Normal HSPC function is MCT4 independent but MCT1 indispensable. (A) Normal CD45.1 LKS was infected with MCT4/MCT1 shRNA or scrambled shRNA and transplanted into primary recipient mice (n = 8-9) with CD45.2 carrier WBM. Reconstituted CD45.1 and CD45.2 white blood cells (WBCs) and myeloid, B, and Tcells were examined every 4 weeks posttransplantation until week 16, and percentage of CD45.1 chimerism was evaluated (combined data of 2 individual shRNA sequences). (B) At week 16 posttransplantation, mouse BM was harvested. Different HSPCs in BM were examined by FACS. (C) WBM from primary transplantation was injected into secondary recipient mice. WBCs and myeloid, B, and T cells were traced for 16 weeks (n = 7-8). (D) HSPCs in BM were harvested and examined at week 16. (E) pHi analysis in CB CD34⁺ cells upon MCT1 or MCT4 KD (n = 4). (F) In vitro BrdU incorporation assay in CB CD34⁺ cells upon MCT1 or MCT4 KD (n = 4). (G) Serial in vitro colony-forming assay of human CB CD34⁺ cells with MCT4 KD (n = 3; triplicate wells for each experiment). (H) In vitro glucose uptake in CB CD34⁺ cells with MCT1 or MCT4 KD (n = 4). (I) In vitro intracellular metabolite profiling by LC-MS showing the relative levels of glycolytic, PPP, and TCA metabolites and nucleotides of MCT4 KD CB CD34⁺ cells in 20% O₂ (n = 3). (J-K) In vitro pHi (J) and in vitro BrdU incorporation assay (K) of normal LKS with MCT1 or MCT4 KD (n = 3). (l) In vitro glucose uptake of normal GMP with MCT1 or MCT4 KD (n = 3). (M) Serial in vitro colony-forming assay of human CB CD34⁺ cells with MCT1 KD (n = 3; triplicate wells for each experiment). (N) Growth of MLL-AF9 AML with KO of different pH regulators in vitro by CRISPR-Cas9 (averaged growth from 3-4 individual gRNA sequences; 4 replicates of experiment). (O) Western blot of MCT1 protein in MLL-AF9 AML with MCT4 KO in vitro. *P < .05, **P < .01, ***P < .001. CFU, colony-forming unit; ns, not significant.