The January 2005 CMC Strategy Forum was devoted to a discussion of live virus vaccines and viral vectors used for gene therapy. The purpose of the meeting was to determine whether consensus positions could be reached among the delegates regarding lot release, stability, characterization, and comparability testing. Part 1 of this two-part report on that meeting describes factors influencing the choices of lot-release assays for vaccines and gene-therapy products (1). Part 2 presents potency testing, characterization, and comparability studies, including case studies and discussion (2).
The morning session featured plenary presentations by Keith Peden (CBER, Office of Vaccines Research and Review) and Denise Gavin (CBER, Office of Cellular, Tissues, and Gene Therapies). Peden presented an overview of factors that influence the choice of lot release assays for vaccines. Gavin described how gene therapy products are delivered through a vector with the intent of directly expressing a gene in vivo or modifying cells ex vivo for subsequent administration. The final speaker was Jim Gombold (Merck & Co., Inc.), who discussed potency testing of live-virus vaccines. His case study exemplified issues that can arise during commercial product testing.
The first panel covered topics from the first three talks:
- FDA requirements for a viral-vectored vaccine differ from those for the same viral vector when it is used in gene therapy
- identity testing, potency testing, and limits for residual DNA and protein differed depending on a product’s intended indication and where that product is reviewed
- allowable levels of host proteins (different agencies holding different views).
In the afternoon session, Ziping Wei (MedImmune) presented an overview of techniques used to characterize virus subpopulations. Khandan Baradaran (Biogen Idec) presented a discussion on comparability studies, which are required when manufacturing changes are made.
The afternoon panel discussed characterization of virus subpopulations and comparability studies following manufacturing changes. Virus subpopulations were defined as aggregates, immature or defective particles, and genetic variants. Several techniques used to characterize virus preparations were presented: field-flow fractionation (FFF), transmission electron microscopy (TEM), quantitative polymerase chain reaction (Q-PCR), density gradient centrifugation, and plaque assays. These techniques are designed to assess particle count, size heterogeneity, morphology, and potency.
1 Gombold J, et al. Lot Release and Characterization Testing of Live-Virus–Based Vaccine and Gene Therapy Products: Part One. BioProcess Int. 4(4) 2006: 46–54; www. bioprocessintl.com/wp-content/uploads/bpi-content/4-4_ Schenerman_CMCp_103112a.pdf.
2 Gombold J, et al. Lot Release and Characterization Testing of Live-Virus–Based Vaccine and Gene Therapy Products: Part Two. BioProcess Int. 4(5) 2006: 56–65; www.