S1PR1 and central nervous system cancer: Chongsathidkiet et al., identified that both glioblastoma patients as well as glioblastoma immune competent murine glioma models suffer from T cell lymphopenia, specifically CD4+ cells that likely contribute to the cold TME.80 The T cells were shown to be sequestered in the bone marrow due to loss of surface expression of the sphingosine 1 phosphate receptor 1 (S1PR1), required for T cells to travel between tissues.