Heterogeneity in the expression of GPRC5D between patients with multiple myeloma.

Abstract

7511 Background: G-protein-coupled receptor class C group 5 member D (GPRC5D) is a protein inducible by all-trans retinoic acid with expression levels that vary depending on cellular differentiation. This protein receptor is targeted by several therapeutic modalities including chimeric-antigen receptor T-cell therapy (CAR-T), T-cell engagers (TCEs) and antibody-drug conjugates (ADCs). However, our understanding of GPRC5D expression levels in multiple myeloma cells and patient-to-patient heterogeneity remains limited. We investigated the expression levels of GPRC5D in the plasma cells of patients with multiple myeloma and compared its level of expression with those of CD38, CD138 and BCMA (TNFRSF17). Methods: Plasma cells from the bone marrow aspirates of 290 patients with multiple myeloma were enriched using CD138 column. RNA was extracted from the CD138 enriched population and sequenced by next generation sequencing (NGS) using a targeted RNA panel of 1600 genes. The RNA expression levels of various genes were quantified and expressed as transcript per million (TPM). Results: There was significant variation in the expression of GPRC5D between myeloma samples. The median and standard deviations for CD38, CD138, BCMA, and GPRC5D were 89 and 113, 69 and 134, 58 and 132, and 10 and 166, respectively. There was significant correlation (P < 0.00001) between CD38, CD138 and BCMA. However, there was no correlation between the levels of GPRC5D and CD38 (R=-0.05, P= 0.4), CD138 (R=0.3, P= 0.6 ) or BCMA (R=0.1, P=0.02). Ten samples (3%) had zero TPM expression of GPRC5D despite relatively high CD138 (between 33 TPM and 487 TPM). The ratio of GPRC5D: BCMA varied from 0 to 39 with one sample with an exceptionally high ratio of 459 due to very low BCMA with high CD138 due to anti-BCMA therapy. Conclusions: Analysis of these data suggests that unlike BCMA, there is a significant patient-to-patient heterogeneity in GPRC5D expression. GPRC5D expression levels show a wide variation with approximately 3% of patients showing an absence of GPRC5D expression. Clinical trials exploring anti-GPRC5D therapy should consider measuring GPRC5D expression levels and potentially explore other therapies that may induce its increased expression given our findings. RNA Expression Levels (TPM) Variable Median Lower Quartile Upper Quartile CD38 89 63 135 CD138 69 44 134 BCMA 58 35 106 GPRC5D 10 2 50 Spearman Correlations Pair of Variables R t(N-2) p-value CD38 & CD138 0.362809 6.60727 0.0000000 CD38 & BCMA 0.383742 7.05224 0.0000000 CD138 & BCMA 0.63282 13.86974 0.0000000 CD138 & GPRC5D 0.028007 0.47548 0.6348020 CD38 & GPRC5D -0.045081 -0.76583 0.4444070 BCMA & GPRC5D 0.138314 2.37004 0.0184450