Faculty Bibliography

Background: Immunotherapy targeting pathological tau is emerging as a promising approach to treat tauopathies such as Alzheimer's disease (AD) and frontotemporal dementia. We have previously shown that prophylactic active or passive tau immunotherapy, starting at 2-3 months of age, clears tau pathology and improves function (Asuni A. et al., J. Neurosci. 2007, Boutajangout A. et al., J. Neurosci. 2010, Boutajangout A. et al., ICAD 2010). Here we assessed if a phospho-specific monoclonal, 4E6G7, targeting the same epitope, would be efficacious if treatment commenced at an advanced stage of tau pathology (8-9 months). Methods: htau/PS1 mice without mouse tau protein (8-9 months) were injected intraperitoneally (250 mg/125 ml) once per week with a novel phospho- specific tau monoclonal, 4E6G7 (n = 9) or pooled mouse IgG (n = 10) for a total of 13 injections. Their behavior was analyzed at 11-12 months of age and brain tissue subsequently harvested for analyses of treatment efficacy. Results: The immunized mice (n = 7-8) performed substantially better than controls (n = 6) on the Radial Arm Maze (p < 0.0001; post hoc, p < 0.01-0.001 on days 2, 3, 5-9), the Closed Field Symmetrical Maze with 35-69% fewer errors in simple, intermediate and complex tasks (p < 0.05-0.003), and the Object Recognition Task (63% time spent with a novel object vs. 46% for controls, p < 0.05). The groups did not differ in various sensorimotor tasks, indicating that the robust cognitive improvements cannot be explained by sensorimotor effects, which further strengthens our results. Interestingly, more controls died during the study (40%) than immunized mice (22%), providing an additional support for the beneficial effect of the monoclonal tau antibody. Histological and biochemical analyses are underway. Conclusions: These results indicate pronounced efficacy of passive tau immunotherapy at an advanced stage of tauopathy, which suggests that this approach may be beneficial after clinical onset of AD and other tauopathies

Background: Immunotherapy holds great promise for Alzheimer's disease (AD) and other conformational disorders. Recent studies from our group have shown that immunization with an AD specific phospho-tau immunogen Tau379-408[P-Ser396,404] alleviates brain levels of aggregated tau and slows the progression of motor deficits or prevents cognitive impairments in two different tangle models (Asuni A. et al. J. Neurosci., 2007, Boutajangout A. et al., J. Neurosci., 2010). To assess potential epitope specificity and safety of this promising therapeutic effect, we are examining several tau epitopes. Here we assessed the efficacy of using a pseudo-phosphorylated tau immunogen. Methods: Homozygous JNPL3 mice were immunized with Tau379-408[ESer396, E-Ser404] in alum adjuvant (n = 13) or with adjuvant only (n = 7), starting at 2 months. Mice were tested on various sensorimotor tasks (rotarod, traverse beam, locomotor activity and grip strength) at 5 and 8 months of age. Antibody titers were determined and at 8 months their brains were processed for tau biochemistry and histology. Results: The vaccine elicited a robust antibody response towards the immunogen, and its phosphorylated and non-phosphorylated analogs. Which is as expected since this region of the tau protein is highly immunogenic. The immunized mice had a 24% reduction in soluble PHF1/total tau ratio on western blots (p = 0.04), and a 42% reduction in PHF1 immunostaining in the dentate gyrus (p < 0.03), compared to alum-treated mice. Levels of sarkosyl insoluble human and total tau were highly variable in both groups and not significantly different. Biochemical and histological analyses with other antibodies and of other brain regions is underway. Disappointingly, potential improvements in motor function of the immunized mice could not be assessed since the animals did not develop overt signs of such impairments at the ages tested, in contrast to our previous observation in the same homozygous model (Asuni A. et al., J. Neurosci., 2007). Unfortunately, such changes in phenotype are commonly observed in transgenic mice. Conclusions: These findings indicate that immunological targeting using a pseudo-phosphorylated tau epitope can reduce pathological tau within the brain, further supporting the feasibility of tau immunotherapy

Background: Active anti-amyloid immunotherapy is a strategy developed against Alzheimer's disease.ApproacheswithAs1-42 orK6As1-30 immunogens in an adjuvant decrease amyloid-s burden and prevent cognitive decline in transgenic mice (Asuni et al, 2006). However, clinical trials of As1-42 immunotherapy have induced side effects like encephalitis and possibly microhemorrhages (Orgogozo et al, 2003; Ferrer et al, 2004). Mouse lemurs can develop As plaques with age (Mestre-Frances et al, 2000). Such a primate modelmay bemore predictive than rodents of human side effects.We studied, by magnetic resonance imaging (MRI), immunotherapies in these primates. Methods: A first cohort was used to compare K6As1-30 (n = 4; 5.8 +/- 0.2 years) and As1-42 (n = 4; 5.9 +/- 0.2 years) immunogens in alum adjuvant. Asecond cohortwas used to evaluateK6As1-30 (n=6; 4.660.2 years) compared to adjuvant alone (n = 6; 4.7 +/- 0.3 years). All the animals were followed- up by MRI (7T PharmaScan-Bruker) to evaluate neuroinflammation, microhemorrhages and other forms of iron deposition, with T2-weighted and T2*-weighted sequences (resolution=(234x234x234)mm³). The hypointense regions from T2*-weighted images were quantified and evaluate by histology. A complementary study of age effectwas performedwith twenty other naive animals (1.5 to 4.9 years). Results: The T2-weighted images did not show any neuroinflammation during immunization, irrespective of the immunogen. Microhemorrhages were detected in the cerebral parenchyma at the histological analysis of the first cohort. The animals treated with K6As1-30 presented less microhemorrhages compared to those treated with As1-42 vaccine (Mann-Whitney, p < 0.05). These small microhemorrhages were not detected on the T2*-weighted images. However hypointense signalwas detected on MRI and corresponded to iron deposits in the choroid plexus. Its volume increasedwith natural aging (r= 0.60; p< 0.001) and withAs1-42 compared to K6As1-30 treatment (ANOVA, p < 0.05). No difference was detected between K6As1-30 and adjuvant alone. Conclusions: The immunotherapies studied in the mouse lemur primate did not lead to any MRI sign of neuroinflammation. The K6As1-30 strategy appears to be safer than theAs1-42 strategy as it provokes less microhemorrhages in the cerebral parenchyma and less iron deposits in the choroid plexus

Recent studies have shown that immunotherapy clears amyloid beta (Abeta) plaques and reduces Abeta levels in mouse models of Alzheimer's disease (AD), as well as in AD patients. Tangle pathology is also relevant for the neurodegeneration in AD, and our studies have shown that active immunization with an AD related phospho-tau peptide reduces aggregated tau within the brain and slows the progression of tauopathy-induced behavioral impairments. Thus, clearance of neurofibrillary tangles and/or their precursors may reduce synaptic and neuronal loss associated with AD and other tauopathies. So far the mechanisms involved in antibody-mediated clearance of tau pathology are yet to be elucidated. In this study we have used a mouse brain slice model to examine the uptake and localization of FITC labeled anti-tau antibodies. Confocal microscopy analysis showed that the FITC labeled anti-tau antibody co-stained with phosphorylated tau, had a perinuclear appearance and co-localized with markers of the endosomal/lysosomal pathway. Additionally, tau and FITC-IgG were found together in an enriched lysosome fraction. In summary, antibody-mediated clearance of intracellular tau aggregates appears to occur via the lysosomal pathway

Harnessing the immune system to clear protein aggregates is emerging as a promising approach to treat various neurodegenerative diseases. In Alzheimer's disease (AD), several clinical trials are ongoing using active and passive immunotherapy targeting the amyloid-beta (Abeta) peptide. Limited emphasis has been put into clearing tau/tangle pathology, another major hallmark of the disease. Recent findings from the first Abeta vaccination trial suggest that this approach has limited effect on tau pathology and that Abeta plaque clearance may not halt or slow the progression of dementia in individuals with mild-to-moderate AD. To assess within a reasonable timeframe whether targeting tau pathology with immunotherapy could prevent cognitive decline, we developed a new model with accelerated tangle development. It was generated by crossing available strains that express all six human tau isoforms and the M146L presenilin mutation. Here, we show that this unique approach completely prevents severe cognitive impairment in three different tests. This remarkable effect correlated well with extensive clearance of abnormal tau within the brain. Overall, our findings indicate that immunotherapy targeting pathological tau is very feasible for tauopathies, and should be assessed in clinical trials in the near future

Alzheimer's disease (AD) is one of the categories of neurodegenerative diseases characterized by a conformational change of a normal protein into a pathological conformer with a high beta-sheet content that renders it resistant to degradation and neurotoxic. In AD, the normal soluble amyloid beta (sAbeta) peptide is converted into oligomeric/fibrillar Abeta. The oligomeric forms of Abeta are thought to be the most toxic, while fibrillar Abeta becomes deposited as amyloid plaques and congophilic angiopathy, which both serve as neuropathological markers of the disease. An additional important feature of AD is the accumulation of abnormally phosphorylated tau as soluble toxic oligomers and as neurofibrillary tangles. Many therapeutic interventions are under investigation to prevent and treat AD. The testing of these diverse approaches to ameliorate AD pathology has been made possible by the existence of numerous transgenic mouse models which each mirror specific aspects of AD pathology. None of the current murine models is a perfect match of the human disease. Perhaps the most exciting of the therapeutic approaches being developed is immunomodulation targeting the aggregating proteins, Abeta and tau. This type of AD therapy is currently being assessed in many transgenic mouse models, and promising findings have led to clinical trials. However, there is a discrepancy between results in murine models and ongoing clinical trials, which highlight the limitations of these models and also of our understanding of the underlying etiology and pathogenesis of AD. Because of these uncertainties, Tg models for AD are continuously being refined with the aim to better understand the disease and to enhance the predictive validity of potential treatments such as immunotherapies

Immunotherapies targeting the amyloid-beta (Abeta) peptide in Alzheimer's disease (AD) have consistently been effective in mouse studies and shown promise in clinical trials, although some setbacks have occurred. First, encephalitis was observed in a small subset of patients. More recent autopsy data from a few subjects suggests that clearance of Abeta plaques may not halt cognitive deterioration once impairments are evident, emphasizing the need for other more effective approaches at that stage of the disease. Another important target in AD is the neurofibrillary tangles and its precursors, composed primarily of hyperphosphorylated tau proteins, which correlate well with the degree of dementia. As Abeta and tau pathologies are likely synergistic, targeting both together may be more effective, and perhaps essential as early diagnosis prior to cognitive decline is currently unavailable. Also, Abeta immunotherapy results in a very limited indirect clearance of tau aggregates, showing the importance of developing a separate therapy that directly targets pathological tau. Our findings in two tangle mouse models indicate that active immunization targeting an AD phospho-tau epitope reduces aggregated tau in the brain and prevents/slows progression of the tangle-related behavioral phenotype, including cognitive impairment. These antibodies enter the brain and bind to pathological tau within neurons although the therapeutic effect may at least in part be due to clearance of extracellular tau that may have biological effects. We are currently clarifying the mechanism of these promising findings, determining its epitope specificity as well as assessing the feasibility of this approach for clinical trials