Imaging Alzheimer-Related Pathological Changes: Immune-Mediated, Therapeutics and Toxicities

Bradley Hyman, M.D., Ph.D.

Massachusetts General Hospital / Harvard University

Funded in June, 2004: $150000 for 3 years
LAY SUMMARY . ABSTRACT . HYPOTHESIS . FINDINGS . SELECTED PUBLICATIONS .

LAY SUMMARY

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Exploring how an Experimental Therapeutic Vaccine for Alzheimer’s Produces Life-Threatening Brain Inflammation

This academic research study will examine how the first experimental therapeutic vaccine, designed to reduce brain accumulation of amyloid in Alzheimer’s disease, caused a life-threatening inflammatory response in some of the patients participating in the initial clinical trial sponsored by the vaccine’s pharmaceutical company developer.  The findings could help guide future development of Alzheimer’s therapies that avoid this serious, and sometimes deadly, inflammatory complication.

Alzheimer’s disease is characterized by accumulation in the brain of the protein called amyloid. A pharmaceutical company recently developed a therapeutic vaccine designed to reduce the build-up of amyloid.  Animal studies indicated that the small amount of amyloid contained in the vaccine stimulated the animals’ immune systems to attack amyloid when they subsequently encountered it in the brain.  Based on the animal testing, the Food and Drug Administration approved a small clinical trial of vaccine in 16 Alzheimer’s patients to determine the vaccine’s relative safety and assess initial indications of its efficacy.  Some vaccine recipients showed evidence of slower rates of cognitive clinical decline compared to untreated patients.

The trial was abruptly halted, however, when five percent of the patients developed life-threatening meningoencephalitis, a devastating inflammation in the brain.  One of these patients died.  An autopsy of this patient’s brain showed decreased amounts of amyloid, compared to the amount usually found at autopsy of Alzheimer’s patients.  This patient’s autopsy also showed evidence that a large number of immune T cells had been activated.

These autopsy findings have prompted Harvard researchers to develop a new mouse model that, when imaged, will help in understanding the interaction between the therapeutic vaccine and the immune T cells’ production of a massive inflammatory response.  While the vaccine is designed to stimulate production of immune T cells to attack the amyloid, it is not clear why the T cells produced the large inflammatory response.  The Harvard researchers' new animal model will try to help address that question.

The investigators have developed a fluorescent compound to label immune T cells, and the T cells’ actions that occur in Alzheimer’s disease in response to the experimental vaccine now can be viewed using microscopy in a new animal model.  The animal model was produced by breeding a mouse model of Alzheimer’s disease with a strain of mice in which specific subpopulations of immune T cells have been engineered to contain fluorescent proteins.  This resultant new Alzheimer’s disease mouse model has T cells that will fluoresce, providing direct visualization of the animals’ immune T cells in different states of activation.  The imaging also will show the fluoresced interaction between the animals’ immune T cells and the antibodies that are stimulated by the vaccine.  This new model is expected to help determine what went wrong in use of the experimental vaccine.  Eventually, this “fluoresced” animal model of Alzheimer’s disease should be able to be used to study the effects of future experimental therapies that are intended to modify the immune system’s response to immunizations designed to reduce amyloid accumulation.

Significance:  This new animal model that allows visualization of fluorescently labeled immune T cell subpopulations may help to reveal how experimental therapeutic immunization to reduce amyloid deposits in Alzheimer’s produces a deadly T cell inflammatory response.  By understanding this harmful immune response, the results may provide new insights into future development of therapies that avoid this consequence.  The animal model and technique will provide a means of determining the effects on immune T cells of such future experimental therapeutic vaccines.

ABSTRACT

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Imaging Alzheimer-Related Pathological Changes: Immune-Mediated, Therapeutics and Toxicities

Immunization against amyloid-β, the peptide that accumulates in senile plaques and in blood vessels in Alzheimer's disease, causes a dramatic immune response that prevents plaque formation and clears accumulated amyloid-β in transgenic mice. In a clinical trial of amyloid-β immunization, 15 of about 300 patients developed meningoencephalitis. Neuropathological investigations of one patient who died during the trial showed promising evidence of clearance of amyloid pathology, but also a powerful immune response involving activated T cells probably underlying the negative effects of the immunization. To continue developing therapies based on amyloid-β immunization, these T cell-mediated inflammatory events must be understood.

In this study, we will develop an in vivo multiphoton imaging technique to investigate leukocyte trafficking in the meninges and cortex. We will combine this with current techniques for in vivo imaging of amyloid pathology to study the effects of amyloid-β immunization in mice transgenic for mutant human amyloid precursor protein (APP). Transgenic mice expressing fluorescent proteins in specific subpopulations of T cells will allow direct imaging of T cells in different states of activation. T cells from these mice will be transferred to APP transgenic and crosses of T cell reporter mice, and APP transgenic mice will be bred, allowing imaging of the interaction of T cells in different states of activation with amyloid pathology during immunization. These experiments will also provide a method of testing the effects of possible Alzheimer's therapeutics that modify the T cell response in amyloid-β immunization. In addition to addressing this clinical problem, the technology to monitor T cell trafficking in the cerebral cortex may also benefit the general field of neuroimmunological investigations.

 

HYPOTHESIS

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Hypothesis:
Leukocyte infiltration underlies Alzheimer vaccine-related meningo-encephalitis.

Goals:
1. Develop methodologies to image leukocyte trafficking in the CNS
2. Image senile plaques and amyloid angiopathy in mouse models
3. Monitor leukocyte infiltration and activation states near amyloid

Methods:
Develop multiphoton imaging technique to detect amyloid plaques as well as T-cell trafficking in the CNS of mouse models of Alzheimer’s disease.

 

FINDINGS

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Lay results:
A novel approach to treating Alzheimer’s disease ran into difficulties several years ago when patients immunized against an Alzheimer related protein developed severe side effects.  This project was aimed at understanding which aspect of the therapy caused the side effects.  The immunization caused two reactions—antibodies were formed and T cells were activated.  We found, using mouse models, that either activating T cells or adding antibodies alone could be done safely, but that the combination caused bleeding at the sites of inflammation.  This may help in the design of the next generations of immunotherapy for Alzheimer disease.

Scientific results:
We examined the immunological underpinnings of hemmorhagic encephalitis following immunization against Aβ in Alzheimer models.  We immunized wild type mice against Aβ42, then used adoptive transfer to expose naïve APP transgenics to activated T cells alone; alternatively we exposed the cortex of APP mice to anti-Ab antibodies, or exposed the mice to both adoptive transfer and antibodies.  No hemorrhage was observed with either antibody treatment or T cell transfer alone; however, the combination of activated T cells and passive antibody treatment led to hemorrhagic consequences in the majority of treated mice.  Intriguingly, even some mice treated with activated T cells but off-target IgG had evidence of hemorrhage, implying a role of the activated T cells in leading to hemorrhagic consequences.  These data suggest that passive immunization, or active immunization using techniques that preclude activation of T cells, may be critical to avoid hemorrhagic complications of Aβ immunization.

 

SELECTED PUBLICATIONS

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Bacskai B.J., Hickey G.A., Skoch J., Kajdasz S.T., Wang Y., Huang G-f, Mathis C.A., Klunk W.E., and Hyman B.T.  Four-dimensional imaging of brain entry, amyloid-binding and clearance of an amyloid-ß ligand in transgenic mice using multiphoton microscopy.  Proc Natl Acad Sci 2003; 100(21):12462-12467.

Bacskai B.J., Kajdasz S.T., Christie R.H., Carter C., Games D., Seubert P., Schenk D., and Hyman B.T.  Imaging of amyloid-ß deposits in brains of living mice permits direct observation of clearance of plaques with immunotherapy.  Nat Med 2001, 7(3): 369-372.