Assessment of IgM DSAs in Transplant Recipients: Relationship to De Novo IgG DSAs and Risk for Antibody Rejection.

Background: The presence of anti-HLA donor-specific antibodies (DSAs) is associated with antibody-mediated rejection (AMR) and inferior graft survival. However, recent data suggest that ~50% of AMR episodes are IgG DSA negative and possibly related to non-HLA DSAs. After the initial activation of B cells to alloantigen, IgM is the first immunoglobulin produced. In addition, both IgM and IgG isotopes can activate the classic complement pathway and induce complement-dependent cytotoxicity to allograft targets. Current practices focus on the assessment of IgG DSAs with little concern for the assessment of IgM DSAs. Methods: Here, we examined anti-HLA IgM in a cohort of 22 patients who developed de novo IgG DSAs by a modified single-antigen bead-based test. Results: We found IgM HLA DSAs developed before IgG DSAs. The median time from the detection of IgM DSAs to the appearance of de novo IgG DSAs was 461 d. Most patients had IgM DSAs against the same HLA-DQ antigens, for which IgG de novo DSAs were also later detected. IgM DSAs were detected in patients with biopsies suspected of AMR. Conclusions: The detection of IgM DSAs could be an early indicator of alloimmune responses to allografts before IgG de novo DSAs appear.

An Assessment of the Value of Donor-derived Cell-free DNA Surveillance in Patients With Preserved Kidney Allograft Function.

BACKGROUND: Donor-derived cell-free DNA (dd-cfDNA) is a biomarker validated to detect rejection when measured to assess kidney allograft dysfunction. However, it remains unclear whether routine surveillance with dd-cfDNA provides additional information over standard monitoring of kidney allografts with creatinine and donor-specific antibodies (DSAs), particularly among those with little suspicion of rejection or injury. We investigated the value of measuring dd-cfDNA in patients with preserved allograft function and describe its association with future events. METHODS: Three-hundred seventeen kidney transplant recipients with a creatinine ≤1.5 mg/dL, no current DSA, and no prior rejection were assessed with dd-cfDNA and categorized into low (dd-cfDNA <0.5%; n = 239), moderate (dd-cfDNA 0.5% to <1.0%; n = 43), and high (dd-cfDNA ≥1.0%; n = 35) groups. The occurrence of rejection, DSA, graft loss, and change in estimated glomerular filtration rate over time after dd-cfDNA assessment was compared. RESULTS: Over follow-up, rejections were more commonly found among patients with high vs low dd-cfDNA (17% versus 5%; P = 0.01); a similar nonsignificant trend was observed among patients with moderate compared to low dd-cfDNA (12% versus 5%; P = 0.13). DSA development was uncommon and not different between groups (low: 4%; moderate: 3%; high: 0%; P = 0.52). There was only 1 graft loss in a patient with low dd-cfDNA, and dd-cfDNA was not associated with graft dysfunction over time. CONCLUSIONS: Most patients with elevated dd-cfDNA in conjunction with preserved allograft function remained stable over follow-up without deterioration in function or graft loss. Studies are needed to differentiate patients with elevated dd-cfDNA who will develop adverse outcomes from those who will remain clinically stable.

Assessment of humoral and cellular immune responses to SARS CoV-2 vaccination (BNT162b2) in immunocompromised renal allograft recipients.

BACKGROUND: Assessing the composition of immune responses to SARS-CoV-2 vaccines is critical for our understanding of protective immunity, especially for immune compromised patients. The Pfizer (BNT162b2) vaccination showed >90% efficacy in protecting individuals from infection. However, these studies did not examine responses in immunocompromised kidney transplant patients (KT). Subsequent reports in KT have shown severe deficiencies in Spike-specific immunoglobin G (IgG) responses prompting booster vaccinations, but a broader understanding of T-cell immunity to vaccinating is lacking. METHODS: We examined SARS-CoV-2 Spike IgG and CD4+/CD8+ Spike-specific T-cell responses in 61 KT patients maintained on different immunosuppressive protocols (ISP) (Tac + mycophenolate mofetil + prednisone) versus (belatacept + MMF + prednisone) and compared to 41 healthy controls. We also examined cytomegalovirus-cytotoxic T-cell responses (CMV-Tc) in both groups to assess T-cell memory. RESULTS: Our data confirmed poor Spike IgG responses in vaccinated KT patients with both ISP (21% demonstrating Spike IgG 1M post-second dose of BNT162b2 vs. 93% in controls). However, 35% of Spike IgG (-) patients demonstrated CD4+ and/or CD8+ T-cell responses. All but one CMV-IgG+ patient demonstrated good CMV-Tc responses. No differences in T-cell immunity by ISP were seen. CONCLUSION: Immunocompromised KT recipients showed severe defects in humoral and T-cell immune response after vaccination. No differences in immune responses to SARS-CoV-2 Spike peptides were observed in KT patients by ISP post-vaccination. The detection of Spike-specific T-cell immunity in the absence of Spike IgG suggests that vaccination in immunocompromised KT patients may provide partial immunity, although not preventing infection, T-cell immunity may limit its severity.

Center-level Variation in HLA-incompatible Living Donor Kidney Transplantation Outcomes.

BACKGROUND: Desensitization protocols for HLA-incompatible living donor kidney transplantation (ILDKT) vary across centers. The impact of these, as well as other practice variations, on ILDKT outcomes remains unknown. METHODS: We sought to quantify center-level variation in mortality and graft loss following ILDKT using a 25-center cohort of 1358 ILDKT recipients with linkage to Scientific Registry of Transplant Recipients for accurate outcome ascertainment. We used multilevel Cox regression with shared frailty to determine the variation in post-ILDKT outcomes attributable to between-center differences and to identify any center-level characteristics associated with improved post-ILDKT outcomes. RESULTS: After adjusting for patient-level characteristics, only 6 centers (24%) had lower mortality and 1 (4%) had higher mortality than average. Similarly, only 5 centers (20%) had higher graft loss and 2 had lower graft loss than average. Only 4.7% of the differences in mortality (P < 0.01) and 4.4% of the differences in graft loss (P < 0.01) were attributable to between-center variation. These translated to a median hazard ratio of 1.36 for mortality and 1.34 of graft loss for similar candidates at different centers. Post-ILDKT outcomes were not associated with the following center-level characteristics: ILDKT volume and transplanting a higher proportion of highly sensitized, prior transplant, preemptive, or minority candidates. CONCLUSIONS: Unlike most aspects of transplantation in which center-level variation and volume impact outcomes, we did not find substantial evidence for this in ILDKT. Our findings support the continued practice of ILDKT across these diverse centers.

Managing highly sensitized renal transplant candidates in the era of kidney paired donation and the new kidney allocation system: Is there still a role for desensitization?

Kidney paired donation (KPD) and the new kidney allocation system (KAS) in the United States have led to improved transplantation rates for highly sensitized candidates. We aimed to assess the potential need for other approaches to improve the transplantation rate of highly sensitized candidates such as desensitization. Using the UNOS STAR file, we analyzed transplant rates in a prevalent active waiting-list cohort as of June 1, 2016, followed for 1 year. The overall transplantation rate was 18.9% (11 129/58769). However, only 9.7% (213/2204) of candidates with a calculated panel reactive antibody ≥99.9% received a transplant, and highly sensitized candidates were less likely to receive a living donor transplant. Among candidates with a CPRA ≥ 99.5% (ie. 100%), only 2.5% of transplants were from living donors (13 total, 7 from KPD). Nearly 4 years after KAS (6/30/2018), 1791 actively wait-listed candidates had a CPRA of ≥99.9% and 34.6% (620/1791) of these had ≥5 years of waiting time. Thus, despite KPD and KAS, many sensitized candidates have not been transplanted even with prolonged waiting time. We conclude that candidates with a CPRA ≥ 99.9% and sensitized candidates with an incompatible living donor and prolonged waiting time may benefit from desensitization to improve their ability to receive a transplant.

Allocation of the Highest Quality Kidneys and Transplant Outcomes Under the New Kidney Allocation System.

RATIONALE & OBJECTIVE: Increased access to transplantation for highly sensitized candidates following implementation of the kidney allocation system (KAS) has been mostly due to higher use of organs with a lower kidney donor profile index (KDPI; a quality metric for donated kidneys), although changes in allocation of these organs was not intended. It is unclear whether clinical outcomes have changed in association with these changes. We investigated the use of kidneys with low and high KDPI scores over time and whether KDPI score affects patient and graft survival differently across varying levels of allosensitization. STUDY DESIGN: Observational cohort study. SETTING & PARTICIPANTS: Adult (aged ≥18 years) recipients of a deceased donor kidney transplant between October 1, 2009, and September 30, 2017 (Organ Procurement and Transplantation Network/United Network for Organ Sharing database; n = 84,451). PREDICTORS: Calculated panel-reactive antibody (cPRA) level (0%, 1%-79%, 80%-89%, 90%-98%, and 99%-100%) and KDPI score (≤20%, 21%-85%, and >85%). OUTCOMES: Death, graft loss. ANALYTICAL APPROACH: Time to event. RESULTS: Allocation of kidneys with KDPI scores ≤ 20% and KDPI scores of 21% to 85% to recipients with cPRA levels ≥ 99% increased 4-fold following implementation of the KAS with little change in allocation of kidneys with KDPI scores > 85%. Patient survival and graft loss were strongly associated with KDPI score, whereas the association with cPRA level was minimal. There was no evidence of a differential effect of KDPI scores across the range of cPRA levels on patient survival (P for interaction=0.06-0.9) or graft loss (P for interaction=0.5-0.9). Patient survival at 5 years among the 5 cPRA groups ranged from 87.2% to 89.8% for recipients of kidneys with KDPI scores ≤ 20% (P=0.2), 82.8% to 85.5% for KDPI scores of 21% to 85% (P=0.04), and 70.2% to 79.2% for KDPI scores > 85% (P=0.2). Cumulative incidence of graft loss by cPRA level ranged from 7.7% to 10.6% for recipients of kidneys with KDPI scores ≤ 20% (P=0.2), 11.8% to 15.0% for KDPI scores of 21% to 85% (P < 0.001), and 19.8% to 29.7% for KDPI scores > 85% (P = 0.4). LIMITATIONS: Lack of data for crossmatches, donor-specific antibodies, and immunomodulation. CONCLUSIONS: Highly sensitized recipients received kidneys with lower KDPI scores following implementation of the KAS, reducing access to these kidneys by less-sensitized candidates. KDPI score has a stronger association with patient survival and graft loss than cPRA level. The association of KDPI score with these outcomes was not modified by the recipient's level of sensitization. The impact of the redistribution of kidneys with low KDPI scores on outcomes among less-sensitized recipients needs further evaluation.

Efficacy, outcomes, and cost-effectiveness of desensitization using IVIG and rituximab.

BACKGROUND: Transplantation rates are very low for the broadly sensitized patient (panel reactive antibody [PRA]>80%; HS). Here, we examine the efficacy, outcomes, and cost-effectiveness of desensitization using high-dose intravenous immunoglobulin (IVIG) and rituximab to improve transplantation rates in HS patients. METHODS: From July 2006 to December 2011, 207 HS (56 living donors/151 deceased donors) patients (donor-specific antibody positive, PRA>80%) were desensitized using IVIG and rituximab. After desensitization, responsive patients proceeded to transplantation with an acceptable crossmatch. Cost and outcomes of desensitization were compared with dialysis. RESULTS: Of the 207 treated patients, 146 (71%) were transplanted. At 48 months, patient and graft survival by Kaplan-Meier were 95% and 87.5%, respectively. The total 3-year cost for patients treated in the desensitization arm was $219,914 per patient compared with $238,667 per patient treated in the dialysis arm. Thus, each patient treated with desensitization is estimated to save the U.S. healthcare system $18,753 in 2011 USD. Overall, estimated patient survival at the end of 3 years was 96.6% for patients in the desensitization arm of the model (based on Cedars-Sinai survival rate) compared with 79.0% for an age, end-stage renal disease etiology, and PRA matched group of patients remaining on dialysis during the study period. CONCLUSIONS: We conclude that desensitization with IVIG+rituximab is clinically and cost-effective, with both financial savings and an estimated 17.6% greater probability of 3-year survival associated with desensitization versus dialysis alone. However, the benefits of desensitization and transplantation are limited by organ availability and allocation policies.

Consensus opinion from the antibody working group on the diagnosis, reporting, and risk assessment for antibody-mediated rejection and desensitization protocols.

During the past few decades, much of the experimental and clinical effort in solid-organ transplantation has been directed toward ameliorating or abrogating T-cell-mediated responses. As a result, universally understood and accepted nomenclature and diagnostic criteria have evolved. Humoral immunity in transplantation has yet to undergo a similar renaissance. Readers of transplant journals regularly find it difficult and often impossible to interpret data on the diagnosis and management of antibody-mediated rejection. The Antibody Working Group was assembled in an attempt to provide guidelines for the standardization of nomenclature, diagnostic criteria, reporting, antibody profiling, and risk assessment.