CD66b⁺ monocytes represent a proinflammatory myeloid subpopulation in cancer

Myeloid-derived suppressor cells (MDSC) populate the peripheral blood and contribute to immune regulation in cancer. However, there is limited knowledge on the myeloid cell types with proinflammatory capacities that may serve as opponents of MDSC. In the circulation of cancer patients, a monocyte subpopulation was identified with a specific immunophenotype and transcriptomic signature. They were predominantly CD14⁺CD33^hiCD16^-/+HLA-DR^+/hi cells that typically expressed CD66b. In accordance with the transcriptomics data, NALP3, LOX-1 and PAI-1 levels were also significantly upregulated. The CD66b⁺ monocytes displayed high phagocytic activity, matrix adhesion and migration, and provided costimulation for T cell proliferation and IFN-γ secretion; thus, they did not suppress T cell responses. Irrespective of clinical stage, they were identified in various cancers. In conclusion, the CD66b⁺ monocytes represent a novel myeloid subpopulation which is devoid of immune regulatory influences of cancer and displays enhanced proinflammatory capacities.