Ensuring HLA-matched platelet support requires an ethnic diverse donor population.

BACKGROUND: Patients refractory for platelet transfusions benefit from human leukocyte antigen (HLA)-matched platelet transfusions. Differences in ethnic background of patients and donors could hamper the availability of sufficient numbers of HLA-matched donors for all patients. We evaluated our HLA-matched donor program and explored the role of ethnic background of patients related to the number of available donors. METHODS: We performed a cohort study among consecutive patients who received HLA-matched platelet concentrates in the Netherlands between 1994 and 2017. The number of available matched donors was determined per patient. Haplotypes were constructed from genotypes with computer software (PyPop). Based on haplotypes, HaploStats, an algorithm from the National Marrow Donor Program, was used to assess the most likely ethnic background for patients with 5 or fewer and 30 or more donors. RESULTS: HLA typing was available for 19,478 donors in September 2017. A total of 1206 patients received 12,350 HLA-matched transfusions. A median of 83 (interquartile range, 18-266) donors were available per patient. For 95 (10.3%) patients, 5 or fewer donors were available. These patients were more likely to have an African American background, whereas patients with 30 or more donors were more often from Caucasian origin, compared with Caucasian origin for patients with 30 donors. CONCLUSION: Adequate transfusion support could be guaranteed for most but not all refractory patients. More non-Caucasian donors are required to ensure the availability of HLA-matched donors for all patients in the Netherlands.

HLA-matched platelet transfusions are effective only in refractory patients with positive HLA antibody screening.

BACKGROUND: Recipients of platelet transfusions with 1-hour corrected count increments (1hCCIs) of 7.5 or less on two subsequent platelet transfusions with random platelets may benefit from human leukocyte antigen (HLA)-matched platelet concentrates. We aimed to quantify the efficacy of HLA-matched platelets concentrates expressed in 1hCCIs. METHODS: We performed a cohort study among consecutive refractory patients who received HLA-matched platelet concentrates in the Netherlands between 1994 and 2017. We performed mixed-model linear regression comparing 1hCCIs after HLA split-antigen-matched transfusions with 1hCCIs after HLA-mismatched transfusions, adjusted for within-patient correlations. A donor-to-patient match was categorized as a split-match if all donor HLA-A and -B antigens were present in the patient as well; that is, donor and patient were HLA identical or compatible. Subgroup analyses were performed for patients with positive or negative HLA antibody screens. Finally, the additional effect of ABO mismatches on 1hCCIs was investigated. RESULTS: The 1hCCI after an HLA-matched transfusion was 14.09 (95% reference interval, 1.13-29.89). This was 1.94 (95% confidence interval [CI], 0.74-3.15) higher than 1hCCI after HLA-mismatched transfusions. In patients with negative HLA antibody screening tests, HLA matching did not affect 1hCCIs. Conditional on HLA matching, 1hCCIs decreased by 3.70 (95% CI, -5.22 to -2.18) with major ABO mismatches. CONCLUSION: Matched platelet concentrates yielded maximal 1hCCIs, whereas mismatched transfusions still resulted in adequate increments. There is no indication for HLA-matched platelets in patients with negative antibody screens.

Platelets from donors with consistently low HLA-B8, -B12, or -B35 expression do not undergo antibody-mediated internalization.

Patients refractory to platelet transfusions because of alloimmunization require HLA-matched platelets, which is only possible if a large HLA-typed donor pool is available. However, even then, patients with broad immunization or rare haplotypes may not have suitable donors. In these patients, transfusions with platelets showing low HLA class I expression may be an alternative to fully HLA-matched transfusions. In this study, we quantified the proportion of donors with consistently low HLA-B8, -B12, and -B35 expression on platelets using human monoclonal antibodies specific for these antigens. Furthermore, as model for in vivo clearance, antibody-mediated internalization of these platelets by macrophages was investigated. The expression of HLA-B8, -B12, or -B35 on platelets was extremely variable between individuals (coefficients of variation, 41.4% to 73.6%). For HLA-B8, but not for HLA-B12 or -B35, this variation was in part explained by zygosity. The variation was most pronounced in, but not exclusive to, platelets. Expression within one donor was consistent over time. Remarkably, 32% of 113 HLA-B8, 34% of 98 HLA-B12, and 9% of 66 HLA-B35 donors showed platelet antigen expression that was not or only minimally above background. Antibody-mediated internalization of platelets by macrophages correlated with antibody opsonization and antigen expression and was absent in platelets with low or minimal HLA expression. In conclusion, our findings indicate that a substantial proportion of donors have platelets with consistently low expression of specific HLA class I antigens. These platelets may be used to treat refractory patients with antibodies directed against these particular antigens, despite HLA mismatches.

Volume-reduced platelet concentrates: optimization of production and storage conditions.

BACKGROUND: Plasma can be removed from platelet (PLT) concentrates (PCs) when volume reduction for PLT transfusion is indicated. Volume-reduced PCs are currently produced from pooled buffy coat (BC) PCs or apheresis PCs by pretransfusion volume reduction, followed by transfer to a syringe for immediate transfusion. We evaluated the maximal storage time of the volume-reduced PCs in gas-permeable containers. STUDY DESIGN AND METHODS: Volume-reduced PCs were produced from BC-derived and apheresis PCs by hard-spin centrifugation. Supernatant was removed and the PLTs were resuspended in 20 mL of retained original PC and had PLT concentrations ranging from 10.8 × 10(9) to 13.8 × 10(9) PLTs/mL. Volume-reduced PCs were stored either in syringes or in containers made from diethylhexyl phthalate (DEHP)-polyvinylchloride (PVC) or butyryl trihexyl citrate (BTHC)-PVC plastic. Units were sampled at t = 0, 1, 3, and 6 hours for in vitro measurements. RESULTS: When prepared from 2-day-old PCs (n = 4), volume-reduced PCs from BCs in a syringe had a pH(37°C) of 5.76 ± 0.04 at t = 6 hours after volume reduction. In the DEHP-PVC container, pH was 5.85 ± 0.15 (not significant), and in the BTHC-PVC, 6.34 ± 0.16 (p < 0.001), at t = 6 hours. When made from 7-day-old PCs, pH was lower for all storage conditions: 5.68 ± 0.06 in the syringe, 5.70 ± 0.09 in the DEHP-PVC container (not significant), and 6.07 ± 0.24 in the BTHC-PVC container (p < 0.01) at t = 6 hours. Volume-reduced 2-day-old apheresis PCs had a pH of 6.47 ± 0.20 at t = 6 hours. CONCLUSIONS: Adult-dose PCs derived from BC or apheresis can be volume-reduced to approximately 20 mL in a closed gas-permeable system. Volume-reduced PCs in BTHC-PVC containers retain a mean pH of more than 6.0 up to 6 hours after production. Syringes allow only 3 hours of storage.

A comparison of volume-reduced versus standard HLA/HPA-matched apheresis platelets in alloimmunized adult patients.

BACKGROUND: Our blood bank prepares, on indication or request, a volume-reduced (VR) platelet (PLT) product with greater than 95% reduced plasma content and a 15-fold higher PLT concentration, potentially minimizing adverse reactions due to plasma, in particular for human leukocyte antigen (HLA)/human PLT antigen (HPA)-matched PLTs when minor ABO incompatibility cannot be avoided. Here we compared the clinical effectiveness of VR apheresis PLTs (APs) with standard APs. STUDY DESIGN AND METHODS: We performed a single-center cohort study among consecutive alloimmunized patients who received either HLA/HPA-matched standard APs and/or VR-APs between 1994 and 2008. The endpoints were corrected count increments (CCIs), time to next transfusion, and frequency of adverse reactions. The CCI of VR PLTs was calculated using the PLT dose before volume reduction. Using a random effects model, 851 transfusions to 68 patients were evaluated for CCI and 731 transfusions to 64 patients for time to next transfusion. The frequency of reported adverse reactions was compared between the groups. RESULTS: The 1-hour CCI was 23% (95% confidence interval [CI], 9%-42%; p < 0.001) lower and the 24-hour CCI was 17% (95% CI, -11% to 59%; p = 0.278) lower after VR-APs. The mean time to next transfusion was similar: standard APs, 3.1 days (95% CI, 2.7-3.5); and VR-APs, 2.8 days (95% CI, 2.5-3.2). Eight adverse reactions were reported: 4 of 619 in the standard AP group and 4 of 1202 in the VR-AP group. CONCLUSION: VR-APs showed lower 1- and 24-hour CCIs than standard-APs, which can be largely explained by the lower PLT dose of VR-APs. The benefits of plasma reduction should seriously be outweighed given these lower increments.

In vivo tracking of transfused platelets for recovery and survival studies: an appraisal of labeling methods.

The measurement of recovery and survival of platelets is an important decisive factor when 'new' platelet products have been developed. Recovery and survival measurements are mostly performed with radioactive-labeled platelets in healthy volunteers. This approach is required by the FDA for acceptance of platelet products that differ substantially in production or storage conditions from standard methods. However, due to regulatory obstacles, such radiolabeling studies are only carried out in designated institutes. Many countries do not require radioactive labeling studies in volunteers prior to accepting new products, and rather rely on surrogate tests. Also, the European guide to the preparation of blood components does not require this step. This paper reviews alternative, non-radioactive methods, which includes biotinylation of platelets, and discrimination of transfused platelets based on HLA discrepancy. The benefits and disadvantages of these methods will be discussed.

Platelet transfusion therapy: from 1973 to 2005.

Platelet transfusions are indispensable for supportive care of patients with hematological diseases. We describe the developments in platelet products for transfusion since the 1970s, when, in particular, support for patients with allo-antibodies against human leukocyte antigens was a laborious exercise with a high failure rate. Currently, due to many stepwise innovations, platelet transfusions are of low immunogenicity and sufficiently available, they have a shelf life up to 7 days, and even matched platelets can often be routinely delivered, provided that there is good communication between all partners in the chain. Future improvements can be expected from uniform type and screen approaches for immunized patients and cross-matching by computer. For efficient use of health care resources, blood banks and stem cell donor banks could share their typed donor files.