Gene therapy in transplantation

Alternatives to immunosuppressive drugs in human islet transplantation

Although intensive insulin therapy has resulted in improved metabolic control and decreases in the incidence of complications, the occurrence of severe hypoglycemia remains an issue, as does the continued potential for complications. Islet transplantation, a promising treatment for type I diabetes, has been shown to improve blood sugar levels and decrease or even abrogate the incidence of hypoglycemia. The lack of tissue availability and the toxic effects of immunosuppressants, however, limit the application of islet transplantation as a cure for diabetes. This article discusses possible alternatives to immunosuppressive drugs in human islet transplantations.

DNA/dendrimer complexes mediate gene transfer into murine cardiac transplants ex vivo

Starburst polyamidoamine dendrimers are synthetic polymers with unique structural and physical characteristics suitable for DNA gene transfer. Our previous studies demonstrated that Starburst dendrimers augment plasmid-mediated gene transfer efficiency in a nonvascularized, cardiac transplantation model. In this study, the fifth generation of ethylenediamine core dendrimer was investigated for its ability to enhance gene transfer and expression in a clinically relevant murine vascularized heart transplantation model. The plasmid pMP6A-beta-gal, encoding beta-galactosidase (beta-Gal), was incubated with dendrimers to form complexes. The complexes were perfused via the coronary arteries during donor graft harvesting, and reporter gene expression was determined by quantitative evaluation of X-Gal staining. The grafts infused with pMP6A-beta-gal/dendrimer complexes showed beta-Gal expression in myocytes from 7 to 14 days. A number of variables for transfer of the DNA/dendrimer complexes were tested, including DNA:dendrimer charge ratios, concentrations of DNA and dendrimer, preservation solutions, ischemic time, and enhancement of vascular permeability by serotonin, papaverine, and VEGF administration. The results showed that DNA/dendrimer complexes containing 20 microg of DNA and 260 microg of dendrimer (1:20 charge ratio) in a total volume of 200 microl resulted in highest gene expression in the grafts. The results also showed that prolonged incubation (cold ischemic time) to 2 h and pretreatment with serotonin further enhanced gene expression.

Feasibility of CTLA4Ig gene delivery and expression in vivo using retrovirally transduced myeloid dendritic cells that induce alloantigen-specific T cell anergy in vitro

Dendritic cells (DC) are highly specialised, bone marrow (BM)-derived antigen-presenting cells (APC) that initiate and regulate immune responses. They provide costimulatory signals (in particular, CD40 and the CD28 ligands CD80 and CD86) necessary for naive T cell activation. Functional expression of CD80 and CD86 is blocked by the fusion protein cytotoxic T lymphocyte antigen 4-immunoglobulin (CTLA4Ig), that promotes tolerance induction in animals. Here, replicating mouse (B10; H2b) myeloid DC progenitors, were retrovirally transduced to express CTLA4Ig using the centrifugal enhancement method. Gene product was detected by immunocyto- or histochemistry. Maximal DC transduction efficiency was 62%. Compared with control, zeomycin-resistance gene (Zeo)-transduced DC, CTLA4Ig-expressing cells showed markedly impaired capacity to stimulate naive allogeneic (C3H; H2k) T cell proliferation and cytotoxic T lymphocyte (CTL) generation. Their ability to induce alloantigen-specific T cell hyporesponsiveness was reversed by exogenous IL-2 in secondary mixed leukocyte reactions (MLR). Following local (s.c.) transfer to allogeneic recipients, the genetically modified DC trafficked to T cell areas of draining lymphoid tissue, where transgene expression was detected. Ex vivo analysis of proliferative and CTL responses revealed donor-specific inhibition of alloimmune reactivity by the CTLA4Ig-transduced DC. This effect was associated with marked inhibition of interferon (IFN)-gamma production, but significant augmentation of IL-4 and IL-10 secretion. Thus, retroviral transduction of DC permits in vivo delivery of CTLA4Ig to the precise microenvironment where antigen (Ag) presentation occurs. Comparatively nonimmunogenic retroviral vectors, that allow permanent transgene expression in DC, and promote localized delivery of the immunosuppressive transgene product, promote immune deviation and Ag-specific T cell hyporesponsiveness.

Transforming growth factor-beta1 gene transfer ameliorates acute lung allograft rejection

BACKGROUND

The aim of the current work was to study the feasibility of functional gene transfer using the gene encoding for transforming growth factor-beta1, a known immunosuppressive cytokine, on rat lung allograft function in the setting of acute rejection.

METHODS

The rat left lung transplant technique was used in all experiments, with Brown Norway donor rats and Fischer recipient rats. After harvest, left lungs were transfected ex vivo with either sense or antisense transforming growth factor-beta1 constructs complexed to cationic lipids, then implanted into recipients. On postoperative days 2, 5, and 7, animals were put to death, arterial oxygenation measured, and acute rejection graded histologically.

RESULTS

On postoperative day 2, there were no differences in acute rejection or lung function between animals treated with transforming growth factor-beta1 and control animals. On postoperative day 5, oxygenation was significantly improved in grafts transfected with the transforming growth factor-beta1 sense construct compared with antisense controls (arterial oxygen tension = 411 +/- 198 vs 103 +/- 85 mm Hg, respectively; P =.002). Acute rejection scores from lung allografts were also significantly improved, corresponding to decreases in both vascular and airway rejection (vascular rejection scores: 2.0 +/- 0. 5 vs 2.8 +/- 0.6; P =.04; airway rejection scores: 1.3 +/- 0.7 vs 2. 3 +/- 0.8, respectively; P =.02). The amelioration of acute rejection was temporary and decreased by postoperative day 7.

CONCLUSIONS

The feasibility of using gene transfer techniques to introduce novel functional genes in the setting of lung transplantation is demonstrated. In this model of rat lung allograft rejection, gene transfer of transforming growth factor-beta1 resulted in temporary but significant improvements in lung allograft function and acute rejection pathology.

Tissue-binding properties of a synthetic peptide DNA vector targeted to cell membrane integrins: a possible universal nonviral vector for organ and tissue transplantation

BACKGROUND

Gene delivery through a nonviral, receptor-mediated system widely expressed in transplanted tissue would have important advantages in transplantation, where gene delivery is performed ex vivo. Integrins are widely expressed cell surface receptors and can be targeted for gene delivery.

METHODS

A synthetic 31 amino acid DNA vector (polylysine-molossin) comprising a 15-amino acid moiety for targeting cellular integrins (derived from the snake venom, molossin) and a 16-amino acid polylysine moiety for DNA-binding, has been evaluated. The 31-amino acid vector, as well as its separate 15-amino acid integrin-binding and (lys)16 components, were individually synthesized, and a monoclonal antibody was raised to the molossin peptide for these studies. Binding to cell lines and tissue sections and capacity for gene delivery were examined.

RESULTS

Flow cytometric studies with the ECV304 cell line demonstrated that the binding of polylysine-molossin and polylysine-molossin/DNA complexes involved both electrostatic and integrin-mediated interactions with the cells, with the electrostatic binding being sufficient for maximal binding. However, binding to cellular integrins was essential for successful gene transfer. Binding studies on frozen tissue sections of the rat and pig demonstrated that the molossin peptide bound to many cell types of interest in transplantation, but not to all. Among the negative tissues were vascular endothelium and pancreatic islets. Small species differences in tissue binding were noted between the rat and pig.

CONCLUSIONS

This study defines the cooperative nature of the binding of this vector system to target cells and establishes the cell types most likely to be effectively targeted for DNA transfer.

Gene transfer of immunomodulatory peptides correlates with heme oxygenase-1 induction and enhanced allograft survival

BACKGROUND

Decapeptides derived from human HLA class I sequences have been shown to prolong allograft survival. The mechanism of action of these peptides has been uncertain, because they act in an MHC unrestricted manner. Recently, it was found that these peptides bind heme oxygenase 1 (HO-1). In the present study, we sought to determine whether local delivery of these peptides through gene transfer could extend allograft survival, and to explore the underlying mechanisms.

METHODS

C57BL/6 neonatal hearts were transplanted to CBA/J recipients and the peptide, or plasmid DNA encoding the peptide, was injected directly into the allograft at the time of the transplant.

RESULTS

Direct injection of 1 microg of the B2702 peptide into the allograft did not prolong survival (13.3+/-0.8 vs. 13.4+/-0.8 days for untreated controls), but injection of 400 microg of peptide did extend survival (22.0+/-0.6). Injection of plasmid DNA encoding the B2702 peptide was superior to peptide delivery, extending graft survival to 30.8+/-1.5 days. Similar results were obtained using another plasmid encoding the rationally designed peptide BC1 (28.5+/-1.7), whereas no significant prolongation was observed using a plasmid encoding the control peptide B2705 (16.5+/-1.0). To explore the hypothesis that these peptides exert their immunosuppressive effect by altering HO-1 activity, animals were treated with iron protoporphyrin, an inducer of HO-1 activity, or tin protoporphyrin, an inhibitor of HO-1. Treatment with iron protoporphyrin alone extended graft survival (24.5+/-1.6) and did not alter the benefit in survival seen with BC1 gene transfer (28.0+/-0.8). In contrast, treatment with tin protoporphyrin abolished the benefit of BC1 gene transfer (17.0+/-0.6).

CONCLUSIONS

These results demonstrate that plasmid mediated gene transfer is an effective means for delivering immunosuppressive peptides to extend allograft survival. The experiments suggest that these peptides may act by increasing HO-1 activity and support a role for HO-1 in immune regulation and allograft survival.

Genetically modified CD34+ cells as cellular vehicles for gene delivery into areas of angiogenesis in a rhesus model

To develop a cellular vehicle able to reach systemically disseminated areas of angiogenesis, we sought to exploit the natural tropism of circulating endothelial progenitor cells (EPCs). Primate CD34+ EPCs were genetically modified with high efficiency and minimal toxicity using a non-replicative herpes virus vector. These EPCs localized in a skin autograft model of angiogenesis in rhesus monkeys, and sustained the expression of a reporter gene for several weeks while circulating in the blood. In animals infused with autologous CD34+ EPCs transduced with a thymidine kinase-encoding herpes virus, skin autografts and subcutaneous Matrigel pellets impregnated with vascular growth factors underwent necrosis or accelerated regression after administration of ganciclovir. Importantly, the whole intervention was perfectly well tolerated. The accessibility, easy manipulation, lack of immunogenicity of the autologous CD34+ cell vehicles, and tropism for areas of angiogenesis render autologous CD34+ circulating endothelial progenitors as ideal candidates for exploration of their use as cellular vehicles when systemic gene delivery to those areas is required. Gene Therapy (2000) 7, 43-52.

Transduction of dendritic cell progenitors with a retroviral vector encoding viral interleukin-10 and enhanced green fluorescent protein allows purification of potentially tolerogenic antigen-presenting cells

BACKGROUND

Dendritic cells (DC) are important antigen-presenting cells that play critical roles in the initiation and modulation of immune responses. Genetic engineering of DC to express immunosuppressive molecules is a novel approach to the inhibition of allograft rejection. Retroviral delivery of viral interleukin (vIL)-10 to replicating myeloid DC progenitors (DCp) impairs their T-cell stimulatory capacity and promotes the induction of antigen-specific T-cell hyporesponsiveness. However, transduction efficiency with retroviral vectors is comparatively low. Enhanced green fluorescent protein (EGFP) is important both as a marker of gene transduction and for the selection of transduced cells. Our aims were to construct a retroviral vector encoding both vIL-10 and EGFP, to positively select transduced DC, and to assess the impact of these highly purified, vIL-10-secreting antigen-presenting cells on allogeneic T-cell responses.

METHODS

DCp propagated from bone marrow of C57BL10 (H2b) mice in granulocyte-macrophage colony-stimulating factor (GM-CSF)+IL-4 were transduced with a retroviral vector encoding both vIL-10 and EGFP by centrifugal enhancement. Gene transfer efficiency was determined by flow cytometry. Transduced cells were flow sorted, and vIL-10 secretion was quantified by ELISA. DC function was assessed by the ability of the cells to induce naive allogeneic (C3H; H2k) T-cell proliferation and cytotoxic T lymphocyte generation.

RESULTS

Retrovirally transduced DC expressed both vIL-10 and EGFP gene products. Approximately 20% of unsorted cells expressed EGFP, as determined by flow cytometry. vIL-10 was produced at a mean rate of 31 ng/40 hr/10(6) cells. After sorting, the incidence of EGFP+ DC was increased dramatically to at least 95%, and the production of vIL-10 was increased approximately three- to fourfold, to a mean of 107 ng/40 hr/10(6) cells. These highly purified, vIL-10-secreting DC exhibited markedly diminished capacity to induce allogeneic T-cell proliferative and cytotoxic responses.

CONCLUSIONS

DCp retrovirally transduced to express both vIL-10 and EGFP can be rapidly identified and sorted to high levels of purity. The availability of highly enriched preparations of vIL-10-transduced DC facilitates studies of their immunoregulatory function and may enhance their therapeutic potential in transplantation or autoimmune disease.

Adenoviral delivery of CTLA4Ig into myeloid dendritic cells promotes their in vitro tolerogenicity and survival in allogeneic recipients

Dendritic cells (DC) are highly specialized antigen-presenting cells (APC) that initiate and modulate immune responses. They are essential for naive T cell activation, but may also play roles both in central and peripheral tolerance. Blockade of costimulatory pathways that provide the crucial second signal for lymphocyte activation is one strategy to augment the potential tolerogenicity of DC. Here, in vitro propagated DC were transduced using an adenoviral (Ad) vector to express the gene encoding cytotoxic T lymphocyte antigen 4-immunoglobulin (CTLA4lg), which blocks interaction of CD80 and CD86 on DC with CD28 on T cells. Supernatants of AdCTLA4lg-transduced DC strikingly inhibited mixed leukocyte reactions (MLR) induced by non-transduced DC. Whereas transduction of marker genes (LacZ or enhanced green fluorescence protein (EGFP)) did not alter their potent allostimulatory activity, DC transduced with CTLA4lg exhibited striking reductions in cell surface staining for CD86, but not MHC class II, and were poor stimulators of T cell proliferation and cytotoxic T lymphocyte (CTL) responses. In addition, they induced alloantigen-specific T cell hyporesponsiveness. They were detected, following local injection, in significantly increased numbers in the lymphoid tissue of unmodified allogeneic recipients. This is the first report of the functional properties of DC genetically engineered to express CTLA4lg.

Retroviral delivery of viral interleukin-10 into myeloid dendritic cells markedly inhibits their allostimulatory activity and promotes the induction of T-cell hyporesponsiveness

BACKGROUND

Dendritic cells (DC) play critical roles in the initiation and modulation of immune responses and may determine the balance between tolerance and immunity. Viral interleukin-10 (vIL-10), encoded by the Epstein-Barr virus, is highly homologous to the "immunosuppressive" cytokine, mammalian IL-10. It impairs antigen-presenting cell function but lacks certain immunostimulatory properties of mammalian IL-10. We accomplished the following: (1) evaluated the effects of vIL-10 protein on DC phenotype and function, (2) transduced mouse bone marrow-derived DC to express vIL-10, and (3) assessed the impact of transgene expression on DC allostimulatory activity.

METHODS

DC progenitors propagated from bone marrow of B10 (H2b) mice in granulocyte-macrophage colony-stimulating factor plus IL-4 were repeatedly transduced by centrifugation, using retroviral supernatant obtained from the BOSC 23 ecotropic packaging cell line. To evaluate transduction efficiency, DC were transduced with the retroviral vector MFG-enhanced green fluorescence protein as a marker gene. Transgene and key cell surface molecule expression were examined by flow cytometry. The level of vIL-10 gene product in the culture supernatant was quantitated by ELISA. DC function was assessed by evaluation of the ability of DC to induce allogeneic (C3H;H2k) T-cell proliferation and cytotoxic T lymphocytes in primary mixed leukocyte reactions. Secondary mixed leukocyte reactions were used to test for T-cell hyporesponsiveness.

RESULTS

The early addition of vIL-10 protein to cultures inhibited DC maturation and function. vIL-10 gene transfer was achieved with an approximate transduction efficiency of 35 to 40%. Transduced DC expressed vIL-10 at a level of 40 ng/10(6) cells/48 hr. In comparison with controls, vIL-10-transduced cells showed decreased surface expression of major histocompatibility complex class II and costimulatory molecules, reduced ability to stimulate T-cell proliferation and cytotoxic T lymphocyte generation, and potential to induce alloantigen-specific hyporesponsiveness.

CONCLUSIONS

DC can be effectively transduced to express vIL-10 and limit their ability to stimulate in vitro. These genetically engineered antigen-presenting cells may have therapeutic potential to inhibit undesired immune responses to allo- or autoantigens.

Soluble HLA class I molecules: biological significance and clinical implications

Soluble class I human leukocyte antigens (sHLAs) have been detected in serum, sweat, lymphatic fluid, urine and cerebrospinal fluid. Their biological function has, however, remained a puzzle. The physiological concentration of sHLA varies more than tenfold depending on the phenotype of the individual, and is significantly upregulated in various diseases and during inflammation. This suggests that sHLAs might serve as a marker of pathological changes. Recent experiments have shown that, in vitro, sHLAs can modulate T-cell reactivity and induce cell-activated apoptosis, implicating sHLAs in the induction and maintenance of peripheral tolerance. Therefore, sHLAs have the therapeutic potential to induce tolerance to transplants.

Efficient transfer of genes into murine cardiac grafts by Starburst polyamidoamine dendrimers

Starburst dendrimer, a structurally defined, spherical macromolecule composed of repeating polyamidoamino subunits, was investigated to augment plasmid-mediated gene transfer efficiency in a murine cardiac transplantation model. The grafts were directly injected with naked pCH110, a plasmid encoding beta-galactosidase (beta-Gal), or pCH110-dendrimer complex, and reporter gene expression determined by X-Gal staining. The grafts injected with pCH110-dendrimer demonstrated widespread and extended beta-Gal expression in both myocytes and the graft infiltrating cells from 7 to 28 days, compared to the grafts injected with naked pCH110 that expressed beta-Gal only in myocytes for less than 14 days. p alphaMHC-vIL-10, as plasmid encoding viral interleukin-10 (vIL-10) under the control of alpha-myosin heavy chain promoter, was able to prolong allograft survival from 13.9 +/- 0.9 days to 21.4 +/- 2.3 days (p < 0.005). When dendrimer G5EDA was used with p alphaMHC-vIL-10, 60-fold less DNA resulted in significant prolongation of graft survival to 38.6 +/- 4.7 days (p < 0.0005). The dose of DNA, the charge ratio of DNA to dendrimer, and the size generation of the dendrimers were all determined to be critical variables for prolongation of allograft survival in this model system. Thus, the use of the Starburst dendrimer dramatically increased the efficiency of plasmid-mediated gene transfer and expression. Production of immunosuppressive cytokines at higher amounts for longer periods of time in a greater expanse of tissue enhanced the immunosuppressive effect and prolonged graft survival further.

A nonviral vector system for efficient gene transfer to corneal endothelial cells via membrane integrins

BACKGROUND

Genetic manipulation of allografts to suppress their ability to induce rejection is a promising approach for controlling rejection responses. A key to this approach is the development of appropriate DNA vectors. We are developing nonviral DNA vector systems based on synthetic peptides containing an integrin-binding segment for cellular targeting and a polylysine segment for DNA binding.

METHODS

Two such peptides have been tested for their ability to deliver the beta-galactosidase reporter gene to the corneal endothelial cells of the rabbit, pig, and man. One peptide was derived from a phage display library, the other from the integrin-binding moiety of the toxin from the American pit viper, Crotalus molossus molossus. Corneas were cultured overnight and then exposed to the DNA/peptide vector under a variety of conditions involving different DNA concentrations, chloroquine concentrations, times of exposure, presence of serum, and presence of polyanion buffers. Expression of the beta-galactosidase gene was determined after 3 additional days in culture. Effects of the treatment on the viability of the endothelium were examined by confocal microscopy.

RESULTS

We report that approximately 30% of corneal endothelial cells can be transfected with our optimal protocol using the molossin-based vector. Transfection is dependent on the presence of chloroquine and is inhibited by polyanion buffers such as HEPES. Viability of the corneal endothelium was excellent, except if corneas were incubated at high concentrations of chloroquine (0.5 mM) for prolonged periods (24 hr).

CONCLUSIONS

Synthetic peptides containing both an integrin targeting and a DNA-binding moiety are promising as simple and highly versatile DNA vectors for use in corneal transplantation.