T cell-deficient mice such as nude mice are often used to generate
tumor xenograft for the development of
anticancer agents. However, the functionality of the other immune cells including macrophages, dendritic cells (DCs), and myeloid-derived suppressor cells (MDSCs) in the xenograft are largely unknown. Macrophages and dendritic cells (DCs) acquire functionally distinct properties in response to various environmental stimuli; the interaction of these cells with MDSCs in tumor microenvironments regulates
cancer progression. Nude mice are less likely to reject human
cancer cells because of major histocompatibility complex (MHC) mismatches. The tumor microenvironment in a xenograft, comprising human and mouse cells, exhibits more complex bidirectional signaling and function than that of allograft. Here, we evaluated the differences of myeloid cells between them. Plasma
interferon-γ and
interleukin-18 concentrations in the xenograft
tumor model after
lipopolysaccharide (LPS) administration were significantly higher than those in the allograft
tumor model. MHC class I, II, and CD80 expression levels were increased in CD11b⁺ and MDSC populations after LPS administration in the spleen of a xenograft
tumor model but not in that of an allograft
tumor model. Additionally, the number of CD80- and
mannose receptor C type 1 (MRC1)-expressing cells was decreased upon LPS administration in the
tumor of the xenograft
tumor. These results suggest that functions of macrophages and DCs are sustained in the xenograft, whereas their functions in response to LPS were suppressed in the allograft. The findings will encourage the consideration of the effects of myeloid cells in the xenograft for drug development.