Coregulation of [CD8.sup.+] T cell exhaustion by multiple inhibitory receptors during chronic viral infection

T cell exhaustion often occurs during chronic infection and prevents optimal viral control. The molecular pathways involved in T cell exhaustion remain poorly understood. Here we show that exhausted [CD8.sup.+] T cells are subject to complex layers of negative regulation resulting from the coexpression of multiple inhibitory receptors. Exhausted [CD8.sup.+] T cells expressed up to seven inhibitory receptors. Coexpression of multiple distinct inhibitory receptors was associated with greater T cell exhaustion and more severe infection. Regulation of T cell exhaustion by various inhibitory pathways was nonredundant, as blockade of the T cell inhibitory receptors PD-1 and LAG-3 simultaneously and synergistically improved T cell responses and diminished viral load in vivo. Thus, [CD8.sup.+] T cell responses during chronic viral infections are regulated by complex patterns of coexpressed inhibitory receptors.