Desensitization for sensitized patients awaiting heart transplant:

The effect of proteasome in heart transplantation: From mechanisms to therapeutic potential

Heart transplantation is a critical treatment for end-stage heart failure. However, its clinical efficacy is hindered by some challenges, such as ischemia-reperfusion injury (IRI) and post-transplant rejection. These complications significantly contribute to graft dysfunction and compromise patient survival. Emerging evidence underscores the involvement of proteasome in the pathophysiology of both IRI and post-transplant rejection. Proteasome inhibition has demonstrated potential in attenuating IRI by limiting oxidative damage and apoptosis while also mitigating rejection through the regulation of adaptive and innate immune responses. Recent advances in the development of proteasome inhibitors, particularly in optimizing specificity and minimizing adverse effects, have further strengthened their prospects for clinical application. This review focuses on the roles of the proteasome and its inhibitors in heart transplantation, with an emphasis on their mechanisms and therapeutic applications in managing IRI and rejection.

Rapid desensitization through immunoadsorption during cardiopulmonary bypass. A novel method to facilitate human leukocyte antigen incompatible heart transplantation

BACKGROUND

Anti-human leukocyte antigen (HLA)-antibody production represents a major barrier to heart transplantation, limiting recipient compatibility with potential donors and increasing the risk of complications with poor waiting-list outcomes. Currently there is no consensus to when desensitization should take place, and through what mechanism, meaning that sensitized patients must wait for a compatible donor for many months, if not years. We aimed to determine if intraoperative immunoadsorption could provide a potential desensitization methodology.

METHODS

Anti-HLA antibody-containing whole blood was added to a Cardiopulmonary bypass (CPB) circuit set up to mimic a 20 kg patient undergoing heart transplantation. Plasma was separated and diverted to a standalone, secondary immunoadsorption system, with antibody-depleted plasma returned to the CPB circuit. Samples for anti-HLA antibody definition were taken at baseline, when combined with the CPB prime (on bypass), and then every 20 min for the duration of treatment (total 180 min).

RESULTS

A reduction in individual allele median fluorescence intensity (MFI) to below clinically relevant levels (<1000 MFI), and in the majority of cases below the lower positive detection limit (<500 MFI), even in alleles with a baseline MFI >4000 was demonstrated. Reduction occurred in all cases within 120 min, demonstrating efficacy in a time period usual for heart transplantation. Flowcytometric crossmatching of suitable pseudo-donor lymphocytes demonstrated a change from T cell and B cell positive channel shifts to negative, demonstrating a reduction in binding capacity.

CONCLUSIONS

Intraoperative immunoadsorption in an ex vivo setting demonstrates clinically relevant reductions in anti-HLA antibodies within the normal timeframe for heart transplantation. This method represents a potential desensitization technique that could enable sensitized children to accept a donor organ earlier, even in the presence of donor-specific anti-HLA antibodies.

Pharmacotherapy in the heart transplant recipient: A primer for nurse clinicians and pharmacists

Heart transplantation (HT) is the definitive treatment for eligible patients with end-stage heart disease. A major complication of HT is allograft rejection which can lead to graft dysfunction and death. The guiding principle of chronic immunosuppression therapy is to prevent rejection of the transplanted organ while avoiding oversuppression of the immune system, which can cause opportunistic infections and malignancy. The purpose of this review is to describe immunosuppressive management of the HT recipient-including agent-specific pharmacology and pharmacokinetics, outcomes data, adverse effects, clinical considerations, and recent guideline updates. We will also provide recommendations for medical prophylaxis of immunosuppressed patients based on the most recent clinical guidelines. Additionally, we highlight the importance of medical therapy adherence and the effect of social determinants of health on the long-term management of HT. HT recipients are a complex and high-risk population. The objective of this review is to describe basic pharmacotherapy in HT and implications for nurses and pharmacists.

An in vitro comparison of intra-operative isohemagglutinin and human leukocyte antigen removal techniques in pediatric heart transplantation

BACKGROUND

Highly sensitized pediatric patients awaiting heart transplantation experience longer wait times and thus higher waitlist mortality. Similarly, children less than 2 years of age have increased waitlist times and mortality when compared to their older peers. To improve the likelihood of successful transplantation in these patients, various strategies have been utilized, including peri-operative plasmapheresis. However, limited data exists comparing plasmapheresis techniques for antibody reduction. This study's aim was to compare the in vitro magnitude of isohemagglutinin titers (IT) and human leukocyte antigen (HLA) antibody removal and the time required between membrane-based plasmapheresis (MP) and centrifuge-based plasmapheresis (CP) incorporated into the extracorporeal (EC) circuit.

METHODS

Two MP (Prismaflex) and two CP (Spectra Optia, Terumo BCT) circuits were incorporated into four separate EC circuits primed with high titer, highly sensitized type O donor whole blood. Assays were performed to determine baseline IT and anti-HLA antibodies and then at 30-minute increments until completion of the run (two plasma volume exchanges) at two hours.

RESULTS

There was a decrease in anti-A and anti-B IgM and IgG titers with both MP and CP. Mean anti-A and anti-B titer reduction was by 4.625 titers (93.7% change) and 4.375 titers (93.8% change) using MP and CP, respectively. At 2 h of apheresis, CP reduced 62.5% of all ITs to ≤ 1:4, while MP reduced 50% of ITs to ≤ 1:4. Additionally, reduction of anti-HLA class II antibody to mean fluorescence intensity (MFI) <3000 was achieved with both MP and CP. At 2 h of apheresis, CP reduced MFI by 2-3.5 fold and MP reduced MFI by 1.7-2.5 fold. Both demonstrated similar hemolytic and thrombotic profiles.

CONCLUSIONS

In this in vitro plasmapheresis model of IT and anti-HLA antibody reduction, both MP and CP incorporated into the EC circuit can be used quickly and effectively to reduce circulating antibodies. While CP may have some greater efficiency, further study is necessary to verify this in vivo.

Heart transplantation: focus on donor recovery strategies, left ventricular assist devices, and novel therapies

Heart transplantation is advocated in selected patients with advanced heart failure in the absence of contraindications. Principal challenges in heart transplantation centre around an insufficient and underutilized donor organ pool, the need to individualize titration of immunosuppressive therapy, and to minimize late complications such as cardiac allograft vasculopathy, malignancy, and renal dysfunction. Advances have served to increase the organ donor pool by advocating the use of donors with underlying hepatitis C virus infection and by expanding the donor source to use hearts donated after circulatory death. New techniques to preserve the donor heart over prolonged ischaemic times, and enabling longer transport times in a safe manner, have been introduced. Mechanical circulatory support as a bridge to transplantation has allowed patients with advanced heart failure to avoid progressive deterioration in hepato-renal function while awaiting an optimal donor organ match. The management of the heart transplantation recipient remains a challenge despite advances in immunosuppression, which provide early gains in rejection avoidance but are associated with infections and late-outcome challenges. In this article, we review contemporary advances and challenges in this field to focus on donor recovery strategies, left ventricular assist devices, and immunosuppressive monitoring therapies with the potential to enhance outcomes. We also describe opportunities for future discovery to include a renewed focus on long-term survival, which continues to be an area that is under-studied and poorly characterized, non-human sources of organs for transplantation including xenotransplantation as well as chimeric transplantation, and technology competitive to human heart transplantation, such as tissue engineering.

Sensitization during short-term mechanical circulatory support. Determinants, therapeutic management, and outcomes after heart transplant

INTRODUCTION AND OBJECTIVES

The development of human-leukocyte antigen antibodies is a well-known adverse effect of the use of long-term ventricular assist devices (VADs). The aim of this study was to determine the incidence of sensitization during short-term mechanical circulatory support with VAD (CentriMag), its determinants, and its impact on posttransplant outcomes.

METHODS

We performed a retrospective review of patients who were bridged to transplant with short-term VAD from 2009 to 2019. Sensitization was defined as a calculated panel-reactive antibody> 10%. The endpoints included overall survival and rejection-free survival.

RESULTS

A total of 89 patients (median age 56.0 [interquartile range, 50.0-59.9] years, 16.8% female) received a short-term VAD as a bridge to transplant. The median duration of support was 23.6 [interquartile range, 16.6-35.0] days. Eleven patients (12.4%) became sensitized during support. The only factor significantly associated with sensitization was female sex (OR, 8.67; 95%CI, 1.93-38.8; P=.005). Of the 89 patients, 21 patients died during support; 68 patients underwent heart transplant. After a mean follow-up of 49.6 ±31.2 months, 8 patients (11.8%) died and 20 (29.4%) had at least 1 rejection episode. On multivariate analysis, sensitization was an independent predictor of acute rejection (HR, 3.64; 95%CI, 1.42-9.33; P=.007), with a nonstatistically significant trend to higher mortality (HR, 4.07; 95%CI, 0.96-17.3; P=.057).

CONCLUSIONS

Sensitization with short-term VADs can occur and is significantly associated with female sex and with rejection. Sensitization also showed a nonstatistically significant trend to higher mortality.

Outcome of urgent desensitization in sensitized heart transplant recipients

BACKGROUND/PURPOSE

Sensitization, the presence of preformed anti-human antibody in recipients, restricts access to ABO-compatible donors in heart transplant. Desensitization therapy works by reducing preformed antibodies to increase the chances of a negative crossmatch or permit safe transplantation across positive crossmatch. There is no consensus regarding the desensitization protocol in cardiac patients, and the outcome of desensitization remains under debate.

METHODS

Twenty-five consecutive sensitized heart transplant recipients received perioperative desensitization in our institution from 2012 to 2019. One-year patient survival and graft rejection rate were analyzed and compared between sensitized recipients and non-sensitized recipients.

RESULTS

Within the first year after transplant, patient survival in sensitized recipients was 76%. Infection was the major cause of death. The cumulative incidence of rejection was 8% for antibody-mediated rejection and 16% for acute cellular rejection. No significant difference in 1-year survival or rejection rate could be demonstrated between sensitized and nonsensitized recipients.

CONCLUSION

Acceptable early outcomes in patient survival and graft rejection could be anticipated in sensitized heart transplant recipients under a perioperative algorithm using complement-dependent cytotoxicity crossmatch- or panel-reactive antibody-directed urgent immunomodulation strategies, while infection remains the major concern.

Outcomes of pre- heart transplantation desensitization in a series of highly sensitized patients bridged with left ventricular assist devices

Desensitization therapy for heart transplantation (HT) candidates can shorten transplant wait times and broaden the donor pool. Specific evidence-based recommendations on both protocols and indications are lacking. We retrospectively assessed left ventricular assist devices-bridged candidates who received pre-HT desensitization therapy. The therapeutic protocol consisted of intravenous immunoglobulin and rituximab followed by bortezomib and plasmapheresis if an insufficient response was achieved. Desensitization was attempted in 10 patients; only 7 tolerated therapy and underwent transplant. For those patients, median decrease in unacceptable calculated panel reactive antibody was 11%; there was no significant decrease for 3 patients. Post-desensitization adverse events were observed in all patients which included coagulopathy, bone marrow suppression, and infection. Median time to first infection was 16 days. One patient had clinically significant rejection and 3 patients had uptrending donor-specific antibodies. Decisions to proceed with desensitization should be individualized understanding potential risks and benefits.

Differential Impact of Class I and Class II Panel Reactive Antibodies on Post-Heart Transplant Outcomes

BACKGROUND

Sensitized patients awaiting heart transplantation spend a longer time on the waitlist and have higher mortality. We are now able to further characterize sensitization by discriminating antibodies against class I and II, but the differential impact of these has not been assessed systematically.

METHODS AND RESULTS

Using United Network for Organ Sharing data (2004-2015), we analyzed 17,361 adult heart transplant patients whose class I and II panel reactive antibodies were reported. Patients were divided into 4 groups: class I and II ≤25% (group 1); class I ≤25% and class II ˃25% (group 2); class II ≤25% and class I >25% (group 3); and both class I and II >25% (group 4). Outcomes assessed were treated rejection at 1-year mortality, all-cause mortality, and rejection-related mortality. Compared with group 1, only group 4 was associated with a higher risk of treated rejection at 1 year (odds ratio 1.31, 95% confidence interval [CI] 1.05-1.64), all-cause mortality (hazard ratio 1.24, 95% CI 1.06-1.46), and mortality owing to rejection (subhazard ratio 1.84, 95% CI 1.18-2.85), whereas groups 2 and 3 were not (P > .05).

CONCLUSIONS

Combined elevation in class I and II panel reactive antibodies seem to increase the risk of treated rejection and all-cause mortality, whereas risk with isolated elevation is unclear.

Management of the sensitized pediatric heart transplant patient

Despite advancements in transplant immunosuppression and techniques for managing critically ill patients awaiting heart transplantation, children who are immunologically sensitized to human leukocyte antigen remain at increased risk for morbidity and mortality, both while awaiting and after heart transplant. In this review we will discuss the epidemiology of sensitization, review the immunologic basis and methods of human leukocyte antigen antibody detection, describe outcomes for sensitized pediatric transplant candidates, and consider both pre- and post-transplant management options for sensitized patients.