anti-MICA Antibodies Research Articles

Post-transplant soluble MICA and MICA antibodies predict subsequent heart graft outcome

The objective of this retrospective study was to evaluate the role of MICA in heart graft acceptance. Pre- and post-transplant sera from 31 patients were evaluated for MICA antibodies by cytotoxicity on recombinant cell lines and soluble MICA (sMICA) concentrations by ELISA. The results demonstrated that the patients with post-transplant anti-MICA antibodies were at a high risk for the development of severe acute rejection (AR) ( p < 0.03; OR = 8.5). However, the presence of post-transplant sMICA was found to be associated with functioning grafts without AR episodes ( p < 0.03, OR = 7.9). In this preliminary survey, the negative association of sMICA with AR was found to be in the absence of MICA antibodies. Further research is needed to clarify the role of sMICA in allograft acceptance. Post-transplant evaluation of humoral immune response to MICA and the measure of sMICA in patient's sera may provide a good predictor of AR.

Association of Kidney Transplant Failure and Antibodies Against MICA

Despite the progress in renal transplantation, acute rejection and graft failure still occur and chronic rejection continues to be the main problem in long-term allograft survival. Although kidney transplant rejection has been linked to anti-HLA antibodies, not all patients with failed kidney transplants have anti-HLA antibodies, indicating that other loci may be involved. Sera of 63 patients who experienced kidney rejection were compared against sera of 82 patients with functioning transplants. Sera were examined for IgG and IgM anti-HLA Class I and II antibodies. They were also tested by cytotoxicity against panels of 26 endothelial cell lines, 8 MHC class I chain-related gene A (MICA) recombinant cell lines, and 28 B lymphoblast cell lines. Among patients whose transplants failed, 65% had anti-HLA antibodies compared with 45% of those with functioning kidneys ( p < 0.05). Similarly, among those whose transplants failed, 41% had anti–endothelial cell antibodies in contrast to 22% in functioning patients ( p < 0.05). Among patients whose grafts failed, 52% had anti-MICA antibodies versus 21% of those with functioning grafts ( p < 0.001). Eleven patients with failed grafts and 32 with functioning grafts were negative for all of the above. However, 6 of the former and 7 of the latter showed positive cytotoxicity against B lymphoblasts ( p < 0.05). Taking all antibodies together, 92% of patients with graft failure had antibodies as opposed to 70% of patients with functioning grafts ( p < 0.001). We postulate that antibodies against HLA, MICA, endothelial cells, and B lymphoblasts could be independently involved in the slow process of chronic graft failure.

Therapy-induced antibodies to MHC class I chain-related protein A antagonize immune suppression and stimulate antitumor cytotoxicity.

The activation of NKG2D on innate and adaptive cytotoxic lymphocytes contributes to immune-mediated tumor destruction. Nonetheless, tumor cell shedding of NKG2D ligands, such as MHC class I chain-related protein A (MICA), results in immune suppression through down-regulation of NKG2D surface expression. Here we show that some patients who respond to antibody-blockade of cytotoxic T lymphocyte-associated antigen 4 or vaccination with lethally irradiated, autologous tumor cells engineered to secrete granulocyte-macrophage colony-stimulating factor generate high titer antibodies against MICA. These humoral reactions are associated with a reduction of circulating soluble MICA (sMICA) and an augmentation of natural killer (NK) cell and CD8(+) T lymphocyte cytotoxicity. The immunotherapy-induced anti-MICA antibodies efficiently opsonize cancer cells for dendritic cell cross-presentation, which is correlated with a diversification of tumor antigen recognition. The anti-MICA antibodies also accomplish tumor cell lysis through complement fixation. Together, these findings establish a key role for the NKG2D pathway in the clinical activity of cytotoxic T lymphocyte-associated antigen 4 antibody blockade and granulocyte-macrophage colony-stimulating factor secreting tumor cell vaccines. Moreover, these results highlight the therapeutic potential of anti-MICA antibodies to overcome immune suppression and effectuate tumor destruction in patients.

Detection of Anti-MICA Antibodies in Patients Awaiting Kidney Transplantation, during the Post-transplant Course, and in Eluates from Rejected Kidney Allografts by Luminex Flow Cytometry

Previously we have reported on the development of antibodies against MICA alleles in kidney transplant recipients. These alloantibodies have now been determined using a new assay using Luminex beads bound to soluble recombinant MICA antigens produced in insect cells. In the present study we have analyzed sera from 85 kidney transplant recipients on the waiting list and 66 patients transplanted within the last 4 years and 59 acid eluates obtained from allograft nephrectomy specimens. Many of the patients in those groups were sensitized and some had previous transplants (waiting list: 15%; post-tx: 7.6%; eluates 22%) and their sera were found to contain anti-human leukocyte antigen (HLA) and anti-MICA antibodies. Anti-MICA antibodies were detected in 21/85 (24.7%) of the waiting list patients and in 15/66 (22.7%) of the transplanted recipients; 11 of the eluates (18.6%) were found to have MICA-specific antibodies (6 of them also had anti-HLA antibodies and 5 did not). These data suggested that immunization against mismatched MICA alleles induces development of anti-MICA antibodies. The finding of MICA allele-specific antibodies in eluates of kidney transplants suggests that anti-MICA antibodies can be involved in the pathogenesis of kidney allograft rejection. Further studies will be required to determine whether patients who produce alloantibodies against MICA alleles are at risk for transplant rejection even when no HLA antibodies are detected.

Detection of anti-MICA antibodies in eluates from rejected kidney allografts by Luminex flow cytometry

Detection of anti-MICA antibodies in eluates from rejected kidney allografts by Luminex flow cytometry

Codominant expression of the polymorphic MICA alloantigens encoded by genes in the HLA region.

The HLA-related, polymorphic MHC class I-related chain A (MICA) gene encodes a 383-amino acid polypeptide, with three extracellular domains (alpha1, alpha2 and alpha3), a transmembrane region and a cytoplasmic tail. We have previously shown that freshly isolated endothelial cells, fibroblasts, keratinocytes and monocytes express MICA, while peripheral blood CD4+, CD8+ or CD19+ lymphocytes do not. This polymorphic MICA molecule is a target for specific alloantibodies in sera from kidney, heart and lung transplant recipients, although its possible role during graft rejection remains to be demonstrated. In this study we investigated whether there is codominance in the expression of MICA. We isolated RNA from a heterozygous cell line (HCT116), previously shown by sequencing-based typing to be MICA*001/MICA*00902, as well as 12 clones derived from it. Thereafter, we retrotranscribed the RNA into cDNA, and performed a molecular typing using MICA-sequence specific oligonucleotides (SSOP). Using this approach, we detected the RNA encoding MICA*001 and MICA*00902 in all the clones and in the parental cell line, indicating that MICA is codominantly expressed. This codominant expression was further confirmed by cloning and sequencing plasmids encoding these two alleles produced from the same HCT116 RNA preparation. We also produced the two recombinant MICA proteins (MICA*001 and MICA*00902). They reacted with rabbit anti-MICA polyclonal antibodies by ELISA and Western blot, indicating that the plasmids carrying the cDNA inserts probably encode functional MICA proteins. This strongly suggests that, like the HLA class I and class II proteins, MICA is codominantly expressed. The codominant expression of the polymorphic, HLA-like MICA alloantigens may have implications for the immune response elicited by the allograft in organ transplantation.

IDENTIFICATION OF MICA AS A NEW POLYMORPHIC ALLOANTIGEN RECOGNIZED BY ANTIBODIES IN SERA OF KIDNEY RECIPIENTS

680 Recently, the HLA related, polymorphic MICA (MHC class I related chain A) gene has been described. It has been suggested that the 383 amino acid-encoded polypeptide has three extracellular domains (α1, α2, and α3), one transmembrane region, and a cytoplasmic tail. The biological function of MICA and MICB still remains unknown, but it has been observed that MICA behaves as a cell stress antigen, and that it may function as restriction element for a subpopulation of intestinal γδ T cells. Using anti-MICA specific rabbit sera we demonstrated that freshly isolated monocytes, keratinocytes, fibroblasts and endothelial cells express MICA, while peripheral blood CD4+, CD8+ or CD19+ lymphocytes do not. We also demonstrated by flow cytometry that MICA is expressed at the cell surface in endothelial cells and fibroblasts. In order to analyze whether MICA may be a target for specific antibodies in sera of transplanted patients, we cloned exons 2 to 4 of the MICA008 allele into an E. coli expression host, and produced a recombinant MICA protein consisting of the α1, α2 and α3 domains. This recombinant MICA protein was used to investigate by ELISA whether specific antibodies against MICA are found in sera of transplant recipients. We found that several patients had specific antibodies against MICA. Most of these antibodies were detected in serum samples collected at different times after kidney rejection. Although this finding raises the question of how these patients became immunized against MICA, the results obtained show that some transplanted patients develop anti-MICA specific antibodies that can be detected in this assay. The fact that the polymorphic, HLA-like MICA molecule, expressed at the cell surface of endothelial cells, is recognized by specific antibodies in sera of transplanted patients, suggests that MICA may be a target in graft rejection.