Based on the observation that depletion of CD8+ T cells significantly increased replication of YK511 (Us3K220M) in the footpads of infected mice at 4 d post-infection, but had no effect on replication of YK513 (Us3-repair), we concluded that Us3 kinase activity resulted in increased viral replication in vivo by evasion of host CD8+ T cells. The gene discussed is CD8A; the disease is infection.