Reaction rates in allogeneic donors.

In Canada and several other countries, there is an upper age limit for blood donation. In order to evaluate the safety of whole blood donation in elderly Canadian allogeneic donors, we analysed reaction rates following whole blood donation. Reactions rates in allogeneic whole blood donors who donated at Canadian Blood Services were reviewed retrospectively. Rates were analysed by age, donation frequency and by donation frequency for each age group. A total of 5478 reactions were available for analysis in 469 837 donors. The highest rate of mild reactions occurred in donors less than 20 years of age. Moderate and severe reactions decreased with increasing age and with donation frequency. Age-adjusted rates for mild reactions were less frequent in donors aged 66-77 years than in donors younger than 20 years. Although age-adjusted moderate reactions varied with donation frequency, after seven donations, rates were not increased for donors aged 60 years or older (0.61% for donors aged less than 20 years compared to 0.03% for donors aged 60-65 years compared to 0% for donors aged 66-71 years). Age-adjusted rates for severe reactions generally did not increase with donation frequency. These results confirm the safety of whole blood donation in regular donors who are 66-71 years of age.

Transfusion-transmitted babesiosis in Ontario: first reported case in Canada.

Babesiosis has only recently been reported in Canada, but a number of transfusion-transmitted cases of this infection have been reported from the United States. We present a case of transfusion-transmitted babesiosis that occurred in Canada. Canadian physicians must consider babesiosis in the differential diagnosis of patients who experience fever or a hemolytic reaction after blood transfusion. Prompt recognition and treatment are important, because Babesia infections can be severe or fatal in certain risk groups. Better strategies to prevent transfusion-transmitted babesiosis are required.

Monoclonal antibody-mediated inhibition of the human HLA alloimmune response to platelet transfusion is antigen specific and independent of Fcgamma receptor-mediated immune suppression.

Presensitization of donor platelets with allo-specific immunoglobulin (Ig)G results in a diminished immune response against subsequent transfusions of platelets. To understand better the mechanism of how alloantibody presensitization results in a decreased alloimmune response, we have used murine monoclonal antibodies directed to polymorphic and non-polymorphic regions of human leucocyte antigen (HLA) as well as platelet-specific molecules. Here, we demonstrated that presensitization with anti-human HLA class I antibodies, as well as beta2-microglobulin-specific antibody, protected against alloantibody production to five subsequent untreated platelet challenges. Use of complement fixing, non-fixing or F(ab')2 fragments of HLA-specific antibody also resulted in complete inhibition of alloantibody production. This protection was not seen when the platelets were presensitized with monoclonal antibodies to CD42a (GPIX), CD32 (low-affinity IgG/Fcgamma receptor) or murine IgG and was thus independent of B-cell FcgammaRII-mediated immune suppression. The inhibition observed was independent of HLA alloantigenic specificity as antibodies directed at the beta2-microglobulin portion of HLA class I were as effective as antibodies against any of the HLA-alpha regions (either polymorphic or non-polymorphic) of class I. This work demonstrates that monoclonal antibody-mediated suppression of the human HLA alloimmune response to platelet transfusion is antigen specific and is independent of FcgammaRII-mediated immune regulation, complement fixing or HLA alloantigenic specificity.

Effect of premedication guidelines and leukoreduction on the rate of febrile nonhaemolytic platelet transfusion reactions.

Platelet transfusion reactions were prospectively studied in haematology/oncology patients at five university teaching hospitals over three consecutive summers. The initial summer study provided baseline information on the use of premedications and the rate of platelet transfusion reactions (fever, chills, rigors and hives). Most (73%) platelet recipients were premedicated and 30% (95% CI 28-33%) of transfusions were complicated by reactions. The second study followed implementation of guidelines for premedicating platelet transfusions. Despite a marked reduction in premedication (50%), there was little change in the platelet transfusion reaction rate, 26% (95% CI 24-29%), or the type of reactions. The third study followed implementation of prestorage platelet leukoreduction while maintaining the premedication guidelines. The reaction rate decreased to 19% (95% CI 17-22%). For nonleukoreduced platelets, there was a statistically significant association between the platelet age and reaction rate (P = 0.04). For leukoreduced platelets, there was no statistically significant association between platelet age and reaction rate (P = 0.5). Plasma reduction of nonleukoreduced platelet products also reduced the reaction rate. These prospective studies document a high rate of platelet transfusion reactions in haematology/oncology patients and indicate premedication use can be reduced without increasing the reaction rate. Prestorage leukoreduction and/or plasma reduction of platelet products reduces but does not eliminate febrile nonhemolytic platelet transfusion reactions.

Inhibition of a secondary human alloimmune response via the soluble active component of CD154 (CD40L) in severe combined immune-deficient mice engrafted with human lymphocytes.

BACKGROUND: Alloimmunization requires a process known as co-stimulation. An important co-stimulatory pathway for most immune responses is mediated by the interaction of CD40 on antigen-presenting cells with CD154 (CD40L) on host T cells. Blockade of this co-stimulatory pathway simultaneous with exposure to challenge with HLA-incompatible cells is hypothesized to inhibit alloimmunization. STUDY DESIGN AND METHODS: Severe combined immune-deficient (SCID) mice were reconstituted with human peripheral blood lymphocytes (Hu-PBL-SCID mice) from a subject primed to HLA antigens and challenged with HLA-incompatible lymphocytes. Mice were challenged in the presence or absence of an 18-kDa soluble recombinant active form of human CD154 (18-kDa CD154). Human IgG production, alloimmunization, and in vitro T-cell responsiveness were assessed. RESULTS: There was no significant effect of 18-kDa CD154 on human IgG levels in these mice, but it inhibited the development of HLA-specific alloantibody in this model to five subsequent untreated white cell challenges. In vitro T-cell proliferation in a mixed lymphocyte culture was also prevented by 18-kDa CD154. CONCLUSION: The recombinant protein 18-kDa CD154 inhibited the ability of the Hu-PBL-SCID mice to mount a secondary immune response to allostimulation. This implies that transfusion-induced alloimmunization utilizes CD40-CD154 co-stimulation and that blockade of this pathway can inhibit T-cell function and interfere with the development of alloimmunization.

Antibody-mediated inhibition of the human alloimmune response to platelet transfusion in Hu-PBL-SCID mice.

Severe combined immune deficient (SCID) mice were engrafted with human (Hu) peripheral blood lymphocytes (PBL) from a previously alloimmunized donor and transfused with HLA-mismatched platelets. We have previously shown this to be a useful model for platelet transfusion. These engrafted mice (Hu-PBL-SCID mice) produced high levels of alloantibody in response to standard platelet preparations. However, when the first platelet challenge was presensitized with anti-HLA antibody and then transfused there was a marked reduction in the amount of alloantibody produced to five subsequent untreated platelet transfusions. Platelets pretreated with platelet-specific anti-HPA-1a (PL(A1)) sera did not induce a decrease in the anti-HLA alloantibody response. This demonstrated that platelet-induced HLA alloimmunization can be blocked by anti-HLA antibody-sensitized cells.

Induction of a secondary human anti-HLA alloimmune response in severe combined immunodeficient mice engrafted with human lymphocytes.

BACKGROUND: Experimental manipulation of transfusion-induced alloimmunization is limited in humans by ethical considerations. Conversely, studies of alloimmunization in animal models may not reflect the human immune system closely enough to be of optimal benefit. The development of an in vivo model of human alloimmunization that is amenable to experimental manipulation is thus desirable. STUDY DESIGN AND METHODS: An in vivo model of human alloimmunization was evaluated by using mice with severe combined immunodeficiency (SCID). SCID mice underwent gamma-radiation (200 cGy) and received an intraperitoneal injection of human peripheral blood lymphocytes (PBLs) from donors immunized to HLA antigens by prior pregnancy (reconstitution). These Hu [human]-PBL-SCID mice were then challenged with HLA-mismatched PBLs. Alloantibodies were evaluated by flow cytometry and a standard two-stage microlymphocytotoxicity assay. RESULTS: Hu-PBL-SCID mice (n = 22) that were challenged with PBLs expressing the HLA antigens to which the donors had previously been immunized, made significantly more IgM and IgG alloantibodies than did the unchallenged mice. Responses were measurable by 1 week after reconstitution and challenge. Prior treatment of SCID mice with anti-asialo GM1, which depletes murine natural killer cells and macrophages, further increased the alloantibody response of challenged mice. The human alloantibodies generated were specific to the challenge HLA antigens as assessed by microlymphocytotoxicity assay. CONCLUSION: Hu-PBL-SCID mice are a useful model system in which to study and manipulate the induction of secondary human alloimmune responses against cellular HLA class I antigens. This model will be valuable for testing the in vivo effect of novel immunotherapies on the inhibition of the human alloantibody response.

White cell depletion of red cell and pooled random-donor platelet concentrates by filtration and residual lymphocyte subset analysis.

This study comparing the relative white cell (WBC)-depleting efficiency of single and double filtration used two filters and new, sensitive, and reliable methods for performing WBC counts on WBC-depleted blood products. A single filtration of red cell (RBC) concentrates with a cotton-wool filter reduced WBC content by 98.64 percent, but the range of residual WBCs was wide, and many filtered units still contained more than the theoretical immunizing dose of 5 to 10 x 10(6) WBCs. A second filtration, however, always produced RBC units that had less than 5 x 10(6) WBCs. Although the degree of WBC depletion observed after a single filtration of a 6-unit pool of random-donor platelet concentrates was greater with a polyester filter than with the cotton-wool filter (98.92 vs. 98.14% reduction, respectively, when mean prefiltration WBC count was less than 600 x 10(6], in both cases, 25 percent of filtered products still contained greater than 5 x 10(6) WBCs; a second filtration (with the cotton-wool filter), however, produced units that were always below the immunizing dose. All double-filtered platelet concentrates had less than 10(6), and one-half had less than 10(4) residual WBCs. Platelet loss was similar with both filters (+/- 16% loss with one filtration). The effectiveness of the filters in producing products that were WBC-depleted below the immunizing dose was dependent on the prefiltration WBC content (but not on the age of the units), and it may be worthwhile to employ methods to ensure that total prefiltration WBC count of the product is less than 400 x 10(6).(ABSTRACT TRUNCATED AT 250 WORDS)