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Biomedical subjects

Howard M Gebel

Publications and source records attributed to Howard M Gebel.

6 recordsLinked to original sources
PubMed2004

Rituximab for reduction of anti-HLA antibodies in patients awaiting renal transplantation: 1. Safety, pharmacodynamics, and pharmacokinetics.

BACKGROUND: Preformed HLA antibodies (Ab), reported as panel-reactive antibody (PRA), prolong patient waiting time for kidney transplantation. We hypothesized that rituximab (RTX) could reduce PRA via B-cell depletion. This initial study reports the safety, pharmacokinetics, and pharmacodynamics of RTX in patients with end-stage renal failure. METHODS: The study was an investigator-initiated single-dose, dose-escalation phase I trial of RTX in chronic dialysis patients (PRA >50%). It was approved by the Institutional Review Board and the Food and Drug Administration. Nine subjects were treated with a single dose of RTX (n=3 per group) at 50, 150, or 375 mg/m. Peripheral lymphocyte cell surface markers and HLA Ab levels (%PRA and titers) were tested using flow cytometry. RESULTS: There were four significant adverse events: a suspected histoplasmosis infection; two Tenchkoff dialysis catheter infections; and fever (38.7 degrees C) during infusion. At 2 days after RTX therapy, there was depletion of CD19 cells (pre-RTX 181+/-137 vs. post-RTX 12+/-5.6, P =0.006). In 2 (22%) of 9 subjects, there was no appreciable change in PRA. Among the other seven patients, one had a decrease in PRA from 87% to 51% with a concurrent decrease in fluorescence intensity; five patients had changes in histogram architecture suggesting loss of antibody specificity; and one patient had a fourfold decrease in PRA titer from 1:64 to 1:16 at 6 months after treatment. In addition, one of the seven patients converted a donor-specific crossmatch to negative and underwent a successful living donor kidney transplantation. CONCLUSIONS: RTX can be safely administered and may be an effective agent to reduce high-titer anti-HLA Abs in subjects awaiting kidney transplantation.

Adult↗
PubMed2004

Unappreciated risk factors for transplant patients: HLA antibodies in blood components.

One of the more aggressive approaches in renal transplantation is the use of plasmapheresis (PP) and intravenous immunoglobulin to eliminate donor-directed human leukocyte antigen (HLA) alloantibodies. A potential complication of a PP protocol is iatrogenic hypocoagulability resulting from the removal of coagulation factors. To prevent bleeding, hypocoagulable patients may require transfusions with fresh frozen plasma (FFP) and/or cryoprecipitate (Cryo). Although HLA alloantibodies in these components have been linked to complications, such as transfusion-related acute lung injury (TRALI), whether they cause complications following transfusion into allograft recipients is unknown. The incidence of complications would be dependent, in part, upon the frequency of HLA alloantibodies in the various blood components. In this study, segments from 77 units of FFP, 66 units of Cryo, 106 units of packed red blood cells (RBCs), and 59 units of apheresis platelets (Plts) were tested for antibodies to HLA class I and class II antigens using FlowPRA, an HLA antigen-specific flow cytometric assay. On average, 22% of blood components tested contained HLA alloantibodies, tenfold greater than previously reported. This unappreciated frequency of HLA alloantibodies in blood components may pose a risk to transplant patients requiring transfusions by promoting allograft dysfunction or loss.

Antibodies↗
PubMed2004

Pronase treatment facilitates alloantibody flow cytometric and cytotoxic crossmatching in the presence of rituximab.

Rituximab (RIT), a murine/human chimeric monoclonal antibody directed against human CD20 is under investigation for its role in transplantation. RIT causes B-cell crossmatches to appear positive. Pronase, a proteolytic enzyme that targets F(c) receptors removes CD20 from B cells. After CD20 is removed, RIT should not bind, making it possible to detect class I or class II antibodies on treated B cells. In this study, we incubated RIT with normal human serum (NHS, negative control) or pooled sera from highly sensitized (>50% panel reactive antibody, HLA+) subjects awaiting renal transplantation (positive control) and then performed B-cell flow cytometric crossmatches using untreated or pronase treated B cells as targets. We observed that untreated B cells incubated with RIT-spiked NHS displayed a significant increase in surface fluorescence compared with NHS without RIT, similar to the fluorescence that occurs with a positive crossmatch. In contrast, when CD20 was cleaved from the B cells with pronase, B cells displayed a negative crossmatch with the RIT-spiked NHS. In addition, there was no change in the crossmatches of pooled high panel reactive antibody (PRA) sera after pronase treatment. RIT could be used without worry about losing the ability to perform transplant immunologic monitoring.

Antibodies, Monoclonal↗
PubMed2004

Evolution of HLA antibody detection: technology emulating biology.

New technological advances in the field of histocompatibility have provided an approach to systematically address the specificity of positive lymphocyte crossmatches. These approaches can now confirm whether a positive crossmatch is (or is not) due to class I and/or class II antibodies directed against donor HLA antigens. The information gained from the application of these sensitive and specific technologies can be used to predict crossmatch results for highly sensitized patients. In summary, these emerging technologies have provided the tools to reliably determine the clinical relevance of a positive lymphocyte crossmatch.

Antibodies↗
PubMed2002

Conundrums with FlowPRA beads.

In 1969, a study by Patel and Terasaki persuaded the renal transplant community that a pre-transplant cross-match should always be performed between donor and recipient to detect HLA antibodies and prevent hyperacute allograft rejection. Although the role of the cross-match among nonsensitized patients is controversial, its importance among sensitized recipients is undeniable. Over the past 30 years, more sensitive techniques, such as the flow cytometric cross-match (FCXM), were developed to identify low levels of antibodies undetectable by other approaches. The clinical relevance of a positive FCXM, however, has been hotly disputed, with some investigators maintaining that the FCXM is 'too sensitive' and rules out acceptable donor-recipient combinations. An alternative explanation is that the FCXM is non-specific, and, at least in certain situations, identifies non-HLA antibodies that are clinically irrelevant. Recently, a solid phase immunoassay utilizing purified HLA Class I or Class II molecules bound to microparticles (FlowPRA) was developed. Ideally, use of the FlowPRA for the identification of HLA antibodies in recipient sera would help ascertain whether a positive FCXM with donor cells was truly the result of an HLA-specific antibody. As shown here, this may not always be true. In this study, two unexpected serum patterns were observed. Pattern 1: FlowPRA beads were positive (with an associated HLA Class I specificity) and the FCXM with cells expressing the HLA antigen(s) to which the antibody was directed, was negative. Sequence analysis of the HLA antigens reactive with this unexpected antibody suggests that the epitope recognized resides on the floor of the groove, a site generally not expected to generate antibody activity. Pattern 2: FlowPRA beads were negative yet the FCXM was T and B cell positive. Further analysis of the FlowPRA negative/FCXM positive sera using a flow cytometric cell-based panel reactive antibody (PRA) approach revealed those sera to have specific anti-HLA Class I activity. We suspect that both types of antibodies described above have clinical relevance. Thus, a negative or positive FCXM (when the FlowPRA against donor antigens is positive or negative, respectively) is not always a straightforward interpretation.

B-Lymphocytes↗