Tumour ERO1A instigates T cell dysfunction by transmission of endoplasmic reticulum stress.

e14533 Background: Infiltrated-excluded tumor microenvironment (TME) predicts poor prognoses in multiple malignancies. T cell dysfunction is a hallmark of immune exclusion in patients and correlates with response to immune checkpoint inhibitors (ICIs). However, strategies to classify TME based on T cell dysfunction for predicting response to ICIs are lacking. Methods: MC-38, LLC, and 4T1 tumours knocked out and restored for endoplasmic reticulum oxidoreductin-1α ( Ero1a) were engrafted subcutaneously into immunocompetent hosts. Anti-PD-1 antibody was injected intraperitoneally every three days. We used immunofluorescence staining and flow cytometry to characterize the intratumoral infiltrates. Coculturing of tumour cells with T cells, single-cell RNA-seq, and western blotting were utilized to unveil the underlying mechanisms. Multi-color immunohistochemistry was used to identify the expression of ERO1A and define TME in patient samples. Results: Here, we show that ERO1A, an oxidoreductase involved in endoplasmic reticulum stress (ER stress)-induced apoptosis, instigates an immune-exclusive TME by transmitting ER stress to T cells. In mouse models, knocking out of Ero1a in Ero1a-expressed tumours promotes the infiltration of CD8+ T cells and enhances responses to anti-PD-1 treatment. By contrast, ectopic expression of Ero1a enhances tolerance to ER stress in tumour cells by activating IRE1α-signaling. Additionally, ero1a promotes the transmission of ER stress to T cells and triggers CHOP-dependent apoptosis, resulting in an immune-exclusive TME. Elimination of ER stress status suppresses tumour growth in immunocompetent mice and promotes response to ICIs. In 37 patients with non-small cell lung cancer treated with neoadjuvant immunotherapy, the expression of ERO1A is negatively correlated with the abundance of tumour infiltrated lymphocytes ( P< 0.001) and responses to ICIs ( P< 0.001). Patients with low expression of ERO1A also exhibit a superior recurrence-free survival compared to those with high expression of ERO1A ( P= 0.039). Conclusions: Together, our findings identify a mechanism for immune-exclusive TME and suggest a potential immunotherapeutic target for terminating T cell dysfunction and apoptosis through eliminating transmissible ER stress.[Table: see text]