CD4 and tuberculosis: To determine whether blockade of the PD-1/PD-L1 signaling pathway in vitro could restore or augment the proliferative capacity of Mtb-specific CD4 T cells in patients with smear+ TB, PBMC were labeled with the cytosolic dye Oregon Green (OG) and cultured for 6 days with Mtb antigens in the presence of an anti-PD-L1 blocking Ab or an isotype-matched control Ab (Figure 6A).