Tonix Pharmaceuticals Holding Corp. (NASDAQ:TNXP) ("Tonix" or the "Company"), a fully integrated, commercial biotechnology company, announced Phase 1 data of TNX-4800 (formerly known as mAb 2217LS)1,2 was presented by Mark S. Klempner, MD, professor of medicine at UMass Chan Medical School, an inventor of TNX-4800 and principal investigator of the study, on March 30, 2026, at the World Vaccine Congress Washington 2026. Tonix also announced its planned strategy for an adaptive Phase 2 field study expected to initiate in the first half of 2027, pending FDA clearance.

TNX-4800 is a long-acting borreliacidal (or bactericidal), human monoclonal antibody (mAb) with an engineered crystallizable fragment (Fc) domain for an extended half-life that targets the outer surface protein A (OspA) of Borrelia burgdorferi, which causes 99.9% of Lyme disease cases in the U.S.3,4 Tonix is developing TNX-4800, which the Company in-licensed from UMass Chan Medical School in 2025, as a prophylactic that is administered in a single subcutaneous (SC) dose expected to provide approximately four months protection to people in endemic areas during the U.S. tick season. There are currently no marketed U.S. Food and Drug Administration (FDA)-approved vaccines or prophylactics to protect against Lyme disease.

"TNX-4800 is expected to provide a preventative option to the 87 million5 people in the United States who are at high risk of contracting the disease because they live, work, or vacation in a tick-endemic area," said Seth Lederman, MD, Chief Executive Officer of Tonix Pharmaceuticals. "As a monoclonal antibody, we believe TNX-4800 offers significant advantages over vaccines in development. Lyme disease vaccines that elicit antibodies to OspA currently in development take more than six months to offer protection and require complex immunization schedules. A previously approved anti-OspA vaccine was withdrawn due to poor uptake,6 potentially relating to its complex immunization schedule."

Dr. Lederman continued, "TNX-4800, targeting Borrelia burgdorferi, the serotype that causes 99.9% of Lyme disease in the U.S., is a single dose subcutaneous administration that potentially offers immunity within two days for a duration of approximately four months. We believe TNX-4800's differentiating characteristics could offer meaningful improvements for people seeking protection from Lyme disease. We believe the Phase 1 pharmacokinetic (PK) data support our plan to conduct an adaptive field study in the first half of 2027, pending FDA clearance, in which protection at four months is the primary endpoint, and protection at six months is a key secondary endpoint."

Phase 1 Results

"Our study demonstrated potentially protective blood levels of TNX-4800 at two days, with protective blood levels sustained for at least four months due to its extended half-life design," said Dr. Klempner. "Additionally, with its differentiated mechanism of action, TNX-4800 has the potential to provide passive immunity by directly supplying neutralizing antibodies, bypassing the need for a vaccine to induce a patient's immune system to generate its own antibodies, which can be associated with other issues. We look forward to further clinical investigation of TNX-4800 as we strive to overcome this major public health challenge."

The primary objective of the Phase 1 study was to evaluate the safety and tolerability of a SC injection of TNX-4800 when administered to healthy male and female subjects ages 19-65 years old. The secondary objective was to evaluate the PK of a SC dose of TNX-4800 when administered to healthy subjects. 44 subjects were enrolled, with 41 subjects completing the study. Subjects received a single SC administration of placebo or TNX-4800 at 0.5, 1.5, 5, or 10 mg/kg.

Results showed no significant clinical or laboratory safety signals, with most adverse events mild or moderate. Peak serum concentration (Cmax) increased by ~25-fold for a 20-times increase in dose. Serum TNX-4800 was measurable at earliest sampling time of two days, indicating rapid systemic absorption. TNX-4800 levels remained quantifiable for >200 days in 80% of subjects at the lowest dose, and for up to 350 days in the majority of subjects at higher doses (i.e., ≥ 1.5 mg/kg). The mean half-life ranged from 62-69 days across TNX-4800 cohorts. Serum concentrations were quantifiable for up to 12 months in most subjects.

  • Mean exposure for the 10 mg/kg cohort had <17% of the highest exposures in a nonclinical toxicology study.
  • The maximum half-life ranged from 81-104 days, with the 10mg/kg cohort at 97 days and 5mg/kg cohort at 87 days.
  • In the 5mg/kg dose cohort, mean serum TNX-4800 concentration was approximately 10 μg/ml at four months, which was approximately twice the minimum effective concentration, or MEC, calculated from in vitro bactericidal activity, and approximately the MEC from in vitro tick-feeding experiments. These data support Tonix's planned evaluation of protection at four months as the proposed primary endpoint.

     

Adaptive Phase 2 Field Study Plans

Pending FDA clearance, the Company plans to initiate an adaptive field study in the first half of 2027. TNX-4800 will be studied in a randomized, double-blind, placebo-controlled, adaptive Phase 2 field study to evaluate the efficacy of a single SC dose of TNX-4800, 350 mg, in preventing the first occurrence of confirmed Lyme disease during the primary efficacy surveillance period (Day 3 through Month 4 following administration). Based on the Phase 1 PK data, a fixed dose of 350 mg was selected for the Phase 2 field study, which is expected to provide exposures comparable to the 5 mg/kg dose evaluated in Phase 1. Participants will include adolescents and adults 16 to 65 years of age in Lyme-endemic areas in the U.S. The primary endpoint will be the prevention of Lyme disease at four months (comparison of TNX-4800 group and placebo group). A key secondary endpoint will be the prevention of Lyme disease at six months (comparison of TNX-4800 and placebo).

The Company expects to have GMP investigational product available for clinical testing in early 2027. Additionally, if necessary and pending FDA clearance, the Company plans to initiate a controlled human infection model (CHIM) study in 2028.