Acute kidney transplant rejection mediated by angiotensin II type 1 receptor antibodies in a pediatric hyperimmune patient.

BACKGROUND: Several cases of severe antibody-mediated rejection (AMR) secondary to antibodies against the angiotensin II type 1 receptor (AT1R-Ab) have been described with variable outcome. CASE-DIAGNOSIS/TREATMENT: We report the case of a 13-year-old boy whose first kidney transplant failed due to steroid-resistant acute cellular rejection, with the subsequent development of sensitization. He received a second kidney transplant which was complicated by early humoral rejection, with weakly positive staining for the complement degradation product C4d. Test results were negative for donor-specific antibodies against human leukocyte antigens (HLA-DSA) and MHC class I-related chain A (MICA) but positive for AT1R-Ab. Retrospective testing of the sera collected during the first kidney transplant was also positive for AT1R-Ab. We therefore hypothesized that the failure of the first transplant was secondary to the same cause. Losartan was immediately introduced into the therapeutic regimen, and the patient showed an excellent clinical and histological recovery. CONCLUSIONS: Testing for AT1R-Ab in any hypertensive patient with acute rejection who tests negative or weakly positive for C4d and negative for HLA-DSA and who is refractory to therapy is highly advisable. Pre-transplant AT1R-Ab may be indicative of the outcome in patients whose first transplant failed. Prompt initiation of treatment with losartan-immediately after transplantation in patients with pre-existing AT1R-Ab-should be encouraged.

The impact of donor-specific antibodies' presence on the outcome post-allogeneic hematopoietic stem cell transplantation: a survey from a single center.

Introduction: Donor-specific antibodies (DSAs) correspond to anti-HLA antibodies of the recipient that are specifically directed to a mismatched antigen of the donor. In the setting of solid organ transplantation DSAs are associated with rejection. Their role is still debated in allogeneic cell transplantation. International guidelines recommend testing patients for DSA before transplant, and if possible, choosing a donor with negative screening. Methods: We collected clinical data of 236 recipients of alloSCT, performed at our institution from March 2019 to October 2023, to evaluate their impact on engraftment. Serum from all patients was tested for DSA. Results: 186 patients (79%) achieved sustained myeloid engraftment within day 30 post alloSCT. Thirty-two out 236 (13%) patients engrafted after day 30 post alloSCT. The median times to neutrophil engraftment and platelet engraftment were respectively 21 days (range 11-121 days) and 19 days (range 10-203 days). Fourteen out 236 patients (6%) experienced PrGF. .Twenty-nine patients (12 %) were DSA-positive. Among 29 patients with DSA positivity, 17 had a haploidentical donor and 12 had a UD donor. DSA positivity directly correlates respectively with neutrophil and platelets engraftment failure at 30 days after alloSCT (p=0.01 and p= 0.0004). Univariate Cox analysis showed that factors, including DSAs positivity, disease type, disease status, donor type, conditioning regimen, patient's age, and CD34+ were correlated with neutrophil and platelet engraftment failure at 30 days after alloSCT. Younger patients with DSA negativity, with acute leukemia, in complete response at the time of transplant, who received a higher dose of CD34+ cells from a sibling donor after a myeloablative conditioning regimen, have a reduced risk of neutrophil and platelet engraftment failure at day +30 post alloSCT.Multivariate analysis confirmed the impact of the presence of DSA only for platelet engraftment, confirming the role of type and status disease, donor type, recipient age, and CD34+ cells infused on engraftment. DSA presence has no impact on TRM, DFS, and OS. Discussion: PrGF has a multifactorial pathogenesis, where DSA is not the only player, but its impact could vary depending on the transplant platform. Thus patient screening may be helpful to choose the best donor and transplant strategy.

Public epitope specificity of HLA class I antibodies induced by a failed kidney transplant: alloantibody characterization by flow cytometric techniques.

BACKGROUND: Patients whose kidney grafts fail develop alloantibodies that react with many HLA molecules. We analyzed the epitope specificity of HLA class I alloantibodies in the sera of 55 patients who had been sensitized by kidney grafts, and investigated the immunogenicity of various polymorphic epitopes. METHODS: HLA class I alloantibodies were detected and characterized by flow cytometry (FlowPRA beads). Potential "immunizing epitopes" were identified by comparing the amino acid sequences of HLA class I antigens/alleles of the donor, recipient and the antibody-reactivity pattern. RESULTS: In the 55 anti-HLA class I-positive patients, 82 different antibody reactivity patterns were identified; all but 5 (94%) were determined by a "public epitope" of donor HLA-A and/or -B molecules. Forty-five of 50 patients who showed HLA-A Res-MMs with their donors produced HLA-A antibodies, but only 31 of 51 subjects with HLA-B Res-MMs produced HLA-B antibodies (P=0.001; O.R.=5.81). The antibody patterns were specific for a "single" epitope of the mismatched donor molecules in 91% of patients. Forty-three of the 120 (36%) mismatched HLA-A and/or -B epitopes were positively correlated with antibody production. The polymorphic determinants of higher immunogenic capacity were b80N (Bw6-associated) and ab82-83LR (Bw4-associated) public epitopes. CONCLUSIONS: The humoral immune response against a kidney graft mainly produces HLA class I antibodies specific for "public epitopes" of mismatched donor molecules. A "single" donor-epitope may determine the production of a spread antibody pattern. In renal transplantation, epitope matching is better than HLA antigen matching for avoiding or minimizing development of HLA antibodies.

B-sides serologic markers of immunogenicity in kidney transplanted patients: report from 2012-2013 flu vaccination experience.

BACKGROUND: Safety and immunogenicity data of seasonal influenza vaccination in transplanted patients (Tps) are controversial. Preexisting cross-reactive antibodies generated by repeated vaccination with drift variant strains could bias interpretation of immunogenicity data in Tp. METHODS: The unadjuvanted 2012-2013 seasonal influenza vaccine was administered to 81 kidney Tps being routinely vaccinated against influenza and 23 healthy controls (HCs). Immunogenicity was evaluated by both strain-specific antibody responses with standard hemagglutination inhibition assay and by memory B-cell enzyme-linked immunosorbent spot. Safety was also evaluated by measuring anti-human leukocyte antigen (HLA) antibodies. RESULTS: The majority of Tps were seroprotected before vaccination (81.5%, 81.5%, and 43.2% vs. 47.8%, 34.8%, and 30.4% in HC for H1N1, H3N2, and B strain, respectively) resulting into lower seroconversion rates (P≤0.01) as compared with HC (40.7%, 39.5%, and 54.3% vs. 73.9%, 82.6%, and 65.2% for H1N1, H3N2, and B strain, respectively). An inverse correlation was found between seroconversion rates and number of previous vaccinations in Tps. On the contrary, similar increase in the frequencies of strain-specific memory B cells were detected by B-cell enzyme-linked immunosorbent spot in both Tps and HCs after vaccination. No serious adverse events have been reported. Donor-specific HLA antibodies increased in two patients after vaccination, and de novo anti-HLA antibodies were identified in two additional patients (non-donor-specific HLA antibodies). CONCLUSION: This report on safety and immunogenicity of the seasonal unadjuvanted 2012-2013 flu vaccination suggests that evaluating immunogenicity of influenza vaccination exclusively by hemagglutination inhibition assay may be misleading in individuals receiving yearly seasonal vaccines. Further investigations are required to understand the relation between vaccination and anti-HLA antibody development.

Post-transplant development of C1q-positive HLA antibodies and kidney graft survival.

The development of de novo human leukocyte antigen (HLA) donor specific antibodies (DSA), detected by both cytotoxic or solid phase assays, was considered the major risk factor for allograft failure in kidney transplantation. However, it was shown that not all patients with persistent production of DSA suffered loss of their grafts. Modified Luminex-Single Antigen assays, able to identify C1q-fixing antibodies, represent a new strategy in assessing the clinical relevance of detected DSA. This study demonstrated that C1q-fixing capability of de novo DSA is a clinically relevant marker of worse outcome and inferior graft survival in kidney transplantation. In fact, our findings evidenced a very low graft survival only in the patients who developed DSA able to fix C1q during post-transplant course, while patients producing C1q-negative DSA had good graft survival, which was comparable to that found in our previous study for DSA-negative patients. Moreover, anti-HLA class II antibodies had a higher incidence than anti-HLA class I, and the ability to fix C1q was significantly more frequent among anti-DQ DSA than anti-DR DSA. Monitoring of de novo C1q-DSA production represents a useful, non-invasive tool for risk stratification and prediction of graft outcome in kidney transplantation.

Post-transplant donor-specific antibody production and graft outcome in kidney transplantation: results of sixteen-year monitoring by flow cytometry.

Our data show that monitoring by sensitive flow cytometric techniques of the de novo production of anti-HLA antibodies in patients receiving kidney transplantation is a useful and noninvasive tool to identify the onset of an immune response towards the graft before any clinical manifestation of antibody-mediated graft injury. Consequently prospective posttransplant monitoring of anti-HLA donor-directed antibodies may offer the chance to realize an effective clinical intervention in order to prevent graft dysfunction and to prolong graft survival. The long follow-up period of the study allowed us to demonstrate a very low graft survival rate in patients who developed donor-specific HLA antibodies in comparison with patients who did not have antibodies, thus confirming the "humoral theory of transplantation". The posttransplant production of anti-HLA antibodies can predict not only graft failure but also chronic dysfunction of the graft. Moreover, our findings suggest that graft survival is influenced by the epitope- and locus-specificity of anti-HLA donor-directed antibodies. The interval between antibody appearance and loss of graft function was short in some patients but reached several years in others. Moreover, some patients showed consistent production of antibodies for many years and an uneventful clinical status. These findings suggest a mechanism of graft "accommodation" or the production of "harmless" antibodies. Immunosuppressive drug combinations able to inhibit T and B cell activation are useful tools to prevent the humoral immune response against graft and consequently to prolong graft survival.