Conventionally the efficiency of an adjuvant is measured by the capaci
ty to induce enhanced antibody serum titres and cell mediated immunity
(CMI) to a given antigen. Nowadays the capacity of an adjuvant is als
o measured by the quality as well as the magnitude of the induced immu
ne response, guided by the protective immune response required. Qualit
y includes isotype and IgG subclass responses, T-helper cell responses
characterized by the cytokine profile and cytotoxic T cells (CTL), In
the early phase of immunization some adjuvants influence the antigen
administration and uptake by a so-called depot effect exemplified by a
luminium hydroxide gel and oil adjuvants, which possibly is not as des
ired as alledged. A modem depot is exerted by slow release formulation
s continuously releasing the antigen over a period of time or by pulse
s at intervals aiming at 'single injection' vaccine. Great efforts are
made to formulate efficient delivery formulations targeting the antig
ens from the site of administration, to draining lymph nodes or distan
t lymphatic tissue or to mucosal surfaces by parenteral or mucosal adm
inistrations. Nowadays, non-replicating carriers besides replicating v
accines are formulated to induce mucosal immune responses encompassing
secretory IgA and CMI. Efforts to evoke immune responses on mucosal m
embranes distant from the site of administration have resulted mostly
in little success. For a long time it was considered that CTL under th
e restriction of MHC Class I only could be evoked by replicating virus
es or intracellular parasites, However, novel adjuvant delivery system
s readily induce CTL by delivering the antigen to the APC resulting in
intracellular transport to the cytosol for the MHC Class I presentati
on system, as well as to the endosomal pathway for the MHC Class II pr
esentation.