Some
inborn errors of metabolism due to deficiencies of soluble lysosomal
enzymes cause global
neurodegenerative disease. Representative examples include the infantile and late infantile forms of the
ceroid lipofuscinoses (CLN1 or CLN2 deficiency, respectively) and
mucopolysaccharidoses type VII (MPS VII), a deficiency of
beta-glucuronidase. Treatment of the central nervous system component of these disorders will require widespread
protein or
enzyme replacement, either through dissemination of the
protein or through dissemination of a gene encoding it. We hypothesize that transduction of brain microcapillary endothelium (BME) with recombinant viral vectors, with secretion of
enzyme product basolaterally, could allow for widespread
enzyme dissemination. To achieve this, viruses should be modified to target the BME. This requires (i) identification of a BME-resident target receptor, (ii) identification of motifs targeted to that molecule, (iii) the construction of modified viruses to allow for binding to the target receptor, and (iv) demonstrated transduction of receptor-expressing cells. In proof of principal experiments, we chose the human
transferrin receptor (hTfR), a molecule found at high density on human BME. A nonamer phage display library was panned for motifs which could bind hTfR. Forty-three clones were sequenced, most of which contained an AKxxK/R, KxKxPK/R, or KxK motif. Ten
peptides representative of the three motifs were cloned into the HI loop of adenovirus type 5 fiber. All motifs tested retained their ability to trimerize and bind
transferrin receptor, and seven allowed for recombinant adenovirus production. Importantly, the fiber-modified viruses facilitated increased gene transfer (2- to 34-fold) to hTfR expressing cell lines and human brain microcapillary endothelia expressing high levels of endogenous receptor. Our data indicate that adenoviruses can be modified in the HI loop for expanded tropism to the hTfR.