mAbs and Ad-vectored IFN-α therapy rescue Ebola-infected nonhuman primates when administered after the detection of viremia and symptoms

ZMAb is a promising treatment against Ebola virus (EBOV) disease that has been shown to protect 50% (two of four) of nonhuman primates (NHPs) when administered 2 days post-infection (dpi). To extend the treatment window and improve protection, we combined ZMAb with adenovirus-vectored interferon-α (Ad-IFN) and evaluated efficacy in EBOV-infected NHPs. Seventy-five percent (three of four) and 100% (four of four) of cynomolgus and rhesus macaques survived, respectively, when treatment was initiated after detection of viremia at 3 dpi. Fifty percent (two of four) of the cynomolgus macaques survived when Ad-IFN was given at 1 dpi, followed by ZMAb starting at 4 dpi, after positive diagnosis. The treatment was able to suppress viremia reaching ∼10 ⁵ TCID₅₀ (median tissue culture infectious dose) per milliliter, leading to survival and robust specific immune responses. This study describes conditions capable of saving 100% of EBOV-infected NHPs when initiated after the presence of detectable viremia along with symptoms.