Abstract 4602: GPRC5D alterations impact CD38 expression and provide proliferative advantage in multiple myeloma
Authors: Umair Munawar, Seungbin Han, Elena Gerhard-Hartmann, Cornelia Vogt, Silvia Nerreter, Shilpa Kurian, Thomas Nerreter, Johanna Thurner, Julia Weingart, Patrick Eiring, Xiang Zhou, Nina Rein, Johanna Lehmann, Max Koeppel, Andreas Rosenwald, Ondrej Slaby, Michael Hudecek, Hermann Einsele, Leo Rasche, Markus Sauer, Johannes Waldschmidt, Bernhard Kuester, Klaus Martin Kortuem
Journal: Cancer Research (2025)

Abstract Background: The treatment landscape in Multiple Myeloma (MM) shifts towards immunotherapies with the G protein-coupled receptor class C group 5 member D (GPRC5D) as a promising antigen for T cell engagers (TCE) and investigational CART constructs. Monoallelic genetic alterations in GPRC5D are present in up to 15% of MM patients prior GPRC5D directed therapy. The incidence of acquired biallelic GPRC5D events following treatment has to be determined. Recently, biallelic loss of GPRC5D was identified as the underlying mechanism for acquired resistance toward talquetamab, the first approved GPRC5D directed TCE. In this study, we modeled GPRC5D genetic alterations and studied their impact on the biology of the disease and responsiveness to anti-MM immunotherapies. Methods: Mono- and bi-allelic GPRC5D knock-out (KO) cell models were created using the MM cell line OPM-2 via CRISPR-Cas9 technology. Surface receptor distribution and epitope quantification of common immunotherapeutic targets was performed via Direct stochastic optical reconstruction microscopy (dSTORM). MM cells were engineered to perform cytotoxicity, functional and clonal competition assays using immunotherapeutic agents in presence of effector T cells from healthy donors. Results: dSTORM revealed a 2-fold reduction in GPRC5D surface expression on GPRC5DWt/Del (0, 16±0, 02 clusters/µm2) vs. WT cells (0, 32±0, 10 clusters/µm2). GPRC5DDel/Del had barely detectable GPRC5D expression with 0, 03±0, 07 clusters/µm2. CD38 expression was unexpectedly diminished in GPRC5D Wt/Del (5, 74±0.43 CD38 clusters/µm2) compared to WT parental cells (9, 59±0, 71 clusters/µm2, p=0.04), with an even greater reduction detected in GPRC5D Del/Del clones (2, 22±0.203 clusters/µm2, p&amp;lt;0, 0001). GPRC5D-altered cells with reduced CD38 expression depicted a significant resistance towards CD38 targeting antibodies (8.01% specific lysis in GPRC5DWt/Del cells, 6.38 % in GPRC5DDel/Del compared to 31.50% in WT cells, p &amp;lt;0.0001). GPRC5DWt/Delcells depicted a significant resistance towards Talquetamab. Additionally, in presence of talquetamab GPRC5DDel/Del models showed a proliferation gain (2 fold, p&amp;lt;0, 0001). High content chemokine profiling using the scioCyto microarray platform revealed significantly altered chemokine profiles, including growth and proliferation promoting cytokines. In addition, upregulation of MAPK and PI3K pathways involved in growth proliferation and downregulation of the RAP1 signaling pathway involved in cell adhesion was observed in GPRC5D altered cells via bulk RNA seq. To decipher potential mechanism of growth induction and a link to CD38, scRNA seq and phospho-proteomic based analysis are ongoing. Conclusion: Our work suggest a link between CD38 and GPRC5D in MM and supports an anti-proliferative function of GPRC5D suggesting treatment over progression with talquetamab may favor tumor growth in GPRC5D deficient cells. Citation Format: Umair Munawar, Seungbin Han, Elena Gerhard-Hartmann, Cornelia Vogt, Silvia Nerreter, Shilpa Kurian, Thomas Nerreter, Johanna Thurner, Julia Weingart, Patrick Eiring, Xiang Zhou, Nina Rein, Johanna Lehmann, Max Koeppel, Andreas Rosenwald, Ondrej Slaby, Michael Hudecek, Hermann Einsele, Leo Rasche, Markus Sauer, Johannes Waldschmidt, Bernhard Kuester, Klaus Martin Kortuem. GPRC5D alterations impact CD38 expression and provide proliferative advantage in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4602.