PEI - a potent, but not harmless, mucosal immuno-stimulator of mixed T-helper cell response and FasL-mediated cell death in mice.

Polyethyleneimine (PEI) is one of the most effective gene delivery systems available today. However, very little is known about its ability to stimulate a systemic immune response and the molecular mechanisms thereof. However, this information is vital for the future development of new gene delivery systems. Here we address this issue by studying gene expression profiles from spleen lymphocytes after in vivo immunization of mice with PEI formulated with a reporter plasmid (PEI+) or the formulation alone (PEI-). PEI- was found to provoke the activation of genes with important immunostimulatory functions, but without the necessary costimulatory signals. PEI+ resulted in: a mixed Th1/Th2 response; activation of both CD8(+) and CD4(+) T cells, with a larger effect on CD4(+); and FasL-mediated antigen-induced cell death. A comparison of the immune responses of PEI+ with that of the clinically used tetanus toxoid-aluminum phosphate vaccine showed that the DNA vaccine provoked a stronger immune response as compared to the protein vaccine. However, many genes involved in other cellular responses such as apoptosis, stress responses and oncogenesis were activated in PEI+, supporting the theory of immunostimulation by danger genes, but also pointing toward possible adverse reactions such as Alzheimer's disease.

Tetanus antigen modulates the gene expression profile of aluminum phosphate adjuvant in spleen lymphocytes in vivo.

Adjuvants play an important role in stimulation of the immune response to antigens. Very little is known about the molecular mechanisms of this stimulation. Here we address this issue by studying gene expression profiles from spleen lymphocytes after in vivo immunization of mice with a clinically relevant vaccine, tetanus toxoid formulated with aluminum phosphate as adjuvant (TT(ADJ)), or the adjuvant alone (ADJ). The Th1/Th2 response to TT(ADJ) was obtained from a combination of up- and downstream markers to conventional cytokines, which were in good agreement with cytokine protein levels. A clustering algorithm revealed that ADJ elicited expression of 47 genes active in cytotoxic lymphocytes, inflammation, oncogenesis, stress, toxicity and cell cycle regulation. In TT(ADJ) these adjuvant-elicited genes were expressed at lower levels and a compensatory onset of protective and inhibitory genes was observed. We conclude that the antigen, to a larger extent than previously recognized, modulates the molecular mechanism of the aluminum phosphate adjuvant and that the identified genes may serve as predictive biomarkers in the development of new adjuvants and vaccines.