Determinants of C1q Binding in the Single Antigen Bead Assay

Background : A modified single antigen bead (SAB) assay measuring C1q binding to human leukocyte antigen antibodies has recently been introduced. The aim of this study was to investigate the determinants of C1q binding on SAB.
Methods : Sera from 73 sensitized patients were analyzed by the generic IgGpan as well as IgG subclass specific SAB assays and correlated with the standard and an anti-human globulin (AHG) enhanced C1q test.
Results : Among 2,665 SABs with positive IgGpan results (mean fluorescence intensity [MFI]>500), strong complement-binding IgG1 and IgG3 subclasses accounted for a median of 99% (interquartile range, 76%–100%) of the total IgG amount. IgGpan MFI alone showed a very strong association with standard C1q positivity (r2=0.72), which was superior to a model including all IgG subclass MFI (r2=0.62). Combining all IgG subclass MFI and IgGpan MFI only marginally improved the prediction of standard C1q positivity compared with IgGpan MFI alone (Δr2=0.02). IgGpan MFI greater than 14,154 predicted standard C1q positivity, with 92% sensitivity and 96% specificity. Notably, 1,840 (93%) of the 1,974 C1q-negative SABs contained human leukocyte antigen antibodies with strong complement-binding IgG1 and IgG3 subclasses. Anti–human globulin significantly enhanced the signal in the C1q assay, but the association of AHG C1q positivity with IgGpan MFI was less strong (r2=0.51).
Conclusion : C1q binding on SAB is strongly associated with IgGpan MFI. IgG subclass information only marginally improves prediction of C1q binding likely because complement-binding IgG1 and IgG3 subclasses dominate regarding frequency and relative amounts. A negative C1q assay result does not indicate the absence of strong complement-binding IgG subclasses (read more)

Analysis of Predictive and Preventive Factors for De Novo DSA in Kidney Transplant Recipients

Background : Development of de novo donor-specific anti-HLA antibodies (dnDSA) has been associated with poor graft outcome, although the preventive factor for its production is still elusive. We analyzed the incidence of dnDSA within 5 years posttransplant in 562 living-kidney transplant recipients to evaluate predicting and preventive factors for dnDSA development.
Materials and Methods : All patients were considered to be non-HLA sensitized, as determined by the preoperative single-antigen bead assay (SABA), although they included various ABO blood type compatibilities. Preoperative administration of rituximab was indicated for 48% of patients, mainly for ABO incompatible transplantation. We retrospectively compared the patients with dnDSA and those without.
Results : Development of dnDSA was observed in 27 of the total 562 patients (5%). Chronic rejection was more frequently observed in patients with dnDSA than in those without (41% vs. 6%, P<0.001). The dnDSA-positive patients showed decreased graft function and poorer graft survival rates than those who tested negative. In multivariate analysis, higher likelihood of dnDSA production was observed in male recipients (odds ratio 6.57, P=0.012) and patients with a higher number of HLA-DR mismatches (odds ratio 2.41, P=0.008), whereas lower likelihood was observed in patients treated with rituximab induction (odds ratio 0.33, P=0.040).
Conclusion : Results suggest that rituximab induction as a standard immunosuppression protocol may have a preventive effect for dnDSA production in the non-HLA sensitized low immunologic risk patients (read more)

Who is the best donor for a related HLA haplotype-mismatched transplant?

The best donor for a related donor for a human leukocyte antigen (HLA) haplotype-mismatched transplant for hematological neoplasms is controversial. We studied outcomes in 1210 consecutive transplant recipients treated on a uniform protocol. Younger donors and male donors were associated with less nonrelapse mortality (NRM; hazard ratio [HR] = 0.30; 95% confidence interval [CI] = 0.01-0.39; P = .008 and HR = 0.65; 95% CI = 0.49-0.85; P = .002) and better survival (HR = 0.73; 95% CI = 0.54-0.97; P = .033 and HR = 0.73; 95% CI = 0.59-0.91; P = .005). Father donors were associated with less NRM (HR = 0.65; 95% CI = 0.45-0.95; P = .02), acute graft-versus-host disease (GVHD) (HR = 0.69; 95% CI = 0.55-0.86; P = .001), and better survival (HR = 0.66; 95% CI = 0.50-0.87; P = .003) compared with mother donors. Children donors were associated with less acute GVHD than sibling donors (HR = 0.57; 95% CI = 0.31-0.91; P = .01). Older sister donors were inferior to father donors with regard to NRM (HR = 1.87; 95% CI = 1.10-3.20; P = .02) and survival (HR = 1.59; 95% CI = 1.05-2.40; P = .03). Noninherited maternal antigen-mismatched sibling donors were associated with the lowest incidence of acute GVHD compared with parental donors and noninherited paternal antigen-mismatched sibling donors. Specific HLA disparities were not significantly correlated with transplant outcomes. Our data indicate which HLA haplotype-mismatched related donors are associated with the best transplant outcomes in persons with hematological neoplasms (read more)

Prolonged Immunosuppression Preserves Nonsensitization Status After Kidney Transplant Failure

Background : When kidney transplants fail, transplant medications are discontinued to reduce immunosuppression-related risks. However, retransplant candidates are at risk for allosensitization which prolonging immunosuppression may minimize. We hypothesized that for these patients, a prolonged immunosuppression withdrawal after graft failure preserves nonsensitization status (PRA 0%) better than early immunosuppression withdrawal.
Methods : We retrospectively examined subjects transplanted at a single center between July 1, 1999 and December 1, 2009 with a non–death-related graft loss. Subjects were stratified by timing of immunosuppression withdrawal after graft loss: early (≤3 months) or prolonged (>3 months). Retransplant candidates were eligible for the main study where the primary outcome was nonsensitization at retransplant evaluation. Non-retransplant candidates were included in the safety analysis only.
Results : We found 102 subjects with non–death-related graft loss of which 49 were eligible for the main study. Nonsensitization rates at retransplant evaluation were 30% and 66% for the early and prolonged immunosuppression withdrawal groups, respectively (P=0.01). After adjusting for cofactors such as blood transfusion and allograft nephrectomy, prolonged immunosuppression withdrawal remained significantly associated with nonsensitization (adjusted odds ratio=5.78, 95% CI [1.37–24.44]). No adverse safety signals were seen in the prolonged immunosuppression withdrawal group compared to the early immunosuppression withdrawal group.
Conclusions : These results suggest that prolonged immunosuppression may be a safe strategy to minimize sensitization in retransplant candidates and provide the basis for larger or prospective studies for further verification (read more)

Caveats of Mesenchymal Stem Cell Therapy in Solid Organ Transplantation

In the past decade, therapeutic use of mesenchymal stem cells (MSCs) has increased dramatically. The weight of existing evidence supports that the short-term application of MSCs is safe and feasible; however, concerns remain over the possibility of unwanted long-term effects. One fundamental difference between MSCs and pharmacotherapy is that, once applied, the effects of cell products cannot be easily reversed. Therefore, a carefully considered decision process is indispensable before cell infusion. In addition to unwanted interactions of MSCs with the host immune system, there are concerns that MSCs may promote tumor progression or even give rise to cancer themselves.
As animal models and first-in-man clinical studies have provided conflicting results, it is challenging to estimate the long-term risk for individual patients. In addition, most animal models, especially rodents, are ill-suited to adequately address questions over long-term side effects. Based on the available evidence, we address the potential pitfalls for the use of MSCs as a therapeutic agent to control alloimmune effects. The aim of this review is not to discourage investigators from clinical studies, but to raise awareness of the intrinsic risks of MSC therapy (read more)

HLA-haploidentical transplantation with regulatory and conventional T-cell adoptive immunotherapy prevents acute leukemia relapse

Posttransplant relapse is still the major cause of treatment failure in high-risk acute leukemia. Attempts to manipulate alloreactive T cells to spare normal cells while killing leukemic cells have been unsuccessful. In HLA-haploidentical transplantation, we reported that donor-derived T regulatory cells (Tregs), coinfused with conventional T cells (Tcons), protected recipients against graft-versus-host disease (GVHD). The present phase 2 study investigated whether Treg-Tcon adoptive immunotherapy prevents posttransplant leukemia relapse. Forty-three adults with high-risk acute leukemia (acute myeloid leukemia 33; acute lymphoblastic leukemia 10) were conditioned with a total body irradiation–based regimen. Grafts included CD34+ cells (mean 9.7 x 10^6/kg), Tregs (mean 2.5 x 10^6/kg), and Tcons (mean 1.1 x 10^6/kg). No posttransplant immunosuppression was given. Ninety-five percent of patients achieved full-donor type engraftment and 15% developed ≥grade 2 acute GVHD. The probability of disease-free survival was 0.56 at a median follow-up of 46 months. The very low cumulative incidence of relapse (0.05) was significantly better than in historical controls. These results demonstrate the immunosuppressive potential of Tregs can be used to suppress GVHD without loss of the benefits of graft-versus-leukemia (GVL) activity. Humanized murine models provided insights into the mechanisms underlying separation of GVL from GVHD, suggesting the GVL effect is due to largely unopposed Tcon alloantigen recognition in bone marrow (read more)

HLA Match Likelihoods for Hematopoietic Stem-Cell Grafts in the U.S. Registry

BACKGROUND : Hematopoietic stem-cell transplantation (HSCT) is a potentially lifesaving therapy for several blood cancers and other diseases. For patients without a suitable related HLA-matched donor, unrelated-donor registries of adult volunteers and banked umbilical cord–blood units, such as the Be the Match Registry operated by the National Marrow Donor Program (NMDP), provide potential sources of donors. Our goal in the present study was to measure the likelihood of finding a suitable donor in the U.S. registry.
METHODS : Using human HLA data from the NMDP donor and cord-blood-unit registry, we built population-based genetic models for 21 U.S. racial and ethnic groups to predict the likelihood of identifying a suitable donor (either an adult donor or a cord-blood unit) for patients in each group. The models incorporated the degree of HLA matching, adult-donor availability (i.e., ability to donate), and cord-blood-unit cell dose.
RESULTS : Our models indicated that most candidates for HSCT will have a suitable (HLA-matched or minimally mismatched) adult donor. However, many patients will not have an optimal adult donor — that is, a donor who is matched at high resolution at HLA-A, HLA-B, HLA-C, and HLA-DRB1. The likelihood of finding an optimal donor varies among racial and ethnic groups, with the highest probability among whites of European descent, at 75%, and the lowest probability among blacks of South or Central American descent, at 16%. Likelihoods for other groups are intermediate. Few patients will have an optimal cord-blood unit — that is, one matched at the antigen level at HLA-A and HLA-B and matched at high resolution at HLA-DRB1. However, cord-blood units mismatched at one or two HLA loci are available for almost all patients younger than 20 years of age and for more than 80% of patients 20 years of age or older, regardless of racial and ethnic background.
CONCLUSIONS : Most patients likely to benefit from HSCT will have a donor. Public investment in donor recruitment and cord-blood banks has expanded access to HSCT (read more)