557. Co-Administration of an Adenovirus Encoding the B Cell Stimulating Factor BAFF with Heat-Inactivated Pseudomonas aeruginosa Leads to Increased Anti-pseudomonal Humoral Immunity
Authors: Christine Tertilt, Stefan Worgall, Michael C. Rivara, Ronald G. Crystal
Journal: Molecular Therapy (2004)

Pseudomonas aeruginosa is an important pathogen in conditions such as severe burns and cystic fibrosis, causing significant morbidity and mortality. Despite many efforts, no clinically effective vaccine against P. aeruginosa is available to date especially in CF patients. In order to optimize an antipseudomonal vaccine and enhance mucosal immunity, we focused our study on the enhancement of the B cell response. Stimulating B cells through B cell activating molecules during immunization against P. aeruginosa may increase the efficiency of a vaccine. B cell activating factor (BAFF), a 34kD single chain TNF-family member, is produced by activated antigen presenting cells and stimulates B cells. Similar to other members of the TNF family, BAFF is secreted as a trimer by cleavage of the protein from the membrane. Following binding to its receptors on B cells BAFF prolongs the life-span of activated B cells by preventing apoptosis and induces T cell independent immunoglobulin class switch in vitro and is crucial for B cell development and for the generation of humoral immune responses in vivo. Based on these findings, we hypothesized that the strong B cell stimulatory properties of BAFF can be exploited for the induction of immunity against P. aeruginosa and that the transient overexpression of BAFF during immunization will favor the development of a rapid, strong humoral immune response. To evaluate this concept, AdmBAFF, an E1-E3- adenovirus expressing full-length murine BAFF under control of a CMV promotor, was constructed. After infection of A549 cells with AdmBAFF, expression of full-length BAFF could be seen in the cell lysate by Western analysis, and a cleaved form of BAFF was detected in the supernatant, demonstrating that the overexpressed BAFF was properly shed from the membrane. To assess the potency of AdmBAFF to induce humoral immunity against P. aeruginosa in vivo, C57Bl/6 mice were injected subcutaneously with 7.51010 particle units of AdmBAFF together with 105 cfu of heat-inactivated P. aeruginosa strain PAO1. Mice injected with AdNull or PBS plus PAO1 served as controls. Serum binding antibodies against PAO1 were evaluated by ELISA 1, 2, 3, and 4 wk following immunization. Mice injected with PAO1 + AdmBAFF showed higher levels of PAO1-specific IgM titers 1 and 2 wk after immunization (1175 506 and 304 118, respectively) compared to mice immunized with PAO1 + AdNull (280 105 and 73 48) or PAO1 + PBS (305 91 and 61 17, p<0.02 for both comparisons at both timepoints). Similarly, higher PAO1-specific total IgG levels were observed 2, 3 and 4 wk following immunization with PAO1 + AdmBAFF (373206, 15835 and 16499, respectively) compared to mice immunized with PAO1 + AdNull (7970, 47 45 and 38 32) or PAO1 + PBS (63 41, 30 9 and 40 15, p<0.05 for both comparisons at all 3 time points). These data indicate that coadministration of AdmBAFF and heat-inactivated P. aeruginosa leads to an increased humoral immune response against P. aeruginosa, and thus overexpression of BAFF may be useful for the development of a genetic vaccine against P. aeruginosa.