While cancer immunotherapies including checkpoint blockade antibodies, adoptive T cell therapy, and even some vaccines have given rise to major clinical responses with durability in many cases, a subset of patients who initially respond subsequently develop secondary resistance to therapy.,Tumor-intrinsic mechanisms of acquired immunotherapy resistance are incompletely understood.,Baseline and treatment-resistant tumors underwent molecular analysis via transcriptional profiling or genomic sequencing for oncogenic alterations and histologic analysis for T cell infiltration to investigate mechanisms contributing to T cell exclusion and acquired resistance to immunotherapy.,We describe two patients with metastatic melanoma who initially showed a durable partial response to either a melanoma-peptide/interleukin-12 vaccine or combined anti-CTLA-4 + anti-PD-1 therapy, but subsequently developed new treatment-resistant metastases.,In the first case, the recurrent tumor showed new robust tumor expression of β-catenin, whereas in the second case genomic sequencing revealed acquired PTEN loss.,Both cases were associated with loss of T cell infiltration, and both pathways have been mechanistically linked to immune resistance preclinically.,Our results suggest that secondary resistance to immunotherapies can arise upon selection for new oncogenic variants that mediate T cell exclusion.,To identify the spectrum of underlying mechanisms of therapeutic resistance, similar evaluation for the emergence of tumor-intrinsic alterations in resistant lesions should be done prospectively at the time of relapse in a range of additional patients developing secondary resistance.
BRAFV600E-mutant malignant melanomas depend on RAF/MEK/ERK (MAPK) signaling for tumor cell growth1.,RAF and MEK inhibitors show remarkable clinical efficacy in BRAFV600E melanoma2, 3; however, resistance to these agents remains a formidable challenge2, 4.,Global characterization of resistance mechanisms may inform the development of more effective therapeutic combinations.,Here, we performed systematic gain-of-function resistance studies by expressing >15,500 genes individually in a BRAFV600E melanoma cell line treated with RAF, MEK, ERK, or combined RAF/MEK inhibitors.,These studies revealed a cyclic AMP-dependent melanocytic signaling network not previously associated with drug resistance, including G-protein coupled receptors, adenyl cyclase, protein kinase A and cAMP response element binding protein (CREB).,Preliminary analysis of biopsies from BRAFV600E melanoma patients revealed that phosphorylated (active) CREB was suppressed by RAF/MEK-inhibition but restored in relapsing tumors.,Expression of transcription factors activated downstream of MAP kinase and cAMP pathways also conferred resistance, including c-FOS, NR4A1, NR4A2 and MITF.,Combined treatment with MAP kinase pathway and histone deacetylase inhibitors suppressed MITF expression and cAMP-mediated resistance.,Collectively, these data suggest that oncogenic dysregulation of a melanocyte lineage dependency can cause resistance to RAF/MEK/ERK inhibition, which may be overcome by combining signaling- and chromatin-directed therapeutics.