Low median fluorescence intensity could be a nonsafety concept of immunologic risk evaluation in patients with shared molecular eplets in kidney transplantation.

Human leukocyte antigen (HLA) antibodies are usually "epitope" and not "antigen" specific. This work presents an interesting case concerning Luminex median fluorescence intensity (MFI) levels in antibodies considered low risk (<1,000), but producing humoral rejection. These low-titer antibodies could play an important role in transplantation. A 42-year-old woman was retransplanted with a deceased donor with negative complement-dependent cytotoxicity cross-matching. Our patient was pretransplant (PrT) sensitized to HLA antigens (single antigens (SA) = 31%) for 1 previous transplant. Thus, the formerly detected sensitized antigens were A32, A30, A31, cross-reacting group 5C, and DQ3 with a MFI(max) ≈ 4,127. In the posttransplantation period (PTP), the patient exhibited important instability in renal function and we detected an increased SA percentage (61%) with MFI(max) = 15,029 (A*32) with other antigens (detected with a low PrT MFI [<1,000]) as anti-A*03 (MFI(max) = 13,301) and anti-A*11 (MFI(max) = 13,714) specificities. Anti-A*03 was a donor-specific antibody (DSA). Renal biopsy was compatible with humoral rejection. The patient was pulsed with methylprednisolone, plasmapheresis, and intravenous immunoglobulin without improvement. Thus, we added anti-CD20 and the initial clinical response was highly favorable. Biopsies resulted in suggestive rejection reversion. MFI A*03 DSA decreased to 6,908 and later to MFI(max) = 5,505. After a 6-month PTP, the patient is well with MFI(max) = 3,124. It was possible to define exactly the potential immunizing epitope eplets whose recognition determined the specific antibody production. A*32:01, A*30:01, A*31:01 (detected PrT), A*11:01, and A*03:01 (detected PTP) alleles have several shared eplets (62QE, 70AQS, and 76VGT), with 62QE being the only eplet present on all alleles. In conclusion, low MFI levels in antibodies considered low risk could be important in posttransplant humoral rejection, although the patient's renal function can be restored. Thus, specific shared eplets should always be investigated with respect to previous transplant mismatches.

Specific "intra-allele" and "intra-broad antigen" human leukocyte antigen alloantibodies in kidney graft transplantation.

Human leukocyte antigen (HLA) antibodies are epitope specific and not antigen specific. This work presents a case of intra-allele (IA) sensitization. A 40-year-old-man underwent transplantion with identical "broad" DR. He was apparently not sensitized to HLA antigens by complement-dependent cytotoxicity (CDC), with one previous transplantation 15 years previously. In post-transplantation monitoring, we detected an "intra-broad antigen" (IBA) anti-DRB1*13 DSA by Luminex. We performed post-transplantation B-cell cross-matching (CM) by CDC, this being completely negative. We detected allele-specific antibodies by single antigens (SA), anti-DRB1*1303 (IBA), -DQB1*0301 (IA), -DRB1*1101, -DRB3*0101, anti-DPB1*0202, and anti-DRB1*0103. These antibodies originated from the first transplantation, HLA-DR6+ homozygous and serologically broad matched, but retrospectively typed as DRB1*1401, *1303; DRB3*0101, *0202; DQB1*0301, *0503; DPB1*0401, *0202 (mismatches in italics). However the second donor was DRB1*1301, *1401 (DR6+ homozygous); DRB3*0202; DQB1*0603, *0503; DPB1*0401 (mismatches in italic). Therefore, the stronger antibodies generated in the first transplantion (anti-DRB1*1303 and -DQB1*0301) were not specific for the specific subtypes (DRB1*1301 and -DQB1*0603) on the second transplantation. Finally, it was possible to exactly define the potential immunizing epitopes the recognition of which determined antibody production. Therefore, our patient had low titers of pretransplantation IBA and IA antibodies that were not prospectively detected by CDC. Post-transplantation with Luminex, we detected these alloantibodies, but as they were not IA and IBA DSA, they did not cause allograft injury.

Pre-formed donor-specific alloantibodies (DSA) detected only by luminex technology using HLA-coated microspheres and causing acute humoral rejection and kidney graft dysfunction.

The different methodologies for the detection of HLA sensitization could have discrepant results. At the moment, luminex technology seems--in our opinion--to be the most sensitive and safest method for antibody detection, and it should be taken into account during the transplantation process and as a means of indicating immunossuppresive regimen modulation.