Giuliana Ferrari

Gene Therapy in Peripheral Blood Lymphocytes and Bone Marrow for ADA− Immunodeficient Patients

Adenosine deaminase (ADA) deficiency results in severe combined immunodeficiency, the first genetic disorder treated by gene therapy. Two different retroviral vectors were used to transfer ex vivo the human ADA minigene into bone marrow cells and peripheral blood lymphocytes from two patients undergoing exogenous enzyme replacement therapy. After 2 years of treatment, long-term survival of T and B lymphocytes, marrow cells, and granulocytes expressing the transferred ADA gene was demonstrated and resulted in normalization of the immune repertoire and restoration of cellular and humoral immunity. After discontinuation of treatment, T lymphocytes, derived from transduced peripheral blood lymphocytes, were progressively replaced by marrow-derived T cells in both patients. These results indicate successful gene transfer into long-lasting progenitor cells, producing a functional multilineage progeny.

Muscle-derived hematopoietic stem cells are hematopoietic in origin

It has recently been shown that mononuclear cells from murine skeletal muscle contain the potential to repopulate all major peripheral blood lineages in lethally irradiated mice, but the origin of this activity is unknown. We have fractionated muscle cells on the basis of hematopoietic markers to show that the active population exclusively expresses the hematopoietic stem cell antigens Sca-1 and CD45. Muscle cells obtained from 6- to 8-week-old C57BL/6-CD45.1 mice and enriched for cells expressing Sca-1 and CD45 were able to generate hematopoietic but not myogenic colonies in vitro and repopulated multiple hematopoietic lineages of lethally irradiated C57BL/6-CD45.2 mice. These data show that muscle-derived hematopoietic stem cells are likely derived from the hematopoietic system and are a result not of transdifferentiation of myogenic stem cells but instead of the presence of substantial numbers of hematopoietic stem cells in the muscle. Although CD45-negative cells were highly myogenic in vitro and in vivo, CD45-positive muscle-derived cells displayed only very limited myogenic activity and only in vivo.

Correction of junctional epidermolysis bullosa by transplantation of genetically modified epidermal stem cells

The continuous renewal of human epidermis is sustained by stem cells contained in the epidermal basal layer and in hair follicles. Cultured keratinocyte stem cells, known as holoclones, generate sheets of epithelium used to restore severe skin, mucosal and corneal defects. Mutations in genes encoding the basement membrane component laminin 5 (LAM5) cause junctional epidermolysis bullosa (JEB), a devastating and often fatal skin adhesion disorder. Epidermal stem cells from an adult patient affected by LAM5-β3–deficient JEB were transduced with a retroviral vector expressing LAMB3 cDNA (encoding LAM5-β3), and used to prepare genetically corrected cultured epidermal grafts. Nine grafts were transplanted onto surgically prepared regions of the patients legs. Engraftment was complete after 8 d. Synthesis and proper assembly of normal levels of functional LAM5 were observed, together with the development of a firmly adherent epidermis that remained stable for the duration of the follow-up (1 year) in the absence of blisters, infections, inflammation or immune response. Retroviral integration site analysis indicated that the regenerated epidermis is maintained by a defined repertoire of transduced stem cells. These data show that ex vivo gene therapy of JEB is feasible and leads to full functional correction of the disease.

Transcript imaging of the development of human T helper cells using oligonucleotide arrays.

Many pathological processes, including those causing allergies and autoimmune diseases, are associated with the presence of specialized subsets of T helper cells at the site of inflammation. Understanding the genetic program that controls the functional properties of T helper type 1 (Th1) versus T helper type 2 (Th2) cells may provide insight into the pathophysiology of inflammatory diseases. We compared the gene-expression profiles of human Th1 and Th2 cells using high-density oligonucleotide arrays with the capacity to display transcript levels of 6,000 human genes. Here we analyse the data sets derived from five independent experiments using statistical algorithms. This approach resulted in the identification of 215 differentially expressed genes, encoding proteins involved in transcriptional regulation, apoptosis, proteolysis, and cell adhesion and migration. A subset of these genes was further upregulated by exposure of differentiated Th1 cells to interleukin-12 (IL-12), as confirmed by kinetic PCR analysis, indicating that IL-12 modulates the effector functions of Th1 cells in the absence of antigenic stimulation. Functional assays and in vivo expression of selected genes have validated the biological relevance of our study. Our results provide new insight into the transcriptional program controlling the functional diversity of subsets of T helper cells.

Safety of retroviral gene marking with a truncated NGF receptor

To the editor—Random integration into the host cell genome and inappropriate transgene expression are major safety concerns for the clinical use of retroviral vectors. Li et al. recently reported a leukemic transformation of mouse bone marrow cells caused by integration of a transgene-carrying retroviral vector into the Evi1 proto-oncogene. They suggested that expression of the transgene, a truncated form of the p75 low-affinity nerve growth factor receptor (∆LNGFR) with most of the intracytoplasmic tail deleted (from residue 248), contributed to the leukemic progression. Because ∆LNGFR is used as a surface marker in gene therapy clinical trials aimed at controlling graft-versus-host disease (GVHD) after bone marrow transplantation (BMT), a critical assessment of the potential risks associated with the use of such a molecule is essential. In a collaborative effort between 17 independent groups of investigators, we have accumulated both pre-clinical and clinical evidence supporting the safety of ∆LNGFR as a cell-marking molecule. Cumulative data obtained from >300 mice transplanted with bone marrow cells transduced with ∆LNGFR-expressing retroviral vectors showed normal engraftment, persistence and differentiation of ∆LNGFR-expressing hematopoietic stemprogenitor cells (HSCs) in primary, secondary and tertiary BMT recipients, with no adverse events (Table 1 and Supplementary Information online). Over 100 of these mice were monitored for >20 weeks after BMT; more than 70 animals, including 16 recipients of secondary or tertiary BMT, were monitored for >28 weeks. Considering that a total of >1 × 10 transduced cells were transplanted, and assuming an average of one retroviral integration per cell, we estimate the risk of oncogenic transformation after transduction with a ∆LNGFR-encoding retroviral vector to be <1 in 10 integration events. Therefore, expression of ∆LNGFR could not have increased the expected frequency of an insertional oncogenesis event, which has been previously estimated at 10 to 10 per insertion event. Expression of ∆LNGFR did not alter the function or survival of T lymphocytes derived from peripheral blood mononuclear cells transduced with a variety of vectors and studied in different animal models. In pre-clinical models of post-BMT GVHD, no difference in the ability to induce donor chimerism or to mediate GVHD was observed for ∆LNGFR-expressing T cells, as compared with control T cells, in 356 mice, 200 rats and 3 dogs (Table 1 and Supplementary Information online), again with no adverse events. Analysis of 102 independent transductions of human peripheral lymphocytes with two different vectors (SFCMM-3 and SFCM) encoding the same ∆LNGFR detected no change in the expression of markers of lineage, activation or adhesion, or in the proliferative capacity of T cells, as assayed by limiting dilution after polyclonal in vitro stimulation. All cells remained strictly dependent on interleukin-2 for growth and survival, and the Safety of retroviral gene marking with a truncated NGF receptor

Failure to correct murine muscular dystrophy.

Bone-marrow cells have the potential to differentiate into other cell types such as muscle fibres, and can be transplanted into acutely or chronically damaged muscle as a way of delivering normal dystrophin (the protein that is defective or missing in Duchennes muscular dystrophy) to the skeletal and heart muscle of mdx mice, an animal model for this disease. But the corrective potential of this approach has been hard to estimate against the high background of muscle fibres that spontaneously revert to synthesizing dystrophin, a feature of the original mdx mutation. Here we test the long-term efficacy of bone-marrow transplantation in a different mdx mutant which is free of this problem and find that it has no impact on murine muscular dystrophy.

Protein Kinase A-Mediated Synapsin I Phosphorylation Is a Central Modulator of Ca2+-Dependent Synaptic Activity

Protein kinase A (PKA) modulates several steps of synaptic transmission. However, the identification of the mediators of these effects is as yet incomplete. Synapsins are synaptic vesicle (SV)-associated phosphoproteins that represent the major presynaptic targets of PKA. We show that, in hippocampal neurons, cAMP-dependent pathways affect SV exocytosis and that this effect is primarily brought about through synapsin I phosphorylation. Phosphorylation by PKA, by promoting dissociation of synapsin I from SVs, enhances the rate of SV exocytosis on stimulation. This effect becomes relevant when neurons are challenged with sustained stimulation, because it appears to counteract synaptic depression and accelerate recovery from depression by fostering the supply of SVs from the reserve pool to the readily releasable pool. In contrast, synapsin phosphorylation appears to be dispensable for the effects of cAMP on the frequency and amplitude of spontaneous synaptic currents and on the amplitude of evoked synaptic currents. The modulation of depolarization-evoked SV exocytosis by PKA phosphorylation of synapsin I is primarily caused by calmodulin (CaM)-dependent activation of cAMP pathways rather than by direct activation of CaM kinases. These data define a hierarchical crosstalk between cAMP- and CaM-dependent cascades and point to synapsin as a major effector of PKA in the modulation of activity-dependent SV exocytosis.

Transcription Factor Binding Sites Are Genetic Determinants of Retroviral Integration in the Human Genome

Gamma-retroviruses and lentiviruses integrate non-randomly in mammalian genomes, with specific preferences for active chromatin, promoters and regulatory regions. Gene transfer vectors derived from gamma-retroviruses target at high frequency genes involved in the control of growth, development and differentiation of the target cell, and may induce insertional tumors or pre-neoplastic clonal expansions in patients treated by gene therapy. The gene expression program of the target cell is apparently instrumental in directing gamma-retroviral integration, although the molecular basis of this phenomenon is poorly understood. We report a bioinformatic analysis of the distribution of transcription factor binding sites (TFBSs) flanking >4,000 integrated proviruses in human hematopoietic and non-hematopoietic cells. We show that gamma-retroviral, but not lentiviral vectors, integrate in genomic regions enriched in cell-type specific subsets of TFBSs, independently from their relative position with respect to genes and transcription start sites. Analysis of sequences flanking the integration sites of Moloney leukemia virus (MLV)- and human immunodeficiency virus (HIV)-derived vectors carrying mutations in their long terminal repeats (LTRs), and of HIV vectors packaged with an MLV integrase, indicates that the MLV integrase and LTR enhancer are the viral determinants of the selection of TFBS-rich regions in the genome. This study identifies TFBSs as differential genomic determinants of retroviral target site selection in the human genome, and suggests that transcription factors binding the LTR enhancer may synergize with the integrase in tethering retroviral pre-integration complexes to transcriptionally active regulatory regions. Our data indicate that gamma-retroviruses and lentiviruses have evolved dramatically different strategies to interact with the host cell chromatin, and predict a higher risk in using gamma-retroviral vs. lentiviral vectors for human gene therapy applications.

Hypomorphic Mutation of the TALE Gene Prep1 (pKnox1) Causes a Major Reduction of Pbx and Meis Proteins and a Pleiotropic Embryonic Phenotype

ABSTRACT The interaction of Prep1 and Pbx homeodomain transcription factors regulates their activity, nuclear localization, and likely, function in development. To understand the in vivo role of Prep1, we have analyzed an embryonic lethal hypomorphic mutant mouse (Prep1i/i). Prep1i/i embryos die at embryonic day 17.5 (E17.5) to birth with an overall organ hypoplasia, severe anemia, impaired angiogenesis, and eye anomalies, particularly in the lens and retina. The anemia correlates with delayed differentiation of erythroid progenitors and may be, at least in part, responsible for intrauterine death. At E14.5, Prep1 is present in fetal liver (FL) cMyb-positive cells, whose deficiency causes a marked hematopoietic phenotype. Prep1 is also localized to FL endothelial progenitors, consistent with the observed angiogenic phenotype. Likewise, at the same gestational day, Prep1 is present in the eye cells that bear Pax6, implicated in eye development. The levels of cMyb and Pax6 in FL and in the retina, respectively, are significantly decreased in Prep1i/i embryos, consistent with the hematopoietic and eye phenotypes. Concomitantly, Prep1 deficiency results in the overall decrease of protein levels of its related family member Meis1 and its partners Pbx1 and Pbx2. As both Prep1 and Meis interact with Pbx, the overall Prep1/Meis-Pbx DNA-binding activity is strongly reduced in whole Prep1i/i embryos and their organs. Our data indicate that Prep1 is an essential gene that acts upstream of and within a Pbx-Meis network that regulates multiple aspects of embryonic development.

MicroRNA and proliferation control in chronic lymphocytic leukemia: functional relationship between miR-221/222 cluster and p27

We investigated functional relationships between microRNA 221/222 (miR-221/222) cluster and p27, a key regulator of cell cycle, in chronic lymphocytic leukemia (CLL). The enforced expression of miR-221/222 in the CLL cell line MEC1 induced a significant down-regulation of p27 protein and conferred a proliferative advantage to the transduced cells that exhibited faster progression into the S phase of the cell cycle. Accordingly, expression of miR-221/miR-222 and p27 was found to be inversely related in leukemic cells obtained from peripheral blood (PB) of 38 patients with CLL. Interestingly, when miR-221/222 and p27 protein were evaluated in different anatomic compartments (lymph nodes or bone marrow) of the same patients, increased expression of the 2 miRNAs became apparent compared with PB. This finding was paralleled by a low expression of p27. In addition, when CLL cells were induced in vitro to enter cell cycle (eg, with cytosine phosphate guanine oligodeoxynucleotide), a significant increase of miR-221/222 expression and a marked down-regulation of p27 protein were evident. These data indicate that the miR-221/222 cluster modulates the expression of p27 protein in CLL cells and lead to suggest that miR-221/222 and p27 may represent a regulatory loop that helps maintaining CLL cells in a resting condition.