MICA Antibodies Research Articles

(343) - Impact of MIC-A Antibodies on Antibody Mediated Rejection (ABMR). Molecular Microscope Results (MMDx)

(343) - Impact of MIC-A Antibodies on Antibody Mediated Rejection (ABMR). Molecular Microscope Results (MMDx)

Posttransplant Thrombotic Microangiopathy: Unraveling a Mystery

A 24 year old lady who was diagnosed with chronic kidney disease stage 5 in 2016 underwent a pre-emptive live related renal transplant in the same year. She had kidney allograft dysfunction and eventually lost the transplant kidney in 2019 requiring hemodialysis. She underwent a deceased donor renal transplant in February 2022. She developed allograft dysfunction with a creatinine of 2.5 mg/dl in October 2022, and a renal allograft biopsy subsequently showed Thrombotic microangiopathy, arteriolar form. There were no features of rejection in the biopsy and Donor specific antibody done by Luminex lysate method was negative. Her Single antigen bead done subsequently was also negative. CMV DNA PCR was not detectable. Tacrolimus was switched to Cyclosporine, however her allograft function continued to worsen. Complement mutation analysis was negative and acquired complement defects were also not detected. Subsequently, Single antigen bead for non HLA antibodies showed positivity for MICA antibodies. She underwent 7 sessions of plasmapheresis and her renal functions did not improve and her creatinine continued to increase to 4.2 mg/dl. Complement activating assay for these MICA antibodies was positive. She was treated with two doses of 300 mg Eculizumab in December 2022, her allograft functions in February 2023 have improved to 2 mg/dl. This case highlights the extensive evaluation for post transplant TMA, the use of non HLA antibody assays and complement activating assays of these antibodies to decide on appropriate use of Eculizumab for salvaging transplant allograft.

Residue-Level Characterization of Antibody Binding Epitopes Using Carbene Chemical Footprinting.

Characterization of antibody binding epitopes is an important factor in therapeutic drug discovery, as the binding site determines and drives antibody pharmacology and pharmacokinetics. Here, we present a novel application of carbene chemical footprinting with mass spectrometry for identification of antibody binding epitopes at the single-residue level. Two different photoactivated diazirine reagents provide complementary labeling information allowing structural refinement of the antibody binding interface. We applied this technique to map the epitopes of multiple MICA and CTLA-4 antibodies and validated the findings with X-ray crystallography and yeast surface display epitope mapping. The characterized epitopes were used to understand biolayer interferometry-derived competitive binding results at the structural level. We show that carbene footprinting provides fast and high-resolution epitope information critical in the antibody selection process and enables mechanistic understanding of function to accelerate the drug discovery process.

Utility of Cardiovascular Magnetic Resonance Imaging in Non-HLA Mediated Cardiac Allograft Dysfunction

<h3>Introduction</h3> Cardiac MRI (cMRI) with late gadolinium enhancement may be beneficial in guiding medical therapy in non-HLA mediated allograft dysfunction in heart transplant recipients (HTR). Cardiac MRI utilizing pre/post-contrast T1/T2 mapping and myocardial delayed enhancement imaging were performed in two HTRs with non-HLA mediated allograft dysfunction. <h3>Case Report</h3> Patient A and B were adult males transplanted for non-ischemic cardiomyopathy with compatible crossmatches at the time of transplant. Patient A received basiliximab induction while patient B received no induction. Both were maintained on tacrolimus, mycophenolate, and prednisone. On surveillance echocardiogram (ECHO) at 90-days post-transplant, a decreased ejection fraction (45%) was noted in both patients. Subsequent biopsies, donor specific antibodies, and MICA antibodies were negative. Biopsy immunofluorescence C4d staining was 90% in patient A and negative in patient B (Table 1). Patient A's cMRI demonstrated mildly increased T1 and T2 values that when combined with the clinical history, was suggestive of acute rejection. He subsequently received treatment with plasmapheresis, immunoglobulin, and rituximab. A repeat cMRI at 1-month post-treatment demonstrated normalization of T1 and T2 values. In contrast, patient B had generally normal T1 and T2 values on initial cMRI, indicating likely absence of acute rejection. Given cMRI findings, combined with a possible alternative etiology of mitochondrial disease contributing to decreased cardiac function, rejection treatment was not pursued and instead, sirolimus was initiated to slow disease progression. Follow-up biopsies and ECHOs in both patients indicate stable allograft function with slight improvements in ejection fraction. <h3>Summary</h3> In the absence of typical rejection findings, aspects of cMRI measurement may have favorable clinical utility and help guide medical management of early post-transplant non-HLA mediated allograft dysfunction.

AMR or CAV without HLA-DSA: Could MICA-DSA Be the Culprit?

<h3>Purpose</h3> The role of non-HLA antibodies, such as MICA and AT1R, in pediatric heart transplant (HTx) is not well delineated. While both may contribute to worse outcomes after HTx, regular surveillance monitoring and B-cell treatment is generally reserved for recipients with HLA-DSA. <h3>Methods</h3> Case report describing the development of non-HLA DSA in a patient who is s/p second HTx with concern for CAV in both allografts. <h3>Results</h3> We introduce a 16-yo male who received a HTx for familial DCM in 2007, at age 2yo. Prior to HTx he was mechanically supported with ECMO (10 dys) and a Berlin Heart (6 wks). PRA were negative and his retrospective cross match (XM) was invalid due to auto-reactivity. Immunosuppression (ISX) was maintained with tacrolimus and sirolimus. Three years (2010) after HTx <i>de novo</i> HLA-DSA (DQ8, DR53) were detected following a period of medical non-compliance; HLA-DSA gradually increased in strength to 20,000 MFI. While all surveillance biopsies since transplant remained without evidence of ACR or AMR, he required treatment for clinical rejection in 2011 (pulse steroids, IVIG) and 2015 (pulse steroids, ATG) and MMF was added to his ISX. He eventually developed micro-vascular CAV, presenting as heart block and diastolic dysfunction, and received a second HTx in 2016. His retrospective XM again showed autoreactivity; he had a negative virtual XM and never developed new HLA-DSA. A recent biopsy, prompted by mild diastolic dysfunction, revealed new endothelial swelling (ACR 1R, AMR 1H, C4D neg). Additional analysis showed high levels of donor-specific MICA, and AT1R antibodies; both remained high despite initiation of B-cell therapy (rituximab, bortezomib, IVIG). Further retrospective analysis revealed that the MICA antibodies were developed <i>de novo</i> against his first heart (targeting a common epitope present on both donors' MICA) alongside the HLA-DSA, while AT1R antibodies were already present before his first HTx. Thus, MICA-DSA may have contributed to accelerated CAV in his first allograft, and cause endothelial swelling and AMR in his second allograft. This may have been further exacerbated by the ongoing presence of AT1R, though their role in our patient's clinical course remains less clear. <h3>Conclusion</h3> Non-HLA DSA can be injurious to cardiac allografts, and the presence of AMR or CAV without HLA-DSA warrants further evaluation for MICA-DSA and AT1R antibodies.

Prevalence and impact of HLA and MICA allele mismatching on donor-specific antibodies induction in kidney transplant rejection.

Donor-recipient antigen mismatching for anti-human leucocyte antigen (HLA) and MICA is one of the risk factors for antibody induction leading to graft rejection. Our aim was to analyze the incidence and specificity of the different DSAs developing and to investigate the impact of HLA and MICA allele mismatches on antibody production in kidney transplant patients experiencing antibody-mediated rejection (AMR). We retrospectively reviewed 253 consecutive recipients of kidney transplant who were diagnosed as experiencing AMR. Our results showed that around 27% of our patients were positive for DSAs over a median follow-up period of 24 months. Antibody to HLA-DQ7 was the most prevalent DSA detected. The allele mismatch number was significantly lower for DQ loci than -A and -B loci (DQ vs. A, p < .001; DQ vs. B, p=.002). Considering each HLA antigen, the incidence rate of DQ-DSA [41.9 (32.92-51.46; 95%CI)] was much higher than the rate observed for DSA directed to -A, -DR and -B loci. Half of the recipients in the DQ-DSA-only group, and the DQ-DSA together with non-DQ group, had MFI > 5000. Only one case developed de novo MICA-DSA (MICA002). Our study indicates that mismatching for HLA and MICA alleles leads to the development of HLA and MICA antibodies in some kidney transplant recipients. We have also demonstrated that DSA to the DQ locus is the most prevalent in kidney transplant patients with AMR. Thus, matching the DQ locus in kidney allocation algorithms may reduce post-transplant development of DSA.

Distribution of MICA alleles and haplotypes associated with HLA-B in Greek population

IntroductionThe Major Histocompatibility Complex Class I-related chain A gene (MICA) is a highly polymorphic functional gene located close to the HLA-B locus. Certain MICA alleles have been related to inflammatory and autoimmune diseases while MICA antibodies have been implicated in organ allograft rejection or graft-versus-host disease (GVHD). AimThe aim of this study was to identify the frequencies of MICA alleles and MICA ~ HLA-B haplotypes in the Greek population since, as far as we know, these data are still limited. MethodsDNA was obtained from 277 unrelated healthy Greek individuals of Caucasian origin, volunteer donors of blood stem cells. HLA-B* and MICA* genotyping was performed by reverse PCR-SSOP. ResultsA total of 18 MICA alleles were defined in the present study. The five most frequent alleles in the Greek population were MICA*008 (24.6%), MICA*009 (22.36%), MICA*018 (16.03%), MICA*002 (8.02%) and MICA*004 (7.17%) which altogether account for 77.8% of all alleles. The most common MICA ~ HLA-B haplotypes were MICA*018 ~ B*18 (12.5%) and MICA*009 ~ B*51(11.5%). ConclusionsThe five most frequent MICA alleles in the Greek population were *008, *009, *018, *002, *004. In other Caucasian populations, two of these alleles (*008, and *004) were observed in similar frequencies. MICA*002 was observed less frequently (8.02%) in the Greek population compared to other Caucasian groups (frequencies > 15%). Also, MICA*009 and MICA*018 had elevated frequencies (above 15%) whereas in other Caucasian populations they were found around 10% or less. These data may be important for the elucidation of the role that MICA polymorphisms play in organ and stem cell transplantation and to identify the relation of certain MICA with susceptibility to specific diseases.

Prevalence of leucocyte antibodies in non-transfused male and female platelet apheresis donors.

In our study group of Thai PLT apheresis donors, we assessed the prevalence of anti-leucocyte antibodies. Antibodies against human leucocyte antigens (anti-HLA), neutrophil antigens (anti-HNA), and major histocompatibility complex class I related chain A (anti-MICA) in blood products can lead to transfusion-related acute lung injury (TRALI). To reduce the risk of TRALI, some blood centres are implementing strategies based on screening platelet (PLT) apheresis donors for the presence of anti-leucocyte antibodies. Blood samples were collected from non-transfused individuals, 340 males and 63 females (50 nulliparous and 13 parous). Anti-HLA class I and II and anti-MICA were analysed using the Luminex assay, and anti-HNA-3 was detected using the granulocyte agglutination test. Anti-HLA was found in 14 of 403 subjects (3.5%). Ten subjects (2.5%) tested positive for HLA class I, 2 (0.5%) for HLA class II, and 2 (0.5%) for both HLA class I and HLA class II. Anti-HLA class I or II were detected in 2 of 13 (15.4%) parous females and only anti-HLA class I was found in 4 (8.0%) nulliparous females. Six of 327 subjects tested (1.8%), all males, were positive for anti-MICA. Anti-HNA-3 was not found in any of the 403 individuals. Screening for anti-HLA class I and II should be implemented for Thai PLT apheresis donors. Although immunisation against HNA and MICA seems to be a rare event in Thais, further work is necessary to decide whether our PLT apheresis donors should be screened for HNA and MICA antibodies.

MICA immune complex formed with alpha 3 domain-specific antibody activates human NK cells in a Fc-dependent manner

BackgroundOne of the mechanisms by which tumors evade immune surveillance is through shedding of the major histocompatibility complex (MHC) class I chain-related protein A and B (MICA/B) from their cell surface. MICA/B are ligands for the activating receptor NKG2D on NK and CD8 T cells. This shedding reduces cell surface levels of MICA/B and impairs NKG2D recognition. Shed MICA/B can also mask NKG2D receptor and is thought to induce NKG2D internalization, further compromising immune surveillance by NK cells.MethodsWe isolated human primary NK cells from normal donors and tested the suppressive activity of soluble recombinant MICA in vitro. Utilizing a panel of novel anti-MICA antibodies, we further examined the stimulatory activities of anti-MICA antibodies that reversed the suppressive effects of soluble MICA.ResultsWe show that suppressive effects of soluble MICA (sMICA) on NK cell cytolytic activity was not due to the down-regulation of cell surface NKG2D. In the presence of an α3 domain-specific MICA antibody, which did not obstruct NKG2D binding, sMICA-mediated NK cell suppression was completely reversed. Reversal of NK cell inhibition by sMICA was mediated by immune complex formation that agonized NKG2D signaling. Furthermore, this restorative activity was dependent on antibody Fc effector function as the introduction of Fc mutations to abrogate Fc receptor binding failed to reverse sMICA-mediated NK cell suppression. Furthermore, MICA immune complexes preformed with an α3 domain-specific antibody (containing a wild-type Fc) induced IFN-γ and TNF-α secretion by NK cells in the absence of cancer cells, whereas MICA immune complexes preformed with the Fc effectorless antibody failed to induce IFN-γ and TNF-α secretion. Finally, we demonstrated that MICA immune complexes formed with the α3 domain-specific antibody activates NKG2D on NK cells leading to the release of IFN-γ.ConclusionsOur results demonstrate that an α3 domain-specific MICA antibody can circumvent sMICA-mediated suppression of NK cell cytolytic activity. Moreover, our data suggest that MICA immune complexes formed with α3-specific antibodies can activate NKG2D receptor and restore NK cell function in a Fc-dependent manner. The clinical utility of α3 domain-specific MICA/B antibodies may hold great promise as a new strategy for cancer immunotherapy.

MON-190 MICA - A MYTH TO REALITY IN CLINICAL PRACTICE

THE MAJOR HISTOCOMPATIBILTY COMPLEX CLASS 1 RELATED CHAIN – is the product of an HLA-related polymorphic gene and is expressed on monocytes keratinocytes fibroblast and endothelial cells. In this study we looked at the incidence of MICA Antibodies in the preop evaluation of kidney transplant patients and serum creatinine levels post kidney transplant using a combination of plasma exchange and rATG peritransplant

Anti MICA Antibody (major histocompatibility complex class I related Chain A) Whether to Treat or Avoid?

Aims To study the role of MICA antibody in living renal transplantation in the absence of anti HLA antibodies. Methods A retrospective study of patients undergone living renal transplantation between 2000-2014 was performed. Recipients were classified in two groups, pre transplantation Anti MICA antibody positive group (n=17) and antibody negative comparison group (n=17). Patients with anti HLA antibodies were excluded and only isolated MICA positive patients were included in the study group. All recipients undergone tolerance protocol and post transplant T-regulatory cells, and were comparable in recipient age, donor age, donor relation, HLA and immunosuppression including induction. Results Patients with pre transplant MICA antibody positivity were associated with increased acute rejection as compared to comparison group (47% vs 11.7 %, p value= 0.02 ). Renal function in MICA positive group and comparison group were comparable over a mean follow up of 6.5 years (mean s.creatinine 1.58 vs 1.53 mg/dl ). Rate of chronic rejection was same in both groups (5.8% ). No patient or graft loss in either group over mean follow up of 6.5 years. Conclusion Isolated Anti MICA antibody positivity is uncommon event. Pre transplant anti MICA antibody positivity is associated with increased acute rejection rates. However chronic rejection rates and renal function are comparable in both groups. Thus our study emphasizes that MICA antibody positive patients may require more aggressive immunosuppression, role of desensitization has to be defined.

Soluble Major Histocompatibility Complex Class I related Chain A (sMICA) levels influence graft outcome following Renal Transplantation

BackgroundSince soluble isoforms of MICA play an important role in modulating the immune response, we evaluated a possible correlation between their levels and development of acute rejection following renal transplantation. MethodsSerum samples collected at pre- and different time points post-transplant from 137 live related donor renal transplant recipients were evaluated retrospectively for sMICA levels and for the presence of MICA antibodies. Samples from 30 healthy volunteers were also tested as controls. ResultsSignificantly higher levels of sMICA were observed in the pretransplant sera of allograft recipients as compared to healthy controls. Patients with acute cellular rejection experienced a significant fall in their levels at the time of diagnosis as compared to their pretransplant values and posttransplant follow up time points (p = .01, .003, .005 and .04 respectively at pre vs biopsy (Bx), POD7 vs Bx, POD 30 vs Bx, POD 90 vs Bx). However, no such difference was noted in patients undergoing antibody mediated rejection. Further the study did not reveal any correlation on the presence/absence of MICA antibodies with either an increase or decrease in sMICA levels. ConclusionsEstimating circulating levels of soluble MICA could provide useful information of prognostic importance in assessing graft outcome following renal transplantation.

The incidence and clinical relevance of anti-HLA and/or MICA antibodies in patients with long-term survival renal allo-grafts

The purpose of this study was to analyze the incidence and clinical relevance of anti-HLA and/or MICA antibodies in renal allo-grafts transplant recipients with long-term renal survival (> 5 years). This retrospective study collected post-transplant serum samples from a total of 110 patients which were used to detect the incidence of anti-HLA and/or MICA antibodies as well as anti-HLA donor specific antibodies. Among these 110 patients, 72 patients had antibodies against HLA and/or MICA at the time of test, 61 had only anti-HLA antibodies, 31 had anti-MICA antibodies, and 38 were antibody negative. There was no difference in the number of patients developing antibodies against non-donor specific antibodies, donor specific antibodies, Class I donor specific antibodies, Class II donor specific antibodies or MICA antibodies between normal function group (serum creatinine level < 2.0 mg/dL) and dysfunction group (serum creatinine level > 2.0 mg/dL). For the serum creatinine level, estimated glomerular filtration rate and blood urea nitrogen level, patients with different antibodies were not statistically different to antibody-negative patients. Cox regression analysis showed that the type of transplantation and HLA mismatch number were significant negative risk factors for the development of anti-HLA (P < 0.05). Our results suggested that the anti-HLA antibody status has little impact on the renal graft function in the long-term survival allo-graft renal recipients.

Role of Anti-MICA Antibodies in Graft Survival of Renal Transplant Recipients of India.

Introduction The MIC (MHC class I chain-related) genes are a group of nonclassical MHC genes, located in the MHC class 1 region of chromosome 6. The aim of the present study was to find the prevalence of MHC class 1 chain-related (MICA) alloantibodies in patients undergoing live-related donor renal transplantation and its role in short-term graft survival. The role of blood transfusion in the formation of these antibodies was also studied. Materials and Methods Pretransplant samples of patients undergoing renal allograft transplantation were tested for anti-MICA antibodies. Association of various demographics, HLA-A + B + DRB1 mismatches, anti-HLA antibody screen, and anti-MICA antibodies was assessed using Pearson's chi-square test. Results Out of 646 serum samples, 94 (14.6%) were positive and 552 (85.4%) were negative for anti-MICA antibodies. Patients with anti-MICA antibody had a graft survival 89.3% as compared to 94.7% in patients without anti-MICA antibody (P < 0.05). The hazard ratio for all patients was 3.0701 (P < 0.05). Out of the 340 patients with no HLA antibodies, the presence of anti-MICA antibodies without any HLA antibodies (n = 43) was associated with poor outcome in the patients (hazard ratio of 2.768, P < 0.05). The presence of MICA antibodies with HLA antibodies did not decrease the graft survival (hazards ratio of 1.3750, P > 0.05). Conclusion Preformed MICA antibodies independently increase the risk of kidney rejection and therefore recommend that guidelines should be formed for mandatory testing of these antibodies prior to renal transplant.

Longitudinal assessment of HLA and MIC-A antibodies in uneventful pregnancies and pregnancies complicated by preeclampsia or gestational diabetes

The significance of antibodies directed against paternal epitopes in the context of obstetric disorders is discussed controversially. In this study anti-HLA and anti-MIC-A antibodies were analysed in sera of women with uneventful pregnancy (n = 101), preeclampsia (PE, n = 55) and gestational diabetes (GDM, n = 36) using antigen specific microbeads. While two thirds of the women with uneventful pregnancy or GDM were HLA and MIC-A antibody positive in gestational week 11 to 13 with a modest increase towards the end of pregnancy, women with PE showed an inverse kinetic: 90% were HLA antibody positive in gestational week 11 to 13 and only 10% showed HLA reactivities at the end of the pregnancy. HLA antibody binding strength was more pronounced in gestational week 14 to 17 in patients with PE compared to women with uneventful pregnancy (maximum median fluorescence intensity of the highest ranked positive bead 7403, IQR 2193–7938 vs. 1093, IQR 395–5689; p = 0.04) and was able to predict PE with an AUC of 0.80 (95% CI 0.67–0.93; p = 0.002). Our data suggest a pathophysiological involvement of HLA antibodies in PE. HLA antibody quantification in early pregnancy may provide a useful tool to increase diagnostic awareness in women prone to develop PE.

P041 Angiotensin receptor type 1, MICA and vimentin antibodies in focal segmental glomerulosclerosis

Aim FSGS is a leading cause of ESRD and recurrent FSGS (rFSGS) post-transplant is common. No definitive tests exist to predict rFSGS. Studies on the role of mismatched HLA in rFSGS and association of a particular HLA type with FSGS and rFSGS have been inconclusive. The role of non-HLA antigens/antibodies in FSGS and rFSGS remains underexplored. Our aim was to assess the profile of HLA, and non HLA antibodies in biopsy-proven FSGS and rFSGS. Methods HLA typing were done by molecular methods. Antibody against Vimentin and fragments of Vimentin were assessed by Western Blot. Angiotensin Receptor Type 1 (AT1R) antibody and MICA antibody were assessed by ELISA and Luminex bead assays respectively using commercial reagents. Twelve pools of pre-transplant and 5 of post-transplant sera from 29 FSGS patients were tested for Vimentin and MICA antibodies. Results Of the 9 FSGS patients tested for AT1R antibodies, 6 (75%) had strong reactivity (>17 U/ML) in pre, post or both serum samples and two had intermediate levels (11–17 U/ML) while one had no reactivity ( Conclusions A recent study has suggested Pre-existing AT1R antibody to be predictive of r-FSGS. The mechanisms of AT1R antibody induction and its potential role in allograft injuries need further study. Previous reports have shown the role of Vimentin antibody in chronic allograft rejection and AT1R antibodies in AMR. Pre-existing Vimentin antibody has been reported to be indicative of IFTA. Vimentin can exist as isoforms and the significance of serum reactivity of FSGS patients to Vimentin fragments needs further research. Download high-res image (198KB) Download full-size image

P263 Analysis of multi-year TRALI testing using luminex solid phase product

Aim Analyze the HLA and MICA antibody detection data from multiple years of screening female blood donors for TRALI mitigation. Methods Over 4000 female blood donors with history of at least 1 pregnancy were screened using One Lambda, Inc. LabScreen Mixed Product. The samples were analyzed using HLA Fusion™ software. Normalized/NBG ratios were used to assign negative or positive results. Previously determined Cutoff Ratios were used: Table 1. Results HLA antibody was detected in over 20 % of the female blood donors that presented for donation. Table 2. Conclusions Significant levels of either HLA Class I or Class II antibody were detected in over 20% of female donors (reporting 1 plus pregnancy). This information is important as blood centers assess the impact of additional testing (i.e. Zika) on recruitment strategy, despite reduced blood product usage. Download : Download high-res image (48KB) Download : Download full-size image Download : Download high-res image (102KB) Download : Download full-size image

Anti MICA (Major Histocompatibility Complex Class I) Related Antibody, Whether to Treat or Avoid in Renal Transplantation?

Introduction Pre-transplantation anti-major histocompatibility complex class-I related chain A (MICA) sensitization is an uncommon event and its role in kidney graft evolution is not completely defined. • Even when kidney allografts are well matched for HLA as in living related transplant and antiHLA antibodies are not detected, graft rejection can still occur. • Anti MICA antibody is reportedly associated with poor transplant outcomes and a high risk of acute and chronic rejection in renal transplantation. Methods A retrospective study of patients undergone living renal transplantation between years 2000-2014 was performed. • Recipients were classified in two groups, pre-transplantation Anti MICA antibody positive group (n=17) and antibody negative comparison group (n=17). • Patients with anti HLA antibodies were excluded and only isolated MICA positive patients were included in the study group. • Both groups were comparable in recipient age, donor age, donor relation, HLA and immunosuppression. Results Patients with pre transplant MICA antibody positivity were associated with increased acute rejection rate as compared to comparison group (47% vs. 11.7 %, p value= 0.02). • Renal function in MICA positive group and comparison group were comparable over a mean follow up of 6.5 years (mean creatinine 1.58 vs. 1.53 mg/dl). Rate of chronic rejection was same in both groups (5.8%). • No patient loss or graft loss occurred in either group over mean follow up of 6.5 years. Conclusion IsolatedAnti MICA antibody positivity is uncommon event. • Pre transplant anti MICA antibody positivity is associated with increased acute rejection rates. However chronic rejection rates and renal function are comparable in both groups. • Thus our study emphasizes that MICA antibody positive patients may require more aggressive immunosuppression. Role of desensitization has to be defined.

Antibody-Mediated Rejection in Kidney Transplantation Without Evidence of Anti-HLA Antibodies?

IntroductionThe definition of antibody-mediated rejection (AMR) is based on serologic (presence and/or development of donor-specific anti-HLA antibodies [DSAs]) and histologic (C4d deposition and endothelial damage) criteria. However, several cases of AMR have been described without C4d deposition, and other cases of histologic AMR without DSAs, which could be driven by other non-HLA alloantibodies such as anti-MICA or anti-angiotensin II type I receptor (AT1R). Here we studied clinical and histologic humoral rejection in kidney transplant recipients without evidence of anti-HLA antibodies. Materials and MethodsFifteen kidney transplant recipients with AMR defined as C4d+ and/or histologic g+ptc without anti-HLA antibodies in screening test were studied. Sera at the moment of biopsy and 2 months earlier were studied for anti-HLA antibodies by Luminex, in neat, diluted 1/160, and sera after treatment with dithiothreitol (DTT) and confirmed by single-antigen test. The anti-AT1R was measured by enzyme-linked immunosorbent assay. ResultsA lack of anti-HLA and MICA antibodies was confirmed after anti-HLA screening test in all conditions (neat, diluted, and DTT-treated) and de novo development of AT1R antibodies was ruled out. Nevertheless, after single-antigen test, 3 patients were identified with a weak reaction against class I antigen and another 4 patients against class II antigen. Due to the lack of locus-C typing in the donors, the DSA assignment cannot be confirmed, whereas anti-HLA class II antigens were DSA. ConclusionsA low sensitivity in the screening of anti-HLA antibody testing was observed. Our results suggest performing single-antigen test in seronegative patients with clinical humoral rejection after screening to confirm the presence of DSA.

P127 Detection of MICA antibodies: Comparison between MICA Screening and Single Antigen tests

Aim The presence of MICA antibodies is associated with worse graft outcome in solid organ transplant. Here, we aim to compare two MICA antibody detection tests: MICA Screening vs. Single Antigen Beads Based Test (SAB). Methods 20 sera with or without EDTA treatment were tested for MICA antibodies by screening (Onelambda LABScreen Mixed) or SAB tests (LABScreen MICA). Ratio of 2 in the screening test and MFI 1,000 in SAB test were used as the cutoff, respectively. Results We determined if EDTA treatment impact MICA SAB testing. Out of 15 samples, 7 samples displayed 23 MICA antibodies in EDTA treated or non-treated sera. In general, no significant difference of MFI (median fluorescence intensity) for MICA antibodies was observed between EDTA treated and non-treated sera. We did observe MFI of one MICA antibody increased from 9167 to 20566 upon EDTA treatment, suggesting this antibody showing prozone effect. We also found EDTA treatment increased MFI of positive control bead significantly (mean 6675 vs 9180). Next we compared results of MICA SAB testing on 20 EDTA treated sera with screening testing. We failed to identify the association between SAB test and screening test results (fig 1A). 4 sera, out of 8 MICA screening+/SAB- sera did not display HLA antibodies. 3 of these 4 patients had no sensitization events, suggesting positivity in these 3 patients is likely due to high background in MICA screening test. The mean ratio of screening testing on sera which were positive in SAB testing trended higher than sera having negative SAB test results, but the difference didn’t reach significance (fig 1B). Strong MICA antibodies (MFI>10,000) detected by SAB testing in two sera showed ratio >100 in screening testing, suggest both these assays can detect strong antibodies. Conclusions EDTA treatment may remove prozone effect for strong antibodies in MICA SAB testing. The screening testing tends to have high background, but strong MICA antibodies can be detected by both screening and SAB testing. The MICA SAB test is more specific than MICA screening test. Download : Download high-res image (71KB) Download : Download full-size image