Tonix Pharmaceuticals Announces Publication in the Peer-Reviewed Journal of Virology Assessing Virulence of the 2022 Outbreak Strain of Mpox in New Animal Models

Tonix Pharmaceuticals Holding Corp. (Nasdaq: TNXP) (“Tonix” or the “Company”), a fully integrated, commercial-stage biotechnology company, today announced the publication of a paper, "Monkeypox virus clade IIb isolate exhibits reduced virulence relative to clade IIa isolates in multiple murine models," in the Journal of Virology, the peer-reviewed publication of the American Society for Microbiology (ASM). The research, conducted at Tonix, found new animal models for investigating mpox pathogenesis and demonstrated significant differences in virulence between the clade IIb circulating in the U.S. and the historic 2003 clade IIa. The manuscript can be accessed at:
https://doi.org/10.1128/jvi.00247-26.

“Global mpox outbreaks that have caused severe human disease continue to occur due to previously unrecognized subclades,” said Seth Lederman, M.D., Chief Executive Officer of Tonix Pharmaceuticals. “New approaches to understand and mitigate the spread of emerging mpox subclades are urgently needed. To examine the pathogenesis of emerging mpox clades, we identified three new murine models susceptible to mpox clade II infection, which revealed significant differences in virulence between clades. As Tonix investigates TNX-801 (live attenuated horsepox vaccine) for the prevention of mpox and smallpox, establishing additional foundational models are important to categorize and ultimately protect against the disease."

“The decreased virulence of clade IIb may have contributed to its ability to spread worldwide,” said Sina Bavari, Ph.D., Executive Vice President of Tonix and site head of Tonix’s Research and Development Center (RDC) in Frederick, Maryland. “Indolent subclinical infection is a risk factor for unintentional spread. Importantly, a deeper understanding of mpox virus (MPXV) pathogenesis will help guide the continued development and positioning of the TNX-801 vaccine platform, a vaccine candidate against mpox. Tonix is committed to advancing the understanding of emerging mpox disease and to developing TNX-801 platform as a potential vaccine candidate to address the continuing global threat posed by mpox.”

Led by Farooq Nasar, Ph.D., Director, Virology, Tonix utilized its state-of-the-art research laboratory capabilities, including a Biosafety Level 3 (BSL-3) lab and an Animal Biosafety Level 3 (ABSL-3) facility, at RDC which is close to the center of the U.S. biodefense research community.

Mpox is an emerging human disease caused by four distinct MPXV subclades (Ia, Ib, IIa, and IIb). Despite their genetic similarities, the case fatality rates differ considerably among the subclades: Ia (~11%), Ib and IIa (~4%), and IIb (~0.2%). Since 2022, multiple mpox outbreaks caused by the previously unrecognized Ib and IIb subclades have led the World Health Organization to declare two Public Health Emergencies of International Concern. Cases are currently increasing in multiple regions of the Americas. This unprecedented global spread and the marked differences in disease severity among MPXV subclades underscore the importance of investigating the pathogenesis of emerging MPXV variants. However, a critical limitation has been the lack of suitable small animal models.

This publication expands on the previously established CAST/EiJ mouse model by evaluating susceptibility to MPXV subclade IIa and IIb infection in both 7- to 8-week-old and 4- to 5-month-old mice. The demonstrated susceptibility of older CAST/EiJ mice to clade IIa infection highlights the utility of this model for evaluating long-term vaccine durability and protective efficacy. In addition, the study describes three novel C57BL/6 mouse models deficient in the interferon-α receptor, interferon-γ receptor, or both receptors for the study of MPXV infection. The study demonstrates that the emerging clade IIb isolate is up to 100,000-fold less virulent than clade IIa isolates. Collectively, these models provide valuable new tools for rapidly investigating the pathogenesis of emerging MPXV subclades and evaluating medical countermeasures, including vaccines.

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