Introduction:
Head and neck squamous cell carcinoma is the sixth most common malignancy worldwide and immune cell escape plays a central role in tumor initiation and progression. Programmed cell death ligand 1 (PD-L1) is an important immunomodulatory protein which is expressed by several cell types and also many tumors. In addition, there is accumulating evidence that platelets can modulate lymphocyte function, thereby influencing their role in anti-tumor immunity and tumor progression.
Methods:
To unravel possible alterations of the expression of immunoregulatory proteins on peripheral blood cells, PD-L1 expression on PBL of cancer patients and healthy donors was analysed by flow cytometry (blood) and immunohistochemistry (cytospins).
Results:
First studies comparing blood of HNSCC patients and healthy donors revealed an increase in the percentage of PD-L1 expressing platelets in HNSCC patients. Furthermore, these platelets were found to form complexes with circulating CD4+ T cells in cancer patients. Immunohistochemistry showed an additional involvement of neutrophils that capture CD4 cells in neutrophil extracellular traps (NETs).
Conclusion:
PD-L1 expressing platelets seem to be involved in complex formation with neutrophils and T cells in HNSCC which results in an impaired antitumor function of the T-cells. Questions remain regarding the initiating player in the process of platelet-neutrophil-T-cell complex formation and which T-cell subpopulation is predominantly affected by agglutination. Understanding the relationship between PD-L1 expressing platelets and an impaired anti-tumor T-cell immunity might improve therapeutic options for HNSCC patients.
