Host cell protein impurities are not a relevant driver of gene therapy-associated immune response

Abstract

Purpose : Gene therapy-associated immune response following adeno-associated virus (AAV) based gene therapy has the potential to impact drug safety and efficacy. AAV based drugs contain manufacturing-associated impurities which are potentially immunogenic. The aim of this analysis was to evaluate the immunogenic potential of a common impurity, host cell protein (HCP), both in vitro and in vivo.

Methods : Two lots of clinical-grade AAV8 vector, which differed only in their amount of host cell proteins (36.9 ng/ml vs. 1433.7 ng/ml) were used to stimulate human plasmacytoid dendritic cells (pDCs), which play a crucial role as first line of defense against viral infections and initiation of anti-viral innate immune response. In addition, we reviewed the clinical outcomes of a 13-week subretinal safety and toxicology study in healthy non-human-primates (NHP), which also used lots that differed only in their HCP content (36.9 ng/ml vs. 582.0 ng/ml).

Results : In vitro stimulation of human pDCs with low vs. high HCP lots did not show a difference in cytokine response (e.g. IP-10: p=0.8535, MIP-1b: p=0.8171, TNF-a: p=0.6424). The main adverse outcome detected in the NHP study were chorioretinal atrophic (CRA) lesions at the injection site. Quantification (mean±SD) by fundus autofluorescence showed no difference (p=0.0912) between groups treated with low (1.488±1.838mm², n=8) vs high HCP lots (0.204±0.477mm², n=12).

Conclusions : In our in vitro essays, significantly elevated levels of HCP had no influence on the innate immune response in pDC. In line with this, there was no association between the HCP levels and size of CRA lesions in NHP after subretinal injection. High levels of HCP may not be a key driver of gene therapy associated immune response.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.