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Pathway Signatures Derived from On-treatment Tumor Specimens Predict Response to Anti-PD1 Blockade in Metastatic Melanoma

ABSTRACT: Both genomic and transcriptomic signatures have been developed to predict responses of metastatic melanoma to immune checkpoint blockade (ICB) therapies; however, most of these signatures were derived from pre-treatment biopsy samples. Here, we developed pathway-based signatures that predict response of metastatic melanoma to anti-PD1-based therapies in four independent datasets with RNAseq and clinical response data available for both pre- and on-treatment metastatic melanomas. We first identified pathway signatures that were significantly enriched in tumor specimens from anti-PD1 responders (R) compared to non-responders (NR) at pre-treatment and on-treatment time points, respectively. We also identified pathway signatures that were differentially expressed in pre-treatment versus on-treatment samples derived from R. Finally, we interrogated the capacity of the two types of signatures in predicting response of metastatic melanoma to anti-PD1 therapies in comparison with existing gene expression signatures. And we also investigated the effect of biopsy sites at the same biopsy time point on predictive performance of response to anti-PD1 therapy. Overall, we demonstrate that pathway-based signatures derived from on-treatment tumor specimens are highly predictive of response to anti-PD1 blockade therapies in patients with metastatic melanoma.

ORGANISM(S): Homo sapiens

PROVIDER: GSE168204 | GEO | 2021/08/15

REPOSITORIES: GEO

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Project description:Although immune checkpoint blockade (CPB) leads to prolonged responses in 15-40% of patients with metastatic melanoma, treatment refractory disease and progression after initial response remain major causes of mortality. While predictors of response have been reported, the common mechanisms of both primary and acquired resistance are poorly understood. To identify mechanisms of resistance and examine the evolving landscape in response to CPB, we performed whole exome sequencing (WES), immunohistochemistry (IHC), and RNA-sequencing (RNAseq) of longitudinal tumor biopsies from 17 metastatic melanoma patients treated with various CPB therapies. We found no significant changes in both mutational and neoantigen loads over time between responders and nonresponders. However, we identified abnormalities in one gene, beta-2-microglobulin (B2M), an essential component of MHC Class I antigen presentation, that were present in samples during disease progression but not regression. In total, we identified B2M aberrations in 29.4% of patients, including multiple early frameshift mutations, loss of heterozygosity (LOH) overlapping B2M, and absence of tumor-specific B2M protein expression. Additional defects in the antigen presentation and IFNγ pathways were identified but were not restricted to progressing lesions in our cohort. In two independent cohorts of 105 and 38 melanoma patients treated with ipilimumab (anti-CTLA4) and pembrolizumab (anti-PD1) respectively, we found that B2M LOH was enriched 3-fold in nonresponders (~30%) vs. responders (~10%) and associated with poorer overall survival (log-rank p=0.01, p=0.006). Loss of both copies of B2M was found only in nonresponders. We also found evidence for association of LOH overlapping IFNGR1 with poorer overall survival exclusively in the anti-PD1 cohort. Thus, B2M loss is likely a common mechanism of primary and acquired resistance to therapies targeting CTLA4 or PD-1.

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Pathway Signatures Derived from On-treatment Tumor Specimens Predict Response to Anti-PD1 Blockade in Metastatic Melanoma

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