The seroprevalence of neutralizing antibodies against the adeno-associated virus capsids in Japanese hemophiliacs

Adeno-associated viral vector integration: implications for long-term efficacy and safety

Adeno-associated virus (AAV) vector gene therapy provides a promising platform for treatment of monogenic inherited disorders. Clinical studies have demonstrated long-term expression with reduction in bleeding using this approach for the treatment of hemophilia. Despite these advances, there are unknowns surrounding the natural history of recombinant AAV (rAAV) vectors and the cellular mechanisms mediating vector persistence. These unknowns underpin questions regarding long-term efficacy and safety. The predominant mechanism via which AAV is proposed to persist is in circular double-stranded extrachromosomal DNA structures (episomes) within the nucleus. Studies of wild-type AAV (WT-AAV) and rAAV have demonstrated that AAV also persists via integration into a host cell's DNA. It is important to determine whether these integration events can mediate expression or could result in any long-term safety concerns. WT-AAV infection affects a large proportion of the general population, which is thought to have no long-term sequelae. Recent studies have highlighted that this WT-AAV has been detected in cases of acute hepatitis in children and in a minority of cases of hepatocellular carcinoma. Integration following treatment using rAAV has also been reported in preclinical and clinical studies. There have been variable reports on the potential implications of integration for rAAV vectors, with data in some murine studies demonstrating recurrent integration with development of hepatocellular carcinoma. These findings have not been seen in other preclinical or clinical studies. In this review, we will summarize current understanding of the natural history of AAV (wild-type and recombinant) with a focus on genomic integration and cellular implications.

The menace of severe adverse events and deaths associated with viral gene therapy and its potential solution

Over the past decade, in vivo gene replacement therapy has significantly advanced, resulting in market approval of numerous therapeutics predominantly relying on adeno-associated viral vectors (AAV). While viral vectors have undeniably addressed several critical healthcare challenges, their clinical application has unveiled a range of limitations and safety concerns. This review highlights the emerging challenges in the field of gene therapy. At first, we discuss both the role of biological barriers in viral gene therapy with a focus on AAVs, and review current landscape of in vivo human gene therapy. We delineate advantages and disadvantages of AAVs as gene delivery vehicles, mostly from the safety perspective (hepatotoxicity, cardiotoxicity, neurotoxicity, inflammatory responses etc.), and outline the mechanisms of adverse events in response to AAV. Contribution of every aspect of AAV vectors (genomic structure, capsid proteins) and host responses to injected AAV is considered and substantiated by basic, translational and clinical studies. The updated evaluation of recent AAV clinical trials and current medical experience clearly shows the risks of AAVs that sometimes overshadow the hopes for curing a hereditary disease. At last, a set of established and new molecular and nanotechnology tools and approaches are provided as potential solutions for mitigating or eliminating side effects. The increasing number of severe adverse reactions and, sadly deaths, demands decisive actions to resolve the issue of immune responses and extremely high doses of viral vectors used for gene therapy. In response to these challenges, various strategies are under development, including approaches aimed at augmenting characteristics of viral vectors and others focused on creating secure and efficacious non-viral vectors. This comprehensive review offers an overarching perspective on the present state of gene therapy utilizing both viral and non-viral vectors.

Seroprevalence of adeno-associated virus types 1, 2, 3, 4, 5, 6, 8, and 9 in a Basque cohort of healthy donors

Adeno-associated viruses (AAVs) are promising gene therapy vectors, but challenges arise when treating patients with preexisting neutralizing antibodies. Worldwide seroprevalence studies provide snapshots of existing immunity in diverse populations. Owing to the uniqueness of the Basque socio-geographical landscape, we investigated the seroprevalence of eight AAV serotypes in residents of the Basque Country. We found the highest seroprevalence of AAV3, and the lowest seroprevalence of AAV9. Additionally, less than 50% of the Basque population has neutralizing antibodies against AAV4, AAV6, and AAV9. Our findings provide insight into AAV infections in the Basque region, public health, and the development of AAV-based therapeutics.

Usefulness of antibody-drug conjugate as preconditioning for hematopoietic stem cell-targeted gene therapy in wild-type and Fabry disease mouse models

BACKGROUND

Fabry disease (FD) is characterized by deficient activity of α-galactosidase A (GLA). Consequently, globotriaosylceramide (Gb3) accumulates in various organs, causing cardiac, renal, and cerebrovascular damage. Gene therapies for FD have been investigated in humans. Strong conditioning is required for hematopoietic stem cell-targeted gene therapy (HSC-GT). However, strong conditioning leads to various side effects and should be avoided. In this study, we tested antibody-based conditioning for HSC-GT in wild-type and FD model mice.

METHODS

After preconditioning with an antibody-drug conjugate, HSC-GT using a lentiviral vector was performed in wild-type and Fabry model mice. In the wild-type experiment, the EGFP gene was introduced into HSCs and transplanted into preconditioned mice, and donor chimerism and EGFP expression were analyzed. In the FD mouse model, the GLA gene was introduced into HSCs and transplanted into preconditioned Fabry mice. GLA activity and Gb3 accumulation in the organs were analyzed.

RESULTS

In the wild-type mouse experiment, when anti-CD45 antibody-drug conjugate was used, the percentage of donor cells at 6 months was 64.5%, and 69.6% of engrafted donor peripheral blood expressed EGFP. When anti-CD117 antibody-drug conjugate and ATG were used, the percentage of donor cells at 6 months was 80.7%, and 73.4% of engrafted donor peripheral blood expressed EGFP. Although large variations in GLA activity among mice were observed in the FD mouse experiment for both preconditioning regimens, Gb3 was significantly reduced in many organs.

CONCLUSIONS

Antibody-based preconditioning may be an alternative preconditioning strategy for HSC-GT for treating FD.

Preexisting antibody assays for gene therapy: Considerations on patient selection cutoffs and companion diagnostic requirements

Recombinant adeno-associated virus (AAV) vectors are the leading delivery vehicle used for in vivo gene therapies. Anti-AAV antibodies (AAV Abs) can interact with the viral capsid component of an AAV-based gene therapy (GT). Therefore, patients with preexisting AAV Abs (seropositive patients) are often excluded from GT trials to prevent treatment of patients who are unlikely to benefit1 or may have a higher risk for adverse events outweighing treatment benefits. On the contrary, unnecessary exclusion of patients with high unmet medical need should be avoided. Instead, a risk-benefit assessment that weighs the potential risks due to seropositivity vs. severity of disease and available treatment options, should drive the decision if patient selection is required. Assays for patient selection must be validated according to their intended use following national regulations/standards for diagnostic assays in appropriate laboratories. In this review, we summarize the current process of patient selection, including assay cutoff criteria and related assay validation approaches. We further provide considerations on regulatory requirements for the development of in vitro diagnostic tests supporting market authorization of a corresponding GT.

Epigenetic targets to enhance antitumor immune response through the induction of tertiary lymphoid structures

Tertiary lymphoid structures (TLS) are ectopic lymphoid aggregates found in sites of chronic inflammation such as tumors and autoimmune diseases. The discovery that TLS formation at tumor sites correlated with good patient prognosis has triggered extensive research into various techniques to induce their formation at the tumor microenvironment (TME). One strategy is the exogenous induction of specific cytokines and chemokine expression in murine models. However, applying such systemic chemokine expression can result in significant toxicity and damage to healthy tissues. Also, the TLS formed from exogenous chemokine induction is heterogeneous and different from the ones associated with favorable prognosis. Therefore, there is a need to optimize additional approaches like immune cell engineering with lentiviral transduction to improve the TLS formation in vivo. Similarly, the genetic and epigenetic regulation of the different phases of TLS neogenesis are still unknown. Understanding these molecular regulations could help identify novel targets to induce tissue-specific TLS in the TME. This review offers a unique insight into the molecular checkpoints of the different stages and mechanisms involved in TLS formation. This review also highlights potential epigenetic targets to induce TLS neogenesis. The review further explores epigenetic therapies (epi-therapy) and ongoing clinical trials using epi-therapy in cancers. In addition, it builds upon the current knowledge of tools to generate TLS and TLS phenotyping biomarkers with predictive and prognostic clinical potential.

Efficient gene transduction in pigs and macaques with the engineered AAV vector AAV.GT5 for hemophilia B gene therapy

Gene therapy using adeno-associated virus (AAV)-based vectors has become a realistic therapeutic option for hemophilia. We examined the potential of a novel engineered liver-tropic AAV3B-based vector, AAV.GT5, for hemophilia B gene therapy. In vitro transduction with AAV.GT5 in human hepatocytes was more than 100 times higher than with AAV-Spark100, another bioengineered vector used in a clinical trial. However, liver transduction following intravenous injection of these vectors was similar in mice with a humanized liver and in macaques. This discrepancy was due to the low recovery and short half-life of AAV.GT5 in blood, depending on the positive charge of the heparin-binding site in the capsid. Bypassing systemic clearance with the intra-hepatic vascular administration of AAV.GT5, but not AAV-Spark100, enhanced liver transduction in pigs and macaques. AAV.GT5 did not develop neutralizing antibodies (NAbs) in two of four animals, while AAV-Spark100 induced serotype-specific NAbs in all macaques tested (4 of 4). The NAbs produced after AAV-Spark100 administration were relatively serotype specific, and challenge with AAV.GT5 through the hepatic artery successfully boosted liver transduction in one animal previously administered AAV-Spark100. In summary, AAV.GT5 showed different vector kinetics and NAb induction compared with AAV-Spark100, and intra-hepatic vascular administration may minimize the vector dose required and vector dissemination.

Prevalence of Neutralizing Antibodies against Adeno-Associated Virus Serotypes 1, 2, and 9 in Non-Injected Latin American Patients with Heart Failure—ANVIAS Study

Neutralizing antibody (NAb) activity against the viral capsid of adeno-associated viral (AAV) vectors decreases transduction efficiency, thus limiting transgene expression. Several reports have mentioned a variation in NAb prevalence according to age, AAV serotype, and, most importantly, geographic location. There are currently no reports specifically describing the anti-AAV NAb prevalence in Latin America. Here, we describe the prevalence of NAb against different serotypes of AAV vectors (AAV1, AAV2, and AAV9) in Colombian patients with heart failure (HF) (referred to as cases) and healthy individuals (referred to as controls). The levels of NAb were evaluated in serum samples of 60 subjects from each group using an in vitro inhibitory assay. The neutralizing titer was reported as the first dilution inhibiting ≥50% of the transgene signal, and the samples with neutralizing titers at ≥1:50 dilution were considered positive. The prevalence of NAb in the case and control groups were similar (AAV2: 43% and 45%, respectively; AAV1 33.3% in each group; AAV9: 20% and 23.2%, respectively). The presence of NAb for two or more of the serotypes analyzed was observed in 25% of the studied samples, with the largest amount in the positive samples for AAV1 (55–75%) and AAV9 (93%), suggesting serial exposures, cross-reactivity, or coinfection. Moreover, patients in the HF group exhibited more common combined seropositivity for NAb against AAV1 d AAV9 than those in the control group (91.6% vs. 35.7%, respectively; p = 0.003). Finally, exposure to toxins was significantly associated with the presence of NAb in all regression models. These results constitute the first report of the prevalence of NAb against AAV in Latin America, being the first step to implementing therapeutic strategies based on AAV vectors in this population in our region.