Recent advances in vaccinology

Archaeosomes as Self-adjuvanting Delivery Systems for Cancer Vaccines*

Archaeal ether glycerolipid vesicles (archaeosomes) efficiently deliver exogenous antigen for induction of humoral and cell-mediated immunity. Because induction of CD8 cytotoxic T cells is critical for protective vaccination against tumors, we compared the ability of various archaeosome lipid compositions to evoke a strong CD8 CTL response to entrapped antigen. Subcutaneous immunization of mice with ovalbumin (OVA) entrapped in all archaeosome lipid compositions evoked a primary (day 10) splenic CTL response indicating processing for MHC class I presentation. Interestingly, several polar lipid compositions from halophilic archaea were very potent to adjuvant this early CTL response. Despite this, the lytic units reduced substantially by weeks 6-7. More importantly, at >50 weeks, only Methanobrevibacter smithii and Thermoplasma acidophilum both rich in bipolar membrane-spanning caldarchaeols, demonstrated recall memory CTLs. Immunization of mice with OVA entrapped in M. smithii, Halobacterium salinarum or T. acidophilum vesicles provided prophylactic protection against challenge with OVA-expressing solid tumors at 6 weeks. Even a dose of 3 microg OVA in archaeosomes significantly delayed tumor growth. Tumor protection was also noted in a therapeutic design wherein OVA-archaeosomes were injected concurrent with the tumor challenge. Interestingly, antigen-free T. acidophilum but not antigen-free H. salinarum archaeosomes provided innate therapeutic protection. Vaccination with a CTL peptide epitope from the melanoma differentiation antigen, tyrosinase-related protein 2, in archaeosomes induced a protective CD8 response against B16OVA metastasis, indicating potential for targeting self, tumor antigens. Thus, lipid structural properties of archaea may differentially modulate primary, long-term and/or innate immunity, impacting adjuvant choice for vaccine design.

IL-23 induces stronger sustained CTL and Th1 immune responses than IL-12 in hepatitis C virus envelope protein 2 DNA immunization

IL-23 is a heterodimeric cytokine consisting of p19 and the p40 subunit of IL-12. IL-23 has been shown to possess IL-12-like biological activities, but is different in its capacity to stimulate memory T cells in vitro. In this study, we investigated whether IL-23 could influence envelope protein 2 (E2)-specific cell-mediated immunity induced by immunization of hepatitis C virus E2 DNA. We found that IL-23 induced long-lasting Th1 and CTL immune responses to E2, which are much stronger than IL-12-mediated immune responses. Interestingly, IL-23N220L, an N-glycosylation mutant showing reduced expression of excess p40 without changing the level of IL-23, exhibited a higher ratio of IFN-gamma- to IL-4-producing CD4(+) T cell frequency than did wild-type IL-23, suggesting a negative regulatory effect of p40 on Th1-prone immune response induced by IL-23. These data suggest that IL-23, particularly IL-23N220L, would be an effective adjuvant of DNA vaccine for the induction of durable Ag-specific T cell immunity.