Poxvirus Vectors Activate Human NK and MAIT Cells in a Type I Interferon, IL-18, and Monocyte-Dependent Manner

Recombinant poxviruses have been extensively studied as vaccine vectors, yet the specific mechanisms by which they engage the immune system remain incompletely understood. ALVAC is a poxviral vector that was a component of the HIV vaccine used in the Thai RV144 trial, showing modest efficacy in reducing HIV acquisition. Here, we show that in vitro ALVAC-HIV infection of peripheral blood mononuclear cells (PBMCs) activates natural killer (NK) and mucosal-associated invariant T (MAIT) cells. This activation was partially dependent on monocytes, cGAS sensing, and production of IL-18 and type I IFN. Furthermore, ALVAC-HIV-mediated activation of NK and MAIT cells contributed to the activation of B cells. Modified vaccinia Ankara (MVA), another poxviral vector used for prevention of smallpox and mpox, similarly activated NK and MAIT cells. Overall, this suggests a conserved mechanism by which NK and MAIT cells could contribute to the immunogenicity of poxviral vectors.