Currently, adeno-associated virus (AAV) is one of the primary gene delivery vectors in gene therapy, facilitating long-term in vivo gene expression. Despite being imperative, it is incredibly challenging to precisely assess AAV particle distribution according to the sedimentation coefficient and identify impurities related to capsid structures. This study performed the systematic methodological validation of quantifying the AAV empty and full capsid ratio. This includes specificity, accuracy, precision, linearity, and parameter variables involving the sedimentation velocity analytical ultracentrifugation (SV-AUC) method. Specifically, SV-AUC differentiated among the empty, partial, full, and high sedimentation coefficient substance (HSCS) AAV particles while evaluating their sedimentation heterogeneity. The intermediate precision analysis of HE (high percentage of empty capsid) and HF (high percentage of full capsid) samples revealed that the specific species percentage, such as empty or full, was more significant than 50%. Moreover, the relative standard deviation (RSD) could be within 5%. Even for empty or partially less than 15%, the RSD could be within 10%. The accuracy recovery rates of empty capsid were between 103.9% and 108.7% across three different mixtures. When the measured percentage of specific species was more significant than 14%, the recovery rate was between 77.9% and 106.6%. Linearity analysis revealed an excellent linear correlation between the empty, partial, and full in the HE samples. The AAV samples with as low as 7.4 × 10 ¹¹ cp/mL AAV could be accurately quantified with SV-AUC. The parameter variable analyses revealed that variations in cell alignment significantly affected the overall results. Still, the detection wavelength of 235 nm slightly influenced the empty, partial, and full percentages. Minor detection wavelength changes showed no impact on the sedimentation coefficient of these species. However, the temperature affected the measured sedimentation coefficient. These results validated the SV-AUC method to quantify AAV. This study provides solutions to AAV empty and full capsid ratio quantification challenges and the subsequent basis for calibrating the AAV empty capsid system suitability substance. Because of the AAV structure and potential variability complexity in detection, we jointly calibrated empty capsid system suitability substance with three laboratories to accurately detect the quantitative AAV empty and full capsid ratio. The empty capsid system suitability substance could be used as an external reference to measure the performance of the instrument. The results could be compared with multiple QC (quality control) laboratories based on the AAV vector and calibration accuracy. This is crucial for AUC to be used for QC release and promote gene therapy research worldwide.

The long-acting growth hormone (LAGH) is a promising alternative biopharmaceutical to treat growth hormone (GH) deficiency in children, and it was developed using a variety of technologies by several pharmaceutical companies. Most LAGH preparations, such as Fc fusion protein, are currently undergoing preclinical study and clinical trials. Accurate determination of bioactivity is critical for the efficacy of quality control systems of LAGH. The current in vivo rat weight gain assays used to determine the bioactivity of recombinant human GH (rhGH) in pharmacopoeias are time-consuming, expensive, and imprecise, and there are no recommended bioassays for LAGH bioactivity in pharmacopoeias. Therefore, we developed a cell-based bioassay for bioactivity determination of therapeutic long-acting Fc-fusion recombinant human growth hormone (rhGH-Fc) based on the luciferase reporter gene system, which is involved in the full-length human GH receptor (hGHR) and the SG (SIE and GAS) response element. The established bioassay was comprehensively validated according to the International Council for Harmonization (ICH) Q2 (R1) guidelines and the Chinese Pharmacopoeia, and is highly precise, time-saving, simple, and robust. The validated bioassay could be qualified for bioactivity determination during the research, development, and manufacture of rhGH-Fc, and other LAGH formulations.

Adeno-associated virus (AAV) is a promising gene therapy vector due to its high transduction efficiency, low pathogenicity, low immunogenicity, and the ability to mediate the long-term stable expression of exogenous genes. The viral particle titer is an essential quality attribute of recombinant adeno-associated virus (rAAV) gene therapy products. Multiangle light scattering (MALS) is an important means of directly measuring the absolute molecular weight and distribution of macromolecular drugs. This study established and validated a method based on SEC-UV-MALS-RI tandem technology for accurately determining rAAV particle titers. The verification results indicated that the method exhibited good specificity, linearity, precision, accuracy, and durability. Several collaborative laboratories used this method to calibrate the standard substances needed for rAAV particle titer determination. The results suggested that combining the SEC-MALS method with standard substances enables the rapid and accurate measurement of the viral particle titers in rAAV gene therapy products.

Bietti crystalline dystrophy (BCD) is a hereditary retinal disease caused by loss-of-function mutations in the CYP4V2 gene. Gene replacement therapy using rAAV-hCYP4V2 represents a promising therapeutic strategy, requiring robust bioassays for product quality control. This study developed and validated a sensitive LC-MS/MS method for quantifying CYP4V2 enzyme activity. Lysates from HeLa-AAVR cells transduced with rAAV-hCYP4V2 (MOI = 3 × 10⁵) were used, with lauric acid as substrate supplemented with cytochrome P450 reductase, cytochrome b5, and NADPH. The ω-hydroxylated product (12-hydroxy lauric acid) was quantified using tolbutamide as an internal standard. Method validation followed ICH guidelines. Results demonstrated excellent specificity with negligible background in negative controls. Linearity was achieved over 0.5–100 ng/mL (R² > 0.99), with an average recovery of 100.6%. Intra-batch and inter-batch precision RSDs were <47.8% and <28.4%, respectively. Product stability was maintained for ≥4 weeks at −80°C. The method was successfully applied to three AAV serotypes (AAV2, AAV8, and AAV2/8), with all RSDs < 23.9%. This validated LC-MS/MS bioassay provides a crucial quality control tool for potency assessment, process development, batch release, and stability studies of rAAV-hCYP4V2 gene therapy products.

Bietti crystalline dystrophy like retinal degeneration (BCD) is an inherited retinal degenerative disease caused by defects in the CYP4V2 gene. Recombinant AAV-based gene replacement therapy holds promise for this disease, yet reliable enzymatic activity assays for product potency evaluation remain urgently needed. This study established and validated a method for determining the enzymatic activity of CYP4V2 based on the bioluminescent substrate Luciferin-MultiCYP.HEK293-AAVR cells were seeded at 1 × 10⁴ cells/well and transduced with rAAV-hCYP4V2 across an MOI gradient (1.17 × 10³–2.4 × 10⁶). After incubating at 37 °C for 72 h, medium was replaced with Opti-MEM containing 20 µM Luciferin-MultiCYP and incubated for 90 min ± 30 min. Next, cell supernatants were mixed with luciferase reagent, and bioluminescence was measured. Methodological validation results revealed that the method has good specificity, with an accuracy recovery rate of 100.94% ± 2.84% (RSD = 2.81%). Repeatability (GCV%) was 4.21%, and intermediate precision (RSD) was 6.16%. Linearity was good within the MOI range of 1.17 × 10³ to 2.4 × 10⁶ (R² = 0.9902 ± 0.0061, n = 9). Lastly, the method was successfully applied to activity testing the products of three AAV serotypes (AAV8, AAV2/8, and AAV2). This bioluminescent method meets regulatory potency assay requirements and serves as an effective QC tool for process development, batch release, and stability evaluation of rAAV-hCYP4V2 products.