Fig 1.
Temporal and spatial regulation of Borrelia outer surface proteins expression during tick-to-host transmission.
During tick feeding, Borrelia alters the expression of its outer surface proteins [4] in response to environmental cues. OspA (yellow) is highly expressed in the midgut of unfed ticks, where it is thought to mediate adherence to the midgut epithelium. As the tick begins feeding, OspA is downregulated, while OspC (orange) is upregulated to facilitate early mammalian invasion. During systemic infection in the vertebrate host, CspZ (blue) becomes expressed and promotes complement evasion through Factor H binding. Insets: Scheme of the Borrelia outer membrane showing lipoprotein anchoring via a triacylated N-terminal cysteine. The proteins depicted as stylised cartoons were derived from OspA: UniProt = P0CL66; Alphafold = AF-P0CL66-F1-v4; OspC (dimer): UniProt = Q07337; Alphafold = AF-Q07337-F1-v4; CspZ: UniProt = O50665; Alphafold = AF-O50665-F1-v4.
Fig 2.
Geographic distribution of major Borrelia species associated with human Lyme disease and their representation in the multivalent OspA-based vaccine VLA15.
The map (top panel) highlights the geographic distribution of the predominant Borrelia species associated with human Lyme disease across regions: B. burgdorferi sensu stricto in North America, and B. afzelii, B. garinii, B. bavariensis and B. burgdorferi sensu stricto in Europe and Asia. These species correspond to six predominant OspA serotypes (1–6), which underpin the multivalent OspA vaccine design and enable broad coverage across the dominant, geographically diverse Borrelia genospecies. The distribution map is based on the CDC’s Lyme Disease Case Map (June 2025) and LD surveillance data from Canada [32], overlayed on a base map sourced from naturalearthdata.com. The schematic (bottom panel) illustrates the VLA15 vaccine composition, which includes OspA C-terminal domains from serotypes 1–6 connected, via a 21-amino acid linker, which is derived by merging two loop regions of the N-terminal domain from serotype 1 (residues 65-GTSDKNNGSG-74 and 43-SKEKNKDGKYS-53, in which residue D53 has been mutated to S). Each subunit contains an introduced disulfide bond to increase stability. To avoid hLFA-1 mimicry, the serotype 1 hLFA-1-like epitope was replaced with the corresponding serotype 2 sequence.
Fig 3.
Schematic overview of current and emerging opportunities in Lyme disease (LD) diagnostics and serology-guided vaccination.
A) During mammalian infection, Borrelia burgdorferi sensu lato (s.l.) expresses surface proteins that elicit a specific humoral immune response. Commonly targeted antigens include VlsE, OspC, and flagellin (p41), whereas antibodies against OspA are rarely detected (≤15% of cases). B) The VLA15 vaccine is composed only of the C-termini of OspA of 6 B. burgdorferi s.l. serotypes. C) The current standard two-tier testing for LD typically combines an enzyme immunoassay (EIA) using a mixture of selected antigens or a single-antigen (e.g., VlsE) with a confirmatory strip-blot assay detecting IgG and IgM antibodies against multiple Borrelia antigens. D) These strip blots often contain full-length OspA antigens, which will also detect antibodies in vaccinated individuals following VLA15 implementation. E) Diagnostic immunostrips can be multiplexed using microchip-based technologies, which can provide more targeted and detailed information by distinguishing infection-induced from vaccine-induced antibody responses. Provided a vaccinated person is sero-negative (grey) for acute (e.g., VlsE) or prolonged LD (N-terminal OspA) infection, such individual will be possibly eligible for VLA15 vaccination. These technologies can also enable quantitative, time-resolved tracking of vaccine-induced antibody levels (C-terminal OspA, yellow). Signal intensity will either indicate the anticipated protective level or significant waning of vaccine induced antibody titres, indicating a call for a vaccine booster. Inclusion of acute infection antigens (e.g., VlsE) in these multiplex immunoassays will also allow to detect breakthrough infections. The correlation between circulating antibody levels and the occurrence of LD infections will help define the precise threshold of protective immunity.