Selection of unrelated compatible platelet donors by lymphocyte HL-A matching

Efficacy of HLA virtual cross-matched platelet transfusions for platelet transfusion refractoriness in hematopoietic stem cell transplantation

BACKGROUND

Cross-matched platelet (cross-matched PLT) transfusion is effective for immune-mediated platelet transfusion refractoriness (PTR), but is more costly and time-consuming for physical cross-match than using standard PLT units. Recent studies have reported the utility of human leucocyte antigens (HLA) virtual cross-matched PLT (HLA-matched PLT) that is defined as HLA-A/B matched or no antibody against donor-specific antigen. Here, we evaluated the effect of HLA-matched PLTs for PTR in post hematopoietic stem cell transplant (HSCT) recipients.

STUDY DESIGN AND METHODS

Our study included a total of 241 PLTs in 16 patients who underwent HSCT at Okayama University Hospital between 2010 and 2017, receiving either HLA-matched or cross-matched PLTs. We calculated the 24-hour corrected count increments (CCI-24) to evaluate the effect of PLTs. A CCI-24 ≥ 4500 was considered to be a successful transfusion.

RESULTS

We analyzed 139 cross-matched PLTs and 102 HLA-matched PLTs. In the immune-mediated PTR, the rate of successful transfusion was 60.5% for cross-matched PLT and 63.4% for HLA-matched PLT (p = 0.825). On the other hand, the median CCI-24 for cross-matched PLT transfusions and HLA-matched PLT transfusions were 1856 and 5824 (p < 0.001), with a success rate of 28.1 and 54.1% in cases with non-immune-mediated PTR, respectively (p = 0.001).

CONCLUSION

The effectiveness of HLA-matched PLT is not inferior to cross-matched PLT. This result indicates that physical cross-match can be omitted in post HSCT PTR.

Flow cytometric quantitation of platelet phagocytosis by monocytes using a pH-sensitive dye, pHrodo-SE

Antibody-mediated phagocytosis of platelets using a flow cytometric monocyte-based phagocytosis assay (FMPA) has been shown to predict the outcome of platelet transfusion. The easy adherence between platelets and monocytes even in the absence of an antibody is regarded as one of limitations of the FMPA. To improve the FMPA for prediction of transfusion outcome, we used the pH-sensitive dye pHrodo succinimidyl ester (pHrodo-SE), which has weak fluorescence at neutral pH and has increased fluorescence intensity in low pH conditions such as in lysomes. Platelets stained with pHrodo-SE were sensitized with an HLA class I monoclonal antibody (w6/32 clone) or anti-HLA class I containing antisera. The platelets were incubated with monocyte-enriched mononuclear cells. Phagocytic activity was assessed by the percentage of monocytes that phagocytosed platelets. Sensitization of platelets with w6/32 significantly increased platelet phagocytosis by monocytes in dose- and time-dependent manners. Anti-HLA class I antibody-containing sera caused platelet phagocytosis in a cognate antigen-antibody-dependent manner. There was a significant correlation (r=0.69, p<0.01) between phagocytic index and titer of HLA class I antibody measured by lymphocyte immunofluorescence test-flow cytometry. In addition, the phagocytic index obtained by FMPA with pHrodo-SE was significantly higher than that obtained by FMPA with the previously used dye, carboxyfluorescein diacetate succinimidyl ester, when platelets were sensitized by w6/32 and anti-HLA class I antibody-containing sera. Because of the higher resolution and higher sensitivity than those of the previous method, the pHrodo-SE-based FMPA may be suitable for more precise quantitation of phagocytosis activity, which would enable qualitative evaluation of transfusion effectiveness.

Extended Small-Dose Platelet Transfusions in Multitransfused Hemato-Oncological Patients: A Single-Center Experience

BACKGROUND

Refractoriness to platelet transfusion, prevalent among 15-20% of hemato-oncological patients, is associated with multitransfusions and inferior outcomes. We evaluated the effectiveness of extended slow-dose transfusion (ESDT) in increasing platelet increments in multitransfused patients.

METHODS

Patients treated after the implementation of ESDT were compared with historical controls treated with standard single-donor platelet (SDP) transfusions. Cohorts of early and late recipients were assembled for comparison, i.e. the 8th or 9th and 11th platelet unit per patient, respectively. Patients in the ESDT group received transfusions equal to half an SDP unit, administered over 4 h. Effectiveness was defined as a higher corrected count increment (CCI) at 1, 12, and 24 h after transfusion.

RESULTS

In the early-recipients cohort, 24-h-posttransfusion increments were available for 29 ESDT patients and 6 standard patients, and did not differ significantly between the groups (p = 0.078). The 24-h-posttransfusion increment was available for 20 ESDT patients and 7 standard patients in the late-recipients cohort. The CCI was significantly higher in the ESDT group (p = 0.042). ABO compatibility improved the CCI (p = 0.01).

CONCLUSIONS

ESDT demonstrated slightly higher increments at 24 h after transfusion in late recipients, suggesting this could be a cost-effective approach for the treatment of thrombocytopenic multitransfused hemato-oncological patients.

CD8+ T cells mediate antibody-independent platelet clearance in mice

Platelet transfusion provides an important therapeutic intervention in the treatment and prevention of bleeding. However, some patients rapidly clear transfused platelets, preventing the desired therapeutic outcome. Although platelet clearance can occur through a variety of mechanisms, immune-mediated platelet removal often plays a significant role. Numerous studies demonstrate that anti-platelet alloantibodies can induce significant platelet clearance following transfusion. In fact, for nearly 50 years, anti-platelet alloantibodies were considered to be the sole mediator of immune-mediated platelet clearance in platelet-refractory individuals. Although nonimmune mechanisms of platelet clearance can often explain platelet removal in the absence of anti-platelet alloantibodies, many patients experience platelet clearance following transfusion in the absence of a clear mechanism. These results suggest that other processes of antibody-independent platelet clearance may occur. Our studies demonstrate that CD8(+)T cells possess the unique ability to induce platelet clearance in the complete absence of anti-platelet alloantibodies. These results suggest a previously unrecognized form of immune-mediated platelet clearance with significant implications in the appropriate management of platelet-refractory individuals.

Living donor liver transplantation for patients immunized against human leukocyte antigen

BACKGROUND/PURPOSE

The clinical features and perioperative management of liver transplant recipients who are already sensitized against human leukocyte antigen (HLA) prior to transplantation are not yet clear.

MATERIALS AND METHODS

Medical records of living donor liver transplant recipients were reviewed and clinical features of the patients possessing anti-HLA antibodies were studied.

RESULTS

Among the 470 consecutive living donor liver transplant recipients, 6 patients (1.3%) had preformed anti-HLA antibodies. A review of the postoperative courses of these patients revealed that the problems included platelet transfusion refractoriness (PTR) due to immune-mediated destruction of platelet and thrombotic microangiopathy (TMA). PTR was observed in patients with anti-HLA class I antibodies and only HLA-matched platelet concentrate (HLA-matched PC) relieved thrombocytopenia. Intravenous gammaglobulin had an additive effect to HLA-matched PC in some cases, and platelet transfusion from close relatives might be a substitute for HLA-matched PC in life-threatening situations. Although the etiology of TMA is unremarkable, the incidence was high (67%, 4/6) compared with that in patients who were not sensitized against HLA (5.6%, 26/464; p < 0.01). Of the four patients, three were complicated with late-onset TMA.

CONCLUSIONS

Considering these clinical features, careful preparation and postoperative management are needed for liver transplant candidates with anti-HLA antibodies.

Efficacy of HLA-matched platelet transfusions for patients with hypoproliferative thrombocytopenia: a systematic review

BACKGROUND

HLA-matched platelets (PLTs) are widely used to transfuse patients but the effectiveness of HLA matching has not been well defined and the cost is approximately five times the cost of preparing the random-donor PLTs. The objective of this systematic review was to determine whether HLA-matched PLTs lead to a reduction in mortality; reduction in frequency or severity of hemorrhage; reduction in HLA alloimmunization, refractoriness, or PLT utilization; or improvement in PLT count increment in patients with hypoproliferative thrombocytopenia.

STUDY DESIGN AND METHODS

We conducted a literature search of MEDLINE, Cochrane Controlled Register of Clinical Trials, EMBASE, and PubMed databases to April 2012.

RESULTS

A total of 788 citations were reviewed and 30 reports were included in the analysis. Most studies did not include technologies currently in use for HLA typing or detection of HLA antibodies as 75% were conducted before the year 2000. None of the studies were adequately powered to detect an effect on mortality or hemorrhage. HLA-matched PLTs did not reduce alloimmunization and refractoriness rates beyond that offered by leukoreduction, and utilization was not consistently improved. HLA-matched PLTs led to better 1-hour posttransfusion count increments and percentage of PLT recovery in refractory patients; however, the effect at 24 hours was inconsistent.

CONCLUSION

The correlation of the PLT increment with other clinical outcomes and the effect of leukoreduction on HLA-matched PLT transfusion could not be determined. Prospective studies utilizing current technology and examining clinical outcomes are necessary to demonstrate the effectiveness of HLA-matched PLT transfusion.

Platelet transfusion refractoriness caused by a mismatch in HLA-C antigens

BACKGROUND

HLA-C antigens have been thought to be of little significance in determining the efficacy of platelet transfusions. However, six alloimmunized patients were encountered who were refractory to platelet transfusions because of anti-HLA-Cw3, -Cw3, -Cw7, or -Cw8.

STUDY DESIGN AND METHODS

Between 1995 and the present, 88 patients with hematologic malignancies became refractory to random-donor platelet transfusions due to HLA antibodies. HLA-A- and HLA-B-compatible platelet transfusions were successful in boosting platelet levels with 82 of the patients. This study concerns the remaining six HLA-immunized patients who were refractory to HLA-A- and HLA-B-compatible platelet transfusions. The response to the platelet transfusions was assessed by calculating both 1- and 24-hour posttransfusion CCIs for each transfusion.

RESULTS

The average CCI(1 hour) and CCI(24 hours) in all patients were 20.0 and 12.8 for HLA-A-, HLA-B-, and HLA-C-compatible transfusions and were 1.4 and 1.2 for HLA-A- and HLA-B-compatible but HLA-C-incompatible transfusions, respectively (p < 0.001).

CONCLUSION

These findings clearly indicate that matching of the HLA-C antigens is also required in some alloimmunized patients to obtain the effectiveness of platelet transfusions.

Platelet alloantibodies in transfused patients

BACKGROUND

Patients receiving cellular blood components may form HLA antibodies and platelet-specific alloantibodies.

STUDY DESIGN AND METHODS

Serum samples from a cohort of 252 patients with hematologic or oncologic diseases who are receiving cellular blood components were studied for platelet-reactive antibodies. Specificity of platelet alloantibodies was determined with a panel of typed platelets

RESULTS

Platelet-reactive antibodies were detected in the sera of 113 patients (44.8% of 252), HLA antibodies in the sera of 108 (42.9%), and platelet-specific antibodies in the sera of 20 (8%). The following platelet-specific antibodies were identified: anti-HPA-5b (n = 10), anti-HPA-1b (n = 4), anti-HPA-5a (n = 2), anti-HPA-1a (n = 1), anti-HPA-2b (n = 1), anti-HPA-1b+5b (n = 1), and anti-HPA-1b+2b (n = 1). Fifteen sera from the 108 patients with anti-HLA (13.9%) contained additional platelet-specific alloantibodies, while in 5 sera, platelet-specific alloantibodies only were detected: anti-HPA-5b (n = 4) and anti-HPA-1a (n = 1). Of the 108 sera with HLA antibodies, 29 (26.9%) showed discordant results when studied with the lymphocytotoxicity test and the glycoprotein-specific immunoassay. Ten sera contained panreactive antibodies against platelet glycoproteins (GP) IIb/IIIa, GPIa/IIa, and/or GPIb/IX. Alloimmunization occurred in 58.3 percent of female patients with previous pregnancies, but in only 23.3 percent of those without previous pregnancies (p = 0.0049).

CONCLUSION

Platelet alloantibody specificities in transfused patients (predominantly anti-HPA-5b and -1b with antigen frequencies <30% among whites) differ significantly from those observed in patients with neonatal alloimmune thrombocytopenia or posttransfusion purpura, in whom anti-HPA-1a (antigen frequency >95%) is the most prevalent specificity. HLA antibody detection yields discordant results when the lymphocytotoxicity assay and a glycoprotein-specific immunoglobulin-binding assay are used.

Algorithm for managing the platelet refractory patient

Refractoriness to platelet transfusions continues to be a major problem for many thrombocytopenic patients. A proposed algorithm for managing these patients is presented which proceeds from easily instituted changes in platelet transfusion therapy such as provision of ABO-compatible and "fresh" platelet transfusions to the more difficult and costly process of selecting compatible platelets for patients who are documented to be alloimmunized. For nonimmunized platelet refractory recipients, multiple clinical and drug factors that may adversely effect transfusion responses have been identified. Identifying which of these factors are causally associated with poor platelet responses in any given patient remains a substantial challenge.

Risks, costs, and alternatives to platelet transfusions

The use of platelet transfusions has increased greatly in the past decade and is likely to continue to escalate because of the risks of thrombocytopenia in patients receiving dose-intensive cancer chemotherapy, the increased use of hematopoietic progenitor cell transplantation, and the prevalence of human immunodeficiency virus infection. Despite marked advances in procedures for ensuring the safety of platelets, including intensive donor screening, infectious disease marker testing, and increased use of leukodepletion techniques, platelet transfusions carry a significant risk for immunologic disorders and transmission of bacterial, viral, and perhaps other diseases and can entail a very high cost. In addition, thrombocytopenia has the potential to interfere with delivery of chemotherapy on schedule and at the planned doses, thus potentially compromising treatment outcome. The limitations of platelet transfusions have prompted the development of agents with the potential to stimulate platelet production and thus reduce or eliminate the need for transfusions. Two such agents, interleukin-11 (IL-11) and thrombopoietin (TPO), have demonstrated promise in clinical trials. In November, 1997, IL-11 received FDA approval for the prevention of severe thrombocytopenia in high risk patients receiving myelosuppressive chemotherapy. Thrombopoietic growth factors have the potential to greatly simplify and increase the safety of transfusion medicine.

Use of HLA- and HPA--matched platelets in alloimmunized patients

Refractoriness for platelet transfusion is mostly due to clinical factors but may also be caused by alloimmunization. Use of leukocyte-depleted blood cells for transfusions of patients with hematological diseases has reduced if not eliminated HLA-alloimmunization. HLA-antibodies reduce the survival time of incompatible platelets complicating seriously the platelet transfusion support in at least 5% of patients. If consecutive transfusions of HLA matched platelets also fail without identifiable clinical causes, HPA-alloimmunization may have occurred. Platelets from donors phenotyped for both HLA and HPA may produce good platelet count increments and allow optimal treatment of the basic disease despite broad spectrum alloimmunization. Additional cross-matching of phenotyped platelets with patient serum may be needed to circumvent platelet-specific antibodies of unknown specificity.

Successful treatment of platelet transfusion refractoriness: the use of platelet transfusions matched for both human leucocyte antigens (HLA) and human platelet alloantigens (HPA) in alloimmunized patients with leukaemia

Six patients, 4 with acute myeloid leukaemia and 2 with a myelodysplastic syndrome who were refractory to random donor platelet transfusions and alloimmunized to human leucocyte antigens (HLA) and human platelet alloantigens (HPA), were treated with HLA- and HPA-matched platelet transfusions. In all the patients refractoriness and alloantibodies to HLA as well as HPA-1b or HPA-5b were detected simultaneously. Sixty-seven transfusions (445 units) of HLA- and HPA-matched platelets were given and responses to them were, in general, satisfactory in all the patients. No major spontaneous bleeding occurred. Four patients underwent bone marrow transplantation despite alloimmunization. The percentages of platelet transfusion days with a platelet nadir below 20x10(9)/l were 88% for the last 3 random donor platelet transfusions and 39% for the first 3 HLA- and HPA-matched platelet transfusions, respectively (p=0.009, Fisher's exact test). Four patients received also HLA-matched platelets, but responses to them were poor. The small number of transfusions with HLA-matched platelets precluded comparisons to either the random donor or HLA- and HPA-matched platelet transfusions. It seems that HLA- and HPA-alloimmunized patients can be successfully supported with HLA- and HPA-matched platelet concentrates.

Procoagulant effect of incompatible platelet transfusions in alloimmunized refractory patients

The clinical effectiveness of platelet transfusion in refractory patients is still a subject of debate. We have evaluated the possible hemostatic effect of platelet transfusion in 16 alloimmunized thrombocytopenic patients whose platelet counts were less than 20,000/microliters. Platelet concentrates were always obtained by apheresis procedures from incompatible donors. The posttransfusion platelet recovery was greater than 15% only in 3 cases. In the first 6 patients, measurements of bleeding time performed immediately before transfusion were in all cases longer than 30 min and did not change significantly 10 and 60 min after platelet transfusions. In all patients, ex vivo perfusion experiments with Baumgartner's platelet adhesion model, using native nonanticoagulated blood, were performed immediately before and 10 and 60 min after transfusion. No difference in platelet deposition onto the subendothelial surface was observed after platelet transfusion. Unexpectedly, the deposition of fibrin on the subendothelial surface was statistically augmented in the posttransfusion studies. Quantification of thrombin-antithrombin complexes (TAT) in plasma showed statistically significant elevations (p < 0.01) in the posttransfusion samples (31.9 +/- 12.6 vs. baseline 5.8 +/- 1.7 ng/ml), not justified by TAT levels in the transfused material (2.3 +/- 0.17 ng/ml). Transfusion of incompatible platelets to refractory patients may activate coagulation mechanisms in the absence of an increase in peripheral platelet count.

Platelet support and the use of cytokines

Severe thrombocytopenia and clinical bleeding remain major clinical problems in leukemic patients undergoing remission induction and those receiving high dose chemotherapy. Prophylactic platelet transfusions have made a major impact on hemorrhagic deaths over the last 20 years. The effectiveness of platelet transfusions is influenced by a number of clinical factors including the status of the spleen, prior bone marrow transplantation, the presence of disseminated intravascular coagulation and the presence of HLA antibodies. Optimal platelet transfusion therapy requires that transfusions be monitored routinely by post-transfusion counts and that a refractory group be clearly defined. The cytokine granulocyte colony stimulating factor (G-CSF) has not had a clinically significant impact on thrombocytopenia. Granulocyte-macrophage colony stimulating factor (GM-CSF) also probably has little clinical relevance, although in a randomized study, thrombocytopenia was worse in GM-CSF-treated patients. Interleukin-3 (IL-3) can increase platelet count and has the potential to protect against thrombocytopenia in patients receiving chemotherapy. This hypothesis is currently being tested in on-going clinical trials.

The collection of platelets by apheresis procedures

Collection of platelets by apheresis has been a major advance in transfusion medicine. It has allowed the supply of a therapeutically beneficial component to grow with medical needs. Donors find fulfillment in more frequent donations than are possible with whole blood and know that their donation fills a special need. New technology allows leukocyte reduction in the collection of the component with or without the use of filtration. Matching for refractory patients is possible. However, platelets collected by apheresis have not been shown to be hemostatically different from platelets separated from whole blood donations, and thus, do not represent an advance in therapeutic efficacy. The use of apheresis platelets does reduce donor exposure, but this has not been shown to be a safety advance, although it seems intuitively obvious that transfusion risk is statistically reduced in some patients requiring only a few platelet transfusions. Support of patients by apheresis platelets may or may not reduce the risk of alloimmunization. Apheresis platelets from some equipment have less white blood cell contamination even in the absence of filtration, which may be an advantage. Apheresis platelets could be a major step in the ultimate customization of blood collection, in which some donors would preferentially donate red blood cells, whereas others would donate platelets or plasma depending on their blood type and ability to donate frequently, and the current medical need of their donation. Perhaps this would be the most significant advance from the medical progress initiated by Cohn almost 50 years ago.

The definition of refractoriness to platelet transfusions

The relationship between the 1 and 20 h post-transfusion platelet count and three parameters used to define refractory transfusions, namely the corrected increment (CI), platelet increment (PI), and percentage platelet recovery (%REC), was studied in 437 non-HLA matched platelet transfusions given to 102 patients with bone marrow failure. The percentage agreement between common definitions of refractoriness was calculated based on these parameters. As the maintenance of platelet counts above 20 x 10(9)/l is a relevant clinical goal for platelet support, the values of the CI, PI and %REC, which best corresponded to 1- and 20-h post-transfusion counts of 20 x 10(9)/l, were identified. A 1-h post-transfusion CI < 3 (PI < 7 x 10(9)/l or % REC < 8%) corresponded to clinically unsuccessful transfusions with a 1-h platelet count < 20 x 10(9)/l. A 1-h CI > or = 5.5 (PI > or = 12 x 10(9)/l or %REC > or = 14%) corresponded to clinically successful transfusions with a 20-h post-transfusion count of > or = 20 x 10/l. These data tie together the end points reported in the literature for defining refractory transfusions.

An alloimmunized, thrombocytopenic patient successfully transfused with acid-treated, random-donor platelets

Alloimmunized, thrombocytopenic patients, refractory to random-donor platelet transfusion, often respond to HLA-identical single-donor platelets. HLA-compatible platelets are expensive, take time to prepare, and donors are sometimes not to be found. We have used random-donor platelets and 'peeled' the HLA-antigen off the platelets, using a modified laboratory method (incubation of platelets with citric acid solution at 0 degrees C). Platelet recovery in two healthy subjects was 72.0% for acid-treated platelets, and 73.5% for untreated control platelets, using 111In-labelled autologous platelets. Survival time (multiple hit) was 6.25 and 7.95 d, respectively. Random-donor platelets that were strongly positive in the crossmatch with serum from a patient became negative after treatment with the acid solution. Furthermore, transfusion of these platelets gave a post-transfusion, platelet-count increment comparable with transfusion of HLA-compatible single-donor platelets.

[Alloimmunization and transfusion refractoriness to thrombocyte substitution]

No generally accepted policy for avoiding HLA-alloimmunization has so far been established. However, several studies suggest that single-donor instead of random-donor transfusions, white cell depletion, UV-radiation of blood products or application of cyclosporine to the recipient may avoid or at least delay alloimmunization. With regard to cost effectiveness, it would be essential to identify patients with the highest risk of developing alloimmunization. For the time being, transfusion of crossmatch-compatible HLA-selected single donor platelets should be restricted to alloimmunized patients, refractory to pooled random donor platelets.

New approach to eliminate HLA class I antigens from platelet surface without cell damage: acid treatment at pH 3.0

A new method was studied for eliminating HLA class I antigens from the surface of platelets without damaging the cells. Platelets were exposed to an acid solution (pH 3.0) to eliminate the antigenicity of HLA class I antigens. The reduction in antigenicities of HLA class I common antigen and individual HLA class I antigens by acid treatment was marked. Patients' sera which contained multispecific HLA antibodies reacted with PBS-treated platelets, but not with acid-treated platelets. No changes were observed in the antigenicities of glycoprotein Ib or glycoprotein IIb/IIIa. The viability of acid-treated platelets was 83%. Ultrastructural investigations revealed no significant difference between the PBS-treated platelets and acid-treated platelets. The platelet function studies showed that the aggregation of acid-treated platelets induced by various agonists was only slightly reduced compared with PBS-treated platelets. We propose that acid-treated platelets are promising for clinical use in patients refractory to platelet transfusions and may be superior to chloroquine-treated platelets for analysis of the specificity of antiplatelet antibodies.

Immunology of platelet disorders

Immune-mediated thrombocytopenias (IMTPs) are frequently-occurring haemostatic disorders in clinical medicine. They may be caused by allo-immunity, autoimmunity, or by drug-induced immune mechanism. All IMTPs are caused by antibodies, which may induce increased platelet destruction but may also hinder platelet function. Many different platelet membrane molecules (i.e. antigens) are involved in the immune processes that play a role in IMTP. Much is already known about the structure of these molecules. Notably the alloantigens involved in alloimmune-mediated thrombocytopenia have been quite well studied. Many of these antigens appear to be polymorphic determinants of adhesion molecules of the integrin superfamily, and are also present on cells other than platelets (endothelial cells, fibroblasts, smooth muscle cells). The methodology for studying platelet antigens and antibodies involved in IMTPs has markedly improved in recent years. This has not only led to better diagnostic tests but also to a better understanding of the immunopathogenesis of these diseases. Platelet immunology is scientifically very much alive, and is expected to remain so in the coming years.

New platelet antigen, Siba, involved in platelet transfusion refractoriness in a Japanese man

Siba, a new platelet-specific alloantigen involved in a case of platelet transfusion refractoriness is reported. The IgG platelet alloantibody was detected in a multiply transfused patient of Japanese extraction (Sib), by the presence of HLA antibodies. After transfusion of HLA-compatible platelets, the patient suffered from refractoriness. Adsorption studies with pooled lymphocytes showed that the serum contained anti-platelet activity. Family studies indicate that Siba is inherited as an autosomal codominant trait and separate from HLA and Baka. As of this report, segregation from Zw(PlA) and Yuk (Pen) antigen systems have not yet been determined. The gene frequency of Siba in the Japanese population is estimated to be 0.136.

A prospective randomized trial of HLA-matched versus mismatched single-donor platelet transfusions in cancer patients

The use of histocompatability antigen (HLA)-matched platelets has been advocated for the support of thrombocytopenic cancer patients. We randomized 78 newly diagnosed cancer patients prospectively (before thrombocytopenia) to receive either HLA-matched or mismatched single-donor platelet transfusions. Three hundred forty-one platelet transfusions were given for 80 separate episodes of therapy-induced thrombocytopenia in 33 patients. Forty-five patients receiving intensive chemotherapy did not develop significant (less than 20,000 platelets/mm3) thrombocytopenia and did not receive a platelet transfusion. No marked difference was observed between the matched and mismatched groups in regard to number of total platelet transfusions per patient (median, 3 vs. 5, respectively; P = 0.076), number of platelet transfusions per episode (median, 3.0 vs. 3.5, respectively; P = 0.28), or days between transfusions (median, 2 vs. 2, respectively, P greater than 0.4). Bleeding episodes, although rare, tended to be of increased severity in the mismatched group. Febrile patients receiving mismatched platelets tended to have a lower posttransfusion increment increase than their nonfebrile counterparts (P = 0.068), although a similar trend could not be demonstrated between febrile and nonfebrile patients who received matched platelets (P = 0.22). Patients treated as outpatients had significantly higher posttransfusion increments than when transfused as inpatients when they were given mismatched platelets (P less than 0.0005). Development of antiplatelet antibody did not appear to affect response to platelet transfusions. Only one patient developed sustained high-level antibody titers. In patients where thrombocytopenia was significant, the transfusion of HLA-matched platelets did not appear to offer a significant advantage. However, HLA-matched platelet transfusions tended to be associated with higher posttransfusion increments in febrile patients and a trend toward fewer severe bleeding episodes. A multi-institution trial containing a large number of patients is needed to evaluate trends observed in this study.

Bone marrow transplantation in patients with leukaemia previously transfused with blood products from family members

Transfusions are withheld, whenever possible, from patients with aplastic anaemia who are potential bone marrow transplant recipients because of the increased risk of graft failure associated with transfusions prior to transplantation. Family members are specifically excluded as blood product donors to reduce the likelihood of sensitizing the recipient to antigens shared by the blood and bone marrow donor. This policy of not using family members, particularly the HLA-matched bone marrow donor, to provide blood products prior to transplantation has been extended to leukaemia as well. To evaluate this policy we reviewed the outcome of bone marrow transplantation in 18 patients with leukaemia transfused prior to transplantation with platelets and/or leucocytes from related family members. In 15 cases in which the outcome could be evaluated, engraftment was rapid and graft failure did not occur. Transfusion of blood products from related family members to patients with leukaemia prior to transplantation does not appear, therefore, to increase the risk of graft rejection.

Lymphocyte subpopulations of plateletapheresis products collected with the Fenwal CS-3000 Cell Separator

To determine whether any lymphocyte subset is preferentially harvested and transfused as a consequence of plateletapheresis with the Fenwal CS-3000 Blood Cell Separator, the proportions of lymphocyte subpopulations in platelet concentrates were compared to their proportions in the donors' peripheral venous blood immediately prior to platelet collection. There was no difference in the proportion of B cells (surface immunoglobulin positive), T cells (OKT3 positive), helper/inducer T cells (OKT4 positive), suppressor/cytotoxic T cells (OKT8 positive), and natural killer cells (Leu 7 positive) in the donors' peripheral venous blood and the plateletapheresis product. Thus, although previous studies have demonstrated the ability to separate lymphocyte subpopulations by density centrifugation and velocity sedimentation, plateletapheresis with the CS-3000 harvests the lymphocyte subpopulations studied in the same proportions in which they circulate in donors' peripheral venous blood.

Canine platelet alloimmunization: the role of donor selection

Five different platelet transfusion programmes were evaluated in a canine model to determine the most effective method of providing long-term platelet support. When a weekly transfusion from a single unrelated donor was used, alloimmune platelet refractoriness developed in 95% of recipients after an average of 3.1 +/- 0.7 transfusions, and donor platelets circulated for a total of 8.2 +/- 2.3 d. When multiple unrelated donors were used, the percentage of refractory recipients was similar (60% versus 77%) whether platelets came from six single donors given sequentially or from a pool of the same six donors given repeatedly. There was, however, a significant difference in the number of transfusions given prior to immunization (14 +/- 5 transfusions lasting 32 +/- 12 d for sequential single donors as compared to 5.5 +/- 1.0 transfusions lasting 13 +/- 2 d for the pooled donors). When littermates were used as platelet donors, the frequency of refractory recipients, the number of transfusions required to immunize, and the circulation time of donor platelets before refractoriness was not better than when multiple unrelated single donors were used. Furthermore, there was no significant difference in effectiveness between DLA-identical and DLA-nonidentical littermate platelet donors. In recipients previously immunized by a pool of six unrelated donors, the same percentage of recipients was refractory to DLA-identical littermate donors as had been observed following only DLA-identical platelet transfusions. This suggests that non-DLA immunizing platelet antigens, not shared between approximately 30% of DLA-identical littermates, are well represented in a random canine population. However, prior random transfusions did not compromise long-term platelet support from 'truly' platelet compatible DLA-identical littermate donors. These studies indicate that single donor transfusions either from littermates or sequential unrelated donors are the most effective method of providing long-term platelet support. However, the use of pooled unrelated donor transfusions, followed by DLA-identical donors in immunized recipients is an equally acceptable alternative.

The kinetics of unmatched and HLA-matched 111in-labelled homologous platelets in recipients with chronic marrow hypoplasia and anti-platelet immunity

The kinetics of homologous platelets, labelled in plasma with 111In-tropolonate, have been studied in five recipients with chronic marrow hypoplasia and severe thrombocytopenia, who were refractory to platelet transfusions as a result of alloimmunization. Mean platelet life span (MPLS), recovery, plasma 111In level and splenic and hepatic uptake kinetics were studied on two occasions, one using HLA-matched platelets and the other unmatched platelets. In each case, recovery of labelled platelets at 1 h post-injection and MPLS improved with HLA matching, although this improvement was highly variable. Only two of the five subjects would have derived any significant benefit from HLA-matched as compared with unmatched platelet transfusions. It was concluded that the need exists for additional cross-matching procedures, possibly related to platelet specific antigens, in patients who remain refractory to platelet transfusion.

An animal model of alloimmune thrombocytopenia. I. The role of the mononuclear phagocytic system (MPS)

To understand better the role of the mononuclear phagocytic system (MPS) in accelerated destruction of donor platelets in man following repeated platelet transfusions, an experimental model has been developed using genetically defined animals. Brown Norway rats were immunized with Lewis platelets. Antibodies were detected by immunofluorescence microscopy, and their effects demonstrated by 111In-labeled platelet clearances in vivo and by measurements of organ radioactivity in sacrificed animals. All immunized rats developed platelet alloantibodies and showed a significant decrease (P less than 0.001) in donor platelet survival with sequestration in both the liver and spleen. Liver to spleen radioactivity ratios in nonimmunized animals were less than 0.1, whereas immunized animals had a ratio between 0.6 and 1.0, indicating relatively greater hepatic clearance of allogenic platelets. Studies currently in progress on the administration of vinca alkaloids to immunized animals suggest that the MPS can be impaired from clearing allogenic platelets. This model, therefore, should be helpful in studying the role of the MPS in platelet destruction.

Prospective platelet crossmatching for selection of compatible random donors

An indirect platelet radioactive antiglobulin test was used in a prospective crossmatch study in 29 patients for selecting compatible random donors for platelet transfusion. Patients received crossmatch-compatible, crossmatch-incompatible and uncrossmatched platelets. A successful outcome for transfusion was defined as a 24 h post-transfusion corrected platelet increment of greater than 4.5 X 10(9)/l. Of 47 predictions based on crossmatch results, the technique successfully predicted the outcome of the transfusion in 90% of cases. In all patients, transfusion of crossmatch-compatible platelets resulted in a significantly higher 24 h corrected platelet increment than was obtained following transfusion of incompatible platelets. The mean +/- SEM 24 h corrected post-transfusion increment (X 10(9)/l) was 17.79 +/- 2.01 in 26 patients who received crossmatch-compatible pooled random donor platelets; in 21 patients who received crossmatch-incompatible platelets, it was 1.19 +/- 0.56; and in 25 patients who received uncrossmatched platelets, 4.42 +/- 0.97. The differences were highly significant. There was an 83% correlation of results with those obtained using an indirect platelet suspension immunofluorescence technique.

Autologous cryopreserved platelets and prophylaxis of bleeding in autologous bone marrow transplantation

Autologous platelets were harvested and cryopreserved in eight consecutive patients elected for ablative chemotherapy and autologous bone marrow transplantation (ABMT) for solid malignancy. There was a 19% loss in platelet count after the freeze thaw and wash procedure; with an in vitro functional loss of 40-60%. No correlation could be found for individual platelet transfusions between in vitro functional tests and in vivo recovery. Six consecutive patients received a total of 16 autologous platelet transfusions in the aplastic phase of ABMT. No bleeding was observed during the study period and there was no CMV infection in the recipients. While improvement in freezing and subsequent handling is desirable, autologous cryopreserved platelets can safely be used for the prophylaxis of bleeding during aplasia in patients treated with ABMT.