Resident and circulating memory T cells persist for years in melanoma patients with durable responses to immunotherapy

While T-cell responses to cancer immunotherapy have been avidly studied, long-lived memory has been poorly characterized. In a cohort of metastatic melanoma survivors with exceptional responses to immunotherapy, we probed memory CD8 + T-cell responses across tissues, and across several years. Single-cell RNA sequencing revealed three subsets of resident memory T (T RM ) cells shared between tumors and distant vitiligo-affected skin. Paired T-cell receptor sequencing further identified clonotypes in tumors that co-existed as T RM in skin and as effector memory T (T EM ) cells in blood. Clonotypes that dispersed throughout tumor, skin and blood preferentially expressed an IFNG / TNF -high signature, which had a strong prognostic value for patients with melanoma. Remarkably, clonotypes from tumors were found in patient skin and blood up to 9 years later, with skin maintaining the most focused tumor-associated clonal repertoire. These studies reveal that cancer survivors can maintain durable memory as functional, broadly distributed T RM and T EM compartments.