OncoMimic peptide-based immunotherapy EO2401 induces shared T cell clusters in patients with adrenal cancer

Background Patients with advanced malignant adrenal tumors face poor prognoses with limited treatment options. Emerging data suggest that these rare tumors exhibit immunogenicity, potentially benefiting from intensified immunotherapy. Methods The SPENCER trial (NCT04187404) evaluates EO2401, an off-the-shelf in vivo peptide immunotherapy containing three synthetic HLA-A*02 restricted-peptides called OncoMimic and derived from human gut commensals that exhibit molecular mimicry to tumor-associated antigens (BIRC5, FOXM1, IL13RA2) combined with nivolumab in patients with locally advanced or metastatic adrenocortical carcinoma (ACC) or malignant pheochromocytoma/ paraganglioma (PPGL). We performed T cell receptor (TCR) repertoire sequencing to profile the TCR architecture in ACC and characterize vaccination imprints. Results Here we show that ACC patients are characterized by a restricted peripheral T cell richness. EO2401 does not expand highly shared TCR clones across patients but diversifies pre-existing T cell clusters. These clusters are not converging on known neoantigen-specific TCRs but exhibit generation probabilities characteristic of public clones some of which being shared across patients. Conclusions These findings suggest that EO2401-based peptide immunotherapy combined with checkpoint inhibition can broaden and activate public, pre-existing T cell clusters, potentially enhancing tumor-specific immune responses.