CD8A and infection: However, infection with high pathological influenza strain, ΔVn1203, which is a recombinant virus with the six internal PR8 genes and surface H5N1 proteins from A/Vietnam/1203/04, similarly induced PD-1high-expressing CD8+ T cells that compromised the protective immunity against influenza clearance, but the in vivo blockade of PD-L1 expression did not rejuvenate or completely rescue the polyfunctionality of the T cells, though the numbers of CD8+ T cells were increased with fairly reduced viral tires [145].