Combination small molecule PPT1 mimetic and CNS-directed gene therapy as a treatment for infantile neuronal ceroid lipofuscinosis.

Infantile neuronal ceroid lipofuscinosis (INCL) is a profoundly neurodegenerative disease of children caused by a deficiency in the lysosomal enzyme palmitoyl protein thioesterase-1 (PPT1). There is currently no effective therapy for this invariably fatal disease. To date, preclinical experiments using single treatments have resulted in incremental clinical improvements. Therefore, we determined the efficacy of CNS-directed AAV2/5-mediated gene therapy alone and in combination with the systemic delivery of the lysosomotropic PPT1 mimetic phosphocysteamine. Since CNS-directed gene therapy provides relatively high levels of PPT1 activity to specific regions of the brain, we hypothesized that phosphocysteamine would complement that activity in regions expressing subtherapeutic levels of the enzyme. Results indicate that CNS-directed gene therapy alone provided the greatest improvements in biochemical and histological measures as well as motor function and life span. Phosphocysteamine alone resulted in only minor improvements in motor function and no increase in lifespan. Interestingly, phosphocysteamine did not increase the biochemical and histological response when combined with AAV2/5-mediated gene therapy, but it did result in an additional improvement in motor function. These data suggest that a CNS-directed gene therapy approach provides significant clinical benefit, and the addition of the small molecule PPT1 mimetic can further increase that response.

Revascularization of ischemic limbs after transplantation of human bone marrow cells with high aldehyde dehydrogenase activity.

The development of cell therapies to treat peripheral vascular disease has proven difficult because of the contribution of multiple cell types that coordinate revascularization. We characterized the vascular regenerative potential of transplanted human bone marrow (BM) cells purified by high aldehyde dehydrogenase (ALDH(hi)) activity, a progenitor cell function conserved between several lineages. BM ALDH(hi) cells were enriched for myelo-erythroid progenitors that produced multipotent hematopoietic reconstitution after transplantation and contained nonhematopoietic precursors that established colonies in mesenchymal-stromal and endothelial culture conditions. The regenerative capacity of human ALDH(hi) cells was assessed by intravenous transplantation into immune-deficient mice with limb ischemia induced by femoral artery ligation/transection. Compared with recipients injected with unpurified nucleated cells containing the equivalent of 2- to 4-fold more ALDH(hi) cells, mice transplanted with purified ALDH(hi) cells showed augmented recovery of perfusion and increased blood vessel density in ischemic limbs. ALDH(hi) cells transiently recruited to ischemic regions but did not significantly integrate into ischemic tissue, suggesting that transient ALDH(hi) cell engraftment stimulated endogenous revascularization. Thus, human BM ALDH(hi) cells represent a progenitor-enriched population of several cell lineages that improves perfusion in ischemic limbs after transplantation. These clinically relevant cells may prove useful in the treatment of critical ischemia in humans.

Immunodeficient mouse models to study human stem cell-mediated tissue repair.

Hematopoietic stem cell transplantation has traditionally been used to reconstitute blood cell lineages that had formed abnormally because of genetic mutations, or that had been eradicated to treat a disease such as leukemia. However, in recent years, much attention has been paid to the new concept of "stem cell plasticity," and the hope that stem cells could be used to repair damaged tissues generated immense excitement. The field is now in a more realistic and critical period of intense investigation and the concept of cell fusion to explain some of the observed effects has been shown after specific types of damage in liver and muscle, both organs that contain a high number of multinucleate cells. The field is still an extremely exciting one, and many questions remain to be answered before stem cell therapy for tissue repair can be used effectively in the clinic. Immune deficient mouse models of tissue damage provide a system in which human stem cell migration to sites of damage and subsequent contribution to repair can be carefully evaluated. This chapter gives detailed instructions for methods to study human stem cell contribution to damaged liver and to promote repair of damaged vasculature in immune deficient mouse models.

Widespread nonhematopoietic tissue distribution by transplanted human progenitor cells with high aldehyde dehydrogenase activity.

Transplanted adult progenitor cells distribute to peripheral organs and can promote endogenous cellular repair in damaged tissues. However, development of cell-based regenerative therapies has been hindered by the lack of preclinical models to efficiently assess multiple organ distribution and difficulty defining human cells with regenerative function. After transplantation into beta-glucuronidase (GUSB)-deficient NOD/SCID/mucopolysaccharidosis type VII mice, we characterized the distribution of lineage-depleted human umbilical cord blood-derived cells purified by selection using high aldehyde dehydrogenase (ALDH) activity with CD133 coexpression. ALDH(hi) or ALDH(hi)CD133+ cells produced robust hematopoietic reconstitution and variable levels of tissue distribution in multiple organs. GUSB+ donor cells that coexpressed human leukocyte antigen (HLA-A,B,C) and hematopoietic (CD45+) cell surface markers were the primary cell phenotype found adjacent to the vascular beds of several tissues, including islet and ductal regions of mouse pancreata. In contrast, variable phenotypes were detected in the chimeric liver, with HLA+/CD45+ cells demonstrating robust GUSB expression adjacent to blood vessels and CD45-/HLA- cells with diluted GUSB expression predominant in the liver parenchyma. However, true nonhematopoietic human (HLA+/CD45-) cells were rarely detected in other peripheral tissues, suggesting that these GUSB+/HLA-/CD45- cells in the liver were a result of downregulated human surface marker expression in vivo, not widespread seeding of nonhematopoietic cells. However, relying solely on continued expression of cell surface markers, as used in traditional xenotransplantation models, may underestimate true tissue distribution. ALDH-expressing progenitor cells demonstrated widespread and tissue-specific distribution of variable cellular phenotypes, indicating that these adult progenitor cells should be explored in transplantation models of tissue damage.

Fluorophore-conjugated iron oxide nanoparticle labeling and analysis of engrafting human hematopoietic stem cells.

The use of nanometer-sized iron oxide particles combined with molecular imaging techniques enables dynamic studies of homing and trafficking of human hematopoietic stem cells (HSC). Identifying clinically applicable strategies for loading nanoparticles into primitive HSC requires strictly defined culture conditions to maintain viability without inducing terminal differentiation. In the current study, fluorescent molecules were covalently linked to dextran-coated iron oxide nanoparticles (Feridex) to characterize human HSC labeling to monitor the engraftment process. Conjugating fluorophores to the dextran coat for fluorescence-activated cell sorting purification eliminated spurious signals from nonsequestered nanoparticle contaminants. A short-term defined incubation strategy was developed that allowed efficient labeling of both quiescent and cycling HSC, with no discernable toxicity in vitro or in vivo. Transplantation of purified primary human cord blood lineage-depleted and CD34(+) cells into immunodeficient mice allowed detection of labeled human HSC in the recipient bones. Flow cytometry was used to precisely quantitate the cell populations that had sequestered the nanoparticles and to follow their fate post-transplantation. Flow cytometry endpoint analysis confirmed the presence of nanoparticle-labeled human stem cells in the marrow. The use of fluorophore-labeled iron oxide nanoparticles for fluorescence imaging in combination with flow cytometry allows evaluation of labeling efficiencies and homing capabilities of defined human HSC subsets.

Human progenitor cells rapidly mobilized by AMD3100 repopulate NOD/SCID mice with increased frequency in comparison to cells from the same donor mobilized by granulocyte colony stimulating factor.

AMD3100 inhibits the interaction between SDF-1 and CXCR4, and rapidly mobilizes hematopoietic progenitors for clinical transplantation. However, the repopulating function of human cells mobilized with AMD3100 has not been characterized in comparison to cells mobilized with granulocyte-colony stimulating factor (G-CSF) in the same donor. Therefore, healthy donors were leukapheresed 4 hours after injection with AMD3100; after 10 days of drug clearance the same donor was mobilized with G-CSF, allowing a paired comparison of repopulation by mobilized cells. Transplantation of mononuclear cells (MNC) or purified CD34(+) cells was compared at limiting dilution into NOD/SCID mice. Human AMD3100-mobilized MNC possessed enhanced repopulating frequency in comparison to G-CSF-mobilized MNC from paired donors, and purified CD34(+) progenitors were at least as efficient as the G-CSF mobilized cells. The frequencies of NOD/SCID repopulating cells (SRC) were 1 SRC in 8.7 x 10(6) AMD3100-mobilized MNC compared to 1 SRC in 29.0 x 10(6) G-CSF-mobilized MNC, and 1 SRC in 1.2 x 10(5) AMD3100-mobilized CD34(+) cells compared to 1 SRC in 1.8 x 10(5) G-CSF-mobilized CD34(+) cells. Hematopoietic differentiation of transplanted progenitors was similar after AMD3100 or G-CSF-mobilization. Thus, AMD3100 mobilized peripheral blood represents a rapidly obtained, highly repopulating source of hematopoietic progenitors for clinical transplantation.

Selection based on CD133 and high aldehyde dehydrogenase activity isolates long-term reconstituting human hematopoietic stem cells.

The development of novel cell-based therapies requires understanding of distinct human hematopoietic stem and progenitor cell populations. We recently isolated reconstituting hematopoietic stem cells (HSCs) by lineage depletion and purification based on high aldehyde dehydrogenase activity (ALDH(hi)Lin- cells). Here, we further dissected the ALDH(hi)-Lin- population by selection for CD133, a surface molecule expressed on progenitors from hematopoietic, endothelial, and neural lineages. ALDH(hi)CD133+Lin- cells were primarily CD34+, but also included CD34-CD38-CD133+ cells, a phenotype previously associated with repopulating function. Both ALDH(hi)CD133-Lin- and ALDH(hi)CD133+Lin- cells demonstrated distinct clonogenic progenitor function in vitro, whereas only the ALDH(hi)CD133+Lin- population seeded the murine bone marrow 48 hours after transplantation. Significant human cell repopulation was observed only in NOD/SCID and NOD/SCID beta2M-null mice that received transplants of ALDH(hi)CD133+Lin- cells. Limiting dilution analysis demonstrated a 10-fold increase in the frequency of NOD/SCID repopulating cells compared with CD133+Lin- cells, suggesting that high ALDH activity further purified cells with repopulating function. Transplanted ALDH(hi)CD133+Lin- cells also maintained primitive hematopoietic phenotypes (CD34+CD38-) and demonstrated enhanced repopulating function in recipients of serial, secondary transplants. Cell selection based on ALDH activity and CD133 expression provides a novel purification of HSCs with long-term repopulating function and may be considered an alternative to CD34 cell selection for stem cell therapies.