OBJECTIVETo study the changes in the intensity and temporal pattern of target gene expression in the tumor tissue of nude mice bearing human nasopharyngeal carcinoma (NPC) following injection of recombinant adeno-associated virus (rAAV) and recombinant adenovirus (AdV) in vivo.

METHODSEBV-positive human NPC cell line C666-1 was inoculated subcutaneouly in nude mice. After the tumor mass reached 3 mm in diameter, 1.5 × 10(11) v.g (virus genome) rAAV-EGFP, 2.5 × 10(8) pfu rAdV-EGFP or their balanced mixture was injected intratumorally. At 5 and 10 days after the injection, the tumor tissues were harvested for immunohistochemical staining of GFP, and the ratio of the GFP-positive cells and the intensity of GFP expression was determined.

RESULTSImmunohistochemistry for GFP showed that 5 days after the injection, GFP expression was detected (1.70 ∓ 0.48) in the tumor tissue in rAAV group, and the peak expression levels was seen in rAdV group (6.00∓1.94); the expression level was comparable between the combination group (6.90 ∓ 1.92) and rAdV group. At 10 days, GFP expression was considerably lowered to 2.00 ∓ 0.67 in rAdV group but increased to 8.00∓1.15 in rAAV group. The expression in the combination group maintained a high level at 10 days (10.10∓1.63), which was significantly higher than that in rAAV group (P%0.001).

CONCLUSIONTransfection with rAAV combined with rAdV allows instant, sustained and significantly enhanced expression of the target gene in the tumor tissue. This approach takes advantages of the two viruses and can be ideal for exogenous gene delivery into the tumor tissues.