Influence of Induction Therapy Using Basiliximab With Delayed Tacrolimus Administration in Heart Transplant Recipients　― Comparison With Standard Tacrolimus-Based Triple Immunosuppression ―

Abstract

Background: Appropriate indications and protocols for induction therapy using basiliximab have not been fully established in heart transplant (HTx) recipients. This study elucidated the influence of induction therapy using basiliximab along with delayed tacrolimus (Tac) initiation on the outcomes of high-risk HTx recipients.

Methods and Results: A total of 86 HTx recipients treated with Tac-based immunosuppression were retrospectively reviewed. Induction therapy was administered to 46 recipients (53.5%) with impaired renal function, pre-transplant sensitization, and recipient- and donor-related risk factors (Induction group). Tac administration was delayed in the Induction group. Induction group subjects showed a lower cumulative incidence of acute cellular rejection grade ≥1R after propensity score adjustment, but this was not significantly different (hazard ratio [HR]: 0.63, 95% confidence interval [CI]: 0.37–1.08, P=0.093). Renal dysfunction in the Induction group significantly improved 6 months post-transplantation (P=0.029). The cumulative incidence of bacterial or fungal infections was significantly higher in the Induction group (HR: 10.6, 95% CI: 1.28–88.2, P=0.029).

Conclusions: These results suggest that basiliximab-based induction therapy with delayed Tac initiation may suppress mild acute cellular rejection and improve renal function in recipients with renal dysfunction, resulting in its non-inferior outcome, even in high-risk patients, when applied to the appropriate recipients. However, it should be carefully considered in recipients at a high risk of bacterial and fungal infections.

Triple immunosuppressive therapy including calcineurin inhibitors (CNIs), mycophenolate mofetil (MMF), and steroids, has substantially improved outcomes for heart transplant (HTx) recipients. Nevertheless, the management of CNI-related nephrotoxicity, fatal acute cellular rejection (ACR), antibody-mediated rejection (AMR), and infections remains challenging.¹ Risk factors for poor clinical prognosis or difficulties for their management by healthcare practitioners for patients necessitate alternative immunosuppression strategies.¹ Induction therapy is a strategy for improving clinical prognosis or making their managements easier in these high-risk HTx recipients,^1,2 and is administered to ~50% of all adult HTx recipients worldwide.^1,3 Nevertheless, studies have shown no definitive evidence of its benefits.^1,4,5

Basiliximab selectively blocks interleukin-2 (IL-2), binding to its receptors (IL-2R) in activated T-lymphocytes, thereby inhibiting IL-2-mediated activated T-lymphocyte proliferation.^4,5 Several previous studies have reported that induction therapy using IL-2R antagonists reduced the frequency of acute rejection^6–9 or reversed worsening of renal function,^10–12 and did not increase incidence of adverse events.^6–12 Conversely, current systematic reviews have not supported routine application of IL-2R antagonists because of a lack of robust evidence.^4,5 Appropriate indications and protocols for administering induction therapy to HTx recipients requires further consideration. Previous studies regarding induction therapy using IL-2R antagonists were hampered by several limitations.^4–13 First, the immunosuppression protocol for induction therapy using IL-2R antagonists varies according to the dosage of CNI administered and applies to those recipients who require CNI-withdrawal with cytolytic therapy for renal dysfunction or as a modification of the standard triple immunosuppressive regimen. Second, most previous studies have been performed in HTx recipients who were administered cyclosporine and not tacrolimus (Tac), for primary immunosuppression. Third, current systematic reviews have not included those recipients who were bridged to transplantation with a left ventricular assist device (LVAD) in situ,⁵ which may influence the efficacy of induction therapy.¹³

The present study aimed to elucidate the influence of induction therapy using basiliximab with delayed administration of Tac on the clinical prognosis of HTx recipients compared to standard Tac-based triple immunosuppression therapy.

Methods

Patient Selection and Study Protocol

We retrospectively reviewed the medical records of 109 consecutive HTx recipients who were treated at the National Cerebral and Cardiovascular Center (NCVC) in Japan from May 1999 to March 2018 (Figure 1). When the present study was initiated, 105 recipients who had undergone HTx ≥6 months before the study were initially screened for inclusion. Next, 2 recipients who were aged <16 years, were excluded, because follow-up protocol for these patients differed from that for adults. Additionally, 17 recipients who were administered cyclosporine as the primary immunosuppressive drug immediately after the HTx, were also excluded. As induction therapy using muromomab-monoclonal CD3 antibodies had been concomitantly administered with cyclosporine only (and not with Tac) before 2006 when basiliximab was introduced at our institution, all transplant recipients treated with muromomab-monoclonal CD3 antibodies were excluded from this study. Finally, 86 recipients who received a transplant after March 2006 and had completed a post-HTx mean follow-up of 4.3±2.9 years (0.5–12.1 years) were included in this study. Of these, 46 (53.5%) underwent induction therapy using basiliximab (Induction group) due to impaired renal function pre-HTx (25; 54.3%), sensitization for anti-human leukocyte antigen (HLA) antibody (12; 26.1%), and recipient-related (10; 21.7%) or donor-related risk factors (4; 8.7%). Four of these patients were positive for overlapping risk factors, with 2 exhibiting both renal dysfunction and recipient-related factors; 1 with both recipient- and donor-related factors, and another with renal dysfunction along with recipient- and donor-related factors. Although donor-related factors are not thought to increase risk of rejection or worsening renal dysfunction, these might be associated with insufficient cardiac performance in the early post-HTx period or high incidence of pre-existing coronary atherosclerosis; subsequently, they might lead to renal dysfunction in the recipient, causing intolerance to immunosuppressants or difficulty of recipients’ management in the early post-HTx period. The remaining 40 recipients underwent standard triple immunosuppressive therapy (No-Induction group). Baseline characteristics were recorded immediately before the HTx procedure.

Figure 1.

Study flowchart. HTx, heart transplant; NCVC, National Cerebral and Cardiovascular Center; Tac, tacrolimus.

We assessed the following factors up to 6 months post-HTx: (1) cumulative incidence of ACR Grade ≥1R (based on International Society of Heart and Lung Transplantation [ISHLT] guidelines¹⁴) and ISHLT-classified AMR of pAMR ≥1¹⁵; (2) infection, defined by treatment with antiviral, antibacterial, or antifungal agents; and (3) changes in renal function between baseline and follow up. We assessed the cumulative incidence of death or malignant disease until the end of the follow-up period.

The study protocol was approved by the local ethics committee of the NCVC. Informed consent was obtained from all participants (NCVC IRB number M30-106).

Immunosuppressive Therapy Protocol and Follow up

Immunosuppressive therapeutic protocols followed in our institution have been detailed previously.^16–18 We perform HTx when the direct cross-match, based on complement-dependent cytotoxicity, is negative for HLA class I between the donor lymphocyte and the recipient serum. We primarily consider induction therapy using basiliximab for recipients with the following characteristics: (1) pre-HTx impaired renal function (low estimated glomerular filtration rate [eGFR] defined as <60 mL/min/1.73 m²) or history of renal dysfunction regardless of eGFR level immediately prior to HTx; (2) sensitization for anti-HLA antibody (≥10% of panel reactivity in a flow cytometry panel reactive antibodies [PRA] screening test until 2016, and >1,000 mean fluorescence intensity [MFI] for at least 1 antibody detected on the Luminex single antigen beads test after 2017); (3) recipient-related risk factors (e.g., pre-HTx elderly age >50 years, or the possibility for delaying the increase in CNI-dosage post-HTx); and (4) donor-related risk factors (high donor age >50 years, low left ventricular ejection fraction [LVEF] <55%, and body weight mismatch). Notably, not all patients who satisfied the inclusion criteria, as mentioned earlier, underwent induction therapy; finally, we made a comprehensive judgment about clinical necessity on the therapeutic indication for induction therapy.

Basiliximab has been used as an immunosuppressant for induction therapy since 2006 for de novo HTx recipients in our institution. Twenty milligrams of basiliximab is administered intravenously <3 h after weaning a HTx patient from cardiopulmonary bypass and on Day 4 after the transplant. In standard triple immunosuppressive therapy, Tac is generally initiated at a dose of 1 mg/day on the first or second postoperative day. Thereafter, Tac dosage is regulated to achieve an initial blood concentration range of 9–12ng/mL within a week. Standard target trough levels of Tac to be maintained during the first year post-HTx are 9–12ng/mL. In the Induction group, Tac was generally initiated at a dose of 1 mg/day, 3 or 4 days after the HTx, when postoperative renal dysfunction had resolved. Tac dosage was then slowly increased to the initial target concentration of 9–12 ng/mL within 1 month, particularly, in recipients with renal dysfunction. MMF was started postoperatively after 1 or 2 days at an initial dose of 1,000 mg/day. Intravenous methylprednisolone was administered at 500 mg at the initiation of the transplant procedure, and the same dose was repeated immediately before unclamping the donor aorta. Thereafter, 125 mg was administered 3 times every 8 h post-HTx, followed by 1 mg/kg/day on postoperative day 1, and then reduced by 0.125 mg/kg/day every 2 days, until a maintenance dose of 20 mg/day was reached, which was continued until 3 weeks after the HTx. Thereafter, the steroid dose was reduced to 15 mg/day until completion of 5 weeks post-HTx, before being finally tapered to 10 mg/day for 6 months post-HTx. All recipients commenced a triple immunosuppression therapy regimen with Tac, MMF, and steroids immediately after HTx. Intravenous methylprednisolone was generally replaced with oral prednisolone when recipients were able to take the medication orally or 3 weeks after HTx. Since 2007, we considered converting from MMF to everolimus (EVL) when worsening renal function or progressive cardiac allograft vasculopathy was observed during the maintenance period after HTx.¹⁶

Routine endomyocardial biopsies were performed at 1, 2, 3, 5, 7, 9, and 11 weeks, and at 4.5 and 6 months after the HTx. Clinical suspicion of ACR or AMR was also an indication for biopsy.

Prophylaxis and Therapy Protocol for Infectious Diseases

We selected peri-operative antibiotic therapy based on microbiologic sensitivities.¹⁹ Prophylaxis for bacterial infections included broad-spectrum drugs against gram-positive and gram-negative bacterium, respectively. Intravenous antifungals were administered for fungal infections. Cytomegalovirus (CMV) seropositive recipients were routinely administered a 5-g dose of CMV immunoglobulin, immediately after the HTx, which was continued until 5 days post-HTx. In CMV-seronegative recipients transplanted with organs from CMV-seropositive donors (CMV mismatch), anti-CMV drugs were administered prophylactically at half the therapeutic dosage until 1 year after the HTx. If CMV was detected in polymerase chain reaction tests, a CMV antigenemia assay was performed. When both tests showed positive results or symptomatic CMV infection was observed, anti-CMV drugs were administered at their respective therapeutic dosages. Epstein-Barr virus (EBV) infection was defined by the development of any symptoms of EBV infection. The presence of BK polyomavirus (BKV) infection was defined by evidence of positive anti-BK virus immunohistochemical staining during urine cytology.

Statistical Analysis

The Fisher’s exact test was used to test for differences in categorical variables between groups. Continuous data were compared using unpaired t-tests or the Wilcoxon rank sum test for non-normally distributed variables. The Wilcoxon signed-rank test was used to compare continuous values regarding renal function at baseline and at 6 months post-HTx in each group. The McNemar’s chi-squared test was used to compare categorical values regarding renal function at baseline and at 6 months post-HTx in each group. Considering the observational nature of the study, baseline imbalances might have existed between the groups. Therefore, adjusted analysis was performed using propensity score (PS)-based methods with regression. Additionally, other PS-based analyses including adjustment with stratification and inverse probability weighting (IPW) were also performed to verify the robustness of findings. The PS for receiving induction therapy was calculated using multivariable logistic regression for factors including recipient age, recipient sex, low eGFR, sensitization for anti-HLA antibodies class I, high donor age, donor sex, and the prevalence of low LVEF of the donor heart. Cox proportional hazards regression analysis was performed, including the PS as a covariate, to compare differences between the groups and to compute hazard ratios (HRs) with 95% confidence intervals (CIs). The log rank test and Cox proportional hazards regression were applied to assess the association of induction therapy with factors including the cumulative incidence of ACR, infections occurring during 6 months post-HTx, death, and composite endpoint (i.e., death or malignancy) for the entire follow-up period. The composite endpoint was whichever of the following occurred first: (1) date of incidence of malignancy; (2) date of death; or (3) 30 April 2018. All recipients were followed up at our institution. No violation of the proportionality assumption was observed in the analyses. P values <0.05 were considered significant. All analyses were performed using Stata^® Version 15 (Stata Corporation, College Station, TX, USA) software.

Results

Baseline Clinical Demographics

Donor age and the prevalence of low LVEF were higher in the Induction group than in the No-induction group (Table 1A), although the differences were not statistically significant (P=0.081 and 0.071, respectively). Induction therapy tended to be administered in older recipients (P=0.022). Most recipients were supported with LVADs before the HTx. Renal function was poorer in the Induction group than in the No-induction group, although the difference was insignificant (P=0.052 for estimated GFR [eGFR] at baseline). The prevalence of pretransplant proteinuria was comparable between the 2 groups. Additionally, no significant differences were observed in the medical history of an increase in the urine β2-macroglobulin, which is one of the biomarkers for tubular disorders, between the 2 groups of 74 recipients undergoing spot urine examination before HTx (12.2% of 41 patients in the Induction group vs. 6.1% of 33 patients in the No-induction group).

Table 1. (A) Baseline Characteristics, (B) Immunosuppression and Blood Concentrations

(A) Variable	Induction group (n=46)	No-induction group (n=40)	P value
Donor-related factors
Donor age, year (mean±SD)	45.2±13.7	40.2±12.3	0.081
High donor age (age >50 years), n (%)	18 (39.1)	10 (25.0)	0.176
Male donor, n (%)	24 (52.2)	28 (70.0)	0.122
Sex mismatch, n (%)	16 (34.8)	12 (30.0)	0.653
Transplantation from female to male, n (%)	12 (26.1)	9 (22.5)	0.803
Numbers of HLA mismatch, (mean±SD)	4.1±1.1	4.1±1.4	0.975
Stratification of numbers of HLA mismatch, n (%)			0.872
HLA mismatch (0–2 antigen mismatches)	6 (13.0)	5 (12.5)
HLA mismatch (3–4 antigen mismatches)	19 (41.3)	19 (47.5)
HLA mismatch (5–6 antigen mismatches)	21 (45.7)	16 (40.0)
Body weight ratio (mean±SD)	0.99±0.19	0.97±0.19	0.592
Weight mismatch (body weight ratio <0.8), n (%)	6 (13.0)	7 (17.5)	0.764
Low LVEF (<60%), n (%)	19 (41.3)	9 (22.5)	0.071
Low LVEF (<55%), n (%)	5 (10.9)	4 (10.0)	0.999
LV hypertrophy, n (%)	4 (2.2)	3 (7.5)	0.999
History of cardiac arrest, n (%)	30 (65.2)	23 (57.5)	0.510
High-dose inotropic support, n (%)	3 (6.5)	7 (17.5)	0.177
History of atraumatic intracranial bleeding, n (%)	4 (8.7)	7 (17.5)	0.333
Ischemic time, min (mean, IQR)	198.5 (177.0–219.0)	187.5 (175.0–207.5)	0.317
Recipient related factors
Recipient age, year (mean±SD)	41.2±14.8	38.7±12.6	0.397
Stratification of recipient age (years), n (%)			0.022
≥60	7 (15.2)	0 (0)
50–59.9	8 (17.4)	10 (21.7)
40–49.9	13 (28.3)	7 (17.5)
<40	18 (39.1)	23 (57.5)
Male recipient, n (%)	32 (69.6)	34 (85.0)	0.126
CMV mismatch (D+/R−), n (%)	9 (19.6)	10 (25.0)	0.608
Primary indication for HTx			0.903
Dilated cardiomyopathy, n (%)	30 (65.2)	25 (62.5)
Hypertrophic cardiomyopathy, n (%)	6 (14.3)	4 (10.0)
Ischemic cardiomyopathy, n (%)	3 (6.5)	4 (10.0)
Other, n (%)	7 (15.2)	7 (17.5)
LVAD support pre-HTx, n (%)	43 (93.5)	39 (97.5)	0.620
Type of LVAD support			0.712
Paracorporeal LVAD, n (%)	19 (41.3)	19 (47.5)
Implantable LVAD, n (%)	24 (52.2)	20 (50.0)
Types of implantable LVAD, n (%)			0.010
EVA Heart	7 (29.2)	5 (25.0)
Dura Heart	5 (20.8)	1 (5.0)
Heartmate II	6 (25.0)	14 (70.0)
Jarvik2000	5 (20.8)	0 (0.0)
Novacor	1 (4.2)	0 (0.0)
No-LVAD support pre-HTx, n (%)	3 (6.5)	1 (2.5)
History of exit site infection of LVAD pre-HTx, n (%)	37 (80.4)	28 (70.0)	0.318
Hypertension, n (%)	3 (6.5)	2 (5.0)	0.999
Hyperlipidemia, n (%)	11 (23.9)	15 (37.5)	0.239
Diabetes mellitus, n (%)	9 (19.6)	5 (12.5)	0.559
Smoking history, n (%)	21 (45.7)	15 (37.5)	0.514
Sensitization for anti HLA antibodies, n (%)
Class 1, n (%)	12 (26.1)	5 (12.5)	0.174
Class 2, n (%)	4 (8.7)	0 (0)	0.120
Serum ALB level pre-HTx, mg/dL (mean±SD)	4.1±0.5	4.3±0.5	0.110
BMI, kg/m2 (median, IQR)	22.1 (20.0–25.0)	21.3 (19.2–26.5)	0.640
eGFR, mL/min/1.73 m2 (mean±SD)	88.0±37.3	116.7±90.3	0.052
Medical history of proteinuria pre-HTx, n (%)	8 (17.4)	6 (15.0)	0.999
(B) Variable	Induction group (n=46)	No-induction group (n=40)	P value
Trough level of Tac, ng/dL (median, IQR)
1 week post-HTx	5.9 (3.3–8.0)	7.6 (5.8–10.0)	0.008
2 weeks post-HTx	8.7 (7.1–10.8)	10.7 (9.3–12.5)	<0.001
3 weeks post-HTx	8.7 (7.6–10.9)	9.9 (8.9–10.9)	0.022
5 weeks post-HTx	10.1 (9.1–11.8)	10.8 (9.3–12.3)	0.179

ALB, albumin; BMI, body mass index; CMV, cytomegalovirus; D+/R−, donor positive/recipient negative; eGFR, estimated glomerular filtration rate; HLA, human leukocyte antigen; HTx, heart transplant; IQR, interquartile range; LV, left ventricular; LVAD, left ventricular assist device; LVEF, left ventricular ejection fraction; SD, standard deviation; Tac, tacrolimus. (A) Continuous data were compared between the Induction and No-induction groups using the Student’s t-test or Wilcoxon rank sum test, as appropriate. Categorical data were analyzed using the Fisher’s exact test. Data are expressed as mean±SD or median (IQR) for continuous values and number of subjects and n (%) for categorical values. Body weight ratio indicated body weight ratio of donor/recipient. High-dose inotropic support indicated patients who required intravenous infusions of >10 μg/kg/min of inotropic agents or epinephrine. eGFR was calculated from the creatinine value and age, using the Modification of Diet in Renal Disease equation modified with a Japanese coefficient (0.881) as follows: eGFR (mL/min/1.73 m²) = 0.881 × 186 × age^−0.203 × Cre^−1.154 (for males). Proteinuria was defined as more than 0.5 g/day in the measurement of protein-to-creatinine ratios in a spot urine sample. (B) Continuous data were compared between the Induction and No-induction groups using a Wilcoxon rank sum test. Data are expressed as median (IQR) for continuous values.

Immunosuppression During the 6 Months Post-HTx

As Tac initiation was delayed and its dosage was slowly increased in the Induction group, the trough level of Tac was significantly lower in the Induction group from 1–3 weeks post-HTx (Table 1B). Compared with recipients receiving induction therapy due to renal dysfunction from 1 to 3 weeks post-HTx, those receiving induction therapy due to pretransplant sensitization likely had a high concentration of Tac (8.9 [4.5–11.5] vs. 5.4 [3.2–7.7], P=0.035 at 1 week; 8.7 [7.8–11.0] vs. 8.8 [6.7–10.8], P=0.770 at 2 weeks; 11.0 [8.7–13.9] vs. 8.1 [7.4–9.2], P=0.001 at 3 weeks). The trough level of Tac in the Induction group achieved similar levels in the No-induction group at 5 weeks post-HTx using our immunosuppressive protocol. EVL use with reduced Tac at 6 months post-HTx was comparable between groups (5 recipients [10.9%] in the Induction group vs. 5 [12.5%] in the No-induction group, P=0.999). No recipients received EVL for 3 weeks post-HTx.

Rejections or Infections 6 Months Post-HTx

Both the Induction and No-induction groups showed a similar cumulative incidence of rejections (ACR and AMR) at 6 months (Table 2). The affected patients did not exhibit any symptoms of functional cardiac impairment and were diagnosed by follow-up endomyocardial biopsies only. Table 3 shows the Cox regression analyses for the cumulative incidence of ACR ≥1R 6 months post-HTx. After adjusting with regression for the associated variables for ACR ≥1R, induction therapy with basiliximab tended to be associated with a lower incidence of ACR ≥1R (Table 3, P=0.093, Model 1; P=0.068, Model 2; and P=0.143, Model 3). Similarly, other PS-based analyses showed similar trends (HR: 0.79, 95% CI: 0.46–1.36, P=0.394 in stratification and HR: 0.84, 95% CI: 0.55–1.30, P=0.431 in IPW). Five female recipients (25%) had a history of pregnancy, and no significant difference was observed in the incidence of ACR ≥1R between those with and without a history of pregnancy (100% vs. 86.7%). No significant difference was observed in the incidence of ACR ≥1R between the 4 groups classified according to the reason for performing induction therapy (Figure 2A). The incidence of ACR ≥1R was comparable between 2 groups in 57 subjects with high risk for rejections, including long ischemic time (≥median time of 194 min), female sex, and pretransplant sensitization (Figure 2B).

Table 2. Outcomes for 6 Months Post-HTx

Variable	Induction group (n=46)	No-induction group (n=40)	P value
All cumulative rejections at 6 months post-HTx, n (%)	35 (76.1)	32 (80.0)	0.796
ACR ≥1R, n (%)
3 weeks post-HTx	9 (19.6)	9 (22.5)	0.795
6 months post-HTx	33 (71.7)	31 (77.5)	0.624
ACR ≥2R, n (%)
3 weeks post-HTx	0 (0.0)	0 (0.0)	1.000
6 months post-HTx	2 (4.3)	1 (2.5)	0.999
AMR ≥ pAMR1, n (%)
3 weeks post-HTx	4 (8.7)	2 (5.0)	0.681
6 months post-HTx	4 (8.7)	3 (7.5)	0.999
All infectious diseases, n (%)	19 (41.3)	11 (27.5)	0.257
CMV infections	12 (26.1)	8 (20.0)	0.612
Non-CMV infections	10 (21.7)	3 (7.5)	0.078
Bacterial or fungal infections	9 (21.7)	1 (2.5)	0.017
Other infections	1 (2.2)	2 (5.0)	0.595
Presence of BK virus in the urine samples within 1-year post-HTx, n (%)	14 (30.4)	16 (40.0)	0.374

ACR, acute cellular rejection; AMR, antibody mediated rejection; CMV, cytomegalovirus; EBV, Epstein Barr virus; HTx, heart transplant. Categorical data were analyzed by using Fisher’s exact test. Data are presented as number of subjects and n (%) for categorical values. All cumulative rejections included ACR and AMR. All infectious diseases included CMV, EBV, bacterial and fungal infections.

Table 3. Univariable and Multivariable Cox Regression Analyses for the Cumulative Incidence of ACR ≥1R Within 6 Months Post-HTx

Variable	Univariable			Model 1			Model 2			Model 3
	HR	95% CI	P value	HR	95% CI	P value	HR	95% CI	P value	HR	95% CI	P value
Induction therapy	0.82	0.50–1.33	0.424	0.63	0.37–1.08	0.093	0.60	0.35–1.04	0.068	0.67	0.40–1.14	0.143
Ischemic time, for 1 min increase	1.01	1.00–1.02	0.029	1.01	1.00–1.02	0.034	1.01	1.00–1.02	0.004	NS	NS	NS
Recipient sex, male	0.55	0.32–0.95	0.031	NS	NS	NS	0.40	0.22–0.72	0.002	NS	NS	NS
Recipient age, for 10-year increase	0.99	0.77–1.26	0.911	NS	NS	NS	0.92	0.72–1.19	0.538	NS	NS	NS

ACR, acute cellular rejection; CI, confidence interval; eGFR, estimated glomerular filtration rate; HR, hazard ratio; HLA, human leukocyte antigen; LVEF, left ventricular ejection fraction; NS, not selected. This table shows the recipient age, sex, and associated variables with the incidence of ACR with P<0.10 in univariable Cox proportional regression analysis (i.e., ischemic time). The propensity score for receiving induction therapy was calculated using multivariable logistic regression and included recipient age (stratified for every 10 years), recipient sex, low eGFR (<60 mL/min/1.73 m²), sensitization for anti-HLA antibodies class 1, high donor age (>50 years), donor sex, and the prevalence of low LVEF (<55%) of donor heart. Model 1: adjusted for propensity score for induction therapy and associated variables for the incidence of ACR ≥1R (i.e., ischemic time). Model 2: adjusted for recipient age, sex, and associated variables for the incidence of ACR ≥1R (i.e., ischemic time). Model 3: adjusted for propensity score for induction therapy.

Figure 2.

(A) Kaplan-Meier estimates of the cumulative ACR ≥1R event-free rate 6 months post-HTx compared between 4 subgroups based on the indication for induction therapy. (B) Kaplan-Meier estimates of the cumulative ACR ≥1R event-free rate 6 months post-HTx compared between the Induction and No-induction groups in 57 recipients with high risk for rejections, including female sex, long ischemic time, and pretransplant sensitization. (C) Kaplan-Meier estimates of the cumulative bacterial or fungal infections event-free rate 6 months post-HTx compared between the Induction and No-induction groups. (D) Kaplan-Meier estimates of the cumulative bacterial or fungal infections event-free rate 6 months post-HTx compared between 4 subgroups based on the indication for induction therapy. ACR, acute cellular rejection; HTx, heart transplantation.

Incidence of infectious diseases, excluding CMV infections, tended to be higher in the Induction group (P=0.078; Table 2), with the incidence of bacterial or fungal infections being significantly higher (P=0.017). In the Induction group, bacterial cholangitis occurred in 3 recipients, whereas mediastinitis, cellulitis, urinary tract infection, catheter infection, clostridium difficile colitis, and fungal spondylitis each affected 1 recipient. In the No-induction group, 1 recipient was treated for surgical site (LVAD removal site) Candida albicans infection. Kaplan-Meier estimates of freedom from bacterial or fungal infections are shown in Figure 2C. PS-based multivariable Cox proportional hazard models showed that induction therapy using basiliximab was independently associated with higher incidence of bacterial or fungal infections (HR 10.61, 95% CI: 1.28–88.2, P=0.029). Other PS-based analyses also showed similar trends (HR: 9.82, 95% CI: 1.16–83.41, P=0.036 in stratification, and HR: 8.69, 95% CI: 1.07–70.32, P=0.043 in IPW). No EBV infection was observed in any recipient for 6 months. Figure 2D shows the difference in the incidence of bacterial or fungal infections between the 4 subgroups based on the reason for performing induction therapy. Recipients receiving induction therapy due to renal dysfunction likely had a higher incidence of bacterial or fungal infections.

Renal Function 6 Months Post-HTx

Renal function in the Induction group tended to be worse than that in the No-induction group at baseline (P=0.056 for occurrence of low eGFR and P=0.052 for eGFR values, Table 4A). In the Induction group, the incidence of low eGFR significantly decreased 6 months post-HTx compared to baseline levels (P=0.029). Conversely, in the No-induction group, there were no significant differences in the incidence of low eGFR. Furthermore, in 17 recipients exhibiting low eGFR at baseline (13 in the Induction group and 4 in the No-induction group) (Table 4B), a significant improvement of renal dysfunction at 6-months post-HTx was observed in the Induction group (P=0.002, P<0.001 and P<0.001, in the incidence of low eGFR, serum Cre levels, and eGFR values, respectively). In the No-induction group, renal function remained unchanged compared to baseline at 6-months post-HTx. Change and percentage change in eGFR at 6 months did not differ significantly between the groups (Tables 4A,4B). No significant differences in any hemodynamic parameters, 6 months post-HTx, were observed between the 2 groups (Table 4C).

Table 4. (A) Renal Function at Baseline and 6 Months Post-HTx, (B) Renal Function at Baseline and 6 Months Post-HTx in Recipients With Low Renal Function (eGFR <60 mL/min/1.73 m²), (C) Hemodynamics Parameters 6 Months Post-HTx

(A) Variable	Induction group (n=46)	No-induction group (n=40)	P value
Low eGFR (<60.0 mL/min/1.73 m2), n (%)
Baseline	13 (28.3)	4 (10.0)	0.056
6 months post-HTx	5 (10.9)	7 (17.5)	0.535
P (baseline vs. 6 months)	0.029	0.317
Serum Cre, mg/dL, (mean±SD)
Baseline	0.95±0.33	0.86±0.32	0.223
6 months post-HTx	0.94±0.26	0.91±0.34	0.295
P (baseline vs. 6 months)	0.722	0.394
eGFR, mL/min/1.73 m2, (mean±SD)
Baseline	88.0±37.3	116.7±90.3	0.052
6 months post-HTx	86.7±44.5	102.9±55.0	0.135
P (baseline vs. 6 months)	0.821	0.075
Change of eGFR after 6 months post-HTx, mL/min/1.73 m2, (mean±SD)	−1.4±40.1	−13.8±47.7	0.191
Percent change of eGFR after 6 months post-HTx, %, (mean±SD)	4.0±31.5	−1.1±32.1	0.456
Proteinuria, n (%)
Baseline	8 (17.4)	6 (15.0)	0.999
6 months post HTx	1 (2.2)	0 (0)	0.999
P (baseline vs. 6 months)	0.008	0.014
(B) Variable	Induction group (n=13)	No-induction group (n=4)	P value
Low eGFR (<60.0 mL/min/1.73 m2), n (%)
Baseline	13 (100.0)	4 (100.0)	1.000
6 months post-HTx	3 (23.1)	1 (25.0)	0.999
P (baseline vs. 6 months)	0.002	0.083
Serum Cre, mg/dL
Baseline	1.33±0.25	1.42±0.44	0.624
6 months post-HTx	1.11±0.32	1.02±0.16	0.568
P (baseline vs. 6 months)	<0.001	0.087
eGFR, mL/min/1.73 m2, (mean±SD)
Baseline	50.9±6.6	46.0±9.3	0.251
6 months post-HTx	64.9±13.7	64.5±6.6	0.957
P (baseline vs. 6 months)	<0.001	0.062
Change of eGFR 6 months post-HTx, mL/min/1.73 m2, (mean±SD)	14.0±11.5	18.5±12.8	0.191
Percent change of eGFR 6 months post-HTx, %, (mean±SD)	27.4±22.7	45.1±34.2	0.243
Proteinuria, n (%)
Baseline	1 (7.7)	1 (25.0)	0.426
6 months post-HTx	1 (7.7)	0 (0)	0.999
P (baseline vs. 6 months)	1.000	0.317
(C) Variables	Induction group (n=46)	No-induction group (n=40)	P value
Heart rate, beats/min (mean±SD)	85.0±14.0	87.7±10.1	0.323
Systolic blood pressure, mmHg (mean±SD)	114.1±13.8	113.2±14.3	0.776
Diastolic blood pressure, mmHg (mean±SD)	68.2±11.2	70.1±10.8	0.427
Mean blood pressure, mmHg (mean±SD)	84.6±11.4	84.4±11.4	0.936
Mean PCWP, mmHg (mean±SD)	7.3±3.0	7.3±3.1	0.979
Mean PAP, mmHg (mean±SD)	14.9±3.7	13.9±3.3	0.199
Mean RAP, mmHg (mean±SD)	3.4±2.3	3.2±2.7	0.663
Cardiac index, L/min/m2	3.4±0.7	3.5±0.7	0.365

ACR, acute cellular rejection; AMR, antibody mediated rejection; CMV, cytomegalovirus; Cre, creatinine; EBV, Epstein Barr virus; eGFR, estimated glomerular filtration rate; HTx, heart transplant; PAP, pulmonary artery pressure; PCWP, pulmonary capillary wedge pressure; RAP, right atrial pressure; SD, standard deviation. (A,B) Continuous data were compared between the Induction and No-induction groups using a Student’s t-test. Categorical data were analyzed using the Fisher’s exact test. The McNemar’s chi-squared test was used to compare categorical values regarding renal function at baseline and at 6 months post-HTx in each group. Data are expressed as mean±SD and number of subjects; n (%) for categorical values. eGFR was calculated from the creatinine value and age, using the Modification of Diet in Renal Disease equation modified with a Japanese coefficient (0.881), as follows: eGFR (mL/min/1.73 m²) = 0.881 × 186 × age^−0.203 × Cre^−1.154 (for males), eGFR = 0.881 × 186 × age^−0.203 ×Cre^−1.154 × 0.742 (for females). Proteinuria was defined as more than 0.5 g/day in measurement of protein-to-creatinine ratios in a spot urine sample. (C) Continuous data were compared between the Induction and No-induction groups using a Student’s t-test. Data are expressed as mean±SD. Cardiac index was calculated by using the cardiac output determined by using a Fick-based assessment, as follows: cardiac index (L/min/m²)=Fick cardiac output / body surface area. Fick cardiac output was calculated from the mixed venous oxygen saturation (in the main pulmonary artery) and an assumed oxygen consumption.

Long-Term Clinical Prognosis

Two recipients each in the Induction group (4.3%) and the No-induction group (5.0%) developed malignant diseases during long-term follow up. Recipients in the No-induction group died due to malignant lymphoma and colon cancer at 3.5 and 11.0 years post-HTx, respectively, whereas the 2 Induction group recipients survived. One recipient in the Induction group (2.2%) died of multiple organ failure due to sepsis at 8.0 months post-HTx. Kaplan-Meier estimates of cumulative freedom from death are shown in Figure 3A. Kaplan-Meier estimates of cumulative freedom from the composite endpoint, including death or malignancy, are shown in Figure 3B. Figure 3C shows the difference in the incidence of composite endpoints between the 4 subgroups based on the reason for initiating induction therapy, and no significant differences were observed. Multivariable Cox proportional hazard models with adjusted PSs showed that induction therapy using basiliximab was not independently associated with the incidence of the composite endpoint (HR 1.44, 95% CI: 0.22–9.54, P=0.708). The other PS-based analyses also showed similar results (HR: 1.12, 95% CI: 0.16–7.81, P=0.912 in stratification, and HR: 1.42, 95% CI: 0.30–6.81, P=0.659 in IPW).

Figure 3.

(A) Kaplan-Meier estimates of cumulative death free rate compared between the Induction and No-induction groups. (B) Kaplan-Meier estimates of composite endpoint including death or malignancy compared between the Induction and No-induction groups. (C) Kaplan-Meier estimates of composite endpoint, including death or malignancy, compared between 4 subgroups based on the indication for induction therapy. HTx, heart transplant.

Discussion

This study suggests that basiliximab-based induction therapy with delayed Tac administration may suppress ACR and improve renal function in recipients with renal dysfunction. Similarly, it may elicit non-inferior outcomes regardless of its administration in high-risk recipients when applied based on our proposed indication criteria. Although basiliximab-based induction therapy with delayed Tac administration might not increase the incidence of LVAD site-related infections, it was associated with a high incidence of other bacterial and fungal infections.

The efficacy of basiliximab-based induction therapy for prevention of rejections remains unclear in HTx recipients.⁹ This study provides novel evidence suggesting that basiliximab-based induction therapy with delayed Tac administration tended to lower the development of mild ACR, compared to standard Tac-based triple immunosuppression. However, this difference was not statistically significant. A previous study showed that, compared to standard cyclosporine-based triple immunosuppression, basiliximab-based induction therapy may likely delay development of ACR requiring treatment, although this difference was not statistically significant.⁹ Notably, similar beneficial effects of basiliximab-based induction therapy were revealed, even in more recent standard immunosuppressive therapy using Tac. In contrast, its clinical significance for clinical outcomes is limited and this needs to be carefully interpreted because the development of mild ACR (≥1R), as evaluated in this study, was not associated with poor outcomes (unlike ACR≥2R). Because of an extremely low incidence of ACR ≥2R in our subjects, the suppressive effects of induction therapy for controlling ACR, which required treatment, could not be elucidated. Therefore, further study encompassing a larger sample size is needed.

Induction therapy using basiliximab is expected to prevent further decline in renal function in recipients with renal impairment, as it allows modification of concomitant CNI dosage.^10,11,20 Our results did not show statistically significant improvement in renal function with basiliximab-based induction therapy along with delayed administration of Tac, when compared to standard Tac-based triple immunosuppression. However, although renal function tended to be improved in both groups at 6 months post-HTx, the Induction group in particular showed a significant decrease in the incidence of low eGFR at 6 months post-HTx. Furthermore, in the sub-analysis, which included recipients with poor renal function just before transplantation, recipients in the Induction group showed significant improvement in renal function 6 months post-HTx. Conversely, no significant difference in the renal function was observed between baseline and 6-months post-HTx in the No-induction group. This result might suggest that basiliximab-based induction therapy with delayed Tac initiation was effective for suppressing further worsening of renal function in recipients with renal dysfunction early on post-HTx. Because baseline renal function did not differ significantly between the 2 groups, the renal dysfunction experienced by the recipients in our study was not as severe as that observed in previous studies. Our results may therefore have underestimated the influence of induction therapy on renal dysfunction.

The 2-dose regimen of basiliximab-based induction therapy administered on Day 0 and Day 4 after transplantation still suppressed T-lymphocyte activation for an average of 40–50 days after administration.^9,21,22 Our results suggest that this protocol, which involved slowly increasing the Tac dosages within 1 month, was feasible based on the approach detailed in earlier reports.^20–22

The potential disadvantages of induction therapy include frequent infections in the early phase and risk of malignancies development in the long term post-HTx.²³ In contrast to previous studies,^6–12 our results might provide additional evidence that basiliximab-based induction therapy might increase the incidence of post-transplant infections. A recent large, retrospective, observational study using worldwide registry data showed that basiliximab-based induction therapy was associated with lower long-term survival in HTx recipients than with induction therapy using anti-thymocyte globulin.²⁴ However, results of other randomized clinical trials have shown that basiliximab might be associated with a lower incidence of infectious diseases than anti-thymocyte globulin.^25,26 Our study suggests that even basiliximab-based induction therapy with delayed Tac administration might increase the incidence of bacterial and fungal infections. The trough level of Tac was significantly lower in the Induction group than in the No-induction group up to 3 weeks post-HTx. Tac dosage in the Induction group was slowly increased to prevent further deterioration of renal dysfunction due to Tac-induced kidney injury for the renal dysfunction group, and to prevent over-immunosuppression following the addition of basiliximab for the pretransplant sensitization group; however, the Induction group showed a higher incidence of infectious diseases. Therefore, the Tac trough level in the Induction group may not be clinically low enough to prevent infectious diseases, which might indicate the need to delay further the administration of or slow down the increase in the dosage of Tac in the Induction group. In the sub-analysis based on the indication for induction therapy, recipients who receiving induction therapy due to renal dysfunction likely had a lower concentration of Tac than those who received induction therapy due to pre-transplant sensitization. Contrary to the results predicted by the difference in Tac concentration, the recipients receiving induction therapy due to renal dysfunction likely had a higher incidence of bacterial or fungal infections as compared with those receiving induction therapy due to pre-transplant sensitization. The balance between under- and over-immunosuppression in recipients receiving induction therapy needs to be properly assessed in each recipient group based on reasons for induction therapy; however, this remains difficult to assess. Therefore, future studies should focus on the indications for basiliximab-based induction therapy in HTx recipients.

All infections, except for those affecting 1 recipient who died of sepsis at 8 months post-HTx, were controlled with appropriate antimicrobials. Furthermore, most recipients received LVAD support in our study, which may cause higher incidence of LVAD-related surgical site infections. Basiliximab-based induction therapy was not associated with a significant increase in LVAD-related, surgical site infections. Our results suggest that basiliximab-based induction therapy might be feasible as a treatment for recipients bridged with LVAD in situ. Considering the shortage of the number of events in this study, the influence of basiliximab-based induction therapy on long-term clinical outcomes including death or malignancy could not be evaluated statistically and needs to be interpreted with discretion.

The appropriate indications for administering induction therapy using basiliximab have not been established. We primarily used this approach in recipients who posed potential difficulty in patient management, including risk of rejection or renal impairment in the early post-HTx phase. Considering that even standard Tac-based immunosuppression might have already suppressed incidences of rejection requiring treatment in our subjects, we may have used unnecessarily stricter criteria for selecting patients for the application of basiliximab-based induction therapy to prevent rejections. The reason why our study subjects showed very low incidence of rejection (regardless of application of induction therapy) is unclear. Our protocol might be responsible for inducing stronger immunosuppression in our HTx recipients. HLA matching or sensitization might explain an incidence rate of rejection. Although the incidence of low HLA mismatch (0–2 mismatch) (12.8% overall) in our study was significantly higher than that reported in the current international registry data (3.8%) (P<0.001), the incidence of high HLA mismatch (5–6 mismatch) (43.0% overall) was not different from that observed in the current international registry data (57.8%).¹ Furthermore, there were no significant differences in the incidence of ACR ≥1R between high and low HLA mismatch patients (data not shown). Our recipients (19.8% overall with %PRA ≥10% or single antigen test >1,000 MFI) might have been more sensitized than those in the international registry (13.5% for PRA ≥10%). The current consensus statement for the management of antibodies in HTx recipients suggests that MFI >5,000 would seem more clinically appropriate.²⁷ Our MFI cutoff of >1,000 might be low and might result in the selection of patients for induction therapy who are not at an increased risk of rejection. Additionally, our results showed that female sex and long ischemic time were associated with acute cellular rejection. A previous study showed that long ischemic time (≥4 h) had increased risk of ACR ≥2R during the first year post-HTx,²⁸ and history of pregnancy was associated with a higher risk of sensitization.²⁹ Although whether both factors are associated with rejection requires further study, these factors might need to be considered as indication criteria for induction therapy.

This study has several limitations. First, the study design was observational and retrospective in nature, without randomization. Considering the observational design, selection bias could not be avoided. Second, we had a small sample size, which limits the robustness of our results. Furthermore, because fewer long-term events were used to compare the incidence of outcomes between groups, it might be difficult to evaluate the influence of basiliximab on long-term prognosis. We used popular PS-based methods, not propensity score matching (PSM), to confirm the robustness of our results. Although PSM has become an increasingly popular method for reducing the effect of treatment-selection bias for estimating causal treatment effects using observational data, this approach has several major issues. The method does not estimate the average causal effect because untreated subjects are always matched with treated subjects using PSs, the size of analysis may be reduced due to matching, and the results of PSM may not be robust as there are several matching methods and thus the result may depend on the particular method employed. Third, induction therapy using basiliximab was administered to HTx recipients predicted to have poor post-transplant clinical outcomes. Therefore, we could not fully compare long-term prognosis between the Induction and No-induction groups. This apparent selection bias may also have led to underestimation of the effects of induction therapy using basiliximab to improve clinical prognosis.

In conclusion, our findings suggest that basiliximab-based induction therapy with delayed Tac administration, applied to those recipients fulfilling our indication criteria, might be feasible and safe. Our results provide additional evidence indicating that basiliximab-based induction therapy may be likely to suppress rejections, may be effective for suppressing further deterioration in the renal function of recipients with renal dysfunction, and may not increase device-related infections in recipients bridged with LVADs. However, as basiliximab-based induction therapy might be associated with an increase in the incidence of bacterial or fungal infections, it needs to be initiated carefully in recipients at a high risk of developing infections.

Acknowledgment

The authors thank Yumiko Hori, RN, Eri Miyoshi, RN, Nobuaki Konishi, RN, and Nana Kitahata for data collection.

Sources of Funding

T.W. was supported by a Japan Heart Foundation Research Grant, MEXT KAKENHI Grant-in-Aid for Young Scientists (B) 15K21697, 19K09256, and Travel Grant from Transplantation Science Symposium Asian Regional Meeting 2018.

Disclosures

The authors declare no conflicts of interest.

IRB Information

This study protocol was approved by the local ethics committee at the National Cerebral and Cardiovascular Center. Informed consent was obtained from all participants (National Cerebral and Cardiovascular Center IRB number M30-106).

Data Availability

The deidentified participant data will not be shared.

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