Platelet Refractoriness In Patients Research Articles

Differentiating patient characteristics between platelet refractory patients with and without antibodies to human leukocyte antigens.

Predicting whether a patient's platelet refractoriness (PR) is due to immune or nonimmune causes can be challenging. This study compared the demographics and clinical history of PR patients with human leukocyte antigen (HLA) antibodies (HLA-PR) versus PR patients without HLA antibodies. A retrospective review of all patients with PR consults at a single institution over a 3-year period was performed. Patient charts were reviewed for all patients with confirmed PR, and demographic information (e.g., sex, race and ethnicity, preferred language) and clinical history (e.g., pregnancy, transfusion, primary diagnosis) were collected. Patient characteristics were compared among the HLA and non-HLA cohorts. A total of 295 patients with confirmed PR were identified, of whom approximately 70% did not have HLA antibodies and 30% did. Approximately 84% of the HLA-PR cohort was female. A history of transfusions was not associated with HLA-PR (p = .1). A history of pregnancy was strongly associated with the occurrence of HLA-PR (p < .001). Splenomegaly was associated with PR in the absence of HLA alloimmunization whereas infection, fever, bleeding, and disseminated intravascular coagulation were not. In this single-institution retrospective review, a history of pregnancy was strongly associated with HLA-PR, whereas a history of transfusion was not.

Comparison of HLA antibody identification methods for the selection of platelet products for HLA-mediated platelet refractory patients.

In an ineffective transfusion context, solid-phase immunoassays using the Luminex platform for the detection and characterization of HLA antibodies are currently used to select HLA-compatible platelet products. A new HLA antibody identification method, the HISTO SPOT® HLA AB test (BAG Health care GmbH, Lich, Germany), based on the detection of antibodies directed against a recombinant single antigen (SA) by colored spots detected by HISTO MATCH HLA AB module software, runs fully automated on the MR.SPOT®. The aim of this study was to compare the ability of the HISTO SPOT HLA AB and C1qScreen™ (C1q SAB) assays with that of the Labscreen single antigen class I (OL SAB) assay to detect anti-HLA class I antibodies in 56 serum samples from 54 platelet refractory acute myeloid leukemia patients who received HLA mismatch platelet concentrates at a single oncohematology center. In total, 1414 class I specificities, 433 HLA-A and 981 HLA-B, were detected by the OL SAB test. The mean fluorescence intensity (MFI) was >5000 for 874 antigens and <5000 for 655 antigens. The HISTO SPOT® HLA AB and C1q SAB tests identified 85% and 79% of OL SA-detected antigens with an MFI >5000, respectively, but did not identify 34% and 44% of OL SAB-detected antigens, highlighting the lower sensitivity of these techniques. Interestingly, the donor-specific antibodies (DSAs) identified by the HISTO SPOT® HLA AB and C1q SAB assays reacted against HLA mismatch platelet concentrates with the same specificity (86%) and positive predictive (77%) value as in the OL SAB test when the MFI threshold was >2000 for DSA detection. Although the HISTO SPOT® HLA AB test is less sensitive than the OL SAB test, this test could be used for the selection of HLA-compatible platelet products.

Use of Human Leukocyte Antigen (HLA)-Incompatible Platelet Units in HLA Platelet-Refractory Patients With Limited Number of or Low-Level HLA Donor-Specific Antibodies Results in Permissive Transfusions.

In human leukocyte antigen (HLA)-mediated alloimmune platelet refractoriness, HLA-incompatible platelets may produce adequate posttransfusion corrected count increment ("permissive transfusion") and increase the donor pool. To determine if a lower number of or low-level anti-HLA donor-specific antibodies (DSAs) predict permissive transfusion and could be used to prioritize platelet selection. We categorized platelets administered from 2016 to 2018 as HLA-compatible or HLA-incompatible based on presence of DSAs against the donor unit. We further divided HLA-incompatible units based on the number of DSAs and the level of DSAs (measured by mean fluorescence intensity [MFI]), where cumulative MFI ≥6000 defines high-level DSA. We compared posttransfusion corrected count increments (CCIs) and transfusion reactions among these transfusions. Of 279 HLA-selected units transfused into 26 platelet-refractory patients, we resorted to using 39 HLA-incompatible units (14%). Posttransfusion CCI and transfusion reaction frequency were similar among units targeted by 1 or low-level DSAs and HLA-compatible units. Units targeted by ≥2 distinct or high-level DSAs produced lower CCIs. Regardless of ABO compatibility, similarly HLA-categorized units yielded comparable CCIs and comparable frequency of transfusion reactions. HLA-incompatible platelets transfused across 1 or low-level DSAs were commonly permissive, whereas those transfused across ≥2 DSAs or high levels of DSA (MFI ≥6000) were nonpermissive. The use of such donor units offers transfusion services alternative platelet units for support of platelet-refractory patients.

Post-Transfusion Overall Survival for HLA- Alloimmunized Platelet Refractorythrombocytopenic Leukemia Patients

BACKGROUND: Platelet alloimmunization and refractoriness is an established complication of platelet (PLT) transfusion, known to be treatment-limiting with potential life-threatening complications for hemato-oncologic patients undergoing chemotherapy (Hess et al.). Previous studies have explored the association of PLT refractoriness with lymphocytotoxic antibody positivity, more frequent platelet transfusion and platelet age (Slichter et al, Blood, 2005). They have also developed cross matching or HLA matching for donor selection as the basis of managing refractory patients. However, the impact of patient characteristics on the clinical outcomes of refractoriness is not fully understood.Objective: To analyze overall survival (OS) of PLT refractory leukemia patients transfused with HLA-matched platelets in association with the demographic and clinical characteristics of these patients.METHODS: We analyzed the demographics, clinical characteristics and platelet refractoriness (defined as two consecutive <24 hr post-transfusion corrected platelet count increments (CCI) of < 5 K/uL), ABO matching (fully compatible, minor mismatch or major mismatch), and HLA match grade (A, B, C). The threshold for transfusion was <7 K/uL and only patients with recorded platelet counts pre- and post-transfusion were included. The majority of post-transfusion counts were performed < 24 hrs. Transfusion efficacy was defined as having: i) difference in platelet counts > 5 pre- and post-transfusion; ii) ABO match or compatible; iii) HLA match grade A or B1.We included two measurements for overall survival (OS): from the date of the first transfusion and also from the last transfusion to the date of last follow-up or date of death. A PLT transfusion record for each measure was obtained using a majority rules algorithm. Group differences in OS were assessed using the log-rank test. For differences in PLT counts, the median value for each patient was used. The association between mean PLT count difference, age, and weight with OS was evaluated using univariate Cox proportional regression models.RESULTS: We identified 33 leukemia patients who received a total of 145 HLA-matched platelet transfusions from 2010-2017. A majority [60%] of the patients had a diagnosis of acute myeloid leukemia or myelodysplastic syndrome and received ≤2 HLA-matched platelet transfusions. Complex cytogenetics was identified in 7 of 23 (30%) patients, while the majority (97%) showed broad reactivity against HLA Class I and Class II antigens. Less than half (45%) of the platelets transfused were HLA match grade B and a third of the platelets (35%) were ABO compatible.The median OS was 16.7 months and the 1-year OS rate was 64%. A significant association between post-transfusion OS with age [p=0.016] and complex cytogenetics [p=0.013] was observed. However, no significant association between OS and gender, weight, ethnicity, and the number of pregnancies was noted. Although the median OS was longer for patients with ABO match/compatible transfusions (vs. incompatible), HLA match grades B2/B3/C platelets (vs. A/B1), and >2 platelets transfusions (vs. ≤ 2), none of these differences were statistically significant (Table 1).CONCLUSIONS: In summary, our findings reveal a significant association of OS was noted with age and complex cytogenetics in platelet refractory hemato-oncologic patients who received HLA-matched platelet transfusions. This association prompts further investigation into how patient profiles may be used in HLA-alloimmunized patients with platelet refractoriness. However, this may need to be studied in a larger cohort of patients in the future. [Display omitted] DisclosuresDiNardo:Celgene: Honoraria, Research Funding; Agios: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding. Cortes:ImmunoGen: Consultancy, Research Funding; ARIAD: Consultancy, Research Funding; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Teva: Research Funding; Sun Pharma: Research Funding; Pfizer: Consultancy, Research Funding. Kantarjian:Delta-Fly Pharma: Research Funding; Amgen: Research Funding; Novartis: Research Funding; Bristol-Meyers Squibb: Research Funding; Pfizer: Research Funding; ARIAD: Research Funding.

The burden of immune-mediated refractoriness to platelet transfusions in myelodysplastic syndromes.

A retrospective analysis of MDS patients enrolled in the SA-MDS registry was performed. HLA data was analyzed from January 2003 to 30 June 2017 to ensure minimum follow-up of 2 years. During the study period, 341 of 681 (50%) MDS patients required at least one PLT transfusion, with 29 of 341 (9%) of all PLT transfusion patients requiring HLA-matched PLT transfusion for PLT-R. Of these 29 patients, 70% were females treated with disease-modifying therapies suggesting that these patients are at high risk of HLA alloimmunization. Immune-mediated PLT-R is common in MDS and can be expensive and difficult to manage once it occurs. Therefore, PLT transfusion practices should be optimized, especially for female MDS patients planned for disease-modifying therapies. This can help save time and streamline management, especially in the provision of PLT products for these patients, where the consequences of alloimmunization and PLT-R can be severe.

The effect of serum pretreatment regimens for the detection of HLA class I antibodies in platelet-refractory patients.

Single antigen bead (SAB) assays are used to identify human leukocyte antigen (HLA) antibodies in patients with platelet refractoriness due to HLA Class I alloimmunization. Some laboratories use serum pretreatment regimens to eliminate interference from immunoglobulin M antibodies and complement. These modifications may contribute to interlaboratory variability, which is a recognized problem with the SAB assay. Five patients' sera were overnight shipped to 12 laboratories in the United States and internationally. Recipients used their lab's SAB procedure to identify HLA Class I antibodies. The resultant mean fluorescence intensity (MFI) data were compared by instrumentation, bead lot, and pretreatment regimens. Laboratory-specific cutoffs for positive antibodies were applied to the results. Interlaboratory variability for MFI values appears to be associated with different pretreatment regimens. The coefficient of variation (CV) of MFI from samples pretreated with ethylenediaminetetraacetic acid, dithiothreitol, or heat inactivation (EDHI) were similar, ranging from 14% to 56% (mean, 22%). For samples with no pretreatment, the CVs were significantly higher than EDHI-treated samples, ranging from 25% to 74% (mean, 39%; 95% confidence interval, 12.10-21.90; p < 0.0001). An intralaboratory comparison of pretreatment regimens confirmed these findings. Some positive antibody specificities present in EDHI-treated samples were negative in corresponding samples with no pretreatment when laboratory-specific cutoffs for positive antibodies were applied. Our results show that greater interlaboratory precision can be achieved when samples are pretreated with EDHI as opposed to no pretreatment, likely because these pretreatments eliminate interference from inhibitors. Inhibitors may mask antibodies, leading to missed (or uncalled) specificities when no pretreatment is used.

How do I … implement diagnostic management teams in transfusion medicine?

Diagnostic management teams (DMTs) were conceptualized approximately twenty years ago in response to increasing subspecialization in medicine. DMTs are a collaboration between diagnostic experts and clinicians that aim to improve accurate and timely diagnosis and treatment of disease. Diagnostic experts provide their expertise in the increasingly complex realm of laboratory testing and interpretation of those test results to guide appropriate test utilization for individual patients. Not only can this approach improve patient care and safety, but DMTs also decrease healthcare costs by reducing unnecessary testing and potential diagnostic errors. Following the DMT construct and principles along with the 2015 National Academy of Medicine recommendations, our transfusion medicine (TM) service streamlined the workup and management of platelet refractory (PR) patients by developing and implementing a formal PR laboratory consult. The goals of this DMT and consult are to improve diagnostic management of PR patients and to decrease delays in providing these patients with appropriate and compatible platelet units. A comprehensive interpretation of test results is directly uploaded to the patient's electronic medical record (EMR), which is associated with a CPT code allowing for compensation for the PR evaluation. Herein we describe the development of and experience with the DMT since its implementation.

Platelet compatibility and platelet antibodies detection: A step towards resolving dilemma in management of platelet refractoriness in oncology patients

Background: Platelet refractoriness complicates the provision of platelet transfusions- a critical and essential part in management of thrombocytopenia in Oncology patients. Platelet refractoriness poses challenge due to alloimmunization to HLA (Class I) and human platelet antigens (HPAs) and is associated with adverse clinical outcomes and increases health care costs. Aim: A prospective, observational study was planned in medical oncology patients having thrombocytopenia to analyse result of platelet compatibility with post-transfusion platelet count increment and to ascertain presence of platelet antibodies as causative factor in platelet refractory patients. Methods: Eighty oncology patients having thrombocytopenia in a tertiary care centre; both solid organ and hematological malignancies, requiring platelet transfusion were included in this study. ABO-compatible, leucoreduced, random donor platelets with less than 72 hours storage and platelet cross matched were transfused. In case of platelet refractoriness and presence of platelet incompatibility, platelet antibody screening test was performed using SPRCA technique. A P-value

HLA-selected platelets for platelet refractory patients with HLA antibodies: a single-center experience.

Platelet refractoriness due to HLA immunization represents a problem in transfusion management of thrombocytopenic hematology patients. Refractory patients can be managed by HLA-selected platelet transfusions, but the optimal matching strategy is debated and how the degree of HLA mismatch influences transfusion outcome is poorly studied. We studied 32 hematology patients who received 142 matched platelet units between 2007 and 2016. Four matching strategies were compared: 1) genomic HLA typing at the two digit level, performed using polymerase chain reaction-sequence-specific oligonucleotide probing; 2) serologic "eplet score" calculated using HLAMatchmaker; 3) cross-matching using lymphocyte cytotoxicity; and 4) matching based on donor-specific antibody (DSA) specificity, determined using Luminex. A 1-hour corrected count increment (CCI) of more than 7.5 × 109 /L was considered a successful response. Selection of platelets with either a complete HLA match or an acceptable HLA mismatch based on genomic typing and DSA information, each predicted 86% successful transfusion responses. For HLA-mismatched transfusions, the eplet score correlated with CCI and the fraction of successful transfusions, but less well compared to DSA matching. Cytotoxic crossmatching was least predictive. For transfusions across one to four DSAs, the antibody reaction strength correlated with the 1-hour CCI, but many transfusions were successful despite the presence of DSA. A complete HLA-A and -B match or an acceptable mismatch based on DSA should guide identification of donors. Still, transfusions across DSAs are often successful, emphasizing that the presence of DSA is necessary but not sufficient for platelet clearance.

HLA testing in the molecular diagnostic laboratory.

The human leukocyte antigen (HLA) system is a highly polymorphic family of genes involved in immunity and responsible for identifying self versus non-self. HLA typing is essential for solid organ and bone marrow transplantation as well as in non-transplant settings such as disease association and pharmacogenomics. Typing of HLA genes differs from most molecular testing as, rather than evaluating differences from an accepted "wild-type" gene, it must distinguish between thousands of similar, but distinct alleles. This article will describe the HLA system and nomenclature. We will then discuss clinical uses of HLA typing including solid organ transplantation, hematopoietic stem cell transplantation, evaluation of platelet refractory patients, disease association, and pharmacogenetics. Finally, we describe common molecular methods of HLA typing.

P095 Antibodies to human platelet antigens: when do they cause an incompatible crossmatch

Aim Our center evaluates approximately 100 platelet refractory patients each year. Previously, we have correlated single antigen bead MFI with platelet crossmatch results in an effort to optimize our process for selection of HLA-compatible platelets. However, we continue to struggle to appreciate when antibodies to human platelet antigens (HPA) are also contributing to the platelet refractory state. In this study, our aim is to understand the relationship between HPA antibody testing (PakPlus, Immucor) and platelet crossmatch (CaptureP, Immucor). Methods One patient sample with a singular & strong specificity, HPA-1a, was identified based on PakPlus testing. This sample was also negative for HLA antibodies based on PakPlus testing. The plasma was then diluted and the PakPlus result, optical density (OD), was determined at each dilution. Ten antigen-positive platelet units were crossmatched with the battery of plasma dilutions. The strength of the platelet crossmatch was graded by one technologist, blinded to the dilution, with 4+ being strong positive to negative. Results The patient sample demonstrated a fairly linear dilution of HPA-1a, beginning with a neat result of OD 1.33. All 10 antigen-positive platelet units were positive at OD 0.42 or greater, yet negative at OD 0.04. There was platelet-specific variability between OD 0.3 and OD 0.06 (see Table 1). Conclusions These results demonstrate that HPA antibodies cause crossmatch positivity at low OD. The variability seen may be due to homozygosity versus heterozygosity of antigen expression. These initial results suggest that a PakPlus result as low as OD 0.06 may cause incompatibility in the platelet crossmatch and could be considered when selecting platelets for the platelet refractory patient. Download : Download high-res image (413KB) Download : Download full-size image

Epitope Matched Platelets: An Effective Way to Provide Platelet Transfusion Support in Platelet Refractory Patients in a Tertiary Care Oncology Centre

Epitope Matched Platelets: An Effective Way to Provide Platelet Transfusion Support in Platelet Refractory Patients in a Tertiary Care Oncology Centre

Factors influencing platelet transfusion refractoriness in patients undergoing allogeneic hematopoietic stem cell transplantation.

Hematopoietic stem cell transplantation has been considered a risk factor for development of platelet transfusion refractoriness. The objective of this study was to assess the platelet transfusion refractoriness rate in patients undergoing allogeneic hematopoietic stem cell transplantation from different sources. We retrospectively reviewed the charts and transfusion records of patients who underwent allogeneic stem cell transplantation at our institution between 2013 and 2015. The evaluation of post-transfusion platelet count was assessed for each transfusion given, from day of progenitor infusion to day 30 after transplantation. Of 167 patients included in this study, 101 received peripheral blood stem cell transplantation (PBSCT) and 66 received umbilical cord blood transplantation (UCBT). Overall, the percentage of platelet transfusions with a 14-h CCI lower than 5000 was 59.3%, being these data significantly higher for UCBT (67.6%) than for PBSCT (31.0%). Seventy-eight percent of patients underwent UCBT become refractory, while 38.6% of patients who received PBSCT were refractory. Factors associated to platelet refractoriness were lower CD34+ cell dose infused, higher number of antibiotics used, presence of anti-HLA I antibodies, and reduced-intensity conditioning regimen. Platelet refractoriness is a frequent and complex adverse event and remains a therapeutic challenge in the management of patients undergoing HSCT. There is a higher rate of platelet refractoriness in patients who received UCBT as compared to patients who received PBSCT.

OR34 Platelet refractoriness in a patient with 0% PRA due to a rare anti-CD36(NAKa) antibody

Platelet transfusion refractoriness in patients with hematological malignancies ranges from 7% to 34%. The etiology of platelet refractoriness in this patient population is typically attributable to due to formation of HLA antibodies (Abs) from pregnancy or previous transfusion. We report platelet refractoriness in the setting of induction chemotherapy for AML from allo-Abs to NAK a antigen/CD36/glycoprotein (GP) IV. A 66yo AAF presented with transfusion dependent AML with 70% circulating peripheral blasts and started on 7 + 3 regimen. She developed profound thrombocytopenia and her platelet count was 0 by day 13. As part of her evaluation for refractoriness, HLA antibody screening was done, but was negative. An Immucor ELISA assay was then performed and revealed positive Abs to GPIV (NAK a antigen/CD36). Abs against GPIIb/IIIa, GPIa/IIa, GPIb/IX, and HLA Class I were all negative. GPIV Abs were confirmed by Blood Center of Wisconsin using monoclonal Ab MBC 131.7 against CD36. Cross-matching was performed at our institution with multiple single donor apheresis platelets, all showing strong positive reactivity. Because CD36 in these units may be soluble, an incompatible leukoreduced, irradiated and washed single donor platelet unit was given which was tolerated well with a resultant increase to 14,000/ μ L. Despite strong reactivity of this unit in the crossmatch, the patient’s platelet count increased and 1 week later was 16,000/μL despite no transfusion support. Platelet refractoriness in the setting of hematological malignancy is well documented. Abs develop from prior pregnancy and transfusion in the setting of prolonged pancytopenia in hematological malignancies. Typically, allo-Abs develop against platelet membrane structures including human platelet antigens, HLA antigens, and rarely NAK a antigen on the CD36 glycoprotein molecule. CD36 is expressed in almost 100% of white Europeans and is not detectably expressed by 2% of sub-Saharan Africans and 10% of Asians. CD36 is a soluble antigen and is expressed on various cells such as erythroblasts and monocytes. We propose that washing platelets may be a useful strategy in treating platelet refractoriness in patients with abs to NAK a antigen as finding CD36 negative donors is extremely difficult and few blood banks in North America test donors for this antigen.

HLAMatchmaker is effective for selecting appropriate platelet units for alloimmunised thrombocytopaenic patients who are refractory to random donor platelets.

HLAMatchmaker has been used in the Irish Blood Transfusion Service (IBTS) to select platelets for HLA-alloimmunised, platelet refractory thrombocytopaenic patients since 2006. Although available since 2002, only three studies have been published supporting the programme's effectiveness for this indication. We sought to examine increments to HLA-matched platelets (HMPs) at various matchmaker scores and to examine the impact of transfusing older platelets and ABO-mismatched platelets to this patient group. A total of 20 consecutive HLA-alloimmunised thrombocytopaenic patients were retrospectively studied. Data collected included: pre- and post-transfusion platelet count, indication for transfusion, HLAMatchmaker score, age of unit and degree of ABO mismatch. Data were also collected on the last 3 U of (RDPs). The Mann-Whitney U-test was used to compare increments between transfusion episodes of random donor platelets (RDPs) vs HMPs with matchmaker scores <3, 4-7 or >8. Increments at <2 h were available for 63 transfusion episodes. Increments at 2-24 h were available for 93 transfusion episodes. Increments were higher when transfusing HMPs than when transfusing RDPs. Increments for HMPs that were ABO mismatched were no different than for ABO-identical units, with the exception of late increments post-transfusing HMPs with a major ABO mismatch. Age of platelets did not influence increments. The use of HLAMatchmaker to select platelet units for thrombocytopaenic HLA-alloimmunised patients produced satisfactory platelet increments. When providing HLAMatchmaker-selected HMPs, ABO mismatch and the use of platelet units that are up to 7 days old should be permissible.

Recognition and management of platelet-refractory bleeding in patients with Glanzmann's thrombasthenia and other severe platelet function disorders.

Patients with rare qualitative platelet disorders or platelet function disorders (PFDs) may present to the hospital physician with severe bleeding episodes or excessive surgical bleeding. Although standard treatment consists of platelet transfusions, repeated transfusions may result in the development of antiplatelet antibodies (APA) or clinical refractoriness, rendering further platelet therapy ineffective. In such settings, an approved treatment option for patients with Glanzmann’s thrombasthenia (GT), one of the well-known rare PFDs, is recombinant activated coagulation factor VII (rFVIIa). Data regarding the efficacy of rFVIIa in patients with GT and platelet refractoriness are available from a large patient registry, an international survey, and multiple case reports and demonstrate efficacy in patients with and without refractoriness or APA. This article reviews the rFVIIa clinical data in patients with GT and platelet refractoriness and discusses clinical implications relevant to the hospital-based physician. Because uncontrolled bleeding can be life-threatening, hospital physicians should be alert to the signs of platelet refractoriness, be able to recognize continued internal or external bleeding, and know how to adapt treatment regimens for the effective management of bleeding. The management of patients who receive rFVIIa should occur in consultation with a hematologist with experience in PFDs, and patients with suspected platelet refractoriness should be referred to such a hematologist as early as possible. A critical unmet need is the development of a definition of an adequate response to platelet transfusion, which would facilitate early recognition of platelet refractoriness in patients with PFDs who exhibit a normal platelet count.

Testing for Platelet Antibody Does Not Predict Results of Platelet Crossmatching in Platelet-Refractory Patients

Testing for Platelet Antibody Does Not Predict Results of Platelet Crossmatching in Platelet-Refractory Patients

HLA‐stripped platelets: preclinical developments and clinical outlooks

Antibodies to foreign HLA class I can form in patients exposed to allogeneic cells, for example during blood transfusion. During platelet transfusions, these anti‐HLA class I antibodies can bind to transfused platelets and mediate their destruction, causing platelet refractoriness. Providing HLA‐matched platelets is a therapeutic option for immunized patients. However, sometimes HLA‐matched donors cannot be found or are too few, leading to suboptimal treatment and risks of bleedings. An alternative is to strip standard platelets of HLA class I using a brief incubation at low pH. Such HLA‐stripping results in a reduction in HLA class I expression at the surface, followed by loss of reactivity to HLA class I‐specific antibodies. HLA‐stripped platelets therefore have therapeutic potential in platelet refractory patients. In this article, we summarize our recent work on HLA stripping of platelets and discuss how the HLA‐stripping process affects platelet function and interactions with cells of the immune system. We also review earlier clinical case studies in which HLA‐stripped platelets have been used In patients, and discuss concerns and considerations that should be taken into account when testing their efficacy in platelet refractory patients in clinical trials.

Platelet Refractoriness Due to Anti-CD-36(NAKa) Ameliorated By Platelet Washing

▪Introduction:Platelet transfusion refractoriness in patients with hematological malignancies ranges from 7-34% (Blood 2015; 126:3484). The etiology of platelet refractoriness in this patient population is typically due to formation of HLA antibodies from pregnancy or previous transfusion. Although these patients receive leukoreduced products, alloimmunization is not completely prevented. We report platelet refractoriness in the setting of induction chemotherapy for acute myeloid leukemia (AML) from alloantibodies to NAKa antigen/CD-36/glycoprotein (GP) IV. We propose that washing platelets may be a potential strategy for treating platelet refractoriness in patients with NAKaantibodies as finding CD36 negative donors is extremely difficult and few blood banks in North America test donors for this antigen.Case:A 66 year old African American female presented with pancytopenia requiring transfusions. She was later diagnosed with AML with 70% circulating peripheral blasts and started on 7+3 regimen (Cytarabine for 7 days and Idarubicin for 3 days). She developed profound thrombocytopenia by day 7 and her platelet count was 0 by day 13. She was refractory to platelet transfusion from the outset. An Immucor ELISA assay was positive for anti-GPIV (NAKaantigen/CD-36). No antibody to GPIIb/IIIa, GPIa/IIa, GPIb/IX, and HLA Class I was present. Anti-GPIV was confirmed by Blood Center of Wisconsin utilizing monoclonal antibody MBC 131.7 (produced by Blood Center of Wisconsin) directed against CD36. Cross-matching was performed at our institution with multiple single donor apheresis platelets, all showing strong positive reactivity. Given the patient’s low platelet count and onset of urinary tract bleeding, an incompatible leukoreduced, irradiated, and washed single donor platelet unit was given. The patient tolerated the transfusion with no adverse events noted during or after transfusion. The patient’s platelet count rose from < 1 to 14,000/µL when measured 4 hours after the transfusion, and her count was sustained through the following day. Despite the strong, positive reactivity of this unit at crossmatch testing, this was the first successful response to multiple platelet transfusions. Unfortunately, her percentage of blasts in the peripheral blood increased and she maintained an absolute neutrophil count of 0. The patient and hematology team decided to switch to hospice as her AML was resistant to therapy and unfit for any other myelotoxic regimens. Her platelet count was checked the following week and it was 16,000/µL despite no transfusion support.Discussion:Platelet refractoriness in the setting of hematological malignancy has been well documented. Alloantibodies develop from prior pregnancy, prior transfusion or multiple transfusions in the setting of prolonged pancytopenia in hematological malignancies, especially AML. Typically, antibody develops against platelet membrane polymorphic structures including human platelet, ABO, HLA, and very rarely NAKa antigens on the CD36 glycoprotein molecule. CD36 is expressed in almost 100% of white Europeans and is not expressed by 2% of sub-Saharan Africans and 10% of Asians (Blood Transfus 2015: 13: 380). In screening of 871 US blood donors, Yamamoto et al. identified three platelet CD36 deficient individuals. Thus finding a CD36 negative platelet donor will most likely take an extended amount of time, which could be a challenge in these patients as bleeding risk is high during or after induction chemotherapy. CD36 is a soluble antigen and is expressed on various cells such as erythroblasts and monocytes. It has been proposed that when ABO mismatched platelets are transfused, circulating immune complexes may form between the soluble ABH antigens and the transfused antibody. Platelets may then be destroyed by binding of immune complexes to the Fc and C1q receptors. We speculate that a similar pathophysiology may occur in CD36 deficient patients as circulating anti-CD36 forms immune complexes with donor soluble CD36 antigen. Washing will remove most soluble CD36 and potentially mitigate the effect of immune complex formation. Based upon the limited experience with this patient, we suggest that washing in this setting may be beneficial and yield a sustained, incremental response in the platelet count in patients with platelet refractorinesssecondary to anti-NAKa. DisclosuresBlumberg:Biomet/Citra Labs: Consultancy, Honoraria.

A Difficult Position: Appendicitis in Platelet Refractory, Severely Neutropenic Patient

Introduction: There is currently no consensus on management of appendicitis in neutropenic and platelet refractory patients. Case Presentation: A 30 year-old female with high-risk acute monoblastic leukemia with 11q23 translocation undergoing Cytarabine and Adriamycin induction therapy (day number 18) experienced acute right lower quadrant abdominal pain. Hospital course had been complicated by persistent neutropenic fevers despite broad-spectrum antibiotics, and transfusion refractory thrombocytopenia. The patient's platelet count was 1 x 10ˆ3 on the particular morning. She was status-post IVIG and dexamethasone and had been receiving platelet transfusions daily with only minimal increases in her platelet count (maximal response of 3,000). No cross-matched or HLA matched platelets were available at the time. A stat CT abdomen/pelvis showed findings consistent with early appendicitis but no perforation. She also had gingival bleeding and had been passing blood clots per rectum. Given her high risk of bleeding, and lack of ability to raise her critical thrombocytopenia, decision was made to treat the patient medically, adding metronidazole to the meropenem she had been receiving. Abdominal exams were monitored serially with potential need for emergent surgery should her clinical status deteriorate. Her pain resolved the following morning with repeat CT abdomen/pelvis a month later showing resolution of the inflammation at the appendix. Discussion: This patient presented with a therapeutic dilemma. The conventional wisdom is to treat patients with appendicitis surgically, given the high mortality rate should an appendix perforation occur. Currently there is no consensus on the optimal treatment of appendicitis should it arise in the setting of treatment for leukemia. The added complexity of thrombocytopenia prompted conservative therapy. It remains unclear whether the dexamethasone that was administered for the patient's thrombocytopenia helped control the pain and inflammation of the appendicitis, as the patient's symptoms had largely resolved by the following morning. To our knowledge, there are no published case reports on conservative treatment of appendicitis in someone with refractory thrombocytopenia and neutropenia.Figure 1