MM-267 expression of CD229 on bone marrow cellular compartment and its relevance in multiple myeloma

Abstract

Context: CD229 has been claimed to be a useful plasma cell (PC) gating marker in MM using Multiparameter flow cytometry (MFC), however, studies are sparse and limited to a small cohort of patient samples enrolled in clinical trials. Objective: This study analyses the expression profile of CD229 on PC and its ability to delineate normal from aberrant PC (NPC vs APC). CD229-based PC gating was also evaluated with that of traditionally used markers (CD138 & CD38). Design: Prospective analysis of patients diagnosed with MM (per standard IMWG criteria). Setting: Tertiary care cancer centre. Patients: A total of 78 patients with a diagnosis of MM (29 treatment naïve & 59 on therapy). Interventions: Bone marrow aspirates from patients diagnosed with MM were collected in EDTA and processed for MFC using a single tube 14-color antibody panel was used which consisted of cy-kappa FITC, cy-lambda PE, CD45 Texas-red, CD19 PE-Cy5.5, CD56 PE-Cy7, CD117 APC, CD38 APC700, CD81 APC-H7, CD138 BV421, CD27 BV510, CD3 BV605, CD20 BV650, CD28 BV711, CD229 BV786. Main Outcome Measures: 1. Differential expression of CD229 on NPC & APC 2. Comparison of CD229-based PC gating with CD138 and CD38 Results: Expression of CD138, CD38, and CD229 was evaluated on PC, hematogones (HGs) and non-PCs. The expression of CD229 was homogenous on both PC and HG compartments as compared to CD38 and CD138. On comparing the expression patterns, it was found to be statistically significant between PC, HG, and non-PC for all three markers (p<0.001). aPC showed under-expression of CD38 and overexpression of and CD138 and CD229 as compared to nPC and was found to be statistically significant for CD138 and CD38 (CD138, p≥0.0001; CD38, p=0.0020) over CD229 (p=0.1134). Conclusions: This study shows that CD229 can be used for the identification of PCs and due to relatively homogenous expression; it can be used as a suitable marker for targeted therapies. However, CD229 is not a satisfactory marker for discriminating NPC from APC, thus limiting its ability as a useful marker of diagnostic relevance and residual disease assessment in MM cases.