A latest review published by Zhao Haitao's team at Peking Union Medical College Hospital (PUMCH) provides the first systematic summary of the clinical application value of peripheral blood PD-1⁺ T cells as a liquid biopsy biomarker in solid tumors.

In oncology diagnosis and treatment, can a single tube of blood be used to assess treatment efficacy, predict survival, and anticipate adverse reactions? This is a prominent direction in the field of liquid biopsy. Recently, Zhao Haitao's team from the Department of Hepatobiliary Surgery at Peking Union Medical College Hospital published a landmark review in the journal International Immunopharmacology, providing the first systematic elucidation of the clinical significance and prognostic applications of peripheral blood PD-1⁺ T lymphocytes in liquid biopsy for solid tumors (the original review is available at the end of this article).

Why PD-1⁺ T Cells?

PD-1 (Programmed Cell Death Protein-1) is an inhibitory receptor expressed on the surface of T cells. Under sustained tumor antigen stimulation, T cells upregulate PD-1 expression and enter a state of "exhaustion," resulting in diminished anti-tumor capacity. Immune checkpoint inhibitors (such as anti-PD-1 antibodies) can block this pathway and restore T cell function.

More importantly, peripheral blood PD-1⁺ T cells share clonal overlap with tumor-infiltrating lymphocytes (TILs), enabling them to reflect the true status of the tumor immune microenvironment. Furthermore, the quantity of PD-1⁺ T cells can be used to assess the kinetics of tumor-specific CD8⁺ T cells, and since they can be obtained through a simple blood draw, they enable true "liquid biopsy."

Core Conclusions

·Peripheral blood PD-1⁺ T cells are a highly promising biomarker for liquid biopsy in solid tumors.

·They can be used for tumor staging assessment, efficacy prediction, and survival prognosis.

·Dynamic changes in PD-1⁺ T cells before and after immunotherapy are a core predictive indicator of treatment efficacy and prognosis.

·Flow cytometry-based detection of peripheral blood PD-1⁺ T cell subpopulations is feasible for clinical implementation.

PD-1⁺ T Cells for Tumor Staging Assessment

Multiple studies have found that the proportion of peripheral blood PD-1⁺ T cells in patients with various solid tumors is significantly higher than in healthy controls, supporting its utility in auxiliary early diagnosis and immune status assessment.

Application of PD-1⁺ T Cells in Chemotherapy, Radiotherapy, and Targeted Therapy

Elevated PD-1⁺ T cell levels after treatment generally indicate poor prognosis; post-treatment dynamic changes can guide the timing of combination immunotherapy.

Application of PD-1⁺ T Cells in Immunotherapy

Dynamic changes in PD-1⁺ T cells during immunotherapy serve as a core predictive indicator for treatment efficacy and prognosis.

Conclusion

This is the first review specifically focused on peripheral blood PD-1⁺ T cells as a liquid biopsy biomarker, covering all solid tumor types. It integrates evidence across multiple therapeutic domains including chemotherapy, radiotherapy, targeted therapy, and immunotherapy, providing clinicians with a non-invasive, dynamic, and reproducible monitoring tool.

References：

Piao M, Zhang N, Li J, Li C, Xun Z, Zhang L, Wang S, Sun B, Li S, Yang X, Yang X, Wang H, Zhao H. Peripheral blood PD-1⁺ T lymphocytes as biomarkers in liquid biopsies for solid tumors: Clinical significance and prognostic applications. Int Immunopharmacol. 2025 Feb 6;147:114052. doi: 10.1016/j.intimp.2025.114052. Epub 2025 Jan 11. PMID: 39799737.