Single Dose of Recombinant Chimeric Horsepox Virus (TNX-801) Vaccination Protects Macaques from Lethal Monkeypox Challenge

The ongoing global Monkeypox outbreak that started in the spring of 2022 has reinforced the importance of protecting the population using live virus vaccines based on the vaccinia virus (VACV). Smallpox also remains a biothreat and although some U.S. military personnel are immunized with VACV, safety concerns limit its use in other vulnerable groups. Consequently, there is a need for an effective and safer, single dose, live replicating vaccine against both viruses. One potential approach is to use the horsepox virus (HPXV) as a vaccine. Contemporary VACV shares a common ancestor with HPXV, which from the time of Edward Jenner and through the 19th century, was extensively used to vaccinate against smallpox. However, it is unknown if early HPXV-based vaccines exhibited different safety and efficacy profiles compared to modern VACV. A deeper understanding of HPXV as a vaccine platform may allow the construction of safer and more effective vaccines against the poxvirus family. In a proof-of-concept study, we vaccinated cynomolgus macaques with TNX-801, a recombinant chimeric horsepox virus (rcHPXV), and showed that the vaccine elicited protective immune responses against a lethal challenge with monkeypox virus (MPXV), strain Zaire. The vaccine was well tolerated and protected animals from the development of lesions and severe disease. These encouraging data support the further development of TNX-801.

The infectivity and host range of the ecotropic porcine endogenous retrovirus, PERV-C, is modulated by residues in the C-terminal region of its surface envelope protein

Endogenous retroviral genetic material serves as a reservoir for the generation of retroviral pathogens by recombination between activated endogenous or exogenous infectious agents. Some porcine tissues actively express infectious porcine endogenous retroviruses (PERVs). Of the three classes of PERV characterized to date, two, PERV-A and B, are capable of infecting human cells in vitro, whereas PERV-C cannot. Here, we demonstrate that the PERV-C envelope surface protein (SU) when disassociated from its C-terminus binds human cells. Further, we show that PERV-C binding to human cells is not inhibited in 293 cells productively infected with PERV-A, confirming that the molecule PERV-C interacts with on human cells is distinct from that used by PERV-A. Moreover, we demonstrate that the envelope region encompassing the proline-rich region is required for binding to cells in addition to the putative variable region A (VRA) and B (VRB). The region in the C-terminus of the SU that alters the binding and infectivity properties of PERV-C differs by only nine residues from the analogous region of PERV-A. Caution may be warranted even when a xenotransplantation product is from source pigs that do not express human-tropic viruses, as minimal mutations within PERV-C combined with selection in a human recipient could render PERV-C infectious in humans.

Selective cytotoxicity of lithium gamma-linolenic acid in human T cells chronically and productively infected with HIV

We sought to extend observations of lithium gamma-linolenic acid (LiGLA)-associated selective cytotoxicity in different models of chronic HIV infection in vitro. In our initial experiments, 8E5, 8E5L and A3.01 cells were allowed to proliferate in the presence of 0-20 microg/ml LiGLA for 4 days. Similarly, OM-10.1 cells (with or without prior stimulation with tumour necrosis factor-alpha (TNF-alpha)) were grown with 0-5 microg/ml LiGLA for 10 days. Significant cytotoxicity was observed in productively infected 8E5 cells (100% cell death by day 2 at the highest concentration) as compared with latently infected 8E5L cells (50% cell death on days 2-4) and uninfected A3.01 cells. No drug-induced viral stimulation was observed in surviving cells. In fact, a mild direct antiviral effect may be present, independent of cytotoxicity. Maximum cytotoxicity to OM-10.1 cells was only observed when active viral replication was induced by TNF-alpha. Our preliminary results are encouraging and suggest that LiGLA should be retained as a candidate antiretroviral agent. Further work is underway to identify the specific mechanism underlying our observations.