CD8A and infection: Interestingly, PD-L1 blockade with anti-PD-L1 antibodies during the early-phase (on days 4–6) of systemic LCMV clone 13 infection also caused vascular permeability and ultimately fatal circulatory collapse (156), but anti-PD-L1 therapy on days 23–40 after infection restored the function of exhausted CD8+ T cells (proliferation, cytokine production, degranulation, and viral control) with or without CD4+ T cell depletion (25).