Deciphering neutrophil heterogeneity in human blood and tumors: Methods for isolating neutrophils and assessing their effect on T-cell proliferation.

Neutrophils were historically considered a homogenous population of cells with functions limited to innate immunity against external threats. However, with the rise of immunotherapy, recent works have shown that neutrophils are also important actors in immuno-oncology. In this context, neutrophils appear as a more heterogenous population of cells. However, many reported neutrophil subpopulations, or neutrophils with various transcriptional states, lack functional characterization to confirm their suspected roles. Thus, we believe that functional assays remain essential to define the role of neutrophils in cancer. In this chapter, we present a T-cell proliferation assay based on the use of allogeneic T-cells to assess the suppressive capabilities of neutrophils isolated from human blood or tumor samples. Allogeneic T-cells are isolated in large quantities from the blood of non-cancerous donors and frozen in aliquots to be used in several experiments. This reduces variability by excluding other cancer-derived factors, which would be present if autologous T-cell were used and allows to isolate the effect of neutrophils on T-cell proliferation. Thawed T-cells have poor proliferative capacities and to initiate proliferation they require co-culture with mature dendritic cells that we generate from monocytes isolated from the same blood sample. Initially developed for lung cancer patients, our method to isolate low-density neutrophils (LDN) and normal-density neutrophils (NDN) can be used with any patient and adapted to other kind of samples (e.g., ascites, urine, …).