Signaling state and abundance of circulating immune cell subpopulations determine cancer response to immunotherapy

We profiled 70,781 peripheral immune cells taken before, during, and after treatment with chemotherapy and immunotherapy of patients with advanced gastrointestinal cancers using single cell RNA sequencing. Prior to therapy, responders had a higher relative abundance of undifferentiated (naïve) CD4+ T cells, while non-responders had more differentiated CD4+ and CD8+ effector memory (EM) cells. Further, the EM cells present in responders were exhausted, suggesting prior recognition of tumor. Upon anti-PD-1 treatment, T cells of responders showed a shift towards increased differentiation and a higher relative abundance of cytotoxic CD8+ T cells than non-responders, with both populations and monocytes showing striking activation of interferon and MHC processing pathways. In addition to T cells, responders were enriched in classical monocytes prior to therapy, with a predominance of high TNF-α and growth factor activity associated with inhibition of NF-κB. The number and signaling activation states of T cells and classical monocytes, as well as their evolution soon after the initiation of therapy, may be predictive markers of immunotherapy response. Examination of GI patient PBMC single cell profiles at mutliple time points using the 10X platform