Leveraging Controlled Release to Create a Single-Injection Post-Exposure Prophylactic for Rabies - PROJECT SUMMARY/ABSTRACT Rabies is the deadliest infectious disease with a case fatality rate of virtually 100%. Fortunately, rabies can be prevented through vaccination or be treated post-exposure prophylaxis (PEP)—the latter of which is much more common. When PEP is administered shortly after exposure to the rabies virus and the full 3- or 4-dose regimen is completed, the prognosis is excellent with a 100% survival rate. Unfortunately, there are 59,000 people that die each year due to the lack of adequate access to rabies PEP. 99% of these individuals are from low- and middle-income countries (LMICs) and 84% of them come from rural areas in those countries, underscoring that poor healthcare infrastructure in these areas is a key factor. Over the past few decades, the World Health Organization (WHO) and other healthcare ministries have sought to decrease the number of doses required to confer protection to improve access. At present, the WHO’s current 3-dose sequence maintains its high efficacy, but further decreases in the number of doses required have not been forthcoming due to substantial sacrifices in efficacy. Therefore, there remains a major clinical need to further truncate rabies PEP—ideally down to the point where only one injection is required. In this project, we will develop a single-injection rabies vaccine for use in PEP. Leveraging the Particles Uniformly Liquified and Sealed to Encapsulate Drug (PULSED) fabrication process that we have pioneered, we will create biodegradable microparticles that release rabies antigen in its native (i.e., bioactive) state at time points that match current rabies PEP schedules known to be safe and effective. PULSED microparticles composed of poly(lactic-co- glycolic acid) (PLGA) can be readily tuned to release their contents after a delay of days to weeks that is dependent on the copolymer ratio, molecular weight, and end group of the PLGA used. By combining and co-injecting particles with different compositions, multiple discrete doses of antigen can be released on the PEP time schedules known to be safe and effective (e.g., on days 0, 3, and 7 according to WHO recommendations) while requiring only a single injection. However, a key challenge in the realization of this strategy is the ability to maintain antigen stability through microparticle fabrication and in vivo release. During these stages, the antigen will be exposed to stressors including drying and short- term heating during particle production and then be exposed to body temperature for up to 2 weeks prior to release inside a particle that is acidifying as the PLGA degrades. These stressors can cause the antigen, which is a whole inactivated virus, to change its conformation, undergo deamidation, aggregate, or otherwise assume an architecture that no longer confers protection against rabies. Therefore, we will implement stabilization strategies that prevent microparticle acidification and protect the antigen from thermal instability. Then, using a rat model, we will evaluate the humoral and cellular immune response to the stabilized single-injection rabies vaccine to assess its non-inferiority to the current standard of care that requires multiple injections.
