Enhancement of both cellular and humoral responses to genetic immunization by co-administration of an antigen-expressing plasmid and a plasmid encoding the pro-apoptotic protein Bax.

Background: Transfecting cells with plasmid DNA encoding the protein Bax causes programmed cell death (apoptosis) and results in the formation of cell fragments (apoptotic bodies). It has been known for some time that when dendritic cells phagocytose apoptotic bodies derived from tumor cells, an immune response to tumor antigens can be generated.

Methods: Gene expression in the skin was evaluated after intradermal injection with plasmids encoding fluorescent proteins. Plasmids encoding foreign antigens were co-injected intradermally with Bax-encoding plasmids or control plasmids to elicit both humoral and cytotoxic immunity. Immune responses to the antigens were assessed by ELISA and cytotoxicity assays.

Results: We demonstrate here that injection of a mixture of reporter gene plasmids into the skin results in the expression of both plasmids in the large majority of the transfected cells. It is known that immune responses to multiple antigens can be elicited by co-injection of separate individual plasmids. When mice were injected with equal quantities of two antigenic plasmids and either the Bax plasmid or a noncoding control plasmid, antibody responses were increased 4-8-fold in the Bax group. Similarly, cytotoxic T lymphocyte (CTL) responses in the Bax group showed an 80% increase in the number of lytic units per million cells.

Conclusions: This data shows that simply including the apoptosis-inducing Bax plasmid along with antigen-expressing plasmids may provide a significant enhancement of immune responses to DNA vaccines. Published in 2004 by John Wiley & Sons, Ltd.