Sequestering of damage-associated molecular patterns (DAMPs): a possible mechanism affecting the immune-stimulating properties of aluminium adjuvants.

Aluminium-based adjuvants (ABAs) have been used in human and veterinary vaccines for decades, and for a long time, the adjuvant properties were believed to be mediated by an antigen depot at the injection site, prolonging antigen exposure to the immune system. The depot hypothesis is today more or less abandoned, and instead replaced by the assumption that ABAs induce an inflammation at the injection site. Induction of an inflammatory response is consistent with immune activation initiated by recognition of molecular patterns associated with danger or damage (DAMPs), and the latter are derived from endogenous molecules that normally reside intracellularly. When extracellularly expressed, because of damage, stress or cell death, a sterile inflammation is induced. In this paper, we report the induction of DAMP release by viable cells after phagocytosis of aluminium-based adjuvants. Two of the most commonly used ABAs in pharmaceutical vaccine formulations, aluminium oxyhydroxide and aluminium hydroxyphosphate, induced a vigorous extracellular expression of the two DAMP molecules calreticulin and HMGB1. Concomitantly, extracellular adjuvant particles adsorbed the DAMP molecules released by the cells whereas IL-1ß, a previously reported inflammatory mediator induced by ABAs, was not absorbed by the adjuvants. Induction of extracellular expression of the two DAMP molecules was more prominent using aluminium hydroxyphosphate compared to aluminium oxyhydroxide, whereas the extracellular adsorption of the DAMP molecules was more pronounced with the latter. Furthermore, it is hypothesised how induction of DAMP expression by ABAs and their concomitant adsorption by extracellular adjuvants may affect the inflammatory properties of ABAs.

DNA methylation in ATRA-treated leukemia cell lines lacking a PML-RAR chromosome translocation.

A deficient retinoic acid signaling has been suggested to be an important cause of the clinical inefficacy of all-trans retinoic acid (ATRA) therapy in non-promyelocytic (non-PML) forms of acute myeloid leukemia (AML). The general aim of the present work was to explore novel ways to take advantage of the anti-leukemic potential of ATRA, and, specifically, to search for a synergism between ATRA and epigenetic drugs. Because previous reports have found no major influence of ATRA on DNA methylation, we investigated whether ATRA-mediated differentiation of the U937 and HL-60 AML cell lines, both lacking a PML-retinoic acid receptor (RAR) fusion product, is accompanied by early-appearing and weak changes in CpG methylation. We report that in HL-60 cells, by using a highly quantitative analysis of a set of genes found to be abnormally expressed in AML, polymerase chain reaction (PCR)-amplified p16 gene promoter molecules (each with 15 CpG sites), exhibited a CpG methylation level of 0-4% in untreated cells, which increased to 4-21% after treatment with ATRA for seven days. In contrast to HL-60 cells, U937 cells exhibited a very high CpG methylation level in p16, and ATRA did not influence the promoter methylation of this gene. In the total CCGG sites of the genome, analysed using a methylation-sensitive restriction enzyme, CpG methylation was significantly lower in ATRA-treated HL-60 (p<0.01) and U937 cells (p<0.05) than in controls. Taken together, our findings show that ATRA can influence DNA methylation, and suggest that future research should investigate whether epigenetic modulation may evoke a clinical effect of ATRA in leukemia.