TNX-4800 Passive Immunization Heads to Phase 2 Field Study

Tonix Pharmaceuticals is advancing TNX-4800, an anti-OspA human monoclonal antibody, toward a randomized, double-blind, placebo-controlled adaptive Phase 2 field study, with initiation targeted for the first half of 2027 pending FDA agreement. With no FDA-approved vaccine or prophylactic currently on the U.S. market for Lyme disease, the regulatory pathway for a passive immunization biologic of this class will draw close attention from biologics development teams and regulatory affairs leads navigating IND strategy under 21 CFR Part 211 and ICH Q10 frameworks.

TNX-4800, licensed by Tonix from UMass Chan Medical School in 2025, is a long-acting borreliacidal monoclonal antibody targeting the outer surface protein A (OspA) of Borrelia burgdorferi, the spirochete responsible for 99.9% of U.S. Lyme disease cases. The molecule was engineered with a modified Fc domain to extend its half-life. The planned Phase 2 regimen consists of two subcutaneous doses: an initial Spring administration followed by a booster two months later, with a primary endpoint of Lyme disease prevention over six months. Each fixed SC dose is designed to deliver exposures comparable to the 5 mg/kg SC dose evaluated in Phase 1. Tonix has scheduled an FDA meeting for early Q3 2026 to align on the Phase 2 design before study initiation.

Phase 1 pharmacokinetic data, presented at the 4th Annual Ticks and Tickborne Diseases Symposium at Johns Hopkins University, were generated by a UMass Chan Medical School team led by Mark S. Klempner, MD, an inventor of TNX-4800. Tonix's CEO Seth Lederman, MD, stated that the PK data support the two-dose field study design and that the compound is expected to provide protection within two days of the first dose. By contrast, OspA subunit vaccines that elicit active immune responses require more than six months to confer protection and involve complex immunization schedules. A previously approved alum-based OspA subunit vaccine was withdrawn from the market, with poor uptake cited as a contributing factor.

Source: Tonix Pharmaceuticals Holding Corp. press release, April 29, 2026, via GlobeNewswire. Phase 1 data poster available under the Scientific Presentations tab at tonixpharma.com.