Table 11.3.

Biomarkers for diagnosis and management of multiple sclerosis

Evaluated biomarkers according to categories	Biomarkers with potential for further development	Biological rationale	Correlation with disease activity	Correlation with disability progression	Correlation with treatment effect	Notesa
Biomarkers reflecting alteration of the immune system						Unlikely candidates for surrogate end points; may prove useful in studying disease heterogeneity and in developing of new therapies
(a) Cytokines and their receptors						The most extensively studied biomarkers in multiple sclerosis
IL-1, IL-2, IL-6, IL-10, IL-12, IL-18, TNF-α, LT-α/β, TGF-β, CD25	IL-6 (+ soluble interleukin sIL-6R and soluble glycoprotein sgp130)	+++b	++/–	+	+/+	Candidate cytokine system linking innate immune system with both arms of adaptive immune responses (T and B cells)
	IL-10	++	++/–	+	+/+	Candidate immunoregulatory cytokine
IL-12 (p70)/IL-23	+++	++	++	+/+/+	Suggested as biomarker that can differentiate between relapsing-remitting and secondary progressive stages of multiple sclerosis
(b) Chemokines and their receptors						Biomarkers that may aid in studying disease heterogeneity and on proof of principle in therapy trials
CCR5, CXCR3, CXCL10, CCR2/CCL2	CCR5	++		ndc	+/–	Suggested as a candidate biomarker of Th1 T cells
CXCR3/CXCL10	++	++	nd	−	Marker of activated T cells
(c) Antibodies						The least systematically studied category with some interesting novel markers; e.g. diagnostic relevance of antibody in neuromyelitis optica. These biomarkers need systematic development and standardization of techniques
CSF IgG index, κ light chains, oligoclonal bands, anti-MBP Ab, anti-MOG Ab	Anti-MBP and anti-MOG Ab	+++	nd	nd	nd	Suggested as a possible diagnostic tool for predicting the development of definite multiple sclerosis after first clinical symptom (clinically isolated demyelinating syndrome)
(d) Complement-related biomarkers						Biomarkers needed for assessment of disease heterogeneity (based on pathological classification of multiple sclerosis lesions) and for development of novel therapies
C3, C4, activated neo-C9. Regulators of complement activation (CD35, CD59)	Activated neo-C9	++	+	+	nd	Biomarker reflecting formation of membrane-attack complex (MAC) that is expected to contribute to demyelination at least in a subgroup of multiple sclerosis patients
(e) Adhesion molecules						It is unlikely that these biomarkers would become more useful than MRI-based markers of blood–brain barrier dysfunction
E-selectin, L-selectin, ICAM-1, VCAM-1, CD31, surface expression of LFA-1 and VLA-4
(f) Biomarkers reflective of antigen processing and presentation						Very important category, little explored; needs further development for multiple sclerosis
CD40/CD40L, CD80, CD86, heat-shock proteins (hsp)	CD40/CD40L	++	+	nd	+	Suggested as candidate biomarker that can differentiate between relapsing–remitting and secondary progressive stages of multiple sclerosis
hsp	+	nd	nd	nd	Dysregulation in the heat-shock protein system is the most prominent and consistent result of gene expression studies in multiple sclerosis and other autoimmune diseases
(g) Other activation markers						Markers reflecting activation of the innate immune system would contribute to studies of disease heterogeneity and aid in selection and screening of prospective novel immunomodulatory agents
CD26, CD30, CD71, perforin, OX-40 (CD134), osteopontin, macrophage-related proteins MRP-8 and MRP-16, neopterin, amyloid A protein, somatostatin	Neopterin	++	++	nd	+/–
(h) Cell-cycle and apoptosis-related biomarkers						Very important category of biomarkers because they may reflect both defects in regulation of immune cells as well as proapoptotic properties of central nervous system components
Fas (CD95) and Fas-L, FLIP, Bcl-2, TRAIL	FLIP	++	+	+	+	Anti-apoptotic protein overexpressed in multiple sclerosis
TRAIL	+/?	nd	nd	+	Suggested as biomarker reflecting clinical response to IFN-β therapy in multiple sclerosis
(i) Biomarkers reflective of immune-mediated neuroprotection						Potentially very interesting biomarkers that need to be developed further; would contribute to disease heterogeneity studies and to development of process-specific therapies
BDNF expression
(j) Changes in cellular subpopulations						Markers studied predominantly in the past; many should be reassessed by new, more precise techniques
NK cells, Vα24+ NKT cells, CD4+/CD25bright and IL-10-producing immunoregulatory T cells, CSF cells, CD45RA−/RO+/CD4+ (memory) T cells	CD4+/CD25bright T cells and IL-10-producing regulatory T cells, regulatory NK cells and NKT cells	+++	+	nd	+/nd	These cellular subpopulations were shown to have important immunoregulatory roles in animal models and other human autoimmune disorders and they merit careful evaluation in multiple sclerosis
(k) Functional assays for immunological reactivity						Although potentially very interesting, these assays are very tedious and therefore are likely to remain restricted to early phases of drug development and to proof-of-principle clinical trials
Proliferation assays (Ag-specific and polyclonal), cytokine-secretion assays, cytotoxic assays
Biomarkers of blood–brain barrier disruption						It is unlikely that these biomarkers would become more useful than MRI-based markers of blood–brain barrier dysfunction
MMPs and their inhibitors (TIMP), platelet-activating factor, thrombomodulin
Biomarkers of demyelination						Would greatly enhance the understanding of MRI/pathological correlations and have a potential for partial surrogacy
MBP and MBP-like material, proteolytic enzymes, endogenous pentapeptide QYNAD, gliotoxin	QYNAD – endogenous peptide with Na-channel blocking properties	++	nd	nd	nd	QYNAD is an endogenous substance in cerebrospinal fluid that probably originates from proteolytic cleavage during inflammation; deserves further evaluation
Biomarkers of oxidative stress and excitotoxicity						Very important biomarkers from the standpoint of disease heterogeneity and potentially for development of novel therapies; need to be developed further
NO and its stable metabolites (nitrite NO2− and nitrate NO3−), uric acid, isoprostane, marker for hypoxia-like tissue damage in multiple sclerosis	NO (+ NO2− and NO3−)	++	+/–	–/nd	nd	May help in disease heterogeneity studies
	Uric acid	++	++	+	+/–	Strong natural peroxynitrate scavenger
Isoprostane	++	nd	+	+	Interesting candidate marker that merits further studies
Marker for hypoxia-like tissue damage in multiple sclerosis	+	nd	nd	nd	Described in pivotal study as an endogenous epitope that is cross-recognized by monoclonal antibody against canine distemper virus and may become a diagnostic tool to identify specific multiple sclerosis subtype
Biomarkers of axonal/neuronal damage						Most likely category of biomarkers with surrogate potential in multiple sclerosis
Cytoskeletal proteins (actin, tubulin and neurofilaments), tau protein	Neurofilaments: light subunit (NF-L)	+++	+	+	nd	Might be the most likely candidate for surrogacy; its development warrants further efforts
Tau protein	++	++	nd	nd	Also potentially very useful biomarker that needs further development
Biomarkers of gliosis						May be useful for disease heterogeneity studies but with unpredictable surrogacy potential
GFAP, S-100 proteins
Biomarkers of remyelination and repair						Much-needed biomarkers that would guide development of repair-promoting strategies in multiple sclerosis and aid in disease heterogeneity studies
NCAM, CNTF, microtubule-associated protein-2 exon 13 (MAP-2 + -13), protein 14-3-3, CPK-BB, peptidylglycine α-amidating monooxygenase (PAM), neural-specific enolase (NSE)	NCAM – neural cell adhesion molecule	+	+	nd	nd	Very sparse data on both biomarkers. However, because these are so far the only potential candidates, their evaluation warrants further effort
	CNTF – ciliary neurotrophic factor	++	nd	nd	nd

Ab = antibody; Ag = antigen; CNTF = ciliary neurotrophic factor; CSF = cerebrospinal fluid; FLIP = Fas-associated death domain-like interleukin-1β-converting enzyme inhibitory protein; GFAP = glial fibrillary acidic protein; hsp = heat-shock protein; ICAM-1 = intracellular adhesion molecule-1; IFN = interferon; Ig = immunoglobulin; IL = interleukin; LP = lumbar puncture; LT-α/β = lymphotoxin α/β; MAC = membrane-attack complex; MBP = myelin basic protein; MOG = myelin oligodendrocyte glycoprotein; MMP = matrix metalloproteinase; NCAM = neural cell adhesion molecule; NF-L = neurofilament light subunit; NK cells = natural killer cells; NKT cells = NK-like T cells; NSE = neuron-specific enolase; OCB = oligoclonal bands; PAM = peptidylglycine α-amidating monooxygenase; TGF-β = transforming growth factor β; TIMP = tissue inhibitor of matrix metalloproteinases; TNF-α = tumour necrosis factor α; VCAM-1 = vascular cell adhesion molecule 1.

BDNF = brain derived neurotrophic factor

CPK-BB = creatine phosphokinase-BB

LFA = lymphocyte function antigen

TRAIL = tumour necrosis factor related apoptosis-inducing ligand

VLA = very late appearing antigen

Simplified summary of reviewed biomarkers in multiple sclerosis taken from Bielekova and Martin (2004).

^aBrief opinion of the authors about the potential use of the biomarkers and the need for further developments.

^bWe attempted to grade the strength of supportive evidence for each characteristic of the biomarker as low (+), medium (++) and high (+++). In treatment effects +/– implies positive correlation with one type of therapy and negative with another.

^cNo reliable data.