparisons of cross-serotype functionality has been hindered by biological differences among the major Bbsl genospecies. To address these issues, we developed a panel of isogenic B. burgdorferi viability reporter strains expressing the seven major OspA serotypes (ST1-7) and probed them with CBS-targeting mAbs to evaluate their complement-dependent borreliacidal activity. The mAbs segregated into three distinct classes with varying degrees of borreliacidal activity: class 1 mAbs exhibited potent killing against all seven OspA serotypes, while classes 2 and 3 had restricted or no activity against two of the seven serotypes. Structural analysis of Fabs derived from each class of mAbs in complex with OspA ST1 showed that they target overlapping epitopes spanning {beta}-strands 6-10 and involve contact with largely invariant residues. Further analysis of B. burgdorferi reporter strains expressing OspA variants from 17 additional Bbsl genospecies identified Lys-107 as a determinant of susceptibility for nearly all CBS mAbs. Taken together, these findings raise the prospect of structure-based design of a broadly protective monovalent Lyme disease vaccine. AUTHOR SUMMARYLyme disease, caused by the spirochete, Borreliella burgdorferi sensu latu (Bbsl), is a potentially debilitating tickborne infection of increasing incidence in North America, Europe and Asia. While vaccines based on Outer surface protein A (OspA) have proven highly efficacious at blocking Bbsl tick-to-human transmission, the genetic and serological heterogeneity of OspA across Borrelia genospecies has complicated matters. In this report, we use a collection of transmission-blocking human monoclonal antibodies to delineate a protective region (epitope) within the central core of OspA that is conserved across all major OspA serotypes. These results have important implications for engineering a broadly reactive Lyme disease vaccine.

immunology↗

bioRxiv2025

An Fc-silent OspA monoclonal antibody passively protects mice from tick and intradermal Borrelia burgdorferi challenge

The monoclonal antibody, LA-2, has played a pivotal role in the development of Outer surface protein A (OspA)-based vaccines for Lyme disease, a multisystem illness caused by the tick-borne spirochete, Borrelia burgdorferi sensu lato. Of particular significance was the demonstration more than three decades ago that LA-2 equivalent antibody titers, defined by a competitive-inhibition ELISA, serve as a reliable correlate of vaccine-induced protection across different species, including humans. In vitro characterization of LA-2 has identified both complement-dependent and -independent activities, although which of these attributes contribute to protection against B. burgdorferi remains unresolved. To address this issue, we generated and characterized an "Fc-silent" version of LA-2 IgG1 carrying so-called LALAPG substitutions (L234A, L235A, P329G). We demonstrate that LA-2 LALAPG retained OspA binding activity but was severely attenuated in in vitro complement deposition and complement-dependent borreliacidal assays. Nonetheless, LA-2 LALAPG was as effective as LA-2 at passively protecting C3H mice against nymphal tick-mediated B. burgdorferi challenge. LA-2 LALAPG was also equivalent to LA-2 in passively protecting BALB/c mice against intradermal B. burgdorferi challenge. In the intradermal challenge model, viable spirochetes were not recoverable 24 h after injection from skin biopsies of mice treated with LA-2 or LA-2 LALAPG, and an influx of pro-inflammatory cytokines and chemokines to the injection site was abrogated. Collectively, these results suggest that LA-2s primary mode of action involves direct physical interactions with the spirochete rather than complement-dependent killing. Elucidating these mechanisms may have implications for understanding the mechanistic correlates of OspA-based vaccine-induced immunity in humans.

immunology↗

bioRxiv2024

A type-specific B cell epitope at the apex of Outer surface protein C (OspC) of the Lyme disease spirochete, Borreliella burgdorferi

Broadly protective immunity to the Lyme disease spirochete, Borreliella burgdorferi, is constrained by an overwhelming antibody response against type-specific epitopes on Outer surface protein C (OspC), a homodimeric helix-rich lipoprotein essential for early stages of spirochete dissemination in vertebrate hosts. However, the molecular basis for type-specific immunity has not been fully elucidated. In this report, we produced and characterized an OspC mouse monoclonal antibody, 8C1, that recognizes native and recombinant OspC type A (OspCA) but not OspC types B or K, and arrests B. burgdorferi motility independent of complement. Epitope mapping by HDX-MS localized 8C1s epitope to a protruding ridge on the apex of OspCA -helix 3 (residues 130-150) previously known to be an immunodominant region of the molecule. Alanine scanning pinpointed 8C1s core binding motif to a solvent exposed patch consisting of residues K141 H142 T143 D144. In parallel, analysis of 26 Lyme disease positive serum samples confirmed antibody reactivity with this region of OspCA, with residues E140 and D144 as being most consequential. Our results underscore the importance of -helix 3 as a target of type-specific epitopes on OspCA across mice and humans that should be taken into consideration in Lyme disease vaccine design.

immunology↗

bioRxiv2024

A refined human linear B cell epitope map of Outer surface protein C (OspC) from the Lyme disease spirochete, Borreliella burgdorferi

A detailed understanding of the human antibody response to Outer surface protein C (OspC) of Borrelellia burgdorferi has important implications for Lyme disease diagnostics and vaccines. In this report, a total of 13 peptides encompassing eight reported OspC linear B cell epitopes from OspC types A, B and K, including the conserved C-terminus (residues 193-210: peptide C10), were evaluated by multiplex immunoassay (MIA) for IgG reactivity with [~]700 human serum samples confirmed positive in a two-tiered Lyme disease diagnostic assay and [~]160 post-treatment Lyme disease (PTLD) serum samples. The VlsE C6-17 peptide was included as a positive control. Diagnostic serum IgG reacted with 11 of the 13 OspC-derived peptides, significantly more than controls, with the C10 peptide being the most reactive. In the PTLD serum samples, two OspC peptides including C10 were significantly more reactive than controls. Spearmans rank correlation matrices and hierarchical clustering indicated a strong correlation between C10 and VlsE C6-17 peptide reactivity but little demonstrable association between C10 and the other OspC peptides or recombinant OspC. OspC peptide reactivities (excluding C10) were strongly correlated with each other and were disproportionately influenced by a subset of pan-reactive samples. In the PTLD cohort, C10 clustered with the other OspC-derived peptides and was distinct from OspC and VlsE C6-17. The asynchronous serologic response to OspC, C10, and the OspC-derived peptides reveals the complexity of B cell responses to B. burgdorferi and confounds simple interpretation of antibody profiles associated with Lyme disease. IMPORTANCELyme disease is an emerging tick-borne infection caused by the spirochete, Borreliella burgdorferi. In humans, antibodies against spirochetal outer surface lipoproteins are proposed to play a role in disease resolution and in protection against reinfection. Some of those same antibodies also serve as diagnostic indicators of an active or history of Lyme disease. In this study, we sought to validate reported antibody binding sites on Outer surface protein C (OspC), a known target of both protective and diagnostic antibodies.

immunology↗