ORIGINAL RESEARCH

Transpl. Int., 09 September 2026

Volume 39 - 2026 | https://doi.org/10.3389/ti.2026.16427

Locus-specific HLA matching and induction therapy in simultaneous pancreas–kidney transplantation: a national UK cohort study

  • 1. Institute of Transplantation, Freeman Hospital, Newcastle upon Tyne, United Kingdom

  • 2. NIHR Blood and Transplant Research Unit, Newcastle University and Cambridge University, Newcastle upon Tyne, United Kingdom

  • 3. Newcastle Fibrosis Research Group, Newcastle University, Newcastle upon Tyne, United Kingdom

  • 4. NHS Blood and Transplant, Bristol, United Kingdom

  • 5. Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom

  • 6. Imperial College Healthcare NHS Trust, London, United Kingdom

  • 7. Edinburgh Royal Infirmary, Edinburgh, United Kingdom

  • 8. Guy’s and St Thomas’ NHS Foundation Trust, London, United Kingdom

  • 9. Manchester University NHS Foundation Trust, Manchester, United Kingdom

  • 10. Cardiff and Vale University Health Board, Cardiff, United Kingdom

  • 11. Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom

Abstract

The impact of HLA mismatch and induction therapy in simultaneous pancreas-kidney transplantation on outcomes remains incompletely defined. We conducted a retrospective cohort study of 1705 SPK recipients transplanted in the UK between 2007 and 2019. Using national transplant registry data, we analysed the impact of locus-specific HLA mismatch and induction therapy (Alemtuzumab vs. Basiliximab) on pancreas graft survival primarily. Kidney graft and patient survival were also analysed as secondary outcomes. Multivariable Cox proportional hazards models were adjusted for donor, recipient, and transplant variables. Pancreas graft survival at 1- and 10-year post-transplant was estimated to be 88.6% and 72.7%, respectively. Kidney graft and patient survival at 10 years were 76.7% and 75.3%. In adjusted analyses, donor age, cold ischaemic time, and HLA-DQ mismatch were significantly associated with pancreas graft loss. No significant survival difference was seen between Alemtuzumab and Basiliximab induction therapy. Induction therapy and HLA-mismatch status were not associated with pancreas graft outcome in this large registry study.

Graphical Abstract

Introduction

Simultaneous pancreas-kidney (SPK) transplantation is the optimum treatment for selected patients with insulin-dependent diabetes mellitus and end-stage kidney disease, offering superior glycaemic control, renal function and survival compared to dialysis or kidney transplantation alone []. Recent improvements in immunosuppression, donor and recipient selection, and perioperative care have contributed to enhanced outcomes over recent decades [, ]. However, long-term pancreas graft survival remains variable, and optimising immunological matching and immunosuppression protocols is warranted to improve graft outcome.

The role of human leucocyte antigen (HLA) mismatching in pancreas transplantation is incompletely understood. HLA matching at the A-, B-, and -DR loci is routine in kidney transplantation [], however the impact of mismatches at the -Cw and -DQ loci is not well studied. Although some studies have suggested that class II mismatches (particularly -DQ) may contribute to de novo donor-specific antibody (DSA) development and chronic rejection following deceased donor kidney transplantation [], such associations are not well-established in SPK transplantation. The clinical significance of individual locus-specific mismatches in SPK graft recipients is uncertain [].

In the UK, organ allocation for SPK transplantation incorporates a HLA mismatch component to favour better-matched donor–recipient pairs. Candidates with fewer HLA mismatches receive higher allocation points, which increases their priority for available organs. The system also accounts for recipient sensitisation, quantified as calculated reaction frequency (cRF, analogous to calculated panel-reactive antibody [cPRA] in the United States), such that highly sensitised patients receive additional priority when a compatible donor becomes available. This scoring framework aims to balance immunological compatibility with equitable access for sensitised recipients.

Induction agents administered at the time of graft implantation vary between centres, with Alemtuzumab (a lymphocyte-depleting agent) and Basiliximab (a non-depleting IL-2 receptor antagonist) the commonest agents used. While both agents are widely used in SPK transplantation, direct comparisons of long-term graft and patient survival are lacking, particularly in relation to HLA-mismatch status.

This cohort study investigated the association between HLA-mismatch status and induction agent in terms of long-term outcome following SPK transplantation in the UK. The aim of this study was to inform immunological risk stratification that may potentially guide future allocation and immunosuppression strategies in SPK transplantation.

Patients and methods

Setting

This study used data extracted from the UK Transplant Registry (maintained by NHS Blood and Transplant), following approval from the Pancreas Advisory Group. All adult (≥18years) patients who underwent SPK transplantation in the UK from 1st April 2007 to 31st March 2019 were included. Patients who received a normothermic-regional perfusion preserved graft, recipients who underwent re-transplantation, recipients who received an induction agent other than Alemtuzumab or Basiliximab, and recipients with missing outcome data were excluded. One centre exclusively uses anti-thymocyte globulin as their induction agent, therefore all patients from this centre were excluded as numbers were too few for any meaningful analysis.

Immunosuppression

Induction immunosuppression was with either Alemtuzumab or Basiliximab, according to local centre protocols. Maintenance immunosuppression typically comprised tacrolimus, mycophenolate mofetil, and corticosteroids (tapered according to centre-specific protocols), but detailed maintenance regimens were not uniformly available in the dataset.

Definitions and outcomes

Demographic and clinical variables included donor and recipient age, sex, ethnicity, blood group, donor type, cytomegalovirus (CMV) status, cause of death, body mass index, creatinine at retrieval, recipient diabetes aetiology, dialysis modality, sensitisation at transplantation, waiting time to transplant, cold ischaemic time, and transplant era (grouped into three time periods by financial year: 2007–2011, 2011–2015, and 2015–2019). HLA mismatches were recorded separately for each of the following loci: A, B, Cw, DR, and DQ. NHS Blood and Transplant defined HLA mismatch groups was also included for comparison (grouped into three categories: Level 1 & 2 due to small numbers of Level 1 transplants, Level 3 and Level 4, Supplementary Table S1).

The primary outcome was pancreas graft survival at 10-year post-transplant. Pancreas graft survival at 1-year post-transplant, and additionally kidney graft survival and patient survival at both horizons were analysed as secondary outcomes. Graft survival was defined as the time from transplant to graft failure, censoring for death with a functioning graft. Patient survival was defined as the time from transplant to patient death. Patients lost to follow-up were censored at the date of last known status.

Acute pancreas graft rejection rates at 3- and 12-month post-transplant were obtained. For follow-up which was ‘Not reported’, it was assumed that no rejection episodes occurred.

Statistical analysis

Demographic and clinical factors are summarised by induction therapy group to describe the cohort. Categorical variables are presented as counts and percentage, and comparisons between the groups made using Fisher’s exact test or Chi-Squared test. Continuous variables are reported as medians and interquartile range (IQR), and comparisons made using the Student’s t-test.

Kaplan-Meier survival analysis was used to estimate the unadjusted survival for each outcome (pancreas graft, kidney graft and patient mortality). Survival curves were stratified by induction therapy group, and log-rank p-values allowed for comparisons between the groups.

Observations with missing data for the outcome or exposure variables were excluded from the analysis. To retain the sample size when multivariable modelling, missing data for the covariates were addressed using simple imputation. For categorical variables, the most frequently occurring category was imputed while continuous variables were imputed using median values. A comparison of this analysis and a complete-case analysis for the primary outcome was performed.

Separate Cox proportional hazards models were built for each survival outcome (pancreas graft, kidney graft, and patient survival). Each model was stratified by transplant centre to account for centre-specific baseline hazard functions. Stepwise backward selection was used, with variables retained if p < 0.10. Continuous variables were assessed for non-linearity using natural cubic splines and included in that form where appropriate.

A final model was created for each outcome incorporating any covariate found to be significant at any time horizon. The proportional hazards assumption was assessed using cumulative hazard function plots. Model checking involved assessing covariate functional form by Martingale residuals and checking for influential observations using df betas and likelihood displacement. Individual HLA locus models and induction therapy covariates were added to the model to evaluate their significance. The final model for analysis of the primary outcome was assessed for multicollinearity using the Variance Inflation Factor.

Further exploratory analyses of these outcomes at 3 and 5 years were performed to assess consistency with the results at other time horizons; however, these results are not presented in this paper. An interaction term between mismatch at HLA-DQ and induction therapy was included in the multivariable model for the primary outcome to assess potential effect modification. A 1-month landmark survival analysis was performed for the unadjusted pancreas graft survival, excluding any patients who died or were censored within the first month of transplantation.

All analyses were performed using SAS Enterprise Guide version 7.13 (SAS Institute Inc., Cary, NC).

Results

Demographics, induction agent and HLA-mismatch status

During the study period, 1897 adult patients underwent first-time SPK transplantation. The final analysis cohort consisted of 1705 SPK graft recipients after excluding recipients transplanted with a graft preserved normothermic regional perfusion (n = 26), recipients who received an induction agent other than Alemtuzumab or Basiliximab (n = 142), and recipients with missing outcome data (n = 24).

The donor and recipient demographic factors for the whole cohort and by induction agent are presented in Table 1 (with further data in Supplementary Table S2). Median recipient age was 43 years (IQR 36–49 years), 720 recipients were female (42.2%), and 70 recipients had Type II diabetes (4.1%). At the time of transplantation, 682 recipients were pre-dialysis (40.0%), and 1,019 recipients (59.8%) were on either haemodialysis (n = 627, 36.8%) or peritoneal dialysis (n = 392, 23.0%). In 1,625 recipients (95.3%), sensitisation was less than 85%. The median waiting time to transplantation was 1.16 years (IQR 0.55–1.17 years), and 1,385 recipients received a graft from a brainstem-death donor (81.2%). Alemtuzumab was used as the induction agent in 1,196 recipients (70.1%) compared to 509 recipients who received Basiliximab (29.9%). The proportion of donation after circulatory death (DCD) graft recipients was greater with Alemtuzumab compared to Basiliximab (20.2% vs. 15.5%, P = 0.025).

TABLE 1

FactorTotal (n = 1705)Alemtuzumab (n = 1,196)Basiliximab (n = 509)P-value
Donor
Transplant era (n, %)<0.0001
1 Apr 2007–31 Mar 2011
1 Apr 2011–31 Mar 2015
1 Apr 2015–31 Mar 2019
564 (33.1%)
612 (35.9%)
529 (31.0%)
361 (30.2%)
424 (35.5%)
411 (34.4%)
203 (39.9%)
188 (36.9%)
118 (23.2%)
Donor type (n, %)0.025
DBD
DCD
1,385 (81.2%)
320 (18.8%)
955 (79.9%)
241 (20.1%)
430 (84.5%)
79 (15.5%)
Donor age (years)
Median (IQR)

36 (23–47)

38 (24–48)

34 (22–44)
<0.0001
Donor BMI (kg/m2)
Median (IQR)
Not reported (n, %)

23.5 (21.4–25.9)
7 (0.4%)

23.6 (21.5–26.0)
4 (0.3%)

23.2 (21.2–25.5)
3 (0.6%)
0.091

Donor CMV status (n, %)
Positive
Negative
Not reported

966 (56.7%)
721 (42.3%)
18 (1.1%)

683 (57.1%)
501 (41.9%)
12 (1.0%)

283 (55.6%)
220 (43.2%)
6 (1.2%)
0.591


Cold ischaemic time (hours)
Median (IQR)
Not reported (n, %)

11.0 (9.5–13.0)
88 (5.2%)

10.6 (9.2–12.5)
69 (5.8%)

12.0 (10.3–14.0)
19 (3.7%)
<0.0001

Recipient
Recipient age (years)
Median (IQR)

43 (36–49)

43 (36–49)

42 (35–48)
0.005
Recipient sex (n, %)
Female
Male

720 (42.2%)
985 (57.8%)

706 (59.0%)
490 (41.0%)

279 (54.8%)
230 (45.2%)
0.108

Recipient blood group (n, %)
O
A
B
AB

739 (43.3%)
717 (4201%)
189 (11.1%)
60 (3.5%)

507 (42.4%)
524 (43.8%)
116 (9.7%)
49 (4.1%)

232 (45.6%)
193 (37.9%)
73 (14.3%)
11 (2.2%)
0.002



Recipient cause of diabetes (n, %)
Type I
Type II
Not reported
1,468 (86.1%)
70 (4.1%)
167 (9.8%)
1,014 (84.8%)
46 (3.9%)
136 (11.4%)
454 (89.2%)
24 (4.7%)
31 (6.1%)
0.597
Waiting time to transplantation (years)
Median (IQR)
Not reported (n, %)

1.16 (0.55–1.71)
1 (0.1%)

1.17 (0.54–1.71)
0 (0.0%)

1.16 (0.55–1.71)
1 (0.1%)
0.479

Recipient sensitisation (n, %)
<85%
>85%

1,625 (95.3%)
80 (4.7%)

1,136 (95.0%)
60 (5.0%)

489 (96.1%)
20 (3.9%)
0.382

Donor and recipient demographics for adult first time simultaneous pancreas and kidney transplants performed in the UK between 1st April 2007 and 31st March 2019.

HLA mismatch distribution varied across loci (Table 2). At the HLA-A locus, 14.8% of recipients were fully matched, 59.8% had one mismatch, and 25.5% had two. For HLA-B, most recipients had either one (47.2%) or two mismatches (48.3%), with complete matches in only 4.5%. HLA-Cw matching was similar: 13.6% had no mismatches, 50.0% had one, and 36.4% had two. A single HLA-DQ mismatch occurred in 58.9%, whereas 34.8% had no mismatches and 6.3% had two mismatches. At the HLA-DR locus, 9.0% were fully matched, while 56.8% and 34.2% had one or two mismatches, respectively. Mismatches were similar across induction agent groups.

TABLE 2

HLA mismatchesTotal (n = 1705)Alemtuzumab (n = 1,196)Basiliximab (n = 509)P-value
HLA-A (n, %)
0
1
2

252 (14.8%)
1,019 (59.8%)
434 (25.5%)

187 (15.6%)
707 (59.1%)
302 (25.3%)

65 (12.8%)
312 (61.3%)
132 (25.9%)
0.311


HLA-B (n, %)
0
1
2

77 (4.5%)
804 (47.2%)
824 (48.3%)

55 (4.6%)
571 (47.7%)
570 (47.7%)

22 (4.3%)
233 (45.8%)
254 (49.9%)
0.704


HLA-Cw (n, %)
0
1
2

231 (13.6%)
853 (50.0%)
621 (36.4%)

163 (13.6%)
595 (49.8%)
438 (36.6%)

68 (13.4%)
258 (50.7%)
183 (36.0%)
0.942


HLA-DQ (n, %)
0
1
2

593 (34.8%)
1,004 (58.9%)
108 (6.3%)

408 (34.1%)
705 (59.0%)
83 (6.9%)

185 (36.4%)
299 (58.7%)
25 (4.9%)
0.248


HLA-DR (n, %)
0
1
2

153 (9.0%)
969 (56.8%)
583 (34.2%)

95 (7.9%)
694 (58.0%)
407 (34.0%)

58 (11.4%)
275 (54.0%)
176 (34.6%)
0.059


HLA mismatch level (n, %)
Level 1 and 2
Level 3
Level 4

86 (5.0%)
550 (32.3%)
1,069 (62.7%)

54 (4.5%)
394 (32.9%)
748 (62.5%)

32 (6.3%)
156 (30.7%)
321 (63.1%)
0.243


HLA mismatches in the whole cohort, and by induction agent.

Pancreas graft, kidney graft, and patient survival

The unadjusted estimated pancreas, kidney, and patient survival were high over the study period. Pancreas graft survival was 88.6% (95% CI 87.0%–90.0%) at 1-year post-transplant and 72.7% (95% CI 70.1%–75.0%) at 10 years. Kidney graft survival was estimated to be higher with rates of 96.3% (95% CI 95.3%–97.1%) and 76.7% (95% CI 74.2%–79.1%) at 1 and 10 years respectively. Patient survival followed a similar trend, with estimated survival rates of 97.2% (95% CI 96.2%–97.9%) at 1 year, and 75.3% (95% CI 72.6%–77.8%) at 10 years. Most of the graft losses and deaths occurred in the first year following transplantation, with relative stability thereafter.

Predictors of pancreas graft outcome and acute pancreas graft rejection

Unadjusted pancreas graft survival, based on induction agent, is presented in Figure 1, with some evidence to suggest significantly better 10-year survival (p = 0.012) in the Alemtuzumab group (74.6%, 95% CI 71.5%–77.3%) compared to Basiliximab (68.4%, 95% CI 63.6%–72.6%). However, after excluding graft failures that occurred in the first 30 days post-transplant, there was no evidence of a difference in long term pancreas graft survival between the groups, as shown in Supplementary Table S3.

FIGURE 1

Multivariable modelling of predictors of pancreas graft survival at 1- and 10-year post-transplant are presented in Table 3. Several factors were associated with pancreas graft survival at 10-year. Increasing donor age and longer cold ischaemic time were significantly associated with a higher risk of graft failure (p < 0.0001 and p = 0.015 respectively), and older recipient age was associated with a reduced risk of graft failure (p < 0.0001). Donor CMV positivity was associated with increased risk of graft loss when compared to CMV negative donors (HR 1.25, 95% CI 1.02–1.53, p = 0.030). A sensitivity analysis for handling missing data is presented in Supplementary Table S4, comparing the 10-year pancreas graft survival model estimates for the simple imputation cohort and a complete-case cohort, but the pattern of results was similar between the cohorts.

TABLE 3

FactorOne-year pancreas graft failureTen-year pancreas graft failure
HR (95% CI)P-valueHR (95% CI)P-value
Era of transplant0.350.038
 Apr 2007-Mar 2011ReferenceReference
 Apr 2011-Mar 20150.81 (0.56–1.15)0.81 (0.64–1.03)
 Apr 2015-Mar 20190.76 (0.51–1.13)0.70 (0.52–0.93)
Donor type0.140.36
 DBDReferenceReference
 DCD1.33 (0.91–1.93)1.14 (0.87–1.49)
Donor age (years)1.03 (1.01–1.04)<0.00011.02 (1.01–1.03)<0.0001
Donor CMV status0.360.03
 NegativeReferenceReference
 Positive1.14 (0.86–1.53)1.25 (1.02–1.53)
Recipient age (years)0.98 (0.96–1.00)0.0310.97 (0.96–0.98)<0.0001
Recipient blood groupGlobal 0.37Global 0.059
 OReferenceReference
 A1.19 (0.88–1.62)1.16 (0.94–1.43)
 B0.84 (0.49–1.42)0.75 (0.52–1.08)
 AB0.68 (0.25–1.88)0.70 (0.37–1.33)
Sensitisation group0.40.22
 <85%ReferenceReference
 ≥85%0.71 (0.33–1.56)0.72 (0.42–1.22)
Cold ischaemic time (hours)1.07 (1.02–1.13)0.0051.05 (1.01–1.08)0.015
HLA-A mismatchesGlobal 0.5Global 0.65
 0ReferenceReference
 11.30 (0.82–2.06)1.11 (0.81–1.51)
 21.16 (0.69–1.95)1.18 (0.84–1.65)
HLA-B mismatchesGlobal 0.26Global 0.008
 0ReferenceReference
 10.87 (0.44–1.75)1.25 (0.74–2.11)
 20.68 (0.33–1.41)0.89 (0.52–1.53)
HLA-Cw mismatchesGlobal 0.081Global 0.14
 0ReferenceReference
 11.28 (0.77–2.12)1.22 (0.88–1.71)
 21.71 (1.00–2.91)1.42 (0.99–2.03)
HLA-DQ mismatchesGlobal 0.33Global 0.033
 0ReferenceReference
 10.79 (0.57–1.09)0.75 (0.59–0.94)
 20.73 (0.36–1.48)0.94 (0.60–1.47)
HLA-DR mismatchesGlobal 0.76Global 0.52
 0ReferenceReference
 10.97 (0.59–1.61)1.10 (0.76–1.59)
  20.86 (0.48–1.52)0.97 (0.64–1.46)
Induction agent0.930.91
 AlemtuzumabReferenceReference
 Basiliximab0.97 (0.55–1.72)0.98 (0.66–1.45)

Multivariable Cox regression model estimates for predictors of pancreas graft survival at 1- and 10-year post-transplant.

Abbreviations: DBD, donor after brainstem death; DCD, donor after circulatory death; CMV, cytomegalovirus; HLA, human leucocyte antigen; HR, hazard ratio; CI, confidence interval.

Regarding immunological factors, HLA mismatches at most loci were not significantly associated with pancreas graft outcomes. However, one HLA-DQ mismatch was associated with improved long-term pancreas graft survival at 10 years (HR 0.75, 95% CI 0.59–0.94, p = 0.033), compared to zero mismatches. This finding was not observed for two DQ mismatches, however the sample size in this category is small (6.3%) presenting high uncertainty in the true effect. HLA-B mismatch status was identified as a predictor of graft loss at 10-year (global p = 0.008), however the confidence intervals for one and two mismatches crossed 1.0, therefore the true effect remains uncertain. No significant associations were identified for mismatches at HLA-A, -Cw, or -DR. Induction therapy type (Alemtuzumab vs. Basiliximab) was not significantly associated with pancreas graft survival at 10 years when adjusted for other factors.

An interaction term between mismatch at HLA-DQ and induction therapy was included in the multivariable model for 10-year pancreas graft survival to explore effect modification. There was no evidence of effect modification by induction therapy (p = 0.71) (Supplementary Table S5).

After adjusting for confounders, there were no significant associations between HLA mismatches at any locus and pancreas graft survival at 1 year and induction therapy was also not significantly associated with this outcome, as all estimates were consistent with no effect. At 3-month post-transplantation, there was a non-significant difference in the incidence of at least one acute pancreas graft rejection episode when comparing Alemtuzumab with Basiliximab (6.1% vs. 4.0%, p = 0.06). There was no difference when comparing HLA-B mismatch status (p = 0.34) or -DQ status (p = 0.99). Follow-up data for acute rejection rates at 12 months post-transplant was available for 1,544 (91%) patients, and was no difference when comparing Alemtuzumab with Basiliximab (6.8% vs. 7.5%, p = 0.60), HLA-B mismatch status (p = 0.17) or -DQ status (p = 0.30).

Predictors of kidney-graft outcome

Unadjusted kidney graft survival is presented in Figure 2, with no evidence to suggest a difference in 10-year graft survival (p = 0.601) when comparing Alemtuzumab (76.7%, 95% CI 73.6%–79.4%) with Basiliximab (77.0%, 95% CI 72.3%–81.0%). Predictors of kidney graft survival at 1- and 10-year post-transplant are presented in Table 4. Kidney graft survival improved significantly, with the most recent era (2015–2019) associated with the lowest risk of graft failure at 10 years (HR 0.62, 95% CI 0.44–0.87, p = 0.008). Donor age showed a significant non-linear association with graft loss at 10 years (p < 0.0001). Higher donor creatinine at retrieval was associated with increased graft failure risk at 10 years (HR 1.29, 95% CI 1.07–1.56, p = 0.008). Non-white donor ethnicity and female recipient sex were significantly associated with increased risk of graft failure at 10 years (HR 1.52, 95% CI 1.04–2.22, p = 0.031; and HR 1.46, 95% CI 1.16–1.85, p = 0.002, respectively).

FIGURE 2

TABLE 4

FactorOne-year kidney graft failureTen-year kidney graft failure
HR (95% CI)P-valueHR (95% CI)P-value
Era of transplantGlobal 0.0001Global 0.008
 Apr 2007-Mar 2011ReferenceReference
 Apr 2011-Mar 20150.25 (0.12–0.51)0.71 (0.54–0.93)
 Apr 2015-Mar 20190.36 (0.18–0.70)0.62 (0.44–0.87)
Donor type0.40.39
 DBDReferenceReference
 DCD1.35 (0.67–2.71)1.15 (0.84–1.57)
Donor age (years)Fitted as natural cubic spline0.042Fitted as natural cubic spline<0.0001
Donor creatinine at retrieval (µmol/L)1.31 (0.85–2.00)0.221.29 (1.07–1.56)0.008
Donor ethnicity0.920.031
 WhiteReferenceReference
 Other ethnic minority0.95 (0.34–2.69)1.52 (1.04–2.22)
Recipient sex0.870.002
 MaleReferenceReference
 Female0.96 (0.56–1.63)1.46 (1.16–1.85)
Recipient age (years)Fitted as natural cubic spline0.13Fitted as natural cubic spline<0.0001
Recipient dialysis statusGlobal 0.15Global 0.005
 Not on dialysisReferenceReference
 Haemodialysis1.81 (0.99–3.27)1.41 (1.09–1.83)
 Peritoneal dialysis1.48 (0.73–2.99)0.89 (0.64–1.23)
HLA-A mismatchesGlobal 0.5Global 0.75
 0ReferenceReference
 11.60 (0.62–4.15)1.10 (0.77–1.56)
 21.83 (0.67–5.04)1.16 (0.79–1.72)
HLA-B mismatchesGlobal 0.99Global 0.66
 0ReferenceReference
 10.92 (0.25–3.40)0.78 (0.46–1.33)
 20.95 (0.25–3.60)0.80 (0.46–1.39)
HLA-Cw mismatchesGlobal 0.63Global 0.54
 0ReferenceReference
 10.89 (0.38–2.08)0.95 (0.66–1.37)
 21.16 (0.48–2.83)1.10 (0.74–1.62)
HLA-DQ mismatchesGlobal 0.96Global 0.76
 0ReferenceReference
 10.97 (0.53–1.78)0.91 (0.69–1.20)
 20.87 (0.31–2.46)1.00 (0.61–1.63)
HLA-DR mismatchesGlobal 0.34Global 0.057
 0ReferenceReference
 11.17 (0.42–3.32)0.92 (0.59–1.41)
 21.76 (0.58–5.34)1.26 (0.79–2.02)
Induction agent0.80.74
 AlemtuzumabReferenceReference
 Basiliximab0.89 (0.36–2.17)0.92 (0.58–1.48)

Multivariable Cox regression model estimates for predictors of kidney graft survival at 1- and 10-year post-transplant.

Abbreviations: DBD, donor after brainstem death; DCD, donor after circulatory death; HLA, human leucocyte antigen; HR, hazard ratio; CI, confidence interval.

Recipient dialysis modality also impacted outcomes, with haemodialysis (vs. no dialysis) significantly associated with worse kidney graft survival at 10 years (HR 1.41, 95% CI 1.09–1.83; p = 0.005). In contrast, peritoneal dialysis was not associated with excess risk when compared to no dialysis at 10 years (HR 0.89, 95% CI 0.64–1.23).

HLA mismatches at all loci were not significantly associated with kidney graft loss at 10 years, when adjusted for other factors. Similarly, induction therapy had no significant impact on kidney graft survival in adjusted models. The same conclusion was observed for 1-year kidney graft survival, as neither the association with HLA mismatch nor induction therapy was significant after adjusting for other factors.

Predictors of patient mortality

Unadjusted patient mortality is presented in Figure 3, with no evidence to suggest a difference in 10-year patient survival (p = 0.699) when comparing Alemtuzumab (75.5%, 95% CI 72.3%–78.4%) with Basiliximab (75.2%, 95% CI 70.1%–79.5%). Predictors of patient survival at 1- and 10-year post-transplant are presented in Table 5. Increasing recipient age was a predictor of higher mortality risk with significant association at 10 years (HR 1.04, 95% CI 1.02–1.05, p < 0.0001). Cold ischaemic time was significantly associated with increased 1-year mortality (HR 1.13, 95% CI 1.02–1.24, p = 0.020), but not at 10-year. Longer waiting time to transplant also emerged as a significant non-linear predictor of mortality at 1- and 10-year post-transplant (p ≤ 0.033.) Neither transplant era, donor age, donor CMV status, nor dialysis modality were significant predictors of early mortality.

FIGURE 3

TABLE 5

FactorOne-year patient mortalityTen-year patient mortality
HR (95% CI)P-valueHR (95% CI)P-value
Era of transplantGlobal 0.23Global 0.5
 Apr 2007-Mar 2011ReferenceReference
 Apr 2011-Mar 20150.75 (0.37–1.52)0.96 (0.73–1.28)
 Apr 2015-Mar 20190.45 (0.18–1.12)0.81 (0.56–1.17)
Donor age (years)1.01 (0.99–1.03)0.341.01 (1.00–1.02)0.053
Donor CMV0.170.071
 NegativeReferenceReference
 Positive0.65 (0.35–1.20)1.24 (0.98–1.56)
Recipient age (years)1.02 (0.99–1.06)0.251.04 (1.02–1.05)<0.0001
Recipient dialysis statusGlobal 0.77Global 0.033
 Not on dialysisReferenceReference
 Haemodialysis1.27 (0.64–2.53)1.19 (0.92–1.54)
 Peritoneal dialysis1.23 (0.56–2.69)0.76 (0.55–1.07)
Cold ischaemic time (hours)1.13 (1.02–1.24)0.021.01 (0.97–1.05)0.61
Waiting time (years)Fitted as natural cubic spline0.033Fitted as natural cubic spline0.019
HLA-A mismatchesGlobal 0.49Global 0.98
 0ReferenceReference
 10.67 (0.31–1.45)0.99 (0.71–1.38)
 20.59 (0.23–1.47)1.01 (0.70–1.47)
HLA-B mismatchesGlobal 0.73Global 0.95
 0ReferenceReference
 10.64 (0.14–3.02)0.96 (0.52–1.77)
 20.79 (0.17–3.78)1.00 (0.54–1.87)
HLA-Cw mismatchesGlobal 0.5Global 0.32
 0ReferenceReference
 11.94 (0.63–5.95)1.33 (0.90–1.97)
 21.92 (0.59–6.31)1.35 (0.89–2.06)
HLA-DQ mismatchesGlobal 0.7Global 0.79
 0ReferenceReference
 11.37 (0.65–2.91)1.06 (0.80–1.39)
 21.46 (0.40–5.31)0.91 (0.52–1.58)
HLA-DR mismatchesGlobal 0.94Global 0.15
 0ReferenceReference
 10.92 (0.28–3.03)0.68 (0.45–1.02)
 21.03 (0.28–3.78)0.75 (0.47–1.17)
Induction agent0.920.7
 AlemtuzumabReferenceReference
 Basiliximab1.06 (0.34–3.26)1.09 (0.70–1.69)

Multivariable Cox regression model estimates for predictors of patient survival at 1- and 10-year post-transplant.

Abbreviations: CMV, cytomegalovirus; HLA, human leucocyte antigen; HR, hazard ratio; CI, confidence interval.

HLA mismatches at all loci and induction therapy regimen were not significantly associated with patient mortality at either timepoint, when adjusted for other factors.

Discussion

In this large, contemporary national cohort of SPK transplant recipients, we demonstrate excellent long-term outcomes, with 10-year pancreas graft, kidney graft, and patient survival rates exceeding 70%. Our analysis identifies donor age, cold ischaemic time, and donor CMV status as key predictors of pancreas graft failure and further highlights the adverse impact of haemodialysis on long-term kidney graft survival. Crucially, we identified an unexpected association between a single HLA-DQ mismatch and improved long-term pancreas graft survival, a finding not observed for kidney or patient outcomes. In contrast, induction therapy choice between Alemtuzumab and Basiliximab was not significantly associated with differences in graft or patient survival.

The 3C study, comparing Alemtuzumab with Basiliximab induction therapy in renal transplantation, demonstrated that alemtuzumab significantly reduced the risk of biopsy-proven rejection without increasing serious infections []. However, in our study we observed no difference in SPK graft, kidney graft or patient survival on adjusted analyses. This may reflect the distinct immunological challenges of SPK recipients, who may have an alloimmune burden distinct to kidney-only recipients. This also underscores the need for caution in extrapolating induction strategies validated in kidney transplantation to SPK recipients.

The observation that a single HLA-DQ mismatch was associated with improved long-term pancreas graft survival is unexpected and, to our knowledge, has not been previously reported. Although two mismatches were not significantly associated with graft outcome, the overlapping confidence intervals suggests that there is no difference in the effect of two mismatches compared with the effect of a single -DQ mismatch. While class II mismatches, particularly at the DQ locus, have been linked to adverse outcomes in kidney transplantation [, ], including increased risk of donor-specific antibody formation and chronic rejection, such associations have not been well established in SPK recipients. This observation could be specific to the model fitted, and not represent true causality warranting cautious interpretation and is, at best, hypothesis-generating. Additionally, the DQ and B mismatches were not associated with acute rejection, suggesting that any observations associated with outcomes may be due to chance rather than a true effect. Further mechanistic investigation using high-resolution HLA typing, epitope analysis, immune profiling, and validation in other populations may provide further insight into the effects of HLA matching on pancreas graft outcomes.

In a retrospective analysis of 1219 pancreas graft recipients (SPK n = 355), HLA mismatch status was not associated with pancreas graft or patient survival following transplantation [], similar to our results. However, the study reported an increased risk of acute rejection with HLA-B and -DR mismatches with -DQ mismatches having no impact, although this observation was not apparent when SPK graft recipients were examined as a subgroup. These results suggest that the immunological relevance of specific HLA loci may differ by transplant type. These findings suggest that while overall HLA mismatch may not influence long-term outcomes, locus-specific mismatching may contribute to pancreas graft loss through immune mechanisms that are not fully mitigated by standard immunosuppression. This highlights the potential importance of considering HLA matching when evaluating immunological risk, particularly in the context of non-depleting induction strategies, warranting further investigation.

The absence of a clear association between HLA mismatch and kidney graft survival in our cohort may, at least in part, reflect the relatively short cold ischaemia times observed in the UK for SPK grafts. Both HLA mismatch and prolonged cold ischaemia are well-established determinants of kidney graft outcomes, and previous large registry studies have demonstrated that the adverse effect of HLA mismatch is attenuated when cold ischaemia times are short [, ]. In our study, the median cold ischaemia time was substantially lower than in comparable international series, likely diminishing the incremental impact of HLA mismatching on kidney graft survival.

Induction therapy did not significantly impact pancreas graft, kidney graft or patient survival on the adjusted analyses. Although unadjusted analyses suggested slightly improved pancreas graft survival with Alemtuzumab, this effect was not observed in multivariable models. The rates of early acute rejection episodes were also comparable between induction agents. Our findings are in line with a retrospective study [], reporting similar pancreas and kidney graft outcomes between Alemtuzumab and Basiliximab in a large single-centre SPK cohort, though with a higher incidence of CMV infection in Alemtuzumab-treated recipients. More recently, Aziz et al. compared T cell–depleting agents with IL-2 receptor blockade in 417 pancreas transplant recipients and similarly found no difference in graft survival on multivariable analysis []. Importantly, both studies highlighted differences in infection profiles rather than survival, with Aziz et al. also noting increased CMV and bacterial infections in the T cell–depleting group. Taken together with our findings, these data suggest that while induction agent choice does not appear to affect long-term graft or patient survival, the decision should be individualised based on recipient risk profile, infection risk, and centre-specific protocols.

Our findings have several potential implications for clinical practice and transplant policy. The absence of a survival benefit from any specific induction agent supports a more individualised approach to induction therapy. Rather than a uniform preference, the choice between T cell–depleting agents and interleukin-2 receptor antagonists may be better guided by recipient comorbidity, CMV serostatus, and institutional experience. Furthermore, we did not observe a significant reduction in graft or patient survival with locus-specific mismatching warranting specific investigation into the organ-specific effects in larger external cohorts.

This study has several limitations inherent to its retrospective design and use of national registry data. While the dataset is robust and population-based, it lacks granularity in certain key areas, including high-resolution HLA typing, DSA status, maintenance immunosuppression regimens, and biopsy-proven rejection. As such, we were unable to explore mechanistic explanations for the observed DQ mismatch effect or evaluate potential interactions between induction, maintenance therapy, and immunological risk. Additionally, selection bias may influence the choice of induction agent, although our multivariable analyses aimed to adjust for relevant confounders. Finally, while the finding of a protective association with a single DQ mismatch is statistically robust and biologically plausible, it is hypothesis-generating and requires validation in other cohorts with complementary mechanistic data.

This national study demonstrates excellent long-term outcomes following simultaneous pancreas–kidney transplantation and provides new insights into the impact of immunological matching and induction therapy. The absence of significant differences in outcomes by induction agent supports a personalised approach to immunosuppression. Although the associations described are observational, and causality cannot be deterimined in this registry study, these findings highlight the complex interplay between immunogenetic matching and induction therapy in SPK transplantation. Our results emphasise the importance of tailoring immunological risk assessment beyond aggregate mismatch scores.

Statements

Data availability statement

The data analyzed in this study is subject to the following licenses/restrictions: The data is held by NHS Blood and Transplant, and may be available upon reasonable request. Requests to access these datasets should be directed to .

Ethics statement

The requirement of ethical approval was waived by Pancreas Advisory Group, NHS Blood and Transplant for the studies involving humans because Retrospective review of anonymised registry data complying with local legislation. The studies were conducted in accordance with the local legislation and institutional requirements. The ethics committee/institutional review board also waived the requirement of written informed consent for participation from the participants or the participants’ legal guardians/next of kin because Retrospective review of anonymised registry data complying with local legislation.

Author contributions

AM, JB, LS, and SW were responsible for the design of the study. AM, JB, LS, and CC performed the analysis. All authors contributed to the interpretation of the results. AM, JB, LS, ST and SW wrote the first draft. All authors contributed to the article and approved the submitted version.

Funding

The author(s) declared that financial support was received for this work and/or its publication. AM and ST are each supported by Clinical Research Training Fellowships from the Medical Research Council (MRZ50502X/1 and MR/Y000676/1, respectively). This study was supported by the National Institute of Health and Care Research (NIHR) Blood and Transplant Research Unit in Organ Donation and Transplantation (NIHR203332), a partnership between NHS Blood and Transplant, the University of Cambridge, and Newcastle University. The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. The views expressed are those of the authors and not necessarily those of UKRI, MRC, NIHR, NHS Blood and Transplant, or the Department of Health and Social Care.

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontierspartnerships.org/articles/10.3389/ti.2026.16427/full#supplementary-material

Abbreviations

CI, Confidence interval; CMV, Cytomegalovirus; cRF, calculated Reaction frequency; cPRA, calculated Panel-reactive antibody; DCD, Donation after circulatory death; DSA, Donor-specific antibody; HLA, Human leucocyte antigen; HR, Hazard ratio; IQR, Interquartile range; SPK, Simultaneous Pancreas-Kidney Transplantation.

References

Summary

Keywords

graft failure, HLA mismatch, induction agent, outcomes, simultaneous pancreas-kidney transplantation

Citation

Malik AK, Banks J, Counter C, Simmonds L, Tingle SJ, Sinha S, Muthasamy A, Sutherland A, Casey J, Drage M, van Dellen D, Callaghan CJ, Elker D, Manas DM, Pettigrew GJ, Russell N, Sheerin NS, Wilson CH and White SA (2026) Locus-specific HLA matching and induction therapy in simultaneous pancreas–kidney transplantation: a national UK cohort study. Transpl. Int. 39:16427. doi: 10.3389/ti.2026.16427

Received

16 February 2026

Revised

30 July 2026

Accepted

20 August 2026

Published

09 September 2026

Volume

39 - 2026

Updates

Copyright

*Correspondence: Abdullah K. Malik,

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All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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