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

Non-viral and viral delivery systems for hemophilia A therapy: recent development and prospects

Recent advancements have focused on enhancing factor VIII half-life and refining its delivery methods, despite the well-established knowledge that factor VIII deficiency is the main clotting protein lacking in hemophilia. Consequently, both viral and non-viral delivery systems play a crucial role in enhancing the quality of life for hemophilia patients. The utilization of viral vectors and the manipulation of non-viral vectors through targeted delivery are significant advancements in the field of cellular and molecular therapies for hemophilia. These developments contribute to the progression of treatment strategies and hold great promise for improving the overall well-being of individuals with hemophilia. This review study comprehensively explores the application of viral and non-viral vectors in cellular (specifically T cell) and molecular therapy approaches, such as RNA, monoclonal antibody (mAb), and CRISPR therapeutics, with the aim of addressing the challenges in hemophilia treatment. By examining these innovative strategies, the study aims to shed light on potential solutions to enhance the efficacy and outcomes of hemophilia therapy.

Engraftment of retrovirally transduced Bet v 1-GFP expressing bone marrow cells leads to allergen-specific tolerance

Molecular chimerism is a promising strategy to induce tolerance to disease-causing antigens expressed on genetically modified haematopoietic stem cells. The approach was employed successfully in models of autoimmunity and organ transplantation. Recently, we demonstrated that molecular chimerism induces robust and lasting tolerance towards the major grass pollen allergen Phl p 5. Since allergens are a group of antigens differing widely in their function, origin and structure we further examined the effectiveness of molecular chimerism using the Phl p 5-unrelated major birch pollen allergen Bet v 1, co-expressed with the reporter GFP. Besides, inhibition of CD26 was used to promote engraftment of modified stem cells. Retrovirus VSV-Betv1-GFP was generated to transduce 5-FU-mobilized BALB/c hematopoietic cells to express membrane-bound Bet v 1 (VSV-GFP virus was used as control). Myeloablated BALB/c mice received Betv1-GFP or GFP expressing bone marrow cells, pre-treated with a CD26 inhibitor. Chimerism was followed by flow cytometry. Tolerance was assessed by measuring allergen-specific isotype levels in sera, RBL assays and T-cell proliferation assays. Mice transplanted with transduced BMC developed multi-lineage molecular chimerism which remained stable long-term (>8 months). After repeated immunizations with Bet v 1 and Phl p 5 serum levels of Bet v 1-specific antibodies (IgE, IgG1, IgG2a, IgG3 and IgA) remained undetectable in Betv1-GFP chimeras while high levels of Phl p 5-specific antibodies developed. Likewise, basophil degranulation was induced in response to Phl p 5 but not to Bet v 1 and specific non-responsiveness to Bet v 1 was observed in proliferation assays. These data demonstrate successful tolerization towards Bet v 1 by molecular chimerism. Stable long-term chimerism was achieved under inhibition of CD26. These results provide evidence for the broad applicability of molecular chimerism as tolerance strategy in allergy.

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.

Thymic gene transfer of myelin oligodendrocyte glycoprotein ameliorates the onset but not the progression of autoimmune demyelination

Tolerance induction, and thus prevention of autoimmunity, is linked with the amount of self-antigen presented on thymic stroma. We describe that intrathymic (i.t.) delivery of the autoantigen, myelin oligodendrocyte glycoprotein (MOG), via a lentiviral vector (LV), led to tolerance induction and prevented mice from developing fulminant experimental autoimmune encephalomyelitis (EAE). This protective effect was associated with the long-term expression of antigen in transduced stromal cells, which resulted in the negative selection of MOG-specific T cells and the generation of regulatory T cells (Tregs). These selection events were effective at decreasing T-cell proliferative responses and reduced Th1 and Th17 cytokines. In vivo, this translated to a reduction in inflammation and demyelination with minimal, or no axonal loss in the spinal cords of treated animals. Significantly intrathymic delivery of MOG to mice during the priming phase of the disease failed to suppress clinical symptoms despite mice being previously treated with a clearing anti-CD4 antibody. These results indicate that targeting autoantigens to the thymic stroma might offer an alternative means to induce the de novo production of tolerant, antigen-specific T cells; however, methods that control the number and or the activation of residual autoreactive cells in the periphery are required to successfully treat autoimmune neuroinflammation.

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.

Induction of transplantation tolerance to fully mismatched cardiac allografts by T cell mediated delivery of alloantigen

Induction of transplantation tolerance has the potential to allow for allograft acceptance without the need for life-long immunosuppression. Here we describe a novel approach that uses delivery of alloantigen by mature T cells to induce tolerance to fully allogeneic cardiac grafts. Adoptive transfer of mature alloantigen-expressing T cells into myeloablatively conditioned mice results in long-term acceptance of fully allogeneic heart transplants without evidence of chronic rejection. Since myeloablative conditioning is clinically undesirable we further demonstrated that adoptive transfer of mature alloantigen-expressing T cells alone into mice receiving non-myeloablative conditioning resulted in long-term acceptance of fully allogeneic heart allografts with minimal evidence of chronic rejection. Mechanistically, tolerance induction involved both deletion of donor-reactive host T cells and the development of regulatory T cells. Thus, delivery of alloantigen by mature T cells induces tolerance to fully allogeneic organ allografts in non-myeloablatively conditioned recipients, representing a novel approach for tolerance induction in transplantation.

Avenues for immunomodulation and graft protection by gene therapy in transplantation

Organ transplantation represents the only definitive therapy for many causes of end-organ failure. However, the universal success of this therapy is limited by chronic allograft rejection, the side effects of chronic immunosuppressive therapy, and a severe shortage of donor organs. Presently, the success of solid-organ transplantation depends on the continuous administration of toxic and nonspecific immunosuppressive agents, therapies that present risks for opportunistic infection, malignancy, and a variety of agent-specific side effects. To promote the use of transplantation with limited risk of long-term sequelae, three dominant research challenges emerge: (i) elimination of the need for exogenous immunosuppression by immunological tolerance induction; (ii) prevention of chronic rejection/graft dysfunction; and (iii) expansion of available organs for transplantation. Gene therapy may provide significant advances and solutions in each of these areas. Rejection of the graft in the immediate post-transplant period has been attacked through the transfer of immunomodulatory molecules in addition to tolerance inducing approaches. Chronic graft rejection may be similarly addressed through permanent tolerance induction or alternatively through the introduction of molecules to resist chronic graft damage. Genetic manipulation of stem cells may ultimately produce transgenic animals to serve as tissue donors to overcome the limited donor organ supply. This review will highlight ongoing developments in the translation of gene therapy approaches to the challenges inherent in transplantation.

Induction of alloreactive CD4 T cell tolerance in molecular chimeras: a possible role for regulatory T cells

Induction of molecular chimerism following reconstitution of mice with autologous bone marrow cells expressing a retrovirally encoded allogeneic MHC class I Ag results in donor-specific tolerance. To investigate the mechanism by which CD4 T cells that recognize allogeneic MHC class I through the indirect pathway of Ag presentation are rendered tolerant in molecular chimeras, transgenic mice expressing a TCR on CD4 T cells specific for peptides derived from K(b) were used. CD4 T cells expressing the transgenic TCR were detected in mice reconstituted with bone marrow cells transduced with retroviruses carrying the gene encoding H-2K(b), albeit detection was at lower levels than in mice receiving mock-transduced bone marrow. Despite the presence of CD4 T cells expressing an alloreactive TCR, mice receiving H-2K(b)-transduced bone marrow permanently accepted K(b) disparate skin grafts. CD4+CD25+ T cells from mice reconstituted with H-2K(b)-transduced bone marrow prevented rejection of K(b) disparate skin grafts when adoptively transferred into immunodeficient mice along with effector T cells, suggesting that induction of molecular chimerism leads to the generation of donor specific regulatory T cells, which may be involved in preventing alloreactive CD4 T cell responses that lead to rejection.

Human gene therapy and imaging in neurological diseases

Molecular imaging aims to assess non-invasively disease-specific biological and molecular processes in animal models and humans in vivo. Apart from precise anatomical localisation and quantification, the most intriguing advantage of such imaging is the opportunity it provides to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Further, molecular imaging can be used to address basic scientific questions, e.g. transcriptional regulation, signal transduction or protein/protein interaction, and will be essential in developing treatment strategies based on gene therapy. Most importantly, molecular imaging is a key technology in translational research, helping to develop experimental protocols which may later be applied to human patients. Over the past 20 years, imaging based on positron emission tomography (PET) and magnetic resonance imaging (MRI) has been employed for the assessment and "phenotyping" of various neurological diseases, including cerebral ischaemia, neurodegeneration and brain gliomas. While in the past neuro-anatomical studies had to be performed post mortem, molecular imaging has ushered in the era of in vivo functional neuro-anatomy by allowing neuroscience to image structure, function, metabolism and molecular processes of the central nervous system in vivo in both health and disease. Recently, PET and MRI have been successfully utilised together in the non-invasive assessment of gene transfer and gene therapy in humans. To assess the efficiency of gene transfer, the same markers are being used in animals and humans, and have been applied for phenotyping human disease. Here, we review the imaging hallmarks of focal and disseminated neurological diseases, such as cerebral ischaemia, neurodegeneration and glioblastoma multiforme, as well as the attempts to translate gene therapy's experimental knowledge into clinical applications and the way in which this process is being promoted through the use of novel imaging approaches.

Correction of murine hemophilia A by hematopoietic stem cell gene therapy

A serious complication of current protein replacement therapy for hemophilia A patients with coagulation factor VIII (FVIII) deficiency is the frequent development of anti-FVIII inhibitor antibodies that preclude therapeutic benefit from further treatment. Induction of tolerance by persistent high-level FVIII synthesis following transplantation with hematopoietic stem cells expressing a retrovirally delivered FVIII transgene offers the possibility of permanently correcting the disease. Here, we transplanted bone marrow cells transduced with an optimized MSCV-based FVIII oncoretroviral vector into immunocompetent hemophilia A mice that had been conditioned with a potentially lethal dose of irradiation (800 cGy), a sublethal dose of irradiation (550 cGy), or a nonmyeloablative preparative regimen involving busulfan. Therapeutic levels of FVIII (42, 18, and 11% of normal, respectively) were detected in the plasma of the transplant recipients for the duration of the study (over 6 months). Moreover, subsequent challenge with recombinant FVIII elicited at most a minor anti-FVIII inhibitor antibody response in any of the experimental animals, in contrast to the vigorous neutralizing humoral reaction to FVIII that was stimulated in naive hemophilia A mice. These findings represent an encouraging advance toward potential clinical application and long-term amelioration or cure of this progressively debilitating, life-threatening bleeding disorder.