CD4 and central nervous system cancer: When screening cell lines widely-used as HIV-1 targets, we found that U87MG glioma cells (U87.CD4.CCR5 or U87.CD4.CXCR4) expressing HIV-1 receptor (CD4) and co-receptor (CCR5 or CXCR4) [27] express M-Sec at equivalent levels as monocyte-derived macrophages (Additional file 1: Fig. S1a) and form the F-actin+ long plasma membrane extensions that do not adhere to substrate (Additional file 1: Fig. S1b), hallmark features of TNTs [10–12].