A new kind of recombinant herpes simplex virus type 1 (HSV 1) was constructed. This recombinant, named HSV1 LaL, contained an unique packaging signal (“a" sequence) flanked by two loxP sites in parallel orientation, named LaL, while the original packaging signals of HSV 1 were deleted. Based on a set of cosmids containing the entire HSV 1 genome except the “a" sequence, the LaL was inserted into HSV 1 UL44 gene on one of the cosmids, cos56, generating cos56/LaL. By co transfecting cos56/LaL with the other cosmids, HSV1 LaL was generated in the cells by recombination. By introducing cos56/LaL or HSV1 LaL respectively into E.coli or BHK cells that expressed Cre recombinase, LaLs on both of them were excised by Cre, which was proved by PCR detection. To study the potential use as helper virus in packaging amplicon vector, HSV1 LaL was compared with a control virus HSV1 lacZ that contained a lacZ gene in the UL44 gene. The titer of amplicon virus generated from HSV1 LaL infected BHK/Cre cells was basically the same as that from HSV1 lacZ infected cells, however,the former contained about 10 fold less helper virus than the later, while HSV1 LaL showed the same replication rate as HSV1 lacZ on standard cells, like BHK 21.
