ABOi With Conventional Immunosuppression Alone–Antiblood Group Antibody Isn’t the Only Contributor to Antibody-Mediated Rejection and/or Thrombotic Microangiopathy

To the Editor: We thank Dr. Focosi et al and Dr. Krishan et al for their comments regarding the recent article describing ABO-incompatible renal transplantation (ABOi) without antibody removal using conventional immunosuppression alone (1.Focosi D. Potential hurdles to ABO-incompatible living donor kidney transplantation without augmented immunosuppression.Am J Transplant. 2015; 15: 1727Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar, 2.Krishnan N Coates R Daga S ABO-incompatible renal transplantation without antibody removal using conventional immunosuppression alone.Am J Transplant. 2015; 15 (et al): 1728-1729Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar). In the manuscript, we highlighted the role of anti-blood group antibody (ABGAb) titer as the major predictor of antibody-mediated rejection (AbMR) in ABOi. The occurrence of AbMR in only 1 of 20 low-titer patients in conjunction with the series of 10 low-titer patients from Cambridge without AbMR (3.Masterson R Hughes P Walker RG ABO incompatible renal transplantation without antibody removal using conventional immunosuppression alone.Am J Transplant. 2014; 14 (et al): 2807-2813Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar), and multiple reports of AbMR occurring primarily in patients with moderate to high baseline ABGAb strongly suggest that titer is the prime (though not sole) predictor of AbMR. Dr. Focosi highlights the recognized idiosyncrasies of measuring ABGAb, reinforcing the need for center specific thresholds in considering the need for antibody removal, and deciding the number of treatments required in the perioperative period (3.Masterson R Hughes P Walker RG ABO incompatible renal transplantation without antibody removal using conventional immunosuppression alone.Am J Transplant. 2014; 14 (et al): 2807-2813Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 4.Flint SM Walker RG Hogan C Successful ABO-incompatible kidney transplantation with antibody removal and standard immunosuppression.Am J Transplant. 2011; 11 (et al): 1016-1024Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). As stated in the study design, we measure ABGAb by three methodologies using both standard and donor-specific cells and donor-specific cells. Clinical monitoring is performed using the ortho method, the clinical utility of which has been described previously.The latter is semi-automated with samples scored by the apparatus, minimizing variability. We agree that overall isoagglutinin titer (direct or indirect), may include specificities (e.g. dependent on chain type), of varying or no clinical relevance. Ultimately, the issue of consequence is the relationship between the observed (institution specific) titer and clinical outcome(s). With regards to expression of different specific carbohydrate moieties, use of donor specific cells in the initial titering procedure establishes whether standard cells provide an equivalent result, or whether serial clinical ABGAb monitoring for a given donor/recipient pair will be more meaningful with use of donor specific cells. The same applies to Dr. Focosi’s comment regarding IgG subclass specificities. As Dr. Krishnan notes, flow cytometry has some advantages, but it is still subject to variability between institutions and even on a day to day basis variability. As Dr. Focosi indicates, where ABO is from a deceased donor, the transplant takes place without the potential benefit of receiving MMF 10 to 14 days pretransplant as occurs with living donor ABOi. This may impact ABGAb rebound with the potential to impact patients whose titers are at the upper end of the lower range. At worst, this might necessitate (additional) posttransplant antibody removal until MMF commenced at transplant has had time to impact on B cells and antibody production (the clinical importance of which remains unproven). Nevertheless, we have already successfully performed ABOi deceased donor transplantation from two non-A2 donors (manuscript in progress), providing proof of principle. Our series, and Torpey’s (5.Brown AL Carter V Howell M Russell K Torpey N. ABO incompatible renal transplantation without augmented immunosuppression or antibody removal—Report of 10 cases.Transplantation. 2012; 94: 66Crossref Google Scholar), coupled with publications reporting “ABOi related AbMR” primarily in patients with higher ABGAb titers, suggests ABGAb levels play a role somewhat analogous to that of the cytotoxic to the cytotoxic lymphocyte crossmatch (CDC) and solid phase assays in assessing the pathogenicity of donor specific antibody (DSAb). Though uncommon, AbMR is well described in patients with negative CDC (historically about 5–10%), and in patients with DSAb of very low mean fluorescence intensity (MFI) or even without detectable alloantibody (6.Grafft CA Cornell LD Gloor JM Antibody-mediated rejection following transplantation from an HLA-identical sibling.Nephrol Dial Transplant. 2010; 25 (et al): 307-310Crossref PubMed Scopus (47) Google Scholar). Other pathologies may mimic AbMR (e.g. other causes of thrombotic microangiopathy [TMA] with associated C4d staining) (7.Chua JS, Baelde HJ, Zandbergen M, et al. Complement factor C4d is a common denominator in thrombotic microangiopathy. J Am Soc Nephrol 2015.Google Scholar). The correspondence from Dr. Krishnan draws attention to phenomena we and others have noted previously with regards to additional factors that may contribute to, produce, or moderate the pathology seen with AbMR; this includes use of lymphocyte-depleting antibodies (6.Grafft CA Cornell LD Gloor JM Antibody-mediated rejection following transplantation from an HLA-identical sibling.Nephrol Dial Transplant. 2010; 25 (et al): 307-310Crossref PubMed Scopus (47) Google Scholar, 8.Colovai AI Vasilescu ER Foca-Rodi A Acute and hyperacute humoral rejection in kidney allograft recipients treated with anti-human thymocyte antibodies.Hum Immunol. 2005; 66 (et al): 501-512Crossref PubMed Scopus (35) Google Scholar, 9.Tinckam KJ Wood IG Ji F Milford EL. ATG induction is associated with an increase in anti-HLA antibodies after kidney transplantation.Hum Immunol. 2004; 65: 1281-1287Crossref PubMed Scopus (12) Google Scholar), particularly in the setting of ABOi (3.Masterson R Hughes P Walker RG ABO incompatible renal transplantation without antibody removal using conventional immunosuppression alone.Am J Transplant. 2014; 14 (et al): 2807-2813Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 4.Flint SM Walker RG Hogan C Successful ABO-incompatible kidney transplantation with antibody removal and standard immunosuppression.Am J Transplant. 2011; 11 (et al): 1016-1024Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). With regards to the expression and pathology of AbMR, the potential for important interactions between pathways governing humoral immunity, coagulation, complement, complement regulatory proteins and other constitutive endothelial protective mechanisms has been noted (3.Masterson R Hughes P Walker RG ABO incompatible renal transplantation without antibody removal using conventional immunosuppression alone.Am J Transplant. 2014; 14 (et al): 2807-2813Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 19.Hughes PD Cohney SJ. Modifiers of complement activation for prevention of antibody-mediated injury to allografts.Curr Opin Organ Transplant. 2011; 16: 425-433Crossref PubMed Scopus (22) Google Scholar). Phenotypic variations/abnormalities in these pathways may alter the pathogenicity of alloantibody, potentially lowering the threshold that triggers AbMR as described in a patient with a factor H mutation (10.Noone D Al-Matrafi J Tinckam K Antibody mediated rejection associated with complement factor h-related protein 3/1 deficiency successfully treated with eculizumab.Am J Transplant. 2012; 12 (et al): 2546-2553Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). We also noted the apparently higher rates of AbMR reported in ABOi series where induction has included lymphocyte-depleting antibodies (4.Flint SM Walker RG Hogan C Successful ABO-incompatible kidney transplantation with antibody removal and standard immunosuppression.Am J Transplant. 2011; 11 (et al): 1016-1024Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). Autoimmunity is well described with alemtuzumab, with reports of pathogenic tissue-specific antibodies, and an association with abnormalities in BAFF/BAFF receptor interaction that may predispose to AbMR (11.Banham G Prezzi D Harford S Elevated pretransplantation soluble BAFF is associated with an increased risk of acute antibody-mediated rejection.Transplantation. 2011; 96 (et al): 413-420Crossref Scopus (56) Google Scholar, 12.Bloom D Chang Z Pauly K BAFF is increased in renal transplant patients following treatment with alemtuzumab.Am J Transplant. 2009; 9 (et al): 1835-1845Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar, 13.Todeschini M Cortinovis M Perico N In kidney transplant patients, alemtuzumab but not basiliximab/low-dose rabbit anti-thymocyte globulin induces B cell depletion and regeneration, which associates with a high incidence of de novo donor-specific anti-HLA antibody development.J Immunol. 2013; 191 (et al): 2818-2828Crossref PubMed Scopus (64) Google Scholar). Pathology indistinguishable from hyperacute rejection (HAR) and AbMR has been described following administration of thymoglobulin in the presence of a negative crossmatch, and the absence of identifiable DSAb (6.Grafft CA Cornell LD Gloor JM Antibody-mediated rejection following transplantation from an HLA-identical sibling.Nephrol Dial Transplant. 2010; 25 (et al): 307-310Crossref PubMed Scopus (47) Google Scholar). Use of T lymphocyte-depleting antibodies has been associated with deposition of complement (14.Baldwin 3rd, WM Armstrong LP Samaniego-Picota M Antithymocyte globulin is associated with complement deposition in cardiac transplant biopsies.Hum Immunol. 2004; 65 (et al): 1273-1280Crossref PubMed Scopus (21) Google Scholar), production of DSAb (9.Tinckam KJ Wood IG Ji F Milford EL. ATG induction is associated with an increase in anti-HLA antibodies after kidney transplantation.Hum Immunol. 2004; 65: 1281-1287Crossref PubMed Scopus (12) Google Scholar), and development of AbMR (9.Tinckam KJ Wood IG Ji F Milford EL. ATG induction is associated with an increase in anti-HLA antibodies after kidney transplantation.Hum Immunol. 2004; 65: 1281-1287Crossref PubMed Scopus (12) Google Scholar, 15.Zachary AA Montgomery RA Ratner LE Specific and durable elimination of antibody to donor HLA antigens in renal-transplant patients.Transplantation. 2003; 76 (et al): 1519-1525Crossref PubMed Scopus (165) Google Scholar). Given the profound changes in immunobiology that occur following administration of either thymoglobulin or alemtuzemab, it is possible they may interfere with subsets of lymphocytes controlling alloantibody production (16.Zwang NA Turka LA. Homeostatic expansion as a barrier to lymphocyte depletion strategies.Curr Opin Organ Transplant. 2014; 19: 357-362Crossref PubMed Scopus (19) Google Scholar), and/or the constitutive mechanisms governing the phenomenon of accommodation (3.Masterson R Hughes P Walker RG ABO incompatible renal transplantation without antibody removal using conventional immunosuppression alone.Am J Transplant. 2014; 14 (et al): 2807-2813Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 4.Flint SM Walker RG Hogan C Successful ABO-incompatible kidney transplantation with antibody removal and standard immunosuppression.Am J Transplant. 2011; 11 (et al): 1016-1024Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). Based on the information presented, it is hard to draw conclusions regarding the patients described by Dr. Krishnan et al. Each was subject to a variety of factors that may have overwhelmed any role played by ABGAb. The 73-year-old ABOi recipient develops hepatotoxicity (more commonly seen as a manifestation of CNI toxicity), raising the possibility of CNI-induced endothelial activation as seen in CNI-mediated TMA. The patient’s MMF was ceased increasing susceptibility to rejection, with concomitant development of septicaemia originating in the urinary tract—another potential contributor to endothelial activation and loss of intrinsic endothelial protective mechanisms. The infection may have played a role for at least 24 h before cultures became positive. The patient then receives thymoglobulin with the potential for triggering an AbMR-like reaction as we have alluded to. The graft is then lost with evidence of infarction, as well as AbMR; the authors do not specify which features of AbMR were seen. The second patient received alemtuzumab induction and Tacrolimus. On day 3, changes of TMA were noted. Tacrolimus was stopped temporarily, though neither serial creatinines nor tacrolimus levels are provided. The authors note, “serum creatinine rose further” (though there is no information on allograft blood flow from ultrasound, or nuclear scan), and a biopsy showed “thrombosis of the graft with AMR,” and the graft was removed the next day. The specific features of AMR are not provided. A significant rise in ABGAb seems to occur predominantly after graft removal. Again it is difficult to make firm conclusions as to the cause of the TMA and/or AMR in this case, and we and others have found changes in ABGAb titer after transplantation to be unreliable with poor sensitivity and specificity (17.Tobian AA Shirey RS Montgomery RA ABO antibody titer and risk of antibody-mediated rejection in ABO-incompatible renal transplantation.Am J Transplant. 2010; 10 (et al): 1247-1253Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar). Rises in ABGAb in the setting of acute inflammation/infection may be an epi-phenomenon, as we have seen in some cases of infection. We reiterate the association of alemtuzumab with production of DSAb (13.Todeschini M Cortinovis M Perico N In kidney transplant patients, alemtuzumab but not basiliximab/low-dose rabbit anti-thymocyte globulin induces B cell depletion and regeneration, which associates with a high incidence of de novo donor-specific anti-HLA antibody development.J Immunol. 2013; 191 (et al): 2818-2828Crossref PubMed Scopus (64) Google Scholar) and the increased incidence of humoral rejection reported by some (18.LaMattina JC Mezrich JD Hofmann RM Alemtuzumab as compared to alternative contemporary induction regimens.Transpl Int. 2012; 25 (et al): 518-526Crossref PubMed Scopus (41) Google Scholar) though not all centers, and particularly in the setting of ABOi (4.Flint SM Walker RG Hogan C Successful ABO-incompatible kidney transplantation with antibody removal and standard immunosuppression.Am J Transplant. 2011; 11 (et al): 1016-1024Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar). Finally, in the concluding remarks of the paper, we noted that this “minimalist” approach to ABOi in patients with low-titer ABGAb should be undertaken with great care and contingency plans, and that some centers may prefer patients receive at least one antibody removal treatment pretransplant. In the case of plasmapheresis (cf. immunoabsorption), this has the added advantage of removing complement (the other key player in AbMR), and a contributor to other transplant-related pathologies (19.Hughes PD Cohney SJ. Modifiers of complement activation for prevention of antibody-mediated injury to allografts.Curr Opin Organ Transplant. 2011; 16: 425-433Crossref PubMed Scopus (22) Google Scholar). The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation.