Tumor cell density dependent IL-8 secretion induces the fluctuation of Tregs/CD8+ T cells infiltration in hepatocellular carcinoma: one prompt for the existence of density checkpoint

Abstract

Abstract Background Tumor cell density is a basic pathological feature of solid tumors. Chemotherapy, radiotherapy and targeted therapy reduce tumor cell density, while unrestricted tumor cell proliferation promotes this feature. The impact of tumor cells on the microenvironment during the process of tumor cell density from low to high is still unclear. In this study, we focused on the response mode of key immune cell subsets to tumor cell density in hepatocellular carcinoma (HCC). Methods We determined the density of tumor cells and immune cells in the same area by section staining. We identified mediator through PCR, Elisa, 3D culture, co culture, flow cytometry and lentivirus intervention. The mechanism of lactate promotion was verified by lactate test kit, bioinformatic methods, western blot and the above methods. The IL-8/DAPK1/lactate/Tregs axis was verified by the mouse liver cancer model. Tumor mutation burden was calculated from maftools in R. Results We found that tumor cell density induced fluctuation in Tregs/CD8+ T cells ratio by secreting IL-8, and IL-8 promoted Tregs infiltration through DAPK1/PK activity/lactate axis. Based on tumor ploidy and mutation burden data, we discussed the potential significance of immune fluctuation in the homeostasis of HCC mutation burden and proposed “density checkpoint” and “entropy model” to describe this phenomenon. Conclusion In summary, we report the infiltration mode of Tregs/CD8+ T cells in response to tumor cell density, and the mechanism and significance of this infiltrating mode in HCC. In addition, we provide new theoretical basis for IL-8 as a therapeutic target and the selection of immunotherapy window period in HCC.