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

Complement as an Immune Barrier in Platelet Transfusion Refractoriness

Patients with hematological cancers often have low platelet counts because of progressing bone marrow failure or cytostatic therapy. A large fraction of those patients need platelet transfusions, which can be life-saving if bleedings occur and also allow diagnostic and therapeutic interventions. The outcomes of platelet transfusions are not always easy to predict in terms of bleeding control or increase in platelet count. Reasons could be disease-specific factors, fever, or infections leading to platelet consumption, but the immune system may also be involved, in particular, in patients previously immunized against foreign human leukocyte antigens (HLA). Mechanisms underlying immune-mediated platelet destruction in the presence of antibodies again HLA are not well understood in clinical situations. This review discusses the role of complement in platelet refractoriness, with a focus on HLA antibody-mediated platelet refractoriness. We summarize recent work in this area, discuss complement-platelet interactions in general terms, and a suggest a possible role of complement in platelet transfusion in general.

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.

C1q-binding anti-HLA antibodies do not predict platelet transfusion failure in Trial to Reduce Alloimmunization to Platelets study participants

BACKGROUND

In the Trial to Reduce Alloimmunization to Platelets (TRAP) study, 101 of 530 subjects became clinically refractory (CR) to platelets (PLTs) without lymphocytotoxicity assay (LCA)-detectable anti-HLA antibodies. The LCA only detects complement-binding antibodies and is less sensitive than newer assays. Utilizing a more sensitive bead-based assay that does not distinguish between complement-binding versus non-complement-binding antibodies, we have previously shown that while many LCA-negative (LCA-) patients do have anti-HLA antibodies, these low- to moderate-level antibodies do not predict refractoriness. As complement can contribute to PLT rejection, we assessed if previously undetected complement-binding antibodies account for refractoriness among LCA- patients.

STUDY DESIGN AND METHODS

Samples from 169 LCA- (69 CR, 100 non-CR) and 20 LCA-positive (LCA+; 10 CR, 10 non-CR) subjects were selected from the TRAP study serum repository. Anti-Class I HLA immunoglobulin (Ig)G and C1q-binding antibodies were measured in serum or plasma with bead-based detection assays. Levels of C1q-binding antibodies were compared between CR and non-CR subjects and correlated with corrected count increments (CCIs).

RESULTS

While some of the LCA- subjects had detectable C1q-binding anti-Class I HLA antibodies, and some LCA+ subjects did not, levels were significantly higher among LCA+ subjects. C1q-binding anti-Class I HLA antibody levels did not differ significantly between CR and non-CR among either the LCA- or the LCA+ subjects. Furthermore, there was no significant correlation observed between CCIs and either C1q-binding or any anti-HLA IgG antibodies.

CONCLUSIONS

This work confirms that low- to moderate-level anti-Class I antibodies do not drive PLT rejection, suggesting a role for antibody-independent mechanisms.

Platelets made HLA deficient by acid treatment aggregate normally and escape destruction by complement and phagocytes in the presence of HLA antibodies

BACKGROUND

The presence of antibodies against HLA Class I can lead to platelet (PLT) transfusion refractoriness, that is, the repeated failure to achieve adequate posttransfusion PLT count increments. PLT refractoriness can be overcome by transfusion of HLA-matched donor PLTs. A different approach is to remove HLA from the PLT surface using low pH. Previous case studies using HLA-stripped PLTs showed encouraging but inconsistent results and lacked information on the biologic effects of acid treatment on PLT function as well as sensitivity to PLT destruction in the presence of HLA antibodies.

STUDY DESIGN AND METHODS

PLTs prepared from buffy coats were stripped from HLA Class I using a brief incubation at pH 2.9. Kinetics of acid stripping, viability, phenotypic alterations, and sensitivity to complement-mediated lysis and phagocytosis were determined by flow cytometry. Functional potential was evaluated using a multiplate analyzer.

RESULTS

Acid-treated PLTs were viable, upregulated activation markers normally and aggregated to a similar extent as untreated PLTs in response to stimulation with three natural agonists. Acid treatment removed 70% to 90% of HLA Class I complexes from the PLT surface, which led to complete protection from HLA antibody-mediated complement lysis and reduced monocyte-mediated phagocytosis in the presence of anti-HLA in vitro.

CONCLUSION

Our study fills an important knowledge gap in how acid treatment affects PLT function and interactions with immune cells, paving the way for controlled clinical trials to evaluate acid-treated PLTs as an alternative to HLA-matched donors in PLT refractoriness.

Anti-human leukocyte antigen antibodies are present in blood of blood donors: is therapy with blood preparations safe for graft recipients?

BACKGROUND

Blood products infusions are often administrated to graft recipients. Post-transfusion reactions of anti-human leukocyte antigen antibodies (anti-HLA) are responsible for transfusion-related acute lung injury, but cases of graft rejection after blood product infusions were recently also proven.

METHODS

The aim of this study was to assess, with the use of the very sensitive Luminex technology and traditional lymphocytotoxic test, the prevalence and cytotoxic activity of anti-HLA in blood donors with different medical histories to evaluate a potential risk of post-transfusion immune complications. Data were analyzed according to different normalized background cutoffs (1.5, 2.2; and the high cutoffs-10.8 for I class and 6.9 for II class anti-HLA).

RESULTS

We observed that anti-HLA may be present in 36% of donors, and even in up to 73.6% of risk groups. Significant risk factors included female sex (23.9% to 64.2% for different cutoffs) and pregnancy history (30% to 72.5%), regardless of the cutoff used in analysis, whereas sera from female donors showed lower cytotoxicity (panel reactive antibodies). Anti-HLA were also detected in men (3.7% to 37%), in donors after a transfusion (0% to 62.5%), and even with no known risk factors (3.8% to 26.9%).

CONCLUSIONS

Luminex technology is a sensitive tool in anti-HLA detection, but consensus in measurement interpretation for blood donors is needed. Selection of blood products on the basis of medical history can be a useful alternative for routine testing of blood donors. The clinical significance of treatment of graft recipients with blood products requires further study; until then, more attention should be paid to possible complications.

Leukoreduction and ultraviolet treatment reduce both the magnitude and the duration of the HLA antibody response

BACKGROUND

Both leukoreduction and ultraviolet (UV) light treatment of blood products have been shown to reduce the incidence of HLA antibody development in recipients, but the impact of these treatments on the magnitude and persistence of the antibody response is less clear.

STUDY DESIGN AND METHODS

Longitudinal samples from 319 subjects taken from four different study cohorts were evaluated for HLA antibodies to determine the effects of leukoreduction and UV treatment on HLA antibody generation and persistence.

RESULTS

Subjects receiving leukoreduced or UV-treated blood products were less likely to generate Class I HLA antibodies, and those receiving leukoreduced blood were also less likely to generate Class II HLA antibodies. Among those receiving nonleukoreduced blood, 55% developed Class I HLA antibodies and 51% developed Class II HLA antibodies compared with 28% (Class I) and 15% (Class II) for those receiving leukoreduced blood and 36% (Class I) and 54% (Class II) for those receiving UV-treated blood. Among alloimmunized subjects, leukoreduction resulted in a significant twofold reduction in the magnitude of Class I HLA antibodies, and UV treatment resulted in a significant threefold reduction in the magnitude of Class II HLA antibodies. Both treatments resulted in shorter persistence of Class I HLA antibodies.

CONCLUSIONS

These data demonstrate that leukoreduction and UV treatment of blood products results not only in a reduction in the incidence of HLA antibody production, but also in lower and more transient HLA antibody levels among sensitized transfusion recipients.

Low-level HLA antibodies do not predict platelet transfusion failure in TRAP study participants

In the Trial to Reduce Alloimmunization to Platelets (TRAP) study, 101 of 530 participants became refractory to platelet transfusions without evidence of HLA or human platelet antigen (HPA) antibodies. We used a more sensitive bead-based assay to detect and quantify HLA antibodies and a qualitative solid-phase enzyme-linked immunosorbet assay for HPA to determine whether low-level antibodies could predict refractoriness in longitudinal panels from 170 lymphocytotoxicity assay (LCA)(-) and 20 LCA(+) TRAP participants. All TRAP recipients who previously tested LCA(+) were HLA antibody(+), using the bead-based system. Levels of HLA or HPA antibodies did not predict refractoriness among LCA(-) recipients, although higher levels of HLA antibodies were associated with refractoriness among LCA(+) recipients. These data demonstrate that weak to moderate HLA antibody levels detectable by modern binding assays are not associated with platelet refractoriness.

Identifying patients with neutrophil elastase (ELANE) mutations from patients with a presumptive diagnosis of autoimmune neutropenia

To differentiate severe congenital neutropenia (SCN) from autoimmune neutropenia (AIN) in patients with persistent neutropenia ≤1000/mm(3) over three months, we evaluated anti-neutrophil auto-antibodies, candidate genes of ELANA, HAX1 and GCSFR, and neutrophil elastase (NE) activity in 38 patients (21 females; average onset age 14.12 ± 2.49 months) in a primary immunodeficiency disease center between 2004 and 2011. In 30 patients, detectable anti-neutrophil auto-antibodies were HNA1a in 16 patients, HNA1c in 15, MHC Class I in 14, HNA1b in eight, MHC Class II in five, and HNA2a in three. Their average neutropenia duration was 27.04 ± 2.08 months. Of eight patients without detectable auto-antibodies, three had ELANE mutations [Ser126Pro, Arg170Phe and Cys223stop] and recurrent muco-cutaneous infections and sepsis. The patient with nonsense ELANE mutation [Cys223stop] had the lowest NE activity (16.8). Thus, patients with ELANE mutations have undetectable antibodies and more severe and younger-onset muco-cutaneous infections, prolonged healing and decreased serum NE activity that require prompt intervention.

The National Heart, Lung, and Blood Institute retrovirus epidemiology donor studies (Retrovirus Epidemiology Donor Study and Retrovirus Epidemiology Donor Study-II): twenty years of research to advance blood product safety and availability

The Retrovirus Epidemiology Donor Study (REDS), conducted from 1989 to 2001, and the REDS-II, conducted from 2004 to 2012, were National Heart, Lung, and Blood Institute-funded, multicenter programs focused on improving blood safety and availability in the United States. The REDS-II also included international study sites in Brazil and China. The 3 major research domains of REDS/REDS-II have been infectious disease risk evaluation, blood donation availability, and blood donor characterization. Both programs have made significant contributions to transfusion medicine research methodology by the use of mathematical modeling, large-scale donor surveys, innovative methods of repository sample storage, and establishing an infrastructure that responded to potential emerging blood safety threats such as xenotropic murine leukemia virus-related virus. Blood safety studies have included protocols evaluating epidemiologic and/or laboratory aspects of human immunodeficiency virus, human T-lymphotropic virus 1/2, hepatitis C virus, hepatitis B virus, West Nile virus, cytomegalovirus, human herpesvirus 8, parvovirus B19, malaria, Creutzfeldt-Jakob disease, influenza, and Trypanosoma cruzi infections. Other analyses have characterized blood donor demographics, motivations to donate, factors influencing donor return, behavioral risk factors, donors' perception of the blood donation screening process, and aspects of donor deferral. In REDS-II, 2 large-scale blood donor protocols examined iron deficiency in donors and the prevalence of leukocyte antibodies. This review describes the major study results from over 150 peer-reviewed articles published by these 2 REDS programs. In 2011, a new 7-year program, the Recipient Epidemiology and Donor Evaluation Study-III, was launched. The Recipient Epidemiology and Donor Evaluation Study-III expands beyond donor-based research to include studies of blood transfusion recipients in the hospital setting and adds a third country, South Africa, to the international program.

Establishing assay cutoffs for HLA antibody screening of apheresis donors

BACKGROUND

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related deaths. Donor HLA antibodies have been implicated in TRALI cases. Blood centers are implementing TRALI risk reduction strategies based on HLA antibody screening of some subpopulations of ever-pregnant apheresis platelet (PLT) donors. However, if screening assay cutoffs are too sensitive, donation loss may adversely impact blood availability.

STUDY DESIGN AND METHODS

Pregnancy history and HLA antibody screening and single-antigen bead data from blood donors in the Retrovirus Epidemiology Donor Study-II Leukocyte Antibody Prevalence Study were evaluated for correlations between assay screening values, HLA antibody titer, and number of HLA antigen specificities. The probabilities of matching a cognate antigen in a recipient were calculated and examined in association with total number of specificities observed and screening values. The relative impact of imposing various screening assay cutoffs or pregnancy stratification was examined in relation to detection of HLA antibody-reactive donations and loss of donors and donations.

RESULTS

We provide evidence that higher HLA antibody screening assay values are associated with maintaining higher screening signals upon dilution and an increased breadth of specificities compared with lower screening values; the latter correlated with an increased risk of a cognate antigen match in potential recipients. Depending on the TRALI risk reduction strategy used, the potential loss of donations ranged between 0.9 and 6.0%.

CONCLUSION

This analysis should enable blood centers to decide upon a TRALI risk reduction strategy for apheresis PLTs that is consistent with how much donation loss the blood center can tolerate.