Frozen platelet plates for platelet antibody detection and cross-match

Frozen Platelets-Development and Future Directions

Storage requirements and outdating of platelets represent a continued challenge for blood banks. These hurdles are confounded for rural area hospitals or in military deployments. Over 60 years of research and development into frozen platelets have generated a stable and reproducible product. Valeri's method to freeze platelets in 6% dimethyl sulfoxide (DMSO) and storage at -80°C allows for long-term storage alleviating burdens placed on blood banks. Clinical studies show that frozen platelet transfusions are safe with no related thrombotic or other serious adverse events. There are ongoing efforts to demonstrate cryopreserved platelet (CPP) superiority in efficacy studies designed in trauma or cardiac surgery patients. Technical advances in CPP manufacturing including closed system manufacturing, applications of pathogen reduction technology and potency standard characterization add to the appeal of CPP as an alternative to traditional liquid-stored platelets (LP) in settings of supply shortages, mass casualty, active bleeding, rapid provision of HLA-compatible platelets, and remote care.

Flow cytometric human leukocyte antigen-B27 typing with stored samples for batch testing

Background

Flow cytometry (FC) HLA-B27 typing is still used extensively for the diagnosis of spondyloarthropathies. If patient blood samples are stored for a prolonged duration, this testing can be performed in a batch manner, and in-house cellular controls could easily be procured. In this study, we investigated various methods of storing patient blood samples.

Methods

We compared four storage methods: three methods of analyzing lymphocytes (whole blood stored at room temperature, frozen mononuclear cells, and frozen white blood cells [WBCs] after lysing red blood cells [RBCs]), and one method using frozen platelets (FPLT). We used three ratios associated with mean fluorescence intensities (MFI) for HLAB27 assignment: the B27 MFI ratio (sample/control) for HLA-B27 fluorescein-5-isothiocyanate (FITC); the B7 MFI ratio for HLA-B7 phycoerythrin (PE); and the ratio of these two ratios, B7/B27 ratio.

Results

Comparing the B27 MFI ratios of each storage method for the HLA-B27+ samples and the B7/B27 ratios for the HLA-B7+ samples revealed that FPLT was the best of the four methods. FPLT had a sensitivity of 100% and a specificity of 99.3% for HLA-B27 assignment in DNA-typed samples (N=164) when the two criteria, namely, B27 MFI ratio >4.0 and B7/B27 ratio <1.5, were used.

Conclusions

The FPLT method was found to offer a simple, economical, and accurate method of FC HLA-B27 typing by using stored patient samples. If stored samples are used, this method has the potential to replace the standard FC typing method when used in combination with a complementary DNA-based method.

A novel assay for the detection of anti-human platelet antigen antibodies (HPA-1a) based on peptide aptamer technology

BACKGROUND

Neonatal alloimmune thrombocytopenia is mostly due to the presence of maternal antibodies against the fetal platelet antigen HPA-1a on the platelet integrin GPIIb-IIIa. Accurate detection of anti-HPA-1a antibodies in the mother is, therefore, critical. Current diagnostic assays rely on the availability of pools of human platelets that vary according to donors and blood centers. There is still no satisfactory standardization of these assays.

DESIGN AND METHODS

Peptide aptamer was used to detect and identify HPA-1a-specific antibodies in human serum that do not require human platelets. A peptide aptamer library was screened using an anti-HPA-1a human monoclonal antibody as a bait to isolate an aptamer that mimics the human platelet antigen HPA-1a.

RESULTS

This is the first report in platelet immunology of the use of a peptide aptamer for diagnostic purposes. This assay gives better results than the MAIPA currently in use, detecting around 90% of the expected alloantibodies.

CONCLUSIONS

This assay could help define a standard for the quantitation of anti-HPA antibodies. This report also demonstrates that peptide aptamers can potentially detect a variety of biomarkers in body fluids; this is of particular interest for diagnostic purposes.

Platelet transfusions

Ever since platelet transfusions were shown to reduce mortality from haemorrhage in patients with acute leukaemia in the 1950s, the use of this therapy has steadily grown to become an essential part of the treatment of cancer, haematological malignancies, marrow failure, and haematopoietic stem cell transplantation. Today, more than 1.5 million platelet products are transfused in the USA each year, 2.9 million products in Europe. However, platelet transfusion can transmit infections and trigger serious immune reactions and they can be rendered ineffective by alloimmunisation. There are several types of platelet components and all can be modified to reduce the chances of many of the complications of platelet transfusion. Transfusion practices, including indications for transfusion, dose of platelets transfused, and methods of treating alloimmunised recipients vary between countries, and even within countries. We review commonly used platelet components, product modifications, transfusion practices, and adverse consequences of platelet transfusions.

Flow-cytometric screening of platelet antibodies with previously frozen cells

In this study the flow-cytometric crossmatch results were compared between fresh cells and cells processed by various cryopreservation and storage methods. Platelets from healthy donors were incubated with 12 sera containing platelet reactive antibodies as well as with 62 control sera from blood donors. Direct comparisons were made between fresh platelets and platelets after freezing at -28 degrees C, -40 degrees C and -80 degrees C and in liquid nitrogen, using 6% DMSO as cryoprotectant. In addition, the effects of using controlled-rate freezing were evaluated. Finally we evaluated the application of the cryoprotectant ThromboSol. The best results were obtained after cryopreservation of the platelets with ThromboSol at -80 degrees C with controlled cooling rates. Using ThromboSol cryopreserved platelets, the sensitivity for the detection of incompatible platelets was 100% and the specificity was 97.1%, using the previous results obtained with flow-cytometry, MAIPA and LCT as a reference.

CONCLUSION

Platelets can be frozen using ThromboSol as the cryoprotectant, with controlled rate freezing and storage at -80 degrees C for the screening of platelet antibodies and for flow-cytometric crossmatch procedures. This system yields a reproducible and logistically simple method for platelet crossmatching that yields results superior to fresh cells and can be easily incorporated into standard clinical laboratory practices.

Refractoriness to platelet transfusion

This review discusses the causes of refractoriness to platelet transfusions and presents three options for its management. Platelet refractoriness is a complication of platelet transfusion that affects variable proportions of patients, mostly depending on their diagnosis, previous immunologic stimuli, and type of blood products used for transfusion. A large recent study showed that platelet refractoriness develops in 13% of patients with acute leukemia transfused with traditional blood products and in 3 to 4% of recipients of white cell-reduced blood components. Options to manage platelet refractoriness include platelets from HLA-typed donors, platelet cross-matching, and the antibody specificity prediction method. The selection of the most convenient approach depends on local skills and the available economic and organizational resources. Finally, emerging concepts are presented which could impact the management of platelet refractoriness.

Monoclonal anti-D specificity and Rh D structure: criteria for selection of monoclonal anti-D reagents for routine typing of patients and donors

The Rh blood group system is the next most important to the ABO system in terms of its clinical significance in blood transfusion. It is vital to the safe, efficient practice of transfusion medicine that Rh D phenotyping tests are selected, executed and interpreted correctly. However, the Rh D blood group antigen has been shown to be subject to many phenotypic variations, and different reagents and typing techniques vary in their ability to detect these variants. The range of D-positive phenotypes are reviewed in terms of their reactivity with monoclonal antibody reagents and their clinical significance. In view of the available evidence, it is suggested that patient typing can be safely achieved by the duplicate use of one high-avidity or two very similar IgM monoclonal anti-D reagents that detect most variants except category DVI in simple tube or microplate saline tests. Antiglobulin testing for weak D should not be carried out on patient samples. Donor typing can be safely achieved by the use of the same monoclonal, used in parallel with a polyclonal anti-D reagent that detects DVI on sensitive automated equipment.