Modulation of antigenic location converts chronic into acute infection by forcing CD8+ T cell recognition.

Pathogens that reside in the phagosomes of infected cells persist despite the presence of potent T cell responses. We addressed the mechanism of immune evasion by using a mouse model of Salmonella typhimurium (ST). Recombinants of ST were generated that translocated antigen to the cytosol or phagosomes of infected cells. We find that the kinetics of antigen presentation and CD8(+) T cell priming is accelerated by cytosolic antigen delivery, although the magnitude of CD8(+) T cell response is not influenced by antigenic location. More importantly, only those targets that readily display antigen on the cell surface, owing to antigenic translocation to the cytosol, are recognized and killed by CD8(+) T cells. Thus, vaccination approaches developed to control phagosomal pathogens should incorporate methods for modulating antigen presentation such that infected target cells can be readily recognized by CD8(+) T cells.

B-cell co-receptor CD72 is expressed on NK cells and inhibits IFN-gamma production but not cytotoxicity.

NK cells have two main functions, namely cell-mediated cytotoxicity and production of cytokines. Multiple inhibitory receptors that regulate NK-cell cytotoxicity have been characterized whereas little is known about receptors regulating cytokine production. Here we report that CD72, which is considered to be an important co-receptor regulating B-cell activation, is also expressed on mouse NK cells. NK cells expressing high levels of CD72, upon stimulation with IL-12 and IL-18 or target cells, produce significantly less IFN-gamma than those expressing low levels of CD72, whereas both subsets are equally cytotoxic. Ectopic expression of CD72 in the murine NK-cell line KY2 inhibits cytokine-induced IFN-gamma production, and the inhibitory effect is diminished by mutations in the inhibitory motifs in the intracellular domain or replacement of the extracellular domain of CD72. Thus, CD72 is an inhibitory receptor on NK cells regulating cytokine production.

Biphasic lipid vesicles as a subcutaneous delivery system for protein antigens and CpG oligonucleotides.

One of the major drawbacks to the development of novel vaccines has been the lack of safe yet effective adjuvants. Biphasic lipid vesicles are formulations suitable for the delivery of proteins, peptides and oligo/polynucleotides. They constitute a new class of delivery system into which antigens and adjuvants can be incorporated. The purpose of these studies was to investigate the ability of biphasic lipid vesicles (Vaccine-Targeting Adjuvants--VTA) to induce immune responses to bacterial antigens and to enhance the adjuvant activity of CpG ODNs. Immunization of mice with bacterial antigen and CpG ODNs in saline was not as effective at inducing immune responses as formulation in VTA vesicles. Results showed that formulation of CpG ODN in VTA significantly enhanced its adjuvanticity.

Mucosal delivery of bacterial antigens and CpG oligonucleotides formulated in biphasic lipid vesicles in pigs.

The ineffectiveness of simple delivery of soluble antigens to mucosal membranes for immunization has stimulated extensive studies of strategies for appropriate delivery systems and adjuvants. Biphasic lipid vesicles are formulations suitable for the delivery of proteins, peptides, and oligo/polynucleotides. The purpose of these studies was to investigate the ability of biphasic lipid vesicles (as vaccine-targeting adjuvants) containing a bacterial antigen and unmethylated oligonucleotides containing CGdinucleotides - CpG motifs (CpG ODNs) to induce systemic and mucosal immune responses in pigs. Results showed that while the protein, either alone or with CpG ODNs, did not induce mucosal immune responses, administration of antigen and CpG ODNs in biphasic lipid vesicles resulted in induction of both systemic and local antibody responses after immunization using a combined mucosal/systemic approach.