Passive transfer of HSV-1 immune serum protected GVHD mice from HSV-1 mortality. GVHD mice were injected with hyperimmune HSV-1 serum or saline on the day following HSV-1 inoculation (2 × 10⁸ pfu). Survival was monitored daily. Survival of the two groups was significantly different (Wilcoxon rank sum test, P= .03).