Assessing Immunogenicity for Expressed Biologics in Gene Therapy

Expressed biologics require a careful assessment of immune responses to the vector, and the transgene protein. We developed an Anti-Drug-Antibody (ADA) assay against expressed IL-12p70 to support the development of gene therapy candidate with IL-12p70 coding sequence incorporated into NDV. We propose the parameters to be considered and highlight the challenges for developing ADA assays against expressed biologics with endogenous counterparts. For IL-12p70, high biological variability was observed in the ADA confirmatory assay, because of presence of pre-existing immunoreactivity, which generated false bridges, and could be inhibited by IL-12p70. Due to the presence of this pre-existing immunoreactivity, screening and confirmatory cut points varied significantly based upon the outlier selection method, which also impact the sensitivity and drug tolerance of the assay. Further characterization demonstrated that pe-existing immunoreactivity is from human IgG, likely to be autoantibodies. The presence of autoantibodies can be observed in patients with the drug that has a endogenous counterpart. Thus, to have a clinically meaningful immunogenicity assessment, it is critical to determine appropriate cut points and interpretate the ADA data in conjunction with the impact on PK, PD and safety.