Alzheimer Disease: Ghochikyan A

Ghochikyan A. · The Institute for Molecular Medicine, Department of Immunology, Huntington Beach, CA 92647, USA. · CNS Neurol Disord Drug Targets. · Pubmed #19355933 No free full text.

Abstract: Amyloid-beta (Abeta) immunotherapy has received considerable attention as a promising approach for reducing the level of Abeta in the CNS of Alzheimer's disease patients. However, the first Phase II clinical trial, for the immune therapy AN1792, was halted when a subset of those immunized with Abeta(42) developed adverse events in the central nervous system. In addition, data from the trial indicated that there was a low percentage of responders and generally low to moderate titers in the patients that received the vaccine. Generated antibodies reduced beta-amyloid deposits in the parenchyma of patients' brains, but no reduction in soluble Abeta or significant improvements in cognitive function of patients were observed. These data and data from pre-clinical studies suggest that reduction in the most toxic oligomeric forms of Abeta is important for prevention or slowing down of the progression of cognitive decline, and that vaccination should be started prior to irreversible accumulation of the oligomeric Abeta, at the early stages of AD. Protective immunotherapy requires a development of safe and effective strategy for Abeta immunotherapy. In this review, the rationale for developing epitope vaccines for the treatment of AD will be discussed. We believe that an epitope vaccine will induce an adequate anti-Abeta antibody response in the absence of potentially adverse self T cell-mediated events, making it possible to start immunization at the early stages of AD.

Petrushina I, Ghochikyan A, Mkrtichyan M, Mamikonyan G, Movsesyan N, Ajdari R, Vasilevko V, Karapetyan A, Lees A, Agadjanyan MG, Cribbs DH. · The Institute for Brain Aging and Dementia, University of California Irvine, Irvine, CA 92697-4540, USA. · J Neuroinflammation. · Pubmed #18823564 links to  free full text

Abstract: BACKGROUND: New pre-clinical trials in AD mouse models may help to develop novel immunogen-adjuvant configurations with the potential to avoid the adverse responses that occurred during the clinical trials with AN-1792 vaccine formulation. Recently, we have pursued an alternative immunization strategy that replaces QS21 the Th1 type adjuvant used in the AN-1792 clinical trial with a molecular adjuvant, mannan that can promote a Th2-polarized immune response through interactions with mannose-binding and CD35/CD21 receptors of the innate immune system. Previously we established that immunization of wild-type mice with mannan-Abeta28 conjugate promoted Th2-mediated humoral and cellular immune responses. In the current study, we tested the efficacy of this vaccine configuration in amyloid precursor protein (APP) transgenic mice (Tg2576). METHODS: Mannan was purified, activated and chemically conjugated to Abeta28 peptide. Humoral immune responses induced by the immunization of mice with mannan-Abeta28 conjugate were analyzed using a standard ELISA. Abeta42 and Abeta40 amyloid burden, cerebral amyloid angiopathy (CAA), astrocytosis, and microgliosis in the brain of immunized and control mice were detected using immunohistochemistry. Additionally, cored plaques and cerebral vascular microhemorrhages in the brains of vaccinated mice were detected by standard histochemistry. RESULTS: Immunizations with low doses of mannan-Abeta28 induced potent and long-lasting anti-Abeta humoral responses in Tg2576 mice. Even 11 months after the last injection, the immunized mice were still producing low levels of anti-Abeta antibodies, predominantly of the IgG1 isotype, indicative of a Th2 immune response. Vaccination with mannan-Abeta28 prevented Abeta plaque deposition, but unexpectedly increased the level of microhemorrhages in the brains of aged immunized mice compared to two groups of control animals of the same age either injected with molecular adjuvant fused with an irrelevant antigen, BSA (mannan-BSA) or non-immunized mice. Of note, mice immunized with mannan-Abeta28 showed a trend toward elevated levels of CAA in the neocortex and in the leptomeninges compared to that in mice of both control groups. CONCLUSION: Mannan conjugated to Abeta28 provided sufficient adjuvant activity to induce potent anti-Abeta antibodies in APP transgenic mice, which have been shown to be hyporesponsive to immunization with Abeta self-antigen. However, in old Tg2576 mice there were increased levels of cerebral microhemorrhages in mannan-Abeta28 immunized mice. This effect was likely unrelated to the anti-mannan antibodies induced by the immunoconjugate, because control mice immunized with mannan-BSA also induced antibodies specific to mannan, but did not have increased levels of cerebral microhemorrhages compared with non-immunized mice. Whether these anti-mannan antibodies increased the permeability of the blood brain barrier thus allowing elevated levels of anti-Abeta antibodies entry into cerebral perivascular or brain parenchymal spaces and contributed to the increased incidence of microhemorrhages remains to be investigated in the future studies.

Movsesyan N, Ghochikyan A, Mkrtichyan M, Petrushina I, Davtyan H, Olkhanud PB, Head E, Biragyn A, Cribbs DH, Agadjanyan MG. · Department of Molecular Immunology, Institute for Molecular Medicine, Huntington Beach, California, United States of America. · PLoS One. · Pubmed #18461171 links to  free full text

Abstract: BACKGROUND: The development of a safe and effective AD vaccine requires a delicate balance between providing an adequate anti-Abeta antibody response sufficient to provide therapeutic benefit, while eliminating an adverse T cell-mediated proinflammatory autoimmune response. To achieve this goal we have designed a prototype chemokine-based DNA epitope vaccine expressing a fusion protein that consists of 3 copies of the self-B cell epitope of Abeta(42) (Abeta(1-11)) , a non-self T helper cell epitope (PADRE), and macrophage-derived chemokine (MDC/CCL22) as a molecular adjuvant to promote a strong anti-inflammatory Th2 phenotype. METHODS AND FINDINGS: We generated pMDC-3Abeta(1-11)-PADRE construct and immunized 3xTg-AD mouse model starting at age of 3-4 months old. We demonstrated that prophylactic immunizations with the DNA epitope vaccine generated a robust Th2 immune response that induced high titers of anti-Abeta antibody, which in turn inhibited accumulation of Abeta pathology in the brains of older mice. Importantly, vaccination reduced glial activation and prevented the development of behavioral deficits in aged animals without increasing the incidence of microhemorrhages. CONCLUSIONS: Data from this transitional pre-clinical study suggest that our DNA epitope vaccine could be used as a safe and effective strategy for AD therapy. Future safety and immunology studies in large animals with the goal to achieve effective humoral immunity without adverse effects should help to translate this study to human clinical trials.

Petrushina I, Ghochikyan A, Mktrichyan M, Mamikonyan G, Movsesyan N, Davtyan H, Patel A, Head E, Cribbs DH, Agadjanyan MG. · The Institute for Brain Aging and Dementia, University of California, Irvine, Irvine, California 92697-4540, USA. · J Neurosci. · Pubmed #18003852 links to  free full text

Abstract: Active vaccination of elderly Alzheimer's disease (AD) patients with fibrillar amyloid-beta peptide (Abeta42), even in the presence of a potent Th1 adjuvant, induced generally low titers of antibodies in a small fraction (approximately 20% responders) of those that received the AN-1792 vaccine. To improve the immunogenicity and reduce the likelihood of inducing adverse autoreactive T-cells specific for Abeta42, we previously tested in wild-type mice an alternative approach for active immunization: an epitope vaccine that selectively initiate B cell responses toward an immunogenic self-epitope of Abeta in the absence of anti-Abeta T cell responses. Here, we describe a second generation epitope vaccine composed of two copies of Abeta(1-11) fused with the promiscuous nonself T cell epitope, PADRE (pan human leukocyte antigen DR-binding peptide) that completely eliminates the autoreactive T cell responses and induces humoral immune responses in amyloid precursor protein transgenic 2576 mice with pre-existing AD-like pathology. Based on the titers of anti-Abeta(1-11) antibody experimental mice were divided into low, moderate and high responders, and for the first time we report a positive correlation between the concentration of anti-Abeta(1-11) antibody and a reduction of insoluble, cerebral Abeta plaques. The reduction of insoluble Abeta deposition was not associated with adverse events, such as CNS T cell or macrophage infiltration or microhemorrhages. Surprisingly, vaccination did not alter the levels of soluble Abeta. Alternatively, early protective immunization before substantial neuropathology, neuronal loss and cognitive deficits have become firmly established may be more beneficial and safer for potential patients, especially if they can be identified in a preclinical stage by the development of antecedent biomarkers of AD.

Mamikonyan G, Necula M, Mkrtichyan M, Ghochikyan A, Petrushina I, Movsesyan N, Mina E, Kiyatkin A, Glabe CG, Cribbs DH, Agadjanyan MG. · Department of Immunology, The Institute for Molecular Medicine, Huntington Beach, California 92647, USA. · J Biol Chem. · Pubmed #17545160 links to  free full text

Abstract: Different strategies proposed as therapy for Alzheimer disease (AD) have aimed to reduce the level of toxic forms of A beta peptide in the brain. Here, we directly analyze the therapeutic utility of the polyclonal anti-A beta(1-11) antibody induced in 3xTg-AD mice vaccinated with the second generation prototype epitope vaccine. Substoichiometric concentrations of purified anti-A beta(1-11) antibody prevented aggregation of A beta(42) and induced disaggregation of preformed A beta(42) fibrils down to nonfilamentous and nontoxic species. Anti-A beta(1-11) antibody delayed A beta(42) oligomer formation but ultimately appeared to stabilize nonfibrillar conformations, including oligomer-like assemblies. The reduced oligomer-mediated cytotoxicity observed upon preincubation of A beta oligomers with the anti-A beta(1-11) antibody in the absence of oligomer disaggregation suggests a possible oligomer rearrangement in the presence of the antibody. These in vitro observations suggest that preventive vaccination may protect from AD or may delay the onset of the disease, whereas therapeutic vaccination cannot disrupt the toxic oligomers and may only minimally alleviate preexisting AD pathology.

Ghochikyan A, Petrushina I, Lees A, Vasilevko V, Movsesyan N, Karapetyan A, Agadjanyan MG, Cribbs DH. · The Institute for Molecular Medicine, Department of Immunology, Huntington Beach, California, USA. · DNA Cell Biol. · Pubmed #17132088 links to  free full text

Abstract: In Alzheimer's disease (AD) the accumulation of pathological forms of the beta-amyloid (Abeta) peptide are believed to be causal factors in the neurodegeneration that results in the loss of cognitive function in patients. Anti-Abeta antibodies have been shown to reduce Abeta levels in transgenic mouse models of AD and in AN-1792 clinical trial on AD patients; however, the clinical trial was halted when some patients developed meningoencephalitis. Theories on the cause of the adverse events include proinflammatory "primed patients," a Th1-inducing adjuvant, and Abeta autoreactive T cells. New immunotherapy approaches are being developed to eliminate these putative risk factors. Mannan, which is recognized by pattern recognition receptors of the innate immune system, can be utilized as a molecular adjuvant to promote a Th2-mediated immune response to conjugated B cell epitopes. The N-terminus of Abeta was conjugated to mannan, and used to immunize mice with low concentrations of immunoconjugate, without a conventional adjuvant. Mannan induced a significant and highly polarized toward Th2 phenotype anti-Abeta antibody response not only in BALB/c, but also in B6SJL F1 mice. New preclinical trials in AD mouse models may help to develop novel immunogen-adjuvant configurations with the potential to avoid the adverse immune response that occurred in the first clinical trial.

Ghochikyan A, Mkrtichyan M, Petrushina I, Movsesyan N, Karapetyan A, Cribbs DH, Agadjanyan MG. · Department of Immunology, Institute for Molecular Medicine, Huntington Beach, CA 92647-3652, USA. · Vaccine. · Pubmed #16368167 links to  free full text

Abstract: Beta-amyloid (Abeta) peptide has been proposed to be a causal factor in Alzheimer's disease (AD). Currently being investigated, active and passive Abeta-immunotherapy significantly reduce Abeta plaque deposition, neuritic dystrophy, and astrogliosis in the brains of APP transgenic (APP/Tg) mice. Immunization with Abeta42 formulated in the Th1-type adjuvant QS21 was beneficial for AD patients with significant titers of anti-Abeta antibodies, however, 6% of participants developed meningoencephalitis, likely due to anti-Abeta-specific autoimmune Th1 cells. Thus, successful Abeta vaccination requires the development of strong antibody responses without Th1-type cellular immunity. In this study, we compared the induction of humoral immune responses with Th1-type (Quil A) and Th2-type (Alum) adjuvants singly and in combination, using our novel epitope vaccine composed of self B cell epitope Abeta(1-15) and foreign T cell epitope PADRE (PADRE-Abeta(1-15)-MAP). Formulated in Quil A, this vaccine resulted in significantly higher anti-Abeta antibody responses in both BALB/c (H-2d) and C57BL/6 (H-2b) mice, compared with Alum. Anti-Abeta antibodies induced by Alum were predominantly IgG1 type accompanied by lower levels of IgG2a and IgG2b. Quil A induced robust and almost equal titers of anti-Abeta antibodies of IgG1 and IgG2a isotypes and slightly lower levels of IgG2b. Switching adjuvants from Alum to Quil A induced higher concentrations of antibodies than injections with Alum only, however slightly lower than Quil A only. Switching both adjuvants did not change the profile of antibody responses generated by the initial adjuvant injected. These results suggest that switching from Alum to Quil A would be beneficial for AD patients because anti-Abeta antibody production was enhanced without changing the initially generated and likely beneficial Th2-type humoral response.

Agadjanyan MG, Ghochikyan A, Petrushina I, Vasilevko V, Movsesyan N, Mkrtichyan M, Saing T, Cribbs DH. · Institute for Molecular Medicine, Department of Immunology, Huntington Beach, CA 92647, USA. · J Immunol. · Pubmed #15661919 links to  free full text

Abstract: Immunization of amyloid precursor protein transgenic mice with fibrillar beta-amyloid (Abeta) prevents Alzheimer's disease (AD)-like neuropathology. The first immunotherapy clinical trial used fibrillar Abeta, containing the B and T cell self epitopes of Abeta, as the immunogen formulated with QS21 as the adjuvant in the vaccine. Unfortunately, the clinical trial was halted during the phase II stage when 6% of the participants developed meningoencephalitis. The cause of the meningoencephalitis in the patients that received the vaccine has not been definitively determined; however, analysis of two case reports from the AN-1792 vaccine trial suggest that the meningoencephalitis may have been caused by a T cell-mediated autoimmune response, whereas production of anti-Abeta Abs may have been therapeutic to the AD patients. Therefore, to reduce the risk of an adverse T cell-mediated immune response to Abeta immunotherapy we have designed a prototype epitope vaccine that contains the immunodominant B cell epitope of Abeta in tandem with the synthetic universal Th cell pan HLA DR epitope, pan HLA DR-binding peptide (PADRE). Importantly, the PADRE-Abeta(1-15) sequence lacks the T cell epitope of Abeta. Immunization of BALB/c mice with the PADRE-Abeta(1-15) epitope vaccine produced high titers of anti-Abeta Abs. Splenocytes from immunized mice showed robust T cell stimulation in response to peptides containing PADRE. However, splenocytes from immunized mice were not reactivated by the Abeta peptide. New preclinical trials in amyloid precursor protein transgenic mouse models may help to develop novel immunogen-adjuvant configurations with the potential to avoid the adverse events that occurred in the first clinical trial.