Prevention of MHC-alloimmunization by UV-B irradiation in a murine model: effects of UV dose and number of transfused cells

The optimal dose of UV-B radiation for prevention of in vivo alloimmunization (AI) against major histocompatibility complex (MHC) antigens was investigated in a murine transfusion model. Two groups with five C57BL/6 mice (H2^b) each were transfused at weekly intervals with 1 x 10⁵ or 1 x 10⁶ DBA/2 (H-2^d) leucocytes. Both suspensions induced anti-H-2^d antibodies in all mice after the second transfusion. The minimal UV-B dose required for abolition of alloreactivity in the mixed leucocyte reaction (MLR) was 0.6 J/cm². This dose completely prevented the onset of MHC-AI in all five mice transfused with six suspensions containing 1 x 10⁵ leucocytes. In contrast, suspensions with 1 x 10⁶ leucocytes and exposed to 0.6 J/cm² induced immunization in 4/5 mice. Further increase of the dose to 1.8 or 5.4 J/cm² did not prevent the onset of MHC-AI. The use of UV radiation for prevention of secondary MHC-AI was investigated in five mice with a primed immune system. Transfusion of suspensions with 1 x 10⁵ leucocytes and irradiated at a dose of 1.8J/cm² did not prevent booster reactions. We conclude that the number of leucocytes per transfusion determines the efficacy of UV irradiation for the prevention of MHC-AI. For UV irradiation of human platelet concentrates (PCs) we propose to reduce the number of leucocytes by centrifugation prior to UV exposure. UV-B irradiation of PCs with high numbers of leucocytes may not be effective for prevention of alloimmunization.     

Differences in Residual White Blood Cell Subset Counts in Buffy Coat-Depleted Red Cell Concentrates Prepared with Bottom and Top or Quadruple-Bag Systems

Background: For preparation of buffy coat-depleted red cell concentrates (RCCs) in additive solution whole blood is currently collected in The Netherlands both in quadruple-bag and bottom and top bag systems. By using the quadruple-bag system both plasma and buffy coat cells are transferred into integrated satellite bags while the red cells remain in the collection bag. When bottom and top bags are used, the buffy coat remains in the collection bag while both red cells and plasma are transferred into satellite bags. The difference in processing prompted us to perform quantitative analysis of residual WBC subsets in buffy coat-depleted RCCs. Differences in removal of specific cells with the buffy coat could improve the outcome of additional filtration procedures aiming at complete removal of specific WBC subsets. Study Design and Methods: The buffy coat was removed in semiautomated procedures (Optipress I; Compomat G4) from units of whole blood collected in both bag systems. Paired samples were taken before and after removal of the buffy coat for counting and analyzing WBC subsets by flow cytometry using subset specific monoclonal antibodies. Results: All RCCs met the criteria from the guidelines of the Council of Europe. The percentage of residual total WBCs was lower (p < 0.001) in RCCs processed in bottom and top bag systems (26% Compomat and 18% Optipress) as compared to RCCs processed in quadruple-bag systems (43% compomat). WBC subset analysis in RCCs processed in quadruple-bag systems showed approximately 25% of residual T cells, B cells and monocytes and 60% of residual granulocytes. In contrast, WBC subset analysis in RCCs processed in bottom and top bag systems showed approximately 2% residual T cells, B cells, and monocytes and 35% residual granulocytes; in about 45% of units, lymphocytes and monocytes were even below the detection limit of flow cytometry analysis. Conclusion: Buffy coat-depleted RCCs are currently processed in bottom and top bag or quadruple-bag systems, the former being superior to the latter due to selective depletion of lymphocytes and monocytes by 98% (2 logs). The bottom and top procedure is an evident contribution to leukodepletion in blood transfusion, both with and without additional filtration.     

Leukocyte depletion of random single-donor platelet transfusions does not prevent secondary human leukocyte antigen-alloimmunization and refractoriness: a randomized prospective study

We studied the value of leukocyte depletion of platelet transfusions for the prevention of secondary human leukocyte antigen (HLA)- alloimmunization in patients with a high-risk of prior immunization induced by pregnancies. Seventy-five female patients with hematologic malignancies (mostly acute leukemia) and a history of pregnancy were randomized to receive either standard random single-donor platelet transfusions (mean leukocytes, 430 x 10(6) per transfusion) or leukocyte-depleted random single-donor platelet transfusions. Leukocyte depletion to less than 5 x 10(6) leukocytes per platelet transfusion (mean leukocytes, 2 x 10(6) per transfusion) was achieved by filtration. Of the 62 evaluable patients, refractoriness to random donor platelets occurred in 41% (14 of 34) of the patients in the standard group and in 29% (8 of 28) of the patients in the filtered group (P = .52); anti-HLA antibodies developed in 43% (9 of 21) of individuals in the standard group and 44% (11 of 25) of cases in the filtered group. The time toward refractoriness and development of anti- HLA antibodies was similar for both groups. We conclude that leukocyte depletion of random single-donor platelet products to less than 5 x 10(6) per transfusion does not reduce the incidence of refractoriness to random donor platelet transfusion because of boostering of anti-HLA antibodies.     

Pharmacokinetics of cytosine arabinoside in acute myeloid leukemia.

In 14 patients with acute myeloid leukemia (AML) the plasma concentration of cytosine arabinoside (Ara-C) was determined at the start of the first course of treatment at various intervals after a bolus injection. In 10 patients plasma concentration/time data were fitted to a biexponential equation and pharmacokinetic parameters were estimated from the coefficient and exponents of such equations. The plasma half-life (t1/2) of Ara-C of the first phase varied from 1.2 to 1.9 min (mean 1.6). The t1/2 of the second phase varied from 8.8 to 18.9 min. All patients were treated with Ara-C alone in a dose of 100 mg/m2 for 10 or 14 days. There was poor treatment response in five patients with second-phase t1/2 of Ara-C ranging from 6.6 to 10.7 min whereas there was complete remission in nine patients with t1/2 exceeding 12.7 min. In three patients plasma Ara-C concentrations were measured during constant-rate infusion of different amounts of drug. It appeared that the plateau concentrations were directly proportional to the dose, which indicated that in the therapeutic range no enzyme capacity-limited elimination occurs.     

Diffusion tensor imaging of left ventricular remodeling in response to myocardial infarction in the mouse

The cardiac muscle architecture lies at the basis of the mechanical and electrical properties of the heart, and dynamic alterations in fiber structure are known to be of prime importance in healing and remodeling after myocardial infarction. In this study, left ventricular remodeling was characterized using diffusion tensor imaging (DTI) in a mouse model of myocardial infarction. Myocardial infarction was induced in mice by permanent ligation of the left anterior descending coronary artery. Serial ex vivo DTI measurements were performed 7, 14, 28, and 60 days after ligation. Apparent diffusion coefficient, fractional anisotropy, the three eigenvalues of the diffusion tensor, and the myofiber disarray served as readout parameters. After myocardial infarction, the mouse hearts displayed extreme wall thinning in the infarcted area, which covered large parts of the apex and extended into the free wall up to the equator. Average heart mass increased by 70% 7-60 days after infarction. Histological analysis showed that the infarct at 7 days consisted of unstructured tissue with residual necrosis and infiltration of macrophages and myofibroblasts. At 14 days after infarction, the necrotic tissue had disappeared and collagen fibers were starting to appear. From 28 to 60 days, the infarct had fully developed into a mature scar. DTI parameters showed dynamic changes as a function of time after infarction. The apparent diffusion coefficient in the infarcted region was lower than in remote regions and increased as a function of time after infarction. The fractional anisotropy was higher in the infarcted region and was maximum at 28 days, which was attributed to the development of structured collagen fibers. Myofiber disarray, which was analyzed by considering the alignment of fibers in neighboring voxels, was significantly higher in infarcted regions. DTI provides a valuable non-destructive tool for characterizing structural remodeling in diseased myocardium.     

Use of leukocyte-depleted platelet concentrates for the prevention of refractoriness and primary HLA alloimmunization: a prospective, randomized trial

Compared with conventional transfusion regimes a strong reduction in HLA alloimmunization and refractoriness to platelet transfusions is obtained when both red blood cell concentrates (RBCs) and platelet concentrates (PCs) are depleted of leukocytes by filtration. Because most of the leukocyte contamination is introduced by transfusion of RBCs, filtration of RBCs appears rational, but uncertainty exists regarding the degree of leukocyte-depletion of PCs needed for the prevention of HLA alloimmunization and refractoriness. We conducted a prospective trial and randomized patients with acute leukemia to receive leukocyte-depleted PCs prepared either by centrifugation (mean leukocyte count 35 x 10(6)/PC of 6 U) or by filtration (mean leukocyte count less than 5 x 10(6)/PC of 6 U). Both groups received RBCs that were filtered after prior removal of the buffy coat. Clinical refractoriness occurred in 46% (12 of 26) of the evaluable patients that were transfused with centrifuged PCs and only in 11% (3 of 27) in the filtered group (P less than .005). De novo anti-HLA antibodies were detected in 42% (11 of 26) patients in the centrifuged group and only in 7% (2 of 27) of the patients receiving filtered PCs (P less than .004). In 8 of 11 alloimmunized patients in the centrifuged group antibodies were detected in the first 4 weeks of transfusion therapy while none of the patients in the filtered group became immunized against HLA antigens during that period. We conclude that for the prevention of HLA alloimmunization and refractoriness to platelet transfusions from random donors, both RBCs and PCs have to be leukocyte-depleted by filtration.     

Differences in the susceptibility of platelets to freezing damage in relation to size

Previous studies have shown that cryopreservation of normal platelets induces a reduction in the contents of secretion granules, the generation of thromboxane B2, and aggregability. The present study investigates whether these changes in the total population occur to the same extent in four size-dependent subpopulations with mean platelet volumes of 4.2, 5.7, 8.0, and 11.1 microns 3, obtained by counterflow centrifugation. Cryopreservation reduced the contents of the alpha granule markers and the generation of thromboxane B2 in the platelets from the four fractions to the same extent as in the platelets from the total suspension. Maximal aggregation of the platelets in response to collagen was measured by optical aggregation. The average decrease in light transmission after freezing was 47 +/- 3 percent (SEM) for the platelets in the total population, 40 +/- 3 percent for the largest platelets, and 65 +/- 5 percent for the smallest platelets, which indicates that aggregability was better preserved in the larger platelets than in the smaller cells. It is possible that, in the smallest platelets, a decrease in thromboxane generation of approximately 70 percent becomes rate-limiting for aggregation. Further improvements in the clinical use of freeze-preserved platelets may be sought in the preparation of concentrates with relatively high counts of large platelets.