Long-term follow-up of pediatric cardiac transplant recipients on a steroid-free regime: the role of endomyocardial biopsy

Medium-term Outcomes in Pediatric Heart Transplant Recipients Managed Using a Steroid Avoidance Immune Suppression Protocol

BACKGROUND

Short-term outcomes using steroid avoidance immune suppression are encouraging in pediatric heart transplant (HT) recipients at low risk of antibody-mediated rejection. We assessed medium-term outcomes in pediatric HT recipients initiated on a steroid avoidance protocol at our institution using surveillance biopsies.

METHODS

All primary HT recipients during 2006-2020 who did not have a donor-specific antibody were eligible for immune suppression consisting of 5-d Thymoglobulin/steroid induction followed by a tacrolimus-based, steroid-free regimen. We assessed freedom from graft failure (death or retransplant), acute rejection, posttransplant lymphoproliferative disease, and cardiac allograft vasculopathy.

RESULTS

Overall, 150 of 181 primary HT recipients were eligible for steroid avoidance regimen. Their median age was 8.7 y, 41% had congenital heart disease, 23% were sensitized, and 35% were on a mechanical support. The median follow-up was 6.1 y. Eleven patients (8%) were on maintenance steroids at discharge and 13% at 1 y. Graft survival was 94% at 1 y and 87% at 5 y. Freedom from rejection was 73% at 1 y and 64% at 5 y. Freedom from posttransplant lymphoproliferative disease was 96% at 1 y and 95% at 5 y. Freedom from moderate cardiac allograft vasculopathy was 94% at 5 y. Eight patients developed diabetes. Estimated glomerular filtration rate was <60 mL/min/1.73 m 2 in 5% of the cohort at 5 y.

CONCLUSIONS

Pediatric HT recipients at low risk of antibody-mediated rejection have excellent medium-term survival and relatively low incidence of posttransplant morbidities when managed using a steroid avoidance immune suppression protocol.

Rejection surveillance in pediatric heart transplant recipients: Critical reflection on the role of frequent and long-term routine surveillance endomyocardial biopsies and comprehensive review of non-invasive rejection screening tools

BACKGROUND

Despite significant medical advances in the field of pediatric heart transplantation (HT), acute rejection remains an important cause of morbidity and mortality. Endomyocardial biopsy (EMB) remains the gold-standard method for diagnosing rejection but is an invasive, expensive, and stressful process. Given the potential adverse consequences of rejection, routine post-transplant rejection surveillance protocols incorporating EMB are widely employed to detect asymptomatic rejection. Each center employs their own specific routine rejection surveillance protocol, with no consensus on the optimal approach and with high inter-center variability. The utility of high-frequency and long-term routine surveillance biopsies (RSB) in pediatric HT has been called into question.

METHODS

Sources for this comprehensive review were primarily identified through searches in biomedical databases including MEDLINE and Embase.

RESULTS

The available literature suggests that the diagnostic yield of RSB is low beyond the first year post-HT and that a reduction in RSB intensity from high-frequency to low-frequency can be done safely with no impact on early and mid-term survival. Though there are emerging non-invasive methods of detecting asymptomatic rejection, the evidence is not yet strong enough for any test to replace EMB.

CONCLUSION

Overall, pediatric HT centers in North America should likely be doing fewer RSB than are currently performed. Risk factors for rejection should be considered when designing the optimal rejection surveillance strategy. Noninvasive testing including emerging biomarkers may have a complementary role to aid in safely reducing the need for RSB.

Long-term surveillance biopsy: Is it necessary after pediatric heart transplant?

Due to limited and conflicting data in pediatric patients, long-term routine surveillance endomyocardial biopsy (RSB) in pediatric heart transplant (HT) remains controversial. We sought to characterize the rate of positive RSB and determine factors associated with RSB-detected rejection. Records of patients transplanted at a single institution from 1995 to 2015 with >2 year of post-HT biopsy data were reviewed for RSB-detected rejections occurring >2 year post-HT. We illustrated the trajectory of significant rejections (ISHLT Grade ≥3A/2R) among total RSB performed over time and used multivariable logistic regression to model the association between time and risk of rejection. We estimated Kaplan-Meier freedom from rejection rates by patient characteristics and used the log-rank test to assess differences in rejection probabilities. We identified the best-fitting Cox proportional hazards regression model. In 140 patients, 86% did not have any episodes of significant RSB-detected rejection >2 year post-HT. The overall empirical rate of RSB-detected rejection >2 year post-HT was 2.9/100 patient-years. The percentage of rejection among 815 RSB was 2.6% and remained stable over time. Years since transplant remained unassociated with rejection risk after adjusting for patient characteristics (OR = 0.98; 95% CI 0.78-1.23; P = 0.86). Older age at HT was the only factor that remained significantly associated with risk of RSB-detected rejection under multivariable Cox analysis (P = 0.008). Most pediatric patients did not have RSB-detected rejection beyond 2 years post-HT, and the majority of those who did were older at time of HT. Indiscriminate long-term RSB in pediatric heart transplant should be reconsidered given the low rate of detected rejection.

Pediatric Cardiac Intensive Care Society 2014 Consensus Statement: Pharmacotherapies in Cardiac Critical Care Immune Therapy

OBJECTIVE

In this Consensus Statement, we review the etiology and pathophysiology of inflammatory processes seen in critically ill children with cardiac disease. Immunomodulatory therapies aimed at improving outcomes in patients with myocarditis, heart failure, and transplantation are extensively reviewed.

DATA SOURCES

The author team experience and along with an extensive review of the medical literature were used as data sources.

DATA SYNTHESIS

The authors synthesized the data in the literature to present current immumodulatory therapies. For each drug, the physiologic rationale, mechanism of action, and pharmacokinetics are synthesized, and the evidence in the literature to support the therapy is discussed.

CONCLUSIONS

Immunomodulation has a crucial role in the treatment of certain pediatric cardiac diseases. Immunomodulatory treatments that have been used to treat myocarditis include corticosteroids, IV immunoglobulin, cyclosporine, and azathioprine. Contemporary outcomes of pediatric transplant recipients have improved over the past few decades, partly related to improvements in immunomodulatory therapy to prevent rejection of the donor heart. Immunosuppression therapy is commonly divided into induction, maintenance, and acute rejection therapy. Common induction medications include antithymocyte globulin, muromonab-CD3, and basiliximab. Maintenance therapy includes chronic medications that are used daily to prevent rejection episodes. Examples of maintenance medications are corticosteroids, cyclosporine, tacrolimus, sirolimus, everolimus, azathioprine, and mycophenolate mofetil. Rejection of the donor heart is diagnosed either by clinically or by biopsy and is treated with intensification of immunosuppression.

Steroid-free and steroid withdrawal protocols in heart transplantation: the review of literature

Corticosteroids (CSs) are still the mainstay of induction, rescue, and maintenance in heart transplantation (HTx). However, their use is associated with significant and well-documented side effects usually related to the dose administered and the duration of therapy. Moreover, CSs interfere with the recipient's quality of life and with the active process of graft tolerance. Physicians have been exploring ways to avoid or reduce CSs in association with other immunosuppressive drugs, minimizing side effects and costs. The regimens are classified as steroid-free or steroid withdrawal protocols. The studies analyzed in this review come to similar conclusions as benefits and adverse consequences: steroid-free protocols should be advisable and mandatory in pediatric patients, insulin-dependent diabetes mellitus (IDDM), presence of infection, familial metabolic disorders/obesity, severe osteoporosis, and in the elderly. On the other hand, steroid withdrawal can be successfully achieved in 50-80%, with late better than early withdrawal, no increase in rejection-related mortality, no adverse impact on survival, and probably a better quality of live. Safety and efficacy can certainly be improved by an individualized approach to the transplant recipient.

Impact of different long-term maintenance immunosuppressive therapy strategies on patients' outcome after heart transplantation

The introduction of cyclosporine in the early 1980s meant a decisive improvement in post-transplant outcomes for all solid-organ transplants and, in particular, it allowed heart transplantation to emerge as a viable therapeutic option for patients with end-stage cardiac failure. Many factors, including recipient and donor selection, organ preservation and the technical aspects of the transplant itself, influence post-operative outcomes following heart transplantation but the continued need to treat the recipient's immune response plays a key role in determining long-term outcomes. Thereby interactions between immunosuppressive drugs used in different combinations play an important role in patients' outcome. After more than two decades, significant controversy still exists as to the best immunosuppressive regimen for long-term maintenance. During the 1990s and 2000s, newer immunosuppressive medications, specifically, tacrolimus, mycophenolate mofetil, sirolimus, everolimus and the IL-2 receptor blockers (daclizumab and basiliximab), were introduced that allow the clinician several options to try to minimize side effects and maximize the desired therapeutic effects. The side effects involve direct organ toxicity (e.g. renal and hepatic dysfunction), metabolic disturbances, (e.g. diabetes, hyperlipidemia and hypertension), neurotoxicity, and several other significant adverse events, such as cholestasis and myelosuppression. Newer immunosuppressive drugs can impair wound healing, induce lung toxicity and produce various cytopenic states. Steroids continue to plague patients with their well-known side effects. This article reviews the current data on the benefits and risks of the various therapeutic regimens available, which are analyzed under three main themes: calcineurin inhibitor based therapies, calcineurin minimization protocols and calcineurin free regimens.

Safety and early outcomes using a corticosteroid-avoidance immunosuppression protocol in pediatric heart transplant recipients

BACKGROUND

Long-term oral corticosteroids have been a mainstay of maintenance immunosuppression in pediatric heart transplantation. In this study, we report early clinical outcomes in a cohort of pediatric heart transplant recipients managed using a steroid-avoidance protocol.

METHODS

Of the 70 patients who underwent heart transplantation during the study period, 55 eligible recipients, including 49 non-sensitized and 6 sensitized (all 55 with negative crossmatch) patients, entered a steroid-avoidance immunosuppression protocol consisting of thymoglobin induction followed by a 2-drug, tacrolimus-based, corticosteroid-free regimen. The primary outcome variable was freedom from moderate rejection (International Society for Heart and Lung Transplantation [ISHLT] Grade 2R/3A or antibody-mediated rejection).

RESULTS

The median age at transplant was 7.1 years (range 2 weeks to 22 years) and median follow-up was 19 months (range 2 to 46 months). Fifty patients survived to discharge after transplantation. Of these patients, 2 (4%) were discharged on steroids and 8 (16%) started on maintenance steroids at follow-up. Rejection was diagnosed in 8 patients (Grade 2R cellular rejection in 3 and antibody-mediated rejection in 5). Freedom from rejection was 92% at 6 months (95% confidence interval [CI] 80% to 97%) and 87% at 1 year (CI 73% to 94%). Post-transplant survival was 91% at 6 months (CI 79% to 96%) and 88% at 12 and 24 months (CI 75% to 95%). There was 1 death due to rejection (antibody-mediated) 8 months after transplantation.

CONCLUSIONS

An immunosuppression protocol consisting of induction followed by corticosteroid avoidance appears to achieve acceptable rejection rates during the first year post-transplant in pediatric heart transplant recipients.

Minimization of steroids in liver transplantation

Because of the markedly improved short-term results of liver transplantation (LT) and persistently high number of long-term complications, the attention of transplant physicians should be focused on minimizing immunosuppressive therapy as much as possible. Steroid-based immunosuppression is responsible for a substantial post-LT morbidity and mortality, hence, minimization of its use is of utmost importance to improve the quality of life of the successfully transplanted liver recipient. This literature review shows that LT can be performed safely with steroid-minimal immunosuppression without compromising graft and patient survival. The tendency in clinical practice is to move more and more from steroid withdrawal to steroid avoidance protocols.

Cardiac transplantation for hypoplastic left heart syndrome

Future improvements can be expected in cardiac transplantation in children. We continue to advance our understanding of the immune system, and to develop more specific immunosuppressive agents. Ultimately, the future for recipients may be improved by strategies such as induction therapy or donor-derived chimeric destined transfusions, designed to enhance the tolerance of the host to a human leukocyte antigen incompatible graft. Improvements in tolerance of the host would allow for reduction or elimination of many, if not all, of the immunosuppressive agents, and for longevity extending well into the adulthood. Survival, particularly for infants, has improved dramatically in the last decade. The most recent results from the registry of the International Society of Heart and Lung Transplantation/United Network for Organ Sharing show that recipients less than one year old at transplantation, who survive the first year, have greater than a 95% survival to four years (Fig. 1). As late outcomes continue to improve, transplantation will provide a better quality and duration of life for infants with hypoplastic left heart syndrome. It is possible, nonetheless, that some infants will require retransplantation, since the half life of a transplanted heart in children has been about 12 years. The alternative is conventional surgery with multiple palliative operations, and the need for later transplantation as end-stage cardiac function is reached. Efforts to increase potential donors and donor utilization can be supported by innovative schemes, such as ABO incompatible transplants. Additional efforts are made more urgent when the current data indicate excellent outcomes after transplantation, but a high mortality while waiting for transplantation.

Advances in methods for surveillance of rejection

Transplantation is an effective treatment modality for infants1 and children2 with end-stage cardiac diseases. Rejection remains a major complication (Figure 1), even in newborn infants.3 Acute rejection can best be operationally defined by clinical findings, histopathology, and/or abnormalities of ventricular function of new origin that require, and respond to, intensified immunosuppression. Mechanistically, the ability to detect acute rejection is critically dependent on the detection of significant new myocytic injury, damage, and/or death. Surveillance for rejection is critically important in determining both long and short-term outcomes following cardiac transplantation. The ideal strategy for surveillance should have a high negative predictive value, correctly identifying the absence of myocytic injury, with high specificity, such that it does not falsely predict such injury.4

Nocturnal enuresis is a common complication following cardiac transplantation

AIMS

To investigate the incidence of nocturnal enuresis post-cardiac transplantation.

METHODS

Seventy two cardiac transplantations have been performed in children under 16 years of age. All recipients who were alive and over 4 years of age at the time of the study received a questionnaire about urinary symptoms; 54 of the 57 eligible children participated.

RESULTS

Twenty five children had persistent nocturnal enuresis post-transplantation. Thirteen of them had previously attained reliable night-time dryness but developed secondary nocturnal enuresis following transplantation, with three subsequently regaining dryness at ages 8, 12, and 17 years; 10 were still wetting mean age 12.3. Twelve children had not achieved night-time dryness when transplanted (all were under 4 years of age at the time) and continued to wet. Only one of these children achieved dryness (at age 12 using oxybutynin); the other 11 remained wet at night at a mean age of 9.3 years. Twenty nine children were dry at night post-transplantation, but 21 of them had nocturia at least three times a week. There is a significant difference in age at transplantation between the primary nocturnal enuretic children (mean age 2.0) and the secondary nocturnal enuretic children (mean age 7.4) as well as between the primary nocturnal enuretic children and the non-enuretic children (mean age 9.0).

CONCLUSIONS

Transplanting young children frequently delays the normal attainment of night-time continence or causes them to start wetting again. It should not be dismissed as a minor problem as it causes low self-esteem and is socially limiting. It is important families are aware it is a direct result of the transplantation process.

Therapy for acute rejection in pediatric organ transplant recipients

Despite the availability of potent immunosuppressive drugs, rejection after organ transplantation in children remains a serious concern, and may lead to significant morbidity, graft loss, and death of the patient. Acute graft rejection in pediatric recipients is first treated with methylprednisolone pulses, followed by progressive taper of corticosteroid doses. After control of the rejection episode, baseline immunosuppression has to be adjusted and closely monitored since rejection (especially late episodes, occurring more than 6 months after transplantation) may be due to a lack of compliance or sub-therapeutic drug concentrations. The management of corticosteroid resistant rejection is not standardized, and depends on the transplanted organ and previous immunosuppressive regimen. In patients experiencing corticosteroid resistant acute rejection while on a cyclosporine-based immunosuppressive regimen, cyclosporine is generally changed to tacrolimus. In case of tacrolimus-based immunosuppression, tacrolimus blood levels may be increased, and/or mycophenolate mofetil (which nowadays tends to replace azathioprine) or sirolimus may be added, although pharmacodynamic data and clinical studies with these agents are still scarce in pediatric recipients. The use of antithymocyte globulins or monoclonal anti-CD3 antibodies, muromonab CD3 (OKT3) is hampered by numerous adverse effects, including a significant risk of over-immunosuppression. These therapies are nowadays indicated in very selected cases. Other treatments such as plasmapheresis and high dose immunoglobulins may be useful in difficult cases. In patients with refractory rejection despite therapeutic escalation, the risks of over-immunosuppression, including opportunistic infections and malignancies (especially the Epstein-Barr virus related post-transplant lymphoproliferative disease) have to be balanced with the consequences of graft loss due to rejection. Detransplantation or retransplantation may, in some instances, be preferable to severe infectious or tumoral complications.

Moderate acute rejection detected during annual catheterization in pediatric heart transplant recipients

BACKGROUND

Acute rejection commonly occurs within the first year after heart transplantation, and then decreases in frequency with time. Recently, the long-term utility of endomyocardial biopsy during routine annual catheterization has been questioned. The purpose of this study was to retrospectively review the prevalence of biopsy-proven rejection during routine annual catheterization in our patient population, determine whether biopsies late after transplant are useful, and identify factors that correlate with late unsuspected rejection.

METHODS

Biopsy results from the annual catheterization were evaluated from 1986 to August 2000. The prevalence of moderate rejection was evaluated and compared with the patient's immunosuppressive regimen; the prevalence of late rejection; and how late rejection correlated with recipient age, number of first-year rejections and presence of sub-therapeutic cyclosporine.

RESULTS

A total of 1108 biopsies were performed in 269 children with a mean follow-up of 5 +/- 3 years (median 5 years, range 1 to 11 years). Three-drug immunosuppressive therapy, including steroids, was used in 93 patients. There was a persistent 8% to 10% prevalence of moderate rejection at up to 10 years post-transplantation. Moderate rejection was more likely in patients: (1). on 3-drug immunosuppressive therapy; (2). with a recipient age >1 year; and (3). with a relatively lower cyclosporine level.

CONCLUSIONS

These data suggest that continued surveillance of pediatric transplant patients for acute rejection is indicated for long-term follow-up.

Pediatric heart transplantation

Heart transplantation is now a treatment option with good outcome for infants and children with end-stage heart failure or complex, inoperable congenital cardiac defects. One-year and 5-year actuarial survival rates are high, approximately 75% and 65%, respectively, with overall patient survival half-life greater than 10 years. To date, survival has been improving as a result of reducing early mortality. Further reductions in late mortality, in part because of graft coronary artery disease and rejection, will allow achievement of the goal of decades-long survival. Quality of life in surviving children, as judged by activity, is usually "normal." Somatic growth is usually at the low normal range but linear growth can be reduced. Of infant recipients, 85% evaluated at 6 years of age or older were in an age-appropriate grade level. Long-term management of childhood heart recipients requires the collaboration of transplant physicians, given the increasing number of immunosuppressive agents and the balance between rejection and infection. Currently, recipients are maintained on immunosuppressive medications that target calcineurin (eg, cyclosporine, tacrolimus), lymphocyte proliferation (eg, azathioprine, mycophenolate mofetil [MMF], sirolimus) and, in some instances antiinflammatory corticosteroids. Emerging evidence now suggests a favorable immunologic opportunity for transplantation in childhood and, conversely, a higher mortality rate in children who have had prior cardiac surgery. Further studies are needed to define age-dependent factors that are likely to play a role in graft survival and possible graft-specific tolerance (eg, optimal conditions for tolerance induction and how immunosuppressive regimens should be changed with maturation of the immune system). As late outcomes continue to improve, the need for donor organs likely will increase, as transplantation affords a better quality and duration of life for children with complex congenital heart disease, otherwise facing a future of multiple palliative operations and chronic heart failure.

Eight-year experience of pediatric heart transplantation: clinical outcome using non-invasive methods for the evaluation of acute rejection

Combined immunosuppression therapy and acute rejection surveillance after heart transplantation may influence clinical outcome. This prospective, longitudinal study investigated 27 pediatric patients (12 days to 12 yr of age; mean 3.0 yr) who underwent a post-operative regimen that included long-term treatment with cyclosporin A and azathioprine (double immunosuppression) and polyclonal anti-thymocyte serum induction therapy. Non-invasive parameters were used to diagnose acute rejection. The actuarial survival, clinical outcomes, and complications were analyzed. The actuarial survival after double immunosuppression and induction therapy with polyclonal anti-thymocyte serum was 89%, 73%, and 57% at 1, 4, and 8 yr, respectively. The rejection frequency was 2.6 episodes/patient and the infection frequency, 3.7 episodes/patient. One year after transplantation, systemic arterial hypertension was detected in 21% of patients. Hence, double immunosuppression with polyclonal anti-thymocyte serum induction therapy combined with surveillance of acute rejection with non-invasive tests may provide promising clinical outcome in pediatric heart transplant recipients.

Pneumatosis intestinalis after pediatric thoracic organ transplantation

OBJECTIVE

To review and describe pneumatosis intestinalis (PI) in children who have undergone thoracic organ transplantation and evaluate potential risk factors.

METHODS

We retrospectively reviewed abdominal radiographs obtained from June 1992 through September 2000 in all pediatric (age <21 years) thoracic organ recipients who survived at least 1 week after transplantation. In this group, a case was defined as an episode of radiographically confirmed PI; those without PI were assigned as controls. Variables analyzed included demographic data, gastroenteritis history (stool cultures or symptoms of gastroenteritis), and transplant-related factors (ie, graft type, rejection history, immunosuppression regimen). Significance was defined as P <.05.

RESULTS

Over this 8-year period, PI occurred in 8 (7%) of 116 patients (0.86% annual risk). No child had >1 diagnosed episode of PI. Of these 8 cases, 7 presented with 1 or more abdominal symptoms. Three of these children had rotavirus antigen isolated in their stool, 2 others were noted to have stool positive for Clostridium difficile toxin, and in the other 3, no pathogen was identified. All cases were treated with a regimen of intravenous antibiotics and total parenteral nutrition. There were no deaths; however, 1 patient developed an Aspergillus pulmonary infection during his course of antibiotic therapy, and another underwent an exploratory laparotomy without bowel resection. Significant risk factors included black race (unadjusted odds ratio: 16), younger age at presentation (age <5 years; unadjusted odds ratio: 9), higher steroid dose (steroid dose >0.5 mg/kg/d; unadjusted odds ratio: 7), and a higher tacrolimus level at presentation (tacrolimus level >1; unadjusted odds ratio: 6). PI did not occur with a steroid dose <0.4 mg/kg/d. Variables not associated with increased risk for developing PI included gender, graft type, total white blood cell count, recent antibiotic use, concurrent use of an antimetabolite, cytomegaloviral infection, past use of extracorporeal membrane oxygenation, and graft rejection history.

CONCLUSIONS

Significant risk factors for the development of PI in our pediatric thoracic organ transplantation population included black race, younger age, higher daily steroid dosing, and a high tacrolimus level at presentation. In the children diagnosed with PI, there were no related deaths, significant gastrointestinal sequelae, or complications. These findings suggest that in this population, PI will often have a benign course when treated aggressively, and that steroid dosing should be reduced to <0.5 mg/kg/d whenever possible.

Pediatric cardiac transplantation: management issues

Pediatric heart transplantation is an effective therapeutic modality for children with end-stage heart disease. The overall survival of young heart recipients is very good: 89% to 92% one year survival. Survival data for the long term indicates that pediatric heart recipients have a very good chance of living for decades. Advances in immunosuppression have lent optimism for the future. There are now alternatives in induction, maintenance, and acute rejection therapy. Immunosuppressants are more specific in action and prevent and treat allograft rejection with less toxic side effects and decreased morbidity. Acute rejection and infection are early complications that reduce in incidence significantly after six months post-transplant. Graft coronary artery disease continues to be the most significant hurdle to long-term survival. Currently there is a plateau in the number of heart transplants performed annually. Lack of available pediatric donors plays a large role in the paucity of pediatric transplants. This review focuses on the key management issues involved in the care of the pediatric heart transplant recipient and incorporates the experiences and protocols of the Stanford University Pediatric Heart Transplant Program.

Efficiency, efficacy, and adverse effects of adenovirus vs. liposome-mediated gene therapy in cardiac allografts

Virus- and nonvirus-mediated immunosuppressive cytokine gene therapy prolongs cardiac allograft survival in various nonfunctional heart transplant animal models, but its cardiac adverse effects have not been addressed. Recently, we developed a functional heterotopic heart transplant model in rabbits. For the first time, we were able to systematically compare the efficiency, efficacy, and adverse effects of optimized adenovirus- and liposome-mediated ex vivo interleukin (IL)-10 gene transfer in functional donor hearts. The efficiency of liposome-mediated gene transfer was greatly improved in physiologically functioning donor hearts and was only three- to fourfold lower than adenovirus-mediated gene transfer. The efficacy of liposome-mediated IL-10 gene transfer was much higher than that mediated by adenovirus. Significant negative inotropic and arrhythmogenic adverse effects on transplanted hearts were observed due to viral cytotoxicity and immunogenesis, which greatly abated the therapeutic efficacy of this first generation adenovirus-mediated gene therapy.