We investigated a gene
vaccine strategy against human papillomavirus (HPV)-induced
cancer and premalignant diseases, using adeno-associated virus (AAV) vector encoding the viral E7
oncoproteins as the
tumor antigens from HPV serotypes 16 (HPV16) and 18 (HPV18). Genetically inactivated E7
proteins were fused with a
heat shock protein 70 (hsp70) to minimize the risk of cell transformation and enhance immune responses. The fusion
protein gene was packaged in AAV serotype 1 or 2 (AAV1 or 2) for efficient in vivo gene expression. Our results showed that after a single
intramuscular injection, the AAV1 vector elicited stronger HPV-specific cytotoxic T lymphocyte (CTL) responses and
interferon-gamma secretion when compared with the AAV2 vector. Prophylactic immunization with AAV1 protected 100% of the mice from
tumor growth for more than 1 year, whereas all the control mice immunized with either a LacZ vector or saline grew large
tumors and died within 6 weeks after inoculation of E7-positive tumor cell line TC-1. In addition, this single-dose AAV1 vaccination completely protected the mice against second and third challenges with higher numbers of TC-1 cells. Despite lower CTL responses against the E7
antigens, AAV2 vector prophylactic immunization was also sufficient to protect 100% of the mice against the initial and second
tumor challenges and 70% of the mice against the third challenge. In addition, therapeutic immunization with AAV1 after palpable
tumor formation inhibited
tumor growth and caused
tumor regression in some mice. Thus, our studies support the potential of AAV vectors as a genetic
vaccine for the prevention and treatment of HPV-induced
malignancies.