Contributions
Abstract: S175
Type: Oral Presentation
Session title: Basic and translational myeloma research
Background
BCMA targeting CAR T-cells or T-cell engaging bispecific antibodies (TCE) show high response rates in relapsed/refractory (RR) multiple myeloma (MM). Beyond BCMA, a number of other plasma cell targets such as SLAMF7, FCRH5, and GPRC5D are currently under investigation with promising preliminary results. Yet, patients continue to relapse and no survival plateau after CAR T-cells or TCEs has been observed so far. Recently, we described the first tumor-intrinsic resistance mechanism to BCMA-directed CAR T-cell therapy, unraveling biallelic loss of the BCMA gene as the cause of antigen escape after anti-BCMA CAR T therapy. Whether this mechanism of resistance is also relevant for TCE therapy, is currently unknown.
Aims
(1) To elucidate the mechanism of resistance to BCMA-directed TCE treatment. (2) To analyze genomic alterations in genes encoding for plasma cell targets in MM patients prior to immunotherapy by WGS and RNA sequencing (RNAseq).
Methods
WGS was performed in 100 MM patients (50 newly diagnosed, 50 RR) with WGS libraries prepared from CD138 purified cells and 2x150bp paired-end sequences generated on NovaSeq6000 with 100x coverage. For RNAseq of 72 patients stranded RNA libraries were produced and 2x100bp paired-end reads were sequenced on NovaSeq6000 with a median of 64 million reads per sample. BCMA protein expression was determined by immunohistochemistry (AF193, R&D systems) on paraffin embedded bone marrow sections.
Results
We report on a RRMM patient who experienced homozygous BCMA gene deletion after relapse from CD3xBCMA TCE therapy. Initially, the patient responded well to TCE therapy and achieved a CR, but relapsed after 6 months of treatment. Retrospective immunohistochemistry on bio-banked trephine biopsies showed strong and consistent BCMA expression prior to TCE therapy but a complete loss of BCMA expression at relapse. Without knowing about BCMA loss at relapse at that time, belantamab mafodotin was administered, to which the patient was primary refractory. Together, irreversible antigen loss and failure of subsequent BCMA-directed therapy, highlights targeted immunotherapies to present an evolutionary bottleneck in MM progression.
To further explore the relevance of this resistance mechanism, we screened for genomic alterations in BCMA and other immunotherapy targets. Indeed, we found heterozygous deletions in GPRC5D (15%), CD38 (10%), SDC1 (5%), TNFRSF17 (4%) and NCAM1 (3%). Overall, heterozygous deletions occurred in 30% of patients, and some patients showed deletions in up to three different immunotarget genes. As expected, we observed a clear trend for more deletions in pretreated patients. Notably, single nucleotide variants (SNV) in genes encoding for immune targets were only found at low frequency. Gains, heterozygous deletions, and SNV in genes encoding for immunotherapy targets did not result in significant changes of gene expression by transcriptome analysis in 72 patients, suggesting that expression of these genes is not solely regulated by their copy number and that antigen loss requires a biallelic event.
Conclusion
(1) Biallelic BCMA gene deletion may be a key immune-evasion mechanism to BCMA targeting T-cell therapies. (2) This mechanism of resistance to immunotherapies may affect alternative antigens as we detected genomic vulnerability in their encoding genes in a significant number of treatment naïve patients. (3) Combination of different immunotargets, e.g. multi-specific CAR T-cells, might be an approach to overcome drug resistance caused by loss of a single antigen.
Keyword(s): Bispecific, Immune therapy, Multiple myeloma, Resistance
Abstract: S175
Type: Oral Presentation
Session title: Basic and translational myeloma research
Background
BCMA targeting CAR T-cells or T-cell engaging bispecific antibodies (TCE) show high response rates in relapsed/refractory (RR) multiple myeloma (MM). Beyond BCMA, a number of other plasma cell targets such as SLAMF7, FCRH5, and GPRC5D are currently under investigation with promising preliminary results. Yet, patients continue to relapse and no survival plateau after CAR T-cells or TCEs has been observed so far. Recently, we described the first tumor-intrinsic resistance mechanism to BCMA-directed CAR T-cell therapy, unraveling biallelic loss of the BCMA gene as the cause of antigen escape after anti-BCMA CAR T therapy. Whether this mechanism of resistance is also relevant for TCE therapy, is currently unknown.
Aims
(1) To elucidate the mechanism of resistance to BCMA-directed TCE treatment. (2) To analyze genomic alterations in genes encoding for plasma cell targets in MM patients prior to immunotherapy by WGS and RNA sequencing (RNAseq).
Methods
WGS was performed in 100 MM patients (50 newly diagnosed, 50 RR) with WGS libraries prepared from CD138 purified cells and 2x150bp paired-end sequences generated on NovaSeq6000 with 100x coverage. For RNAseq of 72 patients stranded RNA libraries were produced and 2x100bp paired-end reads were sequenced on NovaSeq6000 with a median of 64 million reads per sample. BCMA protein expression was determined by immunohistochemistry (AF193, R&D systems) on paraffin embedded bone marrow sections.
Results
We report on a RRMM patient who experienced homozygous BCMA gene deletion after relapse from CD3xBCMA TCE therapy. Initially, the patient responded well to TCE therapy and achieved a CR, but relapsed after 6 months of treatment. Retrospective immunohistochemistry on bio-banked trephine biopsies showed strong and consistent BCMA expression prior to TCE therapy but a complete loss of BCMA expression at relapse. Without knowing about BCMA loss at relapse at that time, belantamab mafodotin was administered, to which the patient was primary refractory. Together, irreversible antigen loss and failure of subsequent BCMA-directed therapy, highlights targeted immunotherapies to present an evolutionary bottleneck in MM progression.
To further explore the relevance of this resistance mechanism, we screened for genomic alterations in BCMA and other immunotherapy targets. Indeed, we found heterozygous deletions in GPRC5D (15%), CD38 (10%), SDC1 (5%), TNFRSF17 (4%) and NCAM1 (3%). Overall, heterozygous deletions occurred in 30% of patients, and some patients showed deletions in up to three different immunotarget genes. As expected, we observed a clear trend for more deletions in pretreated patients. Notably, single nucleotide variants (SNV) in genes encoding for immune targets were only found at low frequency. Gains, heterozygous deletions, and SNV in genes encoding for immunotherapy targets did not result in significant changes of gene expression by transcriptome analysis in 72 patients, suggesting that expression of these genes is not solely regulated by their copy number and that antigen loss requires a biallelic event.
Conclusion
(1) Biallelic BCMA gene deletion may be a key immune-evasion mechanism to BCMA targeting T-cell therapies. (2) This mechanism of resistance to immunotherapies may affect alternative antigens as we detected genomic vulnerability in their encoding genes in a significant number of treatment naïve patients. (3) Combination of different immunotargets, e.g. multi-specific CAR T-cells, might be an approach to overcome drug resistance caused by loss of a single antigen.
Keyword(s): Bispecific, Immune therapy, Multiple myeloma, Resistance