Tonix advances development of TNX-801 to prevent mpox infection

Tonix Pharmaceuticals Holding Corp., a fully-integrated biopharmaceutical company with marketed products and a pipeline of development candidates, has reiterated its commitment to advance development of its live attenuated virus vaccine, TNX-801 , for preventing mpox and other infectious diseases. On August 14, 2024, the World Health Organization (WHO) determined that the upsurge of mpox in a growing number of countries in Africa constitutes a public health emergency of international concern, the second such declaration in the past two years called in response to an mpox outbreak. The current outbreak was caused by Clade 1 monkeypox virus, while the 2022 outbreak was Clade 2 monkeypox virus.

TNX-801 is a live replicating attenuated vaccine candidate based on horsepox that is believed to provide immune protection with better tolerability than 20th century vaccinia viruses. The same vaccine platform upon which TNX-801 is based was selected by the US National Institutes of Health (NIH) for Project NextGen for an engineered version that expresses the spike protein of SARS-CoV-2.

As previously disclosed, TNX-801 protected animals against lethal challenge with intratracheal Clade 1 monkeypox virus. After a single-dose vaccination, TNX-801 prevented clinical disease and lesions and also decreased shedding in the mouth and lungs of non-human primates. These findings are consistent with mucosal immunity and suggest the ability to block forward transmission, similar to Dr. Edward Jenner’s vaccinia vaccine, which eradicated smallpox and kept mpox out of the human population.

“The recent WHO declaration underscores the urgent need for additional treatments to stop these outbreaks and save lives,” said Seth Lederman, M.D., chief executive officer of Tonix. “We are motivated to advance development for our mpox vaccine with urgency given the global public health emergency. Preclinical trials demonstrate that TNX-801 combines immune protection with improved tolerability and safety compared to other vaccines based on orthopoxviruses, and is administered with a single dose which has advantages over two-dose regimens. The durability of protection from 19th century live virus vaccinia vaccines suggests that our attenuated TNX-801 will not require multiple repeated doses at six-month intervals like mRNA vaccines. Also, the stability of live virus vaccines eliminates the need for ultra-cold storage which complicates the widespread use of mRNA vaccines in Africa, where they are needed most right now.”

The global mpox outbreak, which commenced in 2022, has affected over 90,000 persons in countries where mpox had previously not been endemic, including Europe and the US. The spread of Clade IIb strain mpox in 2022 underscores the pandemic potential of mpox. Unlike Clade IIb mpox, the Clade I strain of mpox appears to be spreading to countries neighboring the Democratic Republic of the Congo. Clade I mpox is typically associated with approximately 20 times the case fatality rates than Clade IIb mpox in Africa. According to the US Centers for Disease Control and Prevention (CDC), and other experts, there is a significant risk that the deadlier Clade I strain may appear in the US.

Further, the Bipartisan Commission on Biodefense recently highlighted the renewed dual threats of a more virulent mpox epidemic and a smallpox re-introduction from lab accidents or bad actors. The National Academies of Science, in its review of smallpox preparedness, highlighted the need for new single dose vaccines, like TNX-801 against smallpox.

TNX-801 (recombinant horsepox virus) is a live virus vaccine for percutaneous administration that is being developed to target smallpox, and mpox (monkeypox). TNX-801 is also the basis of the RPV platform based on a horsepox vector, which is being adapted as a Covid-19 vaccine, term TNX-1800. Horsepox is a live replicating, attenuated virus that has been shown to be >1,000-fold more attenuated than 20th century vaccinia (VACV) strains in immunocompromised mice. Horsepox and the vaccinia vaccine viruses are closely related orthopoxviruses that are believed to share a common ancestor. Molecular analysis shows that horsepox is closer than modern vaccinia vaccines in DNA sequence to the vaccine discovered and disseminated by Dr. Edward Jenner. Live replicating orthopoxviruses, like vaccinia or horsepox, can be engineered to express foreign genes and have been explored as platforms for vaccine development because they possess; (1) large packaging capacity for exogenous DNA inserts, (2) precise virus-specific control of exogenous gene insert expression, (3) lack of persistence or genomic integration in the host, (4) strong immunogenicity as a vaccine, (5) ability to rapidly generate vector/insert constructs, (6) readily manufacturable at scale, and (7) ability to provide direct antigen presentation. Relative to vaccinia, horsepox has substantially decreased virulence in mice. The current formulation is a frozen liquid, but we believe that future lyophilized versions can be stored and shipped at standard refrigeration. Horsepox-based vaccines are designed to be single dose, vial-sparing vaccines that can be administered without sterile injection, manufactured using conventional cell culture systems with the potential for mass scale production, and packaged in multi-dose vials.