Characterization and Clinical Application of Human CD34 ⁺ Stem/Progenitor Cell Populations Mobilized into the Blood by Granulocyte Colony‐Stimulating Factor

Abstract

A phase I study was performed to determine the safety and tolerability of injecting autologous CD34؉ cells into five patients with liver insufficiency. The study was based on the hypothesis that the CD34 ؉ cell population in granulocyte colony-stimulating factor (G-CSF)-mobilized blood contains a subpopulation of cells with the potential for regenerating damaged tissue. We separated a candidate CD34؉ stem cell population from the majority of the CD34 ؉ cells (99%) by adherence to tissue culture plastic. The adherent and nonadherent CD34؉ cells were distinct in morphology, immunophenotype, and gene expression profile. Reverse transcription-polymerase chain reactionbased gene expression analysis indicated that the adherent CD34؉ cells had the potential to express determinants consistent with liver, pancreas, heart, muscle, and nerve cell differentiation as well as hematopoiesis. Overall, the characteristics of the adherent CD34 ؉ cells identify them as a separate putative stem/progenitor cell population. In culture, they produced a population of cells exhibiting diverse morphologies and expressing genes corresponding to multiple tissue types. Encouraged by this evidence that the CD34 ؉ cell population contains cells with the potential to form hepatocyte-like cells, we gave G-CSF to five patients with liver insufficiency to mobilize their stem cells for collection by leukapheresis. Between 1 ؋ 10 6 and 2 ؋ 10 8 CD34 ؉ cells were injected into the portal vein (three patients) or hepatic artery (two patients). No complications or specific side effects related to the procedure were observed. Three of the five patients showed improvement in serum bilirubin and four of five in serum albumin. These observations warrant further clinical trials.

Pluripotent plasticity of stem cells and liver repopulation

“…32 Studies on liver regeneration have led to the recognition of hepatic stem cells role in the healing process. 10,29 These cells of ''oval'' morphologic appearance are built up of a primitive structure, making them suitable for this task. Ductular proliferation originating from hepatic stem cells can mostly be recognized in three disease groups: liver regeneration following massive or sub-massive liver necrosis, ductular proliferation without liver insufficiency, and tumorous liver diseases.…”

“…28,65 In humans, fibrosis stage and oval cell numbers, as well as the number of intermediate hepatocyte-like cells, are strongly correlated. 9,10,26,27,35 However, cirrhosis is not required for oval cell accumulation in either species. Rather, as in mice, progenitor cell activation in human FLDs is associated with inhibited replication of mature hepatocytes.…”

“…79,80 A direct correlation between the oval cell response and the degree of hepatic inflammation suggests that inflammatory cytokines and the resultant oxidant stress play a role in the activation of human progenitor cells during chronic viral hepatitis. 9,10,[35][36][37] Although the expression of ATP-binding cassette proteins MRP-1, MRP-3, and MDR-1 is increased in the progenitor cell compartment in various human liver diseases, these transporters are known to be cytoprotective. 81 MRP-1 helps cells to secrete GSSG or the GSH conjugates of 4-hydroxynononeal, products of oxidative stress reactions.…”

“…82 Therefore, the phenotype of oval cells may convey a survival advantage that permits them to accumulate in conditions that severely damage more mature hepatocytes. 9,10,[35][36][37] This helps to explain the positive relationship between oval cells and accumulation or reductions in mature hepatocyte mass through stem hepatocyte-like cells way. In fact oxidant stress reduces the viability and expansion of mature hepatocytes, while sparing less mature hepatic progenitors.…”

“…[7][8][9] Bone marrow (BM) stem cells have recently been shown not to be a potential source of the hepatic oval cells; rather the source of oval cells and small hepatocytes in the injured liver are endogenous liver progenitors which do not arise through trans-differentiation from BM cells. [8][9][10] Both the rodent and human embryonic stem (ES) cell, BM hematopoietic stem cell (HSC), mesenchymal stem cell, umbilical cord blood cell, fetal liver progenitor cell, adult liver progenitor cell as well as the mature hepatocyte have been reported to be capable of self-renewal, giving rise to daughter hepatocytes both in vivo and in vitro. These cells can repopulate livers in animal models of liver injury and seemingly improve liver function.…”