Induction of molecular chimerism by gene therapy prevents antibody-mediated heart transplant rejection

Brain-targeted stem cell gene therapy corrects mucopolysaccharidosis type II via multiple mechanisms

The pediatric lysosomal storage disorder mucopolysaccharidosis type II is caused by mutations in IDS, resulting in accumulation of heparan and dermatan sulfate, causing severe neurodegeneration, skeletal disease, and cardiorespiratory disease. Most patients manifest with cognitive symptoms, which cannot be treated with enzyme replacement therapy, as native IDS does not cross the blood-brain barrier. We tested a brain-targeted hematopoietic stem cell gene therapy approach using lentiviral IDS fused to ApoEII (IDS.ApoEII) compared to a lentivirus expressing normal IDS or a normal bone marrow transplant. In mucopolysaccharidosis II mice, all treatments corrected peripheral disease, but only IDS.ApoEII mediated complete normalization of brain pathology and behavior, providing significantly enhanced correction compared to IDS. A normal bone marrow transplant achieved no brain correction. Whilst corrected macrophages traffic to the brain, secreting IDS/IDS.ApoEII enzyme for cross-correction, IDS.ApoEII was additionally more active in plasma and was taken up and transcytosed across brain endothelia significantly better than IDS via both heparan sulfate/ApoE-dependent receptors and mannose-6-phosphate receptors. Brain-targeted hematopoietic stem cell gene therapy provides a promising therapy for MPS II patients.

Effects of interfering RNA of α-1,3-galactosyltransferase and nuclear factor-kappa B on cardiac xenotransplantation

BACKGROUND

Both α1,3-galactosyltransferase (α1,3GT) and nuclear factor kappa B (NF-κB) play an important role in the immune response of xenotransplantation. The purpose of this study is to investigate the effect of RNAi of α1,3GT and NF-κB on xenotransplantation.

METHODS

Lentiviral vectors with shRNA focusing on α1, 3GT and RelA were constructed. The effect of RNAi on α1, 3GT and RelA was examined in vitro and in vivo. Additionally, we established a mouse-to-rat heterotopic cardiac xenotransplantatic model (donor hearts transplanted to the right side of the neck in rat) using a modified cuff technique. The survival time of donor hearts in each group was monitored. The expressions of α1, 3GT and RelA mRNA, Galα1,3Gal antigen, and RelA protein were detected by RT-PCR, immunofluorescence, and Western blot respectively. The expressions of C3, IgM, IgG, NK, macrophages, ICAM-1 on donor hearts were examined by immunohistochemistry.

RESULTS

High titer lentiviral vectors carrying α1, 3GT and RelA shRNA plasmids had a high and stable transfection rate on EOMA in vitro. In vivo, heart tissue showed a much stronger GFP expression and significant decrease in target gene mRNA expression and protein expression in shRNA interfering groups (p < 0.01). The survival time of α1,3GTi-3 and dual lentiviral vector groups was significantly longer than other groups. The mRNA expression levels of α1,3GT and RelA, as well as Galα(1,3)Gal and RelA proteins, in α1,3GTi-3, RelAi-3, and dual lentiviral vector groups were downregulated and compared to other groups (p < 0.01). The depositions of C3, IgM, IgG in α1,3GTi-3 group and dual lentiviral vector group were less than other groups (p < 0.01). The infiltration of NK, macrophages and ICAM-1 in α1,3GTi-3 group and dual lentiviral vector group was more than other groups (p < 0.01), but the infiltration of NK, macrophages and ICAM-1 in dual lentiviral vector group was less than α1,3GTi-3 group (p < 0.01).

CONCLUSIONS

Our results indicate that RNAi technology with lentiviral vectors is an effective method to transmit exogenous genes into living bodies and stably inhibit the expression of target genes. Moreover, siRNA targeting the α1,3GT gene was found to control the immune process and obviously prolong the survival time of donors, whereas knocking down NF-κB alone showed no differences. However, the RNAi of NF-κB can make the infiltration of macrophages and natural killer cells decrease, and the expression of ICAM-1 in the xenografts also decreases, contributing to the restraining of AVR.

Tolerance to MHC class II disparate allografts through genetic modification of bone marrow

Induction of molecular chimerism through genetic modification of bone marrow is a powerful tool for the induction of tolerance. Here we demonstrate for the first time that expression of an allogeneic MHC class II gene in autologous bone marrow cells, resulting in a state of molecular chimerism, induces tolerance to MHC class II mismatched skin grafts, a stringent test of transplant tolerance. Reconstitution of recipients with syngeneic bone marrow transduced with retrovirus encoding H-2I-A^b (I-A^b) resulted the long-term expression of the retroviral gene product on the surface of MHC class II-expressing bone marrow derived cell types. Mechanistically, tolerance was maintained by the presence of regulatory T cells, which prevented proliferation and cytokine production by alloreactive host T cells. Thus, the introduction of MHC class II genes into bone marrow derived cells through genetic engineering results in tolerance. These results have the potential to extend the clinical applicability of molecular chimerism for tolerance induction.

Cell-based therapy in allergy

IgE-mediated allergy is an immunological disorder occurring in response to otherwise harmless environmental antigens (i.e., allergens). Development of effective therapeutic or preventive approaches inducing robust tolerance toward allergens remains an unmet goal. Several experimental tolerance approaches have been described. The therapeutic use of regulatory T cells (Tregs) and the establishment of molecular chimerism are two cell-based strategies that are of particular interest. Treg therapy is close to clinical application, but its efficacy remains to be fully defined. Recent proof-of-concept studies demonstrated that transplantation of syngeneic hematopoietic stem cells modified in vitro to express a major allergen leads to molecular chimerism and robust allergen-specific tolerance. Here we review cell-based tolerance strategies in allergy, discussing their potentials and limitations.

Gene therapy to inhibit xenoantibody production using lentiviral vectors in non-human primates

Xenoantibodies to the gal alpha1,3 gal (gal) epitope impede the use of pig tissues for xenotransplantation, a procedure that may help overcome the shortage of human organ donors. Stable gal chimerism and tolerance to gal(+) hearts could be achieved in alpha1,3-galactosyltransferase (alpha1,3GT)(-/-) mice using lentiviral vectors expressing porcine alpha1,3GT, the enzyme that synthesizes the gal carbohydrate. In this study, we evaluated whether chimerism sufficient to inhibit anti-gal xenoantibody responses can be achieved using lentivectors in non-human primates. Rhesus macaques were transplanted with autologous, alpha1,3GT-transduced bone marrow (BM) following sublethal irradation. Simian immunodeficiency virus (SIV)- and human immunodeficiency virus (HIV)-1-derived lentiviral constructs were compared. Chimerism was observed in several hematopoietic lineages in all monkeys. Engraftment in animals receiving SIV-based alpha1,3GT constructs was similar to that achieved using the HIV-1-derived lentivector for the first 2 months post-transplantation, but increased thereafter to reach higher levels by 5 months. Upon immunization with porcine hepatocytes, the production of anti-gal immunoglobulin M xenoantibody was substantially reduced in the gal(+) BM recipients compared to controls. This study is the first to report the application of gene therapy to achieve low-level, long-term gal chimerism sufficient to inhibit production of anti-gal antibodies after immunization with porcine cells in rhesus macaques.

Tolerance induction by lentiviral gene therapy with a nonmyeloablative regimen

Antibodies (Abs) directed at the Galα1,3Galβ1,4GlcNAc-R (αGal) carbohydrate epitope initiate xenograft rejection. Previously, we have shown that bone marrow transplantation (BMT) with lentivirus-mediated gene transfer of porcine α1,3 galactosyltransferase (GalT) is able to induce tolerance to αGal-expressing heart grafts following a lethal dose of irradiation. Here we show the first demonstration of permanent survival of αGal+ hearts following transplantation with autologous, lentivirus-transduced BM using a nonmyeloablative regimen. Autologous BM from GalT knockout (GalT–/–) mice was transduced with a lentiviral vector expressing porcine GalT and transplanted into sublethally irradiated (3 Gy) GalT–/– mice. Chimerism in the peripheral blood cells (PBCs) remained low but was higher in the BM, especially within the stromal cell population. Mice reconstituted with GalT did not produce anti-αGal Abs over time. We immunized these mice with αGal-expressing cells and assessed humoral immune responses. Anti-αGal xenoantibodies were not produced in mice reconstituted with GalT, but normal Ab responses to other xenoantigens were detected. Mice reconstituted with GalT accepted αGal+ heart grafts over 100 days. Transduction with lentiviral vectors results in chimerism at levels sufficient to induce long-term tolerance under nonmyeloablative conditions.

Induction of donor-specific tolerance in sublethally irradiated recipients by gene therapy

Donor-specific transplantation tolerance can be established through the induction of molecular chimerism following reconstitution of lethally irradiated mice with autologous bone marrow expressing retrovirally transduced allogeneic MHC antigens. Here, we set out to define nonmyeloablative host conditioning regimens that would allow for establishment of molecular chimerism and the induction of donor-specific tolerance. Recipient mice received various doses of whole-body irradiation, together with costimulatory blockade using anti-CD154 monoclonal antibody prior to reconstitution with syngeneic bone marrow cells transduced with retroviruses carrying the gene encoding H-2K(b). Conditioning consisting of 3 Gy whole-body irradiation and treatment with anti-CD154 was sufficient to induce molecular chimerism resulting in stable multilineage expression of K(b) on hematopoietic cells. T cells from molecular chimeras were unable to lyse allogeneic targets expressing K(b) and contained substantially fewer K(b)-reactive IL-2- and IFN-gamma-producing CD4 T cells than controls receiving mock-transduced bone marrow. Induction of molecular chimerism using nonmyeloablative host conditioning allowed for permanent survival of K(b)-disparate allogeneic skin grafts. These data suggest that nonmyeloablative host conditioning can be used effectively to induce molecular chimerism resulting in transplantation tolerance.

USE OF LENTIVIRAL VECTORS TO INDUCE LONG-TERM TOLERANCE TO GAL+ HEART GRAFTS

BACKGROUND

Tolerance to organ grafts has been achieved by establishing a state of stable mixed-cell chimerism after bone marrow transplantation. Gene therapy has been applied to establish chimerism for cells expressing galactose alpha 1,3 galactose in alpha 1,3 galactosyltransferase deficient (gal knockout) mice using retroviral vectors. Limitations to the success of this methodology include short-term expression of the introduced gene and rejection of gal hearts transplanted into these animals within a month.

METHODS

Autologous bone marrow from gal knockout mice was transduced with a lentiviral vector expressing porcine alpha 1,3 galactosyltransferase and transplanted into lethally irradiated gal knockout mice. Chimerism was monitored by flow cytometry. Hearts from wild type mice (gal/) were transplanted into these animals and palpated daily. Xenoantibodies directed at the gal carbohydrate or porcine xenoantigens were detected by enzyme-linked immunosorbent assay.

RESULTS

Hearts from wild-type gal/ donors were permanently accepted in all mice receiving autologous, transduced bone marrow before heart transplantation. Control mice rejected gal hearts within 12 to 14 days. Histologic analysis demonstrated classical signs of rejection in controls and normal myocardium with no evidence of rejection in mice chimeric for the gal carbohydrate. Anti-gal xenoantibodies were not produced in gal chimeras, but normal antibody responses to other xenoantigens were detected. Specific tolerance for the gal carbohydrate was achieved by this procedure.

CONCLUSIONS

These experiments report the first demonstration of permanent survival of gal hearts after transplantation with autologous, transduced bone marrow. Transduction with lentiviral vectors results in long-term, stable chimerism at levels sufficient to induce long-term tolerance to heart grafts in mice.

Gene therapy progress and prospects: gene therapy in organ transplantation

One major complication facing organ transplant recipients is the requirement for life-long systemic immunosuppression to prevent rejection, which is associated with an increased incidence of malignancy and susceptibility to opportunistic infections. Gene therapy has the potential to eliminate problems associated with immunosuppression by allowing the production of immunomodulatory proteins in the donor grafts resulting in local rather than systemic immunosuppression. Alternatively, gene therapy approaches could eliminate the requirement for general immunosuppression by allowing the induction of donor-specific tolerance. Gene therapy interventions may also be able to prevent graft damage owing to nonimmune-mediated graft loss or injury and prevent chronic rejection. This review will focus on recent progress in preventing transplant rejection by gene therapy.

Engraftment of genetically modified bone marrow cells in sensitized hosts

Expression of retrovirally transduced genes in bone marrow-derived cells can be used to establish stable long-term B- and T-cell tolerance. To determine whether preexisting antibodies may prohibit the use of gene therapy to establish tolerance, we examined the extent to which preexisting antibodies specific for the carbohydrate antigen Gal alpha1-3Gal beta1-4GlcNAc-R (alpha Gal) could affect engraftment and development of bone marrow progenitors expressing the enzyme UDPgalactose:beta-D-galactosyl-1,4-N-acetyl-D-glucosaminide alpha(1-3)galactosyltransferase (E.C. 2.4.1.151), or simply alpha GT, which synthesizes the alpha Gal epitope. Groups of alpha GT knockout mice (GT(0) mice) lacking alpha Gal were presensitized to alpha Gal by immunization and then lethally irradiated and reconstituted with varying numbers of alpha GT-transduced syngeneic bone marrow cells. Whereas unimmunized controls were reconstituted with as few as 2 x 10(6) transduced cells, a significant fraction of immunized mice reconstituted with 2 x 10(6) or 4 x 10(6) alpha GT-transduced cells failed to undergo bone marrow engraftment and died. Immunized mice in which radiation protection was achieved failed to express alpha Gal. However, radiation protection and expression of alpha Gal on bone marrow-derived cells, resulting in tolerance, could be achieved by increasing the number of transduced cells used to reconstitute immunized mice. Thus, although high levels of preexisting antibodies can be a significant barrier to engraftment, this barrier can be overcome by increasing the number of transduced cells used for reconstitution.

Immunoglobulin heavy chain transgenic mice expressing Galalpha(1,3)Gal-reactive antibodies

BACKGROUND

Natural antibodies that bind the carbohydrate antigen Galalpha1-3Galbeta1-4GlcNAc-R (alphaGal) mediate rigorous rejection of porcine xenografts and represent a major immunological hurdle to successful discordant xenotransplantation. However, little is known about how production of antibodies specific for alphaGal is regulated.

METHODS

Transgenic mice expressing an IgM heavy chain isolated from a B-cell hybridoma that produces antibodies specific for alphaGal were constructed. These mice were bred to mutant mice that lack the alphaGal epitope (GT0 mice) or wild-type (GT+) mice to generate animals in which the transgene is expressed in the presence or absence of alphaGal as a "self"-antigen. Development of transgene-expressing B cells and production of alphaGal-specific serum antibodies were then analyzed in transgenic mice on GT0 and GT+ backgrounds.

RESULTS

B cells expressing the transgenic heavy chain and transgene-encoded serum antibodies specific for alphaGal were readily detected in mice on the GT0 background. Most alphaGal-reactive antibodies in GT0 mice used the transgene rather than endogenous Ig heavy chains. In contrast, transgene-encoded serum antibodies specific for alphaGal were not detected in GT+ mice. In transgenic mice on the GT+ background, B cells expressing the transgene underwent deletion as a result of encountering alphaGal during their development, indicating that expression of alphaGal as part of self-mediated efficient negative selection of B cells expressing transgene-encoded alphaGal-specific antibodies.

CONCLUSIONS

The development of transgenic mice expressing a B cell receptor specific for alphaGal provides a novel system to study developmental regulation of B cells making carbohydrate-specific antibodies. In addition, these mice may be useful for examining methods to prevent production of alphaGal-reactive antibodies.