Abstract

The efficient transfer of genes by adenovirus vectors, which is mediated by the capsid proteins, is counteracted by the cellular immune response to transduced cells resulting in transient expression of the transferred gene and the generation of neutralizing antibody by the humoral branch which prevents second administrations of the gene transfer vector. To investigate the role of capsid proteins in virus-cell and virus-immune system interactions capsid gene replacement was employed to generate serotype chimeras based on an E1(-) adenovirus serotype 5 (Ad5) reporter vector.

The fiber protein of adenovirus is involved in cell targeting and is a target of the host immune response. When the Ad5 fiber gene is replaced with the Ad7 fiber protein gene the virus is specifically redirected from the Ad5 receptor to the Ad7 receptor while an Ad5 vector with the Ad41 long fiber protein used the same receptor as Ad5. A chimera expressing and packaging both the long and the short fiber proteins of Ad41 was engineered but the presence of the short fiber protein had no effect on the transduction efficiency of the vector. The construction of this vector demonstrated that Ad5 can be engineered to express two fiber proteins from the major late transcription unit. A unique gene transfer vector was engineered to express both the native Ad5 fiber gene and the Ad7 fiber gene. This virus specifically binds to the Ad5 and Ad7 receptors.

The humoral immune response to adenovirus vectors is directed against the capsid proteins. Sequential administration experiments with serotype chimeras showed that the fiber protein does not contain significant neutralizing epitopes. In contrast, hexon protein serotype chimeras displayed altered neutralization profiles, indicating that the major serotype determinants are in the hexon protein.

The cellular immune response to adenovirus vector transduced cells is able to clear transgene expression in a very short time. Administration of an adenovirus reporter vector to transgenic mice with knockouts in different immune effector pathways demonstrated that the components of the cellular branch that mediate the rapid clearance of transduced hepatocytes in mice are dependent on TNF-α.