VACCINE ADJUVANTS
(see also vaccines, therapeutic vaccines, DNA vaccines and RNA vaccines)

As late as 1989, Janeway aptly called adjuvants: "the immunologist's dirty little secret". This statement reflected the ignorance on the mechanisms of action of most known adjuvants. Yet, rational vaccine design involves a logical choice of adjuvant based on a knowledge of their mode of action and their effects on product efficacy and safety. However, even today the key processes critical for immune induction in general and those evoked by vaccine adjuvants in particular are being disputed among immunologists. The 4 most important concepts likely to explain some of the mechanisms of vaccine adjuvants. They include:

This enables the use of less Ag to achieve the desired immune response, reducing vaccine production costs. With a few exceptions, adjuvants are foreign to the body and cause adverse reactions. These paradigms are based on observations gathered in mammalian species, largely in murine models. In aquatic animals the processes underlying immune induction will at least partly overlap those in mammals. However, due to inherent species differences, certain pathways may be different. Rational vaccine design, a difficult goal in mammals, is further hampered in aquatic animals by the lack of immunological tools in these speciestref. Vaccine delivery : Antigen delivery : Ganoderma lucidum (GL) is one of the most commonly used Chinese herbs in the oriental community, with more than 30% of pediatric cancer patients taking GL. The immunomodulating and anticancer effects exerted by GL extracts have been demonstrated by in vitro and in vivo studies. There was, however, no comparison between the immunomodulating effects of GL mycelium extract (GL-M) and spore extracts on human immune cells. Dendritic cells (DCs) are professional antigen-presenting cells and their role in DC-based tumor vaccine has been well defined. The possibility of GL as natural adjuvant for human DCs remains unknown. A study explored the differential effect of GL-M and GL spore extract (GL-S) on proliferation and Th1/Th2 cytokine mRNA expression of human peripheral blood mononuclear cells (PBMCs) and monocytes. Their effects on the phenotypic and functional maturation of human monocyte-derived DCs were also investigated. GL-M induced the proliferation of PBMCs and monocytes, whereas GL-S showed a mild suppressive effect. Both extracts could stimulate Th1 and Th2 cytokine mRNA expression, but GL-M was a relatively stronger Th1 stimulator. Different from GL-S, GL-M enhanced maturation of DCs in terms of upregulation of CD40, CD80, and CD86, and also reduced fluorescein isothiocyanate-dextran endocytosis. Interestingly, GLM- treated DCs only modestly enhanced lymphocyte proliferation in allogenic mixed lymphocyte culture with mild enhancement in Th development. These findings provide evidences that GL-M has immunomodulating effects on human immune cells and therefore can be used as a natural adjuvant for cancer immunotherapy with DCsref.

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