Research Updates

Vaccination and Immunotherapy for Alzheimer’s Disease

Vaccination against amyloid is a promising approach for the development of Alzheimer’s disease (AD) therapeutics. Approximately half of the investigational new therapeutics in human clinical trials for AD are active or passive immunotherapeutics.

Active vaccination involves the injection of an antigen and relies on the production of antibodies in the vaccinated patient. Four human clinical trials of active vaccination currently are under way. Passive immunization is also a promising strategy that involves the production of antibodies outside of the patient and injection of these antibodies. There are currently 12 clinical trials of passive immunization. You can check for Alzheimer therapeutics in human clinical trials by visiting www.clinicaltrials.gov and searching for key words “Alzheimer’s and immunotherapy.”

Thinking out of the box

The development of vaccinations as a strategy for treating or preventing Alzheimer’s is an example of thinking out of the box. Vaccinations commonly are associated with infectious diseases, like influenza, small pox and polio, which appear to have little in common with neurodegenerative diseases, like Alzheimer’s. Moreover, the brain is an immunoprivileged site with little access to antibodies, so it seems unlikely antibodies would be protective in the brain.

Researchers were pleasantly surprised when Dale Schenk and co-workers at Elan Inc. reported that vaccination of transgenic mouse models of AD against the amyloid Aß peptide prevented amyloid deposition in young animals and removed pre-existing amyloid deposits in older animals. Subsequent work showed that immunization against Aß prevented or reversed many other pathological features and prevented cognitive dysfunction in transgenic mice and non-human primates. This vaccine (Elan AN1792) was tested in human clinical trials, where it showed similar beneficial effects of removing amyloid deposits and slowing cognitive decline in patients with significant levels of anti-Aß antibodies, but the clinical trial was halted because 6 percent of the patients developed meningoencephalitis, an inflammatory side effect.

Second-generation vaccines and passive immunization

To circumvent the unwanted inflammatory side effects, second-generation active vaccines have been developed and passive immunization strategies have been explored. The second-generation vaccines use small pieces of the amyloid Aß sequence to avoid activating the T-cells responsible for meningoencephalitis, while passive immunization bypasses the human immune response by directly supplying antibodies. These newer strategies have shown the same beneficial effects in transgenic mice and passive immunization has shown some promise in a subset of patients in human trials, but they have raised new questions about their effectiveness and potential new side effects. Elan/Wyeth reported preliminary results from clinical trials of their monoclonal antibody, Bapineuzimab, that demonstrated only a small benefit in a subgroup of patients who lack the apoE4 genotype. They also failed to observe an improved benefit with an increased dose of antibody and reported side effects, like a buildup of fluid in the brain. Results of active vaccination human clinical trials with second-generation vaccines remain to be reported.

Third-generation vaccines and antibodies: Thinking perpendicular to the box

Both second-generation vaccines and antibodies suffer from a common problem. They both target linear amino acid sequences found in normal human proteins (the amyloid precursor protein) and in the amyloid deposits themselves. Making antibodies against normal human proteins can cause autoimmune side effects, in which the immune system is attacking normal human cells in addition to the Alzheimer’s pathology. Fortunately, it is difficult to make antibodies against self-proteins because of immune suppression of auto antibodies. Third-generation vaccines seek to overcome these problems of autoimmune side effects and autoimmune suppression by using antibodies that target structures specific to the amyloid aggregates and that do not react with normal human proteins.

Cure Alzheimer’s Fund has been supporting two projects that seek to develop third-generation immunotherapeutics. Dr. Charles Glabe’s laboratory is developing active vaccines and monoclonal antibodies that recognize conformations of the amyloid peptide that only occur in the pathological amyloid oligomer aggregates, while Dr. Rob Moir’s lab is working on cross-linked amyloid peptides (CAPs) that are only found in disease-related aggregates. Dr. Glabe’s strategy relies on the fact that when the Aß peptide aggregates into ß-sheet oligomers, it creates new antibody recognition sites, known as epitopes, that are not found on native proteins. The surprising finding is that these oligomer-specific antibodies recognize amyloid oligomers from other diseases that involve amyloids formed from sequences unrelated to Aß. This means the same antibodies also may be effective for other amyloid-related neurodegenerative diseases, like Parkinson’s disease.

The explanation for why the antibodies are specific for amyloid oligomers that involve several individual peptide strands arranged in a sheet and yet recognize these sheets when they are formed from other amino acid sequences is simple and elegant (Figure 1). It is now known that most pathological amyloids aggregate into simple and very regular structures where the peptide strands are arranged in parallel and where the amino acid sequence is in exact register. This is like a sheet of paper upon which the same sentence is written on each line. The individual amino acids line up and down the sheet in homogeneous tracts, known as “steric zippers.” The steric zippers do not occur in normal protein structures and the oligomer-specific antibodies are thought to recognize these steric zipper patterns on the surface of the sheets. Since all proteins are made up using the same 20 amino acids, any sequence in this parallel, in-register structure gives rise to the same steric zippers regardless of the linear sequence, which can explain why the antibodies recognize the oligomers formed by different proteins.

Dr. Moir’s group is working on CAPs, where Aß is cross-linked by oxidation of a tyrosine residue at position 10 of the peptides’ sequence. Aß is oxidized after it is produced from the amyloid precursor protein as a consequence of the abnormally high level of oxidative activity in a brain with AD and the peptides’ propensity to bind redox active metals. Excessive CAPs generation is associated with the disease state and is not a normal feature of Aß biology. The cross-linking at tyrosine 10 that gives rise to CAPs may serve to align the peptides in a parallel, in-register fashion and promote the generation of still-larger oligomeric aggregates that display steric zippers on their surface.

Dr. Moir and Dr. Rudy Tanzi’s labs found that natural antibodies to CAPs are reduced in the blood of patients with AD. More recently, evidence published by Tony Weiss-Coray’s group at Stanford University supports the idea that antibodies that recognize steric zippers and CAPs may be important for protecting against Alzheimer’s disease. The levels of these antibodies that target the zippers and CAPs were among the highest in young, normal humans; levels dropped with aging and with AD. Furthermore, the results of a recent study supported by Baxter Biosciences of patients that received human antibodies purified from normal individuals (IVIg) reported that antibody treatment reduced the risk of being diagnosed with AD by 42 percent over the five-year study period. This is one of the most remarkable reports of prevention of AD by any therapy. Although the normal human antibodies that target amyloid primarily recognize the steric zippers and CAPs, these antibodies are present at relatively low levels. It is reasonable to imagine that an even greater protective effect might be achieved by boosting the levels of these protective antibodies by either active vaccination or passive immunization.

Figure 1

Figure 1 shows how the same steric zipper patterns are formed on parallel, in-register oligomers from completely different sequences. A segment of the Aß sequences is shown in the upper left corner and a random sequence is shown in the upper right. Each amino acid is designated by a capital letter. Typical antibodies recognize the linear sequence (from left to right) indicated in the horizontal boxes, which is unique to each sequence. When the peptides aggregate to form pathological oligomers, they line up in a parallel, in-register fashion, shown below. This gives rise to steric zippers that run up and down the sheet perpendicular to the sequence, shown in vertical boxes. Aggregation-dependent, disease-specific antibodies recognize the steric zippers from many different amyloid sequences. Zippers from F and V amino acids are shown in boxes, but there are potentially 20 different zippers; one for each of the 20 amino acids.

The fact that a completely random sequence can form the same type of steric zipper as is found in Aß amyloid in Alzheimer’s disease means we can use a non-human, random peptide sequence as a vaccine to produce a protective immune response that has a very low potential for autoimmune side effects. Vaccines based on non-human peptides, like diphtheria and pertussis toxin, are so safe they routinely are given to infants. There is no reason to expect that a vaccine for AD that targets the disease-specific steric zippers wouldn’t be as safe and free of side effects. A goal of the research funded by Cure Alzheimer’s Fund is to do the preclinical investigations that are a necessary prelude to getting these third-generation vaccines and monoclonal antibodies that target disease-specific epitopes into human clinical trials.

Special Science Update from Cure Alzheimer's Fund

Science Update CoverThis Science Update gives you an overview about what is know about the science behind Alzheimer’s disease and how at Cure Alzheimer's Fund we are funding research to get to a cure as quickly as possible.

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A Vaccine for Alzheimer's Disease?

A brief summary of important potential treatments and CAF’s related research.

The AlzGene Database

Cure Alzheimer’s is funding the management and continued development of a revolutionary web based database.

Alzheimer's Disease Making Headlines

Research Update

There has been a spate of announcements about promising drug therapies, “new” genes and environmental factors affecting Alzheimer’s disease (AD) in the news lately. These are likely to increase as the media becomes more sensitized to the looming disaster that Alzheimer’s presents to the world.

We thought it would be useful to bring you up to date on our research agenda. Cure Alzheimer's Fund’s supported research is active in basic genetic research and early stages of drug development, and also addresses several key environmental factors.

New Research Linking Alzheimer's to Stroke Provides New Window on Cure and Treatment

From an article in Medical News Today about a paper recently released in the journal Neuron, June 7, 2007:

Researchers from the MassGeneral Institute for Neurodegenerative Disorders (MGH-MIND) have discovered how brain cells affected by stroke or head injury may cause generation of amyloid-beta protein, which is a key factor in the Alzheimer’s disease story.

Research Update: October 2007

Cure Alzheimer's Fund's core research effort continues to be the Alzheimer’s Genome Project™ initiative. Using whole genome association to analyze DNA, the objective is to identify all the genes that affect risk for AD. That project, largely based at Massachusetts General Hospital and Harvard Medical School, continues and is on time for completion by summer of 2008.

The Science Behind the Alzheimer's Genome Project

Photo of GeneChipThe core research effort currently funded by Cure Alzheimer’s Fund is the Alzheimer's Genome Project™ initiative. This project, entirely funded by Cure Alzheimer’s Fund, is being led by Dr. Rudolph Tanzi at Massachusetts General Hospital. The objective is to identify all genes that contribute significant risk for Alzheimer’s disease, thereby identifying more targets for the development of therapeutic interventions.

Targeting Amyloid Oligomers in Alzheimer's Disease

By Charles Glabe, Ph.D. University of California at Irvine
Professor, Molecular Biology and Biochemistry, School of Biological Sciences.

The current treatments for AD target the disease symptoms and to prevent or cure AD, new treatments are needed that target the causes of the disease.  Aß oligomers are a leading candidate for causing AD, so it makes sense to develop strategies to prevent their formation, promote their elimination or inhibit their toxic activity.

Oligomers-Fibrils

Alzheimer’s disease (AD) is the most wide spread and debilitating disease that robs otherwise healthy individuals of essential functions, such as memory and cognitive ability.  One of the critical aspects of AD is accumulation of misfolded proteins as deposits in regions of the brain involved in learning and memory that are known by the general term “amyloid”.  One of the curious aspects of amyloid is that it also accumulates in other degenerative diseases associated with aging, like Parkinson’s and Huntington’s diseases and type II diabetes.  In AD, the amyloid deposits are primarily made up of a small protein known as “amyloid beta”, or Aß, while in other degenerative diseases a different type of protein forms the amyloid.  In most of these diseases, mutations in the amyloid forming protein promote the misfolding of the protein and are associated with rare inherited forms of disease, providing strong evidence that amyloid formation is closely linked to the disease.

Amyloids grow into long, thin fibrils by the addition of misfolded proteins on to the ends much like the addition of a single Lego block on to a stack.  Proteins are linear strands of amino acids that fold into complex globular shapes that are critical for the proteins function.  In order for a normal protein to form an amyloid fibril, it must undergo a change in its original shape from a globular form to an unwound abnormal shape that allows it’s self-assembly with other misfolded protein strands like Lego blocks.  This assembly can go on infinitely, so that each amyloid fibril may contain a million or more individual subunits or blocks.  
Although amyloid accumulation is a key feature of AD, it also presented an enigma because the accumulation of insoluble amyloid fibril deposits is poorly correlated with dementia.  Some cognitively normal individuals were found to have the same amount of insoluble amyloid deposits as AD patients, indicating that these deposits are not always associated with disease.  Similarly, other AD patients have been observed with relatively little of the insoluble amyloid deposits.  These observations refocused research away from the insoluble amyloid deposits to other types of amyloid aggregates known as “oligomers”.  More recent research in amyloid aggregation has discovered that the amyloid formation pathway also includes smaller aggregates, or oligomers and these oligomers have a different shape or conformation of the protein than that found in amyloid fibrils.  Like Duplo blocks and Lego blocks, the oligomer conformation does not co-assemble with the fibril building blocks, but rather only supports the self-assembly of small aggregates of about 3-24 individual peptide strands.  Amyloid oligomers have been observed for AD and other amyloid-related degenerative diseases.  There is increasing evidence that these small oligomers, rather than the long fibrils, are the primary toxic or pathogenic species that cause all of these degenerative diseases.  Oligomers are more toxic to cells and their presence correlates better with disease than the fibrils.  Determination of the structures of these toxic oligomers, what they do to cause disease and how we may prevent their toxic activity are the primary objectives of Cure Alzheimer’s Fund Research Consortium Collaborative.

The Cure Alzheimer's Fund Research Consortium Collaborative consists of five of the members of the Research Consortium and a member of the Cure Alzheimer’s Fund Science Advisory Board. This highly innovative collaborative project investigates critical aspects of amyloid oligomers in AD.  The project is in it’s second year of funding.

For a full summary of the funded researchers and their projects, please visit our website www.curealzfund.org and see the
The laboratories of Dr. Charles Glabe, University of California at Irvine, and Dr. Virginia Lee, University of Pennsylvania, are making monoclonal antibodies that specifically recognize distinct types of amyloid oligomers.  These properties of specific antibodies are very important for the development of passive immunotherapy and vaccines for AD, which is one of the leading strategies for therapeutic development (see “A Vaccine for Alzheimer’s disease?” by Dr. David Holtzman in the Fall 2006 quarterly report for more details about vaccine development.)  Oligomer specific monoclonal antibodies are also useful for screening for drugs that prevent oligomer formation and as diagnostic agents.  Although diagnostic agents may not seem to have much utility until better treatments are available for AD, they are critical for  developing new therapies by allowing clinicians to recruit more homogeneous populations of individuals at risk for disease onset for human clinical trials.  They are also crucial for drug development by allowing pharmaceutical companies to directly evaluate the effectiveness of drugs that target amyloid oligomers.

Drs. Rudy Tanzi and Robert Moir of Massachusetts General Hospital/Harvard Medical School are working on the discovery of drugs that prevent the formation of a novel type of amyloid oligomer knows as “cross-linked amyloid protein species” (CAPS).  These results suggest that immunization with anti-CAPS antibodies and drugs that prevent the formation of CAPS might provide therapeutic benefit for AD.  Drs. Tanzi and Moir are also providing CAPS to other members of the Cure Alzheimer Fund research consortium for analysis of their immunological properties and toxic activity.

Drs. Sangram Sisodia, University of Chicago, and Sam Gandy of Mt. Sinai Medical School are working on amyloid oligomers in transgenic mouse models of AD.  Dr. Sisodia’s laboratory is working on Aß*56, a particular type of amyloid oligomer that is closely associated with the development of cognitive dysfunction in Tg2576 mice.  Dr. Sisodia’s lab focuses on the molecular analysis of Aß*56 structure and function and how exercise may impact the formation of Aß oligomers.  Dr. Gandy’s laboratory is developing new transgenic mouse models of AD that have different types of amyloid oligomers and these animal models will be shared with other members of the consortium.  These animal models are very important for development of new therapeutics because they provide a means of determining the pathological significance of amyloid oligomers and they can be used for testing new drugs and vaccines for effectiveness.

Drs. Paul Greengard of The Rockefeller University, David Holtzman of Washington University at St. Louis and Dr. Tae-Wan Kim of Columbia University Medical Center are investigating the relationship between oligomers and neuronal synapse function.  Synapses are critical for neuronal communication in learning and memory and there is evidence that synaptic loss and dysfunction play a role in AD.

Why target Aß oligomers?

The current treatments for AD target the disease symptoms and to prevent or cure AD, new treatments are needed that target the causes of the disease.  Aß oligomers are a leading candidate for causing AD, so it makes sense to develop strategies to prevent their formation, promote their elimination or inhibit their toxic activity.  Vaccination against Aß has shown considerable promise in human clinical trials, but one of the hurdles that must be overcome in order to develop an effective vaccine is to develop vaccines that lack undesirable inflammatory side effects.  Vaccines that specifically target the misfolded conformation specific to amyloid oligomers may eliminate oligomers or block their toxicity and overcome these side effects.  Since the structures recognized by the antibodies are specific for the disease state and do not recognize the normal, non-disease related protein structures, vaccination against the oligomeric conformation may be less likely to cause inflammatory complications. Conformation dependent monoclonal antibodies may be more effective therapeutic agents because they bind only to the pathological oligomers that are present at low concentrations and will not bind to amyloid plaques.  Similarly, drugs that specifically target Aß oligomer formation or toxicity may be more effective because lower concentrations of drugs may be needed to achieve a therapeutic benefit and they may have lower side effects as a consequence.  The Cure Alzheimer’s Fund Research Consortium Collaborative has a broad and integrated research program that is focused on developing therapeutic agents that prevent or cure AD by targeting the cause of AD.

 

Research Update: May 2008

Two papers, supported in part by Cure Alzheimer’s Fund,  have just been published in two leading research journals. The findings show links between certain kinds of anesthesia and pathological features of Alzheimer’s disease.