Combination Of BMI, DLS And Visual Inspection To Resolve Particle Formulation Issues In Formulations Commonly Used In Gene Therapy

By A. Stockinger, P. Beck, and S. Schermann

The development of gene therapies requires a rigorous approach to ensure both product safety and efficacy. Traditionally, the consideration of subvisible particles in formulation development has been postponed to later stages due to resource-intensive methods such as light obscuration (LO) and micro flow imaging (MFI). Given the limited material available in early-stage gene therapy, low-volume, high-throughput methods for detecting both subvisible and visible particles are essential. This study highlights the use of Backgrounded Membrane Imaging (BMI) as a low-volume method for identifying optimal buffer conditions that minimize subvisible and visible particle formation early in formulation development. Using a standard PBS AAV formulation with a protein excipient, we screened a variety of excipient conditions at room temperature over 7 days to determine the best formulation to prevent particle formation. BMI’s low-volume requirement allowed us to conduct the study with only 150 µl of sample per condition.

In addition to BMI, Dynamic Light Scattering (DLS) and Visual Inspection (VI) were used to support our findings, which revealed that particle aggregation could be resolved by introducing a common surfactant to the formulation buffer and optimizing its concentration. BMI enabled the characterization of particles in both the subvisible and visible ranges (0.2 µm - 5 mm) at low volumes, complementing DLS, which detects smaller aggregates (less than 1 µm), and VI, which identifies larger particles (>150 µm). However, there is a potential blind spot for particles between 1 µm and 2 µm, which presents a challenge to achieving full characterization of the particle size range. Nonetheless, combining BMI, DLS, and VI provides a comprehensive and synergistic approach to addressing the challenges of particle formation in gene therapy formulation development.