Liver-directed lentiviral gene therapy corrects hemophilia A mice and achieves normal-range factor VIII activity in non-human primates

GP64-pseudotyped lentiviral vectors target liver endothelial cells and correct hemophilia A mice

Lentiviral vectors (LV) are efficient vehicles for in vivo gene delivery to the liver. LV integration into the chromatin of target cells ensures their transmission upon proliferation, thus allowing potentially life-long gene therapy following a single administration, even to young individuals. The glycoprotein of the vesicular stomatitis virus (VSV.G) is widely used to pseudotype LV, as it confers broad tropism and high stability. The baculovirus-derived GP64 envelope protein has been proposed as an alternative for in vivo liver-directed gene therapy. Here, we perform a detailed comparison of VSV.G- and GP64-pseudotyped LV in vitro and in vivo. We report that VSV.G-LV transduced hepatocytes better than GP64-LV, however the latter showed improved transduction of liver sinusoidal endothelial cells (LSEC). Combining GP64-pseudotyping with the high surface content of the phagocytosis inhibitor CD47 further enhanced LSEC transduction. Coagulation factor VIII (FVIII), the gene mutated in hemophilia A, is naturally expressed by LSEC, thus we exploited GP64-LV to deliver a FVIII transgene under the control of the endogenous FVIII promoter and achieved therapeutic amounts of FVIII and correction of hemophilia A mice.

In vivo macrophage engineering reshapes the tumor microenvironment leading to eradication of liver metastases

Liver metastases are associated with poor response to current pharmacological treatments, including immunotherapy. We describe a lentiviral vector (LV) platform to selectively engineer liver macrophages, including Kupffer cells and tumor-associated macrophages (TAMs), to deliver type I interferon (IFNα) to liver metastases. Gene-based IFNα delivery delays the growth of colorectal and pancreatic ductal adenocarcinoma liver metastases in mice. Response to IFNα is associated with TAM immune activation, enhanced MHC-II-restricted antigen presentation and reduced exhaustion of CD8+ T cells. Conversely, increased IL-10 signaling, expansion of Eomes CD4+ T cells, a cell type displaying features of type I regulatory T (Tr1) cells, and CTLA-4 expression are associated with resistance to therapy. Targeting regulatory T cell functions by combinatorial CTLA-4 immune checkpoint blockade and IFNα LV delivery expands tumor-reactive T cells, attaining complete response in most mice. These findings support a promising therapeutic strategy with feasible translation to patients with unmet medical need.

Current limitations of gene therapy for rare pediatric diseases: Lessons learned from clinical experience with AAV vectors

Gene therapy using adeno-associated viral (AAV) vectors is a promising therapeutic strategy for multiple inherited diseases. Following intravenous injection, AAV vectors carrying a copy of the missing gene or the genome-editing machinery reach their target cells and deliver the genetic material. Several clinical trials are currently ongoing and significant success has already been achieved with at least six AAV gene therapy products with market approval in Europe and the United States. Nonetheless, clinical trials and preclinical studies have uncovered several limitations of AAV gene transfer, which need to be addressed in order to improve the safety and enable the treatment of the largest patient population. Limitations include the occurrence of immune-mediated toxicities, the potential loss of correction in the long run, and the development of neutralizing antibodies against AAV vectors preventing re-administration. In this review, we summarize these limitations and discuss the potential technological developments to overcome them. © 2023 Published by Elsevier Masson SAS on behalf of French Society of Pediatrics.

Gene therapy for hemophilia, a clinical viewpoint

Gene therapy for hemophilia has been investigated for decades but no breakthroughs were made until Nathwani et al. achieved a significant and sustainable factor IX increase in hemophilia B patients in 2011. About eleven years later, in August 2022, the first hemophilia A gene therapy product was approved by the European Commission and hemophilia treatment entered a new era. This review does not focus on the newest advances but rather the practical aspects of gene therapy aiming to provide an overview for physicians who treat hemophiliacs who did not participate in the clinical trials. The current status of gene therapy, focusing particularly on products likely to be clinically available soon, are reviewed and summarized. Currently, possible limitations of gene therapy are pre-existing neutralizing antibodies toward the vector, liver health, age, and inhibitor status. Possible safety concerns include infusion reactions, liver damage, and adverse effects from immune suppressants or steroids. In summary, generally speaking, gene therapy is effective, at least for several years, but the exact effect may be unpredictable and intensive monitoring for several months is needed. It can also be considered safe with careful practice on selected patients. In its current form, gene therapy will not replace all hemophilia treatments. Advances in non-factor therapy will also improve hemophilia care greatly in the future. We envisage that gene therapy may be included in multiple novel therapies for hemophilia and benefit some hemophilia patients while novel non-factor therapies may benefit others, together fulfilling the unmet needs of all hemophilia patients.

Innate Immune Response to Viral Vectors in Gene Therapy

Viral vectors play a pivotal role in the field of gene therapy, with several related drugs having already gained clinical approval from the EMA and FDA. However, numerous viral gene therapy vectors are currently undergoing pre-clinical research or participating in clinical trials. Despite advancements, the innate response remains a significant barrier impeding the clinical development of viral gene therapy. The innate immune response to viral gene therapy vectors and transgenes is still an important reason hindering its clinical development. Extensive studies have demonstrated that different DNA and RNA sensors can detect adenoviruses, adeno-associated viruses, and lentiviruses, thereby activating various innate immune pathways such as Toll-like receptor (TLR), cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING), and retinoic acid-inducible gene I-mitochondrial antiviral signaling protein (RLR-MAVS). This review focuses on elucidating the mechanisms underlying the innate immune response induced by three widely utilized viral vectors: adenovirus, adeno-associated virus, and lentivirus, as well as the strategies employed to circumvent innate immunity.

Hemophilia treatment innovation: 50 years of progress and more to come

With the goal of emphasizing the striking advances that materialized in hemophilia care particularly in the last 10 years, the progress of knowledge that started from the 1970s will first be sketched as background. Subsequently, the unmet needs pertaining to therapeutic adherence and thus to prophylaxis effectiveness led to the availability of factor VIII and IX products with an extended plasma half-life as well as to emicizumab, the first nonfactor medicine for subcutaneous administration in patients with hemophilia A with or without inhibitor. The issue of a still lacking cure for the disease is approached by means of gene therapy, the first products of which were approved in 2022 for adults with both hemophilia types. Finally, views will be offered on further progress that is expected in the next few years and how patients and their care providers may make personalized choices among the wide array of therapeutic options.

Gene therapy for liver diseases - progress and challenges

Gene therapy is poised to revolutionize modern medicine, with seemingly unlimited potential for treating and curing genetic disorders. For otherwise incurable indications, including most inherited metabolic liver disorders, gene therapy provides a realistic therapeutic option. In this Review, we discuss gene supplementation and gene editing involving the use of recombinant adeno-associated virus (rAAV) vectors for the treatment of inherited liver diseases, including updates on several ongoing clinical trials that are producing promising results. Clinical testing has been essential in highlighting many key translational challenges associated with this transformative therapy. In particular, the interaction of a patient's immune system with the vector raises issues of safety and the duration of treatment efficacy. Furthermore, several serious adverse events after the administration of high doses of rAAVs suggest greater involvement of innate immune responses and pre-existing hepatic conditions than initially anticipated. Finally, permanent modification of the host genome associated with rAAV genome integration and gene editing raises concerns about the risk of oncogenicity that require careful evaluation. We summarize the main progress, challenges and pathways forward for gene therapy for liver diseases.