TFPI improves LTR potential of HSPCs by inhibiting CD26 activity. (A) Progeny of 200 CD45.1 murine KLS cells from cultures with ST with or without TFPI was injected along with 1 × 10⁶ CD45.2 BM cells in lethally irradiated mice. Peripheral blood chimerism derived from CD45.1 cells in primary recipients was analyzed after 3 months (n = 12); 1 × 10⁶ BM cells from primary recipients were injected into lethally irradiated secondary recipient and peripheral blood chimerism from CD45.1 cells was analyzed after 3 months (n = 12). (B) Fifty thousand cells obtained from KLS cells cultured for 5 days with or without TFPI were allowed to migrate through a 3-μm pore-size membrane toward CXCL12 (n = 5). Percentage of cells migrated was assessed. (C) One hundred thousand cells obtained from KLS cells cultured for 5 days with or without TFPI were injected in lethally irradiated hosts (n = 8). The fraction of transplanted Colony forming unit cells that homed into the BM after 16 hours of transplantation was assessed. (D) CD26 activity in KLS cells cultured for 5 days were compared by CD26 enzyme assay (n = 8). Error bars represent SEM. (E) CD26 activity of human UCB derived lin⁻CD34⁺, cultured for 2 days with or without TFPI (n = 5). (F) One hundred thousand cells obtained from human lin⁻CD34⁺ cells cultured for 2 days with or without TFPI were allowed to migrate through a 3-μm pore-size membrane toward CXCL12 (n = 5). (G) One hundred thousand human lin⁻CD34⁺ cells cultured for 2 days with or without TFPI were transplanted in lethally irradiated Rag1^−/− preinjected with anti-NK1.1 antibodies. After 16 hours, mice were sacrificed and human HSPCs homed in the BM were quantified by flow cytometric detection of human CD45⁺lin⁻CD34⁺ cells. Total number of HSPCs homed was compared with the number of HSPCs injected and the proportion of homed cells was plotted for different conditions (n = 8, P = .039). Error bars represent SEM; *P < .05; ST, SCF TPO.