A monospecific HLA-B27 fluorescein isothiocyanate-conjugated monoclonal antibody for rapid, simple and accurate HLA-B27 typing

Developments and recent advancements in the field of endogenous amino acid selective bond forming reactions for bioconjugation

Bioconjugation methodologies have proven to play a central enabling role in the recent development of biotherapeutics and chemical biology approaches. Recent endeavours in these fields shed light on unprecedented chemical challenges to attain bioselectivity, biocompatibility, and biostability required by modern applications. In this review the current developments in various techniques of selective bond forming reactions of proteins and peptides were highlighted. The utility of each endogenous amino acid-selective conjugation methodology in the fields of biology and protein science has been surveyed with emphasis on the most relevant among reported transformations; selectivity and practical use have been discussed.

Application of a Simple In-House PCR-SSP Technique for HLA-B* 27 Typing in Spondyloarthritis Patients

Background. Microlymphocytotoxicity (MLCT) and flowcytometry (FC) are the conventional serological methods to detect HLA-B* 27. Due to some disadvantages in these methods, most of the HLA laboratories have now switched over to molecular methods. Molecular techniques based on commercial kits are expensive; as such many laboratories with limited funds in developing countries cannot afford these techniques. Aims. Our main aim was to standardize a simple inexpensive in-house PCR-SSP technique for HLA-B* 27 typing. Materials and Methods. Sequence Specific primers were designed to amplify all the subtypes of B* 27 using IMGT-HLA sequence database. Accuracy was checked by retyping of 90 PCR-SSOP typed controls. Results. The presence of 149 bp specific band with control band on 2% agarose gel showed B* 27 positivity. No discrepancies were found when compared with PCR-SSOP results. The frequency of HLA-B* 27 was found to be significantly increased (68.75% versus 4.40%, O.R 46.909: P value 6.62E − 32) among 700 SpA patients as compared to controls. Clinically, 54% of patients had polyarticular arthritis with SI joints involvement (68%) and restricted spine flexion (60%). Conclusion. In-house PCR-SSP technique is very simple and inexpensive technique to detect B* 27 allele, which was strongly associated with SpA patients from Western India.

Long-term stabilized blood samples as controls for flow cytometric HLA-B27 screening: a feasibility study

BACKGROUND

Long-term stabilized blood samples are potentially useful as positive or negative procedure controls for flow cytometric HLA-B27 screening, and could serve as test samples in an external quality assessment (EQA) scheme. We evaluated long-term stabilized whole blood specimens as prepared for the UK NEQAS for Leucocyte Immunophenotyping EQA scheme (Sheffield, UK).

METHODS

Peripheral blood samples were obtained from nine blood bank donors with known HLA-B typing. Short-term stabilization with Trans-FIXtrade mark was performed before shipment to Sheffield. Thereafter, long-term stabilization was performed. Commercially available HLA-B27 mAb were tested periodically between 1 week and 12 months on (i) fresh, (ii) short-term stabilized, and (iii) long-term stabilized blood samples using a stain, lyse, and wash technique. We compared the forward scatter (FSC), sideward scatter (SSC), and fluorescence signals of lymphocytes as a function of time. Furthermore, a pilot send-out with stabilized blood samples of four blood bank donors was distributed among the participants to the Benelux EQA scheme for HLA-B27 screening, and results were compared with historical EQA data obtained using nonstabilized blood samples from the same donors.

RESULTS

There were no major effects on FSC and SSC characteristics of lymphocytes. Background fluorescence of stabilized samples increased and specific fluorescence of stabilized HLA-B27 positive samples decreased as compared with fresh samples. However, discrimination between the investigated HLA-B27 positive and HLA-B27 negative samples remained feasible poststabilization. In the pilot send-out, the results obtained with stabilized samples were less concordant than with the corresponding fresh samples due to variable quality of the stabilized samples.

CONCLUSION

Long-term stabilized whole blood samples are potentially useful as true HLA-B27 positive and true HLA-B27 negative control cells for daily and longitudinal quality control of flow cytometric HLA-B27 screening. In the same way, long-term stabilized samples may be used for EQA purposes. However, these samples are currently not feasible for reagent validation purposes. Extensive quality control of long-term stabilized samples is necessary before distribution in multicenter surveys.

A high-resolution polymerase chain reaction-sequence-specific primer HLA-B*27 typing set and its application in routine HLA-B27 testing

We designed a set of 35 polymerase chain reaction sequence-specific primers (PCR-SSP) in 29 SSP mixtures to assign 29 HLA-B*27 4-digit level alleles (B*2701-B*2721 and B*2723-B*2730). This was used in conjunction with our 41 PCR-SSP primer mixture low-resolution HLA-B typing set to fully differentiate B*27 from all other HLA-B alleles. Successful typing set validation used 521 B*27 samples covering 13 (B*2701-B*2710 and B*2712, B*2717, B*2723) alleles. The distribution of B*27 alleles was determined in a random population of 4020 local blood donors and the use of PCR-SSP B*27 typing in our routine flow cytometry-based HLA-B27/B2708 typing strategy is described.

HLA-B27 testing in Thai patients using the PCR-SSP technique

We develop the HLA-B27 test kit using the PCR-SSP technique. Five hundred forty blood samples were tested for HLA-B27 by microlymphocytotoxicity test (LCT) and PCR-SSP. It was found that 127 (23.5%) and 134 (24.8%) of these samples were positive for HLA-B27 by LCT and PCR-SSP, respectively. The sensitivity and specificity of the PCR-SSP were 94.8 and 100%, respectively, when using LCT as the standard method. The PCR-SSP positive predictive value was 100%, negative predictive value was 98.3%, and a concordance rate of 98.7%. This study shows that the PCR-SSP is simple, convenient, and a more cost-effective in-house test kit.

Flow cytometric HLA-B27 screening: cross-reactivity patterns of commercially available anti-HLA-B27 monoclonal antibodies with other HLA-B antigens

BACKGROUND

Some 50 clinical laboratories in the Benelux perform flow cytometric HLA-B27 screening and participate in the Benelux external quality assessment scheme operational since 1995. Results from this scheme indicate that cross-reactivity of HLA-B27 monoclonal antibodies (mAbs) is a major problem.

METHODS

We analyzed cross-reactivity patterns of commercially available mAbs for HLA-B27 screening. Three clones of HLA-B27 mAb (ABC-m3, n = 3; FD705; and GS145.2) from five manufacturers were evaluated. Test cells were selected as to express HLA-B antigens with known serologic cross-reactions (HLA-B7, B12, B13, B16, B17, B22, B37, B40, B41, B42, B47, and B48). Cells without B27 cross-reactive antigens (B5, B8, B14, B15, B21, and B35) and cells positive for B27 were included as controls. All tests were performed and interpreted as recommended by the manufacturers. Cross-reactivity was defined as increased fluorescence intensity in comparison with the baseline reactivity observed with the corresponding immunoglobulin G isotype control mAb.

RESULTS AND CONCLUSIONS

All mAbs tested showed cross-reactivity, ranging from weak (+/-) to strong (+), with different antigens and different degrees of intensity-ABC-m3: (+/-) B12, B16, B17, B41, B47, and B48 and (+) B7, B13, B22, B37, B40, and B42; GS145.2: (+/-) B13, B17, B22, B40, and B47 and (+) B7, B16, B37, B42, and B48; FD705: (+/-) B12, B13, B16, and B48 and (+) B17, B37, and B47. If one mAb had been used for HLA-B27 screening, ABC-m3 would have yielded nine false-positive B27 assignments, FD705 would have yielded seven, and GS145.2 would have yielded two. This problem largely canbe avoided by the combined use of two different mAb clones. The combination of FD705 and GS145.2 yielded the best results, with one false-positive HLA-B27 assignment among the 99 HLA-B27(-) samples of this highly selected panel.

Monocytes that have ingested Yersinia enterocolitica serotype O:3 acquire enhanced capacity to bind to nonstimulated vascular endothelial cells via P-selectin

Reactive arthritis is usually a self-limiting polyarthritis which develops after certain gastrointestinal or urogenital infections. Microbial antigens found in the inflamed joints are thought to play a key role in the development of this disease. It is not known how antigens of the pathogenic organisms migrate from the mucosal tissues into the joints. The data presented here show that mononuclear phagocytes which mediate the dissemination of several intracellular pathogens acquire an enhanced capacity to bind to nonstimulated vascular endothelial cells after phagocytosis of Yersinia enterocolitica O:3, one of the causative organisms of reactive arthritis. The increased binding to previously nonstimulated endothelial cells was mediated by P-selectin, whose translocation to the endothelial cell surface was induced by monocytes with intracellular Yersinia bacteria. These results suggest that mononuclear phagocytes may be responsible for the dissemination of bacterial antigens and the initiation of the joint inflammation in reactive arthritis.

HLA-B27 phenotyping with flow cytometry: further improvement by multiple monoclonal antibodies

To establish the optimal flow cytometric method for HLA-B27 phenotyping, we compared several strategies, using three monoclonal anti-B27 antibodies (from the HLA-ABC-m3, GS145.2, and FD705 clones). We used a triple-color direct immunofluorescence assay, including a T-lymphocyte-specific antibody as an internal control and an anti-HLA-Bw4 antibody. Blood samples from >400 subjects were tested. From ROC curve analysis none of the three antibodies appeared to be suitable for use as a single typing reagent. The efficiency of the test was affected by cross-reactions with other HLA antigens, notably the HLA-B7 antigen. Preincubation with anti-B7 serum efficiently inhibited this cross-reaction and raised the test efficiency considerably. We concluded that none of the anti-B27 antibodies investigated is suitable for use as a single typing reagent. Additional typing of Bw4 is not valuable, whereas inhibition of cross-reactions due to the B7 antigen will considerably improve the performance of the test. We recommend that two different monoclonal anti-B27 antibodies be used for accurate and reliable HLA-B27 phenotyping with flow cytometry.

Yersinia enterocolitica serotype O:3 alters the expression of serologic HLA-B27 epitopes on human monocytes

The expression of serologic HLA-B27 epitopes on leukocytes of patients with reactive arthritis or ankylosing spondylitis has been shown to be modified in the course of the disease. The purpose of this work was to study whether phagocytosis of arthritis-triggering microbes in vitro alters the expression of HLA-B27 molecules on human antigen-presenting cells and to characterize the underlying mechanisms. Human monocytes and HLA-B27- or HLA-A2-transfected human U-937 cells were exposed to Yersinia enterocolitica serotype O:3. The expression of different epitopes of HLA-B27 was monitored by using immunofluorescence, and their synthesis was determined by quantitative immunoprecipitation. Our results show that phagocytosis of Y. enterocolitica serotype O:3 changed the expression of serological HLA-B27 epitopes. This was due to the reduced synthesis of HLA-B27 molecules. The expression of especially the epitopes which depend on the presence of peptides in the antigen-binding groove was changed. The expression of the ME1 epitope, which has been shown to be important for T-cell recognition in patients with reactive arthritis, was decreased. Down-regulation of epitopes important for the T-cell recognition may impair the elimination of arthritis-triggering microbes and lead to persistent infection. In addition, Y. enterocolitica serotype O:3 seemed to alter the repertoire of peptides presented by the HLA-B27 molecules on human monocytes. This may have a role in the pathogenesis of reactive arthritis via an autoimmune mechanism.

Automated routine HLA-B27 typing by flow cytometry

An increasing demand for HLA-B27 typing as one of the tests used in the diagnosis of ankylosing spondylitis had led us to develop a rapid, automated, flow cytometric assay using whole blood and an HLA-B27 specific monoclonal antibody FD705. This article shows the data from 2093 samples tested during a 2 year period of routine HLA-B27 typing. 21.6% were clearly HLA-B27 positive whilst 73.2% were HLA-B27 negative, the remaining 5.2% required further testing before assignment of HLA-B27 status. Additional work was carried out on blood samples from individuals positive for the newly described subtype HLA-B2708.

Discrimination of HLA-B27 alleles by group-specific amplification followed by solid-phase sequencing

HLA-B27 is known to be highly associated with ankylosing spondylitis. Until now, nine B27 subtypes have been sequenced and may contribute in different fashions to ankylosing spondylitis. Additionally, the divergent subtypes may be of clinical importance in bone marrow transplantation with alternative donors. The purpose of this study was to determine the different subtypes of HLA-B27 by a direct sequencing approach. The typing strategy is based on a group-specific amplification of the second and third exon followed by automated fluorescence sequencing of the polymorphic regions. The extensive sharing of sequence motifs between the different B alleles made it impossible to specifically amplify the B27 group under the precondition of including all sequence variations necessary for a postamplification specificity step. Therefore, for setting up a direct sequencing approach of B27, co-amplified B alleles had to be taken into account. In order to get unambiguous sequencing chromatograms without any heterozygous positions, nested sequencing primers were used which selectively matched sequence motifs only present in the second and third exon of the amplified B27 alleles. This strategy allowed in all cases investigated a clear separation of the haplotypes, revealing unequivocal sequencing results. Using this method, we have investigated 93 B27-positive individuals. Sequencing identified the alleles B*2702, 2703, 2704, 2705, and 2707. B*2701, 2706, 2708, and 2709 were not represented in the population studied.

HLA-B27 screening by flow cytometry

A flow cytometric assay for lymphocyte HLA-B27 expression using a two-color direct immunofluorescent assay was compared to traditional microlymphocytotoxicity testing on 209 clinical samples. For the flow cytometric assay, whole blood was mixed with a monoclonal anti-B27 conjugated to fluorescein-isothiocyanate (FITC) and anti-CD3 conjugated to phycoerythrin (PE). The samples were analyzed with flow cytometry by gating on CD3 positive events and anti-B27 staining intensity was evaluated as median channel fluorescence of the histogram peak. The median channel fluorescence was least with B27 negative and B7 negative samples (84 +/- 17), intermediate with samples that were B27 negative but B7 positive (118 +/- 13), and greatest with samples that were B27 positive (155 +/- 13). In addition to cross-reactivity with the B7 antigen (n = 38), the monoclonal anti-B27 cross-reacted with HLA-B37 positive samples (n = 3) and HLA-B39 positive samples (n = 3). Using a median channel fluorescence cutoff of 136, 39 of the 40 B27 positive samples gave positive results in the flow cytometric assay for a sensitivity of 97.6%. The specificity was 95.9% with 7 false positives of 169 B27 negative samples. The flow cytometric HLA-B27 assay is a convenient, useful screening test. For greatest specificity, samples positive by flow cytometry should be confirmed by conventional microlymphocytotoxicity or by use of other monoclonal antibodies directed against B27.

Comparison of monoclonal antibodies for flow cytometric analysis of HLA-B27 antigen

HLA-B27 is an antigen associated with the disease ankylosing spondylitis. Ninety percent of Caucasians with ankylosing spondylitis possess the HLA-B27 antigen. However, only 20% of Caucasians with the HLA-B27 antigen will develop the disease. Defining the presence or absence of the HLA-B27 antigen can be helpful in differentiating ankylosing spondylitis from juvenile rheumatoid arthritis. In this study, we evaluated the application of two monoclonal antibodies (MoAbs), using flow cytometric analysis for the detection of HLA-B27 antigen. After an initial comparison of HLA-B27 analysis by flow cytometry to the standard microlymphocytotoxicity assay, cutoffs were established to differentiate HLA-B27 positive from HLA-B27 negative. One MoAb showed very reliable results with > 99% accuracy in discriminating HLA-B27 positive from HLA-B27 negative samples. Various parameters were investigated to obtain the optimum results and showed that incubation time, reagent lot, and the flow cytometric instrument can affect the results. We concluded that a reliable MoAb and flow cytometry are valuable for the rapid and inexpensive determination of HLA-B27 typing in the clinical setting. However, testing conditions can affect the accuracy of results; therefore, adequate parallel testing in various conditions must be performed in order to establish the proper standards.

Automated HLA-B27 testing using the FACSPrep/FACScan system

Tissue typing can help in the diagnosis of the seronegative arthropathy ankylosing spondylitis. Using an automatic sample preparation system and flow cytometry (FACSPrep/FACScan) we have developed a test for HLA-B27 screening using whole blood which is both rapid, reproducible, and permits simultaneous screening of large numbers of samples. We have used both indirect (248 cases) and direct (126 cases) monoclonal antibody staining techniques. Results were assessed using median channel shift (CS) from the negative control and relative fluorescence intensity. There is known cross-reactivity between HLA-B27 and HLA-B7 with the monoclonal antibody (MoAb) HLA-ABC-m3. Using this antibody and indirect staining, HLA-B7 samples had a significantly lower CS value than HLA-B27 samples. In 60% of these cases there was a clear distinction between HLA-B27 and HLA-B7. All HLA-B27 and HLA-B7 negative samples had a CS of 0 (P < 0.001). Using direct dual staining with CD3 and HLA-B27, all HLA-B27 and HLA-B7 negative samples had a low CS value (15 maximum), HLA-B7 samples had an intermediate CS value (20-85), and HLA-B27 samples had the highest CS values (70 upward). This system permits large scale rapid negative screening of samples with the elimination of over 60% as negatives (CS < 15). Limitations as a definitive test for HLA-B27 are due to MoAb cross-reactivity with HLA-B7 which necessitates other confirmatory techniques. The substitution of the HLA-ABC-m3 with the recently available HLA-B27 specific MoAb FD705 would substantially increase the value of this technique for routine HLA-B27 typing.

Utilization of commercial antisera and flow cytometry in HLA-B27 typing

The study of large groups of individuals (from reactive arthritis epidemics, for example) for epidemiologic and genetic data has been hampered by the techniques by which HLA typing is performed. Microlymphocytotoxicity is costly not only in materials but also in the time required to perform a given assay and thus does not lend itself to large scale testing. To study such epidemics, in the best way, one must be able to respond as soon as possible after the epidemic is recognized and on a large scale. We thus examined HLA-B27 typing by flow cytometry and commercially available monoclonal antibodies. Two commercially available monoclonal HLA-B27 antibodies were compared. We conclude that the utilization of monospecific HLA-B27 antibodies and flow cytometry allows for the determination of HLA-B27 and HLA-B7 phenotype of a large number of individuals over a short period of time, thereby making the study of a large group both economical and feasible.