Reply.

Abstract

Potential conflict of interest: Nothing to report. Author names in bold designate shared co‐first authorship. We read with great interest the Zou et al. correspondence and appreciate the important comments on our findings. In this study,1 we used a xenograft model for our investigation on the interactions between hepatocellular carcinoma (HCC) cells and tumor‐associated macrophages (TAMs). This model was established at our institute by Dr. Tang and provides a platform for research on HCC metastasis.2 Although BALB/c nude mice are immunodeficient and lack T cells, other immune cells, such as macrophages and neutrophils, are normal and functional. In the tumor microenvironment, a variety of nonmalignant stromal cells may interact with one another in many ways, which cannot all be investigated in one study. In our study, we emphasized cross‐talk between HCC cells and TAMs. However, the interactions between TAMs and T cells were not within the scope of the study. Furthermore, we confirmed the direct effect of human interleukin‐34 (IL‐34) on the proliferation and chemotactic migration of human macrophages through its receptor, CSF1R. Although the amino acid sequence of human IL‐34 shares only 68.2% homology with mouse IL‐34, animal studies revealed similar results as our in vitro experiments.1 We proposed that the IL‐34 secreted by human HCC cells can be recognized by mouse CSF1R on the cell surface of macrophages, to promote their proliferation and migration. Zou et al. also stated that colony‐stimulating factor 1 (CSF1) should be considered when studying the miR‐28‐5p‐IL‐34‐macrophage feedback loop in HCC cells. In our identification of target genes, alterations of miR‐28‐5p had no effect on expression of CSF1 by HCC cells, so we proposed that although the CSF1/macrophage axis may exist in the HCC microenvironment, the miR‐28‐5p‐IL‐34‐macrophage feedback loop in HCC cells is independent of CSF1. Macrophages in different tumor microenvironments have distinct roles,4 but they have the general characteristic of tumor promotion in HCC cells,5 which we confirmed in our study. The specific role played by TAMs in the HCC microenvironment will be a focus of our future studies.