Partial T-cell responses to anti-PD-1 or anti-PD-L1 alone and evidence of a noninflamed TME in CLL. (A) Autologous T-cell killing function against patient CLL cells pulsed with superantigen (sAg) (target cells) (n = 10) as detected by cytotoxicity assays following treatment with isotype control antibody (Ab), anti-PD-1, or anti-PD-L1 blocking Abs. Data presented as mean ± standard error of the mean (SEM). Aged-matched healthy donor T cell activity against autologous B cells pulsed with sAg (target cells) was included as controls. Percentage positive PD-1⁺ cells (B) and PD-L1⁺ cells (C) on unstimulated or anti-CD3 + anti-CD28 stimulated patient T cells (CD4⁺, CD8⁺) (n = 19). PD-L1 expression on freshly isolated CD5⁺ CD19⁺ CLL cells is also shown in panel C. Representative multispectral immunofluorescence images of nonmalignant reactive (n = 5) or CLL/SLL (n = 34) lymph node formalin-fixed paraffin-embedded biopsy tissues for (D) PD-1 (white) and (E) PD-L1 (white) expression on T cells (CD4, red; CD8, green) and B cells (CD20, blue). Original magnification, ×20 medial optical section images (far left, scale bar = 100 μm), cropped images (middle panels, scale bars = 50 μm) and 3D volume rendered confocal images of intercellular PD-1⁺ or PD-L1⁺ T-cell interactions (far right) (cropped, ×20 images). **P < .01; ns, not significant using a repeated measures 1-way ANOVA with Tukey's multiple comparisons test (or an unpaired t test for comparing CLL T-cell activity with healthy donor T cells) (A) and Wilcoxon signed-rank tests for comparisons between unstimulated and stimulated T-cell subsets (B-C). Data presented as mean ± SEM.