We have investigated the immune response to El-deleted adenovirus vect
ors encoding the lacZ gene introduced into the brains of adult mice. I
njection of these nonreplicating vectors caused a marked inflammatory
response in the brain as assessed by immunocytochemistry and flow cyto
metry of leukocytes. Infiltrating leukocytes were detectable within 2
days of injection and reached a maximum by 9 days. Thereafter, the num
ber of infiltrating cells decreased, but a small number persisted in t
he brain until day 60. Between 2 and 4 days after injection, the perce
ntage of CD8(+) cells detectable increased whereas the percentage of C
D4(+) cells present in the infiltrating population did not significant
ly increase until day 6, peaking on day 15. Activated CD25(+) T cells
were detectable between days 6 and 15. beta-Galactosidase (beta-Gal),
the product of the lacZ gene encoded by the vector, was also detected,
both at the injection site in the striatum and also in the substantia
nigra. Expression peaked between 4 and 6 days but a small number of b
eta-Gal(+) cells was still seen at 60 days after injection. This study
demonstrates that a quantitative analysis of the immune responses cau
sed by a nonreplicating adenovirus vector is possible in the brain. El
-deleted adenoviral vectors trigger a strong inflammatory response in
the brain, but this immune response is not sufficient to eliminate com
pletely expression of genes encoded by the adenoviral construct.