Oncolytic bovine herpesvirus type 1 induces immune microenvironment remodeling and enhances treatment responses in...

Despite therapeutic advances, multiple myeloma (MM) remains incurable due to the development of drug resistance by malignant plasma cells (PC) and a severe immunosuppressive bone marrow (BM) microenvironment. Oncolytic virotherapy offers the dual benefit of tumor cell lysis and immune activation, but the efficacy of human viruses is often hampered by pre-existing antiviral immunity. Here, we demonstrate that bovine herpesvirus type 1 (BoHV-1), a virus that is non-pathogenic to humans, efficiently infected MM cells, inducing mitochondrial apoptosis and suppressing pro-survival programs, including MYC targets, oxidative phosphorylation, and the unfolded protein response. Infected tumor cells up-regulated NK-activating ligands and down-regulated MHC class I, enhancing susceptibility to NK-mediated cytotoxicity. In patient-derived BM mononuclear cells (BMMC), BoHV-1 selectively reduced malignant PC and immunosuppressive myeloid subsets, while sparing lymphoid populations and hematopoietic progenitors. The infection promoted activation of CD8⁺ T cells, natural killer cells, and mono/macrophages, driving a shift toward a pro-inflammatory M1-like polarization. Monocyte depletion in BMMC attenuated the BoHV-1 anti-MM effect, confirming their functional contribution. This pronounced immune remodeling was accompanied by an inflammatory cytokine storm dominated by type I/II interferons and key innate immune mediators. Co-treatment of BoHV-1 with either bortezomib or lenalidomide increased anti-MM cytotoxicity. Finally, BoHV-1 up-regulated CD38 on both MM cells and immune effectors, thereby increasing sensitivity to the anti-CD38 daratumumab. These findings establish BoHV-1 as a promising immunovirotherapy agent, effective as a single agent and in combination strategies, by coupling direct oncolysis with broad immune remodeling of the BM microenvironment.