SPHK1 and head and neck squamous cell carcinoma: Furthermore, when the HNSCC cell lines SAS and SCC15 with overexpression of SPHK1 were co-cultured with activated human T cells, knocking down MMP1 rescued the increased survival rate of HNSCC cells co-cultured with T cells induced by overexpression of SPHK1 (Figure 5G-H).