PTEN and acute lymphoblastic leukemia: Leucine is preferentially transported by System L amino acid transporters which are heterodimers consisting of CD98 and either SLC7A5 (LAT1), SLC7A8 (LAT2); SLC7A7 (y+LAT1) or SLC7A6 (y+LAT2).42 Mass spectrometry proteomic analysis of primary ex vivo PTEN−/− T-ALL cells from three tumor-bearing Ptenfl/flLck-Cre+ mice identified that these cells expressed CD98, SLC7A5 and SLC7A6, with SLC7A5 always more abundant than SLC7A6 (Figure 4b).