Cell therapy for Alzheimer

A phase I clinical trial in eight individuals with mild Alzheimer disease appears to have slowed the decline of cognitive function. The treatment involved transplantation into the brain of autologous fibroblasts genetically modified to express nerve growth factor (NGF). Although the benefits of NGF therapy have been extensively validated in animal models of cholinergic neuronal degeneration, clinical applications have been hindered by a lack of precise delivery methods, as indiscriminate delivery can cause serious side effects. Tuszynski and colleagues found that injection of NGF-expressing fibroblasts into the cholinergic basal forebrain had no adverse consequences during the monitoring period of 18–24 months. Moreover, the yearly rate of decline of cognitive function over an average of 22 months, as measured by the Mini-Mental Status Examination, decreased to 49% of the pretreatment rate. A second test, the Alzheimer Disease Assessment Scale–Cognitive subcomponent, indicated a modest benefit in the first 12 months after treatment. The authors caution that NGF therapy is not a cure for Alzheimer disease because it targets only one component of the pathological process, the cholinergic neuron. Nevertheless, if the results of this small noncontrolled trial are reproducible, the approach represents an important therapeutic advance. (Nat. Med. 11, 545–549, 2005) KA

SNPs on beads

Effective genotyping studies will require hundreds of thousands of SNP assays. The latest estimate from the haplotyping project puts the number of genetic variants in humans at 10 million, of which 200,000 to 300,000 might be sufficient to genotype an individual. Although arrays that can perform massive multiplexing of SNPs assays exist, technologies are still needed to simplify the procedure. In their whole genome genotyping assay (WGA), researchers from Illumina, Ambion and Prognosys Bioscience describe a platform that combines several simple technologies to assay an unlimited number of sites at single base resolution. WGA uses whole genome amplification, followed by capture of fragments on high-density bead arrays containing sets of probes for each allele. Primer extension with biotin-labeled nucleotides labels the captured strand, followed by signal amplification with streptavidin-phycoerythrin conjugates. In a pilot study, the authors demonstrate that their approach can genotype over 800 loci with 99% accuracy, which compares favorably with existing techniques. By increasing the number and density of hybridization sites, they estimate that they could assay 500,000 sites in a single experiment. The assay may also be applicable to other kinds of studies, such as expression profiling and loss of heterogeneity measurements. (Nat. Genet. 37, 549–554, 2005) LD

Signals and noise

Two papers in Science describe the use of synthetic gene regulatory cascades in Escherichia coli for determining what intrinsic and extrinsic factors contribute to gene expression fluctuations and how these fluctuations or 'noise' are transmitted through gene cascades within single cells. Rosenfeld et al. investigate the quantitative relationship between transcription factor concentration and the production rate of downstream targets in a synthetic 'λ-cascade' system; Pedraza et al. determine how noise propagates in a gene network incorporating the lac repressor (LacI) and the tet repressor (TetR). To allow real-time 'quantitative' measurement of gene expression, the two teams tracked fluorescence of E. coli strains engineered with fusions of different fluorescent reporter genes, each linked to a specific protein in one of the pathways. Rosenfeld et al. then examined how factors, such as biochemical parameters, noise and varying cellular states, affect gene regulation; Pedraza et al. identified and measured what determines noise propagation in a single gene, including noise from other cellular factors affecting global gene expression (extrinsic noise), noise from fluctuations due to factors inherent to the expression of an individual gene (intrinsic noise) and noise transmitted from upstream genes. Both studies provide important insights for understanding noise in cellular gene expression and its implications for the design of synthetic networks. (Science 307, 1962–1965, 2005; Science 307, 1965–1969, 2005) NC

Smaller carriers deliver

Synthetic, positively charged and high-molecular-mass polyethylenimines (PEIs) have been a mainstay for liposomal delivery of drugs and nucleic acids. Thus far, however, these have proven to be much less efficient and organ-specific than viral vectors. Now, Thomas et al. have significantly increased the delivery efficiency and specificity of PEIs by removing N-acyl groups from commercial PEIs. By deacylating a commercial, 25-kDa linear PEI (PEI25), they found the aliphatic polyamine to be 21 times more efficient in vitro. Three other de novo synthesized PEIs devoid of N-acyl groups proved even more efficient. When applied to mice, deacylated PEI25 delivered DNA with a 1,500-fold increase in specificity to lungs and an overall 10,000-fold jump in efficiency compared to the acylated molecule. Finally, to prove the therapeutic potential of deacylated PEIs, the authors applied one of the de novo synthesized PEIs, PEI87, together with a short interfering RNA (siRNA) to combat influenza in mouse and observed a 94% drop of virus titers in lung. (Proc. Natl. Acad. Sci. USA 102 5679–5684, 2005) MZ

mAbs against West Nile virus

The spread of West Nile virus, a zoonotic agent that can cause meningitis and encephalitis in the elderly and immunocompromised, is adding urgency to the search for new treatments to supplement human polyclonal antibodies. To develop a monoclonal antibody (mAb) with potent virus neutralizing capacity, Diamond and coworkers raised 46 mAbs by immunizing mice with the West Nile virus envelope (E) protein. Error-prone PCR mutagenesis was then used to rapidly map mutations in domain III (DIII) of E protein displayed on the surface of yeast that affect mAb binding. For in vitro protection assays, only two of the 46 mAbs rapidly neutralized the virus in human adrenal carcinoma cells. The most potent of these mAbs, E16, boosted survival of a West Nile Virus Disease mouse model from 10% to 90%. E16 further mapped to the same neutralizing epitope as human antibodies derived from people convalescing from West Nile viral infection, suggesting its potential as a human therapeutic. Indeed, chimeric mouse-human antibodies based on E16 increased the survival of wild-type mice from 46% to 67%. (Nat. Med. 11, 522–530, 2005) TM

Research Highlights written by Kathy Aschheim, Nadia Cervoni, Laura DeFrancesco, Teresa Moogan and Mark Zipkin.