Increased frequency of OFD1-derived peptide-3-pentamer-positive CD8 cells and proliferation of PBMCs from MGUS patients in HLA-A2–restricted fashion. (A) When PBMCs from HLA-A2⁺ subjects were stained with OFD1-derived peptide-3 pentamers, the frequency of pentamer-positive cells in the CD8 population was increased in both MGUS and MM patients compared with isotype and healthy donor samples. (B) Composite results of pentamer staining in PBMCs were summarized from tested subjects (control = 4, MGUS = 6, and MM = 5). (C) PBMCs were isolated from HLA-A2⁺ subjects (control = 4, MGUS = 9, and MM = 5) and incubated with or without peptides (2 μg/mL) for 7 days. Proliferation was determined by thymidine incorporation. Results represent mean values with SEM compared with cells alone. *Statistical significance among the 3 groups (P < .05).