WO2018226098A2

WO2018226098A2 - Methods for typing neurological disorders and cancer, and devices for use therein

Info

Publication number: WO2018226098A2
Application number: PCT/NL2018/050370
Authority: WO
Inventors: Maarten TITULAER
Original assignee: Erasmus University Medical Center Rotterdam
Priority date: 2017-06-07
Filing date: 2018-06-07
Publication date: 2018-12-13
Also published as: WO2018226098A3

Abstract

The invention relates to a method for detecting antibodies against a GABAB receptor in a sample of a subject, comprising the steps of providing a sample from a subject, wherein said sample comprises, or is suspected of comprising, antibodies against a GABAB receptor; providing a composition comprising a GABAB receptor and a KCTD protein; contacting said sample with said composition, and performing an immunoassay to determine the presence of an antibody against a GABAB receptor in said sample.

Description

Title: Methods for typing neurological disorders and cancer, and devices for use therein. FIELD OF THE INVENTION

The invention is in the field of clinical diagnostics. In particular, the present invention is directed to an assay for diagnosis of an immune disorder known as autoimmune encephalitis with epilepsy, which disorder is associated with seizures, memory loss and cancer, and to the identification of patients suffering, or suspected of suffering, from said neurological autoimmune disorder. The present invention relates to immunoassays for detecting autoantibodies in a biological sample of a patient that are indicative of said neurological disorder. The invention provides improved methods of classifying patient samples, and compounds and systems for use in such methods. The invention further relates to the identification of patients having an increased likelihood of suffering from a tumor associated with the neurological disorder (i.e. paraneoplastic syndrome). The invention further relates to methods of identifying patients eligible for treatment, and to methods of treating cancer or epilepsy associated with autoimmune encephalitis, said methods comprising performing diagnostic tests according to this invention. The invention further relates to devices for performing immunoassays, in particular device containing cells transfected with antigens that are recognized by autoantibodies.

BACKGROUND OF THE INVENTION

Autoimmune encephalitis (AIE) is a group of disorders in which autoantibodies directed at antigens located on the plasma membrane of neurons induce severe neurological symptoms, including seizures, confusion, memory deficits, behavioral disorders, paranoia and hallucinations. The detection of autoantibodies against neuronal surface antigens in patients' serum or cerebrospinal fluid (CSF) has serious consequences for the patients' treatment and follow-up, and requires the availability of sensitive and specific diagnostic tests. This is especially important because AIE patients generally respond well to immunotherapy, warranting an effective diagnosis.

Various diagnostic tools are available and known to one of skill in the art for the detection of autoantibodies against different neuronal cell surface antigens, in particular cell -based immunoassays. Some of these cell- based assays allow for the detection of autoantibodies against a single cell surface antigen, such as the GABAB receptor, or multiple cell surface antigens. Other cell-based assays for detecting autoantibodies, such as autoantibodies against the GABAB receptor, are for instance described in Lancaster et al., Lancet Neurol., 9(l):67-76 (2010). Alternative diagnostic tools in this field are immunohistochemistry on antibodies in patient serum or CSF against brain proteins, and immunocytochemistry on living primary hippocampal neurons, the latter relating to assessing antibody reactivity towards extracellular epitopes on live cultured primary rat hippocampal neurons incubated with patients' serum or CSF.

GABAB receptors, also referred to as GABABR, are metabotropic transmembrane receptors for gamma-aminobutyric acid (GABA) that are linked via G-proteins to potassium channels. The changing potassium concentrations hyperpolarize the cell at the end of an action potential.

GABAB receptors are inhibitory receptors and are composed of two subunits, GABABI and GABAB2, which assemble as heterodimers in neuronal membranes. It is described that antibodies against self-GABAB receptors are associated with neurological autoimmune diseases such as autoimmune encephalitis (Lancaster et al., Lancet Neurol, 9(l):67-76 (2010)).

There is still a need for further improving known immunoassays for detecting autoantibodies against GABAB receptors, as these tests are considered insufficiently sensitive, and therefore not all patients with GABAB receptor autoantibodies are identified. This leads to inadequate diagnosis of AIE. As indicated above, AIE patients have a high likelihood of suffering from paraneoplastic syndrome, that is the presence of

autoantibodies against GABAB receptors is associated with cancer, such as small-cell lung cancer (SCLC) (Lancaster et al., Lancet Neurol., 9(l):67-76 (2010)). Hence, insufficient sensitivity of immunoassays for detecting autoantibodies against GABAB receptors results in failure to diagnose and provide adequate treatment of an underlying tumor or cancer.

A cell-based immunoassay is available for detecting autoantibodies against GABAB receptors. The procedure involves the insertion of DNA encoding the target antigens into a plasmid, transfection of this plasmid into vector cells, reaction of vector cells with the patient's serum or CSF, and detection of specific antibodies via immunofluorescence. At present there are no cell-based immunoassays for detecting neuronal cell surface antigens that are designed to detecting autoantibodies against at least two different targets in combination in a single reaction volume.

It is an aim of the invention to improve the current immunoassays for detecting autoantibodies against GABAB receptors. In addition, it is an aim of the invention to provide immunoassays that allow for a reliable identification of patients that are at risk of suffering from a tumor that is associated with autoantibodies against GABAB receptors. It is a further aim of the present invention to provide for a combined cell -based immunoassay.

The present inventors have surprisingly estabhshed that a method for detecting antibodies against a GABAB receptor in a sample of a subject can be improved by providing the antigen, a GABAB receptor, in the presence of a KCTD protein, and performing an immunoassay. It was found that the sensitivity of the test, in terms of titer of antibodies against a GABAB receptor measured, is improved when an immunoassay is performed wherein a KCTD protein is present together with the GABAB receptor (Figures ID and 2).

It was also unexpectedly found that a subject suffering from a neurological autoimmune disorder, such as AIE, can be typed or diagnosed for having a risk or increased likelihood of suffering from a tumor, by determining the presence of autoantibodies against a KCTD protein in a sample of said subject (Figures 3A and 3B). Such autoantibodies against a KCTD protein have hitherto not been described. SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method for detecting antibodies against a GABAB receptor in a sample of a subject, comprising the steps of:

- providing a sample from a subject, wherein said sample comprises, or is suspected of comprising, antibodies against a GABAB receptor;

- providing a GABAB receptor in the presence of a KCTD protein;

- contacting said sample with said GABAB receptor in the presence of a KCTD protein;

- performing an immunoassay to determine the presence of an antibody against a GABAB receptor in said sample.

The step of providing a GABAB receptor in the presence of a KCTD protein as referred to herein in aspects of the invention and contacting said sample with said GABAB receptor in the presence of a KCTD protein as referred to herein in aspects of the invention, may suitably comprise the preparation or provision of a composition comprising a GABAB receptor and a KCTD protein and contacting said sample with said composition. Such a composition may be in the form of a cell, i.e., the composition may be a cell, or be the contents of a cell, preferably comprising a part of the cell membrane. Without wishing to be bound by theory, it is considered that the presence of the KCTD protein alters the conformation of the GABAB receptor, as a result of which the reaction with the antibody against the GABAB receptor is improved.

The immunoassay for determining the presence of an antibody against a GABAB receptor in said sample may for instance comprise an immunoassay wherein binding of anti GABAB receptor antibody to a GABAB receptor is detected by use of an antibody against the GABAB receptor- antibody.

In a preferred embodiment of aspects of the invention, the method is for typing a subject for the presence or absence of a neurological autoimmune disorder; and whereby the presence of said antibody in said sample indicates a neurological autoimmune disorder in said subject.

In another preferred embodiment of aspects of the invention, the GABAB receptor and the KCTD protein are provided by or in(side) a cell co- expressing a GABAB receptor and a KCTD protein. Preferably, the immunoassay is a cell-based immunoassay.

In yet another preferred embodiment of aspects of the invention, the cell is a recombinant mammalian cell transfected with a nucleic acid encoding a GABAB receptor and a nucleic acid encoding a KCTD protein.

In yet another preferred embodiment of aspects of the invention, the GABAB receptor comprises a GABABI subunit and/or a GABAB2 subunit.

In still a further preferred embodiment of aspects of the invention, the KCTD protein is selected from the group formed by, or consisting of, KCTD8, KCTD 12 and KCTD 16.

In yet another preferred embodiment of aspects of the invention, the neurological autoimmune disorder is an anti-GABAB receptor

neurological disorder, preferably anti-GABAB receptor encephalitis such as anti-GABAB receptor limbic encephalitis.

In yet another preferred embodiment of aspects of the invention, the sample is a serum sample or a cerebrospinal fluid sample. In yet another preferred embodiment of aspects of the invention, the KCTD protein is selected from the group consisting of KCTD proteins 8, 12, 12b and 16.

In another aspect, the invention provides a method for identifying a subject at risk of having, or suffering from, a tumor, comprising the steps of:

- providing a sample from a subject suffering, or suspected of suffering, from a neurological disorder;

- providing a GABAB receptor in the presence of a KCTD protein;

- performing an immunoassay to determine the presence of an antibody against a KCTD protein in said sample;

whereby the presence of an antibody against a KCTD protein in said sample indicates that the subject is at risk of having a tumor. In preferred embodiments of aspects of this invention, the tumor is a tumor associated with AIE, for instance a paraneoplastic tumor.

- providing a KCTD protein;

- contacting said sample with said KCTD protein;

whereby the presence of an antibody against a KCTD protein in said sample indicates that the subject is at risk of having, or suffering from, a tumor. Immunoassays in aspects of the invention may suitably comprise an immunoassay wherein binding of the autoantibody to its target is detected by use of an antibody against the autoantibody.

In a preferred embodiment of a method for identifying a subject at risk of having, or suffering from, a tumor, the KCTD protein is provided in the presence of a GABAB receptor.

In a preferred embodiment of a method for identifying a subject at risk of having, or suffering from, a tumor, a sample of said subject comprises antibodies against a GABAB receptor.

In a preferred embodiment of a method for identifying a subject at risk of having, or suffering from, a tumor, the neurological disorder is a neurological autoimmune disorder, preferably anti-GABAB receptor encephalitis such as anti-GABAe receptor limbic encephalitis. In a preferred embodiment of a method for identifying a subject at risk of having, or suffering from, a tumor, the tumor is a lung tumor such as small cell lung cancer (SCLC) or a thymic neuroendocrine tumor.

In another aspect, the invention provides a cell expressing a GABAB receptor and a KCTD protein, wherein at least one of the cell, receptor or protein is recombinant, preferably wherein the KCTD protein is selected from KCTD8, KCTD 12, KCTD 12b and KCTD 16. In a preferred embodiment of a cell expressing a GABAB receptor and a KCTD protein according to the invention, the cell is a recombinant mammalian cell transfected with a nucleic acid encoding a GABAB receptor and a nucleic acid encoding a KCTD protein.

In another aspect, the invention provides a kit-of-pats for performing an immunoassay, comprising a cell expressing a GABAB receptor and a KCTD protein as described above, and a anti-human IgG secondary antibody, preferably said anti-human IgG secondary antibody being labelled. In another aspect, the invention provides a device for performing an immunoassay (1), comprising

- a substrate (1) defining a first reaction surface (11, 12, 13);

- a set of cells expressing, or having expressed, a GABAB receptor and a KCTD protein, wherein said set of cells are connected to said first reaction surface (13).

In a preferred embodiment of this aspect of the invention, the set of cells is fixated on said first reaction surface (13).

The term fixated is used herein to indicated crosslinking of the cell, for instance by (para)form aldehyde or glutaraldehyde to preserve or kill the cell, and/or to immobilize the cell by crosslinking to an (optionally modified) device surface as described herein.

In another preferred embodiment of this aspect of the invention, the substrate (10) is a slide, preferably a transparent slide.

In an alternative embodiment, substrates may be microbeads for preforming immunoassays by flow cytometry.

In another aspect, the invention provides the use of a device according to the invention in typing a subject for the presence or absence of a neurological autoimmune disorder, or for identifying a subject at risk of having, or suffering from, a tumor associated with a neurological

autoimmune disorder.

In another aspect, the invention provides a device for performing an immunoassay (1), comprising

- a substrate (1) defining a first reaction surface (11, 12, 13);

- a cell or a set of cells expressing, or having expressed, a KCTD protein and optionally a GABAB receptor, wherein said cell or set of cells is/are

connected to said first reaction surface (13), preferably immobilized.

In a preferred embodiment of this aspect of the invention, the set of cells is fixated on said first reaction surface (13). In another preferred embodiment of this aspect of the invention, the substrate (10) is a slide, preferably a transparent slide.

In another aspect, the invention provides the use of the device comprising a set of cells expressing, or having expressed, a KCTD protein and optionally a GABAB receptor, of the invention, for identifying a subject at risk of having, or suffering from, a tumor associated with a neurological autoimmune disorder.

In another aspect, the invention provide the use of a KCTD protein as antigen in an immunoassay for detecting antibodies in a sample of a subject.

In another aspect, the invention provides a method for detecting antibodies against a KCTD protein in a sample of a subject, comprising the steps of: - providing, or obtaining, a sample from a subject, wherein said sample comprises, or is suspected of comprising, antibodies against a KCTD protein; - providing a KCTD protein; - contacting said sample with said

KCTD protein; - performing an immunoassay to determine the presence of an antibody against a GABAB receptor in said sample.

In another aspect, the invention provides the use of a KCTD protein as antigen in an immunoassay for detecting antibodies in a sample of a subject suffering, or suspected of suffering, from a neurological disorder and identifying subjects at risk of having, or suffering from, a tumor associated with a neurological disorder.

In a preferred embodiment of this aspect, said KCTD is in the presence of a GABAB receptor, such as when both are present in a composition.

In another aspect, the invention provides the use of a GABAB receptor in the presence of a KCTD protein, in an immunoassay for detecting antibodies against said GABAB receptor and/or said KCTD protein in a sample of a subject and for typing a subject for the presence or absence of a neurological disorder, and/or for identifying a subject at risk of having, or suffering from, a tumor associated with a neurological autoimmune disorder.

In another aspect, the invention provides a human antibody directed against a KCTD protein, preferably KCTD protein 16, more preferably human KCTD protein 16.

In a preferred embodiment of this aspect, the human antibody is isolated or purified, preferably by performing an immunoassay for determining the presence of an antibody against a KCTD protein in a sample of a subject.

In a preferred embodiment of this aspect, the antibody is bound to said KCTD protein.

In a preferred embodiment of said previous embodiment, said antibody is bound by a detectably labelled antibody specifically directed against human antibodies.

In another aspect, the invention provides a method for detecting antibodies against a KCTD protein in a sample of a subject, comprising the steps of: - providing, or obtaining, a sample from a subject, wherein said sample comprises, or is suspected of comprising, antibodies against a KCTD protein; - providing a KCTD protein; - contacting said sample with said KCTD protein; - performing an immunoassay to determine the presence of an antibody against a GABAB receptor in said sample.

In another aspect, the invention provides an anti-KCTD protein antibody, preferably wherein said antibody is selected from one or more of an autoantibody, an IgG, IgA or IgM antibody, preferably a human antibody. In preferred embodiments of this aspect, the anti-KCTD protein antibody is an anti-KCTD protein 16 antibody. In other preferred

embodiments, the antibody is bound to a KCTD protein, e.g. representing an autoantibody-KCTD protein complex. In still other preferred embodiments, the antibody may be an isolated antibody, it may be a monoclonal antibody, and/or it may be a labelled antibody. Further aspects of the invention include a set of an anti-KCTD protein antibody as described above and a secondary antibody, preferably said secondary antibody being an anti-human IgG antibody, and preferably said secondary antibody being labelled with a detectable label. In preferred embodiments of this aspect, the antibody is bound to a KCTD protein, and the secondary antibody is bound to the anti-KCTD protein antibody, e.g. forming an (auto)antibody-KCTD protein-secondary antibody complex.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Diagnostic tests for anti-GABAe receptor antibodies.

(A) Immunohistochemistry of adult rat brain stained with patient CSF or control CSF. The patient CSF shows brain-wide neuropil staining, here exemplified by a picture of the hippocampus. Scale bars: 500 μιη. (B)

Immunocytochemistry of living rat hippocampal neurons. Labelling with the patient serum (patient serum positive for anti-GABAbR antibodies) results in a dot-like pattern along the neurites. Scale bars: 10 μιη. (C) Live cell based assay of HEK-cells transfected with GABABI-GFP and GABA_B2-GFP and stained with patient serum or control serum. The patient serum labels the surface of cells transfected with GABAB receptor. Scale bars: 20 μηι. (D) Bar diagram representing the percentages of positive and negative tests for the different laboratory techniques that are used for the detection of anti- GABAB receptor antibodies. Figure 2. Endpoint titrations with fixed cell-based assay.

(A) Titration of patient serum (negative for anti-KCTD 16 antibodies, positive for anti-GABAi,R antibodies) using a fixed cell based assay of HEK- cells transfected with GABABI-GFP and GABAB2-GFP with or without co- transfection of KCTD 16. Staining of cells co-transfected with KCTD 16 can be detected up to a dilution of 1:3200, as opposed to without KCTD 16 co- transfection, up to a dilution of 1:800. (B) Serum titers detected with a fixed CBA with or without co-transfection of KCTD 16. Higher serum titers are detected with the addition of KCTD 16 to the CBA. Wilcoxon signed ranked test: p = 0.0003. (C) CSF titers detected with or without co-transfection of KCTD 16. Higher CSF titers are detected with the addition of KCTD 16 to the CBA. Wilcoxon signed ranked test: p = 0.022. (D) Serum and CSF titers detected with a fixed CBA without KCTD 16 co-transfection. Patients with an underlying tumor do not have higher titers in serum and CSF than patients without an underlying tumor. Mann-Whitney test, serum p = 0.22, CSF p = 0.24.

Figure 3. KCTD16 antibodies are associated with an underlying tumor.

(A) Bar diagram depicting percentages of patients with or without an underlying tumor. Patients with anti-KCTD 16 antibodies more frequently have an underlying tumor. Fisher exact test, p = 0.0014. (B) IHC of SCLC tissue from patient 5, stained with hematoxylin-eosin (HE), normal rabbit serum and KCTD 16 antibody. The picture shows specific KCTD 16 expression in tumor cells, which is absent in healthy lung tissue. Staining was performed on sequential slides, pictures were taken in the same area of the sample. Scale bars: 25 μηι.

Figure 4. Device 1 for performing an immunoassay.

Figure 4 shows a top-view of a device 1 for performing an immunoassay of the invention, wherein a substrate 10 is shown having multiple reaction fields 11. These reaction fields are subdivided in reaction subfields 12 and 13, some of them 13 containing cells fixated on said field or surface. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the detection of antibodies against neuronal surface antigens in samples of subjects that are suffering, or suspected of suffering, from a neurological autoimmune disorder and relates to the subsequent typing or diagnosis of said subject. The method and means for detecting antibodies in biological samples are generally known in the art. The invention also relates to standard-of-care therapy for subjects that are typed as having a neurological autoimmune disorder associated with antibodies against a GABAB receptor according to a method of the invention, and to standard-of-care therapy for a subject identified with a method of the invention as being at risk of having a tumor present in the body. The invention also relates to devices for performing an immunoassay.

Definitions and preferred embodimen ts

The term "antibody", or "antibodies", as used herein, refers to a protein comprising one or more polypeptides substantially encoded by immunoglobulin genes or fragments of immunoglobulin genes. This term encompasses polyclonal antibodies, monoclonal antibodies, and fragments thereof, as well as molecules engineered from immunoglobulin gene sequences. The recognized immunoglobulin genes include the kappa, lambda, alpha, gamma, delta, epsilon and mu constant region genes, as well as myriad immunoglobulin variable region genes. Light chains are classified as either kappa or lambda. Heavy chains are classified as gamma, mu, alpha, delta, or epsilon, which in turn define the immunoglobulin classes, IgG, IgM, IgA, IgD and IgE, respectively.

A typical immunoglobulin (antibody) structural unit is known to comprise a tetramer. Each tetramer is composed of two identical pairs of polypeptide chains, each pair having one "light" (about 25 kD) and one "heavy" chain (about 50-70 kD). The N-terminus of each chain defines a variable region of about 100 to 110 or more amino acids primarily responsible for antigen recognition. The terms "variable light chain (VL)" and "variable heavy chain (VH)" refer to these light and heavy chains respectively. A preferred antibody is a human antibody, more preferably a human autoantibody.

The term "autoantibody", as used herein, refers to an antibody produced by the immune system of a subject and is directed against one or more of said subject's own - self - antigens such as an epitope of a protein, a peptide, or a non-protein epitope. In the context of the invention, the terms "autoantibody" and "antibody against, or directed against" can be used interchangeable if the targeted antigen is a self- antigen or resembles a self- antigen. It should be clear that in in vitro methods of the invention it is not necessary to employ antigens of human origin, as it is shown that a rat antigenic protein, resembling a corresponding human antigen, can suitably be employed in a method of the invention. Preferably, the antibody is an antibody directed against a GABAB receptor, which can also be referred to as anti-GABAB receptor antibody. It is described that autoantibodies against a GABAB receptor are associated with neurological autoimmune disorders such as autoimmune encephalitis. An autoantibody is preferably of mammalian, more preferably human, origin.

The term "antigen", as used herein, refers to a molecule or a portion of a molecule recognized by an antibody. An antigen may have one, or more than one, epitope. The specific reaction referred to above is meant to indicate that the antigen will react, in a selective manner, with its

corresponding antibody. A preferred antigen of the invention is a GABAB receptor, preferably a GABABI receptor, optionally dimerized to a GABAB2 receptor. Such an antigen is preferably provided in a method of the invention in the presence of a KCTD protein and is preferably associated with said KCTD protein in a complex or co-assembly or is in a fluid connection with said KCTD protein for associating with said KCTD protein. This can for instance be in a complex or co-assembly on a plasma membrane of a cell. Alternatively, the GABAB receptor as antigen can be isolated as such, or in complex or co-assembly with a KCTD protein and used in an immunoassay. Another preferred antigen is a KCTD protein. Alternatively, or in addition, antibodies against other neuronal antigens are to be detected. Such neuronal antigens are inter alia selected from the group formed by glutamate receptor (type NMD A), glutamate receptor (type AMPAl), glutamate receptor (type AMPA2), contactin-associated protein 2 (CASPR2), leucine-rich glioma-inactivated protein 1 (LGIl), dipeptidyl aminopeptidase- like protein 6 (DPPX). The antigens are preferably mammalian antigens, more preferably rat or human antigens. Preferably, the antigens referred to herein are expressed, or have been expressed, in a cell and are presented by such a cell.

The term "antigenic determinant", or "epitope", as used herein, refers to the region of an antigen molecule that specifically reacts with a particular antibody. Preferably, the epitope of a GABAB receptor that interacts with an antibody described herein is located on the extracellular domain of a GABABI receptor.

The term "risk", as used herein, can be used interchangeably with the terms "increased likelihood" and "increased risk", and refers to an increased probability, e.g. of having a predisposition to suffer from or of suffering from of damage, injury, disease, or any other negative occurrence, in particular to an increased probability of suffering from having a tumor, relative to a reference subject, for instance as compared to the probability of a reference subject having, or suffering from, a tumor, wherein said reference subject is typed as negative for antibodies against a KCTD protein and optionally typed as positive for antibodies against a GABAB receptor.

The term "detecting antibodies", as used herein, refers to determining the presence or absence of antibodies against an antigen in a sample of subject. Measured antibody levels are generally denoted by an antibody titer value. An antibody titer value results from a measurement of how much antibody an organism has produced that recognizes a particular epitope, expressed as the inverse of the greatest dilution (in a serial dilution) that still gives a positive result. It is established herein that an antibody titer value is "increased" when a KCTD protein is provided in such a manner that it is freely associable with a GABAB receptor (Figures ID and Figure 2). A cut-off antibody titer value can be used to distinguish between subjects that should be typed as having a neurological autoimmune disorder, and subjects that should be typed as not having a neurological autoimmune disorder. The same principle can be applied to distinguish between subjects that are identified as being at risk of having a tumor, and subjects that are not at risk of having a tumor. The skilled person trivially knows how to estabhsh such a cut-off antibody titer value. Examples of suitable cut-off antibody titer values for typing a subject for the presence of a neurological disorder in the present invention are 1, 5, 10, 20, 30, 40, 50 or 60, preferably 40, for serum samples, and undiluted, 1, 2, 3, 4, 5 or 6, preferably 2, for CSF samples.

The term "subject", as used herein, refers to a mammal, preferably a human. The terms "patient" and "subject" are used interchangeable herein. The subject is more preferably a human suffering, or suspected of suffering, from a neurological disorder such as a neurological autoimmune disorder. In instances, the term "subject" may suitably refer to a sample of said subject.

The term "sample", as used herein, refers to a biological sample, in particular of a subject. The sample may be any body sample, such as a tissue, organ, or body fluid sample, preferably a biological fluid sample such as blood, serum, or cerebrospinal fluid (CSF) sample, most preferably serum or CSF. The skilled person is aware of any suitable methods to obtain a serum or cerebrospinal fluid sample of subject. To obtain a serum sample, a venipuncture can be performed and blood cells and clotting factors can be removed by methods generally known in the art. A cerebrospinal fluid sample can be obtained by for instance a lumbar puncture.

The term "a GABAB receptor", as used herein, refers to a gamma- aminobutyric acid type B receptor, and includes reference to the individual monomeric subunits of said receptor commonly denoted as gamma- aminobutyric acid type B receptor subunit 1 (also referred to as GABAB ι or GABBRl) and gamma-aminobutyric acid type B receptor subunit 2 (also referred to as GABAB2 or GABBR2). GABAB receptors are metabotropic transmembrane receptors for gamma-aminobutyric acid (GABA) that are linked via G-proteins to potassium channels. Subunits GABABI and GABAB2 are components of a heterodimeric G-protein coupled receptor for gamma- aminobutyric acid (GABA). Within the heterodimeric GABA receptor, GABBRl binds agonists, while GABBR2 mediates coupling to G proteins. Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors, such as adenylate cyclase. Preferably, a GABAB receptor is a heterodimer formed by a GABABI and a GABAB2 subunit.

GABAB receptors are well known in the art and the skilled person is readily capable to identify and provide a gamma-aminobutyric acid type B receptor. Preferably, the GABAB receptor is a human or rat GABAB receptor. Other mammalian orthologs of a GABAB receptor are envisaged herein and form part of the invention.

Also included in the term "a GABAB receptor" are protein variants of a GABAB receptor that are recognizable by antibodies against a native GABAB receptor, such as a rat or human GABAB receptor, and have at least 90%, more preferably 91%, 92%., 93%, 94%, 95%., 96%, 97%, 98%, 99% or 100% sequence identity to the amino acid sequence of (i) rat GABBRl (UniProtKB Acc No. Q9Z0U4, any one of isoforms 1A-1E, also indicated with UniProtKB Acc. No. Q9Z0U4-1 - Q9Z0U4-5), (ii) human GABBRl

(UniProtKB Acc. No. Q9UBS5, any one of isoforms 1A-1E, indicated with UniProtKB Acc. No. Q9UBS5-1 - Q9UBS5-5, (iii) rat GABBR2 (UniProtKB Acc. No. 088871, last modified: January 11, 2001 - v2) and (iv) human GABBR2 (UniProtKB Acc. NO. 075899, last modified: November 1, 1998 - vl). Said sequence identity is preferably measured over the full length of the reference proteins. Preferably, the sequence identity is calculated by not taking into account signal peptides in the reference proteins. For instance, said sequence identity is calculated over amino acid residues (i) 17-991 of rat GABBRl (UniProtKB Acc No. Q9Z0U4-1), (ii) 15-961 of human GABBRl (UniProtKB Acc. No. Q9UBS5), (iii) 41-940 of rat GABBR2 (UniProtKB Acc. No. 088871) and (iv) 42-941 of human GABBR2 (UniProtKB Acc. NO.

075899). Preferably, said variants have the propensity to form a

heterodimeric G-protein coupled receptor for GABA and assist in signahng through guanine nucleoti de-bin ding proteins (G proteins).

The term "KCTD protein", as used herein, refers to proteins of the family of potassium channel tetramerization domain (KCTD) proteins that are subunits, such as auxiliary subunits, of a GABAB receptor. The term "KCTD protein ", as used herein includes KCTD proteins 8, 12 and 16 (also referred to as KCTD8, KCTD 12 and KCTD 16), preferably mammalian KCTD proteins 8, 12 and 16, more preferably rat or human KCTD proteins 8, 12 and 16. Preferably, KCTD proteins 8, 12 and 16 associate with, or are in the presence of, the GABAB receptor, preferably the carboxy terminus of the GABAB receptor in the form of homo-oligomers or hetero-oligomers such as homo-tetramers or hetero-tetramers. In the case of hetero-tetramers, all possible combinations of KCTD proteins 8, 12 and 16 are envisaged.

Preferably, a KCTD protein associates or interacts with a GABAB receptor. Mammalian KCTD proteins 8, 12 and 16 are included in this term. Also included in this term are KCTD protein variants associable with a GABAB receptor, preferably as tetramers, and having at least 90%, more preferably 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% sequence identity to the amino acid sequence of (i) rat KCTD protein 8 (GenBank Acc. No.: ΝΡ_001093642.1), (ii) human KCTD protein 8 (Genbank Acc. No.:

NP_938167.1), (iii) rat KCTD protein 12 (Genbank Acc. No.: EDM02446.1), (iv) human KCTD protein 12 (Genbank Acc. No.: NP_612453.1), (v) rat KCTD protein 16 (Genbank Acc. No.: NP_001165626.1) and (vi) human KCTD protein 16 (Genbank Acc. No.: NP_065819.1).

It is preferred in a method of the invention that the GABAB receptor subunits, and the KCTD protein, originate from the same mammal, such as a rat or a human.

The term "immunoassay", as used herein, refers to a test for detection or quantification of an antibody, generally by contacting or incubating a sample of a subject with an antigen and performing an antibody detection and/or quantification step. Preferably, the immunoassay is a cell-based immunoassay.

The term "cell-based immunoassay", as used herein, refers to an immunoassay wherein an antigen is expressed, or has been expressed, in a cell and wherein the cell with the expressed antigen are used in the immunoassay. Such a cell is preferably a transfected mammalian cell, for instance a cell of a mammalian cell line such as the human embryonic kidney 293 (HEK 293) cell line. Alternatively, such a cell can be a primary hippocampal neuron having developed axons and synapses. The skilled person is aware of starting materials and culturing conditions to provide such cells. Such a cell can be either alive or dead. A cell-based immunoassay as described herein is preferably a fixed CBA, i.e. a CBA in which a cell is fixated, which for example refers to crosslinking of the cell, for instance by (para)form aldehyde or glutaraldehyde to preserve or kill the cell, and/or to immobihze the cell by crosslinking to an (optionally modified) device surface as described herein.

The term "cell", as used herein, includes reference to a cell recombinantly expressing a nucleic acid encoding an antigen as described herein. The term "typing", as used herein, refers to the attribution of a status to a subject, such as positive or negative for the presence of a neurological autoimmune disorder in a subject. The term "typing" can be used interchangeably with the term "diagnosing". Preferably, a method for typing of the invention is for typing a sample of a subject.

The term "neurological disorder", as used herein, refers to any neurological disorder of the nervous system, including neuro-psychiatric disorders. Neurological disorders can be categorized according to the primary location affected, the primary type of dysfunction involved, or the primary type of cause. The broadest division is between central nervous system disorders and peripheral nervous system disorders. Symptoms of neurological disorder are various and may include paralysis, muscle weakness, poor coordination, loss of sensation, seizures, confusion, pain and altered levels of consciousness. The neurological disorder is preferably a neurological autoimmune disorder.

The term "neurological autoimmune disorder", as used herein, refers to neurological disorders wherein the immune system of a subject is targeting its own neurons, for instance by autoantibodies binding to neuronal surface antigens. Preferably, the neurological autoimmune disorder is autoimmune encephalitis, which relates to inflammation of the brain associated with autoimmunity. Preferably, autoimmune encephalitis is associated with symptoms such as seizures, psychiatric symptoms, abnormality in cognition and behavior, movement disorder or abnormal movements, decreased level of consciousness, hypoventilation, amnesia or a memory deficit, or combinations thereof. One form of autoimmune

encephalitis is limbic encephalitis. Preferably, the neurological autoimmune disorder is an anti-GABAB receptor neurological disorder, more preferably anti-GABAB receptor autoimmune encephalitis such as anti-GABAB receptor hmbic encephalitis. A neurological autoimmune disorder can be associated with, and optionally indirectly caused by, a tumor in a subject. Therefore, a neurological autoimmune disorder as referred to herein is in embodiments a paraneoplastic neurological autoimmune disorder, such as paraneoplastic autoimmune encephalitis including paraneoplastic limbic encephalitis.

The term "paraneoplastic neurological disorder", as used herein, refers to a heterogeneous group of neurological disorders associated with cancer and are generally caused by mechanisms other than metastases, metabolic and nutritional deficits, infections, coagulopathy, or side effects of cancer treatment. These syndromes may affect any part of the nervous system from cerebral cortex to neuromuscular junction and muscle, either damaging one area or multiple areas.

The term "tumor", as used herein, refers to a class of conditions or diseases in animals such as humans, characterized by uncontrolled cellular growth. The tumor is preferably malignant and can be referred to as a cancer. Preferably, the tumor is a sohd tumor, more preferably a carcinoma such as lung cancer including small cell lung cancer, thymic cancer including thymic neuroendocrine tumor, and prostate cancer. Preferably, the tumor is an occult tumor. Examples of tumors include ovarian teratoma, testicular cancer, a cervical cancer, head and neck cancer, breast cancer, melanoma, sarcoma, lymphoma, leukemia, mesothelioma, glioma,

choriocarcinoma, pancreatic cancer, ovarian cancer, gastric cancer, pulmonary adenocarcinoma or colorectal adenocarcinoma. The term "tumor" may thus refer to a tumor that is associated with a neurological disorder, preferably a neurological autoimmune disorder.

The term "occult tumor", as used herein, refers to a tumor that is identified by an incidental discovery that can occur when a subject is being evaluated for other reasons, or at the time of autopsy. In other words, an occult tumor is present in a subject but such a tumor has not been identified yet and the subject is thus at that moment undiagnosed for the presence of such a tumor. In the context of the invention, an occult tumor may induce a paraneoplastic neurological autoimmune disorder. The term "substrate", as used herein, refers to a material for carrying, holding and or presenting an antigen in an immunoassay. The substrate is preferably a sohd-phase substrate and can be shaped as a plate including a microplate, panel or a slide. Preferably, the substrate is transparent, for instance from glass or polycarbonate, which allows for monitoring and visualization of an antibody-detection signal, such as a fluorescence signal, under a microscope such as a fluorescence microscope. The substrate can be the base of a device of the invention, or is connected to such a base. The substrate does not participate in the reaction of detecting antibodies, but instead provides a solid medium having a reaction surface and/or reaction volume wherein the reaction of detecting antibodies takes place. An antigen can be fixated to a reaction surface of the substrate, or can freely move within the boundaries of the reaction surface and/or reaction volume as defined by the substrate. Preferably, a substrate defines at least two, more preferable 3, 4, 5 or 6 reaction surfaces and/or reaction volumes, which can be referred to as reaction fields, which are separated from each other - i.e. not in a fluid connection with each other -, for instance by an upstanding protrusion or rim on said substrate, or by a recess (hollow space or volume) in said substrate). A substrate can contain more than one reaction field, such as 2, 3, 4, 5, 6, 7, 8, 9 or 10 reaction fields, wherein different or the same antibody detection reaction is to be performed. A reaction field can be subdivided in more than one subfield, such as at least, more preferably 2, 3, 4 ,5 or 6 subfLelds, wherein the same or a different antibody detection reaction can be performed. Such a design allows for the detection of antibodies against various antigens, preferably neuronal antigens, more preferably neuronal antigens recognized by autoantibodies associated with neurological diseases, including the neuronal antigens:

glutamate receptor (type NMD A), glutamate receptor (type AMPAl), glutamate receptor (type AMPA2), contactin-associated protein 2 (CASPR2), leucine-rich glioma-inactivated protein 1 (LGI1), dipeptidyl aminopeptidase- like protein 6 (DPPX), and GABAB receptor. In principle, each subfielcl within a single reaction field contains a different antigen. The term

"substrate", as used herein, also includes a solid-phase reactant. Substrates as referred to herein are known in the art, and are for instance marketed by EUROIMMUN Medizinische Labordiagnostika AG (Germany).

The term "reaction surface", as used herein, refers to a surface on a substrate whereon an antibody detection reaction is to occur. When an immunoassay is performed, an antigen, including a cell expressing or having expressed an antigen, and presenting such an antigen, is present on said reaction surface if it is connected to said reaction surface, for instance by being (i) spotted or immobilized thereon, (ii) adherent thereon, and (iii) present in a medium, such as a liquid medium, that is in contact with said reaction surface. In other words, such a connection between antigen and reaction surface is thus either directly, or indirectly through for instance a medium or through the cell that presents the antigen.

The term "reaction volume", as used herein, refers to a volume or space defined by the substrate in which an antibody detection reaction is to occur. Most basically, such a reaction volume is a volume facing a reaction surface, whereby the antigen is connected to said reaction surface as described hereinbefore. Such a connection is thus either directly, or indirectly through for instance a medium such as a reaction medium, or through the cell that expresses the antigen.

The term "therapeutically effective amount" refers to a quantity of a specified agent sufficient to achieve a desired effect in a subject being treated with that agent. Ideally, a therapeutically effective amount of an agent is an amount sufficient to inhibit or treat the disorder or condition without causing a substantial cytotoxic effect in the subject. The

therapeutically effective amount of an agent will be dependent on the subject being treated, the severity of the affliction, and the manner of administration of the therapeutic agent. Preferably, the term refers to (i) an amount sufficient to treat a neurological disorder such as a neurological autoimmune disorder or (ii) cancer. It is within the knowledge and

capabihties of the skilled practitioner to determine therapeutically effective dosage regimens.

The term "administering", as used herein, refers to the physical introduction of an agent or therapeutic compound to a subject, using any of the various methods and delivery systems known to those skilled in the art. The skilled person is, per disorder and agent for administration, aware of suitable methods for administration and dosage forms. Administration of small molecules can be performed by non-parenteral administration such as by oral and enteral administration. Preferred route of administration for protein-based agents such as antibodies is by parenteral administration, including intravenous, intramuscular, subcutaneous, intraperitoneal, spinal or other parenteral routes of administration, executed inter alia by injection or infusion in the form of a solution. Administering can be performed, for example, once, a plurality of times, and/or over one or more extended periods of time.

As used herein, a "standard-of-care therapeutic agent" is a therapeutic compound, or combination of such compounds, that is/are considered by medical practitioners as appropriate, accepted, and/or widely used for a certain type of patient, disease or clinical circumstance. Standard- of-care therapies for different types of cancer are well known by persons of skill in the art. For example, the National Comprehensive Cancer Network (NCCN) publishes the NCCN Clinical Practice Guidelines in Oncology (NCCN GUIDELINES) that provide detailed up-to-date information on standard-of-care therapies for a wide variety of cancers. For example, standard-of-care therapy for patients suffering from cancer include surgery, chemotherapy, radiation therapy, hormonal therapy and/or targeted cancer therapy such as immunotherapy and tyrosine-kinase inhibition therapy. Standard-of-care therapy for a neurological autoimmune disorder, such as autoimmune encephalitis, are known by medical practitioners and include immunotherapy including administration of anti-inflammatory agents, removal - surgical or by other forms of therapy - of a tumor which triggers the autoimmune response, intravenous immunoglobulins or plasmapheresis - the removal, treatment, and return or exchange of blood plasma or components thereof from and to the blood circulation. Second-line standard- of-care therapy of autoimmune encephalitis includes the administration of an immunosuppressant including rituximab, mycophenolic acid and cyclophosphamide. Specific standard-of-care therapeutic agents for use in the treatment of a neurological autoimmune disorder and/or cancer include tocilizumab, alemtuzumab, bortezomib, natalizumab, inepibilizumab and eculizumab.

The term "container", as used herein, refers to a receptacle adapted for holding or storing cells. The receptacle may suitable be a vial or a bottle.

The term "antigen array", as used herein, refers to arrays for performing an immunoassay, wherein one or more antigens are orderly provided in spots on a substrate. Such a spot is also referred to as herein as a reaction field or reaction subfield.

The term "detectable label", or shortly "label", as used herein, refers to any moiety that generates a measurable signal via optical, electrical, or other physical indication of a change of state of a molecule or molecules coupled to the moiety. Such physical indicators encompass spectroscopic, photochemical, biochemical, immunochemical,

electromagnetic, radiochemical, and chemical means, such as but not hmited to fluorescence, chemifluorescence, chemiluminescence, and the like.

The present inventors have found that certain forms of

autoimmune encephalitis allow classification on the basis of the frequencies of antibodies known to be associated with the disorder, and further on the basis of new, currently unknown, autoantibodies, that show to have a causative relationship to the disease, and to the presence of cancer in patients suffering from autoimmune encephalitis. The discovery of these associated autoantibodies provides new options for treating these conditions in patients.

The present inventors have studied a population of patients with acquired chronic focal epilepsy without known cause, new onset status epilepticus, and new onset seizures with signs of encephalitis and unknown cause, and discovered that the sensitivity of tests for the detection of antibodies against a γ-aminobutyric acid-B receptor (GABABR) in serum samples of such patients can be considerably improved by the detection of autoantibodies against potassium channel tetramerization domain (KCTD) proteins in the diagnosis of these types of disorders.

The present invention now provides, inter alia, in one embodiment, a method for detecting autoantibodies against a γ-aminobutyric acid-B receptor (GABABR) in a mammalian sample, said method comprising the step of performing immunostaining to detect an autoantibody against a potassium channel tetramerization domain (KCTD) protein. Preferably, the method comprises the steps of:

a) providing an antigen for detection of autoantibodies against a

potassium channel tetramerization domain (KCTD) protein

b) providing an antigen for detection of autoantibodies against a GABAB receptor;

c) providing a sample of a patient suspected of suffering from

autoimmune encephalitis associated with seizures, memory loss and SCLC;

d) contacting said antigens under a) and b) with said sample;

e) acquiring a detection signal indicating the presence of autoantibodies against a KCTD protein and a detection signal indicating the presence of autoantibodies against a GABAB receptor; and f) establishing the qualitative or quantitative presence of either of said autoantibodies by comparing the detection signals acquired under step e) with positive and/or negative controls.

In a preferred embodiment of such a method, the antigen for detection of autoantibodies against a potassium channel tetramerization domain (KCTD) protein is a KCTD protein, more preferably KCTD16.

In preferred embodiments of this invention, the mammalian sample is suitably a serum or cerebrospinal fluid (CSF) sample.

In preferred embodiments of this invention, the autoantibodies are IgG antibodies.

The present invention also provides assays for detecting

autoantibodies in a sample of a patient suspected of suffering from

autoimmune encephalitis associated with seizures, memory loss and SCLC, said assay comprising a method comprising the steps of:

a) providing an antigen for detection of autoantibodies against a

potassium channel tetramerization domain (KCTD) protein;

c) providing a sample of a patient suspected of suffering from

autoimmune encephalitis associated with seizures, memory loss and SCLC;

d) contacting said antigens under a) and b) with said sample;

e) acquiring a detection signal indicating the presence of autoantibodies against a KCTD protein and a detection signal indicating the presence of autoantibodies against a GABAB receptor; and

f) estabhshing the qualitative or quantitative presence of either of said autoantibodies by comparing the detection signals acquired under step e) with positive and/or negative controls. Detecting and quantification of antibodies in methods of the invention.

The invention provides a method for diagnosing in a patient the presence of an immune disorder known as autoimmune encephalitis, which disorder is associated with seizures, memory loss and cancer. The invention provides improved methods of classifying patient samples, and compounds and systems for use in such methods.

In methods of the invention, detection and/or quantification of antibodies in a sample can be determined by a variety of methods using standard techniques, including enzyme-linked immunosorbent assay

(ELISA), solid phase radioimmunoassay, or other solid phase immunoassays (see Ausubel, F. M. et al., eds., Current Protocols in Molecular Biology, John Wiley & Sons, 1996, especially units 11.2 (ELISA) and 11.16 (Determination of Specific Antibody Titer); the entire teachings of this reference are incorporated herein by reference). In a typical solid-phase immunoassay, the amount of antibody bound to an antigen attached to a solid-phase substrate is determined using a developing reagent, such as a detection antibody that binds to the antibody of interest, the latter preferably being an antibody against a GABAB receptor or an antibody against a KCTD protein.

The detection antibody can be linked or conjugated to another molecule, such as an enzyme or fluorophore, including GFP, to facilitate detection. Alternatively, the detection antibody is iodinated. If more than one antigen of interest is employed in an immunoassay, such as inter alia described hereinbefore, such as at least two different neuronal surface antigens, different detection antibodies can be used to detect each antibody to each neuronal surface antigen of interest. For example, a detection antibody that binds to an antibody to one antigen of interest can be conjugated to a first fluorophore, and a detection antibody that binds to an antibody to a second antigen of interest can be conjugated to a second fluorophore that is distinguishable from the first fluorophore. Alternatively, if the same detection reagent, such as a detection antibody, is used, the different antigens of interest can be attached to the substrate reactant at a different, identifiable location, such a different reaction field on a reaction surface on said substrate, such that the presence of a detection reagent in a particular field or subfield corresponds to the presence of antibodies against an antigen that is connected to the substrate in predetermined field or subfield.

Preferably, the immunoassay described herein is an indirect immunofluorescence assay, such as an indirect ELISA, which is an immunoassay employed for antibody detection. In such a method, an antigen, including a cell expressing, or having expressed, an antigen, and presenting such an antigen, is before, or during, the assay immobilized onto a solid phase via methods known in the art, such as physical adsorption or fixation to the sohd phase by incubating cells with a fixator such as paraformaldehyde (PFA) or glutar aldehyde. The antibody in a sample reacts with the antigen bound on the solid phase to form an immuno-complex, and thus the target antibody is captured on the solid phase from a fluid sample. Then a labeled detection antibody with specificity for the target antibody is added and incubated. Following washing off unbound labeled detection antibody , the amount of the target antibody is measured by detecting the signal produced by the label of the bound detection antibody on the solid phase. Indirect ELISA also has a useful modification, the double indirect ELISA, which involves a third antibody. The third antibody carries a label and reacts with the unlabeled detection antibody already bound to the target antibody. After washing to remove unbound substances, the signal of the label is measured, and the signal of the label is directly correlated with the amount of the target antibody present in sample.

Methods and kits for detection of antibodies as described herein are well known in the art, and are described, for example, in Ances BM et al., Brain, 128: 1764-1777 (2005) and Vitaliani et al., Ann Neurol, 58:594-604 (2005). Further methods, kits and antibodies for detection of anti-GABAe receptor antibodies are inter alia described in Lancaster et al., Lancet Neurol. 9(l):67-76 (2010); Hoftberger et al., Neurology 22;81(17): 1500-6 (2013); and are provided in the form of anti-GABAe receptor antibody kits by EUROIMMUN Medizinische Labordiagnostika AG (Germany). The contents of these documents on the point of methods and kits for detection of anti-GABAe receptor antibodies are incorporated herein by reference.

Detection of antibodies can be monitored and visuahzed by any method known in the art. Preferably, detection is performed by assessing and quantifying an antibody-detection signal with a microscope, preferably a fluorescence microscope such as a Nikon Eclipse 80i fluorescence microscope.

Preferably, in a method of detecting antibodies against a GABAB receptor of the invention, said method further comprises the step of performing an immunoassay to determine the presence of an antibody against a KCTD protein in said sample. More preferably, in a method of typing a subject for the presence or absence of a neurological autoimmune disorder, said method further comprises the step of performing an

immunoassay to determine the presence of an antibody against a KCTD protein in said sample, whereby the presence of an antibody against a

KCTD protein in said sample indicates that the subject is at risk of having a tumor, and/or whereby the absence of an antibody against a KCTD protein in said sample indicates that said subject is not at risk, or has a lower risk, of having, or suffering from, a tumor.

A method for detecting antibodies against a GABAB receptor in a sample of a subject, in aspects of this invention, is thus preferably

performed on a bocly(fluicl) sample of a subject, contacting said sample with a composition comprising a GABAB receptor and a potassium channel tetramerization domain (KCTD), and performing an immunoassay to determine the presence of an antibody against a GABAB receptor in said sample. The immunoassay may comprise positive and or negative controls, such as samples void of GABABR-antibodies as negative controls, and or samples spiked with various amounts of GABABR-antibodies as positive controls, and wherein the immunoassay comprises an assay based on selective binding between GABABR-antibodies and the GABAB receptor, wherein binding is detected through the use of secondary antibodies that are immobilized when binding has occurred thereby producing an

immunoassay detection signal, and wherein said secondary antibodies are washed away when no binding has occurred, thereby producing no immunoassay detection signal, and optionally comparing the detection signal to a positive or negative control signal.

Cell-based immunoassays

A most preferred immunoassay described herein is a cell-based immunoassay (CBA), which in the context of the invention is preferably an indirect immunofluorescence assay wherein the antigen is provided and presented by a cell, preferably recombinant^/, for instance by a cell transfected with a nucleic acid encoding said antigen, and wherein said cell is on a sohd-phase substrate or reactant. As a further step, said cell is preferably fixated to said solid-phase substrate or reactant before, during or after: (i) a step of incubating or contacting a sample with the antigen, or (ii) a step of adding detectably labelled antibodies to the antigen-antibody complex thus formed.

The detectably labelled antibodies, also referred to as secondary antibodies, are preferably anti-human antibody antibodies, more preferably anti-human IgG antibody antibodies conjugated to a detectable label such as alexa fluor 488.

A cell in a CBA is preferably a HEK293 cell transfected with one or more nucleic acids that encode one or more of the antigens described herein. The cells may be stably or transiently transfected. The nucleic acids referred to herein are preferably DNA or RNA, the first preferably being

incorporated in an expression vector under the control of a suitable promotor. It is within the common general knowledge of the skilled person to provide such transfected cells with general molecular cloning techniques, such as described in Green and Sambrook, Molecular Cloning, 4th edition, July 2012, the contents of which are herein incorporated by reference.

Preferably, the KCTD protein constructs are incorporated in a pCI vector, under the control of a CMV promotor. Preferably, GABAB receptor

constructs are incorporated in a pGW2 vector, using a modified CMV promotor as described in Spangler et al., Biochemical Society Transactions, 35: 1278-1282 (2007).

In a cell-based immunoassay, as a further step, executed before or during incubation of the sample with the antigen, the cells can be

permeabilized to allow antibodies to have access to the inside of the cell, if necessary. If a cell-based immunoassay is employed to detect the presence of an antibody against a KCTD protein in said sample, said cell is preferably permeabilized before contacting said sample with said KCTD protein.

Permeabilization agents are generally known in the art and include ethanol, acetone, saponin, triton X-100 and tween-20.

It is expressly envisaged herein that a method of the invention can be performed by employing a device of the invention. It is therefore envisaged that a device of the invention is provided in a method of detecting, typing or identifying of the invention and that the immunoassay is

performed with such a device.

In a method of typing of the invention, typing of a subject for the presence or absence of a neurological autoimmune disorder requires the detection of an antibody against a GABAB receptor. A cut-off antibody titer value can be employed to determine whether antibodies against a GABAB receptor are present in a sample. It is within the common general knowledge of a clinician to determine such a cut-off antibody titer value for diagnostic purposes.

The invention also provides methods for identifying a subject at risk of having a tumor. It was estabhshed with the invention that the presence of both anti-GABAn receptor antibodies and anti-KCTD protein antibodies indicate that the subject is at risk of having a tumor, preferably an occult tumor.

In a method of identifying of the invention, an additional step involves determining the presence of antibodies against a GABAB receptor in a sample, in the manner as described herein.

Methods of treatmen t of the invention

The methods of typing and identifying of subjects as described herein allow for the definition of patient groups that benefits from certain treatment regimens.

Therefore, the invention provides a standard-of-care therapeutic agent for use in the treatment of a subject suffering from a neurological autoimmune disorder, wherein said subject is typed as having a neurological autoimmune disorder according to a method of typing of the invention.

In the same manner, the invention provides a use of a standard-of- care therapeutic agent in the manufacture of a medicament for treating a subject suffering from a neurological autoimmune disorder, wherein said subject is typed as having a neurological autoimmune disorder according to a method of typing of the invention.

In the same manner, the invention provides a method for treating a subject suffering from a neurological autoimmune disorder, comprising the step of: - providing, preferably administering a therapeutically effective amount, standard-of-care therapy, preferably a standard-of-care therapeutic agent, to a subject suffering from a neurological autoimmune disorder, wherein said subject is typed as having a neurological autoimmune disorder according to a method of typing of the invention.

The invention also relates to a standard-of-care therapeutic agent for use in the treatment of a subject suffering from cancer, wherein said subject is identified as being at risk of having a tumor according to a method for identifying a subject according to the invention. It is noted that the term "identifying" can be replaced by "typing" or "diagnosing" herein.

In the same manner, the invention also provides a use of a standard-of-care therapeutic agent in the manufacture of a medicament for treating a subject suffering from cancer, wherein said subject is identified as being at risk of having a tumor according to a method for identifying a subject according to the invention.

In the same manner, the invention also provides a method for treating a subject suffering from cancer, comprising the step of: - providing, preferably administering a therapeutically effective amount of, standard-of- care therapy, preferably a standard-of-care therapeutic agent, to a subject suffering from cancer, wherein said subject is identified as being at risk of having a tumor according to a method for identifying a subject according to the invention.

A device of the invention

The invention also relates to a device for performing an

immunoassay. Such a device is preferably an antigen array for performing an immunoassay. When the antigens on the array are to be provided by a cell presenting such antigens, the invention envisages a kit comprising (i) a device for performing an immunoassay, comprising - a substrate defining a first reaction surface; and (ii) a container for holding cells, comprising a medium with a cell expressing, having expressed, or transfected to express, a GABAB receptor and a KCTD protein. In such a kit, the device does not yet comprise an antigen. The cells in the container can be cryopreserved, for instance in one of the generally available media for cryopreserving cells, optionally containing a cryoprotective agent such as DMSO or glycerol. Media for cryopreserving mammalian cells are known in the art and include Recovery™ Cell Culture Freezing Medium (Thermo Fisher Scientific) and PSC Cryopreservation Kit, both of Thermo Fisher Scientific, which are inter alia suitable for cryopreserving and recovering HEK293 cells.

Alternatively, the invention provides a device for performing an immunoassay, comprising (i) a substrate defining a first reaction surface, and (ii) a GABAB receptor in the presence of a KCTD protein, connected to said first reaction surface.

Figure 4 shows a non-limiting example of a device 1 of the invention. The device contains a substrate 10 which is a shde, but can in principle be any type of substrate that is adapted for holding and fixation of cells. The slide is preferably of a transparent material such as glass. The substrate defines a plurality of reaction surfaces 11, also referred to herein as reaction fields 11. A first reaction surface in the sense of the invention can be any one of the indicated reaction fields 11 or reaction subfields 12 and 13. Reaction subfields 12 and 13 are comprised within a reaction field

11 and allow for performing an antibody detection reaction against at least one antigen that is in contact with said reaction subfields 12 and 13.

The reaction field 11 can be any surface of the substrate 10, preferably of the surface facing away from the surface on which the device is to be laid down, such as a lab table. Reaction field 11, or reaction subfields

12 and 13, do thus not necessarily have to be defined by a recess or a protrusion on the substrate, as long as separate reaction fields, or reaction subfields, allow for conduction of separate immunoassays. However, preferably, reaction fields 11 and subfields 12 and 13 are defined by a recess in, or a protrusion on, the substrate 10.

The cells presenting the antigen are connected to said reaction field 11 or reaction subfields 12 and 13 either directly by fixation or through suspension in a medium that is in contact with the reaction field 11 or reaction subfields 12 and 13. It is thus envisaged that the cells connected to said reaction field 11 or reaction subfields 12 and 13 are either ahve or dead before, during or after executing the immunoassay.

When employed in a method of the invention, a sample of a subject is added to a reaction field 11 or reaction subfields 12 and 13 to allow for the formation of an antigen-antibody immuno-complex. After such a first incubation step, a washing step can be performed to remove unbound antibodies. A second incubation step with detectably labelled antibodies is performed to visualize the presence of antigen-specific antibodies, for instance under a fluorescence microscope.

The invention also provides a use of a device of the invention in typing a subject for the presence of a neurological autoimmune disorder or a tumor associated with a neurological autoimmune disorder. In the same manner, the invention also provides a use of a cell expressing a GABAB receptor and a KCTD protein in typing a subject for the presence of a neurological autoimmune disorder or a tumor associated with a neurological autoimmune disorder.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include

embodiments having combinations of all or some of the features described. This is for instance the case for a method for detecting antibodies against a KCTD protein of the invention.

The contents of the publication mentioned herein, are incorporated by reference. EXAMPLES

Materials and methods Patient inclusion

A total of 2300 samples of patients clinically suspected to have immune mediated encephalitis were tested prospectively (May 2011 - December 2016) by routine diagnostic testing with IHC. A total of 282 samples, collected for diagnostic testing of onconeuronal antibodies prior to the identification of GABABR as an autoantigen (2000-2010), were tested retrospectively with IHC and an in-house developed cell based assay (in life CBA and fixed CBA format) for the presence of anti-GABABR antibodies. Lastly, in a cohort of 384 patients with clinical suspicion of Creuzfeldt- Jakob disease, 22 patients were retrospectively diagnosed with autoimmune encephalitis by a neuropathologist. Subsequently these 22 CSF samples were tested with IHC and in-house fixed CBA. All diagnostic tests were performed by the Erasmus Medical Center (Rotterdam, the Netherlands), the Dutch national referral center for paraneoplastic neurological

syndromes (PNS) and AIE. This study was approved by the institutional review board and informed consent was obtained from patients or their relatives.

The controls included plasma or serum from 46 anonymous blood bank donors, 13 reuma factor positive patients, 50 patients with SCLC without neurological symptoms (13 with limited disease, 31 with extensive disease, 6 with unknown disease grading), 26 patients with Hu antibodies and SCLC, 50 patients with Amyotrophic Lateral Sclerosis (ALS) and 123 patients clinically suspected of AIE (Titulaer et al., J Clin Oncol.,

10;27(26):4260-7 (2009); Huisman et al., JAMA Neurol, 72(10): 1155-62 (2015)). Incidence of the occurrence of GABABR mediated encephalitis was calculated using the number of patients identified prospectively in 2015 and 2016 and the number of Dutch inhabitants as provided by the Statistics Netherlands (CBS).

Clinical description

Clinical information was obtained retrospectively from medical records and telephone interviews with patients, relatives or treating physicians. Reduced consciousness was included as a symptom if not caused by a status epilepticus or induced by medication. We included the results of the first MRI, EEG and CSF examination performed after disease onset. The number of antiepileptic drugs includes all medication known to control seizures that were administered (according to clinical letters), including intravenous drugs during ICU admittance. Seizure types were classified according to the International League Against Epilepsy Seizure

Classification 2016 (Fisher RS, Cross JH, French JA, et al. Operational Classification of Seizure Types by the International League Against

Epilepsy. 2016). Severity of clinical symptoms were scored according to the Modified Ranking Scale (mRS) (Van Swieten et al., Stroke, 19(5):604-7 (198).

Statistical analysis

Statistical analysis was performed using IBM SPSS Statistics 21 and GraphPad Prism 6.0. The following statistical tests were used when appropriate: Fisher Exact Test, Mann-Whitney U test, and Wilcoxon signed rank test.

Laboratory procedures for diagnostic tests

IHC for detecting neuronal autoantibodies in tissue sections was performed as described previously (Ances et al., Brain, 128(8): 1764-77 (2005)). In short, rat brains were fixed with paraformaldehyde (PFA), cryoprotected, snap frozen and cut into sagittal sections. Sections were incubated with patients' serum (1:200) or CSF (1:2). The staining was visualized with diaminobenzidine and shdes were counterstained with hematoxylin. Antigen retrieval using sodium citrate (pH 6) of paraffin embedded SCLC tissue samples was performed prior to staining with rabbit anti-KCTD 16 (1:200) (Sigma Aldrich).

Neuronal cultures (hippocampal neurons) and staining for autoantibodies (like the GABABR or the NMDA receptor (NMDAR)) were performed essentially as described previously (Kaech et al., Nat Protoc, 1(5):2406-15 (2006); and Hughes et al., J Neurosci., 28;30(17):5866-75 (2010)). In short, living hippocampal neurons of at least 14 days in vitro were incubated with patients' serum (1:200) or CSF (1:2) and were subsequently fixed and stained with a fluorescently labelled secondary antibody.

For in house CBAs, HEK cells were transfected with GFP-GABABI and GFP-GABAB2 (kind gift dr. Lily Jan, UCSF, San Francisco) with or without co-transfection of FLAG™-tagged KCTD 16, KCTD12 or KCTD8 proteins (kind gift dr. Martin Gassmann, University of Basel, Basel), and were stained with patient serum (1:40) or CSF (1:2). For live CBA, incubation with the patient sample (serum 1:40, CSF 1:2) was performed in culturing medium prior to fixation of the cells.

For in house fixed CBA (GABABR and KCTD), LabTek slides (8 wells) are coated for 30 minutes with 0.5ml 2.5% gelatin per well.

Subsequently HEK cell suspension (1:20 in medium; 0.5ml per well) is added to the slide, and grown at 37 degrees Celsius and 5% CO2 for 24 hours. For transfection, DMEM is warmed for 30 minutes at 37°C;

meanwhile the constructs are spinned for 3 minutes and Fugene is mixed by switching it upside down at room temperature. Per well, 20ul of DMEM is mixed with 1 ug of DNA construct (or twice 0.5ug in case of a double transfection) and mixed for 5 minutes at room temperature. Three ul of Fugene is added to the medium (per well) and mixed for another 15 minutes. Twenty-four ul of this suspension is added to the wells drop by drop. Wells are placed 24 hours at 37°C and 2.5% CO2. As cells are grown on LabTec slides, no harvesting is necessary. For the staining, medium is aspirated (try to work fast: cells are still alive). Addition of 300 or 400 ul 4% PFA, and left at room temperature for 15 minutes. Chambers are removed. Wash 5 min at room temperature with ~ 100 ml PBS Triton (PBS

homemade, and 0.2% Triton X-100). Wash 2 times 15 minutes at room temperature with PBS+ (made by adding 2.5g BSA [bovine serum albumin] and 0.007g Glycin to 500ml of PBS). While incubating prepare Primary

Antibody 50 ul per well (dilute Sera 1:40 or CSF l:2i, n PBS+, spin mixture 5 minutes at 13200rpm). Put slides in dark/moist chamber (prevents bleaching/drying). Apply primary antibody mixture, and leave for 1 hour at room temperature (or overnight at 4°C). Wash 3 times 10 minutes at room temperature with PBS Tween (soft washing: PBS + 0.05%. Tween 20). While incubating prepare Secondary Ab (50 ul per well; dilute Donkey Anti- Human CY3 1:200 [Jackson Immuno Research 709- 166- 149] in PBS+, spin mixture 5 minutes at 13200rpm). Apply secondary antibody mixture per well. Put slides in dark/moist chamber for 1 hour at room temperature. Wash 3 times 10 minutes at room temperature with PBS Tween. Wash once 5 minutes at room temperature with homemade lxPBS (only to remove Tween). Remove gelatin (with forceps and the rest with a scalpel so the coverslip will be lying straight). Dry 15 minutes at room temperature (or overnight is also possible). Mount with Vectashield (H- 1500 hard set or H- 1200)+ coverglass.

For in house live CBA (GABABR), LabTek slides (8 wells) are coated for 5 minutes with 0.2ml Poly-L-Lysine per well. Wells are washed with sterile water (Accugene over 0,2 um filter), and dried for 2 hours at room temperature. Subsequently, CHO cell suspension (1:20 in medium; 0.5ml per well) is added to the slide, and grown at 37 degrees Celsius and 5% CO2 for 24 hours. For transfection, DMEM+FCS+P/S is warmed for 30 minutes at 37°C; meanwhile the DNA constructs are spinned for 3 minutes at

13.200rpm. Maxpei (22/04/14 Diya, Polyscience.com 24765) is used to prepare the transfection medium: Per well, mix 1 (1.5ul Pei and 50ul PBS is mixed and left for 5 minutes at room temperature) and mix 2 (0.5ug of DNA [or two time 0.25 ug if two constructs are transfected simultaneously] with 50 ul PBS is mixed and left at room temperature for 5 minutes) are combined, mixed and left at room temperature for 20 minutes. Five hundred ul of DMEM+FCS+P/S is added per well and mixed. This is added to the cells and left overnight at 37°C and 2.5% CO2. As cells are grown on LabTec slides, no harvesting is necessary. For the staining, dilute sera 1:40 (or CSF 1:2; both after spinning 1 minute at 3200 rpm) with the medium that you take directly out of the plate where the cells are growing (in total lOOul).

Aspirate the other medium from the cells, and add the medium with serum (or CSF). Incubate 30 minutes at 37°C. Cool cell culture PBS and 4%PFA at Cool cell culture PBS at 4°C. Wash short with PBS (-2.5 minutes). Fix 5 minutes with cold 4% PFA. Wash 3 times 5 minutes with PBS. Wash 5 minutes with PBS + 0.3% Triton X- 100. Wash 3 times 5 minutes with PBS. Incubate secondary antibody (Donkey anti-Human CY3 1:200 [Jackson Immuno Research 709- 166-149], 100 ul/well, in PBS + 1% BSA, spin mixture 5 minutes at 13200rpm), in dark/moist chamber for 1 hour at room temperature. Wash 3 times 5 minutes at room temperature with demiwater. Dry 15 minutes at room temperature. Mount with Vectashield+DAPI (H- 1500 hard set) + coverglass.

The GFP-GABABI construct encodes the amino acid sequence of rat

Gamma-aminobutyric acid type B receptor subunit 1 as indicated by

UniProtKB Acc. No. Q9Z0U4, and was comprised in a pGW2 vector, using a modified CMV promotor as described in Spangler et al., Biochemical Society Transactions, 35: 1278-1282 (2007). The GFP-GABAB2 construct encodes the amino acid sequence of rat Gamma-aminobutyric acid type B receptor subunit 2 as indicated by

UniProtKB Acc. No. 088871 (last modified: January 11, 2001 - v2), and was comprised in a pGW2 vector, using a modified CMV promotor as described in Spangler et al., Biochemical Society Transactions, 35: 1278-1282 (2007).

The FLAG-KCTD constructs for KCTD8, KCTD12 and KCTD16 encoded rat KCTD protein 8 (GenBank Acc. No.: NP_001093642.1), rat KCTD protein 12 (Genbank Acc. No.: EDM02446.1) and rat KCTD protein 16 (Genbank Acc. No.: NP_001165626.1), respectively. These constructs were comprised in a p CI vector, under the control of a CMV promotor.

Luminescent assay

A Dual-Luciferase Assay System (Promega) was used in which HEK cells were transfected with DNA constructs encoding the GABABR subunits (GABABIO, GABAB2), a G-protein (Qi5 (Addgene)), G-protein responsive firefly luciferase (PGL4.33 [Luc2P/SRE/Hygro] (Promega)) and Renilla luciferase (PRL/TK (Promega)) as an internal control. 4-6 hours after transfection cells were changed to serum-free media. The next morning, cells were treated with serum or CSF in serum free medium for 1 hour. Then 10 μΜ baclofen was applied. After 6 hours of induction with baclofen, wells were washed with PBS and lysed. A luciferase substrate was added and the luminescence signal was read in LB942 luminometer

(Bertkold) and normalized to the Renilla luminescent signal. Each patient sample was compared to a paired healthy control serum sample within the same experiment.

Mass Spectrometry

Immunoprecipitation and mass spectrometry analysis was performed as described previously (Van Coevorden-Hameete et al., Neurol Neuroimmunol Neuroinflamm., 2(5):el56 (2015); and De Graaff et al., Ann Neurol., 71(6):815-24 (2012)). In short, protein extract was made from adult rat brains and was incubated overnight with 10 μΐ of serum. The following morning protA/G sepharose beads (GE Healthcare Life Sciences) were added. The beads were washed, boiled and supernatant was loaded on a 4- 12% Bis-Tris gel (Invitrogen) and send for mass spectrometry analysis.

Microscopy

IHC were scored visually on an Olympus BX50F. CBAs and live neurons were scored visually by two independent observers using a Nikon eclipse 80i upright microscope. Confocal images were acquired with a Zeiss LSM 700 using the 40x and 63x (oil) objectives. Images were processed using ImageJ.

Results

Patients and clinical phenotype.

Characteristics of patients with anti-GABABR encephalitis are summarized in Table 1.

Table 1. Patient characteristics (n=23)

ICU = Intensive Care Unit. AED = Antiepileptic drugs. Pleiocytosis = >5 cells/ mm³. Elevated protein = >0.58 gr/L. SCLC = Small Cell Lung

Carcinoma. OCB = Oligoclonal bands. # paresis arm, facialis paresis, apraxia.

Λ myoclonia (2x). @ repiratory depression, bradycardia. $ One patient

developed mesiotemporal T2 FLAIR hyperintensities later in the disease

course and one patient developed mesiotemporal atrophy later in the disease

course. * Hu_: VGCC, GABAAR, ΛΜ Ι'ΛΙί (2x).

Twelve patients were male (52%). The median age at disease onset was 65 years. Incidence of anti-GABAeR encephalitis (calculated from January 2015- December 2016) was 0.24/1.000.000 inhabitants/year.

LE was the main clinical syndrome in most patients (20/23; 87%). The three remaining patients had a rapidly progressive encephalopathy,

panencephalitis or seizures only. Most frequently, patients presented at the emergency room with seizures (61%), while the first symptoms in the remaining patients were subacute cognitive decline or behavioral change. Over the course of the disease all except one patient (96%) developed cognitive and/or behavioral problems. Nearly all patients (96%) experienced seizures. In all cases seizures were generalized, in 15%> these were clear focal to bilateral tonic clonic seizures. In addition, 5 patients (25%) experienced focal seizures with impaired awareness. In two cases the type of seizures was not described. Often the seizures were refractory to

antiepileptic drugs. Ten patients (43%) developed a super refractory status epilepticus for which admittance to the intensive care unit (ICU) was required. Additional symptoms that occurred most frequently were reduced consciousness (26%), language/ speech problems (26%), headache (22%) and psychosis/hallucinations (22%). The median mRs was 5 (IQR: 3-5; range: 2- 5) at maximum disease severity.

Ancillary testing

Initial CSF findings were available in 22 patients and were abnormal in all cases. The findings mainly included mild pleiocytosis (86%) and increased protein level (28%). Increased IgG index and/or oligoclonal bands were reported in 6/8 patients, but were not determined in 14 patients. Initial MRI results were often abnormal (65%), most frequently T2/FLAIR- hyperintensities of the mesiotemporal lobe (9/20; 3 unilateral and 6 bilateral), while three patients had (aspecific) white matter abnormalities and one patient had atrophy of the mesiotemporal lobe. Initial EEG results showed focal slowing (85%) often in combination with epileptic discharges (53%.).

Anti-KCTD16 antibodies are associated with an underlying SCLC.

A total of 24 patients with anti-GABABR encephalitis were identified. Informed consent was obtained in 23 patients of which 11 were diagnosed prospectively and 8 retrospectively. In four patients IHC showed neuropil staining and live neurons were positive but in house GABABR-CBA was scored negative. In those patients antibodies to the GABABR were detected using immunoprecipitation and mass spectrometry analysis. Next to the GABABR subunits GABABI and GABAB2, in two patients the GABABR accessory protein KCTD16 was precipitated. Using a fixed KCTD16-CBA a subgroup of 16/23 (70%.) anti-GABA_BR encephalitis patients and 1/26 (4%) Hu-SCLC patients had anti-KCTD16 antibodies. Anti-GABABR encephalitis patients with anti-KCTD16 antibodies more frequently had an underlying tumor. Out of 20 patients that underwent sufficient tumor screening, 13/13 patients with KCTD16 and 2/7 patients without KCTD16 antibodies had an underlying tumor (p = 0.0014) (Figure 3A). No other factors (anti-GABAB titers in serum and CSF, maximum mRS during disease, frequency of status epilepticus and response to immuno- and/or chemotherapy) differed significantly between patients with or without KCTD16 antibodies. SCLC biopsy tissue from a patient with anti-KCTD16 antibodies expressed

KCTD16, whereas normal lung tissue did not (Figure 3B); similarly SCLC tissue from a patient without anti-KCTD16 antibodies did not express KCTD 16 (data not shown). Tumor association and response to treatment.

Tumor screening with (FDG-PET) CT of thorax and abdomen or autopsy was performed in 20 patients, 12 of which (60%) had an underlying SCLC and three (15%) had a tumor of unknown type. Besides anti-GABAeR antibodies two patients with an unknown tumor type had other SCLC- associated antibodies (anti-AMPAR and anti-VGCC). Median time to tumor diagnosis after the first contact with a physician was 5 weeks (IQR: 1-7; range: 1-62). One patient was screened by a pulmonologists for suspected lung cancer prior to the onset of the neurological symptoms, the other patients were diagnosed after the onset of neurological symptoms.

Patients were treated with a combination of immuno- and tumor therapy (41%), immunotherapy alone (36%), tumor therapy alone (9%) or remained untreated (14%). The majority of the patients (95%) responded to treatment, with a median best mRS score of 2 (IQR: 1-3; range: 1-5) after treatment. Seizure frequency often responded faster than cognitive and behavioral symptoms. The one patient that did not respond had a poor cardiopulmonal condition and died shortly after immunotreatment before effects were assessable. Three patients did not receive treatment because of poor overall condition or because their disease presented prior to discovery of AIE with neuronal surface antibodies. One of those showed spontaneous

improvement. In one patient no information about treatment was available. Two patients relapsed after 4 and 6 months respectively. No tumor was found at relapse. At last follow up, 9/23 patients were still alive (median follow up 12 months; IQR: 9-16; range 2-82). Median mRS at last follow up was 2 (IQR: 2-3; range 0-4). Median survival for deceased patients was 9 months (IQR: 4-16; range: 1-26). Five patients died of tumor progression, 2 patients of infection and 1 of neurological deterioration, in 6 patients the cause of death was not reported. In 4 patients no initial improvement occurred prior to death of which 3 were not treated with immunotherapy. Until deterioration leading to death, the remaining patients responded (partially), resulting in a median mRS of 2 (IQR 2-3; range 1-4).

Addition of KCTD16 to GABABR-CBA improves detection.

The patients' sera (n=22) and CSF (n=14) samples were tested for the presence of anti-GABABR antibodies using a set of different laboratory techniques (Figure 1A-C). All sera and CSF samples showed neuropil staining on IHC (Figure 1A, ID), labelled the surface of culture hippocampal neurons (Figure IB, ID) and were anti-GABABR positive using live CBA (Figure 1C,D). In house fixed CBA detected GABABR antibodies in 18/23 (78%) of the sera and 12/15 (80%) of the CSF samples. When GAB Am and GABAB2 subunits were co-transfected with the GABABR assessory subunit KCTD16, the sensitivity for serum improved to 20/23 (87%) and in CSF to 15/15 (100%) (Figure ID).

To validate the improvement of the fixed CBA by the addition of

KCTD16, we performed serial dilution of 22 sera and 10 CSF samples on fixed CBA with and without co-expression of KCTD16. We observed a significant increase in titer in the CBA with KCTD16 co-expression (Figure 2A-C). This effect was seen in both serum and CSF (serum 16/22 [73%, p = 0.0003, Wilcoxon signed rank test], CSF 5/10 [50%., p = 0.022, Wilcoxon signed rank test]). Titers increased 4-fold (range 0-64) in serum and 2-fold in CSF (range 0-64). The addition of KCTD16 to the fixed CBA did not result in a reduction of specificity as 172 healthy and diseased control samples tested negative. The addition of KCTD8 and KCTD12 provided for an improvement in detection of anti-GABABR antibodies compared to GABABR subunits Bl and B2 only, as is shown in Table 2 below. No differences were found between titers of patients with and without underlying tumors

(Figure 2D). B1/B2 B1/B2/8 B1/B2/12 B1/B2/16

Serum Positive 10 12 12 15

Negative 5 4 4 2

Questionable 2 1 1 0

CSF Positive 6 5 5 8

Negative 2 1 1 0

Questionable/Unknown 0 2 2 0

Table 2. Soring of test samples for detection of GAB A receptor

autoantibodies. B1/B2: GABAb l/b2R test; B1/B2/8: GABAbl/b2R + KCTD8 test; B1/B2/12: GABAb l/b2R + KCTD12 test; B1/B2/16: GABAb l b2R + KCTD16 test.

Functional effects of anti-GABABR antibodies

Next we assessed the functional effects of anti-GABABR antibodies on GABABR signaling using an in vitro luciferase reporter assay. This assays showed that both high and low titer anti-GABABR antibodies were able to reduce the downstream signaling of the GABABR in response to baclofen, and that this response was more outspoken if more serum was added.

Claims

1. A method for detecting antibodies against a GABAB receptor in a sample of a subject, comprising the steps of:

- providing a composition comprising a GABAB receptor and a potassium channel tetramerization domain (KCTD) protein;

- contacting said sample with said composition;

2. The method according to claim 1, whereby the method is for typing a subject for the presence or absence of a neurological autoimmune disorder; and whereby the presence of said antibody in said sample indicates the presence of a neurological autoimmune disorder in said subject.

3. The method according to claim 1 or claim 2, whereby the GABAB receptor and the KCTD protein are provided by a cell co-expressing a

GABAB receptor and a KCTD protein; and whereby the immunoassay is a cell-based immunoassay.

4. The method according to claim 3, wherein the cell is a

recombinant mammalian cell transfected with a nucleic acid encoding a GABAB receptor and a nucleic acid encoding a KCTD protein.

5. The method according to any one of the previous claims, wherein the KCTD protein is selected from KCTD8, KCTD 12, KCTD 12b and

KCTD 16.

6. The method according to any one of claims 2-5, wherein the neurological autoimmune disorder is an anti-GABAB receptor neurological disorder, preferably anti-GABAB receptor encephalitis.

7. The method according to any one of the previous claims, wherein the sample is a serum sample or a cerebrospinal fluid sample.

8. A method for identifying a subject at risk of having, or suffering from, a tumor, comprising the steps of:

- providing a KCTD protein;

- contacting said sample with said KCTD protein;

whereby the presence of an antibody against a KCTD protein in said sample indicates that the subject is at risk of having, or suffering from, a tumor.

9. The method according to claim 8, wherein the neurological disorder is a neurological autoimmune disorder, preferably anti-GABAB receptor encephalitis.

10. The method according to claim 8 or 9, wherein the tumor is a small cell lung cancer (SCLC) or a thymic neuroendocrine tumor.

11. A cell expressing a GABAB receptor and a KCTD protein, wherein at least one of the cell, receptor or protein is recombinant, preferably wherein the KCTD protein is selected from KCTD8, KCTD 12, KCTD 12b and KCTD 16.

12. Cell according to claim 11, wherein the cell is a recombinant mammalian cell transfected with a nucleic acid encoding a GABAB receptor and a nucleic acid encoding a KCTD protein.

13. A kit-of-pats for performing an immunoassay, comprising a cell according to claim 11 or 12 and a anti -human IgG secondary antibody, preferably said anti-human IgG secondary antibody being labelled.

14. A device for performing an immunoassay, comprising

- a substrate (1) defining a first reaction surface (11, 12, 13);

- a cell expressing a GABAB receptor and a KCTD protein, wherein said cell is immobilized on said first reaction surface (13).

15. The device according to claim 14, wherein the substrate (10) is a microscope slide or a microtiter plate, preferably in transparent form.

16. Use of a KCTD protein as antigen in an immunoassay for detecting autoantibodies in a sample of a subject, preferably wherein said KCTD protein is KCTD protein 16.

17. An anti-KCTD protein antibody,

preferably wherein said antibody is selected from one or more of:

an autoantibody,

an IgG, IgA or IgM antibody, and

- a human antibody.

18. The anti-KCTD protein antibody of claim 17, wherein said KCTD protein is KCTD protein 16.

19. The anti-KCTD protein antibody of claim 17 or 18, wherein said antibody is bound to a KCTD protein.