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AAV Gene Therapy: Vector Shedding In Clinical Studies

Vector shedding refers to the release or shedding of viral vectors from cells transduced with the vectors. AAV (adeno-associated virus) is a commonly used viral vector in gene therapy. Studying its fate after the administration to the clinical trial subjects is critical to understanding the shedding route and the duration. Although AAVs are noninfectious, replication incompetent and do not propagate outside the cells, understanding the route and duration of the shedding would enable the mitigation of any potential risk of viral vectors including:

  • spread of AAV vectors beyond treated subjects/patients (both horizontal and vertical transfer)
  • deleterious effects on persons other than the study subjects.

Method for Evaluation of Vector Shedding and Clearance (Duration)

Vector DNA biodistribution is assessed by qPCR in blood and vector DNA shedding was assessed by qPCR in semen, saliva, urine, and stool. The biodistribution and shedding of potentially infectious vector DNA may be further characterized in plasma and semen by evaluating concentrations of encapsidated vector DNA using immunoprecipitation-coupled qPCR (iqPCR). 

Vector Clearance (Duration): 
The maximum time to achieve vector DNA clearance, evaluated by qPCR assay, defined as 3 consecutive BLQ samples, in blood, saliva, semen, and stool is observed.




The biodistribution of vector DNA in blood was further characterized through qPCR analysis of PBMC, RBC and plasma fractions of whole blood. The contiguity and structural characteristics of vector DNA in whole blood and PBMCs were further evaluated using droplet digital PCR (ddPCR) methods

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