HLA – Basics (or how to recognize “self”)

Directors’ Affairs Committee plus others (with our gratitude) Overview

• Some Definitions – MHC and HLA – Class I and Class II – Nomenclature • Class II extended haplotypes • HLA Typing Technology • HLA Immunogenicity • Solid Phase Antibody detection methods • HLA and Disease Associations • HLA and Pharmacogenetics • Review

2 Human Leukocyte Antigens

Polymorphism slide-new alleles each year

3 Major Histocompatibility Complex (MHC)

• MHC in humans is named “Human Leukocyte Antigens” (HLA) as they were first defined on the surface of peripheral blood leukocytes • HLA Class I in humans is found on virtually all nucleated cells and platelets • HLA Class II (constitutive expression) is restricted to specialized cells of the immune system (macrophages, B cells, etc.) • HLA genes are highly polymorphic

4 HLA Protein Structure CD8 Tcell cytosol • Class I is heterodimeric with a polymorphic alpha chain and a plasma membrane common beta-2 microglobulin – Alpha chain is composed of 3 TCR extra-cellular domains ( α1, α2, and α3) – α1 and α2 form a groove like structure with a floor of β α2 α1 pleated sheets and ridges of α helices CD8 – presents peptides derived from α3 β2 m internal cellular proteins to the T cell receptor of CD8 T cells. plasma membrane – involved in the immune response cytosol against intra-cellular parasites, Antigen Presenting Cell viruses and cancer

5 HLA Class I Molecule Influenza M1 A view down the peptide groove of an HLA-A2 ααα1 domain molecule ααα2 domain βββ2 microglobulin

ααα3 domain

6 HLA Protein Structure (con’t)

CD4 Tcell • Class II is also heterodimeric with cytosol

a polymorphic beta chain and a plasma membrane much less polymorphic alpha chain TCR – both chains are composed of 2 extra-cellular domains ( α1, α2, and β1, β2) β1 α1 – Together the two first domains create a peptide binding groove which presents processed peptides, from extra cellular CD4 β2 α2 proteins, to CD4+ T cells plasma membrane – involved in the immune response cytosol against extra cellular infectious agents and non-self HLA Antigen Presenting Cell molecules 7 HLA Class II Molecule HLA-A2 peptide

A view down the ααα chain groove of an HLA- DR1 molecule βββ chain

8 HLA Polymorphism

Serologic methods resolve only a small fraction of all known alleles (est. 3%) Molecular techniques have emerged as the method of choice for HLA typing, since strategies have been developed that resolve most/all known alleles and provide a tool for identification of new alleles.

CLASS I CLASS II 3,107 A alleles 1,726 DRB1 alleles 3,887 B alleles 95 DRB3,B4,B5 alleles 2,623 C alleles 54 DQA1 alleles 780 DQB1 alleles 39 DPA1 alleles 520 DPB1 alleles (status April 2015)

9 HLA Polymorphism

http://hla.alleles.org HLA Polymorphism

HLA sequences and a current list of known HLA alleles are found at the IMGT/HLA database: http://www.ebi.ac.uk/ipd/imgt/hla/

The IMGT/HLA Database provides a specialist database for sequences of the human major histocompatibility complex (HLA) and includes the official sequences for the WHO Nomenclature Committee For Factors of the HLA System.

The IMGT/HLA Database is part of the international ImMunoGeneTics project ( IMGT ).

Robinson J, Halliwell JA, Hayhurst JH, Flicek P, Parham P, Marsh SGE The IPD and IMGT/HLA database: allele variant databases Nucleic Acids Research (2015) 43 :D423-431 11 HLA Nomenclature

• Assignments are made under the auspices of World Health Organization (WHO) Nomenclature committee • Aim is to provide unique identification for: – Loci – Alleles – Haplotypes • Therefore the system must be very conservative but adaptable to change – Must not serve personal or national vanity – Nomenclature should optimize not maximize the amount of information in the code

12 HLA Nomenclature (con’t)

• Haplotype – The combination of alleles from two or more loci located on the same chromosome – Does NOT imply any linkage disequilibrium • Genotype – The combination of two haplotypes; one from each parent, inherited by an individual • Linkage Disequilibrium – Presence of two alleles that are inherited together more frequently than would be expected based on the gene frequencies

13 HLA Nomenclature (con’t) • Each allele is initially identified by a letter(s) indicating “locus” A, B, C, DR, DQ, and DP • Then identified by individual specificity e.g. A1, B27, DR8, etc. (numbered in order of discovery) – Specificities were initially defined by using antisera (antibodies) • Historically these were sera obtained from multiparous women • Initially HLA Labs maintained large banks of specific sera – Patient cells were mixed with various sera, incubated and then Complement and a vital dye were added. • If a cell had the corresponding antigen, then the antibody would bind, complement fixed and cell death ensued. • Most sera were “cross reactive” such that a technologist had to interpret results, e.g.,: One well had antibody reactive with A23, A24 (Pos); but another well with anti-A2, A23 might be negative; thus suggesting a patient typing of A24

14 HLA Nomenclature (con’t) • HLA specificities can also be determined by genetic analysis by identifying the presence/absence of the gene encoding the HLA protein. • Techniques include direct DNA sequencing, PCR using Sequence Specific Primers (SSP) and PCR using sequence specific oligonucleotide probes (SSO) – Technique specifics will be discussed later • Again the initial identification is the locus letter(s): A, B, C, etc. – To differentiate from serological identification we use an asterisk (*) and a place marker, such as: A*01, B*27, etc.

15 HLA Nomenclature (con’t)

• Class II molecular specificities are identified at the level of the gene encoding a particular chain, that is alpha or beta. But remember most of the polymorphism for Class II is in the beta chain thus common identification reflects that: DRB1*01, DQB1*02, etc. • The molecular two digit specificity is referred to as “Low Resolution” typing e.g., A*01, B*27, etc. • “High Resolution” typing are sub-specificities of the main group e.g., A*01:01, A*01:02, B*27:01, B*27:100 – Each representing a change in at least one AA

16 HLA Nomenclature (con’t) Expanded Allele Nomenclature:

Molecular Colon Typing Delimiters LOCUS Allele Level Intron “Subtype” Substitutions

Suffix to denote HLA-DRB4 *01 :03 :01 :02N changes in Expression eg N=Null Synonymous “Non- “MHC” Coding” Substitutions Antigen Level or Allele Family

17 http://hla.alleles.org/nomenclature/naming.html HLA Nomenclature (con’t)

• Quiz Question - What does the “--” (Blank) in the following typing indicate? A*01, --; B*08, --; DRB1*03, DRB1*15 • Most molecular and certainly all serological typing can NOT distinguish between a single versus a double presence of any particular allele • Given that both A*01 and B*08 are common in the N. Amer. population it is highly likely that the “real” typing is as follows: A*01, A*01; B*08, B*08; DRB1*03, DRB1*15 • Another but much, much less likely possibility is that the individual is carrying an allele that can not be detected by the specific molecular technique employed

18 HLA Nomenclature (con’t) PROBLEM: • Many registry donors have been tested by serological methods – The vast majority of these do not have good documentation of which antigens were tested for and which were not • The majority of HPC transplant candidates have been tested by molecular (DNA-based) methodologies • The nomenclature of antigens (serology) and alleles (DNA) is in some cases NOT concordant

19 HLA Nomenclature (con’t) • Quiz Question – Is this Donor/Recipient pair a good match from an HLA perspective? Donor: A19, A10; B12, B62; DR5, DR2 Recipient: A*29, A*26; B*44, B*15; DRB1*11, DRB1*15

• Answer: Maybe but possibly yes – A19 (serological) was split: A*29, *30, *31, *32, *33, *74 – A10 (serological) was split: A*25, *26, *34, *66 – B12 (serological) was split: B*44, *45 – All the others are also splits although the molecular B*15 includes the very different serological specificities B62, 63, 70, 71, 72, 75, 76 and 77

20 DRB Haplotype Variations Expressed DPA1 DPB1 DQA1 DQB1 Genes DRA Pseudo- genes

DR1, DR10 DRB1 DRB6 DRB9

DR15,16, 51 DRB1 DRB6 DRB5 DRB9 (51 ) DR11, 12, 13, 14, 3 (17,18), 52 DRB1 DRB6 DRB2 DRB3 DRB9 (52 ) DR4, 7*, 9, 53 *about 1/3 of DR7 DRB1 DRB6 DRB7 DRB8 DRB4 DRB9 (53 ) haplotypes lack an expressed DR8 DRB4 (DR53) gene DRB1 DRB9 Almost always inherited as a predictable haplotype 21 How do we do HLA typing?

Historically, HLA typing has been done at the protein level, microlymphocytoxicity test being the standard method. HLA typing at the DNA level has become the method of choice for clinical laboratories. DNA methods are more robust and reproducible and provide more information.

22 Genomic DNA: HLA-A, B or C locus

5’UTR E1 E2 E3 E4 E5 E6 E7 E8 3’UTR

PCR

SSP SSO SBT Sequence Hybridization with set of Sequencing Specific oligonucleotide probes PCR amplification corresponding to the polymorphic sites

23 PCR Amplification

The majority of molecular assays for HLA typing require the amplification of the target sequence of DNA via Polymerase Chain Reaction, or PCR. A sample of the patient’s DNA, called the template, is allowed to react with specific primers. The primers bind to the template DNA just upstream of the sequence of DNA that is intended for amplification. PCR Amplification Let’s say the DNA sequence below is located on the Major Histocompatibility Complex on the short arm of chromosome 6, at exon 2 of the –DRB1 gene. The region we want to amplify is the sequence ‘GTTTAACGGCAT’. The primer would bind immediately upstream of the target sequence. 3’ 5’ C A T G G C G T T T A A C G G C A T A C A G G G A C

Target sequence Template DNA PCR Amplification

A DNA polymerase enzyme (most frequently Taq), recognizes the primer bound to the template, and begins to add nucleotides to the 3’ end. When it reaches the end of the template, it adds a final adenine to complete the reaction.

5’Primer 3’

G T A C C G Taq C A A A T T G C C G T A T G T C C C T G A C A T G G C G T T T A A C G G C A T A C A G G G A C 3’ 5’ Target sequence Template DNA PCR Amplification

There are three major steps to PCR amplification. Once the required buffers, templates, nucleotides, polymerase, and primers have been added to a reaction tube, the temperature is raised to about 94 degrees Celsius to denature the double stranded DNA. This step is called ‘melting’.

Template DNA

Note: The template DNA shown above has been inverted. The 5’ – 3’ strand is on the bottom, and the 3’ – 5’ strand is on top.

27 PCR Amplification Next, the temperature is reduced to 50-60 degrees to allow the bind- ing of the primers to the template DNA. Two primers are needed for amplification. One binds upstream to the target sequence on the sense strand of the template, and one binds upstream to the target sequence on the antisense strand. This step is called ‘annealing’.

Template DNA

After enough time to allow for the binding of the primers (roughly 30 seconds), the temperature is raised to 72 degrees to allow the DNA polymerase to extend the primer in the step called ‘extension’. After extension, the temperature is ramped up once again to about 94 degrees, and melting occurs again.

28 PCR Amplification

The temperature is again reduced to 50-60 degrees to allow new primers to anneal to both the original template DNA, and the newly created DNA strands from the previous PCR cycle.

This is followed by another round of extension.

29 PCR Amplification The third cycle of melting, annealing, and extension produces the “short product”, a length of double stranded DNA that is the exact length of the target sequence bordered by a primer on each side. With each subsequent cycle, the short product is doubled.

Short Products

After 25 to 35 cycles are completed a single DNA template may generate over a billion target DNA short products. It is these products that are utilized in molecular assays for HLA typing.

30 HLA Typing using SSO (SSO = Sequence specific oligonucleotides)

• Using PCR and generic primers amplify large amounts of virtually all alleles (versions) of, for e.g., HLA-A • Then using heat to again separate the dsDNA into single strands (ss) • Allow these to interact with ss specific oligo- nucleotide probes bound to a solid matrix (microarray Beads) • Based on the pattern of which probes were bound deduce the HLA type of the specimen

31 PCR-SSO / Microarray Beads

1. PCR amplification 2. Denaturation

3. Hybridization 4. Labeling / Detection

32 HLA Typing using SSO

Interpretation is based on both negative and positive beads when compared against a panel of control beads

33 SSP: Sequence Specific Primers • As suggested by the name, SSP, does NOT use generic primers but rather “Sequence Specific Primers” • Therefore the only DNA that is amplified is that which matches the primers – However this technique is quite labor-intensive and unlike SSO can not be used in a “batch” mode i.e., only one sample at a time

34 DNA SSP Gel Electrophoresis

None +

35 Based on well position of positive reactions on the SSP gel, the type can be assigned

36 Sequence Based Typing

• Both alleles (one from each copy of chromo- some 6) are sequenced simultaneously • Ambiguities arise when particular allele combinations are present due to sequences in common across multiple alleles. These cis/trans ambiguities can be resolved.

37 Sequence Based Typing

38 Polymorphism: Two different nucleotides at the same position on the individual’s two different chromosomes

39 Nucleotide Base Codes

A = Adenine Polymorphisms G = Guanine • R = A + G C = Cytosine • M = A + C W = A + T T = Thymine • • S = G + C • K = G + T • Y = C + T

40 The MHC in Transplant • Allogeneic cellular response • Alloantibody response • Long-term graft survival correlated to degree of HLA antigen mismatch for both solid organ and BMT • Antigens consist of epitopes (T cell or B cell) that can trigger a cellular or humoral response

41 41 HLA-A+B+DR Mismatches Deceased Donor, First Kidney Tx, 2000-2011

CTS Collaborative Transplant Study

42 Opelz G. Transplantation 2013; 95:4-7 Even a single nucleotide/amino acid change can be immunogenic

43 43 HLA Matching & Immunogenicity

• T cell immunogenicity: A nascent science and almost non- existent with regard to HLA antigens – Likely to be the most important aspect of HLA immunogenicity in BMTx • Current knowledge is driven by vaccine development – While T cell repertoire is important, most work is looking at HLA Class I and II supertypes – HLA is extremely polymorphic (concentrated in the peptide binding region) with each variant believed to be capable of binding a unique set of peptide ligands – BUT most HLA molecules are clustered into groups (Supertypes - 12) with overlapping peptide binding specificities

44 44 HLA Matching & Immunogenicity

• With all of the above it becomes almost impossible for a transplant program to determine the best mismatch (from a group of MM donors) • Currently the best we can do is: – List the number and kind of aa MM between various alleles (within a single antigen group – See http://histocheck.org) or – Use known/suspected serological epitopes as an approximation of T cell epitopes • An important advancement in this area came with Dr. Rene Duquesnoy’s MatchMaker program (www.hlamatchmaker.net) • This program tallies the number of likely epitope (eplets - B cell) differences between different antigens and alleles

45 45 Patient is A*02:07 No exact match but …

A*02:07 vs A*02:01 A*02:07 vs A*02:03 One aa difference Four aa difference Total Dissimilarity: 1.83 Total Dissimilarity: 5.81

http://www.mh-hannover.de/institute/transfusion/histocheck/ 46 46 Knowing Structure of MHC

• Allows re-examination of the nature of the allo-immune response • Not an antigenic response • But an epitope response

• If you cannot match antigens… can you match epitopes?

47 47 HLA Matchmaker Concept

The HLA type of the antibody producer determines what structural components of an immunizing HLA antigen can be “seen” as non-self

48 Structural Basis of a HLA-B51 Mismatch

Polymorphic “Seen” by “Seen” by “Seen” by A2, A68; A2, A68; A2, A24; Residues on B51 B27, B44 B35, B44 B7, B8

49 HLA Matchmaker Concept

Matching at the Epitope Level Provides an Additional Assessment of HLA Compatibility

50 PRA - Panel Reactive Antibody - Percent Reactive Antibody

• PRA can be a qualitative and/or quantitative assessment of allo-immunization in transplant patients. PRA only reflects the breadth of the response. Optimally, PRA testing should identify the specificity of an antibody and provide the “transplantability” of a patient. • More importantly, PRA testing should correlate with (i.e:, Predict ) the final crossmatch.

51 Bead Based PRA

• Antibodies to HLA (actual not putative as in cell-based assay) are detected by a panel of beads each with its own fluorometric signature • Commercially available beads with bound HLA molecules from more than 50 different cell lines covering the range of typical N. American donors • Antibodies are detected using fluorescent labeled second antibody • Can now perform the equivalent of a 50 cell PRA for any individual within one week • Software can also assist in identifying antibody specificities

52 PRA – Bead Based

Sample Number: 08-151553 Session Number: 2008-02-29-I-ID %PRA: 34 34% Lot ID: 111507-LMI Draw Date: 2/26/2008 Expiration Date: 11/7/2008 Patient HLA Type: A26,30; B13,38 Negative Controls: 128, 95, 229.5, 142 Reviewer: ______Positive Control: 13558.5

Bead DonorID AdjVal1 AdjVal2 AdjVal3 AdjValC Assigned Raw Val Class I Antigens

148 432 45.82 60.22 23.17 33.02 Positive 6182 A2 A36 B7 B72 Bw6 Cw2 Cw7 142 372 43.26 57.06 21.79 30.69 Positive 5900 A2 A23 B35 B61 Bw6 Cw15 Cw4 154 633 42.52 55.66 21.06 29.74 Positive 5824 A2 A23 B63 B65 Bw4 Bw6 Cw16 Cw8 139 404 41.87 54.6 20.32 29.02 Positive 5778 A2 A24 B51 B52 Bw4 Cw1 Cw12 144 215 40.51 52.75 19.51 27.52 Positive 5586 A2 A3 B50 B57 Bw4 Bw6 Cw18 Cw6 161 587 37.54 49 18.37 25.92 Positive 5159 A68 A74 B42 B57 Bw4 Bw6 Cw17 Cw7 113 2BW 36.56 47.87 17.95 25.58 Positive 4998 A2 A3 B13 B56 Bw4 Bw6 Cw1 Cw6 166 850 35.22 45.88 16.7 24.03 Positive 4895 A2 A24 B27 B44 Bw4 Cw1 Cw5 136 44DFW 34.41 45 16.53 23.75 Positive 4776 A2 A25 B44 B47 Bw4 Cw16 Cw6 152 258 32.43 42.41 15.6 22.26 Positive 4519 A11 A68 B18 B38 Bw4 Bw6 Cw4 Cw6 157 765 31.98 41.64 15.36 21.7 Positive 4452 A24 A68 B39 B55 Bw6 Cw3 Cw7 155 79LB 31.08 40.44 14.84 21.2 Positive 4300 A2 A33 B49 B71 Bw4 Bw6 Cw3 Cw7 147 247 19.94 25.16 8.62 12.41 Positive 2896 A1 A69 B35 B8 Bw6 Cw12 Cw7 133 17LB 13.32 16.25 4.41 6.51 Positive 2087 A1 A6602 B52 B58 Bw4 Cw12 Cw7 162 480 3.66 3.61 -0.34 -0.46 Positive 819 A29 A3 B58 B7 Bw4 Bw6 Cw7 138 60LB 1.82 0.97 -1.74 -2.41 Positive 589 A33 B49 B58 Bw4 Cw7 129 397 1.31 0.48 -1.4 -2.22 Positive 506 A3 A34 B57 B71 Bw4 Bw6 Cw3 Cw7 128 103 -0.17 -2.44 -3.29 -4.59 Negative 376 A24 A29 B37 B7 Bw4 Bw6 Cw6 Cw7 149 416 -0.27 -1.74 -2.37 -3.92 Negative 332 A29 A33 B78 B81 Bw6 Cw16 Cw18 124 531 0.24 -1.2 -2.11 -2.76 Negative 320 A34 A80 B18 B53 Bw4 Bw6 Cw2 Cw6 114 109 -0.7 -2.77 -3.47 -4.57 Negative 303 A31 A33 B35 B46 Bw6 Cw1 Cw4 165 206 -0.82 -2.29 -2.9 -3.95 Negative 285 A3 A74 B45 B8 Bw6 Cw16 Cw7 PRA can be calculated automatically Antibody identification is interpreted from the results 53 Class I: 100% PRA

Specificity???

54 Single Antigen Bead Assay Specificity: A2,68,69 B8,13,15,18,35,37,39,40,41, 42,44,45,47,51,52,53,54,58, 78,81,82 Include?: B27,48,49,50,55, 57

How to Report Allele Specific Antibodies?

55 Calculated PRA (cPRA)

• With Single Antigen Bead Testing we can identify the antibodies a patient has, but we can no longer have a measured PRA • However if PRA is “Percent Reactive Antibody” with a panel of cells (or beads) representative of the donor population to give a measure of “transplantability” then: • Knowing both the antibodies in a patient and the HLA typing of actual donors locally, regionally, or even nationally then we can Calculate the PRA by asking how many of these previous donors would this patient have had antibodies to? i.e. Calculated PRA cPRA calculator http://optn.transplant.hrsa.gov/resources/allocationcalculators.asp 56 Antigenic Structure of HLA

• Serologically defined epitopes that were originally thought to occur on only one gene product such as HLA-A2 were referred to as “ Private Epitopes ” • Other anti-HLA antibodies that reacted with more than one gene product, e.g., anti-HLA A2, A9, and A28, were thought to detect a shared or cross reactive epitope, termed “ Public Epitope ” • Antibodies to public epitopes have been used to categorize HLA molecules into major Cross Reactive Groups (CREG’s) – Each CREG can contain more than one Public Epitope

57 Same Donor - Different Patients

Immunizer Patient Antibody A1, 24; B27, 57 A2 A2, 28 A2, 2; B27, 27 A24, 28; B27, 57 A2

A1, 3; B27, 51 A2 A2, 28 A2, 28, 24 A2, B57

2C CREG = A2; A9 (23, 24); A28 (68, 69); B17 (57, 58) 58 “New” Issues in Antibody Nomenclature

• Reminder: Class II HLA antigens are comprised of two different polypeptides – the alpha and beta chains – each coded for by different polymorphic genes • Anti-HLA antibodies were thought to have been directed to the more polymorphic beta chain were named accordingly • Thus anti-DQ2 antibodies are reactive with antigens containing DQB1*02 proteins

59 “New” Issues in Antibody Nomenclature (continued)

• BUT some antibodies are highly specific for the alpha chain • So for example: Patient is: DQB1*02:01 with DQA1*02:01 while the donor is: DQB1*02:01 with DQA1*05:01 • And the patient has “anti-DQ2” antibodies but which are reactive exclusively with the alpha “05:01” • There is NO STANDARD Nomenclature with which to identify such antibodies!

60 HLA Testing for other Clinical Purposes

• Disease Risk Assessment

• Pharmacogenomics

• Immunotherapy

• Infectious Disease Vaccines

• Tumor Vaccines

61 HLA Association with Disease Risk Certain diseases have a strong association with certain HLA types. Examples include:

• HLA-B27: Ankylosing Spondylitis and Acute Anterior Uveitis • HLA-A29: Birdshot Retinopathy • HLA-B51: Behçet's Disease • HLA-Cw6: Psoriasis • HLA-DQ2,8: Celiac Disease • HLA-DR15,DQ6: Narcolepsy • HLA-DR3,4-DQ2,8: Diabetes • HLA-DR4: Rheumatoid Arthritis

62 HLA Association with Narcolepsy

• Our knowledge evolving over the years:

• HLA-DR2-DQ1

• HLA-DR15-DQ6

• HLA-DRB1*15:01-DQB1*06:02

• HLA-DQA1*01:02-DQB1*06:02

63 HLA Association with Celiac Disease

Our knowledge evolving over the years:

• HLA-A1

• HLA-A1/B8/DR3

• HLA-DR3/DQ2

• HLA-DQ2 and DQ8

64 HLA Association with Celiac Disease

• Association with: HLA-DQ2 and HLA-DQ8 usually with the “DQ2 cis” heterodimer: DQA1*05, DQB1*02 coded on a DRB1*03:01 (DR17) haplotype but can be “trans”: DQA1*05 coded on a DRB1*11, DRB1*12 or DRB1*13 haplotype and the DQB1*02 coded on a DRB1*07 haplotype • The risk with DQ8 haplotype is usually: DQA1*03 with DQB1*03:02 coded on a DR4 haplotype

65 HLA and Pharmacogenetics

• Severe allergic or hypersensitivity reaction to drugs – Stevens-Johnson Syndrome (SJS) – Toxic Epidermal Necrolysis (TEN)

• Association between allergy or hypersensitivity to a medication and HLA type

• HLA typing allows risk stratification of the patients

66 Drugs Associated with Hypersensitivity Reactions

• Antiepileptic agents: Carbamazepine, Phenytoin, Phenobarbital, Lamotrigine

• Allopurinol

• Nevirapine

• Anti-inflammatories in oxicam family

• Sulfonamides

67 HLA and Drug Adverse Reactions

• HLA-B*57:01 hypersensitivity to Abacavir

• HLA-B*15:02 carbamazepine induced SJS or TEN

• HLA-B*58:01 allopurinol induced SJS or TEN

• HLA-DRB1*01 hypersensitivity to nevirapine

• HLA-DRB1*07 ximelagatran induced hepatotoxicity

68 HLA and Vaccine Development

• Vaccines producing cellular immunity require peptide HLA binding • Cancer cells can express “tumor specific antigens” • Infectious disease agents have immunogenic peptides • Vaccine trials use peptides binding to common HLA alleles (e.g., A*02:01) • After proof of principal, trials include peptides binding to other HLA alleles

69 Review and Conclusions

• MHC = Major Histocompatibility Complex which in humans is called the “human leukocyte antigens” • Class I: A, B, and C; Class II: DR, DQ, and DP – Highly polymorphic and co-dominantly expressed • Nomenclature: letter designating the locus and a number designating specificity – Low resolution: one field; High resolution: two or more fields separated by colons – Differences in serological vs molecular designations • Typing can be done serologically or molecularly • Antibody Identification is critical in the proper interpretation of PRA • HLA typing to help diagnosis of certain diseases • HLA typing to help prevent adverse drug reactions

70