Adeno-associated virus type 2 (AAV-2) targeting vectors have been generated by insertion of ligand peptides into the viral capsid at amino acid position 587. This procedure ablates binding of heparan sulfate proteoglycan (HSPG), AAV-2's primary receptor, in some but not all mutants. Using an AAV-2 display library, we investigated molecular mechanisms responsible for this phenotype, demonstrating that peptides containing a net negative charge are prone to confer an HSPG nonbinding phenotype. Interestingly, in vivo studies correlated the inability to bind to HSPG with liver and spleen detargeting in mice after systemic application, suggesting several strategies to improve efficiency of AAV-2 retargeting to alternative tissues.Adeno-associated virus type 2 (AAV-2) is gaining increasing attention as a gene therapy vector. However, the wide distribution of its primary receptor, heparan sulfate proteoglycan (HSPG) (11), hampers selective transduction of target tissue. Vectors aiming to redirect AAV-2's tropism have been generated by insertion of ligands at position 587/588 of the capsid (1, 2). This is likely to interfere with the HSPG binding of at least two (R585 and R588) of the five positively charged amino acids of the recently identified HSPG binding motif (5, 7), explaining the ablation of HSPG binding of some targeting vectors (3,4,6,8,10). In some cases, however, binding was only partially affected (12) or was even restored (4,8,14). To investigate molecular mechanisms responsible for these differences, we applied a library of AAV-2 capsids carrying insertions of seven randomized amino acids at position 587 (8) to a heparin affinity column (13) to separate binding from nonbinding mutants. We sequenced and statistically analyzed (Table 1) at least 80 clones from (i) the original DNA-library, (ii) the viral AAV-2 display library, (iii) the flowthrough fraction (nonbinders were designated the NB-AAV-pool), and (iv) the 1 M NaCl eluted fraction (binders were designated the B-AAV-pool).The DNA library showed a higher than expected presence of alanines, which originates from the oligonucleotide synthesis procedure. Occurrence of every other amino acid met statistical expectations for an unselected library.The AAV-2 display library showed an excess of the amino acids P, G, and A and a defect of C, L, F, W, and Y (Table 1B). Since P, G, and A are three of the four smallest amino acids, whereas F, Y, and W are three of the four biggest, this bias suggests that the packaging process selects against bulky inserts which would introduce dramatic structural rearrangements and have a deleterious effect on capsid structure. In addition, prolines could favor spatial accommodation of the peptide by introducing kinks and reducing its bulkiness.The B-AAV-pool showed a significant increase of arginine residues (Table 1B). Strikingly, arginines were particularly frequent at the seventh position of the peptide (30%). In contrast, in the AAV-2 display library and the NB-AAV-pool, the frequency of R at this position (15% and 9%, resp...

To allow the direct visualization of viral trafficking, we genetically incorporated enhanced green fluorescent protein (GFP) into the adeno-associated virus (AAV) capsid by replacement of wild-type VP2 by GFP-VP2 fusion proteins. High-titer virus progeny was obtained and used to elucidate the process of nuclear entry. In the absence of adenovirus 5 (Ad5), nuclear translocation of AAV capsids was a slow and inefficient process: at 2 h and 4 h postinfection (p.i.), GFP-VP2-AAV particles were found in the perinuclear area and in nuclear invaginations but not within the nucleus. In Ad5-coinfected cells, isolated GFP-VP2-AAV particles were already detectable in the nucleus at 2 h p.i., suggesting that Ad5 enhanced the nuclear translocation of AAV capsids. The number of cells displaying viral capsids within the nucleus increased slightly over time, independently of helper virus levels, but the majority of the AAV capsids remained in the perinuclear area under all conditions analyzed. In contrast, independently of helper virus and with 10 times less virions per cell already observed at 2 h p.i., viral genomes were visible within the nucleus. Under these conditions and even with prolonged incubation times (up to 11 h p.i.), no intact viral capsids were detectable within the nucleus. In summary, the results show that GFP-tagged AAV particles can be used to study the cellular trafficking and nuclear entry of AAV. Moreover, our findings argue against an efficient nuclear entry mechanism of intact AAV capsids and favor the occurrence of viral uncoating before or during nuclear entry.

Our results demonstrate that combinatorial engineering overcomes the limitations of rational design approaches posed by incomplete understanding of the infectious process and at the same time offers a powerful tool to dissect basic viral biology by reverse genetics.

Recent work has identified L1CAM (CD171) as a novel marker for human carcinoma progression. Functionally, L1CAM promotes tumor cell invasion and motility, augments tumor growth in nude mice, and facilitates experimental tumor metastasis. These functional features qualify L1 as an interesting target molecule for tumor therapy. Here, we generated a series of novel monoclonal antibodies (mAb) to the L1CAM ectodomain that were characterized by biochemical and functional means. All novel mAbs reacted specifically with L1CAM and not with the closely related molecule CHL1, whereas antibodies to the COOH terminal part of L1CAM (mAb2C2, mAb745H7, pcytL1) showed cross-reactivity. Among the novel mAbs, L1-9.3 was selected and its therapeutic potential was analyzed in various isotype variants in a model of SKOV3ip cells growing i.p. in CD1 nude mice. Only therapy with the IgG2a variant efficiently prolonged survival and reduced tumor burden. This was accompanied by an increased infiltration of F4/80-positive monocytic cells. Clodronate pretreatment of tumor-bearing animals led to the depletion of monocytes and abolished the therapeutic effect of L1-9.3/IgG2a. Expression profiling of tumor-derived mRNA revealed that L1-9.3/IgG2a therapy induced altered expression of cellular genes associated with apoptosis and tumor growth. Our results establish that anti-L1 mAb therapy acts via immunologic and nonimmunologic effector mechanism to block tumor growth. The novel antibodies to L1CAM could become helpful tools for the therapy of L1-positive human carcinomas.