Analysis of cutoffs for screening sensitized blood donors for HLA alloantibodies using a cytometric microbead assay

Prevalence of anti-HLA antibodies in COVID-19 convalescent plasma donors: an Indian experience

BACKGROUND

COVID-19 convalescent plasma is one of the experimental therapies used widely in moderately sick COVID-19 patients. However, there are a few risks involved in plasma transfusion; notably, transfusion-related acute lung injury (TRALI) caused by antibodies against human leukocyte antigens (HLA). This study was designed to assess the prevalence of anti-HLA antibodies in convalescent plasma donors using the single antigen bead method.

STUDY DESIGN AND METHODS

This was a hospital-based observational study of consecutive plasma donors. A total of 252 samples were screened for anti-HLA Class I and Class II antibodies using the microbead assay with the identification of anti-HLA Ab in positive samples being performed using a single antigen bead assay. Luminex-based normalized background cutoff ratios of 10.8 for Class I and 6.9 for Class II and mean fluorescence intensity cutoffs of 2500 for Class I and 1500 for Class II were used for screening and the single bead assay, respectively.

RESULTS

Of 252 screened samples, 28 (11.1 %) were positive for Class I, Class II or both Class I and Class II anti-HLA antibodies in donors with no history of a previous immunizing event. Moreover, 20/252 (7.9%) donors without any history of prior immunization had specific anti-HLA antibodies of Class I or Class II or both by the single bead assay.

CONCLUSIONS

The high prevalence of anti-HLA antibodies in our cohort of donors raises an urgent and immediate need for anti-HLA antibody screening in all convalescent plasma donors for safe therapy of COVID-19 patients.

Approach of using established and new laboratory tests to more comprehensively investigate noninfectious and nonhemolytic transfusion reactions--along with the experience in Japan

BACKGROUND AND OBJECTIVES

Noninfectious and nonhaemolytic transfusion reactions are the most common type of transfusion reactions. Several new tests have been made, helping diagnosis and understanding of their pathogenesis. This manuscript provides a review of the literature on currently available tests in association with the approach in Japan.

MATERIALS & METHODS

Primarily by using key words, more than 100 pertinent articles in the Medline database were identified and reviewed.

RESULTS

Numbers of laboratory tests are available including those for plasma protein levels, plasma protein antibodies, leucocyte and platelet antibodies, serum N-terminal-pro-brain natriuretic peptide levels, serum tryptase levels and genetic microchimerism. Cross-match tests, such as basophil activation test and neutrophil activation test, are also available to determine a causal relationship between the reaction and transfusion.

CONCLUSIONS

Several tests should help to confirm diagnosis and determine causal relationship between adverse reactions and transfusion and to gain an insight into the mechanism of the reaction in some cases, although some of the recently developed tests have not been completely validated.

Lot-to-lot variability in HLA antibody screening using a multiplexed bead-based assay

BACKGROUND

Identifying antibodies to HLA (anti-HLA) by solid-phase assays is used to screen blood donors to mitigate transfusion-related acute lung injury risk. Various cutoffs for detection assays have been proposed in the literature; however, these do not take into consideration lot-to-lot variability of commercially available assays.

STUDY DESIGN AND METHODS

Samples from 93 nontransfused males were tested using five different lots of a multiplex bead-based anti-HLA detection kit. A subset of 17 samples was tested on 5 days using a single lot. An additional 96 samples from donations with varied anti-HLA levels were tested using kits from two different lots. Results were reported as a normalized background (NBG) ratio.

RESULTS

For the 93 nontransfused donors, NBG values generated using the reference lot were significantly higher than those obtained with three of the four comparator lots. However, for the 96 samples with low-, moderate-, and higher-level anti-HLA, Class I (CL-I) values were 1.4 times lower and Class II (CL-II) values were 1.2 times lower using the reference versus comparator lot. For CL-I antibodies the between-lot standard deviation (SD) was 1.36 (95% confidence interval [CI], 1.19-1.60), while the between-day SD was 1.27 (95% CI, 1.08-1.52). Similarly, for CL-II antibodies the between-lot SD was 0.81 (95% CI, 0.70-0.95), while the between-day SD was 0.50 (95% CI, 0.43-0.60).

CONCLUSIONS

There is interlot variability in the tested HLA detection assay as well as significant bias between lots. It may be reasonable to develop a new cutoff when a new lot is obtained.

TRALI-new challenges for histocompatibility and immunogenetics in transfusion medicine

Antibodies against human leukocyte antigens (HLAs) have long been associated with transfusion-related acute lung injury (TRALI). In contrast to febrile transfusion reactions and refractoriness to platelet transfusions in immunized patients, the causative antibodies in TRALI are present in the transfused blood component, i.e. they are formed by the blood donor and not by the recipient. Consequently, blood components with high plasma volume are particularly associated with TRALI. In addition to antibodies against HLAs, antibodies directed against human neutrophil antigens (HNAs) present in the plasma of predominantly multiparous female blood donors can induce severe TRALI reactions. Especially, antibodies to HLA class II and HNA-3a antigens can induce severe or even fatal ALI in critically ill patients. Over the last decade, the clinical importance of TRALI as major cause for severe transfusion-related morbidities has led to the establishment of new guidelines aimed at preventing this condition, including routine testing for HLA and -HNA antibodies for plasma donors with a history of allogeneic sensitization. This, in turn, poses new challenges for close collaboration between blood transfusion centers and histocompatibility and immunogenetics laboratories, for sensitive and specific detection of the relevant antibodies.

Neutrophil antibody diagnostics and screening: review of the classical versus the emerging

BACKGROUND AND OBJECTIVES  Severe transfusion-related acute lung injury (TRALI) events have been linked to donor-derived neutrophil antibodies. The journey to developing mass donor neutrophil antibody screening platforms is challenged by the fragility of neutrophils and their unique-specific antigenic characteristics. MATERIAL AND METHODS  This article critically evaluates the capabilities and potential of five emerging antibody screening platforms designed to detect neutrophil reactive antibodies relevant to TRALI. They are compared with established neutrophil serological methods. RESULTS  Data from two recombinant antigen platforms and a method using human neutrophil antigens-expressing KY cells indicated high specificity. Two mixed cellular flow cytometric assays have the advantage of presenting native conformation of the human polymorphonuclear neutrophil antigenic epitopes. CONCLUSIONS  To date, the number and specificity of test sera applied to each platform is small. This needs to be substantially increased and further rigorous serological evaluation is yet needed to compare the sensitivity and specificity limits of each new platform with classical methods. With a limited world supply of TRALI-relevant test sera, a collaborative effort of laboratories with neutrophil and TRALI investigation expertise is required.

The incidence, risk factors, and outcome of transfusion-related acute lung injury in a cohort of cardiac surgery patients: a prospective nested case-control study

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related morbidity and mortality. Both antibodies and bioactive lipids that have accumulated during storage of blood have been implicated in TRALI pathogenesis. In a single-center, nested, case-control study, patients were prospectively observed for onset of TRALI according to the consensus definition. Of 668 patients, 16 patients (2.4%) developed TRALI. Patient-related risk factors for onset of TRALI were age and time on the cardiopulmonary bypass. Transfusion-related risk factors were total amount of blood products (odds ratio [OR] = 1.2; 95% confidence interval [CI], 1.03-1.44), number of red blood cells stored more than 14 days (OR = 1.6; 95% CI, 1.04-2.37), total amount of plasma (OR = 1.2; 95% CI, 1.03-1.44), presence of antibodies in donor plasma (OR = 8.8; 95% CI, 1.8-44), and total amount of transfused bioactive lipids (OR = 1.0; 95% CI, 1.00-1.07). When adjusted for patient risk factors, only the presence of antibodies in the associated blood products remained a risk factor for TRALI (OR = 14.2; 95% CI, 1.5-132). In-hospital mortality of TRALI was 13% compared with 0% and 3% in transfused and nontransfused patients, respectively (P < .05). In conclusion, the incidence of TRALI is high in cardiac surgery patients and associated with adverse outcome. Our results suggest that cardiac surgery patients may benefit from exclusion of blood products containing HLA/HNA antibodies.