SUL-109 Protects Hematopoietic Stem Cells from Apoptosis Induced by Short-Term Hypothermic Preservation and Maintains Their Engraftment Potential.

The newly developed 6-hydroxychromanol derivate SUL-109 was shown to provide protection during hypothermic storage of several cell lines, but has not been evaluated in hematopoietic stem cells (HSCs). Hypothermic preservation of HSCs would be preferred over short-term cryopreservation to prevent cell loss during freezing/thawing and would be particularly useful for short-term storage, such as during conditioning of patients or transport of HSC transplants. Here we cultured human CD34+ umbilical cord blood (UCB) cells and lineage-depleted (Lin-) Balb/c bone marrow (BM) cells for up to 7 days in serum-free HSC expansion medium with hematopoietic growth factors. SUL-109-containing cultures were stored at 4°C for 3 to 14 days. The UCB cells were tested for viability, cell cycle, and reactive oxygen species (ROS). DMSO-cryopreserved Lin- BM cells or Lin- BM cells maintained for 14 days at 4°C were transplanted into RAG2-/- Balb/c mice and engraftment was followed for 6 months. The addition of SUL-109 during the hypothermic storage of expanded CD34+ UCB cells provided a significant improvement in cell survival of the immature CD34+/CD38- fraction after 7 days of hypothermic storage through scavenging of hypothermia-induced ROS and was able to preserve the multilineage capacity of human CD34+ UCB cells for up to 14 days of cold storage. In addition, SUL-109 protected murine BM Lin- cells from 14 days of hypothermic preservation and maintained their engraftment potential after transplantation in immune-deficient RAG2-/- mice. Our data indicate that SUL-109 is a promising novel chemical for use as a protective agent during cold storage of human and murine HSCs to prevent hypothermia-induced apoptosis and promote cell viability.

Efficacy of lentivirus-mediated gene therapy in an Omenn syndrome recombination-activating gene 2 mouse model is not hindered by inflammation and immune dysregulation.

BACKGROUND: Omenn syndrome (OS) is a rare severe combined immunodeficiency associated with autoimmunity and caused by defects in lymphoid-specific V(D)J recombination. Most patients carry hypomorphic mutations in recombination-activating gene (RAG) 1 or 2. Hematopoietic stem cell transplantation is the standard treatment; however, gene therapy (GT) might represent a valid alternative, especially for patients lacking a matched donor. OBJECTIVE: We sought to determine the efficacy of lentiviral vector (LV)-mediated GT in the murine model of OS (Rag2R229Q/R229Q) in correcting immunodeficiency and autoimmunity. METHODS: Lineage-negative cells from mice with OS were transduced with an LV encoding the human RAG2 gene and injected into irradiated recipients with OS. Control mice underwent transplantation with wild-type or OS-untransduced lineage-negative cells. Immunophenotyping, T-dependent and T-independent antigen challenge, immune spectratyping, autoantibody detection, and detailed tissue immunohistochemical analyses were performed. RESULTS: LV-mediated GT allowed immunologic reconstitution, although it was suboptimal compared with that seen in wild-type bone marrow (BM)-transplanted OS mice in peripheral blood and hematopoietic organs, such as the BM, thymus, and spleen. We observed in vivo variability in the efficacy of GT correlating with the levels of transduction achieved. Immunoglobulin levels and T-cell repertoire normalized, and gene-corrected mice responded properly to challenges in vivo. Autoimmune manifestations, such as skin infiltration and autoantibodies, dramatically improved in GT mice with a vector copy number/genome higher than 1 in the BM and 2 in the thymus. CONCLUSIONS: Our data show that LV-mediated GT for patients with OS significantly ameliorates the immunodeficiency, even in an inflammatory environment.

The potential for chemical mixtures from the environment to enable the cancer hallmark of sustained proliferative signalling.

The aim of this work is to review current knowledge relating the established cancer hallmark, sustained cell proliferation to the existence of chemicals present as low dose mixtures in the environment. Normal cell proliferation is under tight control, i.e. cells respond to a signal to proliferate, and although most cells continue to proliferate into adult life, the multiplication ceases once the stimulatory signal disappears or if the cells are exposed to growth inhibitory signals. Under such circumstances, normal cells remain quiescent until they are stimulated to resume further proliferation. In contrast, tumour cells are unable to halt proliferation, either when subjected to growth inhibitory signals or in the absence of growth stimulatory signals. Environmental chemicals with carcinogenic potential may cause sustained cell proliferation by interfering with some cell proliferation control mechanisms committing cells to an indefinite proliferative span.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead.

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety 'Mode of Action' framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.

Recombination-activating gene 1 (Rag1)-deficient mice with severe combined immunodeficiency treated with lentiviral gene therapy demonstrate autoimmune Omenn-like syndrome.

BACKGROUND: Recombination-activating gene 1 (RAG1) deficiency results in severe combined immunodeficiency (SCID) caused by a complete lack of T and B lymphocytes. If untreated, patients succumb to recurrent infections. OBJECTIVES: We sought to develop lentiviral gene therapy for RAG1-induced SCID and to test its safety. METHODS: Constructs containing the viral spleen-focus-forming virus (SF), ubiquitous promoters, or cell type-restricted promoters driving sequence-optimized RAG1 were compared for efficacy and safety in sublethally preconditioned Rag1(-/-) mice undergoing transplantation with transduced bone marrow progenitors. RESULTS: Peripheral blood CD3(+) T-cell reconstitution was achieved with SF, ubiquitous promoters, and cell type-restricted promoters but 3- to 18-fold lower than that seen in wild-type mice, and with a compromised CD4(+)/CD8(+) ratio. Mitogen-mediated T-cell responses and T cell-dependent and T cell-independent B-cell responses were not restored, and T-cell receptor patterns were skewed. Reconstitution of mature peripheral blood B cells was approximately 20-fold less for the SF vector than in wild-type mice and often not detectable with the other promoters, and plasma immunoglobulin levels were abnormal. Two months after transplantation, gene therapy-treated mice had rashes with cellular tissue infiltrates, activated peripheral blood CD44(+)CD69(+) T cells, high plasma IgE levels, antibodies against double-stranded DNA, and increased B cell-activating factor levels. Only rather high SF vector copy numbers could boost T- and B-cell reconstitution, but mRNA expression levels during T- and B-cell progenitor stages consistently remained less than wild-type levels. CONCLUSIONS: These results underline that further development is required for improved expression to successfully treat patients with RAG1-induced SCID while maintaining low vector copy numbers and minimizing potential risks, including autoimmune reactions resembling Omenn syndrome.

Assessment of non-myelotoxic agents as a preparatory regimen for hematopoietic stem cell gene therapy.

RAG2 deficiency is characterized by a lack of B and T lymphocytes, causing severe lethal infections. Currently, RAG2 deficiency is treated with a Hematopoietic Stem Cell transplantation (HSCT). Most conditioning regimens used before HSCT consist of alkylating myelotoxic agents with or without irradiation and affect growth and development of pediatric patients. Here, we developed a non-myelotoxic regimen using G-CSF, VLA-4I or AMD3100. These agents are known HSC mobilizers or affect bone marrow (BM) permeability and may support the homing of HSCs to the BM, without inducing major side effects. Female Rag2-/- mice were pre-treated with Busulfan (BU), G-CSF, VLA-4I or AMD3100 and transplanted with male BM cells transduced with a lentiviral vector carrying codon optimized human RAG2 (RAG2co). Peripheral blood cell counts increased significantly after G-CSF, VLA-4I and AMD3100 treatment, but not after BU. Reconstitution of PB lymphocytes was comparable for all groups with full immune reconstitution at 6 months post transplantation, despite different methods of conditioning. Survival of mice pre-treated with non-myelotoxic agents was significantly higher than after BU treatment. Here, we show that the non-myelotoxic agents G-CSF, VLA-4I, and AMD3100 are highly effective as conditioning regimen before HSC gene therapy and can be used as an alternative to BU.

Magselectofection: an integrated method of nanomagnetic separation and genetic modification of target cells.

Research applications and cell therapies involving genetically modified cells require reliable, standardized, and cost-effective methods for cell manipulation. We report a novel nanomagnetic method for integrated cell separation and gene delivery. Gene vectors associated with magnetic nanoparticles are used to transfect/transduce target cells while being passaged and separated through a high gradient magnetic field cell separation column. The integrated method yields excellent target cell purity and recovery. Nonviral and lentiviral magselectofection is efficient and highly specific for the target cell population as demonstrated with a K562/Jurkat T-cell mixture. Both mouse and human enriched hematopoietic stem cell pools were effectively transduced by lentiviral magselectofection, which did not affect the hematopoietic progenitor cell number determined by in vitro colony assays. Highly effective reconstitution of T and B lymphocytes was achieved by magselectofected murine wild-type lineage-negative Sca-1(+) cells transplanted into Il2rg(-/-) mice, stably expressing GFP in erythroid, myeloid, T-, and B-cell lineages. Furthermore, nonviral, lentiviral, and adenoviral magselectofection yielded high transfection/transduction efficiency in human umbilical cord mesenchymal stem cells and was fully compatible with their differentiation potential. Upscaling to a clinically approved automated cell separation device was feasible. Hence, once optimized, validated, and approved, the method may greatly facilitate the generation of genetically engineered cells for cell therapies.

Correction of murine Rag2 severe combined immunodeficiency by lentiviral gene therapy using a codon-optimized RAG2 therapeutic transgene.

Recombination activating gene 2 (RAG2) deficiency results in severe combined immunodeficiency (SCID) with complete lack of T and B lymphocytes. Initial gammaretroviral gene therapy trials for other types of SCID proved effective, but also revealed the necessity of safe vector design. We report the development of lentiviral vectors with the spleen focus forming virus (SF) promoter driving codon-optimized human RAG2 (RAG2co), which improved phenotype amelioration compared to native RAG2 in Rag2(-/-) mice. With the RAG2co therapeutic transgene, T-cell receptor (TCR) and immunoglobulin repertoire, T-cell mitogen responses, plasma immunoglobulin levels and T-cell dependent and independent specific antibody responses were restored. However, the thymus double positive T-cell population remained subnormal, possibly due to the SF virus derived element being sensitive to methylation/silencing in the thymus, which was prevented by replacing the SF promoter by the previously reported silencing resistant element (ubiquitous chromatin opening element (UCOE)), and also improved B-cell reconstitution to eventually near normal levels. Weak cellular promoters were effective in T-cell reconstitution, but deficient in B-cell reconstitution. We conclude that immune functions are corrected in Rag2(-/-) mice by genetic modification of stem cells using the UCOE driven codon-optimized RAG2, providing a valid optional vector for clinical implementation.

Keratinocyte growth factor and stem cell factor to improve thymopoiesis after autologous CD34+ cell transplantation in rhesus macaques.

Deficient thymopoiesis and retarded recovery of naive CD4(+) T cells are important determinants of insufficient immune-competence following hematopoietic stem cell transplantation (HSCT). Although keratinocyte growth factor (KGF) may protect the thymic epithelium, stem cell factor (SCF) is involved in early thymopoiesis. We evaluated whether KGF alone or combined with SCF would affect thymopoiesis and hematologic recovery following myeloablative autologous HSCT into rhesus macaques. Purpose-bred adult rhesus macaques received 10(6) autologous CD34(+)-selected mononuclear bone marrow cells (BMC)/kg after 9 Gy myeloablative conditioning. Animals were treated with phosphate-buffered saline (PBS) (n = 2), KGF alone (n = 2), or KGF combined with SCF (n = 2). KGF-treated animals showed accelerated hematologic recovery, improved thymopoiesis, and enhanced naive T-cell recovery following transplantation. Improved T cell recovery was not associated with protection against cytomegalovirus reactivation nor with improved antibody response to tetanus toxoid vaccination. Animals treated with KGF and SCF experienced severe adverse events that precluded evaluation of thymopoiesis and T cell recovery. Collectively, our data confirm that KGF may enhance thymopoiesis.

Lentiviral gene therapy of murine hematopoietic stem cells ameliorates the Pompe disease phenotype.

Pompe disease (acid alpha-glucosidase deficiency) is a lysosomal glycogen storage disorder characterized in its most severe early-onset form by rapidly progressive muscle weakness and mortality within the first year of life due to cardiac and respiratory failure. Enzyme replacement therapy prolongs the life of affected infants and supports the condition of older children and adults but entails lifelong treatment and can be counteracted by immune responses to the recombinant enzyme. We have explored the potential of lentiviral vector-mediated expression of human acid alpha-glucosidase in hematopoietic stem cells (HSCs) in a Pompe mouse model. After mild conditioning, transplantation of genetically engineered HSCs resulted in stable chimerism of approximately 35% hematopoietic cells that overexpress acid alpha-glucosidase and in major clearance of glycogen in heart, diaphragm, spleen, and liver. Cardiac remodeling was reversed, and respiratory function, skeletal muscle strength, and motor performance improved. Overexpression of acid alpha-glucosidase did not affect overall hematopoietic cell function and led to immune tolerance as shown by challenge with the human recombinant protein. On the basis of the prominent and sustained therapeutic efficacy without adverse events in mice we conclude that ex vivo HSC gene therapy is a treatment option worthwhile to pursue.

Gene therapy: is IL2RG oncogenic in T-cell development?

The gene IL2RG encodes the gamma-chain of the interleukin-2 receptor and is mutated in patients with X-linked severe combined immune deficiency (X-SCID). Woods et al. report the development of thymus tumours in a mouse model of X-SCID after correction by lentiviral overexpression of IL2RG and claim that these were caused by IL2RG itself. Here we find that retroviral overexpression of IL2RG in human CD34+ cells has no effect on T-cell development, whereas overexpression of the T-cell acute lymphoblastic leukaemia (T-ALL) oncogene LMO2 leads to severe abnormalities. Retroviral expression of IL2RG may therefore not be directly oncogenic--rather, the restoration of normal signalling by the interleukin-7 receptor to X-SCID precursor cells allows progression of T-cell development to stages that are permissive for the pro-leukaemic effects of ectopic LMO2.

Correction of murine SCID-X1 by lentiviral gene therapy using a codon-optimized IL2RG gene and minimal pretransplant conditioning.

Clinical trials have demonstrated the potential of ex vivo hematopoietic stem cell gene therapy to treat X-linked severe combined immunodeficiency (SCID-X1) using γ-retroviral vectors, leading to immune system functionality in the majority of treated patients without pretransplant conditioning. The success was tempered by insertional oncogenesis in a proportion of the patients. To reduce the genotoxicity risk, a self-inactivating (SIN) lentiviral vector (LV) with improved expression of a codon optimized human interleukin-2 receptor γ gene (IL2RG) cDNA (coγc), regulated by its 1.1 kb promoter region (γcPr), was compared in efficacy to the viral spleen focus forming virus (SF) and the cellular phosphoglycerate kinase (PGK) promoters. Pretransplant conditioning of Il2rg(-/-) mice resulted in long-term reconstitution of T and B lymphocytes, normalized natural antibody titers, humoral immune responses, ConA/IL-2 stimulated spleen cell proliferation, and polyclonal T-cell receptor gene rearrangements with a clear integration preference of the SF vector for proto-oncogenes, contrary to the PGK and γcPr vectors. We conclude that SIN lentiviral gene therapy using coγc driven by the γcPr or PGK promoter corrects the SCID phenotype, potentially with an improved safety profile, and that low-dose conditioning proved essential for immune competence, allowing for a reduced threshold of cell numbers required.

Insertion sites in engrafted cells cluster within a limited repertoire of genomic areas after gammaretroviral vector gene therapy.

Vector-associated side effects in clinical gene therapy have provided insights into the molecular mechanisms of hematopoietic regulation in vivo. Surprisingly, many retrovirus insertion sites (RIS) present in engrafted cells have been found to cluster nonrandomly in close association with specific genes. Our data demonstrate that these genes directly influence the in vivo fate of hematopoietic cell clones. Analysis of insertions thus far has been limited to individual clinical studies. Here, we studied >7,000 insertions retrieved from various studies. More than 40% of all insertions found in engrafted gene-modified cells were clustered in the same genomic areas covering only 0.36% of the genome. Gene classification analyses displayed significant overrepresentation of genes associated with hematopoietic functions and relevance for cell growth and survival in vivo. The similarity of insertion distributions indicates that vector insertions in repopulating cells cluster in predictable patterns. Thus, insertion analyses of preclinical in vitro and murine in vivo studies as well as vector insertion repertoires in clinical trials yielded concerted results and mark a small number of interesting genomic loci and genes that warrants further investigation of the biological consequences of vector insertions.

Mobilization of hepatic mesenchymal stem cells from human liver grafts.

Extensive studies have demonstrated the potential applications of bone marrow-derived mesenchymal stem cells (BM-MSCs) as regenerative or immunosuppressive treatments in the setting of organ transplantation. The aims of the present study were to explore the presence and mobilization of mesenchymal stem cells (MSCs) in adult human liver grafts and to compare their functional capacities to those of BM-MSCs. The culturing of liver graft preservation fluids (perfusates) or end-stage liver disease tissues resulted in the expansion of MSCs. Liver-derived mesenchymal stem cells (L-MSCs) were equivalent to BM-MSCs in adipogenic and osteogenic differentiation and in wingless-type-stimulated proliferative responses. Moreover, the genome-wide gene expression was very similar, with a 2-fold or greater difference found in only 82 of the 32,321 genes (0.25%). L-MSC differentiation into a hepatocyte lineage was demonstrated in immunodeficient mice and in vitro by the ability to support a hepatitis C virus infection. Furthermore, a subset of engrafted MSCs survived over the long term in vivo and maintained stem cell characteristics. Like BM-MSCs, L-MSCs were found to be immunosuppressive; this was shown by significant inhibition of T cell proliferation. In conclusion, the adult human liver contains an MSC population with a regenerative and immunoregulatory capacity that can potentially contribute to tissue repair and immunomodulation after liver transplantation.

Vector integration is nonrandom and clustered and influences the fate of lymphopoiesis in SCID-X1 gene therapy.

Recent reports have challenged the notion that retroviruses and retroviral vectors integrate randomly into the host genome. These reports pointed to a strong bias toward integration in and near gene coding regions and, for gammaretroviral vectors, around transcription start sites. Here, we report the results obtained from a large-scale mapping of 572 retroviral integration sites (RISs) isolated from cells of 9 patients with X-linked SCID (SCID-X1) treated with a retrovirus-based gene therapy protocol. Our data showed that two-thirds of insertions occurred in or very near to genes, of which more than half were highly expressed in CD34(+) progenitor cells. Strikingly, one-fourth of all integrations were clustered as common integration sites (CISs). The highly significant incidence of CISs in circulating T cells and the nature of their locations indicate that insertion in many gene loci has an influence on cell engraftment, survival, and proliferation. Beyond the observed cases of insertional mutagenesis in 3 patients, these data help to elucidate the relationship between vector insertion and long-term in vivo selection of transduced cells in human patients with SCID-X1.

Gammaretrovirus-mediated correction of SCID-X1 is associated with skewed vector integration site distribution in vivo.

We treated 10 children with X-linked SCID (SCID-X1) using gammaretrovirus-mediated gene transfer. Those with sufficient follow-up were found to have recovered substantial immunity in the absence of any serious adverse events up to 5 years after treatment. To determine the influence of vector integration on lymphoid reconstitution, we compared retroviral integration sites (RISs) from peripheral blood CD3(+) T lymphocytes of 5 patients taken between 9 and 30 months after transplantation with transduced CD34(+) progenitor cells derived from 1 further patient and 1 healthy donor. Integration occurred preferentially in gene regions on either side of transcription start sites, was clustered, and correlated with the expression level in CD34(+) progenitors during transduction. In contrast to those in CD34(+) cells, RISs recovered from engrafted CD3(+) T cells were significantly overrepresented within or near genes encoding proteins with kinase or transferase activity or involved in phosphorus metabolism. Although gross patterns of gene expression were unchanged in transduced cells, the divergence of RIS target frequency between transduced progenitor cells and post-thymic T lymphocytes indicates that vector integration influences cell survival, engraftment, or proliferation.

Lentiviral Hematopoietic Stem Cell Gene Therapy Corrects Murine Pompe Disease.

Pompe disease is an autosomal recessive lysosomal storage disorder characterized by progressive muscle weakness. The disease is caused by mutations in the acid α-glucosidase (GAA) gene. Despite the currently available enzyme replacement therapy (ERT), roughly half of the infants with Pompe disease die before the age of 3 years. Limitations of ERT are immune responses to the recombinant enzyme, incomplete correction of the disease phenotype, lifelong administration, and inability of the enzyme to cross the blood-brain barrier. We previously reported normalization of glycogen in heart tissue and partial correction of the skeletal muscle phenotype by ex vivo hematopoietic stem cell gene therapy. In the present study, using a codon-optimized GAA (GAAco), the enzyme levels resulted in close to normalization of glycogen in heart, muscles, and brain, and in complete normalization of motor function. A large proportion of microglia in the brain was shown to be GAA positive. All astrocytes contained the enzyme, which is in line with mannose-6-phosphate receptor expression and the key role in glycogen storage and glucose metabolism. The lentiviral vector insertion site analysis confirmed no preference for integration near proto-oncogenes. This correction of murine Pompe disease warrants further development toward a cure of the human condition.

Enhancement of mouse hematopoietic stem/progenitor cell function via transient gene delivery using integration-deficient lentiviral vectors.

Integration-deficient lentiviruses (IdLVs) deliver genes effectively to tissues but are lost rapidly from dividing cells. This property can be harnessed to express transgenes transiently to manipulate cell biology. Here, we demonstrate the utility of short-term gene expression to improve functional potency of hematopoietic stem and progenitor cells (HSPCs) during transplantation by delivering HOXB4 and Angptl3 using IdLVs to enhance the engraftment of HSPCs. Constitutive overexpression of either of these genes is likely to be undesirable, but the transient nature of IdLVs reduces this risk and those associated with unsolicited gene expression in daughter cells. Transient expression led to increased multilineage hematopoietic engraftment in in vivo competitive repopulation assays without the side effects reported in constitutive overexpression models. Adult stem cell fate has not been programmed previously using IdLVs, but we demonstrate that these transient gene expression tools can produce clinically relevant alterations or be applied to investigate basic biology.