Mark S. Freedman, BSc, MSc, MD
This year's American Academy of Neurology (AAN) Annual Meeting was ripe with many new ideas that originated from attempts to further understand the immunopathogenesis of multiple sclerosis (MS). Rather than try to discuss all this data selected presentations from each session best serve as examples of important areas of research to which many investigators have contributed.
Gene Microarrays and Proteomics
Gene microarrays and proteomics are one of the hottest new areas of research resulting from advances in biotechnology. New technology can reduce the human genome or all of the known proteins to a small biological "microchip," onto which either purified nuclear material, cellular extracts, serum, or cerebrospinal fluid (CSF) can be analyzed. Older technologies required a target gene or protein but this newer technology allows what amounts to huge "fishing" expeditions. This affords the ability to search for hundreds and even thousands of genes or gene products specific to the immune system that may be unique to MS, associated with a particular course of disease, or indicative of a response to therapy. In essence, this technology is aiding the search for the "holy grail" in MS -- a specific biomarker that is unique to the disease and may indicate when MS is active or progressing.
Using gene microarrays or proteomics, several groups reported on a number of potential "leads" worthy of further study. For example, using total RNA extracted regularly from mononuclear cells, Singh and colleagues followed patients who injected themselves weekly with interferon-beta-1a (IFN-betã-1a); patients mostly had relapsing-remitting MS but at least 1 patient was in the progressive phase. In addition to the hundreds of genes known to turn on in response to IFN-beta-1a, they also found genes for several other inflammatory molecules and were able to profile these into pre- and posttreatment samples. Of note, the 1 patient with progressive MS had a profile similar to the pretreatment profiles, which suggests this individual might no longer respond to treatment in the same way. Similarly, several groups used variations of proteomic chips to examine serum or CSF in the hope of identifying certain proteins unique to MS. Irani and colleagues found 1 small molecule in MS CSF that seemed to increase only in MS patients who had experienced a recent attack. Now, the long and arduous task begins of validating this in a much greater number of patients than the 29 subjects they tested, and more importantly, identifying the protein. Traditional approaches also sought to associate certain immune substances with disease "subsets" of MS, such as interleukin (IL)-6 with transverse myelitis, and soluble CD26, CD30, and a number of chemokines with relapsing neuromyelitis optica.[4,5]
Looking for the Cause of Axonopathy in MS
Yet another interesting finding was generated by the laboratory of Lawrence Steinman at Stanford University, Stanford, California, who was honored this year with the prestigious JJ Dystel Award for his contributions to the understanding of MS and its disease process. Realizing that an integral part of MS pathogenesis is the early involvement of axonal disease, Fontoura and colleagues (Steinman's group) focused on specific peptides of an important central nervous system-specific myelin molecule that is associated with the arrest of axonal development termed "NOGO." It appears that if antibodies are induced to the intracellular portion of this molecule, they block the actions of NOGO and facilitate axonal regrowth in a model of spinal cord injury. Steinman's group wondered what would happen in response to immune reactions to the extracellular portion of this molecule. He and his colleagues synthesized various peptides and immunized mice in the same way that other myelin peptides have been demonstrated to cause experimental autoimmune encephalomyelitis (EAE). They were surprised to find that they were able to induce EAE in at least 1 strain of mice that was similar to traditional EAE with other myelin peptides. Immunologically, they found strong T-cell responses that were specific to the immunized NOGO peptide; however, when they examined the specificity of the B-cell responses, they found not only NOGO-specific antibodies but also those from other myelin peptides, which is indicative of epitope spreading (the mechanism by which the immune system spreads its long-lasting reactivity to myelin). This suggested that NOGO could behave as an autoantigen similar to other myelin molecules. This finding is of great interest because immunity to 1 portion of the molecule (the intracellular component) promotes axonal regrowth, whereas immune reactions to the extracellular component could lead to autoimmune-mediated demyelination.
Qin and coworkers examined the B-cell response to axonal antigens in humans. These investigators made antibodies on the basis of immunoglobulin gene expression from clonally expanded B cells that were derived from the CSF of MS patients and stained brain tissue. They then used these antibodies to stain MS brain tissue and found specific reactivity to areas of transected and degenerating axons in chronic MS lesions. Of interest, however, was that although antibodies were based on different gene sequences, the pattern of staining was the same, which suggests a common antigen.
Finally, a fascinating study was presented of living mouse brain slices treated with a calcium-sensitive dye, onto which T cells -- typical of the kind capable of inducing EAE and labeled with red dye -- were co-incubated for up to 3 hours. Researchers noted that myelin-specific T cells penetrated the brain slices (as viewed by tracking the red-labeled cells) and produced lethal increases of calcium in contact with the neurons. This phenomenon could be blocked by a substance known to inhibit the release of the cytotoxic molecule perforin from T cells or by inhibitors of glutamate-induced neurotoxicity. This suggests that T-cell-induced neuronal injury might involve 1 or both of these substances.
Mechanisms of Disease-Modifying Therapies
There were many presentations on proposed mechanisms of action of the current disease-modifying medications, IFN-beta and glatiramer acetate (GA), but 1 was of particular interest. Graber and colleagues evaluated a cohort of patients participating in the EVIDENCE study, which compared 30 mcg of IFN-beta-1a given once a week vs 44 mcg 3 times weekly. As we eagerly await the results of clinical studies with monoclonal antibodies directed at adhesion molecules on lymphocytes (eg, VLA-4 integrin), these researchers examined the sera from 15 patients over a 24-week period for the presence of soluble VCAM (the endothelial cell ligand for VLA-4 on lymphocytes). Earlier research has shown that IFN-beta induces soluble VCAM (sVCAM) and that higher levels of sVCAM correlated with a reduction in MRI lesions. The patients randomized to the high-dose, high-frequency regimen experienced a sustained 56% mean increase in VCAM as compared with only a 14% increase over pretreatment values with once-weekly eek IFN-beta. sVCAM would have the same effect as antibodies on VLA-4 in terms of blocking the lymphocyte reactivity with endothelial cells. Anti-VLA-4 antibody therapy might therefore do more to complement low-dose IFN-beta therapy, but may not have the same effect with high-dose IFN-beta given this phenomenon of higher sVCAM already produced.
In reference to GA, Israeli researchers demonstrated the effects of GA-treated T cells in the brains of animals with EAE. They were able to extract these T cells from GA-treated animals and show that they secreted protective cytokines and the brain-derived neurotrophic factor when challenged in vitro with either GA or myelin basic protein antigen. Although the "statin" drugs continue to be investigated for their "other" role as immunoregulators, Olaf Stuve and other members of the laboratory of Scott Zamvil demonstrated that these agents, given in standard doses, could enhance the clinical benefit of GA on ameliorating the signs of EAE. This raises the possibility of trials in humans, combining these agents to achieve greater efficacy.
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