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.
