Abstract 3784: Intraoperative changes of low density granulocyte (LDG) in gastrointestinal cancer surgery

Abstract

Abstract Background: Low density granulocytes (LDG) have been shown to be increased in peripheral blood of autoimmune disease, severe sepsis and cancer. In this study, we examined the frequency and function of the LDG in patients who received abdominal surgery for gastrointestinal malignancy. Method: In 57 patients who received laparotomy due to the gastrointestinal cancer ( 5 esophageal, 25 gastric , 27 colorectal cancer), peripheral blood was collected before and after operative procedure in operation room. After Ficoll-Hypaque centrifugation, intermediate layer which consists mainly of mononuclear cells was collected and immunestained with mAbs to CD66b, CD45 as well as 7AAD and their expressions were examined with flow cytometer. CD66b(+) CD45(+) cells were defined as LDG and the ratios of LDG in total CD45(+) leukocytes were calculated in 7AAD(-) live cell fraction. Next, CD66b(+) LDG and CD66b(-) mononuclear cells were separated with MACS method, and LDG were cultured and examined for extracellular traps (NETs) formation in vitro. Finally, CD66b(-) mononuclear cells were cultured on anti-CD3 mAb coated plate with or without autologous LDG, and proliferation of T lymphocytes was examined with CFSE dilution method. Results: The ratio of the LDG is low (median= 1.14%, 0.62 ~1.66%, n=57) at a beginning of surgery. In contrast, the ratio was markedly increased (median= 8.10%, 5.91~10.3%, n=57, p<0.001) at the end of surgery. The ratio of postoperative LDG showed significant correlation with operation time and positive trend with intraoperative bleeding. The LDG showed relatively week expression of CD11b and CD66b, but highly expressed in IL8 receptor and CD62L, suggesting immature LDG. The short-term culture of the LDG produced massive SYTOX-positive web like stricture which was characteristic for NETs. The mixture of tumor cells on the LDG culture demonstrated that many tumor cells were trapped in the NETs within 5 min incubation and vigorously grew thereafter. Finally, addition of the LDG on mononuclear cell culture strongly suppressed the anti-CD3 stimulated T cell division. Conclusion: LDG with immature phenotype increase in circulating blood of the patients who underwent gastrointestinal cancer surgery, probably due to the surgical stress. The LDG produce NETs which may efficiently trap circulating tumor cells, and can inhibit T lymphocyte mediated-immune reaction. Thus, the LDG provide tumor permissive microenvironment in target organ and have supportive roles on the development of postoperative hematogenous metastasis in gastrointestinal cancer. Citation Format: Yuko Kumagai. Intraoperative changes of low density granulocyte (LDG) in gastrointestinal cancer surgery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3784.