The development of a new combined adjuvant vector for mucosal immunization CTA1-DD/ISCOM

Abstract

The CTA1-DD/ISCOMs vector is a rationally designed mucosal adjuvant that was developed to host the distinctive properties of either adjuvant alone or in a combination that hosted additive enhancing effects on mucosal immune responses. Here I demonstrate that CTA1-DD can be incorporated into the ISCOM with greatly augmented immunogenicity of both incorporated and admixed antigen. The combined vector was a highly effective enhancer of a broad range of immune responses including specific antibodies and CD4+ T cell immunity. In particular, mucosal specific IgA responses in the respiratory and the genital tracts were strongly augmented by the combined vector, a mechanism that was enzyme dependent since the presence of the enzymatically inactive CTA1R7K-DD component failed to enhance the response above that with ISCOMs alone. Antigen incorporated into the combined vector could be presented by B cells as well as dendritic cells (DC). I also found that B cells in the lymph node were indeed targeted by the combined vector, but not by ISCOMs alone. The CTA1-DD/ISCOMs vaccine vector combines properties from two distinctive adjuvant systems. The ISCOM targets DC while the CTA1-exerts ADP-ribosylating functions. Following subcutaneous injection the CTA1-DD/ISCOMs vector induced a substantial increase in the cellularity of the draining lymph node, which was particularly evident for B cells and even more for granulocytes. These effects were enzyme-dependent as the inactive mutant CTA1R7K-DD/ISCOMs did not elicit a similar pattern. Functional studies of highly enriched DC in vitro demonstrated that the combined vector was superior at stimulating pro-inflammatory cytokines and chemokines, notably IL-1β, MIP-1 and RANTES, compared with ISCOMs alone. These effects appeared not to be due to better binding/up-take of the combined vector in DC, rather they depended on an intact enzymatic activity of the CTA1-enzyme. These findings help explain which are the critical properties added by the CTA1-DD to the ISCOM adjuvant. In my final article I used an adoptive transfer system to investigate the specific induction of genital tract CD4+ T cells by using ovalbumin (OVA) as our model antigen. Transfer of OVA specific T cell receptor (TCR) transgenic CD4+ T cells to naïve normal mice allows for tracking these cells using a TCR-specific antibody, KJ.126, after immunizations with or without adjuvant vectors. I found that hormones play an important role in the priming of T cells, since estrogen-treated mice failed to respond and progesterone-treated mice greatly expanded their OVA-specific T cells following immunization. Progesterone treatment expanded the OVA-specific T cells in a dose dependent way in regional lymph nodes. I also investigated the role of local verses systemic immunization on activation of genital tract T cells and found that both vaginal and intranasal immunizations with cholera toxin conjugated to OVA (CT-OVA) strongly expanded KJ.126+ T cells in the draining lymph node (Para aortic lymph node). However, local immunization was significantly more effective and was also an absolute requirement to attract T cells to the genital tract mucosa. These results convincingly demonstrate that not only antibody responses, but also antigen-specific T cell responses are effectively primed and boosted by local genital tract immunizations.