Reduced reporter activity upon repeated administration of adeno-associated virus 5 in murine airways.

Sumner-Jones SG, Gill DR, Hyde SC

Download

British Society of Gene Therapy Conference, London, 2006

Recombinant AAV5 is a promising vector for long term airway gene transfer, as it uses apically-localised sialic acid as receptor. Previously, we have demonstrated luciferase reporter expression from rAAV5/5Lux persisting in mouse nasal and lung epithelia for many months. However for chronic lung diseases such as Cystic Fibrosis, repeated administration of the virus may be required due to the turnover of the terminally differentiated airway cells. Following a single dose of rAAV5/5Lux (1011 genome copies) to BALB/c mice by nasal instillation (n = 6-8), anti-AAV neutralising activity was detected in the serum within 1 week of dosing, which was maintained for the duration of the studies (over 7 months in nose, 12 months in lung). We have tested the impact of this immune response on the efficacy of repeated administration with rAAV5 vectors in the mouse airways (n = 5-8 per group). In the lung, luciferase activity following a single dose (1011 GC) of rAAV5/5 (19.33 ± 5.12 RLU/mg protein) was reduced on a second dose (0.23 ± 0.06 RLU/mg protein) and abolished following a third (0.07 ± 0.04 RLU/mg protein, p > 0.05 compared with naïve mice). Strategies to overcome this problem included: 1) increasing the interval between doses (from 8 weeks to 36 weeks); 2) the simultaneous expression of the immunosuppressor CTLA4Ig; 3) repeat administration in the nose. We did not see an improvement in luciferase activity after the second or third dose, and in each case the lack of reporter expression correlated with the presence of anti-AAV5 antibodies in serum. These studies indicate that alternative strategies to block or circumvent the immune response will be required to facilitate efficacious repeated administration of rAAV5 in the mouse airways