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.
Epithelial-Mesenchymal Transition (EMT) is a critical step in the progression of cancer.,Malignant melanoma, a cancer developed from pigmented melanocytes, metastasizes through an EMT-like process.,Ten-eleven translocation (TET) enzymes, catalyzing the conversion of 5-methylcytosine (5mC) to 5-hydroxylmethylcytosine (5-hmC), are down regulated in melanoma.,However, their roles in the progression and the EMT-like process of melanoma are not fully understood.,Here we report that DNA methylation induced silencing of TET2 and TET3 are responsible for the EMT-like process and the metastasis of melanoma.,TET2 and TET3 are down regulated in the TGF-β1-induced EMT-like process, and the knocking down of TET2 or TET3 induced this EMT-like process.,A DNA demethylating agent antagonized the TGF-β-induced suppression of TET2 and TET3.,Furthermore, a ChIP analysis indicated that enhanced recruitment of DNMT3A (DNA Methyltransferase 3A) is the mechanism by which TGF-β induces the silencing of TET2 and TET3.,Finally, the overexpression of the TET2 C-terminal sequence partially rescues the TGF-β1-induced EMT-like process in vitro and inhibits tumor growth and metastasis in vivo.,Hence, our data suggest an epigenetic circuitry that mediates the EMT activated by TGF-β.,As an effector, DNMT3A senses the TGF-β signal and silences TET2 and TET3 promoters to induce the EMT-like process and metastasis in melanoma.