Other studies have investigated the role of PD-L1/PD-1 axis in the impairment of T cells function during viral infection and the potential importance of rescuing these T cells to improve disease outcome, including Hepatitis C virus (HCV), human metapneumovirus (HMPV), influenza virus, simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) (Urbani et al, 2006; Erickson et al, 2012; McNally et al, 2013; Rutigliano et al, 2014; Velu et al, 2009; Palmer et al, 2013). Here, CD274 is linked to viral infectious disease.