Richard J. Sassetti

Alloimmunization to RhD by platelet transfusions in autologous bone marrow transplant recipients

Abstract. Platelet transfusions from RhD‐positive (D‐positive) donors are often given to RhD‐negative (D‐negative) cancer patients. The low observed rate of alloimmunization has been attributed to disease and therapy‐related immunosuppression. We have studied the occurrence of alloimmunization in 16 D‐negative patients who did not have detectable anti‐D prior to autologous bone marrow transplantation for malignant disease. All received D‐positive platelets, but no other D‐positive blood product. Three patients (19%) developed anti‐D at 13, 24 and 83 days, respectively, after first receiving D‐positive platelets, and after a total dose of 53, 65 and 119 D‐positive platelet unit equivalents, respectively. Two of them also developed anti‐C. The 13 patients in whom anti‐D was not detected were also heavily transfused with D‐positive platelets (mean ± SD = 136 ± 82 platelet unit equivalents). In 6 of them, the last recorded antibody screen was less than 3 months after the first D‐positive platelets, and may not exclude a primary immune response. Thus, despite profound immunosuppression associated with autologous marrow transplantation, alloimmune responses to D‐positive red cells in platelet concentrates can occur in some D‐negative recipients.

Complement activation by plasma separator membranes

Because of their structural similarity to dialysis membranes, six plasma separator membranes were evaluated for the ability to activate complement, as judged by immunoconversion of the third component of complement in crossed Immunoelectro‐phoresis. A polysulfone and two cellulose acetate membranes were relatively strong alternative pathway activators. Polypropylene, poly[vinylidine fluoride] and polyvinyl‐chloride derivative membranes were weak activators in some sera. Membrane activation was inhibited in citrate‐anticoagulated but not in heparin‐anticoagulated plasma. The results of such in vitro screening should be of value in selecting materials and anticoagulation regimens for membrane plasma separators.

Effects of Desmopressin on Normal Donors in Plasma Exchange Donations

The use of desmopressin (DDAVP) to stimulate increased factor VIII in plasmapheresis donors was an evolutionary step in our efforts to use cryoprecipitate produced by repetitive large volume (2-3 L) plasma exchange of dedicated donors for treatment of hemophilia A.1, 2,3 The donation procedure evolved from our experience in the treatment of cryoglobulinemia by plasmapheresis.4 To reduce replacement fluid cost and minimize the risk of disease transmission for patients undergoing repeated plasmapheresis we had explored the feasibility of using the cryoglobulin-depleted plasma from a previous donation as the replacement fluid in a therapeutic plasma exchange. Being persuaded of the efficacy and safety of the procedure, we were led to consider an analogous procedure, performed on dedicated blood donors, as a source of large quantities of cryoprecipitate. The principle advantage perceived for such a program was a reduction in the risk of disease transmission by minimizing the number of donors to which a hemophilic patient is exposed. Awareness that desmopressin should raise donor factor VIII to levels 3 to 4 times baseline suggested that it might enhance the performance of the donation, resulting in higher yields and lower per-unit cost.