Clinical outcomes and correlative analyses in patients with smoldering myeloma treated with pembrolizumab. (A) Paraprotein 1 and 2 levels in the serum in the extraordinary responder (patient 3) at baseline and after start of pembrolizumab therapy. Arrows indicate day 1 of start of cycles 1, 2, 3, and 4 (C1, C2, C3, C4). Treatment was stopped after C3 due to transaminitis. (B) Immunohistochemistry for plasma cells was performed on bone marrow samples at baseline and after therapy with pembrolizumab using CD138 stain. Baseline sample showed 50% infiltration of plasma cells, and posttherapy sample showed 1% to 2% plasma cells, all of which were of normal phenotype by flow cytometry (data not shown). Original magnification ×5. (C) Best response during treatment period as determined by percent change in serum paraprotein or light chain (in light chain only patients) levels from baseline in all 13 patients. (D) Duration of response and/or clinical benefit in all 13 patients calculated from day 1 of last cycle of pembrolizumab. Number of months of ongoing response, SD, or progressive disease is shown for each patient. (E) Mean fluorescence intensity (MFI) values for expression of various immune stimulatory (CD137 and ICOS) and inhibitory (PD-1, TIM-3, CTLA-4, LAG-3, and BTLA) receptors on CD8⁺ effectors T cells in bone marrow samples available at baseline from 12 patients are shown as a heat map. (F) Fold change in MFI for the receptors on CD8⁺ effectors T cells in bone marrow samples from baseline to end of treatment period is shown as a heat map (N = 12 patients). (G) Correlation between IFN-γ gene signature in the CD138⁻ cells in the bone marrow samples at baseline and percent change in paraprotein level (or light chain in light chain–only patients) in serum with therapy. (H) Heat map showing GEP of a curated list of immune stimulatory and immune checkpoint genes in CD138⁻ (Neg) cells from bone marrow samples obtained from patients before (B) and/or after (A) treatment with pembrolizumab.