Recent developments in adjuvants for vaccines against infectious diseases.

New generation vaccines, particularly those based on recombinant proteins and DNA, are likely to be less reactogenic than traditional vaccines, but are also less immunogenic. Therefore, there is an urgent need for the development of new and improved vaccine adjuvants. Adjuvants can be broadly separated into two classes, based on their principal mechanisms of action; vaccine delivery systems and 'immunostimulatory adjuvants'. Vaccine delivery systems are generally particulate e.g. emulsions, microparticles, iscoms and liposomes, and mainly function to target associated antigens into antigen presenting cells (APC). In contrast, immunostimulatory adjuvants are predominantly derived from pathogens and often represent pathogen associated molecular patterns (PAMP) e.g. LPS, MPL, CpG DNA, which activate cells of the innate immune system. Once activated, cells of innate immunity drive and focus the acquired immune response. In some studies, delivery systems and immunostimulatory agents have been combined to prepare adjuvant delivery systems, which are designed for more effective delivery of the immunostimulatory adjuvant into APC. Recent progress in innate immunity is beginning to yield insight into the initiation of immune responses and the ways in which immunostimulatory adjuvants may enhance this process. However, a rational approach to the development of new and more effective vaccine adjuvants will require much further work to better define the mechanisms of action of existing adjuvants. The discovery of more potent adjuvants may allow the development of vaccines against infectious agents such as HIV which do not naturally elicit protective immunity. New adjuvants may also allow vaccines to be delivered mucosally.

Infection of human dendritic cells by a sindbis virus replicon vector is determined by a single amino acid substitution in the E2 glycoprotein.

The ability to target antigen-presenting cells with vectors encoding desired antigens holds the promise of potent prophylactic and therapeutic vaccines for infectious diseases and cancer. Toward this goal, we derived variants of the prototype alphavirus, Sindbis virus (SIN), with differential abilities to infect human dendritic cells. Cloning and sequencing of the SIN variant genomes revealed that the genetic determinant for human dendritic cell (DC) tropism mapped to a single amino acid substitution at residue 160 of the envelope glycoprotein E2. Packaging of SIN replicon vectors with the E2 glycoprotein from a DC-tropic variant conferred a similar ability to efficiently infect immature human DC, whereupon those DC were observed to undergo rapid activation and maturation. The SIN replicon particles infected skin-resident mouse DC in vivo, which subsequently migrated to the draining lymph nodes and upregulated cell surface expression of major histocompatibility complex and costimulatory molecules. Furthermore, SIN replicon particles encoding human immunodeficiency virus type 1 p55(Gag) elicited robust Gag-specific T-cell responses in vitro and in vivo, demonstrating that infected DC maintained their ability to process and present replicon-encoded antigen. Interestingly, human and mouse DC were differentially infected by selected SIN variants, suggesting differences in receptor expression between human and murine DC. Taken together, these data illustrate the tremendous potential of using a directed approach in generating alphavirus vaccine vectors that target and activate antigen-presenting cells, resulting in robust antigen-specific immune responses.

Plasmid DNA adsorbed onto cationic microparticles mediates target gene expression and antigen presentation by dendritic cells.

Dendritic cells (DC) play a key role in antigen presentation and activation of specific immunity. Much current research focuses on harnessing the potency of DC for vaccines, gene therapy, and cancer immunotherapy applications. However, DC are not readily transfected in vitro by traditional nonviral techniques. A novel DNA vaccine formulation was used to determine if DC are transfected in vitro. The formulation consists of plasmid DNA adsorbed on to cationic microparticles composed of the biodegradable polymer polylactide-co-glycolide (PLG) and the cationic surfactant, cetyltrimethylammonium bromide (CTAB). Using preparations of fluorescent-labeled plasmid DNA formulated on PLG-CTAB microparticles to study internalization by macrophages and dendritic cells in vitro and in vivo, we found that most, but not all, of the fluorescence was concentrated in endosomal compartments. Furthermore, uptake of plasmid DNA encoding HIV p55 gag adsorbed to PLG-CTAB microparticles by murine bone marrow-derived dendritic cells resulted in target gene expression, as detected by RT-PCR. The antigen was subsequently processed and presented, resulting in stimulation of an H-2kd-restricted, gag-specific T cell hybridoma. Activation of the hybridoma, detected by IL-2 production, was dose-dependent in the range of 0.1-20 microg DNA (10-2000 microg PLG) and was sustained up to 5 days after transfection. Thus, adsorption of plasmid DNA on PLG-CTAB microparticles provides a potentially useful nonviral approach for in vitro transfection of dendritic cells. Gene Therapy (2000) 7, 2105-2112.

Role of ceramide in lipopolysaccharide (LPS)-induced signaling. LPS increases ceramide rather than acting as a structural homolog.

Ceramide and ceramide-activated enzymes have been implicated in responses to bacterial lipopolysaccharide (LPS) and the proinflammatory cytokines tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1). Although TNF and IL-1 cause elevation of cellular ceramide, which is thought to act as a second messenger, LPS has been proposed to signal by virtue of structural similarity to ceramide. We have investigated the relationship between ceramide and LPS by comparing the effects of a cell-permeable ceramide analog (C2-ceramide) and LPS on murine macrophage cell lines and by measuring ceramide levels in macrophages exposed to LPS. We found that while both C2-ceramide and LPS activated c-Jun N-terminal kinase (JNK), only LPS also activated extracellular signal-regulated kinases (ERKs). C2-ceramide was also unable to activate NF-kappaB, a transcription factor important for LPS-induced gene expression. Upon measurement of cellular ceramide in macrophage lines, we observed a small but rapid rise in ceramide, similar to that seen upon IL-1 or TNF treatment, suggesting LPS induces an increase in ceramide rather than interacting directly with ceramide-responsive enzymes. We found that C2-ceramide activated JNK and induced growth arrest in macrophages cell lines from both normal mice (Lpsn) and mice genetically unresponsive to LPS (Lpsd), whereas only Lpsn macrophages made these responses to LPS. Surprisingly, LPS treatment of Lpsd macrophages induced a rise in ceramide similar to that observed in LPS-responsive cells. These results indicate that the wild type Lps allele is not required for LPS-induced ceramide generation and suggest that ceramide elevation alone is insufficent stimulus for most responses to LPS.

Phosphorylation of p105 PEST sequence via a redox-insensitive pathway up-regulates processing of p50 NF-kappaB.

The p105 Rel protein has dual functions; it is the precursor of the p5O subunit of NF-kappaB, and it acts as an IkappaB-like inhibitor to retain other Rel subunits in the cytoplasm. We have investigated the posttranslational regulation of p105 following activation of Jurkat T cells and find that a rapid and sustained phosphorylation of p105 is induced. The inducible phosphorylation occurs on multiple serines in the C-terminal-most 150 amino acids of the molecule, a region rich in Pro, Glu, Ser, and Thr residues. Phosphorylation of p105 in Jurkat cells treated with phorbol 12-myristate 13-acetate/ionomycin or with okadaic acid, another activator of NF-kappaB, is correlated with an increase in proteolytic processing to p5O. Intact PEST sequences are required for the phorbol 12-myristate 13-acetate/ionomycin-induced p105 processing, as a 68-amino acid C-terminal deletion abolishes the response to stimulation. When compounds that block Ikappa B alpha phosphorylation and degradation were tested, the serine protease inhibitors L-1-tosylamido-2-phenylethyl chloromethyl ketone and 1-chloro-3-tosyl-amido-7-amino-2-heptanone blocked inducible p105 phosphorylation, but the antioxidants pyrrolidine dithiocarbamate and butylated hydroxyanisol did not. Thus, while regulation of the p105 IkappaB resembles that of lkappaBa, involving inducible serine phosphorylation and proteolysis of the inhibitory ankyrin repeat domain, it depends on a different, redox-insensitive, signaling pathway.

Effects of granulocyte colony-stimulating factor therapy on in vitro hemopoiesis in myelodysplastic syndromes.

We evaluated the effects of 2 months of G-CSF treatment on in vitro hematopoiesis in 17 patients with myelodysplastic syndromes (MDS). Although in vitro marrow myeloid progenitor cell (CFU-GM) growth stimulated by G-CSF generally remained subnormal, in the majority of neutrophil responders significantly augmented incremental change (termed AIC) of CFU-GM numbers occurred after treatment, as did neutrophilic differentiation. The neutrophil non-responders had less prominent in vitro myeloid responses and lower basal neutrophil levels (p < 0.05). Following G-CSF treatment, the initially subnormal erythroid burst-forming unit (BFU-E) values underwent AIC in five of 11 patients along with increased reticulocyte responses in vivo, whereas four of the five patients who lacked AIC of BFU-E did not. Three patients with persisting cytogenetic abnormalities and increased neutrophilic differentiation in vitro also responded in vivo, suggesting that G-CSF induced in vivo cellular differentiation from the abnormal clone. Two of the three patients who developed blastic responses in vivo had increased CFU-GM growth pre- and post-therapy. These results indicate in vivo-in vitro correlations for myeloid and erythroid responses of MDS marrow cells which related to treatment with G-CSF.

The precursor of NF-kappa B p50 has I kappa B-like functions.

The C-terminal half of the p105 precursor of the NF-kappa B p50 subunit contains ankyrin-like repeats similar to those in I kappa B molecules, which are known to retain NF-kappa B complexes in the cytoplasm. We demonstrate that in various cell lines p105 is found associated with either c-rel or p65 in the cytoplasm and serves I kappa B-like functions. p105 retains c-rel or p65 in the cytoplasm in cotransfection experiments in COS cells. It also inhibits DNA binding by c-rel in gel retardation assays. Stable interaction of p105 with c-rel or p65 requires the putative dimerization domain in the conserved rel homology region of p105, as well as a second contact with the I kappa B-related C-terminal part of p105. Pulse-chase experiments indicate that cytoplasmic complexes of p105 with c-rel or p65 give rise to cytoplasmic as well as nuclear p50-c-rel and p50-p65, respectively, probably through processing of p105. Thus, p105, like the I kappa Bs, controls the subcellular localization and hence the transcriptional activity of at least two other members of the rel/NF-kappa B family.

Impact of marrow cytogenetics and morphology on in vitro hematopoiesis in the myelodysplastic syndromes: comparison between recombinant human granulocyte colony-stimulating factor (CSF) and granulocyte-monocyte CSF.

Marrow cells from 36 patients with myelodysplastic syndromes (MDS) (13 refractory anemia [RA], 14 refractory anemia with excess of blasts [RAEB], 9 RAEB in transformation [RAEB-T]) were evaluated for their in vitro proliferative and differentiative responsiveness to recombinant human granulocyte colony-stimulating factor (G-CSF) or granulocyte-monocyte CSF (GM-CSF). GM-CSF exerted a stronger proliferative stimulus than G-CSF for marrow myeloid clonal growth (CFU-GM) in these patients (44 v 12 colonies per 10(5) nonadherent buoyant bone marrow cells [NAB], respectively, P less than .025). GM-CSF stimulated increased CFU-GM growth in the 16 patients with abnormal marrow cytogenetics in comparison with the 20 patients who had normal cytogenetics (52 and 30 colonies per 10(5) NAB, respectively, P less than .05), whereas no such difference could be demonstrated with G-CSF (11 and 16 colonies per 10(5) NAB, respectively). In contrast, granulocytic differentiation of marrow cells was induced in liquid culture by G-CSF in 15 of 32 (47% patients), while GM-CSF did so in only 4 of 18 (22%) patients (P less than .025) including, for RAEB/RAEB-T patients: 9 of 18 versus 0 of 9, respectively (P less than .025). For MDS patients with normal cytogenetics, G-CSF- and GM-CSF-induced marrow cell granulocytic differentiation in 12 of 18 (67%) versus 3 of 11 (27%), respectively (P less than .025), contrasted with granulocytic induction in only 3 of 14 (21%) and 1 of 7 (14%) patients with abnormal cytogenetics, respectively. We conclude that G-CSF has greater granulocytic differentiative and less proliferative activity for MDS marrow cells than GM-CSF in vitro, particularly for RAEB/RAEB-T patients and those with normal cytogenetics.