SEMA4D and neoplasm: In vitro, studies have shown that the HN6 cell line associated with Sema4D plays a role in the upregulation of MDSC (24, 26) and that Sema4D inhibition in HN6 causes downregulation of extracellular matrix deposition by fibroblasts (11), suggesting HN6 cell line as an in vitro model mimicking the Sema4D-positive HIS-IE tumor cells.