Gene therapy for alpha 1-antitrypsin deficiency with an oxidant-resistant human alpha 1-antitrypsin

Liver directed adeno-associated viral vectors to treat metabolic disease

The liver is the metabolic center of the body and an ideal target for gene therapy of inherited metabolic disorders (IMDs). Adeno-associated viral (AAV) vectors can deliver transgenes to the liver with high efficiency and specificity and a favorable safety profile. Recombinant AAV vectors contain only the transgene cassette, and their payload is converted to non-integrating circular double-stranded DNA episomes, which can provide stable expression from months to years. Insights from cellular studies and preclinical animal models have provided valuable information about AAV capsid serotypes with a high liver tropism. These vectors have been applied successfully in the clinic, particularly in trials for hemophilia, resulting in the first approved liver-directed gene therapy. Lessons from ongoing clinical trials have identified key factors affecting efficacy and safety that were not readily apparent in animal models. Circumventing pre-existing neutralizing antibodies to the AAV capsid, and mitigating adaptive immune responses to transduced cells are critical to achieving therapeutic benefit. Combining the high efficiency of AAV delivery with genome editing is a promising path to achieve more precise control of gene expression. The primary safety concern for liver gene therapy with AAV continues to be the small risk of tumorigenesis from rare vector integrations. Hepatotoxicity is a key consideration in the safety of neuromuscular gene therapies which are applied at substantially higher doses. The current knowledge base and toolkit for AAV is well developed, and poised to correct some of the most severe IMDs with liver-directed gene therapy.

Alpha-1 Antitrypsin Deficiency

Alpha-1 antitrypsin (AAT) deficiency is a common monogenic disorder in which there is a strong founder effect of a single missense mutation in SERPINA1, the gene encoding this major circulating serum anti-protease that is normally expressed primarily in hepatocytes. These features make AAT deficiency particularly attractive as a target for therapeutic gene editing using a wide variety of approaches.

Assessment of Residual Full-Length SV40 Large T Antigen in Clinical-Grade Adeno-Associated Virus Vectors Produced in 293T Cells

Efficient production of adeno-associated virus (AAV) vectors is a significant challenge. Human embryonic kidney HEK293T cells are widely used in good manufacturing practice facilities, producing higher yield of AAV vectors for clinical applications than HEK293 through the addition of a constitutive expression of SV40 large T antigen (SV40T), which stimulates Rep expression. However, the theoretical potential for tumorigenic consequences of a clinical AAV product containing residual DNA encoding SV40T, which may inhibit p53 growth suppressive functions is a safety concern. Although the risk is theoretical, to assure a low risk/high confidence of safety for clinical drug development, we have established a sensitive assay for assessment of functional full-length transcription competent SV40T DNA in HEK293T cell-produced AAV vectors. Using HEK293T generated 8, 9, and rh.10 serotype AAV vectors, the presence of SV40T in purified vector was assessed in vitro using quantitative polymerase chain reaction (qPCR) targeting a 129 bp amplicon combined with nested PCR targeting full-length SV40T DNA. Although low levels of the smaller amplicon were present in each AAV serotype, the full-length SV40T was undetectable. No transcription competent full-length SV40T DNA was observed by reverse transcription-quantitative polymerase chain reaction using an in vivo amplification of signal in mouse liver administered (2-10 × 1010 gc) 129 bp amplicon-positive AAV vectors. As a control for gene transfer, high levels of expressed transgene mRNAs were observed from each serotype AAV vector, yet, SV40T mRNA was undetectable. In vivo assessment of these three liver-tropic AAV serotypes, each with amplicon-positive qPCR SV40T DNA, demonstrated high transgene mRNA expression but no SV40T mRNA, that is, detection of small segments of SV40T DNA in 293T cell produced AAV inappropriately leads to the conclusion of residuals with the potential to express SV40T. This sensitive assay can be used to assess the level, if any, of SV40T antigen contaminating AAV vectors generated by HEK293T cells. ClinicalTrials.gov identifier: NCT03634007; NCT05302271; NCT01414985; NCT01161576.

Novel Gene-Correction-Based Therapeutic Modalities for Monogenic Liver Disorders

The majority of monogenic liver diseases are autosomal recessive disorders, with few being sex-related or co-dominant. Although orthotopic liver transplantation (LT) is currently the sole therapeutic option for end-stage patients, such an invasive surgical approach is severely restricted by the lack of donors and post-transplant complications, mainly associated with life-long immunosuppressive regimens. Therefore, the last decade has witnessed efforts for innovative cellular or gene-based therapeutic strategies. Gene therapy is a promising approach for treatment of many hereditary disorders, such as monogenic inborn errors. The liver is an organ characterized by unique features, making it an attractive target for in vivo and ex vivo gene transfer. The current genetic approaches for hereditary liver diseases are mediated by viral or non-viral vectors, with promising results generated by gene-editing tools, such as CRISPR-Cas9 technology. Despite massive progress in experimental gene-correction technologies, limitations in validated approaches for monogenic liver disorders have encouraged researchers to refine promising gene therapy protocols. Herein, we highlighted the most common monogenetic liver disorders, followed by proposed genetic engineering approaches, offered as promising therapeutic modalities.

High-level production of wild-type and oxidation-resistant recombinant alpha-1-antitrypsin in glycoengineered CHO cells

Alpha-1-antitrypsin (A1AT) is a serine protease inhibitor which blocks the activity of serum proteases including neutrophil elastase to protect the lungs. Its deficiency is known to increase the risk of pulmonary emphysema as well as chronic obstructive pulmonary disease. Currently, the only treatment for patients with A1AT deficiency is weekly injection of plasma-purified A1AT. There is still today no commercial source of therapeutic recombinant A1AT, likely due to significant differences in expression host-specific glycosylation profile and/or high costs associated with the huge therapeutic dose needed. Accordingly, we aimed to produce high levels of recombinant wild-type A1AT, as well as a mutated protein (mutein) version for increased oxidation resistance, with N-glycans analogous to human plasma-derived A1AT. To achieve this, we disrupted two endogenous glycosyltransferase genes controlling core α-1,6-fucosylation (Fut8) and α-2,3-sialylation (ST3Gal4) in CHO cells using CRISPR/Cas9 technology, followed by overexpression of human α-2,6-sialyltransferase (ST6Gal1) using a cumate-inducible expression system. Volumetric A1AT productivity obtained from stable CHO pools was 2.5- to 6.5-fold higher with the cumate-inducible CR5 promoter compared to five strong constitutive promoters. Using the CR5 promoter, glycoengineered stable CHO pools were able to produce over 2.1 g/L and 2.8 g/L of wild-type and mutein forms of A1AT, respectively, with N-glycans analogous to the plasma-derived clinical product Prolastin-C. Supplementation of N-acetylmannosamine to the cell culture media during production increased the overall sialylation of A1AT as well as the proportion of bi-antennary and disialylated A2G2S2 N-glycans. These purified recombinant A1AT proteins showed in vitro inhibitory activity equivalent to Prolastin-C and substitution of methionine residues 351 and 358 with valines rendered A1AT significantly more resistant to oxidation. The recombinant A1AT mutein bearing an improved oxidation-resistance described in this study could represent a viable biobetter drug, offering a safe and more stable alternative for augmentation therapy. This article is protected by copyright. All rights reserved.

Recent advancements in understanding the genetic involvement of alpha-1 antitrypsin deficiency associated lung disease: a look at future precision medicine approaches

INTRODUCTION

Alpha-1 antitrypsin deficiency occurs in individuals with deleterious genetic mutations on both chromosomes (maternal and paternal) in SERPINA1, the gene encoding the alpha-1 antitrypsin protein. There has been substantial progress in understanding the genetic variation that underlies the heterogeneous penetrance of lung disease in alpha-1 antitrypsin deficiency.

AREAS COVERED

This review will cover SERPINA1 gene structure and genetic variation, population genetics, genome-wide genetic modifiers of lung disease, alternative mechanisms of disease, and emerging therapeutics - including gene and cell therapy - related to alpha-1 antitrypsin deficiency-associated lung disease.

EXPERT OPINION

There remains ample opportunity to employ precision medicine in the diagnosis, prognosis, and therapy of alpha-1 antitrypsin deficiency-associated lung disease. In particular, a genome-wide association study and subsequent polygenic risk score is an important first step in identifying genome-wide genetic modifiers contributing to the variability of lung disease in severe alpha-1 antitrypsin deficiency.

A reactive center loop-based prediction platform to enhance the design of therapeutic SERPINs

Serine proteases are essential for many physiological processes and require tight regulation by serine protease inhibitors (SERPINs). A disturbed SERPIN-protease balance may result in disease. The reactive center loop (RCL) contains an enzymatic cleavage site between the P1 through P1' residues that controls SERPIN specificity. This RCL can be modified to improve SERPIN function; however, a lack of insight into sequence-function relationships limits SERPIN development. This is complicated by more than 25 billion mutants needed to screen the entire P4 to P4' region. Here, we developed a platform to predict the effects of RCL mutagenesis by using α1-antitrypsin as a model SERPIN. We generated variants for each of the residues in P4 to P4' region, mutating them into each of the 20 naturally occurring amino acids. Subsequently, we profiled the reactivity of the resulting 160 variants against seven proteases involved in coagulation. These profiles formed the basis of an in silico prediction platform for SERPIN inhibitory behavior with combined P4 to P4' RCL mutations, which were validated experimentally. This prediction platform accurately predicted SERPIN behavior against five out of the seven screened proteases, one of which was activated protein C (APC). Using these findings, a next-generation APC-inhibiting α1-antitrypsin variant was designed (KMPR/RIRA; / indicates the cleavage site). This variant attenuates blood loss in an in vivo hemophilia A model at a lower dosage than the previously developed variant AIKR/KIPP because of improved potency and specificity. We propose that this SERPIN-based RCL mutagenesis approach improves our understanding of SERPIN behavior and will facilitate the design of therapeutic SERPINs.

Augmentation therapy with alpha 1-antitrypsin: present and future of production, formulation, and delivery

Alpha 1-antitrypsin is one of the first protein therapeutics introduced on the market - more than 30 years ago - and, to date, it is indicated only for the treatment of the severe forms of a genetic condition known as alpha-1 antitrypsin deficiency. The only approved preparations are derived from plasma, posing potential problems associated with its limited supply and high processing costs. Moreover, augmentation therapy with alpha 1-antitrypsin is still limited to intravenous infusions, a cumbersome regimen for patients. Here, we review the recent literature on its possible future developments, focusing on i) the recombinant alternatives to the plasma-derived protein, ii) novel formulations, and iii) novel administration routes. Regulatory issues and the still unclear noncanonical functions of alpha 1-antitrypsin - possibly associated with the glycosylation pattern found only in the plasma-derived protein - have hindered the introduction of new products. However, potentially new therapeutic indications other than the treatment of alpha-1 antitrypsin deficiency might open the way to new sources and new formulations.

Alpha-1 antitrypsin deficiency and recombinant protein sources with focus on plant sources: Updates, challenges and perspectives

Alpha-1 antitrypsin deficiency (A1ATD) is an autosomal recessive disease characterized by low plasma levels of A1AT, a serine protease inhibitor representing the most abundant circulating antiprotease normally present at plasma levels of 1-2 g/L. The dominant clinical manifestations include predispositions to early onset emphysema due to protease/antiprotease imbalance in distal lung parenchyma and liver disease largely due to unsecreted polymerized accumulations of misfolded mutant A1AT within the endoplasmic reticulum of hepatocytes. Since 1987, the only FDA licensed specific therapy for the emphysema component has been infusions of A1AT purified from pooled human plasma at the 2020 cost of up to US $200,000/year with the risk of intermittent shortages. In the past three decades various, potentially less expensive, recombinant forms of human A1AT have reached early stages of development, one of which is just reaching the stage of human clinical trials. The focus of this review is to update strategies for the treatment of the pulmonary component of A1ATD with some focus on perspectives for therapeutic production and regulatory approval of a recombinant product from plants. We review other competitive technologies for treating the lung disease manifestations of A1ATD, highlight strategies for the generation of data potentially helpful for securing FDA Investigational New Drug (IND) approval and present challenges in the selection of clinical trial strategies required for FDA licensing of a New Drug Approval (NDA) for this disease.

Post-Translational Modifications of Circulating Alpha-1-Antitrypsin Protein

Alpha-1-antitrypsin (AAT), an acute-phase protein encoded by the SERPINA1 gene, is a member of the serine protease inhibitor (SERPIN) superfamily. Its primary function is to protect tissues from enzymes released during inflammation, such as neutrophil elastase and proteinase 3. In addition to its antiprotease activity, AAT interacts with numerous other substances and has various functions, mainly arising from the conformational flexibility of normal variants of AAT. Therefore, AAT has diverse biological functions and plays a role in various pathophysiological processes. This review discusses major molecular forms of AAT, including complex, cleaved, glycosylated, oxidized, and S-nitrosylated forms, in terms of their origin and function.