High densities of PD-1⁺ T cells proximal to HRS cancer cells. mIF imaging was performed to quantify tumor-infiltrating T cells. Cells were phenotyped as PD-1⁻ CD4⁺ T cells, PD-1⁺ CD4⁺ T cells, PD-1⁻ CD8⁺ T cells, PD-1⁺ CD8⁺ T cells, or HRS cells. Representative images (scale bar, 50 μm) with displayed phenotypes are shown for a patient with CR (A) and a patient with PR (B). Cell counts within 50 μm of a HRS cell were quantified (C). Mean counts of total CD4⁺ and CD8⁺ T cells (D), PD-1⁻ and PD-1⁺ CD4⁺ T cells (E), and PD-1⁻ and PD-1⁺ CD8⁺ T cells (F) for each tissue assessed are shown. Mean counts within 50 μm of an HRS cell of PD-1⁺/⁻ CD4⁺ T cells (G) and PD-1⁺/⁻ CD8⁺ T cells (H) were also compared between patients with CR or PR/SD/PD. Similarly, CD4⁺ densities (I), percentage of CD4⁺ T cells expressing PD-1 (J), CD8⁺ densities (K), and percentage of CD8⁺ T cells expressing PD-1 (L) in patients with CR compared with those with PR/SD/PD. Statistics are generated using unpaired Student t tests.