Figure 2. Neutrophils can be reprogrammed in the tumor microenvironment to acquire features of PMN-MDSC: low density, increased LOX-1 expression, and T-cell suppressor function.

Ascites fluid supernatants (ASC) from patients with newly diagnosed metastatic ovarian cancer were used as a biologically important component of the TME. A) ASC exposure increased the proportion of low-density neutrophils (LDN). Representative Wright-Giemsa-stained slides show abundance of LDN in the PBMC monolayer following ASC exposure. Buffy coat cells from healthy donor blood were incubated in ASC or media for 1hr, then subjected to gradient centrifugation. The PBMC monolayer consisted of 34.5% vs. 10.5% LDN following exposure to ASC or media, respectively. Data representative of two independent experiments. B) ASC exposure increased LOX-1 expression on neutrophils. Healthy donor neutrophils (CD15+) were incubated in media, ASC or 20nM PMA (positive control) for 1.5 hours, then analyzed by flow cytometry. Representative gating shows effects of media, PMA, and ASC on LOX-1 expression. C) Healthy donor naïve, central memory, and effector memory T cells were purified, and incubated with autologous neutrophils (PMN), ASC, or ASC + PMN, and anti-CD3/CD28-stimulated T cell proliferation was assessed at 96h by thymidine incorporation. Data are from Singel et al.⁶⁶ and Emmons et al.⁶⁷.