A33-07 Il-21r Signaling Plays a Key Role in Mounting Humoral and Cell-mediated Immune Response to Adenoviral and Adeno-associated Viral Vectors in the Lung

Abstract Rationale Although cystic fibrosis (CF) was discovered ∼ a century ago, it remains without an available cure for all mutations. 8-10% of CF patients remain without therapy options despite advancements in targeting misfolded CFTR. Gene therapy is an active area of investigation to address this unmet need; however, the need for re-dosing remains a challenge for any means of viral vector delivery. Thus, mitigating the immune response may be the key to overcoming this challenge. Given the central role of IL-21R in regulating T and B cell immune response, we hypothesized that targeting IL-21R may attenuate B and T cell responses and enhance secondary transgene expression. Methods Naïve or Il21r-/- mice received 4x1010 viral particles and 1x1011 viral particles intratracheally of an Ad5 vector for first and repeat doses, respectively, at days 0 and ∼27. Serum anti-vector antibodies were assayed 2 weeks post-dosing. All mice were euthanized 3 days following 2nd viral dose. Lung tissue was harvested for analysis of B cells and CD8 tissue resident memory (TRM) cells, as well as secondary transgene expression. Similarly, naïve or Il21r-/- mice received 1x1011 vg of adeno-associated virus 6.2 (AAV6.2) by endotracheal intubation and monitored with In Vivo imaging system (IVIS) to assess for transgene expression. Results At 2 weeks, serum anti-AdV IgG (P 0.05) and IgG1 (P 0.01) were significantly decreased in the IL21R-/- mice by 2-way ANOVA. Flow cytometry analysis showed a significant reduction of CD8 TRM cells in IL-21R-/- mice (P 0.01) by nonparametric T-test and a reduction in CD19 B cells (P 0.05) by 2-way ANOVA. Moreover, secondary transgene expression was significantly enhanced in IL-21R-/- mice compared to B6 controls (P 0.01). Similarly, in the context of AAV, the generation of anti-AAV IgG requires IL-21R signaling (P 0.0001). IVIS also showed significantly enhanced secondary transgene expression of AAV6.2 in IL-21R-/- (P 0.0001). Conclusions Our results consistently showed how IL-21R and IL-21 play an important role in the development of humoral and CD8 TRM-mediated response to adenoviral and AAV vectors. This suggests how targeting IL-21R signaling may be the key to overcoming challenges for gene therapy using viral vectors as a means of delivery. Future studies will investigate the role of IL-21R in adult mice using antibody blockade. This abstract is funded by: NHLBI Grant R38HL155774 StARR program at Tulane University and Dr Kolls’s KOLLS25G0 CFF grant