Donor-specific antibodies (DSA)

Donor-specific antibodies (DSA) are antibodies in a transplant recipient that are directed against the human leukocyte antigens (HLA) of that recipient's specific organ donor.[1][2] DSA are the central mediators of antibody-mediated rejection (AMR) and are among the most important predictors of graft injury and graft loss across solid-organ transplantation.[1][3] They are distinguished by timing into preformed DSA, present before transplantation as a result of sensitization, and de novo DSA (dnDSA), which develop after transplantation in response to the graft.[2][3] DSA are detected by the same solid-phase antibody assays used for sensitization assessment and are the immunologic basis of the Crossmatch (CDC, flow, virtual) and of Panel-reactive antibody / cPRA and sensitization.

What DSA are

A recipient's immune system can produce antibodies against any HLA molecule it perceives as foreign. When such an antibody is specific for an HLA antigen expressed by the recipient's own donor, it is a donor-specific antibody.[1][2] Because HLA molecules are densely expressed on graft vascular endothelium, circulating DSA can bind the endothelium and initiate injury through complement activation, recruitment of natural killer cells and macrophages (antibody-dependent cellular cytotoxicity), and direct endothelial activation.[1][3] DSA may target class I HLA (HLA-A, -B, -C) or class II HLA (HLA-DR, -DQ, -DP); de novo class II DSA, particularly anti-HLA-DQ, are the most commonly observed de novo specificities and carry significant prognostic weight.[2][4]

Preformed versus de novo DSA

• Preformed DSA are present before transplantation owing to prior sensitizing events, pregnancy, transfusion, or a previous transplant. High-titer preformed DSA against the donor cause a positive crossmatch and, untreated, hyperacute or early accelerated AMR; their detection is the purpose of the pre-transplant crossmatch and unacceptable-antigen listing.[1][3] Transplantation in the presence of lower-level preformed DSA may proceed in selected programs under augmented immunosuppression and close monitoring.[5]
• De novo DSA arise weeks to years after transplantation, often in the setting of HLA mismatch (especially at the DQ locus), inadequate immunosuppression, or non-adherence to medication.[2][4] dnDSA are associated with subsequent AMR, transplant glomerulopathy and chronic allograft injury, and reduced long-term graft survival, and their appearance is increasingly used as an early warning of immunologic risk.[4]

Detection and characterization

DSA are identified with solid-phase immunoassays, principally the single-antigen bead (SAB) assay on a multiplexed flow platform, in which beads coated with individual recombinant HLA molecules are exposed to recipient serum and bound antibody is quantified as mean fluorescence intensity (MFI).[1][6] Knowing the donor's HLA type, the laboratory assigns which detected antibodies are donor-specific.[1][6] Characterization beyond mere presence includes:[6][7]

• Strength, estimated by MFI and, more rigorously, by titration (serial dilution), since a single neat MFI value is affected by saturation and inhibition (prozone) effects.
• Complement-fixing capacity, assessed by C1q or C3d modifications of the bead assay, which may identify antibodies at higher risk of causing complement-mediated injury.
• IgG subclass, which influences effector function.

These features, together with the clinical and biopsy context, inform how a given DSA is weighted; antibody assignment and risk interpretation are histocompatibility-laboratory and transplant-team decisions.[6][7]

Clinical significance and management

DSA are the serologic hallmark in the diagnosis of antibody-mediated rejection, which the Banff classification defines by a combination of histologic evidence of antibody interaction with the endothelium (microvascular inflammation), evidence of current or recent antibody activity (such as C4d deposition), and serologic DSA.[3][8] Beyond acute rejection, persistent DSA drive chronic, antibody-mediated allograft injury and are a leading immunologic cause of late graft loss.[4][8] See Transplant rejection.

Management strategies span prevention, monitoring, and treatment.[5][7] Prevention emphasizes adequate immunosuppression, adherence, and, increasingly, limiting HLA (and molecular/eplet) mismatch to reduce dnDSA formation. Many programs perform protocolized post-transplant DSA monitoring. Treatment of DSA-associated AMR is not standardized and rests on a limited evidence base, but commonly combines antibody removal (plasmapheresis), intravenous immunoglobulin, and B-cell- or plasma-cell-directed and complement-directed agents; outcomes of chronic AMR in particular remain poor.[5][7] Specific regimens are individualized clinical decisions.

See also

• Crossmatch (CDC, flow, virtual)
• Panel-reactive antibody / cPRA and sensitization
• Human leukocyte antigen (HLA) and tissue typing
• Transplant rejection
• Immunosuppression in transplantation

References

• Justiz Vargas AN, et al. Transplantation Immunology. StatPearls. NBK538218. https://www.ncbi.nlm.nih.gov/books/NBK538218/
• Zhang R. Donor-Specific Antibodies in Kidney Transplant Recipients. Clin J Am Soc Nephrol. 2018;13(1):182-192. PMID:28446536. https://pmc.ncbi.nlm.nih.gov/articles/PMC5753302/
• Acute Transplantation Rejection. StatPearls. NBK535410. https://www.ncbi.nlm.nih.gov/books/NBK535410/
• Wiebe C, et al. Evolution and clinical pathologic correlations of de novo donor-specific HLA antibody post kidney transplant. Am J Transplant. 2012;12(5):1157-1167. PMID:22429309. https://pubmed.ncbi.nlm.nih.gov/22429309/
• Schinstock CA, et al. Recommended Treatment for Antibody-mediated Rejection After Kidney Transplantation: TTS Working Group Consensus Report. Transplantation. 2020;104(5):911-922. PMID:31895348. https://pubmed.ncbi.nlm.nih.gov/31895348/
• Tambur AR, et al. Sensitization in Transplantation: Assessment of Risk (STAR) 2017 Working Group Meeting Report. Am J Transplant. 2018;18(7):1604-1614. PMID:29603851. https://pubmed.ncbi.nlm.nih.gov/29603851/
• Tait BD, et al. Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation. Transplantation. 2013;95(1):19-47. PMID:23238534. https://pubmed.ncbi.nlm.nih.gov/23238534/
• Loupy A, et al. The Banff 2019 Kidney Meeting Report (antibody-mediated rejection criteria). Am J Transplant. 2020;20(9):2318-2331. PMID:32463180. https://pubmed.ncbi.nlm.nih.gov/32463180/