Developing a Much-Needed New Shot for Lyme Disease with mRNA

Sep 22, 2023

Who has not heard of Lyme disease by now? The end of the summer should bring a much-needed break from the risk of exposure to this illness, at least for some areas of the US where winter months reduce outdoor activities and hence the potential for tick encounters. Still, the risk, while diminished during winter, is not eliminated. Ticks are active throughout the year, and for some US areas with mild winter seasons, a risk of infection remains year-round. Lyme disease is the most prevalent vector-borne disease in the US, with over 300,000 cases reported annually based on regular surveillance (Kugeler et al. 2021).

What is Lyme disease?

First identified in Lyme, Connecticut, in the mid-seventies, Lyme disease was linked to a bacterial infection in 1981 by Dr. Willy Burgdorfer at NIAID Rocky Mountain Laboratories. At the time, ticks were the suspected vector of a Lyme disease-causing virus, yet Burgdorfer's discovery of spirochetes, and specifically Borrelia burgdorferi, in deer ticks was critical to understanding and treating the disease (Bugdorfer 1982, Bauer, 2015).

Cycle of Lyme disease transmission. Tick larvae and nymphs become infected with various species and strains of Borrelia burgdorferi when feeding on infected rodents. Infected nymphs and adult ticks bite and spread the bacteria to humans and deer.

Currently, it is generally accepted that while a bite by an infected tick is required for infection, ticks must be attached for a long period, over 36 hours, to transmit the bacteria to humans. Following bacterial infection, Lyme disease progresses in stages, affecting multiple body systems. From the initial bite site, inflammation begins, and over time, various symptoms develop, such as fever, muscle aches and pains, and fatigue. However, more severe symptoms, such as arthritis, carditis, and neurological problems, are also common at later stages (Adkison and Embers 2023).

Current treatment options

As typically done for bacterial infections, the predominant treatment for Lyme disease is antibiotic-based, which may be administered orally or systemically (IV) depending on disease severity. Newly infected patients respond well to antibiotics, especially if treated within three days following exposure (Nigrovic and Thompson 2007). Even receiving treatment within four weeks of disease onset seems to improve the odds of recovery. For patients experiencing symptoms related to central or peripheral nervous system involvement, intravascular antibiotic administration is often preferred.

However, not everyone recovers immediately from the disease, especially following diagnosis and treatment delays. In fact, about 10-30% of patients fail to respond to antibiotic therapy (Adkison and Embers 2023).

Antibiotic failure in Lyme disease patients. Several mechanisms have been implicated in Lyme disease treatment failure, including autoimmune processes, immune-mediated consequences of the primary infection, and bacterial persistence. Retrieved from Adkison and Embers 2023. https://creativecommons.org/licenses/by/4.0/

Are vaccines an option?

The first attempt at a prophylactic solution for Lyme disease came with the approval of LYMErix®, developed by SmithKline Beecham and FDA-approved in 1997. Formulated as a recombinant Borrelia burgdorferi outer-surface lipoprotein A (OspA) vaccine, LYMErix® was administered in three doses and demonstrated a high level of protection from new infections while also showing efficacy against latent infections (Steere et al. 1998). However, the availability of LYMErix® was short-lived. Manufacturing was soon halted in 2002 due to a combination of factors, including an efficacy below 80%, achieved only after multiple doses, limited strain coverage, and no availability for children, a critical population not included in safety and efficacy testing. Combined with consumers' fears of side effects and negative media coverage, these factors plummeted vaccine demand, leading to its market withdrawal (Nigrovic and Thompson 2007).

Nonetheless, vaccines represent the best alternative to curve the incidence of this often misdiagnosed and debilitating disease. Therefore, several candidates are currently under development, including two mRNA vaccines by Moderna and a multivalent protein subunit vaccine from Pfizer (VLA15), which would confer protection against six of the most common Borrelia burgdorferisensu's OspA serotypes prevalent in North America and Europe. Among these candidates, Pfizer's VLA15 is further down the pipeline, having initiated phase 3 (NCT05477524) clinical evaluation in 2022 (Pfizer).

A look at a new mRNA vaccine candidate at preclinical stage

Encouraged by the success of mRNA vaccines against SARS-CoV2, a team at the University of Pennsylvania has been developing an mRNA-lipid nanoparticle vaccine for Lyme disease (Pine et al. 2023). They have leveraged mRNA and lipid nanoparticles (LNP) to produce their new experimental vaccine, which uses OspA, the same immunogen in previous protein-based formulations. Their preclinical findings support the safety and high efficacy of an OspA mRNA vaccine, opening new opportunities to control the high incidence of Lyme disease.

To produce their experimental vaccine, the team sourced GenScript's codon-optimized gene synthesis and plasmid preparation services for manufacturing an OspA gene-containing plasmid corresponding to the OspA sequence from B. burgdorferi strain B31. mRNA synthesis was carried out by the team from the linearized plasmid through in vitro transcription (IVT), followed by its encapsulation into LNPs. Intramuscular administration of their OspA mRNA candidate as a single dose induced innate responses similar to those elicited by an adjuvanted recombinant OspA protein vaccine. They found that administering OspA as either RNA or protein similarly mobilized neutrophils, dendritic cells, macrophages, and monocytes. However, CD4 and CD8 T cells were more effectively activated by the OspA mRNA vaccine.

To evaluate T cell induction, splenocytes from mice immunized with either the OspA mRNA or recombinant OspA protein vaccine were incubated with a pool of 66 overlapping 15-mer OspA peptides synthesized by GenScript's peptide library services. The activation of T cells was then evaluated by flow cytometric analysis of cytokine production, revealing that the OspA mRNA was more efficient than the recombinant protein immunogen at inducing cellular responses. Similarly, OspA mRNA generated higher levels of antigen-specific T follicular helper (Tfh) cells and germinal center B cells in draining lymph nodes. These findings indicated that the mRNA vaccine may lead to better antibody responses.

Therefore, the team evaluated B cell memory responses in immunized mice's spleen and bone marrow. They found the OspA mRNA vaccine induced higher numbers of antigen-specific memory B cells and long-lived plasma cells than the recombinant OspA protein vaccine. In agreement with this, priming and boosting with OspA mRNA was more effective, eliciting a more robust and durable antibody response, as opposed to the outcome with two doses of the recombinant OspA protein vaccine. Lastly, in vivo challenge experiments demonstrated that the immunity induced by a single dose of OspA mRNA could protect mice from infection.

Overall, this study provides further support for using OspA as an effective immunogen to induce protective immunity against B. burgdorferi. Moreover, it reaffirms the effectiveness of mRNA-LNP formulations in eliciting robust humoral and cellular immunity against yet another significant pathogen of concern.

Reference

• Adkison, H., & Embers, M. E. (2023). Lyme disease and the pursuit of a clinical cure. Frontiers in Medicine, 10, 1183344. https://doi.org/10.3389/FMED.2023.1183344/BIBTEX
• Bauer. (2015, February 2). The Great Willy Burgdorfer, 1925–2014. https://irp.nih.gov/. Retrieved September 1, 2023, from https://irp.nih.gov/blog/post/2015/02/the-great-willy-burgdorfer-1925-2014
• Cotechini, T., Medler, T. R., & Coussens, L. M. (2015). Myeloid Cells as Targets for Therapy in Solid Tumors. Cancer Journal (Sudbury, Mass.), https://doi.org/10.1097/PPO.0000000000000132
• Burgdorfer, W., Barbour, A. G., Hayes, S. F., Benach, J. L., Grunwaldt, E., & Davis, J. P. (1982). Lyme disease-a tick-borne spirochetosis? Science (New York, N.Y.), 216(4552), 1317–1319. https://doi.org/10.1126/SCIENCE.7043737
• Kugeler, K. J., Schwartz, A. M., Delorey, M. J., Mead, P. S., & Hinckley, A. F. (2021). Estimating the Frequency of Lyme Disease Diagnoses, United States, 2010–2018. Emerging Infectious Diseases, 27(2), 616. https://doi.org/10.3201/EID2702.202731
• Nigrovic LE, Thompson KM. (2007). The Lyme vaccine: a cautionary tale. Epidemiol Infect. 2007 Jan;135(1):1-8. doi: 10.1017/S0950268806007096
• Pfizer and Valneva Initiate Phase 3 Study of Lyme Disease Vaccine Candidate VLA15. (2022, August 8). https://www.pfizer.com/. Retrieved August 30, 2023, from https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-valneva-initiate-phase-3-study-lyme-disease
• Pine, M. et al. (2023). Development of an mRNA-lipid nanoparticle vaccine against Lyme disease, Molecular Therapy, https://doi.org/10.1016/j.ymthe.2023.07.022
• Teere, L. A., et al. (1998). Vaccination against Lyme Disease with Recombinant Borrelia burgdorferi Outer-Surface Lipoprotein A with Adjuvant. Https://Doi.Org/10.1056/NEJM199807233390401, 339(4), 209–215. https://doi.org/10.1056/NEJM199807233390401