Sources of Human Hematopoietic Stem Cells for Transplantation–A Review

Using Eukaryotic Expression Systems to Generate Human α1,3-Fucosyltransferases That Effectively Create Selectin-Binding Glycans on Stem Cells

Recruitment of circulating cells toward target sites is primarily dependent on selectin/ligand adhesive interactions. Glycosyltransferases are involved in the creation of selectin ligands on proteins and lipids. α1,3-Fucosylation is imperative for the creation of selectin ligands, and a number of fucosyltransferases (FTs) can modify terminal lactosamines on cells to create these ligands. One FT, fucosyltransferase VI (FTVI), adds a fucose in an α1,3 configuration to N-acetylglucosamine to generate sialyl Lewis X (sLe^x) epitopes on proteins of live cells and enhances their ability to bind E-selectin. Although a number of recombinant human FTVIs have been purified, apart from limited commercial enzymes, they were not characterized for their activity on live cells. Here we focused on establishing a robust method for producing FTVI that is active on living cells (hematopoietic cells and mesenchymal stromal cells). To this end, we used two expression systems, Bombyx mori (silkworm) and Pichia pastoris (yeast), to produce significant amounts of N-terminally tagged FTVI and demonstrated that these enzymes have superior activity when compared to currently available commercial enzymes that are produced from various expression systems. Overall, we outline a scheme for obtaining large amounts of highly active FTVI that can be used for the application of FTVI in enhancing the engraftment of cells lacking the sLe^x epitopes.

Stem Cell Transplantation in the Fetus

BACKGROUND

In utero transplantation (IUT) of hematopoietic stem cells has the potential to treat a large number of hematologic and metabolic diseases amenable to partial replacement of the hematopoietic system.

METHODS

A review of the literature was conducted that focused on the clinical and experimental experience with IUT and, in this context, the development of the hematopoietic and immune systems.

RESULTS

Successful application of IUT has been limited to the treatment of various types of immunodeficiencies that affect lymphocyte development and function. Other congenital defects such as the thalassemias have not resulted in clinically significant engraftment. Recent efforts at understanding and overcoming the barriers to engraftment in the fetus have focused on providing a selective advantage to donor stem cells and fostering immune tolerance toward the donor cells. The critical cellular components of the graft that promote engraftment and tolerance induction are being evaluated in animal models. Improvements in engraftment have resulted from the inclusion of T cells and/or dendritic cells in the graft, as well as a strategy of combined prenatal and postnatal transplantation.

CONCLUSIONS

The advantages, necessity, and benefits of early treatment will continue to encourage development of IUT as a means to treat hematopoietic and other types of birth defects.

Supplementation of conventional freezing medium with a combination of catalase and trehalose results in better protection of surface molecules and functionality of hematopoietic cells

Our previous studies had shown that a combination of the bio-antioxidant catalase and the membrane stabilizer trehalose in the conventional freezing mixture affords better cryoprotection to hematopoietic cells as judged by clonogenic assays. In the present investigation, we extended these studies using several parameters like responsiveness to growth factors, expression of growth factor receptors, adhesion assays, adhesion molecule expression, and long-term culture-forming ability. Cells were frozen with (test cells) or without additives (control cells) in the conventional medium containing 10% dimethylsulfoxide (DMSO). Experiments were done on mononuclear cells (MNC) from cord blood/fetal liver hematopoietic cells (CB/FL) and CD34(+) cells isolated from frozen MNC. Our results showed that the responsiveness of test cells to the two early-acting cytokines, viz. interleukin-3 (IL-3) and stem cell factor (SCF) in CFU assays was better than control cells as seen by higher colony formation at limiting concentrations of these cytokines. We, therefore, analyzed the expression of these two growth factor receptors by flow cytometry. We found that in cryopreserved test MNC, as well as CD34(+) cells isolated from them, the expression of both cytokine receptors was two- to three-fold higher than control MNC and CD34(+) cells isolated from them. Adhesion assays carried out with CB/FL-derived CD34(+) cells and KG1a cells showed significantly higher adherence of test cells to M210B4 than respective control cells. Cryopreserved test MNC as well as CD34(+) cells isolated from them showed increased expression of adhesion molecules like CD43, CD44, CD49d, and CD49e. On isolated CD34(+) cells and KG1a cells, there was a two- to three-fold increase in a double-positive population expressing CD34/L-selectin in test cells as compared to control cells. Long-term cultures (LTC) were set up with frozen MNC as well as with CD34(+) cells. Clonogenic cells from LTC were enumerated at the end of the fifth week. There was a significantly increased formation of CFU from test cells than from control cells, indicating better preservation of early progenitors in test cells. Our results suggest that use of a combination of catalase and trehalose as a supplement in the conventional freezing medium results in better protection of growth factor receptors, adhesion molecules, and functionality of hematopoietic cells, yielding a better graft quality.

Cryopreservation of human hematopoietic cells with membrane stabilizers and bioantioxidants as additives in the conventional freezing medium

Cord blood (CB) and fetal liver (FL) cells are two alternative sources of human hematopoietic stem cells. Optimization of cryopreservation protocols is an important aspect in the banking of these tissues. Out of the multiple factors responsible for cryodamage of cells, membrane leakage and oxygen free-radical generation have been shown to contribute substantially toward the process. We have studied the effect of certain additives, like membrane stabilizers and bioantioxidants, to the conventional freezing medium on viability, nucleated cell recovery, and clonogenic potential of frozen cells. Our results show that trehalose, a membrane stabilizer, when used in combination with 10% dimethyl sulfoxide (DMSO) affords better cryoprotection as evidenced by significantly increased colony formation as compared to 10% DMSO alone. The cryoprotection afforded by trehalose persists at least for 1.5 years and there is no bias toward protection of a particular lineage. We also found that this increased cryoprotective effect of trehalose is seen both at -196 degrees C and -80 degrees C storage temperatures. Addition of taurine, an amino acid, another membrane stabilizer, and a natural cryoprotectant to the traditional freezing medium also results in beneficial effect. Of the three bioantioxidants tested, i.e., ascorbic acid, alpha-tocopherol acetate, and catalase, catalase shows maximum cryoprotective effect both at -196 degrees C and at -80 degrees C. Because the mode of cryoprotective action of catalase and trehalose are totally different, we tried a combination of these two compounds along with 10% DMSO. At -196 degrees C the protection afforded by the combination was significantly better than that afforded by individual components. At -80 degrees C, however, the combination did not give any added protection as compared to the individual single additives, although it was significantly better than 10% DMSO alone. These results indicate that the addition of membrane stabilizers and antioxidants to the conventional freezing medium may help to improve post thaw recovery of hematopoietic cells.

Treatment of HIV infection with cytoreductive agents

Advances in antiretroviral therapy have resulted in significant improvement in virological markers and clinical end points. However, studies have demonstrated that HIV can be recovered from patients in whom HIV RNA has been undetectable for prolonged periods of time, suggesting that the elimination half-life of latently infected cells may be longer than previously speculated. When used in the appropriate setting, cytoreductive agents may help expedite the elimination of the long-lived viral reservoir, and result in shorter administration of antiviral agents. In this article we discuss the potential use of cytoreductive agents as adjunctive therapy to antiretrovirals. In addition, we review those agents most likely to impact the viral reservoir and describe ongoing clinical trials designed to define the effect of cytoreductive therapy on those reservoirs. If a positive effect is demonstrated, these agents could ultimately be a powerful addition to the potent drugs currently being used to block HIV replication.