Stem cell and neutrophilic granulocyte kinetics

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, …).

Protracted exposure of C57BL/6 mice to 300 ppm benzene depresses B- and T-lymphocyte numbers and mitogen responses. Evidence for thymic and bone marrow proliferation in response to the exposures

Groups of C57BL/6J, male mice were exposed to 300 ppm benzene via inhalation for 115 exposures (6 h/day, 5 days/week), a regimen known to cause thymic lymphoma in these animals. The effects of these exposures on lymphoid parameters were determined by measuring the numbers of B- and T-lymphocytes and mitogen-induced proliferation of B- and T-lymphocytes in bone marrow, spleen, and thymus after 6, 30, and 115 exposures. The numbers of B-lymphocytes in bone marrow and spleen and the numbers of T-lymphocytes in thymus and spleen were found to be markedly reduced after all 3 periods. Mitogen-induced proliferation of bone marrow and splenic B-lymphocytes exhibited a progressive depression throughout the exposure period reaching a point of no observable response after 115 exposures. Splenic T-cell mitogen-induced proliferation was also markedly depressed throughout the exposures, but there was no evidence of a progressive decline in this response during the exposures. Bone marrow cellularity increased 3-fold and the numbers of thymic T-cells increased 15-fold in benzene-exposed mice between the 6th and 30th exposure. No corresponding increase in splenic cells was observed in benzene-exposed mice during this interval. The marked increases in the numbers of cells in bone marrow and thymus are interpreted as arising from compensatory proliferation of a subpopulation of cells in response to the exposures. The absence of increases in cell number in the spleen is interpreted as reflecting the lack of lymphoid restorative capacity in this organ. The marked increases of thymic and bone marrow cellularity are discussed relative to the known ability of this benzene exposure regimen to produce thymic lymphoma in these animals.

The importance of pluripotential stem cells in benzene toxicity

Several schedules of benzene exposure were evaluated for their effects on peripheral white blood cell counts, bone marrow cellularity and transplantable colony forming units (CFU-S) in male C57 Bl/6 mice. Intermittent exposure to 4000 ppm benzene in air produced leukopenia without altering the bone marrow cellularity. This same treatment, however, decreased the number of CFU-S to 30% of control values. Uninterrupted exposure to lower levels of benzene decreased peripheral cell counts within 24 h, and later decreased marrow cellularity. Exposure of a non-dividing population of stem cells (CFU-S) to benzene for up to 24 h produced no detectable effect on the subsequent development of spleen colonies, suggesting that the effect of benzene on CFU-S occurs only after peripheral cells are depleted. These findings indicate that benzene has affects on both differentiated cells and undifferentiated stem cells. An effect on the pluripotential stem cell is an important aspect of benzene toxicity, but not its exclusive or initial site of action.