A comparison of two robotic platforms to screen plateletpheresis donors for HLA antibodies as part of a transfusion-related acute lung injury mitigation strategy

An association between ABO group and HLA antibody detection

BACKGROUND

US blood centers can screen female plateletpheresis donors with a history of one or more pregnancies for both Class I and Class II anti-HLA antibodies using one of two platforms. One is a flow-based assay that yields a quantitative result and the other an enzyme-linked immunosorbent assay (ELISA) that yields either a positive or a negative result (above or below cutoff).

STUDY DESIGN AND METHODS

The results of HLA antibody screening tests were analyzed by donor ABO group. Results from large and small American blood collection centers using both platforms were analyzed. Positivity rates were compared by chi-square test and the results stratified by parity using the Mann-Whitney test.

RESULTS

No differences in parity were noted among donors of different ABO groups, but a significantly higher rate of HLA antibody positivity was observed among group O donors for the ELISA (31% of group O donors vs. 21% of non-group O donors, p < 0.0001). The higher rate of positivity was primarily due to Class I reactivity. This difference in antibody frequency was not observed at centers using the flow-based assay.

CONCLUSION

Centers using the ELISA may have a higher rate of permanent deferral from plateletpheresis donation among group O female donors. Although the reasons for the higher rate of reactivity on Class I ELISA testing are unknown, this could result from test system characteristics or differences in group O donor antibody strength or specificity.

Donor Specific Anti-HLA Antibody and Risk of Graft Failure in Haploidentical Stem Cell Transplantation

Outcomes of allogeneic hematopoietic stem cell transplantation (AHSCT) using HLA-half matched related donors (haploidentical) have recently improved due to better control of alloreactive reactions in both graft-versus-host and host-versus-graft directions. The recognition of the role of humoral rejection in the development of primary graft failure in this setting has broadened our understanding about causes of engraftment failure in these patients, helped us better select donors for patients in need of AHSCT, and developed rational therapeutic measures for HLA sensitized patients to prevent this unfortunate event, which is usually associated with a very high mortality rate. With these recent advances the rate of graft failure in haploidentical transplantation has decreased to less than 5%.

Sustained donor engraftment in recipients of double-unit cord blood transplantation is possible despite donor-specific human leukoctye antigen antibodies

The impact of human leukocyte antigen (HLA) donor-specific antibodies (DSA) on cord blood (CB) engraftment is controversial. We evaluated the influence of pre-existing HLA-antibodies (HLA-Abs) on engraftment in 82 double-unit CB recipients (median age, 48 years) who underwent transplantation for hematologic malignancies. Of 28 patients (34%) with HLA-Abs, 12 had DSA (median mean fluorescence intensity 5255; range, 1057 to 9453). DSA patients had acute leukemia (n = 11) or myelodysplasia (n = 1) and all received either high-dose or reduced-intensity (but myeloablative) conditioning. After myeloablative CB transplantation (CBT) (n = 67), sustained donor engraftment was observed in 95% without HLA-Abs (median, 23 days), 100% with nonspecific HLA-Abs (median, 23 days), and 92% with DSA (median, 31 days, P = .48). Of 6 patients with HLA-Abs to 1 unit, 3 engrafted with that unit and 3 with the other. Of 6 patients with HLA-Abs against both units, 1 had graft failure despite being 100% donor, and 5 engrafted with 1 unit. Successful donor engraftment is possible in patients with DSA after myeloablative double-unit CBT. Our data suggest potential deleterious effects of DSA can be abrogated in patients with hematologic malignancies.

Blood donors implicated in transfusion-related acute lung injury with patient-specific HLA antibodies are more broadly sensitized to HLA antigens compared to other blood donors

BACKGROUND

The prevalence of HLA antibodies in randomly surveyed blood donors was compared to the prevalence of antibody in donors who were associated with transfusion-related acute lung injury (TRALI) cases reported to Canadian Blood Services (CBS).

STUDY DESIGN AND METHODS

Current operating procedure mandates that the CBS TRALI Medical Review Group (TMRG) refer possible TRALI cases to the (CBS) Platelet Immunology Laboratory for investigation. Donor samples from these TRALI cases were screened for HLA antibodies. In parallel, a survey was conducted to screen serum samples from blood donors who were not associated in TRALI cases. A comparison analysis of HLA antibody profiles in the two groups of donors was performed.

RESULTS

We studied 121 TRALI-associated donors (TDs) who were recalled in a total of 44 cases reported to CBS and classified by TMRG. We also studied 149 survey donors (SDs) who were deferred for donation for varied reasons and consented to participate in a survey for HLA antibody screening. Twenty-two percent of SDs and 50.4% of TDs tested positive for HLA antibodies. In addition, TDs who were implicated in TRALI demonstrated broader sensitization and higher level of quantitative HLA antibody compared to nonimplicated TDs and SDs.

CONCLUSION

Patient-specific Class I and II HLA antibodies are directly related to the risk of TRALI. Moreover, it supports the concept that HLA antibody strength is directly related to the risk of TRALI when the HLA antibody is patient specific; however, no clear cutoff as defined by mean fluorescence intensity is evident.

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.

Agreement among HLA antibody detection assays is higher in ever-pregnant donors and improved using a consensus cutoff

BACKGROUND

HLA antibodies might contribute to the pathogenesis of transfusion-related acute lung injury (TRALI). HLA antibody detection methods include ELISA, flow cytometry, and multiplex bead-based assays, as well as the older lymphocytotoxicity assay, and it is not obvious how to compare results across platforms.

STUDY DESIGN AND METHODS

Five hundred twenty-five serum samples were selected from 7841 donors in the Leukocyte Antibody Prevalence Study (LAPS) repository based on risk for the development of HLA antibodies, using the number of pregnancies as the risk factor. Subjects included 81 males and females with 0 (n = 187), 1 (n = 67), or 2+ pregnancies (n = 190). Replicate frozen serum aliquots were sent blinded to four different HLA antibody assay manufacturers for detection using five different assays.

RESULTS

The flow cytometry and multiplex bead based-assays typically resulted in a larger proportion of HLA antibody positive samples compared with ELISA based assays. Latent variable analysis was used to derive a new set of consensus cutoffs, which yielded similar sensitivities across test platforms and increased concordance amongst assays. Assay agreement was higher in ever pregnant females than in males and never-pregnant females.

CONCLUSIONS

Different assays resulted in varied positivity rates when the manufacturer's suggested cutoffs were used, demonstrating that care needs to be taken when comparing clinical outcomes data generated using different HLA antibody assays and testing platforms. The method used here, involving latent variable analysis, presents one possible approach to calculating comparable cutoffs that result in broad agreement across assays with respect to positivity designation.

Mechanism of transfusion-related acute lung injury induced by HLA class II antibodies

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-associated mortality in the United States and other countries. In most TRALI cases, human leukocyte antigen (HLA) class II antibodies are detected in implicated donors. However, the corresponding antigens are not present on the cellular key players in TRALI: neutrophils and endothelium. In this study, we identify monocytes as a primary target in HLA class II–induced TRALI. Monocytes become activated when incubated with matched HLA class II antibodies and are capable of activating neutrophils, which, in turn, can induce disturbance of an endothelial barrier. In an ex vivo rodent model, HLA class II antibody–dependent monocyte activation leads to severe pulmonary edema in a relevant period of time, whenever neutrophils are present and the endothelium is preactivated. Our data suggest that in most TRALI cases, monocytes are cellular key players, because HLA class II antibodies induce TRALI by a reaction cascade initiated by monocyte activation. Furthermore, our data support the previous assumption that TRALI pathogenesis follows a threshold model. Having identified the biologic mechanism of HLA class II antibody–induced TRALI, strategies to avoid plasma from immunized donors, such as women with a history of pregnancy, appear to be justified preventive measures.