A PROTEOLIPOSOME-BASED ZNT8 SELF-ANTIGEN FOR TYPE 1 DIABETES DIAGNOSIS
1. A method of detecting ZNT8 antibodies in serum comprising:
- providing a collection of proteoliposomes having an interior and an exterior wherein some proteoliposomes have protein sequences of a transmembrane domain (TMD) of a ZnT8 on its exterior and other proteoliposomes comprise protein sequences of a cytosolic domain (CTD) of a ZnT8 protein exposed on its exterior;
adding serum comprising antibodies targeting the protein sequences of TMD and/or CTD forming proteoliposomes bound to the antibodies;
adding a labelled captured autoantibody that binds to the antibodies bound to the proteoliposomes; and
measuring the amount of antibodies targeting the protein sequences of TMD and/or CTD bound to the proteoliposomes.
Methods of detecting ZNT8 antibodies in serum are described. The methods include proteoliposomes comprising a transmembrane domain (TMD) and a cytosolic domain (CTD) of ZnT8 proteins exposed on the exterior of the proteoliposome; serum comprising antibodies targeting the ZnT8 proteins; and labelled captured autoantibodies that bind to ZnT8 antibodies.
- 1. A method of detecting ZNT8 antibodies in serum comprising:
providing a collection of proteoliposomes having an interior and an exterior wherein some proteoliposomes have protein sequences of a transmembrane domain (TMD) of a ZnT8 on its exterior and other proteoliposomes comprise protein sequences of a cytosolic domain (CTD) of a ZnT8 protein exposed on its exterior; adding serum comprising antibodies targeting the protein sequences of TMD and/or CTD forming proteoliposomes bound to the antibodies; adding a labelled captured autoantibody that binds to the antibodies bound to the proteoliposomes; and measuring the amount of antibodies targeting the protein sequences of TMD and/or CTD bound to the proteoliposomes.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
- 23. A method of detecting ZNT8 antibodies in serum comprising:
forming a mixture by combining proteoliposomes having an interior and an exterior comprising protein sequences of a transmembrane domain (TMD) and a cytosolic domain (CTD) of a ZnT8 proteins exposed on the exterior of the proteoliposomes;
serum comprising antibodies targeting the protein sequences;
a labelled captured autoantibody that binds to the antibodies targeting the protein sequences; and
measuring the amount of antibodies bound to the protein sequences.
This application claims the benefit of U.S. Provisional Patent application 62/531,525, filed Jul. 12, 2017, which are hereby incorporated by reference for all purposes as if fully set forth herein.
This invention was made with government support under grant no. R01GM065137 awarded by the National Institutes of Health. The government has certain rights in the invention.
The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jun. 27, 2018, is named P14838-02_SL.txt and is 12,449 bytes in size.
The incidence of type 1 diabetes (T1D) in children has been increasing by 3% to 5% per year worldwide since the 1960s, which makes the sensitive and specific T1D diagnosis imperative. Detection of T1D-related autoantibodies can quantify the extent of risk for symptomatic T1D onset, as well as afford enrollment into trails seeking to prevent overt disease development. Unlike the earlier established autoantibodies against insulin, islet antigen 2 (IA2), and glutamic acid decarboxylase (GAD) as three major biomarkers for T1D diagnosis, zinc transporter 8 autoantibody (ZnT8A) was discovered more recently as another major biomarker for T1D diagnosis through bioinformatics, expanding the panel of T1D diagnostic autoantibodies. In pre-diabetic individuals, ZnT8A appears in the prodromal phase months to years prior to the clinical onset of disease and its detection can improve the accuracy of T1D prediction, rendering ZnT8A as one of the most important biomarkers to evaluate the risk of T1D development.
ZnT8 is a specialized zinc transporter found predominantly in insulin secretory granules of pancreatic beta-cells4. It is a multi-spanning transmembrane protein consisting of two functional modules, a transmembrane domain responsible for zinc transport and a cytosolic zinc-sensing unit of N- and C-terminal domains (NTD and CTD, respectively). The transport activity of ZnT8 yields a highly enriched granular zinc content for crystalline packaging of insulin molecules in complex with zinc ions. During insulin secretion, granule exocytosis exposes ZnT8 to the surface membrane, subjecting its transmembrane domain to extracellular ZnT8A surveillance. The cytosolic domains of ZnT8 only become accessible to ZnT8A following the destruction of beta-cells. Approximately half of the ZnT8 structure lies within six membrane-spanning regions, presenting a challenge to develop assays for ZnT8A detection due to the difficulty of maintaining its tertiary structure outside a membrane environment.
Thus far, most assays for ZnT8A detection are based on antigens of cytosolic domains of ZnT8 (i.e., CTD and NTD) or construction of single-chain molecules fusing the two domains. Due to the fact that CTD encompassing amino acid (aa) 275-369 can produce a robust detection performance relative to the less efficient detection performance based on NTD, ZnT8A detection has focused on two variants of CTD that differ by a single aa at position 325 (i.e., arginine, 325R or tryptophan, 325W). Although thus far the combination of the two variants of CTD has been used for effective ZnT8A detection, the best candidate for ZnT8A detection could be full-length ZnT8 that contains the complete auto-reactive sites (both intracellular and extracellular ones) accessible to ZnT8A. However due to the instability of purified full-length ZnT8 protein in its detergent-solubilized form, full-length ZnT8 has thus far not been used successfully for ZnT8A detection.
Other researchers have tried to incorporate a full-length ZnT8 protein into synthetic nano-discs containing phospholipid and apolipoproteins (Janet M. Wenzlau and John C. Hutton, Curr Diab Rep. 2013 October; 13(5): doi: 10.1007/s 1892-013-0405-9). A nanodisc is a synthetic model membrane system that assists in the study of membrane proteins. It is composed of a lipid bilayer of phospholipids with the hydrophobic edge screened by two amphipathic proteins. These proteins are called membrane scaffolding proteins (MSP) and align in double belt formation. Nanodiscs are structurally very similar to high-density lipoproteins (HDL) and the MSPs are modified versions of apolipoprotein A1 (apoA1), the main constituent in HDL. Nanodiscs are useful in the study of membrane proteins because they can solubilize and stabilize membrane proteins and represent a more native environment than liposomes, detergent micelles, bicelles and amphipols.
One embodiment of the present invention is a method of detecting ZNT8 antibodies in serum comprising: forming a mixture by combining proteoliposomes having an interior and an exterior comprising protein sequences of a transmembrane domain (TMD) and a cytosolic domain (CTD) of ZnT8 proteins exposed on the exterior of the proteoliposomes; serum comprising antibodies targeting the protein sequences; a labelled captured autoantibody that binds to the antibodies targeting the protein sequences; and measuring the amount of antibodies bound to the protein sequences. The transmembrane domain and the cytosolic domain may be from the same ZnT8 protein or from different full length ZnT8 proteins.
Another embodiment of the present invention is a method of detecting ZNT8 antibodies in serum comprising the following steps. Providing a collection of proteoliposomes having an interior and an exterior wherein some proteoliposomes have protein sequences of a transmembrane domain (TMD) of a ZnT8 on its exterior and other proteoliposomes comprise protein sequences of a cytosolic domain (CTD) of a ZnT8 protein exposed on its exterior. Adding serum comprising antibodies targeting the protein sequences of TMD and/or CTD forming proteoliposomes bound to the antibodies. Adding a labelled captured autoantibody that binds to the antibodies bound to the proteoliposomes and measuring the amount of antibodies targeting the protein sequences of TMD and/or CTD bound to the proteoliposomes.
Suitable protein sequences of a TMD and a CTD used in the present invention may be full length TMD and CTD domains part of a full length ZnT8 protein, for example. Other suitable sequences include parts (or fragments) of TMD or CTD that are antigenic and bind to the antibodies targeting TMS and/or CTD. Suitable ZnT8 proteins used in the present invention include a wild type human ZnT8 protein and variants thereof. Examples of variants include an “a” form of a ZnT8 protein including a signal sequence, and a “b” form of a ZnT8 protein without a signal sequence. Please see the Methods Section for examples of ZnT8 protein sequences used in the present invention. In addition, both the “a” form and the “b” form of ZnT8 may be a R325W variant.
A collection of proteoliposomes used in the present invention may comprises “inside out” proteoliposomes and “right side out” proteoliposomes. The “inside out” proteoliposomes preferably comprise CTD protein sequences on its exterior. The “right side” out proteoliposomes preferably comprise TMD protein sequences on its exterior.
The proteoliposomes used in the methods of the present invention may be placed on a chip. Please see
Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this invention belongs. The following references provide one of skill with a general definition of many of the terms used in this invention: Singleton et al., Dictionary of Microbiology and Molecular Biology (2nd ed. 1994); The Cambridge Dictionary of Science and Technology (Walker ed., 1988); The Glossary of Genetics, 5th Ed., R. Rieger et al. (eds.), Springer Verlag (1991); and Hale & Marham, The Harper Collins Dictionary of Biology (1991). As used herein, the following terms have the meanings ascribed to them below, unless specified otherwise.
The term “activity” refers to the ability of a gene to perform its function such as Indoleamine 2,3-dioxygenase (an oxidoreductase) catalyzing the degradation of the essential amino acid tryptophan (trp) to N-formyl-kynurenine.
The term “antibody,” as used in this disclosure, refers to an immunoglobulin or a fragment or a derivative thereof, and encompasses any polypeptide comprising an antigen-binding site, regardless of whether it is produced in vitro or in vivo. The term includes, but is not limited to, polyclonal, monoclonal, monospecific, polyspecific, non-specific, humanized, single-chain, chimeric, synthetic, recombinant, hybrid, mutated, and grafted antibodies. Unless otherwise modified by the term “intact,” as in “intact antibodies,” for the purposes of this disclosure, the term “antibody” also includes antibody fragments such as Fab, F(ab′)2, Fv, scFv, Fd, dAb, and other antibody fragments that retain antigen-binding function, i.e., the ability to bind, for example, PD-L1, specifically. Typically, such fragments would comprise an antigen-binding domain.
The terms “antigen-binding domain,” “antigen-binding fragment,” and “binding fragment” refer to a part of an antibody molecule that comprises amino acids responsible for the specific binding between the antibody and the antigen. In instances, where an antigen is large, the antigen-binding domain may only bind to a part of the antigen. A portion of the antigen molecule that is responsible for specific interactions with the antigen-binding domain is referred to as “epitope” or “antigenic determinant.” An antigen-binding domain typically comprises an antibody light chain variable region (VL) and an antibody heavy chain variable region (VH), however, it does not necessarily have to comprise both. For example, a so-called Fd antibody fragment consists only of a VH domain, but still retains some antigen-binding function of the intact antibody.
Binding fragments of an antibody are produced by recombinant DNA techniques, or by enzymatic or chemical cleavage of intact antibodies. Binding fragments include Fab, Fab′, F(ab′)2, Fv, and single-chain antibodies. An antibody other than a “bispecific” or “bifunctional” antibody is understood to have each of its binding sites identical. Digestion of antibodies with the enzyme, papain, results in two identical antigen-binding fragments, known also as “Fab” fragments, and a “Fc” fragment, having no antigen-binding activity but having the ability to crystallize. Digestion of antibodies with the enzyme, pepsin, results in a F(ab′)2 fragment in which the two arms of the antibody molecule remain linked and comprise two-antigen binding sites. The F(ab′)2 fragment has the ability to crosslink antigen. “Fv” when used herein refers to the minimum fragment of an antibody that retains both antigen-recognition and antigen-binding sites. “Fab” when used herein refers to a fragment of an antibody that comprises the constant domain of the light chain and the CHI domain of the heavy chain.
By “agent” is meant any small molecule chemical compound, antibody, nucleic acid molecule, or polypeptide, or fragments thereof.
By “ameliorate” is meant decrease, suppress, attenuate, diminish, arrest, or stabilize the development or progression of a disease.
By “alteration” is meant a change (increase or decrease) in the expression levels or activity of a gene or polypeptide as detected by standard art known methods such as those described herein. As used herein, an alteration includes a 10% change in expression levels, preferably a 25% change, more preferably a 40% change, and most preferably a 50% or greater change in expression levels.”
By “analog” is meant a molecule that is not identical, but has analogous functional or structural features. For example, a polypeptide analog retains the biological activity of a corresponding naturally-occurring polypeptide, while having certain biochemical modifications that enhance the analog'"'"'s function relative to a naturally occurring polypeptide. Such biochemical modifications could increase the analog'"'"'s protease resistance, membrane permeability, or half-life, without altering, for example, ligand binding. An analog may include an unnatural amino acid.
By “Diagnostic” means identifying the presence or nature of a pathologic condition, i.e., type 1 diabetes. Diagnostic methods differ in their sensitivity and specificity. The “sensitivity” of a diagnostic assay is the percentage of diseased individuals who test positive (percent of “true positives”). Diseased individuals not detected by the assay are “false negatives.” Subjects who are not diseased and who test negative in the assay, are termed “true negatives.” The “specificity” of a diagnostic assay is 1 minus the false positive rate, where the “false positive” rate is defined as the proportion of those without the disease who test positive. While a particular diagnostic method may not provide a definitive diagnosis of a condition, it suffices if the method provides a positive indication that aids in diagnosis.
By “disease” is meant any condition or disorder that damages or interferes with the normal function of a cell, tissue, or organ. Examples of diseases include cancer.
By “DS-ZnT8” is meant purified full-length ZnT8 protein in detergent micelles.
By “effective amount” is meant the amount of a required to ameliorate the symptoms of a disease relative to an untreated patient. The effective amount of active compound(s) used to practice the present invention for therapeutic treatment of a disease varies depending upon the manner of administration, the age, body weight, and general health of the subject. Ultimately, the attending physician or veterinarian will decide the appropriate amount and dosage regimen. Such amount is referred to as an “effective” amount.
By “express” is meant the ability of a gene to express the gene product including for example its corresponding mRNA or protein sequence (s).
By “fragment” is meant a portion of a polypeptide or nucleic acid molecule. This portion contains, preferably, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the entire length of the reference nucleic acid molecule or polypeptide. A fragment may contain 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 nucleotides or amino acids.
By “hybridization” is meant hydrogen bonding, which may be Watson-Crick, Hoogsteen or reversed Hoogsteen hydrogen bonding, between complementary nucleobases. For example, adenine and thymine are complementary nucleobases that pair through the formation of hydrogen bonds.
By “immunoassay” is meant an assay that uses an antibody to specifically bind an antigen (e.g., a marker). The immunoassay is characterized by the use of specific binding properties of a particular antibody to isolate, target, and/or quantify the antigen.
By “liposome” is meant an aqueous compartment enclosed by a bimolecular phospholipid membrane; a lipid vesicle. A proteoliposome is a liposome into which one or more proteins have been inserted, usually by artificial means.
By “obtaining” as in “obtaining an agent” is meant synthesizing, purchasing, or otherwise acquiring the agent.
By “mAb” is meant a monoclonal antibody. Antibodies of the invention comprise without limitation whole native antibodies, bispecific antibodies; chimeric antibodies; Fab, Fab′, single chain V region fragments (scFv), fusion polypeptides, and unconventional antibodies.
By “marker” is meant any protein or polynucleotide having an alteration in expression level or activity that is associated with a disease or disorder. The term “biomarker” is used interchangeably with the term “marker.”
By “measuring” is meant methods which include detecting the presence or absence of marker(s) in the sample, quantifying the amount of marker(s) in the sample, and/or qualifying the type of biomarker. Measuring can be accomplished by methods known in the art and those further described herein, including but not limited to immunoassay. Any suitable methods can be used to detect and measure one or more of the markers described herein. These methods include, without limitation, ELISA and bead-based immunoassays (e.g., monoplexed or multiplexed bead-based immunoassays, magnetic bead-based immunoassays).
By “PLR-ZnT8” is meant purified full length ZnT8 protein in proteoliposomes.
The terms “polypeptide,” “peptide” and “protein” are used interchangeably herein to refer to a polymer of amino acid residues. The terms apply to amino acid polymers in which one or more amino acid residue is an analog or mimetic of a corresponding naturally occurring amino acid, as well as to naturally occurring amino acid polymers. Polypeptides can be modified, e.g., by the addition of carbohydrate residues to form glycoproteins. The terms “polypeptide,” “peptide” and “protein” include glycoproteins, as well as non-glycoproteins.
By “reduces” is meant a negative alteration of at least 10%, 25%, 50%, 75%, or 100%.
A “reference” refers to a standard or control conditions such as a sample (human cells) or a subject that is a free, or substantially free, of an agent such as one or more inhibitors of IDO1 and/or a vaccine.
A “reference sequence” is a defined sequence used as a basis for sequence comparison. A reference sequence may be a subset of or the entirety of a specified sequence; for example, a segment of a full-length cDNA or gene sequence, or the complete cDNA or gene sequence. For polypeptides, the length of the reference polypeptide sequence will generally be at least about 16 amino acids, preferably at least about 20 amino acids, more preferably at least about 25 amino acids, and even more preferably about 35 amino acids, about 50 amino acids, or about 100 amino acids. For nucleic acids, the length of the reference nucleic acid sequence will generally be at least about 50 nucleotides, preferably at least about 60 nucleotides, more preferably at least about 75 nucleotides, and even more preferably about 100 nucleotides or about 300 nucleotides or any integer thereabout or there between.
As used herein, the term “sensitivity” is the percentage of subjects with a particular disease.
As used herein, the term “specificity” is the percentage of subjects correctly identified as having a particular disease i.e., normal or healthy subjects. For example, the specificity is calculated as the number of subjects with a particular disease as compared to non-cancer subjects (e.g., normal healthy subjects).
By “specifically binds” is meant a compound or antibody that recognizes and binds a polypeptide of the invention, but which does not substantially recognize and bind other molecules in a sample, for example, a biological sample, which naturally includes a polypeptide of the invention.
As used herein, the term “subject” is intended to refer to any individual or patient to which the method described herein is performed. Generally the subject is human, although as will be appreciated by those in the art, the subject may be an animal. Thus other animals, including mammals such as rodents (including mice, rats, hamsters and guinea pigs), cats, dogs, rabbits, farm animals including cows, horses, goats, sheep, pigs, etc., and primates (including monkeys, chimpanzees, orangutans and gorillas) are included within the definition of subject.
Nucleic acid molecules useful in the methods of the invention include any nucleic acid molecule that encodes a polypeptide of the invention or a fragment thereof. Such nucleic acid molecules need not be 100% identical with an endogenous nucleic acid sequence, but will typically exhibit substantial identity. Polynucleotides having “substantial identity” to an endogenous sequence are typically capable of hybridizing with at least one strand of a double-stranded nucleic acid molecule. Nucleic acid molecules useful in the methods of the invention include any nucleic acid molecule that encodes a polypeptide of the invention or a fragment thereof. Such nucleic acid molecules need not be 100% identical with an endogenous nucleic acid sequence, but will typically exhibit substantial identity. Polynucleotides having “substantial identity” to an endogenous sequence are typically capable of hybridizing with at least one strand of a double-stranded nucleic acid molecule. By “hybridize” is meant pair to form a double-stranded molecule between complementary polynucleotide sequences (e.g., a gene described herein), or portions thereof, under various conditions of stringency. (See, e.g., Wahl, G. M. and S. L. Berger (1987) Methods Enzymol. 152:399; Kimmel, A. R. (1987) Methods Enzymol. 152:507).
For example, stringent salt concentration will ordinarily be less than about 750 mM NaCl and 75 mM trisodium citrate, preferably less than about 500 mM NaCl and 50 mM trisodium citrate, and more preferably less than about 250 mM NaCl and 25 mM trisodium citrate. Low stringency hybridization can be obtained in the absence of organic solvent, e.g., formamide, while high stringency hybridization can be obtained in the presence of at least about 35% formamide, and more preferably at least about 50% formamide. Stringent temperature conditions will ordinarily include temperatures of at least about 30° C., more preferably of at least about 37° C., and most preferably of at least about 42° C. Varying additional parameters, such as hybridization time, the concentration of detergent, e.g., sodium dodecyl sulfate (SDS), and the inclusion or exclusion of carrier DNA, are well known to those skilled in the art. Various levels of stringency are accomplished by combining these various conditions as needed. In a preferred: embodiment, hybridization will occur at 30° C. in 750 mM NaCl, 75 mM trisodium citrate, and 1% SDS. In a more preferred embodiment, hybridization will occur at 37° C. in 500 mM NaCl, 50 mM trisodium citrate, 1% SDS, 35% formamide, and 100.mu·g/ml denatured salmon sperm DNA (ssDNA). In a most preferred embodiment, hybridization will occur at 42° C. in 250 mM NaCl, 25 mM trisodium citrate, 1% SDS, 50% formamide, and 200 μg/ml ssDNA. Useful variations on these conditions will be readily apparent to those skilled in the art.
For most applications, washing steps that follow hybridization will also vary in stringency. Wash stringency conditions can be defined by salt concentration and by temperature. As above, wash stringency can be increased by decreasing salt concentration or by increasing temperature. For example, stringent salt concentration for the wash steps will preferably be less than about 30 mM NaCl and 3 mM trisodium citrate, and most preferably less than about 15 mM NaCl and 1.5 mM trisodium citrate. Stringent temperature conditions for the wash steps will ordinarily include a temperature of at least about 25° C., more preferably of at least about 42° C., and even more preferably of at least about 68° C. In a preferred embodiment, wash steps will occur at 25° C. in 30 mM NaCl, 3 mM trisodium citrate, and 0.1% SDS. In a more preferred embodiment, wash steps will occur at 42 C in 15 mM NaCl, 1.5 mM trisodium citrate, and 0.1% SDS. In a more preferred embodiment, wash steps will occur at 68° C. in 15 mM NaCl, 1.5 mM trisodium citrate, and 0.1% SDS. Additional variations on these conditions will be readily apparent to those skilled in the art. Hybridization techniques are well known to those skilled in the art and are described, for example, in Benton and Davis (Science 196:180, 1977); Grunstein and Hogness (Proc. Natl. Acad. Sci., USA 72:3961, 1975); Ausubel et al. (Current Protocols in Molecular Biology, Wiley Interscience, New York, 2001); Berger and Kimmel (Guide to Molecular Cloning Techniques, 1987, Academic Press, New York); and Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York.
By “substantially identical” is meant a polypeptide or nucleic acid molecule exhibiting at least 50% identity to a reference amino acid sequence (for example, any one of the amino acid sequences described herein) or nucleic acid sequence (for example, any one of the nucleic acid sequences described herein). Preferably, such a sequence is at least 60%, more preferably 80% or 85%, and more preferably 90%, 95% or even 99% identical at the amino acid level or nucleic acid to the sequence used for comparison.
Sequence identity is typically measured using sequence analysis software (for example, Sequence Analysis Software Package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison, Wis. 53705, BLAST, BESTFIT, GAP, or PILEUP/PRETTYBOX programs). Such software matches identical or similar sequences by assigning degrees of homology to various substitutions, deletions, and/or other modifications. Conservative substitutions typically include substitutions within the following groups: glycine, alanine; valine, isoleucine, leucine; aspartic acid, glutamic acid, asparagine, glutamine; serine, threonine; lysine, arginine; and phenylalanine, tyrosine. In an exemplary approach to determining the degree of identity, a BLAST program may be used, with a probability score between e−3 and e−100 indicating a closely related sequence.
Ranges provided herein are understood to be shorthand for all of the values within the range. For example, a range of 1 to 50 is understood to include any number, combination of numbers, or sub-range from the group consisting 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50.
As used herein, the terms “treat,” treating,” “treatment,” and the like refer to reducing or ameliorating a disorder and/or symptoms associated therewith. It will be appreciated that, although not precluded, treating a disorder or condition does not require that the disorder, condition or symptoms associated therewith be completely eliminated.
The term “ZnT8” is intended to refer to the (SLC30A8) gene and variants as well as products including nucleic acid and protein sequences derived therefrom. ZnT8 includes modified nucleic acid and amino acid sequences including tags for visualization for example. Examples of ZnT8 nucleic acid and protein sequences suitable for the present invention include: Homo sapiens clone SLC30A8 DNA sequence having a NCBI Accession Number KR712225.1 and Homo sapiens SLC30A8 protein sequence having a NCBI Accession Number ABQ59023.1 as examples. An example of a ZnT8 gene sequence is SLC30A8 solute carrier family 30 member 8 [Homo sapiens (human)] having an NCBI Gene ID: 169026. The ZnT8 used in the present invention may be eukaryotic including human and animal or prokaryotic including bacterial ZnT8 transporters.
Unless specifically stated or obvious from context, as used herein, the term “or” is understood to be inclusive. Unless specifically stated or obvious from context, as used herein, the terms “a”, “an”, and “the” are understood to be singular or plural.
Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. About can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from context, all numerical values provided herein are modified by the term about.
The recitation of a listing of chemical groups in any definition of a variable herein includes definitions of that variable as any single group or combination of listed groups. The recitation of an embodiment for a variable or aspect herein includes that embodiment as any single embodiment or in combination with any other embodiments or portions thereof.
Any compositions or methods provided herein can be combined with one or more of any of the other compositions and methods provided herein.
As used herein, the terms “prevent,” “preventing,” “prevention,” “prophylactic treatment” and the like refer to reducing the probability of developing a disorder or condition in a subject, who does not have, but is at risk of or susceptible to developing a disorder or condition.
Such treatment (surgery and/or chemotherapy) will be suitably administered to subjects, particularly humans, suffering from, having, susceptible to, or at risk for pancreatic cancer or disease, disorder, or symptom thereof. Determination of those subjects “at risk” can be made by any objective or subjective determination by a diagnostic test or opinion of a subject or health care provider (e.g., genetic test, enzyme or protein marker, a marker (as defined herein), family history, and the like).
The present invention is a method of detecting ZnT8 antibodies in a serum. The steps include making a mixture of proteoliposomes preferably comprising a transmembrane domain (TMD) and a cytosolic domain (CTD) of a full length ZnT8 protein on their exterior surfaces. Specifically, the methods of the present invention produce a mixture of proteoliposomes having two distinct transmembrane orientations. The “inside out” proteoliposomes place CTD sequences of full-length ZnT8 on its exterior surface. The “right side out” proteoliposomes exposed TMD sequences on its exterior surface so when this mixture of proteoliposomes are mixed with a serum antibodies targeting TMD and the CTD sequences they are able to bind to these sequences. A labelled captured autoantibody then binds to the antibodies present in the serum bound to the TMD and the CTD sequences on the “inside out” and “right side out” proteoliposomes. Finally, the amount of antibody binding to the CTD and the TMD protein sequences are measured.
It is very difficult to express CTD protein sequences on the exterior of proteoliposomes. Surprisingly the inventors were able to identify a method of producing both “inside out” and “right side out” proteoliposomes comprising a full length ZnT8, as an example. A ZnT8 protein is more antigenic in a liposome prepared by the methods of the present invention for the following reasons. Purification of multi-spanning full-length ZnT8 by conventional methods requires detergent solubilization resulting in the lack of structural stability of ZnT8 posing a major challenge to maintaining the proper folding of conformational epitopes. The harsh antigen handling procedures of conventional methods (e.g., drying, rehydration) further exacerbated the loss of bio-activity of full length ZnT8. To overcome these limitations, the inventors developed a proteoliposome-based approach that can dramatically improve the structural stability and proper folding of full-length ZnT8 in a protective lipid matrix, rendering auto-reactive sites accessible to ZnT8 with high bio-activity.
As uncovered to be a major biomarker for type 1 diabetes (T1D) diagnosis, zinc transporter 8 autoantibody (ZnT8A) has shown promise for staging disease risk and disease diagnosis. However, existing assays for ZnT8 autoantibody (ZnT8A) are limited to detection by soluble domains of ZnT8 due to difficulties in maintaining proper folding of a full-length ZnT8 protein outside its native membrane environment. The present invention, through a combination of bioengineering and nanotechnology, was developed using a novel proteoliposome-based full-length ZnT8 self-antigen (full-length ZnT8 proteoliposomes, PLR-ZnT8) for efficient ZnT8A detection on a plasmonic gold chip (pGOLD). The protective lipid matrix of proteoliposomes of the present invention improved the proper folding and structural stability of full-length ZnT8, facilitating PLR-ZnT8 immobilized on pGOLD (PLR-ZnT8/pGOLD) to achieve high-affinity capture of ZnT8A from T1D sera. PLR-ZnT8/pGOLD of the present invention resulted in efficient ZnT8A detection for T1D diagnosis with ˜76% sensitivity and ˜97% specificity (n=307), superior to assays based on detergent-solubilized full-length ZnT8 (DS-ZnT8) and C-terminal domain of ZnT8 (CTD). Multiplexed assays using pGOLD were also developed for simultaneous detection of ZnT8A, islet antigen 2 autoantibody (IA2A), and glutamic acid decarboxylase autoantibody (GADA) for T1D diagnosis by assessing the three kinds of autoantibodies combined.
The inventors have showed that a single variant of full-length ZnT8 (i.e., 325R) can be used for highly sensitive and specific ZnT8A detection on a gold plasmonic chip. Through expression in human embryonic kidney cells 293 (HEK293), purification of the monodispersed full-length ZnT8 protein and subsequent reconstitution within liposomes, a complex (˜146 nm) of full-length ZnT8 proteoliposomes (PLR-ZnT8) with high bio-activity was obtained at a high purity >95%. When immobilized on pGOLD, liposomes can maintain the proper folding of full-length ZnT8, rendering auto-reactive sites accessible to ZnT8A. Owing to the novel PLR-ZnT8 and a near-infrared (NIR) fluorescence-enhanced pGOLD platform8-13, the inventors achieved excellent assay performance of ZnT8A detection with ˜76% sensitivity and ˜97% specificity for T1D diagnosis using 307 human sera from 138 T1D patients and 169 healthy individuals. The result was superior to the performance of assays based on other ZnT8-related antigens (˜2% sensitivity/˜94% specificity and ˜59% sensitivity/˜94% specificity based on DS-ZnT8 and CTD, respectively). Further, the pGOLD-based microarray also demonstrated the potential of multiplexed detection of ZnT8A, IA2A and GADA for future T1D diagnosis.
Human ZnT8 is encoded by the SLC30A8 gene expressed in pancreatic beta-cells to produce two protein isoforms. Isoform-1 is a full-length 369-aa protein while isoform-2 is a product of alternative splicing with a 49 aa deletion from the N-terminus. The N-terminal domain of ZnT8 is largely missing in isoform-2. A major arginine variation at position 325 (325R) of human ZnT8 is an immunoreactivity determinant for ZnT8A. The inventors over-expressed the human 325R variant of isoform-2 in HEK293 cells, and purified the recombinant full-length ZnT8 in detergent micelles (DS-ZnT8) or proteoliposomes (PLR-ZnT8,
PLR-ZnT8 Immobilized on pGOLD for Efficient ZnT8A Detection
Previously the inventors developed a plasmonic gold substrate for near-infrared fluorescence enhanced (NIR-FE) biological detections, and performed a pilot study of T1D autoantibody assay using a small number of human sera and whole blood such as finger-prick samples10. Here we adopted this pGOLD (from Nirmidas Biotech. Inc) platform to evaluate the ability of PLR-ZnT8 for ZnT8A detection in hundreds of human serum samples. [COULD EXPAND THIS SECTION] For simply printed PLR-ZnT8 on a pGOLD slide, proteoliposomes presented a large number of full-length ZnT8 free of direct contact or interactions with the gold surface, efficiently maintaining the proper folding of full-length ZnT8 and thus enabling auto-reactive sites accessible to ZnT8A. The gold nano-islands structure on pGOLD were arranged in such a way that the edges of adjacent islands conformed to each other for the generation of abundant nano-gaps that supported strong electric field enhancement. This and surface plasmonic resonance coupling with NIR fluorophore excited states afforded increased radiative emission and thus fluorescence enhancement by ˜100-fold10, boosting the sensitivity of the NIR-based bio-assay. PLR-ZnT8 immobilized on pGOLD (PLR-ZnT8/pGOLD) was used to capture ZnT8A in human serum samples diluted by 20-fold with fetal bovine serum (FBS), and the captured autoantibody was subsequently labeled with NIR fluorophore-conjugated secondary antibody (i.e., anti-human IgG-IRDye800). The amounts of ZnT8A were then analyzed through the fluorescence intensity of the fluorophore (
First, the inventors participated in the 2016 Islet Autoantibody Standardization Program (IASP) workshop to evaluate the ability of PLR-ZnT8/pGOLD for ZnT8A detection. For 140 human sera from 50 T1D patients and 90 healthy individuals, PLR-ZnT8/pGOLD achieved 66% sensitivity and ˜100% specificity by blind tests. The assay performance can be adjusted to ˜76% sensitivity and ˜95% by lowering the cutoff according to the receiver operating characteristic (ROC) curve analysis (
Subsequently another set of 167 human sera from 88 T1D patients and 79 healthy individuals provided by University of Florida were combined with sera samples from IASP to form a large number of samples for further evaluation of ZnT8A detection by PLR-ZnT8/pGOLD (i.e., 307 human sera in total, including 138 T1D and 169 non-diabetic sera). With this combined serum set, our PLR-ZnT8/pGOLD assay still achieved ˜76% sensitivity and ˜97% specificity, effectively discriminating T1D samples from non-diabetic samples (
For comparison, DS-ZnT8 and CTD were also immobilized on pGOLD in parallel with PLR-ZnT8 (unless otherwise mentioned, all ZnT8 related antigens we used were the 325R variant). Under the same experimental conditions, DS-ZnT8 did not afford useful ZnT8A detection ability presumably due to the loss of structural integrity during the assay, while CTD provided ˜17% lower sensitivity than that of PLR-ZnT8 (
For simplex ZnT8A assay, compared to conventional ZnT8A detection methods (e.g., enzyme-linked immunosorbent assay18, radioimmuoassay19, electrochemiluminescence20, luciferase immunoprecipitation systems21), our PLR-ZnT8/pGOLD assay developed here demonstrated improved sensitivity and specificity (˜76% sensitivity and ˜97% specificity for 307 human serum samples), rapid assay process (˜4 h), low sample volume requirement (5 μL), and low cost (10 dollars per sample) (See Methods for detailed experimental procedures).
In addition to PLR-ZnT8, we also performed simultaneous detection of IA2A and GADA using robotically printed microarrays of IA2 (fragments encompassing 604-979 aa from Kronus Inc.) and GAD (recombinant protein from Diamyd Medical Inc.) antigens, which were two additional major biomarkers for T1D diagnosis. After incubation with 5 μL human serum diluted by 100 μL FBS, washing away excess biomolecules and labeling with anti-human IgG-IRDye800 conjugates, autoantibodies captured by corresponding antigens were quantified based on the fluorescence intensity.
For samples from IASP (i.e., 50 T1D and 90 non-diabetics sera), we obtained ˜68% sensitivity and ˜92% specificity for IA2A detection, and a relatively poor ˜50% sensitivity and ˜94% specificity for GADA detection (
ZnT8A is thought to be conformation specific, mainly recognizing the ZnT8 self-antigen in its native conformation. Purification of multi-spanning full-length ZnT8 requires detergent solubilization, but the lack of structural stability of DS-ZnT8 poses a major challenge to maintain the proper folding of conformational epitopes. The harsh antigen handling procedures (e.g., drying, rehydration) further exacerbate the loss of bio-activity when full-length ZnT8 is immobilized on pGOLD. To overcome these limitations, after a series of optimization efforts, the inventors developed a proteoliposome-based approach that can dramatically improve the structural stability and proper folding of full-length ZnT8 in a protective lipid matrix, rendering auto-reactive sites accessible to ZnT8A with high bio-activity13. Even under strict drying and rehydration experimental conditions, a majority of full-length ZnT8 in PLR-ZnT8 still remain intact, in sharp contrast to a complete loss of structural integrity of full-length ZnT8 in DS-ZnT8 under identical experimental conditions.
According to literature, the main ZnT8A detected by CTD were the ones released from beta-cells after their destruction, revealing a late stage of T1D. In this regard, the detection of ZnT8A captured by CTD can validate T1D but may lack the ability to predict T1D in the earliest stages of disease. Our results suggested that the PLR-ZnT8 may provide additional auto-reactive sites outside of CTD to capture more ZnT8A, contributing to an improved assay sensitivity. These autoantibodies are presumed to be from the extracellular matrix, which may represent the products formed in the early stages of T1D by either beta-cells or immune responses.
In sum, taking advantage of the novel structure of PLR-ZnT8, we developed an efficient microarray-based assay for T1D autoantibody detection. Proteoliposomes efficiently maintained the proper folding of full-length ZnT8, enabling ZnT8A to access auto-reactive sites. PLR-ZnT8 immobilized on pGOLD achieved ZnT8A detection performance of ˜76% sensitivity with ˜97% specificity for 307 human sera from 138 T1D patients and 169 healthy individuals, superior to those of ˜2% sensitivity with ˜94% specificity and ˜59% sensitivity with ˜94% specificity based on DS-ZnT8 and CTD, respectively. Moreover, pGOLD was also applied for multiplexed detection of other T1D-related autoantibodies, IA2A and GADA from over 300 serum samples, with outcomes of ˜71% sensitivity with ˜95% specificity and ˜40% sensitivity with ˜95% specificity, respectively; leading to an overall multiplex assay performance of ˜89% sensitivity with ˜93% specificity by assessing the three kinds of autoantibodies combined.
Our current work established proteoliposomes on pGOLD as a promising platform for ZnT8A detection with high sensitivity and specificity. A future direction is to improve GADA detection and optimize the overall performance of multiplexed assay for screening presymptomatic T1D in at-risk populations. Diagnosing the disease at earlier stages will provide safe and effective therapeutic options for prevention.
Any of the compositions described herein may be comprised in a kit. In a non-limiting example, a proteoliposome having an interior and an exterior comprising a ZnT8 protein with a cytosolic domain exposed on the exterior of the proteoliposomes, such as PLR-ZnT8, may be comprised in a kit.
The kits may comprise a suitably aliquoted of a proteoliposomes comprising ZnT8 of the present invention, such as PLR-ZnT8, and, in some cases, one or more additional agents, such as a chip or captured autoantibodies that binds to antibodies targeting ZnT8, as an examples. The component(s) of the kits may be packaged either in aqueous media or in lyophilized form. The container means of the kits will generally include at least one vial, test tube, flask, bottle, syringe or other container means, into which a component may be placed, and preferably, suitably aliquoted. Where there are more than one component in the kit, the kit also will generally contain a second, third or other additional container into which the additional components may be separately placed. However, various combinations of components may be comprised in a vial. The kits of the present invention also will typically include a means for containing proteoliposomes comprising ZnT8 of the present invention and any other reagent containers in close confinement for commercial sale. Such containers may include injection or blow-molded plastic containers into which the desired vials are retained.
When the components of the kit are provided in one and/or more liquid solutions, the liquid solution is an aqueous solution, with a sterile aqueous solution being particularly preferred. However, the components of the kit may be provided as dried powder(s). When reagents and/or components are provided as a dry powder, the powder can be reconstituted by the addition of a suitable solvent. It is envisioned that the solvent may also be provided in another container means.
The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter. The following Examples are offered by way of illustration and not by way of limitation.
Hyclone fetal bovine serum (FBS) was purchased from Fisher Chemicals. IRDye800-NHS ester was purchased from Licor Biosciences. GAD65 was purchased from Diamyd Medical and IA2 (ICA512) was purchased from Kronus Inc. Goat anti-human IgG antibody was purchased from Vector Lab. Plasmonic gold chips (pGOLD) were purchased from Nirmidas Inc. Human serum Institutional Review Board approval for this study was obtained from Stanford University. And human serum samples were provided from University of Florida and Islet Autoantibody Standardization Program (IASP). Samples were aliquoted and stored at −80° C. until processing.
Below are examples of four ZnT8 protein sequences used in the present invention. Two of them are an “a” form, and two of them are a “b” form. Both the “a” form and the “b” form have the R325W variant. The Wild Type ZnT8 protein is R325, which is based on the “a” form. The W325 form is a variant.
The 325R polymorphic variant of human ZnT8 isoform-2 was over-expressed in HEK293 cells, and purified in reconstituted proteoliposomes as described previously. Briefly, full-length ZnT8 was solubilized by n-dodecyl β-D-maltoside (DDM), partially purified via Ni-NTA affinity to a C-terminal polyhistidine tag, and then further purified by reconstitution into proteoliposomes (the lipids containing 1,2-dioleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phospho-(1′-rac-glycerol), and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine at a ratio of 2:1:1 were premixed, dried, sonicated and detergent destabilized with DDM before reconstitution of full-length ZnT8) followed by proteoliposome washing with a detergent-free assay buffer (20 mM HEPES, 100 mM NaCl, 1 mM TCEP, pH 7.0). The C-terminal domain (275-369 aa) of the 325R variant was His-tagged, over-expressed in HEK293 cells, and Ni-NTA affinity purified, followed by dialysis against the assay buffer. Purified full-length ZnT8 in proteoliposomes were suspended in the same assay buffer. Full-length ZnT8 in detergent micelles were prepared by solubilizing proteoliposomes with 0.1% DDM in the assay buffer. The purified full-length ZnT8, either in detergent micelles or proteoliposomes, was analyzed by SDS-PAGE with Coomassie blue staining.
Purified full-length ZnT8 either in detergent micelles or proteoliposomes was dried by nitrogen gas evaporation, or then kept under a vacuum for over 60 min to remove a trace amount of liquids. The completely dried full-length ZnT8 samples were rehydrated by adding ddH2O with 0.1% lauryl maltose-neopentyl glycol (LMNG) and 0.1 mM fluorescein-5-maleimide (FM), a thiol-reactive fluorescence label. Unreacted FM was removed by passing the rehydrated mixture through a desalting column pre-equilibrated with the assay buffer. The resultant LMNG-solubilized and FM-labeled full-length ZnT8 were analyzed by size-exclusion HPLC using the FM fluorescence readout to facilitate the detection of full-length ZnT8 and lipids. An aliquot of proteoliposome suspension or DS-ZnT8 in the assay buffer was HPLC-analyzed in parallel as a control.
Preparation of T1D-Related Antigens Microarray on pGOLD.
As-prepared PLR-ZnT8 (0.2 mg/mL), IA2 (0.088 mg/mL), and GAD (0.13 mg/mL) antigens were printed onto pGOLD using GeSiM Nano-Plotter 2.1. Each microarray consisted of three spots of PLR-ZnT8, IA2, and GAD antigens. ˜5 nL of antigen solution was delivered to each spot. Microarray followed a 3×3 layout. Spot diameter was ˜400 μm and the distance between each spot was ˜1000 μm. 16 identical microarrays were formed on each pGOLD. The prepared pGOLD were vacuum-sealed and stored at −20° C. before use. In a different microarray preparation process, as-prepared DS-ZnT8 and CTD were also immobilized on pGOLD under the same experimental conditions with PLR-ZnT8 for antibody detection.
The prepared pGOLD was integrated in a module in which 16 identical microarrays on each biochip were separated into 16 wells to process 16 samples. Each well was incubated with 5 μL human serum diluted with 100 μL FBS (20-fold) for 1.5 h, followed by incubation with anti-human IgG-IRDye800 conjugates at the final concentration of 4 nM diluted by FBS for 45 min. Each well was washed with washing buffer between each incubation procedure. 14 samples, together with two reference samples (one serum sample, IgG positive for GAD, and one serum sample with negative IgG binding to all T1D-related antigens) were applied to each biochip. The assay system was composed of the printed antigen array on a pGOLD slide, slide frame, buffers, plate washer and a dual-channel (700/800 nm) scanner, which can be easily deployed in clinical and public-health laboratories.
After the assay process, each biochip was scanned with a MidaScan-IR near-infrared scanner. MidaScan-IR is a dual channel (700 and 800 nm) near-infrared confocal microscope scanner for imaging tissues, cells and microarrays on standard glass or plasmonic slides. IRDye680 and IRDye800 fluorescence images were generated, and the median fluorescence signal for each channel on each microarray spot was quantified by MidaScan software. For each sample, each antigen and each channel, the average of the three median fluorescence signals for three spots was calculated and normalized by reference samples through a two-point calibration. On each pGOLD we added one T1D positive sample to be used as the reference for normalization of other samples'"'"' MFI signal to attenuate the difference caused by experimental conditions. Cutoff was determined by the ROC curve analysis. Measurements were performed three times for all values presented in this work.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.