Current Desensitization Research Articles

Membranes and Synaptosomes Used to Investigate Synaptic GABAergic Currents in Epileptic Patients.

Among the most prevalent neurological disorders, epilepsy affects about 1% of the population worldwide. We previously found, using human epileptic tissues, that GABAergic neurotransmission impairment is a key mechanism that drives the pathological phenomena that ultimately lead to generation and recurrence of seizures. Using both a "microtransplantation technique" and synaptosomes preparations from drug-resistant temporal lobe epilepsies (TLEs), we used the technique of two-electrode voltage clamp to record GABA-evoked currents, focusing selectively on the synaptic "fast inhibition" mediated by low-affinity GABAA receptors. Here, we report that the use-dependent GABA current desensitization (i.e., GABA rundown, which is evoked by applying to the cells consecutive pulses of GABA, at high concentration), which is a distinguishing mark of TLE, is mainly dependent on a dysfunction that affects synaptic GABAA receptors. In addition, using the same approaches, we recorded a depolarized GABA reversal potential in synaptosomes samples from the human epileptic subicula of TLE patients. These results, which confirm previous experiments using total membranes, suggest an altered chloride homeostasis in the synaptic area. Finally, the lack of a Zn2+ block of GABA-evoked currents using the synaptosomes supports the enrichment of "synaptic fast inhibitory" GABAA receptors in this preparation. Altogether, our findings suggest a pathophysiological role of low-affinity GABAA receptors at the synapse, especially during the fast and repetitive GABA release underlying recurrent seizures.

Immunotherapy targeting B cells and long-lived plasma cells effectively eliminates pre-existing donor-specific allo-antibodies

Pre-existing anti-human leukocyte antigen (HLA) allo-antibodies constitute a major barrier to transplantation. Current desensitization approaches fail due to ineffective depletion of allo-specific memory B cells (Bmems) and long-lived plasma cells (LLPCs). We evaluate the efficacy of chimeric antigen receptor (CAR) Tcells targeting CD19 and B cell maturation antigen (BCMA) to eliminate allo-antibodies in a skin pre-sensitized murine model of isletallo-transplantation. We find that treatment of allo-sensitized hosts with CAR Tcells targeting Bmems and LLPCs eliminates donor-specific allo-antibodies (DSAs) and mitigates hyperacute rejection of subsequent isletallografts. We then assess the clinical efficacy of the CAR T therapy for desensitization in patients with multiple myeloma (MM) with pre-existing HLA allo-antibodies who were treated with the combination of CART-BCMA and CART-19 (ClinicalTrials.gov: NCT03549442) and observe clinically meaningful allo-antibody reduction. These findings provide logical rationale for clinical evaluation of CAR T-based immunotherapy in highly sensitized candidates to promote successful transplantation.

Chimeric HLA antibody receptor T cells to target HLA-specific B cells in solid organ transplantation.

HLA-sensitized patients on the transplant waiting list harbor antibodies and memory B cells directed against allogeneic HLA molecules, which decreases the chance to receive a compatible donor organ. Current desensitization strategies non-specifically target circulating antibodies and B cells, warranting the development of therapies that specifically affect HLA-directed humoral immune responses. We developed Chimeric HLA Antibody Receptor (CHAR) constructs comprising the extracellular part of HLA-A2 or HLA-A3 coupled to CD28-CD3ζ domains. CHAR-transduced cells expressing reporter constructs encoding T-cell activation markers, and CHAR-transduced CD8+ T cells from healthy donors were stimulated with HLA-specific monoclonal antibody-coated microbeads, and HLA-specific B cell hybridomas. CHAR T cell activation was measured by upregulation of T cell activation markers and IFNγ secretion, whereas CHAR T cell killing of B cell hybridomas was assessed in chromium release assays and by IgG ELISpot. HLA-A2- and HLA-A3-CHAR expressing cells were specifically activated by HLA-A2- and HLA-A3-specific monoclonal antibodies, either soluble or coated on microbeads, as shown by CHAR-induced transcription factors. HLA-A2 and HLA-A3 CHAR T cells efficiently produced IFNγ with exquisite specificity and were capable of specifically lysing hybridoma cells expressing HLA-A2- or HLA-A3-specific B-cell receptors, respectively. Finally, we mutated the α3 domain of the CHAR molecules to minimize any alloreactive T-cell reactivity against CHAR T cells, while retaining CHAR activity. These data show proof of principle for CHAR T cells to serve as precision immunotherapy to specifically desensitize (highly) sensitized solid organ transplant candidates and to treat antibody-mediated rejection after solid organ transplantation.

#6402 IMPACT OF DARATUMUMAB AND BELATACEPT ON HLA ANTIBODIES IN KIDNEY TRANSPLANT CANDIDATES WITH 100% CPRA: EARLY RESULTS OF ATTAIN (ITN090ST)

Abstract Background and Aims Despite high allocation priority, <10% of kidney transplant candidates with cPRA 100% can find a compatible donor. Current desensitization strategies are ineffective due to antibody rebound. Adding costimulation blockade to plasma cell (PC) depletion prevents antibody rebound in nonhuman primates by countering nodal B cell and Tfh expansion. Method ATTAIN is a pilot, phase I/II trial of daratumumab, a CD38 mAb used in multiple myeloma, plus belatacept, a high affinity CTLA4-Ig, to desensitize kidney transplant candidates with cPRA ≥99.9%. Enrolled subjects receive daratumumab (6 doses: 8 mg/kg) and belatacept (4 doses: 10 mg/kg) over 10 weeks with bone marrow and blood assessments pre-and post-treatment. The primary efficacy endpoint (PE) is a composite of (1) elimination of ≥1 HLA antibody specificity, (2) ≥50% reduction in the MFI of ≥3 HLA antibody specificities, or (3) kidney transplant from a previously incompatible donor. Target accrual is 15, enrolled in 2 cohorts (5+10). Results Cohort 1 (n = 5, mean age 44, 60% with previous transplant) has been enrolled and treated, with 5-31 weeks follow-up to date. The treatment was tolerated well in all 5 patients who showed a significant reduction in most HLA antibodies after treatment without manifestation of rebound. 3 of 5 participants reached the PE and 5 of 5 had >50% bone marrow (BM) PC depletion. One patient received a kidney transplant from a previously incompatible deceased donor and is doing well at 7 months post-transplant without rejection or rebound of HLA antibody. Treatment was temporarily paused in 3 subjects due to AEs (acute cholecystitis and COVID, upper GI bleed, fevers); no cases of opportunistic infection or malignancy occurred. Conclusion A novel HLA desensitization regimen consisting of PC depletion with Daratumumab and costimulatory blockade with Belatacept appears safe and successful in the ongoing ATTAIN clinical trial. In the initial subject, this regimen led to transplant without HLA antibody rebound or acute rejection. Longer follow-up and additional subjects are needed to confirm these promising results. ATTAIN (NCT04827979) is a trial conducted by the Immune Tolerance Network and sponsored by NIAID (award UM1AI109565).

Charged residues in the GABA-a receptor intracellular domain impact channel activation and desensitization.

Opening and closing of GABA receptor (GABAR) channels regulate inhibitory signaling in the brain. Mechanisms underlying channel open, closed, desensitized transitions remain unclear. Although GABAR cryo-EM structures provide details about its extracellular and transmembrane domains, little is understood about its intracellular domain (ICD) and its role in regulating channel gating. We constructed a GABAR homology model based on the 5HT-type-3 receptor, which revealed a helix (MX) at the C-terminal end of M3 that is lysine rich in the α1 (6 lysines) and γ2 (8 lysines) subunits. Charged residues in the α and γ subunits were mutated to alanine. Effects on GABA EC50 were measured using two-electrode voltage clamping of oocytes expressing α1β2γ2L WT and mutant GABARs. αK327A significantly increased GABA EC50 6-fold in comparison to WT and significantly reduced GABAR macroscopic desensitization. Extent of current desensitization after 10 seconds in saturating GABA (10 mM) was 6.86 ± 2.28% (n=7) versus WT (23.7 ± 7.29%, n=10). Neutralizing charge at αK328, K330 and K335 had no functional effects. γK328A, γ2K330A and γ2K332A significantly increased GABA EC50 by 2 to 3 fold. γ2K330A reduced GABAR desensitization (extent after 10 seconds 7.36 ± 2.37%, n=2). Our data indicate structural perturbations in the α and γ MX regions of the GABAR ICD alter GABAR channel activation and desensitization. Interestingly, in our GABAR structural model, α1R312 (in MX) interacts with α1R249 (M1-M2 linker). Single charge reversals at these positions increased GABA EC50 and the rate of GABA desensitization. A charge swap (R312E - E249R) rescued receptor function to WT suggesting a functional electrostatic interaction and that these residues form a salt bridge, providing support for our homology model.

Successful combined auxiliary partial liver and intestinal transplantation in two highly sensitized, cross-match positive patients.

Sensitization to human leukocyte antigen (HLA) creates an immunological barrier to intestinal transplantation (ITx). Current desensitization therapies are limited and ineffective in the most highly sensitized patients. A co-transplanted whole liver transplant can protect a kidney, heart, or intestinal allograft from antibody-mediated injury. Whether an auxiliary partial liver allograft provides effective protection for highly sensitized intestinal transplant recipients is unknown. Two patients with strong HLA donor-specific antibody at high titer against their deceased donors underwent combined auxiliary partial liver and ITx across a positive cross-match. The left lateral lobes from the combined-graft recipients and the right liver lobes from the deceased donors were transplanted as a domino procedure to other four patients. Two combined-graft recipients have had an uneventful postoperative course without major complications at a 12- and 24-month follow-up, respectively. Intestinal graft function has been excellent with no evidence of humoral or cellular rejection. While a positive cross-match turned negative, titers of donor-specific HLA antibodies gradually declined over time after transplant. The left liver lobes procured from the combined-graft recipients were successfully transplanted into two pediatric patients (age 1.9, 2.4years) and the right lobes from two deceased donors were successfully transplanted into two adult patients. All transplant procedures went well, without post-operative complications related to the splitting technique. Our results indicate that an auxiliary liver transplant can effectively protect a co-transplanted intestinal allograft against rejection and suggest that this combined procedure may serve as a useful therapeutic adjunct for a highly sensitized intestinal transplant candidate.

Identification of a Partial and Selective TRPV1 Agonist CPIPC for Alleviation of Inflammatory Pain.

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel, predominantly expressed in a subset of peripheral sensory neurons for pain signaling. Topical application of agonist capsaicin for desensitizing TRPV1 currents has been approved for relief of chronic pain. However, the potent TRPV1 capsaicin is not ingestible and even topical capsaicin causes common side effects such as skin irritation, swelling, erythema and pruritus, suggesting that a mild TRPV1 agonist might be helpful for reducing side effects while reliving pain. In this study, we reported on a partial and selective TRPV1 agonist 4-(5-chloropyridin-2-yl)-N-(1H-indazol-6-yl)piperazine-1-carboxamide named CPIPC that was modified based on targeting the residue Arg557, important for conversion between the channel antagonism and agonism. Whole-cell patch clamp recordings indicated a concentration-dependent activation of TRPV1 currents by CPIPC with an EC50 of 1.56 ± 0.13 μM. The maximum efficacy of CPIPC (30 μM) was about 60% of saturated capsaicin (10 μM). Repetitive additions of CPIPC caused TRPV1 current desensitization in both TRPV1-expressing HEK293 cells and dorsal root ganglion (DRG) sensory neurons. Oral administration of CPIPC dose-dependently alleviated inflammatory pain in mice. Further site-directed mutagenesis combined with molecular docking revealed that residue Arg557 is critical for TRPV1 activation by CPIPC. Taken together, we identified a novel partial and selective TRPV1 agonist CPIPC that exhibits antinociceptive activity in mice.

Leveraging CAR T cells to Achieve Desensitization and Enable Transplantation

Abstract Pre-existing allo-antibodies (allo-Abs), that preclude transplant due to the risk of hyperacute rejection, lead to prolonged wait times and high mortality rates. Current desensitization approaches are ineffective as they do not adequately deplete allo-specific B cells and plasma cells (PCs). We hypothesize that stringent depletion of these cells is required to eliminate pre-existing allo-Abs. We leverage the exquisite ability of CAR T cells to eliminate target cells to desensitize transplant candidates. We constructed CARs targeting murine CD19 or BCMA, which cover the entire B cell-PC continuum. We first evaluated the function of CAR T cells against B cells and PCs in vitro. C57BL/6 mice were sensitized with BALB/c skin grafts. After skin rejection, sensitized mice received total body irradiation followed by treatment with either control T cells, CART-19 T cells, or a combination of CART-19 and CART-BCMA T cells (combo-CART). Allo-Abs, total Ig, and B cells were measured over 13 weeks. Functional desensitization was then assessed by induction of diabetes followed by BALB/c-derived islet cell transplant and glucose were measured to assess graft survival. CD19- and BCMA-targeted CARs effectively depleted primary B cells and PCs in vitro and in vivo. Control and CART-19 T cells were ineffective at desensitizing mice, but combo-CART treatment resulted in significant decrease of allo-Abs. Islet cell grafts succumbed to hyperacute rejection in 80% of control and CART-19 treated mice. However, combo-CART treatment resulted in prolonged graft survival in all mice (mean 35 days, range 16–60). Thus, CAR T cells targeting B cell and PC antigens represent a promising approach to desensitization and could enable lifesaving transplantation.

Current Desensitization Strategies in Heart Transplantation.

Heart transplant candidates sensitized to HLA antigens wait longer for transplant, are at increased risk of dying while waiting, and may not be listed at all. The increasing prevalence of HLA sensitization and limitations of current desensitization strategies underscore the urgent need for a more effective approach. In addition to pregnancy, prior transplant, and transfusions, patients with end-stage heart failure are burdened with unique factors placing them at risk for HLA sensitization. These include homograft material used for congenital heart disease repair and left ventricular assist devices (LVADs). Moreover, these risks are often stacked, forming a seemingly insurmountable barrier in some cases. While desensitization protocols are typically implemented uniformly, irrespective of the mode of sensitization, the heterogeneity in success and post-transplant outcomes argues for a more tailored approach. Achieving this will require progress in our understanding of the immunobiology underlying the innate and adaptive immune response to these varied allosensitizing exposures. Further attention to B cell activation, memory, and plasma cell differentiation is required to establish methods that durably abrogate the anti-HLA antibody response before and after transplant. The contribution of non-HLA antibodies to the net state of sensitization and the potential implications for graft longevity also remain to be comprehensively defined. The aim of this review is to first bring forth select issues unique to the sensitized heart transplant candidate. The current literature on desensitization in heart transplantation will then be summarized providing context within the immune response. Building on this, newer approaches with therapeutic potential will be discussed emphasizing the importance of not only addressing the short-term pathogenic consequences of circulating HLA antibodies, but also the need to modulate alloimmune memory.

Rebound and overshoot of donor‐specific antibodies to human leukocyte antigens (HLA) during desensitization with plasma exchanges in hematopoietic progenitor cell transplantation: A case report

Donor-specific antibodies (DSA) to HLA have been associated with graft loss in hematopoietic progenitor cell (HPC) transplantation. Limited data associate therapeutic plasma exchange (TPE) with desensitization and successful engraftment. We report an attempt of desensitization and observed overshooting of DSA during transplantation. A 27-year-old female with cutaneous T cell lymphoma was scheduled for HPC transplantation from her HLA-haploidentical half-sister, who carried the HLA-DRB1*13:03:01 allele. The patient had the corresponding DSA. Lacking an alternative donor option at the time, we attempted a desensitization approach by immunosuppression with tacrolimus and mycophenolate mofetil (MMF). Unexpectedly, DSA increased from a mean fluorescence intensity (MFI) of 1835 on day -63 to 9008 on day -7. The MFI increased further during 3 TPE procedures and intravenous immunoglobulin (IVIG) until day -1. After transplantation, the DSA remained elevated despite 2 more TPE/IVIG procedures and graft-versus-host disease prophylaxis with high-dose cyclophosphamide, sirolimus, and MMF. Flow cytometric crossmatch, initially negative, turned positive after transplantation. Primary graft failure occurred and was attributed to antibody-mediated rejection. A second transplantation from a 7/8 HLA-matched unrelated donor, not carrying DRB1*13:03 allele, resulted in successful engraftment. Unexpected and rapid increases of a DSA can occur despite the use of current desensitization approaches. This is problematic when conditioning has already started, as such increases are unlikely to be overcome by TPE or other interventions for desensitization. Overshoot of DSA in HPC transplantation has rarely been reported. Its cause remains unclear and can include underlying disease, immunotherapy, chemotherapy, or TPE.

Heart-After-Liver Transplantation Attenuates Rejection of Cardiac Allografts in Sensitized Patients

BackgroundIn patients undergoing heart transplantation, significant allosensitization limits access to organs, resulting in longer wait times and high waitlist mortality. Current desensitization strategies are limited in enabling successful transplantation. ObjectivesThe purpose of this study was to describe the cumulative experience of combined heart-liver transplantation using a novel heart-after-liver transplant (HALT) protocol resulting in profound immunologic protection. MethodsReported are the results of a clinical protocol that was instituted to transplant highly sensitized patients requiring combined heart and liver transplantation at a single institution. Patients were dual-organ listed with perceived elevated risk of rejection or markedly prolonged waitlist time due to high levels of allo-antibodies. Detailed immunological data and long-term patient and graft outcomes were obtained. ResultsA total of 7 patients (age 43 ± 7 years, 86% women) with high allosensitization (median calculated panel reactive antibody = 77%) underwent HALT. All had significant, unacceptable donor specific antibodies (DSA) (>4,000 mean fluorescence antibody). Prospective pre-operative flow cytometric T-cell crossmatch was positive in all, and B-cell crossmatch was positive in 5 of 7. After HALT, retrospective crossmatch (B- and T-cell) became negative in all. DSA fell dramatically; at last follow-up, all pre-formed or de novo DSA levels were insignificant at <2,000 mean fluorescence antibody. No patients experienced >1R rejection over a median follow-up of 48 months (interquartile range: 25 to 68 months). There was 1 death due to metastatic cancer and no significant graft dysfunction. ConclusionsA heart-after-liver transplantation protocol enables successful transplantation via near-elimination of DSA and is effective in preventing adverse immunological outcomes in highly sensitized patients listed for combined heart-liver transplantation.

Influence of GABA-A Receptor Intracellular Domain on Channel Activation and Desensitization

Rapid opening and closing of GABA-A receptor (GABAR) channels regulate signaling in the brain. Mechanisms underlying channel open, closed, desensitized transitions remain unclear. GABAR cryo-EM structures provide details about its extracellular and transmembrane domains, but little information exists about its intracellular domain (ICD) and its role in regulating channel gating. We constructed a GABAR ICD homology model based on a cryo-EM 5HT3AR structure, which revealed a helix (MX) at the C-terminal end of M3 and a helix (MA) at the N-terminal end of M4 projecting intracellularly. Four residues with potential interactions between these helices were mutated to alanine (α1K327A in MX, α1K390A in MA, and γ2K409A and γ2Y413A in MA). Mutations effects on GABA-EC50 and current desensitization were measured using two-electrode voltage clamping of oocytes expressing wild-type (WT) and mutant GABARs. α1K327A increased GABA EC50 ∼6-fold compared to α1β2γ2 WT (35.98 ± 1.03 μM, n=9) and significantly reduced GABAR desensitization. Extent of current desensitization after 60 seconds in saturating GABA (10mM) was 30.16 ± 2.24 % (n=9) versus WT (62.96 ± 4.15 %, n=13). α1K390A had no effect on GABA EC50 or desensitization, and mutation of the aligned residue in γ2 subunit, γ2K409A, decreased GABA EC50 ∼2 fold without affecting desensitization. γ2Y413A significantly increased desensitization and increased GABA EC50 by 2-fold. Desensitization extent after 10 seconds was 76.57 ± 2.09 % (n=18) compared to WT (23.71 ± 2.30 %, n=10). These data indicate that structural perturbations of the α1MX and γ2MA regions in the GABAR ICD can influence macroscopic GABAR current desensitization. Interestingly, GABAR MX regions are lysine rich. We speculate that mechanisms underlying GABAR gating transitions may involve charged interactions between MX and other regions of the GABAR ICD (e.g. MA). Experiments are underway to test this idea.

P1785KIDNEY TRANSPLANTATION ACROSS VERY HIGH DONOR SPECIFIC ANTIBODIES(DSA) - A SINGLE CENTER EXPERIENCE OF A TERTIARY LEVEL HOSPITAL FROM INDIA

Abstract Background and Aims Kidney Transplantation across very high donor specific antibodies (DSA) poses a significant challenge even today . With our current understanding and precise desensitization techniques, we are now able to do kidney transplantation across such high DSA . Here we are reporting ten such cases where baseline DSA were more than 10,000 mean fluroscent intensity (MFI) on Single Antigen Bead (SBA) Luminex. Method: It is a retrospective analiysis of ten kidney transplant patients from January 2017 to March 2019 . Patients with MFI more than 10,000 to class II HLA antigens at baseline with negative CDC and flow cytometry cross match were included in this study. All patients were treated with 1 dose of Rituximab (375mg/M? before plasma exchanges (PLEX) were started . Each session of PLEX was followed by 10 grams of intravenous human immunoglobulin (IVIg). Solid based SBA Luminex for both class I and II antigens was repeated after the third exchange and fifth exchange and seventh exchange depending on the level of MFI . Results Ten patients ( seven males three females ) of age 37± 7 years were included in this study . History of blood transfusion with 5±2 units was present in 7 patients . All females were multiparous ( 3±1children). Mean solid based SBA Luminex for class I HLA antigens was 12000 ± 1500 and for II HLA antigens with MFI 16500 ± 3500 (Chart 1). Mean number of PLEX needed was 5 ± 2 . All patients had solid based SBA MFI was 1500±300 and for class II antigens 2500 ± 1500 before transplantation(Chart 2).There was no incidence of acute antibody mediated rejection . Baseline serum creatinine at discharge was1.35±0.35mg%. There were 3 (30%) biopsy proven cases of acute cellular rejection . There was evidence of BK viremia in 3(30%) patients, CMV infection in 1 (10%) patient, Klebsiella pneumonia in 1(10%) patient and cryptosporium infection in 1 (10%) patient each . There was no mortality and mean serum creatinine at 6 months follow-up was 1.55±1.05mg%. All 3 patients of BK Viremia were treated with modification of immunosupression with substitution of leflunamide for mycophenolate and all are doing well with good graft function with a mean serum creatinine of 1.75±0.55mg% . Other infections were treated accordingly. Conclusion: Transplantation across very high donor specific antibodies is possible with excellent immediate and short term graft function with judicious de-sensitization techniques . There was increase in infection rate but none was life threatening and can be managed with proper care.

Desensitization Therapy for Mechanical Circulatory Support Patients with Existing Driveline Infection: Is It Safe with Current Desensitization Therapies?

Patients with end-stage heart failure may undergo mechanical circulatory support (MCS) as a bridge to transplant. This strategy may be complicated by sensitization due to blood transfusions as well as driveline infections. As sensitization narrows the donor pool, desensitization may be performed. The purpose of this study was to determine the impact of desensitization therapy on infections in MCS patients with an existing driveline infection. We reviewed 45 MCS patients who developed a driveline infection between 2012-2018. Patients were divided into: sensitized (PRA >10%, n=22) and not sensitized (n=23). Sensitized patients were divided into: desensitization (when CPRA > 50%; n=7) and no desensitization (n=15). Desensitization included IVIG, rituximab, bortezomib and/or plasmapheresis. Outcomes were assessed 1 year after the driveline infection: survival, freedom from readmission, freedom from new driveline infection, and freedom from any infection. There was no difference between sensitized and non-sensitized MCS patients with a driveline infection in 1-year survival, freedom from readmissions, or freedom from any subsequent infection. There was no difference in outcomes between sensitized patients who received desensitization therapy and those who did not. Desensitization appears to be safe in MCS patients with an existing driveline infection to potentially expand the compatible donor pool.

Desensitization and Recovery of Crayfish Photoreceptors Upon Delivery of a Light Stimulus.

A method to study desensitization and recovery of crayfish photoreceptors is presented. We performed intracellular electrical recordings of photoreceptor cells in isolated eyestalks using the discontinuous single electrode-switched voltage-clamp configuration. First, with a razor blade we made an opening in the dorsal cornea to get access to the retina. Thereafter, we inserted a glass electrode through the opening, and penetrated a cell as reported by the recording of a negative potential. Membrane potential was clamped at the photoreceptor's resting potential and a light-pulse was applied to activate currents. Finally, the two light-flash protocol was employed to measure current desensitization and recovery. The first light-flash triggers, after a lag period, the transduction ionic current, which after reaching a peak amplitude decays towards a desensitized state; the second flash, applied at varying time intervals, assesses the state of the light-activated conductance. To characterize the light-elicited current, three parameters were measured: 1) latency (the time elapsed between light flash delivery and the moment in which current achieves 10% of its maximum value); 2) peak current; and 3) desensitization time constant (exponential time constant of the current decay phase). All parameters are affected by the first pulse. To quantify recovery from desensitization, the ratio p2/p1 was employed versus time between pulses. p1 is the peak current evoked by the first light-pulse, and p2 is the peak current evoked by the second pulse. These data were fitted to a sum of exponential functions. Finally, these measurements were carried out as function of circadian time.

Desensitization in the Era of Precision Medicine: Moving From the Bench to Bedside.

Patients with antibodies to HLA wait longer for transplant and are at increased risk of adverse outcomes. For more than a decade, drug therapy approaches have been tested to modulate the immune system to prevent or reduce donor-specific antibody levels. Despite some studies reporting success in facilitating transplant, many patients do not respond or experience donor-specific antibody rebound, highlighting the diversity of the individual patient's immune response. While advances in immunomodulatory therapies have resulted in escalating efforts to successfully treat highly sensitized patients, further insight into the human immune system has uncovered its enormous complexity and diversity calling for a personalized approach. Yet, even defining the sensitized transplant candidate can be troublesome and much remains to be understood about the interaction between an individual's immune system as a whole and their response to our current desensitization strategies. The shift toward a personalized approach calls for a reevaluation of what we know and what remains to be determined; a process that will require iterative translational approaches. This review will focus on new insights into how the interaction between immune risk assessment, the patient's immunological history, and the clinical context can be reconciled to develop a precision-based approach to pretransplant management.

APRIL/BLyS Blockade Reduces Donor-specific Antibodies in Allosensitized Mice.

Highly sensitized candidates on the transplant waitlist remain a significant challenge, as current desensitization protocols have variable success rates of donor-specific antibody (DSA) reduction. Therefore, improved therapies are needed. A proliferation-inducing ligand (APRIL) and B-lymphocyte stimulator (BLyS) are critical survival factors for B-lymphocytes and plasma cells, which are the primary sources of alloantibody production. We examined the effect of APRIL/BLyS blockade on DSA in a murine kidney transplant model as a possible novel desensitization strategy. C57BL/6 mice were sensitized with intraperitoneal (IP) injections of 2 × 10 BALB/c splenocytes. Twenty-one days following sensitization, animals were treated with 100 μg of BLyS blockade (B-cell activating factor receptor-immunoglobulin) or APRIL/BLyS blockade (transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin), administered thrice weekly for an additional 21 days. Animals were then euthanized or randomized to kidney transplant with Control Ig, BLyS blockade, or APRIL/BLyS blockade. Animals were euthanized 7 days posttransplant. B-lymphocytes and DSA of BLyS blockade only or APRIL/BLyS blockade-treated mice were assessed by flow cytometry, immunohistochemistry, and enzyme-linked immunospot. APRIL/BLyS inhibition resulted in a significant reduction of DSA by flow crossmatch compared with controls (P < 0.01). APRIL/BLyS blockade also significantly depleted IgM- and IgG-secreting cells and B-lymphocyte populations compared to controls (P < 0.0001). APRIL/BLyS blockade in transplanted mice also resulted in decreased B-lymphocyte populations; however, no difference in rejection rates were seen between groups. APRIL/BLyS blockade with transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin significantly depleted B-lymphocytes and reduced DSA in this sensitized murine model. APRIL/BLyS inhibition may be a clinically useful desensitization strategy for sensitized transplant candidates.

Clinical significance of isoagglutinin titre with the current desensitization protocol in ABO-incompatible kidney transplantation.

ABO-incompatible (ABOi) kidney transplantation (KT) has become a routine procedure with graft survival rates comparable to those of ABO-compatible KT. However, the clinical significance of the isoagglutinin titre in ABOi KT remains uncertain. Therefore, in this study, we analysed the clinical outcomes of ABOi KT according to the baseline and post-operative isoagglutinin titre. All patients who received ABOi KT between 2009 and 2013 were reviewed and followed up until December 2016. The patients were classified according to baseline (<1:128 or ≥1:128) and post-operative rebound isoagglutinin titre (<1:16 or ≥1:16), and the clinical outcomes of KT were compared. Patients with a high baseline isoagglutinin titre showed a poor titre reduction rate (1.48 ± 0.41 vs 1.32 ± 0.34, P = 0.008), and more patients experienced titre rebound ≥1:16 after KT (15.0% vs 35.8%, P = 0.002). The occurrence of both T-cell-mediated rejection and antibody-mediated rejection did not show a significant difference (P = 0.805 and 0.714, respectively). The rate of rejection-free survival was not different among groups (P = 0.680, log-rank test). Furthermore, the rate of death-censored graft survival was not different among groups (P = 0.701, log-rank test). Urinary tract infection was the most frequently reported infectious complication overall. The incidence of urinary tract infection, pneumonia and viral infections (BK virus and cytomegalovirus) was not different among groups. In conclusion, high baseline isoagglutinin titre was associated with a high rebound isoagglutinin titre, low titre reduction rates and more sessions of plasmapheresis. However, the isoagglutinin titre may not be as important as it was in the past in ABOi KT if appropriate desensitization is performed.

Long-term Outcomes of ABO-incompatible Pediatric Living Donor Liver Transplantation.

BackgroundABO-incompatible (ABOi) living donor liver transplantation (LDLT) has been performed to compensate for donor shortage. To date, few studies have reported detailed B-cell desensitization protocols and long-term outcomes of ABOi pediatric LDLT.MethodsTwenty-nine pediatric ABOi LDLT recipients were retrospectively analyzed. We compared the clinical outcomes between ABOi (n = 29) and non-ABOi (n = 131) pediatric LDLT recipients. Furthermore, we evaluated the safety and efficacy of our rituximab-based regimen for ABOi pediatric LDLT (2 ≤ age < 18; n = 10).ResultsThere were no significant differences in the incidence of infection, vascular complications, biliary complications, and acute cellular rejection between ABOi and non-ABOi groups. The cumulative graft survival rate at 1, 3, and 5 years for non-ABOi group were 92.1%, 87.0%, and 86.1%, and those for ABOi group were 82.8%, 82.8%, and 78.2%, respectively. Rituximab-based desensitization protocol could be performed safely, and reduced CD19+ lymphocyte counts effectively. Although rituximab-treated ABOi group showed comparable clinical outcomes and graft survival rate, 2 patients developed antibody-mediated rejection.ConclusionsABOi LDLT is a feasible option for pediatric end-stage liver disease patients. However, it should be noted that current desensitization protocol does not completely prevent the onset of antibody-mediated rejection in several cases.

Outcome of the risk-stratified desensitization protocol in donor-specific antibody-positive living kidney transplant recipients: a retrospective study.

Acceptable outcomes of donor-specific antibody (DSA)-positive living kidney transplantation (LKT) have recently been reported. However, LKT in crossmatch (XM)-positive patients remains at high-risk and requires an optimal desensitization protocol. We report our intermediate-term outcomes of XM-positive LKT vs. XM-negative LKT in patients who underwent LKT between January 2012 and June 2015 in our institution. The rate of acute antibody-mediated rejection (ABMR) within 90 days postoperation, graft function, and patient, and graft survival rates at 4 years were investigated. Patients were divided into three groups: XM-DSA- (n = 229), XM-DSA+ (n = 36), and XM + DSA+ (n = 15). The XM + DSA+ group patients underwent desensitization with high-dose intravenous immunoglobulin, plasmapheresis, and rituximab. The rates of ABMR within 90 days in the XM-DSA-, XM-DSA+, and XM + DSA+ groups were 1.3%, 9.4%, and 60.0%, respectively (P < 0.001). There were no significant differences in the graft function throughout the observational period, the 4-year patient or graft survival rates among three groups. This study showed that intermediate-term outcomes of XM-positive LKT were comparable to XM-negative LKT. However, our current desensitization protocol cannot avert ABMR within 90 days, and XM positivity is still a significant risk factor for ABMR. Further refinement of the current desensitization regimen is required.