Immune recognition of exposed xenoantigens on the surface of PEGylated bovine red blood cells.

Due to potential problems that can occur during blood transfusion and increasing blood shortages, our group engineered methoxypolyethylene glycol conjugated bovine red blood cells (mPEG-bRBCs) as a potential universal oxygen therapeutic. This current work investigates the immunological properties of mPEG-bRBCs incubated with human plasma (hP) and correlates these properties to exposed Galalpha(1,3)Gal xenoantigens. After mPEG-bRBCs were incubated with hP, the amount of bound IgG and IgM was assessed via flow cytometry. Flow cytometry also assessed the amount of GS-IB4 bound to exposed Galalpha(1,3)Gal xenoantigens. The results of this study demonstrate that most hP samples strongly promote agglutination of mPEG-bRBCs regardless of the extent of mPEG surface coverage or donor blood type. IgG and IgM from hP bound strongly to mPEG-bRBCs. In general, the Galalpha(1,3)Gal xenoantigen remains exposed at all levels of PEG surface coverage. PEGylation did block some of the xenoantigens as the amount of exposed Galalpha (1,3)Gal decreased with increased mPEG surface coverage. However, this was not sufficient to prevent a strong agglutination reaction. Taken together, the results of this study indicate that the current strategy for PEGylating bRBCs is unsatisfactory for the development of immunologically silent oxygen therapeutics.

Relationship between ADAMTS13 activity in clinical remission and the risk of TTP relapse.

Idiopathic thrombotic thrombocytopenic purpura (TTP) is characterized by frequent recurrences. Effective screening for relapses will enable intervention prior to overt episodes of TTP. The present study used a modified assay to detect ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, 13) activity as low as 0.5%. This analytical improvement permits adequate measurement of ADAMTS13 activity levels in 97% of remission samples used for statistical modelling. ADAMTS13 activity and ADAMTS13 antibody (IgG) were measured in 157 serial samples prospectively collected from 24 TTP patients during periods of clinical remission. These patients were followed-up quarterly for an average of 23 months, during which time nine episodes of TTP relapse occurred among six patients. Finally, logistic regression modelling was used to define the relationship between ADAMTS13 activity levels (0.5-100%) and the probability of TTP relapses. Our data demonstrated that lower ADAMTS13 activity and younger age were significantly associated with higher risk of relapse in the 3 months after specimens were taken. In contrast, ADAMTS13 antibody IgG levels were not predictive of TTP relapses. Identification of low ADAMTS13 activity during clinical remission as a key risk factor for TTP relapses provides a new screening strategy to identify patients who may benefit from prophylactic therapy prior to disease relapses.

Cyclosporin and plasma exchange in thrombotic thrombocytopenic purpura: long-term follow-up with serial analysis of ADAMTS13 activity.

We hypothesized that cyclosporin (CSA) as adjunct to plasma exchange (PE) improves the efficacy of PE in idiopathic thrombotic thrombocytopenic purpura (TTP) via suppression of the antibody inhibitor of ADAMTS13. Our preliminary findings with CSA and PE as the upfront treatment of TTP suggested that the addition of CSA to PE significantly decreased the exacerbation (disease recurrence within 30 d of the last PE) rates compared to a cohort that received corticosteroids and PE as their upfront therapy of TTP. We present an updated analysis with long-term follow-up of 18 patients with idiopathic TTP treated with concurrent CSA and PE with analysis of serial measurements of ADAMTS13 activity, antigen and inhibitor concentration in the context of clinical outcome data. Overall, 16/18 (89%) patients achieved remission, similar to historical remission rates in idiopathic TTP with PE with only one patient suffering an exacerbation. Clinical responses correlated with improvements in ADAMTS13 activity and suppression of the antibody inhibitor of ADAMTS13. These data suggest that the efficacy of CSA is at least in part related to its suppression of the antibody inhibitor of ADAMTS13 and a subsequent improvement in ADAMTS13 activity and antigen.

An evaluation of cyclosporin and corticosteroids individually as adjuncts to plasma exchange in the treatment of thrombotic thrombocytopenic purpura.

We present the results of two consecutively performed cohort studies that evaluated the clinical effects of corticosteroids or cyclosporin as an adjunct to plasma exchange (PE) for the treatment of an acute episode of thrombotic thrombocytopenic purpura (TTP). In comparing 12 corticosteroid-treated patients with eight cyclosporin-treated patients, none of the cyclosporin-treated patients suffered an exacerbation or recurrence of TTP in the first 30 d after discontinuing PE compared with 6/10 (60%) of the corticosteroid-treated patients (P = 0.042). These data suggest that cyclosporin may have advantages over corticosteroids as an adjunct to PE therapy in the initial treatment of idiopathic TTP.

Severe hemolysis due to passenger lymphocyte syndrome after hematopoietic stem cell transplantation from an HLA-matched related donor.

A 61-year-old white man (group A, Rh-positive) was allotransplanted for acute myelogenous leukemia from his HLA-matched related sister (group O, Rh-positive) in 2 separate infusions. Three days after the second graft infusion, the patient's front blood type converted to O Rh-positive, with a negative direct antiglobulin test and elevated anti-A1 titer. Severe hemolysis developed, and the patient expired 14 days posttransplantation.

The transfusion trigger and number of units transfused in patients with HIV: associations with disease stage and functional status.

BACKGROUND: The influence of quality of life (QOL), physical functioning, and HIV disease stage on the transfusion trigger and the number of units transfused was investigated. STUDY DESIGN AND METHODS: The Viral Activation Transfusion Study, a randomized, double-blind study at 11 participating sites, enrolled HIV-positive patients with anemia who required RBC transfusion; 428 patients were included in the analysis of the first transfusion. The QOL scores, Perceived Health Index, Karnofsky score, CD4+ cell count, HIV viral load, and site were analyzed for relationships with the Hb level and the number of units transfused. RESULTS: The transfusion trigger was lower in patients with higher levels of Karnofsky score, Perceived Health Index, CD4+ cell count, and a number of QOL scales. Both the Hb trigger and the number of units transfused had a significant site variation. Males were transfused at a significantly lower Hb level than females. In multivariate analysis, the CD4+ cell count remained significant, but the Karnofsky score or the Perceived Health Index did not. The number of RBC units transfused was associated with the Hb level, CD4+ cell counts, and Karnofsky scores in unadjusted analysis but with only Hb in adjusted analysis. CONCLUSIONS: In this group of HIV+ patients, lower CD4+ cell counts prompted transfusion at higher Hb levels. However, after controlling for the Hb level, the number of units transfused was associated with only the Hb level. The HIV stage appears to influence the decision to transfuse at a particular Hb level but not to influence the number of RBC units transfused. The functional status does not appear to influence the decision to transfuse.

Leukocytoreduction for acute leukemia.

Both in children and adults, acute leukemia may present with extremely high blast counts; a phenomenon known as hyperleukocytosis. Respiratory failure, intracranial bleeding, and severe metabolic abnormalities frequently occur in acute hyperleukocytic leukemias (AHLs) and are the primary determinants of the high early mortality (20% to 40%) observed. The process leading to these complications has long been known as leukostasis, but the biological mechanisms underlying its development and progression have remained unclear. Traditionally, leukostasis has been attributed to overcrowding of leukemic blasts in the microcirculation, and its treatment has focused on prompt leukocytoreduction. However, it is becoming increasingly evident that leukostasis results from the adhesive interactions between leukemic blasts and the endothelium; a mechanism that none of the current therapies directly addresses. The endothelial damage associated with leukostasis is likely to be mediated by cytokines released in situ and by subsequent migration of leukemic blasts in the perivascular space. The adhesion molecules displayed by the leukemic blasts and their chemotactic response to the cytokines in the vascular microenvironment are probably more important in causing leukostasis than the cell number. This may explain why leukostasis may develop in some patients with AHL and not in others, and why some patients with acute leukemia without hyperleukocytosis (<50,000 blasts/mm(3)) develop leukostasis and respond to leukocytoreduction. Leukapheresis effectively reduces the blast count in many patients with AHL and is routinely used for immediate leukocytoreduction. However, the most appropriate use of leukapheresis in acute leukemia remains unclear, and the procedure may not prevent early death more efficiently than fluid therapy, hydroxyurea, and prompt induction chemotherapy. The use of cranial irradiation remains very controversial and is not generally recommended. The identification of the adhesion molecules, soluble cytokines, and chemotactic ligand-receptor pairs mediating endothelial cell damage in AHL should become a priority if better outcomes are desired.