Readministration of helper-dependent adenoviral vectors to mouse airway mediated via transient immunosuppression.

The efficacy of adenovirus-mediated gene therapy is attenuated by the host immune responses to both vector and transgene products. Even for helper-dependent adenoviral (HD-Ad) vectors, which have all viral-coding sequences deleted, the viral capsid proteins still cause immune reactions. In order to improve the efficiency in transgene expression during HD-Ad vector readministration, we administered cyclophosphamide to transiently modulate the mouse immune system. We delivered a high dose (5 × 10(10) vector particles (vp) per mouse) of empty HD-Ad to the mouse airway to induce an initial immune response. After 4 weeks, the mice were readministered with an HD-Ad vector containing either the reporter gene, LacZ, or the gene for the human cystic fibrosis transmembrane conductance regulator (CFTR) (1.5 × 10(10) vp per mouse). We found that the expression of both transgenes was greatly improved by the administration of cyclophosphamide when compared with the expression in mice without the immunosuppressing drug. We also found that the high dose of the empty HD-Ad vector administered intranasally does not induce an acute systemic immune response, but it does elicit an acute local response of proinflammatory cytokine production. Antibodies against Ad vector, including the neutralizing antibodies, were greatly reduced by the presence of cyclophosphamide in vector readministratiton. Moreover, cyclophosphamide reduced the infiltration of inflammatory cells, including total leukocytes, lymphocytes, CD4+ and CD8+T cells. These results indicate that transient administration of immunosuppressive agent can be used to extend transgene expression as well as attenuating immunogenicity to HD-Ad vectors in airway readministration.