CXCL8 and neoplasm: Importantly, taking into account the species specificity of the antibodies included in the assay, the presence of some circulating human cytokines detected in the nonhumanized NSG mice (e.g., granulocyte-macrophage colony-stimulating factor [GM-CSF], interleukin [IL]-6, and IL-8) were considered to have originated from the PDX because their levels, which were among the highest of the panel, were also clearly detected in the tumor collected from nonhumanized NSG mice.