ERBB2 signaling drives immune cell evasion and resistance against immunotherapy in small cell lung cancer II

Small cell lung cancer (SCLC) represents ~15% of all lung cancers and is characterized by its highly aggressive phenotype and its dismal outcome. Though the addition of immune checkpoint blockade to carboplatin and etoposide treatment has improved outcome in SCLC patients, SCLC cells finally acquire the ability to evade immunosurveillance and resistance against immune checkpoint blockade. To elaborate molecular mechanisms that mediate SCLC immune evasion, we performed high dimensional profiling of human and murine SCLC specimens. We herein comprehensively analyzed matched human samples of primary and metastatic SCLC and found a loss of MHC-I in SCLC metastases indicating that MHC-I loss mediates SCLC immune evasion. Silencing MHC-I in SCLC cells drastically diminished immune cell infiltration and facilitated the formation of metastasis in mice by circumventing immune surveillance. Using mass spectrometry and phospho-tyrosine kinase analysis, we discovered that ERBB2 signaling suppresses MHC-I expression in SCLC cells and stimulates immune modulating transcripts. Mechanistically, genetic and/or pharmacologic blockade of the ERBB2 signaling axis was sufficient to induce MHC-I expression and to prevent immune evasion in autochthonous murine SCLC in a STING-dependent manner. Finally, we demonstrate that the ERBB2 signaling axis regulates MHC-I expression on SCLC cells and is critical in maintaining immune evasion in SCLC. Most strikingly, we here uncover synergistic treatment efficacy by combining ERBB2 inhibition with PD-1 blockade eliciting profound responses in preclinical SCLC models and circumventing MHC-I loss under immunotherapy, suggesting this combination for future clinical trials in patients with SCLC. Overall design: We used an autochthonous Rb1/Trp53-deleted mouse model to generate tumor-derived cell lines. Three cell lines were established from primary lung tumors of individual mice, and one from a liver metastasis of a separate mouse. All were cultured under identical conditions and subjected to bulk RNA sequencing to compare transcriptional profiles between primary and metastatic tumor-derived cells.