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

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 a IFNG / TNF-high signature, which had a strong prognostic value for melanoma patients. Remarkably, clonotypes from tumors were found in patient skin and blood up to nine 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.