How Myeloma Plays Hide and Seek With CAR T Cells

TOPLINE:

G protein-coupled receptor, class C, group 5, member D (GPRC5D) loss after chimeric antigen receptor (CAR) T-cell therapy in multiple myeloma (MM) occurs through biallelic genetic inactivation and hypermethylation-driven epigenetic silencing. Among 10 patients who relapsed, eight showed GPRC5D loss, while two had mixed expression.

METHODOLOGY:

• Researchers conducted whole-genome sequencing (WGS) and whole-genome bisulfite sequencing (WGBS) analysis on MM samples from 10 patients who relapsed after GPRC5D CAR T-cell therapy.
• Analysis included CD138+ MM cells isolated from bone marrow samples with purity exceeding 80%, with tumor samples sequenced at 100× coverage and matched normal samples at 30× coverage.
• Investigators performed targeted bisulfite sequencing to evaluate methylation status of GPRC5D regulatory regions across seven MM cell lines, with library construction and sequencing conducted by specialized institutes.
• Patient characteristics included median age of 57.5 years (range, 44-66 years), equal gender distribution, and 90% having high-risk cytogenetic abnormalities.

TAKEAWAY:

• Genetic alterations were identified in three cases: one with homozygous deletion in GPRC5D gene, another with biallelic loss in regulatory regions, and a third with homozygous deletions in both TNFRSF17 and GPRC5D after sequential anti-B-cell maturation antigen and anti-GPRC5D CAR T-cell therapies.
• Multiple hypermethylation sites were present in transcriptional regulatory elements of GPRC5D gene in five posttreatment MM samples, with no genetic changes detected at GPRC5D locus in seven cases.
• GPRC5D expression showed inverse correlation with methylation levels in regulatory regions of MM cell lines, with azacitidine treatment inducing GPRC5D messenger RNA and protein expression in hypermethylated MM cell lines.
• All 10 patients achieved complete response or better as best response with median time to best response of 2.5 months (range, 0.5-15.3 months), though median time to disease progression was 15.9 months (range, 3.0-26.5 months).

IN PRACTICE:

“Our findings highlight that biallelic genetic inactivation and hypermethylation-driven epigenetic silencing are key mechanisms contributing to GPRC5D loss and treatment resistance,” wrote the authors of the study.

SOURCE:

The study was led by Mingshan Niu, Blood Diseases Institute, Xuzhou Medical University in Xuzhou, China. It was published online in Blood.

LIMITATIONS:

According to the authors, the structural variant deletions on chromosomes may be missed by 100× WGS in patients with a clone size less than 20%. The limit of detection for quantitative polymerase chain reaction ranged from 16 to 50 copies per reaction, indicating sensitivity limitations of these detection methods. Additionally, genetic alterations in the GPRC5D locus could either be acquired after CAR T-cell therapy or selected from preexisting clones, necessitating more sensitive detection methods for dynamic monitoring.

DISCLOSURES:

The research received support from the National Natural Science Foundation of China (82270181) and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (21KJA320005). The authors reported having no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.