Long-term outcome of highly sensitized African American patients transplanted with deceased donor kidneys

Impact of low-level pretransplant donor-specific antibodies on outcomes after kidney transplantation

Background

The effect of low‐level pretransplant donor‐specific antibody (DSA) on kidney transplant outcomes is not well described. The goal of this study was to compare outcomes among patients of varying immunologic risk, based on the level of pretransplant DSA.

Methods

We retrospectively reviewed all adult kidney transplant recipients who had undergone a transplant at our center between January 2013 and May 2017. Patients were grouped as negative DSA (mean fluorescence intensity, [MFI_SUM < 100]), low‐level DSA (MFI_SUM 100–1000), and positive DSA (MFI_SUM > 1000). Rejection, infection, graft, and patient survival were outcomes measured.

Results

Of 952 patients, 82.1% had negative DSA, 10.7% had low‐level DSA, and 7.1% had positive DSA. The positive DSA group had the highest rate of antibody‐mediated rejection (10.3%), followed by low‐level DSA (7.8%) and the negative DSA group (4.5%) (p = .034). The rate of BK viremia was highest in the positive DSA group (39.7%), followed by the low‐level group (30.4%) and the negative DSA group (25.6%), (p = .025). None of the other outcomes, including graft or patient survival, were different between the groups.

Conclusion

While low‐level DSA should not prevent proceeding with kidney transplantation, it should not be ignored. Future studies are needed to investigate the long‐term effects of varying levels of pre‐transplant DSA on outcomes.

Donor-Specific Antibodies in Kidney Transplant Recipients

Donor-specific antibodies have become an established biomarker predicting antibody-mediated rejection. Antibody-mediated rejection is the leading cause of graft loss after kidney transplant. There are several phenotypes of antibody-mediated rejection along post-transplant course that are determined by the timing and extent of humoral response and the various characteristics of donor-specific antibodies, such as antigen classes, specificity, antibody strength, IgG subclasses, and complement binding capacity. Preformed donor-specific antibodies in sensitized patients can trigger hyperacute rejection, accelerated acute rejection, and early acute antibody-mediated rejection. De novo donor-specific antibodies are associated with late acute antibody-mediated rejection, chronic antibody-mediated rejection, and transplant glomerulopathy. The pathogeneses of antibody-mediated rejection include not only complement-dependent cytotoxicity, but also complement-independent pathways of antibody-mediated cellular cytotoxicity and direct endothelial activation and proliferation. The novel assay for complement binding capacity has improved our ability to predict antibody-mediated rejection phenotypes. C1q binding donor-specific antibodies are closely associated with acute antibody-mediated rejection, more severe graft injuries, and early graft failure, whereas C1q nonbinding donor-specific antibodies correlate with subclinical or chronic antibody-mediated rejection and late graft loss. IgG subclasses have various abilities to activate complement and recruit effector cells through the Fc receptor. Complement binding IgG3 donor-specific antibodies are frequently associated with acute antibody-mediated rejection and severe graft injury, whereas noncomplement binding IgG4 donor-specific antibodies are more correlated with subclinical or chronic antibody-mediated rejection and transplant glomerulopathy. Our in-depth knowledge of complex characteristics of donor-specific antibodies can stratify the patient's immunologic risk, can predict distinct phenotypes of antibody-mediated rejection, and hopefully, will guide our clinical practice to improve the transplant outcomes.

Influence of de novo donor-specific antibody on early renal allograft function recovery

BACKGROUND

The aim of the present study is to investigate the impact of de novo donor-specific antibodies (dnDSA) on early graft function, to provide objective reference for early clinical diagnosis and reasonable individualized treatment.

METHODS

305 cases of renal transplant patients for the first time were observed in this study. Follow-up time for all recipients was 6 months after operation. HLA antibody, DSA, renal function were monitored after transplant.

RESULTS

In total of 305 cases, 66 cases (21.64%) were HLA antibody positive and 21 cases (6.89%) showed acute rejection (AR) in 6 months after transplant. The HLA antibody-positive patients included six cases of dnDSA-positive and 60 cases of dnDSA-negative. The incidence of AR was 2.09% (5/239) in HLA antibody-negative patients, 18.33% (11/60) in HLA antibody positive with DSA-negative patients, and 83.33% (5/6) in HLA antibody-positive patients with DSA-positive. There was a big difference between DSA-negative and DSA-positive patients (p < 0.01). The recovery time of AR patients with DSA-positive were longer than DSA-negative patients, and the recovery graft function of AR patient with DSA-positive were not as good as those with DSA-negative.

CONCLUSIONS

The appearance of dnDSA in the early stage of kidney transplantation is a warning sign of AR occurrence. Dynamic monitoring of HLA antibody and DSA could predict the state of graft function, and play an important role in the prevention of AR, timely and effectively.

Monoclonal antibody therapy and renal transplantation: focus on adverse effects

A series of monoclonal antibodies (mAbs) are commonly utilized in renal transplantation as induction therapy (a period of intense immunosuppression immediately before and following the implant of the allograft), to treat steroid-resistant acute rejections, to decrease the incidence and mitigate effects of delayed graft function, and to allow immunosuppressive minimization. Additionally, in the last few years, their use has been proposed for the treatment of chronic antibody-mediated rejection, a major cause of late renal allograft loss. Although the exact mechanism of immunosuppression and allograft tolerance with any of the currently used induction agents is not completely defined, the majority of these medications are targeted against specific CD proteins on the T or B cells surface (e.g., CD3, CD25, CD52). Moreover, some of them have different mechanisms of action. In particular, eculizumab, interrupting the complement pathway, is a new promising treatment tool for acute graft complications and for post-transplant hemolytic uremic syndrome. While it is clear their utility in renal transplantation, it is also unquestionable that by using these highly potent immunosuppressive agents, the body loses much of its innate ability to mount an adequate immune response, thereby increasing the risk of severe adverse effects (e.g., infections, malignancies, haematological complications). Therefore, it is extremely important for clinicians involved in renal transplantation to know the potential side effects of monoclonal antibodies in order to plan a correct therapeutic strategy minimizing/avoiding the onset and development of severe clinical complications.

Essential concept of transplant immunology for clinical practice

Our understanding of transplant immunology has advanced from gross allograft rejection to cellular response and to current molecular level. More sensitive assays have been developed to characterize patient sensitization and to detect pre-existing donor-specific antibodies (DSA) in pre-transplant crossmatch. After a transplant, pre-existing or de novo DSA are increasingly monitored to guide clinical management. Therefore, it is important for clinicians to understand the basic concepts and key components of transplant immunology as well as be familiarized with the modern immunological techniques used in kidney transplantation.

Impact of alloantibody strength in crossmatch negative DSA positive kidney transplantation

OBJECTIVES

The clinical relevance of pre-transplant "low-level" donor specific anti-HLA antibodies (DSAs) in crossmatch negative kidney transplant recipients remains unclear. To determine what level of DSA associates with antibody mediated rejection (AMR) could be the way to measure the clinical relevance of pre-transplant "low-level" donor specific anti-HLA antibodies (DSAs) in crossmatch negative kidney transplant recipients.

DESIGN AND METHODS

A retrospective analysis of 221 patients from October 2008 to December 2009 was included in this study. Sera were obtained pre-transplant and two weeks post-transplant and tested for DSA using LABScreen single antigen beads.

RESULTS

Among the 221 patients, 11 experienced AMR within 200days after transplant (5%). Pre-transplant DSA was associated with AMR at multiple mean fluorescence intensity (MFI) cutoffs (500, 1000, 2000, 3000, 5000; p=0.003, 0.001, 0.007, 0.003, and 0.003, respectively). No correlation was seen between acute T-cell mediated rejection (CMR) and pre-transplant DSA at any of the same MFI cutoffs. There was an increased risk of AMR with higher levels of pre-transplant DSA. Finally, an increase in DSA MFI from pre- to two weeks post-transplant was indicative of a higher probability of AMR.

CONCLUSION

Overall, this data supports using the single antigen bead to detect "low-level" DSA both pre- and post- as having a positive and persistent DSA may be predictive of higher AMR rates and poorer graft survival.

Antibody induction therapy in adult kidney transplantation: A controversy continues

Antibody induction therapy is frequently used as an adjunct to the maintenance immunosuppression in adult kidney transplant recipients. Published data support antibody induction in patients with immunologic risk to reduce the incidence of acute rejection (AR) and graft loss from rejection. However, the choice of antibody remains controversial as the clinical studies were carried out on patients of different immunologic risk and in the context of varying maintenance regimens. Antibody selection should be guided by a comprehensive assessment of immunologic risk, patient comorbidities, financial burden as well as the maintenance immunosuppressives. Lymphocyte-depleting antibody (thymoglobulin, ATGAM or alemtuzumab) is usually recommended for those with high risk of rejection, although it increases the risk of infection and malignancy. For low risk patients, interleukin-2 receptor antibody (basiliximab or daclizumab) reduces the incidence of AR without much adverse effects, making its balance favorable in most patients. It should also be used in the high risk patients with other medical comorbidities that preclude usage of lymphocyte-depleting antibody safely. There are many patients with very low risk, who may be induced with intravenous steroids without any antibody, as long as combined potent immunosuppressives are kept as maintenance. In these patients, benefits with antibody induction may be too small to outweigh its adverse effects and financial cost. Rituximab can be used in desensitization protocols for ABO and/or HLA incompatible transplants. There are emerging data suggesting that alemtuzumab induction be more successful than other antibody for promoting less intensive maintenance protocols, such as steroid withdrawal, tacrolimus monotherapy or lower doses of tacrolimus and mycophenolic acid. However, the long-term efficacy and safety of these unconventional strategies remains unknown.

Risk stratification by the virtual crossmatch: a prospective study in 233 renal transplantations

The virtual crossmatch (virtual-XM) has been proposed for accurate identification of donor-specific HLA-antibodies, but large prospective studies assessing its value for pretransplant risk stratification are lacking. A total of 233 consecutive renal allograft recipients were prospectively stratified according to the virtual-XM. In patients with a negative virtual-XM (n=190, 82%), prospective cytotoxicity crossmatches (CDC-XM) were omitted, and they received standard immunosuppression. Virtual-XM positive patients were only transplanted if CDC-XM were negative. They received additional induction with anti-T-lymphocyte-globulin and intravenous immunoglobulins (n=43, 18%). The cumulative incidence of clinical/subclinical antibody-mediated rejection (AMR) at 1 year was lower in the negative virtual-XM than in the positive virtual-XM group [15/190 (8%) vs. 18/43 (42%); P<0.0001]. After a median follow-up of 2.6 years, allograft loss because of AMR occurred less often in the negative virtual-XM group (1% vs. 7%; P=0.04) and death-censored allograft survival at 2 years was higher (98% vs. 91%; P=0.02). Serum creatinine was not different at the last follow-up (129 μm vs. 130 μm; P=0.58). We conclude that a negative virtual-XM defines patients at low risk for AMR and early allograft loss, while a positive virtual-XM represents a significant risk for AMR despite enhanced induction therapy. This supports the utility of the virtual-XM for risk stratification and treatment allocation.