Each year, 55 000 organ transplants are performed worldwide. Cumulatively, the number of living organ recipients is now estimated to be over 300 000. Most of these transplant recipients will remain on immunosuppressive drugs for the remainder of their lives to prevent rejection episodes. Controlled doses of these drugs are required to prevent over-medication, which may leave the patient susceptible to opportunistic infection and drug toxicity effects, or under-dosing, which may lead to shortened graft survival because of rejection episodes. This paper describes the result of a multicenter study conducted at the Universities of Pittsburgh, Alabama and Maryland to evaluate an in vitro assay (CylexTM Immune Cell Function Assay) for the measurement of global immune response in transplant patients receiving immunosuppressive therapy. The assay uses a whole blood sample to maintain the presence of the drug during incubation. Following overnight incubation of blood with phytohemagglutinin (PHA), CD4 cells are selected using paramagnetic particles coated with a monoclonal antibody to the CD4 epitope. The CD4-positive cells are targeted as major immunosuppressive drugs are designed to specifically inhibit T-cell activation which has been implicated in rejection. The data generated at these three sites were submitted in support of an Food and Drug Association (FDA) application for the use of this assay in the detection of cell-mediated immunity in an immunosuppressed population. The assay was cleared by the FDA on April 2, 2002. This cross-sectional study was designed to establish ranges for reactivity of this bioassay in the assessment of functional immunity for an individual solid organ recipient at any point in time.

The recent focus on islet transplantation as primary therapy for type 1 diabetes has heightened interest in the reversal of type 1 diabetes in preclinical models using minimal immunosuppression. Here, we demonstrated in a preclinical rhesus model a consistent reversal of all measured glycemic patterns of streptozotocin-induced type 1 diabetes. The model used single-donor islet transplantation with induction of operational tolerance. The term "operational tolerance" is used to indicate durable survival of single-donor major histocompatibility complex (MHC)-mismatched islet allografts without maintenance immunosuppressive therapy and without rejection or loss of functional islet mass or insulin secretory reserve. In this operational tolerance model, all immunosuppression was discontinued after day 14 posttransplant, and recipients recovered with excellent health. The operational tolerance induction protocol combined peritransplant anti-CD3 immunotoxin to deplete T-cells and 15-deoxyspergualin to arrest proinflammatory cytokine production and maturation of dendritic cells. T-cell deficiency was specific but temporary, in that T-celldependent responses in long-term survivors recovered to normal, and there was no evidence of increased susceptibility to infection. Anti-donor mixed lymphocyte reaction responses were positive in the long-term survivors, but all showed clear evidence of systemic T-helper 2 deviation, suggesting that an immunoregulatory rather than a deletional process underlies this operational tolerance model. This study provides the first evidence that operational tolerance can protect MHC nonhuman primate islets from rejection as well as loss of functional islet mass. Such an approach has potential to optimize individual recipient recovery from diabetes as well as permitting more widespread islet transplantation with the limited supply of donor islets.

De novo DSA formation, particularly early in the posttransplant course may be associated with trends toward worse outcomes. However, its significance in the pathophysiology of AR remains uncertain. Studies focusing mechanisms of DSA-related graft injury and intragraft DSA detection might provide further insight into this issue.

Formation of de novo donor-specific antibodies (dn-DSAs) has been associated with longterm immunologic complications after liver transplantation (LT). We hypothesized that human leukocyte antigen (HLA) epitope/eplet mismatch (MM) is a marker of immunogenicity and a risk factor for dn-DSA formation. Sera from 80 LT recipients were prospectively screened for dn-DSA by a Luminex single-antigen test (One Lambda, Inc., Canoga Park, CA) at 1, 2, 3, 6, 12, 18, 24, and 36 months after LT. HLA typing of the recipients and donors was performed using polymerase chain reaction (PCR)-SSP and PCR-SSOP Luminex low-resolution methods (One Lambda, Inc.). The HLAMatchmaker computer algorithm was used for identification of MM eplets at HLA-DRB1 and -DQA1/B1 loci. Luminex single-antigen bead solid phase assay was used for antibody analysis. Standard immunosuppression included thymoglobulin-rituximab induction and tacrolimus maintenance. There were 27 (34%) patients who developed dn-DSA. There were no episodes of antibody-mediated rejection, and 9 (11%) developed acute cellular rejection (ACR). A positive crossmatch status and a higher number of HLA-A, -B, -DR, and -ABDR MMs were not associated with dn-DSA formation. Patients developing dn-DSA had a significantly higher number of total (38 ± 2.7 versus 28 ± 2.3; P = 0.01) and antibody-verified (AbVer; 14 ± 1.1 versus 10 ± 1; P = 0.015) class II MM eplets. By a multivariate regression analysis, the number of class II MM eplets was strongly associated with risk of class II dn-DSA formation (odds ratio [OR], 1.2; P < 0.01). Patients with ACR had a significantly higher number of total (20.2 ± 1.3 versus 13.9 ± 0.9; P < 0.01) as well as AbVer (10.7 ± 1.1 versus 7.5 ± 0.6; P = 0.03) class I MM eplets. In conclusion, donor-recipient HLA epitope MM is associated with a risk of dn-DSA formation and rejection after LT. However, further studies are required to evaluate the clinical utility of epitope matching in LT.