Robert Pawliuk

Angiogenic synergism, vascular stability and improvement of hind-limb ischemia by a combination of PDGF-BB and FGF-2

The establishment of functional and stable vascular networks is essential for angiogenic therapy. Here we report that a combination of two angiogenic factors, platelet-derived growth factor (PDGF)-BB and fibroblast growth factor (FGF)-2, synergistically induces vascular networks, which remain stable for more than a year even after depletion of angiogenic factors. In both rat and rabbit ischemic hind limb models, PDGF-BB and FGF-2 together markedly stimulated collateral arteriogenesis after ligation of the femoral artery, with a significant increase in vascularization and improvement in paw blood flow. A possible mechanism of angiogenic synergism between PDGF-BB and FGF-2 involves upregulation of the expression of PDGF receptor (PDGFR)-α and PDGFR-β by FGF-2 in newly formed blood vessels. Our data show that a specific combination of angiogenic factors establishes functional and stable vascular networks, and provides guidance for the ongoing clinical trials of angiogenic factors for the treatment of ischemic diseases.

Placenta growth factor-1 antagonizes VEGF-induced angiogenesis and tumor growth by the formation of functionally inactive PlGF-1/VEGF heterodimers.

Tumor growth and metastasis require concomitant growth of new blood vessels, which are stimulated by angiogenic factors, including vascular endothelial growth factor (VEGF), secreted by most tumors. Whereas the angiogenic property and molecular mechanisms of VEGF have been well studied, the biological function of its related homolog, placenta growth factor (PlGF), is poorly understood. Here we demonstrate that PlGF-1, an alternatively spliced isoform of the PlGF gene, antagonizes VEGF-induced angiogenesis when both factors are coexpressed in murine fibrosarcoma cells. Overexpression of PlGF-1 in VEGF-producing tumor cells results in the formation of PlGF-1/VEGF heterodimers and depletion of the majority of mouse VEGF homodimers. The heterodimeric form of PlGF-1/VEGF lacks the ability to induce angiogenesis in vitro and in vivo. Similarly, PlGF-1/VEGF fails to activate the VEGFR-2-mediated signaling pathways. Further, PlGF-1 inhibits the growth of a murine fibrosarcoma by approximately 90% when PlGF-1-expressing tumor cells are implanted in syngeneic mice. In contrast, overexpression of human VEGF in murine tumor cells causes accelerated and exponential growth of primary fibrosarcomas and early hepatic metastases. Our data demonstrate that PlGF-1, a member of the VEGF family, acts as a natural antagonist of VEGF when both factors are synthesized in the same population of cells. The underlying mechanism is due to the formation of functionally inactive heterodimers.

Permanent and panerythroid correction of murine β thalassemia by multiple lentiviral integration in hematopoietic stem cells

Achieving long-term pancellular expression of a transferred gene at therapeutic level in a given hematopoietic lineage remains an important goal of gene therapy. Advances have recently been made in the genetic correction of the hemoglobinopathies by means of lentiviral vectors and large locus control region (LCR) derivatives. However, panerythroid β globin gene expression has not yet been achieved in β thalassemic mice because of incomplete transduction of the hematopoietic stem cell compartment and position effect variegation of proviruses integrated at a single copy per genome. Here, we report the permanent, panerythroid correction of severe β thalassemia in mice, resulting from a homozygous deletion of the β major globin gene, by transplantation of syngeneic bone marrow transduced with an HIV-1-derived [β globin gene/LCR] lentiviral vector also containing the Rev responsive element and the central polypurine tract/DNA flap. The viral titers produced were high enough to achieve transduction of virtually all of the hematopoietic stem cells in the graft with an average of three integrated proviral copies per genome in all transplanted mice; the transduction was sustained for >7 months in both primary and secondary transplants, at which time ≈95% of the red blood cells in all mice contained human β globin contributing to 32 ± 4% of all β-like globin chains. Hematological parameters approached complete phenotypic correction, as assessed by hemoglobin levels and reticulocyte and red blood cell counts. All circulating red blood cells became and remained normocytic and normochromic, and their density was normalized. Free α globin chains were completely cleared from red blood cell membranes, splenomegaly abated, and iron deposit was almost eliminated in liver sections. These findings indicate that virtually complete transduction of the hematopoietic stem cell compartment can be achieved by high-titer lentiviral vectors and that position effect variegation can be mitigated by multiple events of proviral integration to yield balanced, panerythroid expression. These results provide a solid foundation for the initiation of human clinical trials in β thalassemia patients.

Optimization of retroviral-mediated gene transfer to human NOD/SCID mouse repopulating cord blood cells through a systematic analysis of protocol variables

Retroviral transduction of human hematopoietic stem cells is still limited by lack of information about conditions that will maximize stem cell self-renewal divisions in vitro. To address this, we first compared the kinetics of entry into division of single human CD34+CD38- cord blood (CB) cells exposed in vitro to three different flt3-ligand (FL)-containing cytokine combinations. Of the three combinations tested, FL + hyperinterleukin 6 (HIL-6) yielded the least clones and these developed at a slow rate. With either FL + Steel factor (SF) + HIL-6 + thrombopoietin (TPO) or FL + SF + interleukin 3 (IL-3) + IL-6 + granulocyte-colony-stimulating factor (G-CSF), >90% of the cells that formed clones within 6 days undertook their first division within 4 days, although not until after 24 hours. These latter two, more stimulatory, cytokine combinations then were used to assess the effect of duration of cytokine exposure on the efficiency of transducing primitive CB cells with a gibbon ape leukemia virus-pseudotyped murine retroviral vector containing the enhanced green fluorescent protein (GFP) cDNA and the neomycin resistance gene. Fresh lin- CB cells exposed once to medium containing this virus plus cytokines on fibronectin-coated dishes yielded 23% GFP+ CD34+ cells and 52-57% G418-resistant CFC when assessed after 2 days. Prestimulation of the target cells (before exposing them to virus) with either the four or five cytokine combination increased their susceptibility. In both cases, the effect of prestimulation assessed using the same infection protocol was maximal with 2 days of prestimulation and resulted in 47-54% GFP+ CD34+ cells and 67-69% G418-resistant CFC. Repeated daily addition of new virus (up to three times), with assessment of the cells 2 days after the last addition of fresh virus, gave only a marginal improvement in the proportion of transduced CD34+ cells and CFC, but greatly increased the proportion of transduced LTC-IC (from 40% to >99%). Transplantation of lin- CB cells transduced using this latter 6-day protocol into NOD/SCID mice yielded readily detectable GFP+ cells in 10 of 11 mice that were engrafted with human cells. The proportion of the regenerated human cells that were GFP+ ranged from 0.2-72% in individual mice and included both human lymphoid and myeloid cells in all cases. High-level reconstitution with transduced human cells was confirmed by Southern blot analysis. These findings demonstrate that transplantable hematopoietic stem cells in human CB can be reproducibly transduced at high efficiency using a 6-day period of culture in a retrovirus-containing medium with either FL + SF + HIL-6 + TPO or FL + SF + IL-3 + IL-6 + G-CSF in which virus is added on the third, fourth, and fifth day.

Lentiviral-mediated gene delivery to synovium: potent intra-articular expression with amplification by inflammation

Clinical translation of gene-based therapies for arthritis could be accelerated by vectors capable of efficient intra-articular gene delivery and long-term transgene expression. Previously, we have shown that lentiviral vectors transduce rat synovium efficiently in vivo. Here, we evaluated the functional capacity of transgene expression provided by lentiviral-mediated gene delivery to the joint. To do this, we measured the ability of a lentiviral vector containing the cDNA for human interleukin-1 receptor antagonist (LV-hIL-1Ra) to suppress intra-articular responses to IL-1beta. Groups of rats were injected in one knee with 5 x 10(7) infectious units of LV-IL-1Ra. After 24 h, a range of doses of fibroblasts (3 x 10(3), 10(4), 3 x 10(4), or 10(5) cells) genetically modified to overexpress IL-1beta was injected into both knees. Intra-articular delivery of LV-hIL-1Ra strongly prevented swelling in all treated knees, even in those receiving the greatest dose of IL-1beta(+) cells. Cellular infiltration, cartilage erosion, and invasiveness of inflamed synovium were effectively prevented in LV-hIL-1Ra-treated knees and were significantly inhibited in contralateral joints. Beneficial effects were also observed systemically in the lentivirus-treated animals. Interestingly, intra-articular expression of the IL-1Ra transgene was found to increase in relation to the number of IL-1beta(+) cells injected. Further experiments using GFP suggest this is due to the proliferation of cells, stably modified by the integrative lentivirus, in response to inflammatory stimulation.

Long-term cure of the photosensitivity of murine erythropoietic protoporphyria by preselective gene therapy.

Definitive cure of an animal model of a human disease by gene transfer into hematopoietic stem cells has not yet been accomplished in the absence of spontaneous in vivo selection for transduced cells. Erythropoietic protoporphyria is a genetic disease in which ferrochelatase is defective. Protoporphyrin accumulates in erythrocytes, leaks into the plasma and results in severe skin photosensitivity. Using a mouse model of erythropoietic protoporphyria, we demonstrate here that ex vivo preselection of hematopoietic stem cells transduced with a polycistronic retrovirus expressing both human ferrochelatase and green fluorescent protein results in complete and long-term correction of skin photosensitivity in all transplanted mice.

Retroviral Vectors Aimed at the Gene Therapy of Human β‐Globin Gene Disordersa

Abstract: We are focusing on the development of complex retroviral vectors containing human β‐globin gene and β‐LCR for the gene therapy of sickle cell disease and β‐thalassemias. First generation vectors containing mutated splice‐sites to insure stability of proviral transfer enabled long‐term reconstitution in 10/12 transplanted mice for a least 8 months with high expression levels in 2 out of 3 mice analyzed (5% and 20% murine β). Transfer and expression were also achieved in secondary recipients (range: 3–11% murine β). Position independent expression was not observed. In an effort to increase the efficiency of gene transfer and obtain complete reconstitution of recipient mice with exclusively transduced cells while enriching for proviral integration into active chromatin regions, we have incorporated a cassette expressing CD24 or the green fluorescent protein (GFP). Stable transfer to murine bone marrow cells allowed efficient FACS‐sorting of pure populations of transduced cells. A family of vectors based on these principles and containing segments of γ‐ or δ‐globin genes were also designed for systematic analysis of their anti‐sickling properties.

Tolerance by selective in vivo expansion of foreign major histocompatibility complex-transduced autologous bone marrow.

Background. Application of gene therapy to induce antigen-specific immune tolerance could be important for transplantation or treatment of autoimmune diseases. Hematopoietic stem cell-based gene therapy has been hampered by relatively weak gene expression in vivo and loss of transduced cells over time. Selective expansion of transduced hematopoietic stem cells has been accomplished by incorporating the dihydrofolate reductase (DHFR) gene into the gene transfer vector. Methods. To assess whether this strategy could be applied to transplantation, we constructed a retroviral vector plasmid (KA274) containing the cDNA encoding human leukocyte antigen (HLA)-A2.1 and a tyr22 mutant DHFR and generated vesicular stomatitis virus-G-pseudotyped recombinant retrovirus by transfection into 293GPG cells. Bone marrow cells from C57BL/6 mice were infected with KA274 at a multiplicity of infection of 100, and transplanted into lethally irradiated syngeneic mice. Results. After transplantation with transduced bone marrow, the proportion of peripheral blood cells expressing HLA-A2 ranged from 3.2% to 38% and increased 2- to 4.9-fold after selection for DHFR-expressing cells using trimetrexate and nitrobenzylmercaptpurine riboside 5′ monophosphate. HLA-A2 expression remained above pretreatment levels throughout the study. Cytotoxic spleen cells from reconstituted mice lysed third-party HLA-B7–expressing targets but were unable to lyse HLA-A2–expressing targets. All KA274 reconstituted C57BL/6 mice accepted skin grafts from HLA-A2.1 transgenic mice for more than 245 days but rejected third-party Balb/c skin grafts in 12 days. Conclusion. Long-term transgene expression and immunologic tolerance to retrovirus-encoded HLA-A2, equivalent to that obtained by donor bone marrow transplantation, was accomplished, and selective expansion of transduced bone marrow cells was induced using DHFR as a selectable marker.

In Vitro and in Vivo Gene Delivery using a Lentiviral Vector

The delivery of antiarthritic genes to the synovial lining of joints is an effective strategy for the treatment of experimental models of rheumatoid arthritis (RA). Moreover, in two clinical studies it has proved possible to transfer the human interleukin-1 receptor antagonist (hIL-1Ra) cDNA to human rheumatoid joints. These protocols, however, utilized an ex vivo approach to gene delivery. While useful for establishing proof of concept, ex vivo methods do not lend themselves well to widespread clinical application. For this reason, we are devoting increasing attention to developing clinically acceptable in vivo methods of gene delivery to synovium. Because chronic conditions such as RA will probably require extended periods of intra-articular gene expression, integrating vectors are more attractive. In preclinical experiments, two such vectors, adeno-associated virus and high-titer Moloney-based retrovirus, have shown promise for in vivo gene delivery to synovium. Lentiviral vectors also possess favourable properties in this regard, but there are no published data on their suitability for in vivo gene delivery to joints. Here we report preliminary data from the use of lentiviruses to deliver genes to articular tissues. The recent generation of packaging systems able to produce high titers of replication-incompetent HIV-based retroviruses, and the pseudotyping of lentiviral vectors with the vesicular stomatitis virus G-protein (VSV-G) which increase the target cell range and allow concentration by centrifugation have facilitated these studies. In culture we have found that human synoviocytes, and both human and rat chondrocytes were efficiently transduced by high titer (>109 pfu/ml) of VSV-G pseudotyped HIV-1-based lentiviral vectors containing the β-galactosidase gene (lacZ). Similar patterns of expression were observed using rabbit synovial fibroblast line, HIG-82, murine 3T3 cells, and primary cultures of rat skin cells. Direct, intra-articular gene delivery was performed by injecting similar lentiviral preparations into the knees of Wistar rats. Histological analyses of the knee joints revealed the expression of lacZ in the synovial membrane for at least one week following injection. No lacZ staining was observed following the injection of empty viruses. Based on the ability to successfully deliver and express the lacZ marker gene in synoviocytes in culture and in the synovial lining in vivo, a recombinant vector containing hIL-1Ra has been constructed and is being evaluated.