Analysis of mitochondrial mass, potential and polarisation between PD-1+CD127+ and PD-1+CD127- virus-specific CD8+ T cells in cHBV and cHCV infection revealed significantly reduced mitochondrial polarisation in the more exhausted PD-1+CD127- subset, independent of aetiology of viral infection (figure 3A–C). The gene discussed is PDCD1; the disease is viral infectious disease.