B7-1 gene transfer into human cancer cells by infection with an adenovirus-B7 (Ad-B7) expression vector

Transfection of the costimulatory molecule B7-1 into some murine tumors can increase antitumor immunity and eradicate tumor growth. The purpose of this work was to construct an adenovirus-B7 (Ad-B7) expression vector and study B7-1 gene transfer into human cancer cells.

The human B7-1 cDNA was ligated into an expression cassette containing the human cytomegalovirus immediate early gene promoter and then inserted into the E1 region of the Ad5 genome by homologous recombination. The resulting Ad-B7 vector was used to infect established cancer cell lines and freshly resected cancers. Resected tumors were disaggregated into single cell suspensions by mechanical mincing and enzymatic digestion. Surface expression of B7-1 after infection was verified by flow cytometry.

Expression kinetics in three cell lines showed that infected cells began to express B7-1 within 24 h. The proportion of B7-1+ cells continued to increase during the next 48 h, after which expression remained relatively constant during the next 5 days (up to 98% B7-1+ cells). Fresh tumor cells from various cancers displayed similar kinetics, but with greater variability in the proportion of cells expressing B7-1 (13% to 95% B7-1+ cells). Cancers which were successfully infected included 3 colorectal adenocarcinomas, 2 leiomyosarcomas, 2 lung squamous cell carcinomas, and 1 renal cell carcinoma.

The Ad-B7 vector is a rapid and efficient means of gene transfer which does not require host cell proliferation. The ultimate objective is to engineer autologous tumors to express B7-1 and vaccinate cancer patients in an adjuvant or palliative setting.