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Checkpoint blockade mediates a proliferative response of tumor-infiltrating CD8 + T lymphocytes (TILs). The origin of this response has remained elusive because chronic activation promotes terminal differentiation or exhaustion of tumor-specific T cells. Here we identified a subset of tumor-reactive TILs bearing hallmarks of exhausted cells and central memory cells, including expression of the checkpoint protein PD-1 and the transcription factor Tcf1. Tcf1 + PD-1 + TILs mediated the proliferative response to immunotherapy, generating both Tcf1 + PD-1 + and differentiated Tcf1 - PD-1 + cells. Ablation of Tcf1 + PD-1 + TILs restricted responses to immunotherapy. Tcf1 was not required for the generation of Tcf1 + PD-1 + TILs but was essential for the stem-like functions of these cells. Human TCF1 + PD-1 +  cells were detected among tumor-reactive CD8 + T cells in the blood of melanoma patients and among TILs of primary melanomas. Thus, immune checkpoint blockade relies not on reversal of T cell exhaustion programs, but on the proliferation of a stem-like TIL subset., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Host defense depends on orchestrated cell migration guided by chemokines that elicit selective but biased signaling pathways to control chemotaxis. Here, we showed that different inflammatory stimuli provoked oligomerization of the chemokine receptor CCR7, enabling human dendritic cells and T cell subpopulations to process guidance cues not only through classical G protein-dependent signaling but also by integrating an oligomer-dependent Src kinase signaling pathway. Efficient CCR7-driven migration depends on a hydrophobic oligomerization interface near the conserved NPXXY motif of G protein-coupled receptors as shown by mutagenesis screen and a CCR7-SNP demonstrating super-oligomer characteristics leading to enhanced Src activity and superior chemotaxis. Furthermore, Src phosphorylates oligomeric CCR7, thereby creating a docking site for SH2-domain-bearing signaling molecules. Finally, we identified CCL21-biased signaling that involved the phosphatase SHP2 to control efficient cell migration. Collectively, our data showed that CCR7 oligomers serve as molecular hubs regulating distinct signaling pathways., (Copyright © 2016 Elsevier Inc. All rights reserved.)