Correlative studies. (A) PD-L1 expression by immunohistochemistry in myeloma cells. Results are reported as percentage of myeloma cells showing membranous staining for PD-L1 (proportion score). Shown are BM samples with a proportion score of <1% (i), 1% to 49% (ii), and >50% (iii). The lower panels show corresponding MUM1 stain. PD-L1 stain is shown by the presence of brown chromogen, and the red color is MUM1 stain for myeloma cells. (B) CD3 and PD-1 expression by immunohistochemistry on T lymphocytes. CD3 staining (i) and PD-1 staining (ii). BM infiltrating T lymphocytes were graded as negative (<5% CD3, <1% PD-1) or positive (≥5% CD3, ≥1% PD-1). Original magnifications ×100 (Aii, upper panel; Aiii, lower panel; and Bi-ii), ×200 (Ai-ii, upper panels), and ×400 (Ai-ii, lower panels).