Adjuvant System 04 (AS04) combines the TLR4 agonist MPL (3-O-desacyl-4′-monophosphoryl lipid A) and aluminum salt. It is a new generation TLR-based adjuvant licensed for use in human vaccines. One of these vaccines, the human papillomavirus (HPV) vaccine Cervarix, is used in this study to elucidate the mechanism of action of AS04 in human cells and in mice. The adjuvant activity of AS04 was found to be strictly dependent on AS04 and the HPV Ags being injected at the same i.m. site within 24 h of each other. During this period, AS04 transiently induced local NF-κB activity and cytokine production. This led to an increased number of activated Ag-loaded dendritic cells and monocytes in the lymph node draining the injection site, which further increased the activation of Ag-specific T cells. AS04 was also found to directly stimulate those APCs in vitro but not directly stimulate CD4+ T or B lymphocytes. These AS04-induced innate responses were primarily due to MPL. Aluminum salt appeared not to synergize with or inhibit MPL, but rather it prolonged the cytokine responses to MPL at the injection site. Altogether these results support a model in which the addition of MPL to aluminum salt enhances the vaccine response by rapidly triggering a local cytokine response leading to an optimal activation of APCs. The transient and confined nature of these responses provides further supporting evidence for the favorable safety profile of AS04 adjuvanted vaccines.

The quaking (Qk) locus expresses a family of RNA binding proteins, and the expression of several alternatively spliced isoforms coincides with the development of oligodendrocytes and the onset of myelination. Quaking viable (Qk(v)) mice harboring an autosomal recessive mutation in this locus have uncompacted myelin in the central nervous system owing to the inability of oligodendrocytes to properly mature. Here we show that the expression of two QKI isoforms, absent from oligodendrocytes of Qk(v) mice, induces cell cycle arrest of primary rat oligodendrocyte progenitor cells and differentiation into oligodendrocytes. Injection of retroviruses expressing QKI into the telencephalon of mouse embryos induced differentiation and migration of multipotential neural progenitor cells into mature oligodendrocytes localized in the corpus callosum. The mRNA encoding the cyclin-dependent kinase (CDK)-inhibitor p27(Kip1) was bound and stabilized by QKI, leading to an increased accumulation of p27(Kip1) protein in oligodendrocytes. Our findings demonstrate that QKI is upstream of p27(Kip1) during oligodendrocyte differentiation.

Quaking viable (qk(v)) mice fail to properly compact myelin in their central nervous systems. Although the defect in the qk(v) mice involves a mutation affecting the expression of the alternatively spliced qk gene products, their roles in myelination are unknown. We show that the QKI RNA binding proteins regulate the nuclear export of MBP mRNAs. Disruption of the QKI nucleocytoplasmic equilibrium in oligodendrocytes results in nuclear and perikaryal retention of the MBP mRNAs and lack of export to cytoplasmic processes, as it occurs in qk(v) mice. MBP mRNA export defect leads to a reduction in the MBP levels and their improper cellular targeting to the periphery. Our findings suggest that QKI participates in myelination by regulating the mRNA export of key protein components.

Alzheimer's disease (AD) is the most common cause of dementia worldwide. The pathogenesis of this neurodegenerative disease, currently without curative treatment, is associated with the accumulation of amyloid β (Aβ) in brain parenchyma and cerebral vasculature. AD patients are unable to clear this toxic peptide, leading to Aβ accumulation in their brains and, presumably, the pathology associated with this devastating disease. Compounds that stimulate the immune system to clear Aβ may therefore have great therapeutic potential in AD patients. Monophosphoryl lipid A (MPL) is an LPS-derived Toll-like receptor 4 agonist that exhibits unique immunomodulatory properties at doses that are nonpyrogenic. We show here that repeated systemic injections of MPL, but not LPS, significantly improved AD-related pathology in APP swe /PS1 mice. MPL treatment led to a significant reduction in Aβ load in the brain of these mice, as well as enhanced cognitive function. MPL induced a potent phagocytic response by microglia while triggering a moderate inflammatory reaction. Our data suggest that the Toll-like receptor 4 agonist MPL may be a treatment for AD.lzheimer's disease (AD) is a neurodegenerative pathology characterized by the accumulation of amyloid beta (Aβ) and neurofibrillary tangles in the brain parenchyma (1). Inflammation, which occurs in parallel with the progression of the disease, is featured by the production of cytokines by activated microglia. The role of these cells in the pathogenesis of AD remains unclear and is an area of active investigation. Whereas chronic activation of microglial cells by Aβ can trigger the exaggerated release of cytokines and neurotoxic mediators that could be detrimental to neurons, microglia can also clear Aβ via increased phagocytosis and proteolytic degradation, which may be neuroprotective (2).Toll-like receptors (TLRs) on the surface of microglial cells have been shown to bind Aβ, which triggers downstream intracellular signaling cascades (3, 4). Microglia deficient in TLR2, TLR4, or the coreceptor CD14 are not activated by Aβ and do not exhibit a phagocytic response (5). Transgenic AD mice lacking TLR4 have markedly elevated levels of diffuse and fibrillar Aβ (3). Furthermore, stimulation of microglial cells with TLR2-, TLR4-, or TLR9-specific agonists accelerates Aβ clearance both in vitro and in vivo (3, 6, 7).Monophosphoryl lipid A (MPL) is a chemically detoxified lipid A moiety derived from Salmonella minnesota R595 LPS (8). This TLR4 ligand is at least 100-fold less pyrogenic than LPS yet maintains many of the immunomodulatory properties of LPS (9). Importantly, MPL is safe in humans and has been administered to millions of patients as a component of several vaccine formulations such as the Cervarix vaccine (10). We investigated herein the chronic use of the nonpyrogenic TLR4 agonist MPL and compared it with a strong TLR4 ligand (LPS) in a mouse model of AD.Although the therapeutic potential of innate immune activation for AD is being evaluated in preclinical models, this conc...