Clinical significance of low pre-transplant donor specific antibodies (DSA) in living donor kidney recipients with negative complement-dependent cytotoxicity crossmatches (CDCXM), and negative flow cytometry crossmatches (FLXM) - A single-center experience.

BACKGROUND: It is controversial whether all donor-specific antibodies (DSA) detected by the solid-phase single antigen bead (SAB) assay negatively affect kidney transplantation outcomes. The study aimed to evaluate the possible clinical significance of low pre-transplant DSA in living donor kidney recipients. We analyzed a group of patients with HLA-A, B, and -DR DSA reactivities below a virtual crossmatch (VXM) value of 5000 MFI but with all VXM DSA reactivities at HLA-DQ, -DP, and -Cw, which were not typed routinely for donors prior to transplantation. We also investigated the incidence of persistent and de novo DSAs in available posttransplant SAB assays. METHODS: From the historical cohort of living donor recipients transplanted between 2014 and 2018 at our center (n = 82), 55 patients met the inclusion criteria, namely: these patients were > 18 years old with non-HLA identical sibling donors, who were not desensitized, who had available pre-transplant SAB results, and who had negative both complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FLXM) results. An additional donor HLA typing, performed for all 55 recipients, identified donor additional HLA-DQ, -DP, and -Cw DSA reactivities. These patients were then divided by SAB reactivity into three groups: 1) those with DSA-positive reactivities; 2) those with non-donor-specific anti-HLA reactivities (NDSA); and, 3) those who were anti-HLA-negative. All these recipients were followed for three years and checked for their de novo or persistent DSA. RESULTS: In the studied cohort, DSA-positive, NDSA reactive, and anti-HLA negative recipients constituted 33%, 36%, and 31% of 55 patients, respectively. Non-routinely considered pre-transplant HLA-DQ, -DP, and -Cw DSA-positive reactivities were shown in as many as 78% of DSA-positive cases (group 1) with the lowest MFI value of 319 to DP4 and the highest MFI of 5767 to DQ2. Of the pre-transplant HLA-A, B, and -DR DSA reactivities, only -DR52 DSA reactivity reached the highest MFI value of 2191. These detected DSAs did not reduce the mean estimated glomerular filtration rate (eGFR) values and did not increase the incidence of proteinuria in recipients. While the 3-year graft survival was lower in the DSA-positive group (94.4%) with one recipient who lost kidney transplant, the difference was not significantly different (p = 0.7) from the NDSA (100%) and negative (100%) groups. In terms of the incidence of de novo acute antibody-mediated rejection (AMR) at three years after transplantation, no case has been reported in the cohort. This may suggest that low DSA-positive recipients do not experience higher rejection rate. However, DSA-positive recipients had a tendency for a higher frequency of C4d deposits in peritubular capillaries (PTC) and de novo DSA. CONCLUSION: Our 3-year follow-up of patients with low pre-transplant DSA found no association with a deterioration in graft function and worse graft survival. Furthermore, we did not observe an increase in AMR in our patients with low DSA. A larger cohort and a longer follow-up period may be needed to evaluate the tendency of low DSA-positive recipients towards the higher incidence of C4d deposits in PTC and/or de novo DSA.

Accuracy of virtual crossmatch (VXM) prediction of physical crossmatch (PXM) results of donor specific antibody (DSA) in routine pretransplant settings-a single-center experience.

BACKGROUND: Virtual crossmatch (VXM) is a new powerful tool in pre-transplant risk assessment. However, the ability of VXM to predict physical crossmatch (PXM) results remains controversial. Our work evaluated the predictive potential of VXM results, measured by SAB (single antigen bead assay), for CDCXM (complement-dependent cytotoxicity crossmatch) and FLXM (flow cytometry crossmatch) results of DSA (donor specific antibody) in sensitized patients. METHODS: In total, 261 CDCXM and FLXM measurements were performed for 180 potential kidney transplant candidates, each with a single HLA-A, B, or -DR DSA against a potential deceased donor. Analysis was conducted with two SAB datasets of four-month distant and collected prior to and after PXM results. Optimal MFI (mean fluorescence intensity) thresholds and likelihood ratios were assigned based on low (<2000 MFI), medium (2001-5000 MFI) and high risk (>5000 MFI). The impact of VXM predictability was determined by the ROC curves comparison. In addition, inter-assay changes of MFI were evaluated. RESULTS: The accuracy of VXM to predict CDCXM was inferior to that of FLXM with the AUC (area under ROC curve) of 0.644 vs. 0.849. In contrast, the initial ROC analysis showed that the VXM prediction was good for both T-FLXM with ROC value of 0.849 and by B-FLXM with ROC value of 0.706 for a single antigen of HLA-A, B, or -DR DSA. In fact, the best VXM prediction was for FLXM with good sensitivity for B-FLXM against HLA-DR-specific DSA (0.851). Similar results of VXM predictability were observed for pre- and post-crossmatch ROC curves. CONCLUSION: VXM predictability is better for positive/negative FLXM than for positive/negative CDCXM results to evaluate a single HLA-A, B, -DR DSA disparity. This may be related to the fact that VXM and FLXM rely on binding of antibodies to beads or cells, respectively. In contrast, VXM is less predictive for CDCXM because the latter measures complement-dependent cytotoxic function. We intend expand VXM analysis to correlate their results with FLXM results to select low/medium risk patients for kidney transplantation in Poland.

Inactivation of IgM Antibodies as a Crucial Element of Diagnostics in Sensitized Patients Awaiting Kidney Transplant.

BACKGROUND: The positive result of complement-dependent cytotoxicity crossmatch (CDC XM) may not constitute a contraindication to renal transplantation, unless it is mediated by IgM antibodies, particularly of the autologous type. The current work presents the evaluation of the frequency of reactive IgM antibodies in sensitized kidney patients in Poland and their influence on panel-reactive antibodies (PRAs) readout and allocation status. PATIENTS AND METHODS: Results of PRA CDC assay with and without dithiothreitol were elaborated in 53 prospective recipients with historic PRA of ≥50%. Delta PRA (dPRA) was calculated. Retrospective analysis of the results in the context of age, sex, transplant number, and cause of end-stage renal failure was performed. RESULTS: Reactive IgM antibodies were detected in 81% of patients. Panel reactivity completely disappeared in 4% and in 51% of recipients PRA decreased by 2 to 77 percentage points. In 14 patients, PRA increased, and in 10, its level did not change. The allocation was altered in 36% of recipients. Priority status was lost in 8 and gained in 3 cases. Additional points for high sensitization were obtained in 1 and lost in 7 patients. dPRA was significantly greater in patients awaiting the first transplant compared with the second (P = .007) and third (P = .002). Higher dPRA was also symptomatic for autoimmune patients (P = .025). CONCLUSIONS: Reactive IgM antibodies affected PRA level and allocation in a considerable group of sensitized patients in Poland. Discrimination of IgM from IgG antibodies should be introduced to the recipient qualification algorithm.

Phage as a modulator of immune responses: practical implications for phage therapy.

Although the natural hosts for bacteriophages are bacteria, a growing body of data shows that phages can also interact with some populations of mammalian cells, especially with cells of the immune system. In general, these interactions include two main aspects. The first is the phage immunogenicity, that is, the capacity of phages to induce specific immune responses, in particular the generation of specific antibodies against phage antigens. The other aspect includes the immunomodulatory activity of phages, that is, the nonspecific effects of phages on different functions of major populations of immune cells involved in both innate and adaptive immune responses. These functions include, among others, phagocytosis and the respiratory burst of phagocytic cells, the production of cytokines, and the generation of antibodies against nonphage antigens. The aim of this chapter is to discuss the interactions between phages and cells of the immune system, along with their implications for phage therapy. These topics are presented based on the results of experimental studies and unique data on immunomodulatory effects found in patients with bacterial infections treated with phage preparations.