Monitoring PD-1 Phosphorylation to Evaluate PD-1 Signaling during Antitumor Immune Responses

  • Cancer Immunol Res. 2021 Dec;9(12):1465-1475. doi: 10.1158/2326-6066.CIR-21-0493.
Xia Bu  #  1 ,  Vikram R Juneja  #  2  3  4 ,  Carol G Reynolds  1 ,  Kathleen M Mahoney  1 ,  Melissa T Bu  1 ,  Kathleen A McGuire  3  4 ,  Seth Maleri  3  4 ,  Ping Hua  1 ,  Baogong Zhu  1 ,  Sarah R Klein  1 ,  Edward A Greenfield  1 ,  Philippe Armand  1 ,  Jerome Ritz  1 ,  Arlene H Sharpe  #  3  4 ,  Gordon J Freeman  #  5
Affiliations
  • 1. Department of Medical Oncology, Dana-Farber Cancer Institute, and Department of Medicine, Harvard Medical School, Boston, Massachusetts.
  • 2. Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts.
  • 3. Department of Immunology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts.
  • 4. Evergrande Center for Immunologic Diseases, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts.
  • 5. Department of Medical Oncology, Dana-Farber Cancer Institute, and Department of Medicine, Harvard Medical School, Boston, Massachusetts. [email protected].
  • # Contributed equally.
PMID: 34635486 DOI: 10.1158/2326-6066.CIR-21-0493
Abstract

PD-1 expression marks activated T cells susceptible to PD-1-mediated inhibition but not whether a PD-1-mediated signal is being delivered. Molecular predictors of response to PD-1 immune checkpoint blockade (ICB) are needed. We describe a monoclonal antibody (mAb) that detects PD-1 signaling through the detection of phosphorylation of the immunotyrosine switch motif (ITSM) in the intracellular tail of mouse and human PD-1 (phospho-PD-1). We showed PD-1+ tumor-infiltrating lymphocytes (TILs) in MC38 murine Tumors had high phosphorylated PD-1, particularly in PD-1+TIM-3+ TILs. Upon PD-1 blockade, PD-1 phosphorylation was decreased in CD8+ TILs. Phospho-PD-1 increased in T cells from healthy human donors after PD-1 engagement and decreased in patients with Hodgkin Lymphoma following ICB. These data demonstrate that phosphorylation of the ITSM motif of PD-1 marks dysfunctional T cells that may be rescued with PD-1 blockade. Detection of phospho-PD-1 in TILs is a potential biomarker for PD-1 immunotherapy responses.

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