Impact of pretransplant donor-specific antibodies and human leukocyte antigen mismatches on graft and patient outcomes: A cohort from Saudi Arabia

Abstract

BACKGROUND

Pretransplant donor-specific antibodies (DSA) are frequently encountered in kidney transplant recipients, but their combined effect with human leukocyte antigen (HLA) mismatches on post-transplant outcomes is as yet not fully understood, particularly in Middle Eastern populations.

AIM

To evaluate the effect of pretransplant DSA, HLA mismatches, and early graft function on acute rejection, graft loss, and patient survival, using detailed immunologic profiling and longitudinal follow-up to inform transplant management strategies.

METHODS

We conducted a retrospective study of 260 kidney transplant recipients with available pretransplant HLA typing and DSA assessment. Patients were followed for graft function, acute rejection, graft loss, and mortality. Multivariable logistic regression was used to identify predictors of preformed DSA and acute rejection, and Cox proportional hazards models were applied to evaluate factors associated with a composite outcome of acute rejection, graft loss, or death. Event-free survival was assessed using Kaplan-Meier analysis.

RESULTS

Acute rejection occurred in 10 patients (3.8%). In exploratory multivariable analyses, a higher HLA mismatch burden and suboptimal early graft function at 4 months post-transplant were associated with acute rejection; however, these findings should be interpreted cautiously because of the limited number of events. Pretransplant DSA was present in a subset of patients but was not independently associated with outcomes after adjustment for HLA mismatch and early graft function. A mismatch burden ≥ 7, reduced early graft function, and a history of sensitizing events were associated with a higher risk of the composite outcome. Kaplan-Meier analysis showed significantly lower event-free survival among patients with ≥ 7 HLA mismatches, while reduced early graft function further improved risk discrimination over time.

CONCLUSION

Pretransplant DSA and HLA mismatch burden were both associated with post-transplant outcomes; however, the prognostic signal was largely driven by HLA mismatch and early graft function rather than DSA alone. A mismatch burden ≥ 7 was associated with reduced event-free survival, and early graft function further stratified risk. Induction therapy with antithymocyte globulin may have reduced the clinical impact of preformed DSA in sensitized recipients.

Key Words: Kidney transplantation; Donor-specific antibodies; Human leukocyte antigen mismatch; Acute rejection; Graft function; Middle East

Core Tip: In this large single-center study from the Middle East, pretransplant donor-specific antibodies (DSA) were frequently observed but were not independently associated with rejection or survival after accounting for other factors. Instead, a higher human leukocyte antigen mismatch burden (≥ 7) and poorer early graft function were more closely associated with adverse outcomes. These findings suggest that with current induction strategies, particularly the widespread use of antithymocyte globulin (ATG), the effect of preformed DSA may be less pronounced than traditionally expected. In everyday practice, this highlights the importance of looking beyond antibody status alone and paying closer attention to donor-recipient matching and early graft performance when assessing risk after transplantation. However, the high use of ATG and the relatively short follow-up may have attenuated or delayed the detectable impact of DSA on graft outcomes, particularly late rejection or chronic antibody-mediated injury.

INTRODUCTION

End-stage kidney disease is a significant health problem. Globally, the number of patients requiring renal replacement therapy is currently estimated to range from 4.902 to 9.701 million, predominantly in low- and middle-income countries[1]. Renal replacement therapy is costly, with an annual expense of US$31993.12 for hemodialysis and US$25282.00 for peritoneal dialysis[2]. The 5-year survival of end-stage kidney disease patients, even in developing countries, ranges from 41%-60%, which is significantly lower than that of kidney transplantation[3], which remains the preferred treatment for suitable patients, offering improved survival and quality of life compared with dialysis[4,5].

Despite advances in immunosuppression, long-term graft survival has not improved significantly[6]. Ongoing immunologic injury plays an important role in graft fibrosis[7] but the presence of preformed or de novo donor-specific antibodies (DSA) remains a challenge for transplant physicians, as DSA is a well-established risk factor for antibody-mediated rejection (AMR) and graft failure[8]. Similarly, the degree of human leukocyte antigen (HLA) mismatch influences alloimmune activation and graft outcomes[9]. However, the relative contribution of DSA and HLA mismatch burden in real-world clinical practice, particularly regarding early graft function, remains incompletely understood.

Most large studies examining DSA and HLA mismatches have been conducted in Western[10,11] or Asian[12] populations, which differ in sensitization profiles, immunosuppression protocols, and genetic backgrounds compared with those of Middle Eastern transplant recipients. Several studies from Turkey and Iran have investigated the immunologic landscape, primarily focusing on HLA matching and short-term graft outcomes[13,14]. However, evidence from Arab Middle Eastern countries remains sparse. Previous studies have explored pretransplant DSA and HLA mismatches in small cohorts, with limited data on their impact on graft outcomes[15,16]. In addition, data integrating immunologic risk (DSA and HLA mismatch) with early post-transplant graft function as a combined prognostic framework are limited.

This single-center study, one of the largest from the Arab Middle East region, aims to evaluate the effect of pretransplant DSA, HLA mismatches, and early graft function on acute rejection, graft loss, and patient survival, using detailed immunologic profiling and longitudinal follow-up to inform transplant management strategies.

MATERIALS AND METHODS

Study design, population, and sample selection

This retrospective observational study was conducted at King Fahad Armed Forces Hospital in Jeddah and included patients who underwent transplantation between 2021 and 2024. The institutional ethics review committee approved the study in accordance with the principles outlined in the Declaration of Helsinki. Informed consent was obtained from the study participants or their next of kin.

We included kidney transplant recipients aged 14 years or older who had received a living or deceased donor kidney and had pretransplant immunologic data available, including DSA testing and HLA typing. All these patients were managed under the adult transplant program using uniform immunosuppression protocols. Patients were required to undergo longitudinal follow-up for graft function and post-transplant outcomes, as per standard institutional protocols. We excluded patients who were multi-organ transplant recipients, pediatric patients ≤ 14 years, and patients with missing critical immunologic or outcome data. A total of 260 kidney transplant recipients met the inclusion criteria and were included in the final analysis.

The primary objective of this study was to evaluate the impact of pretransplant DSA on graft function, acute rejection, and post-transplant outcomes in kidney transplant recipients. Secondary objectives included identifying risk factors associated with acute rejection, graft loss, and patient mortality. We also aimed to characterize the immunologic profile and to examine longitudinal trends in renal function by DSA status. In addition, we explored the interaction between HLA mismatch burden, early graft function, and immunologic risk in determining post-transplant outcomes.

Study variables

The primary exposure variable was pretransplant DSA status (positive vs negative). Other variables included recipient and donor characteristics such as age, gender, donor type (living vs deceased), HLA mismatches, and pre-transplant sensitizing events. Induction therapy, maintenance immunosuppression, and antithymocyte globulin (ATG) dose were also recorded.

The primary outcomes were acute rejection, graft function [as measured by serum creatinine and estimated glomerular filtration rate (eGFR) at multiple time points], graft loss, and patient mortality. Secondary outcomes included post-transplant infections, such as cytomegalovirus (CMV) and BK virus (BKV), and longitudinal trends in renal function. A composite outcome of acute rejection, graft loss, or death was also defined for time-to-event analyses.

Immunologic workup, induction and maintenance immunosuppression, and prophylaxis

All potential kidney transplant recipients were screened for HLA antibodies using single-antigen bead assays. ABO compatibility and HLA matching were ensured for all donor-recipient pairs while HLA typing for both donors and recipients was performed using the reverse sequence-specific oligonucleotide method on the Luminex 3D platform (Luminex Corporation, Austin, TX, United States). Genomic DNA was extracted from peripheral blood samples and HLA mismatches were calculated based on donor-recipient differences at six loci: HLA-A, -B, -C, -DR, -DQ, and -DP. Each locus was scored as 0, 1, or 2 mismatches depending on allele differences. The total mismatch score was the sum across all loci, yielding a possible range of 0-12 mismatches. For analysis, HLA mismatch burden was categorized as < 7 vs ≥ 7. All typings were performed at low to intermediate resolution (first-field level). Match grades were assigned based on antigen-level equivalence as routinely reported in clinical laboratories.

Anti-HLA antibody detection and identification were performed using a solid-phase single antigen bead (SAB) assay on the Luminex 3D platform (Luminex Corporation, Austin, TX, United States). DSA were defined as anti-HLA antibodies directed against donor HLA antigens, identified using SAB assays. A positive DSA was defined based on a mean fluorescence intensity (MFI) threshold of ≥ 500, as determined by the manufacturer’s software and laboratory interpretation. All assays included manufacturer-recommended positive and negative controls. For analytical purposes, only DSA with MFI ≥ 500 were included so as to capture clinically relevant sensitization while retaining low-level antibody reactivity. We recognize that MFI thresholds used to define clinically relevant DSA vary across centers and studies. The threshold of ≥ 500 reflects our institutional laboratory reporting practice and was selected to capture the full spectrum of pretransplant sensitization. However, inclusion of low-level antibodies may increase the apparent prevalence of DSA and does not necessarily imply equivalent clinical significance across all antibody strengths. Only the most recent pretransplant serum sample was used for DSA assessment. Panel reactive antibody testing is not performed in our unit.

All recipients underwent Centers for Disease Control (CDC) and flow-cytometry crossmatch prior to transplantation. Patients with pre-transplant DSA were managed using a risk-based induction strategy with ATG alone or in combination with intravenous immunoglobulin (IVIG) and plasmapheresis as needed. Our center predominantly employs ATG as the standard induction therapy in kidney transplantation although basiliximab is used in selected cases, including patients with contraindications to lymphocyte-depleting therapy (e.g., leukopenia or infection risk) or at the discretion of the transplant team in lower-risk recipients. ATG may also be administered to selected low-immunological-risk patients per institutional protocol. Transplants were not performed across a positive CDC crossmatch. Risk stratification considered DSA presence and HLA mismatch burden.

ATG (thymoglobulin) was administered at 1.5 mg/kg per dose for four doses (total 4-6 mg/kg, adjusted for white blood cell and platelet counts), with occasional basiliximab in selected low-risk patients without DSA or leukopenia. Methylprednisolone was given perioperatively and tapered to oral prednisolone. Maintenance therapy included tacrolimus, mycophenolate mofetil (MMF) (500 mg during ATG, increased to 1000 mg twice daily after completion), and prednisolone; cyclosporine was used occasionally based on clinical considerations.

All patients received valganciclovir 450 mg for 3-6 months, depending on CMV serostatus. Pneumocystis jirovecii prophylaxis was provided using cotrimoxazole (trimethoprim-sulfamethoxazole, 80/400 mg once daily) for 12 months. Oral nystatin suspension (100000 units/mL; 1 mL, swished and swallowed four times daily) was given for one month.

Rejection episodes were classified according to Banff criteria in use at the time of biopsy (Banff 2019 or Banff 2022)[17,18].

Clinical follow-up

Patients were followed in the outpatient transplant clinic at regular intervals. Graft function was monitored using serum creatinine and eGFR and kidney biopsies were performed in cases of graft dysfunction. Universal CMV prophylaxis was administered, and no routine post-transplant CMV surveillance was conducted. Screening for BKV was performed using quantitative polymerase chain reaction in blood. Biopsies were performed when graft dysfunction occurred, particularly in the setting of elevated BK viral load, to evaluate for BK virus nephropathy.

Management of rejection episodes

Acute T-cell-mediated rejection (TCMR) was initially treated with intravenous methylprednisolone at 5 mg/kg/day (maximum 500 mg) for three consecutive days. If no response was observed, treatment was extended to five days. Steroid-resistant TCMR was treated with ATG.

AMR was managed with alternate-day plasma exchange combined with IVIG (100 mg/kg after each session) for five sessions. Persistent or resistant AMR was treated with rituximab (375 mg/m²) followed by an additional cycle of plasma exchange and IVIG. Treatment decisions were guided by Banff histological classification and clinical response.

Statistical analysis

Continuous variables were summarized as median and interquartile range (IQR) and categorical variables were expressed as counts and percentages. Univariate comparisons were conducted between groups (e.g., DSA-positive vs DSA-negative recipients, or patients with and without acute rejection). The Mann-Whitney U test was used for continuous variables, and the χ² or Fisher’s exact test was used for categorical variables, as appropriate. Statistical significance was defined as P < 0.05.

A multivariable logistic regression analysis was performed to explore factors associated with acute rejection. Given the limited number of acute rejection events, this analysis was considered exploratory, and the number of covariates included in the model was restricted to minimize overfitting. Therefore, the results of the multivariable analysis should be interpreted with caution and considered hypothesis-generating rather than confirmatory. Adjusted odds ratios (OR) with 95% confidence intervals (CI) were reported.

Longitudinal trends in renal function (eGFR) were evaluated using repeated-measures analyses, comparing trajectories between DSA-positive and DSA-negative recipients. Interaction analyses were performed to assess the combined effect of DSA status, HLA mismatch burden, and early graft function.

Survival analyses for a composite outcome (acute rejection, graft loss, or mortality) were performed using Kaplan-Meier curves, and differences were assessed using the log-rank test. Cox proportional hazards regression was used to identify independent predictors of the composite outcome. Models were adjusted for clinically relevant variables, including HLA mismatches, DSA status, early graft function, ATG dose, sensitizing events, and recipient gender. Hazard ratios (HR) with 95%CI were reported. Model performance was assessed using the concordance index (C-index).

Missing data were handled using listwise deletion. Visualizations of antibody distributions, DSA strength, and individual patient follow-up were generated to complement quantitative analyses. All analyses were conducted using Python (version 3) in a Jupyter Notebook environment. A two-sided P value < 0.05 was considered statistically significant.

RESULTS

Pretransplant DSA distribution and its association with recipient characteristics and graft outcomes

A total of 260 patients were included. The participants were predominantly male recipients (n = 155, 59.6%) and living donors (n = 238, 91.5%), with a median recipient age of 43 years. Preformed DSA was present in 151 (58.1%) patients. ATG-based induction was used in 214 (82.3%), and nearly all patients received tacrolimus, MMF, and prednisone (n = 256, 98.5%) for maintenance immunosuppression.

Clinical outcomes were favorable overall, with low rates of acute rejection (n = 10, 3.8%), graft loss (n = 12, 4.6%), delayed graft function (n = 12, 4.6%), and mortality (n = 8, 3.1%). Median graft function remained stable, with serum creatinine of 89.0 μmol/L and eGFR of 83.0 mL/minute/1.73 m² at one year, which was sustained through two years. Table 1 summarizes baseline characteristics.

Table 1 Baseline characteristics, median (interquartile range).

Variable	Category	n (%)
Recipient gender	Male	155 (59.6)
	Female	105 (40.4)
Donor gender	Male	178 (68.5)
	Female	82 (31.5)
Donor type	Living	238 (91.5)
	Deceased	22 (8.5)
DSA presence	Present	151 (58.1)
	Absent	109 (41.9)
Induction therapy	ATG-based	214 (82.3)
	Basiliximab-based	43 (16.5)
	Mixed	3 (1.2)
Plasma exchange	Yes	8 (3.1)
Sensitizing events	None	243 (93.5)
	Re-transplantation	4 (1.5)
	Pregnancy	10 (3.8)
	Blood Transfusion	3 (1.2)
Maintenance therapy	FK + MMF + Pred	256 (98.5)
	CSA + MMF + Pred	4 (1.5)
Re-transplantation	No	255 (98.5)
	Yes	4 (1.5)
IVIG use	No	165 (63.7)
	Yes	94 (36.3)
Acute rejection	Yes	10 (3.8)
	No	250 (96.2)
Graft loss	Yes	12 (4.6)
	No	248 (95.4)
Delayed graft function	Yes	12 (4.6)
	No	248 (95.4)
Mortality	Yes	8 (3.1)
	No	252 (96.9)
CMV infection	Yes	5 (1.9)
	No	255 (98.1)
BKV infection	Yes	5 (2.1)
	No	234 (97.9)
Variable
Recipient age, years	43.0 [31.0-59.2]
Donor age, years	34.0 [28.0-42.0]
ATG dose, mg/kg	4.0 [4.0-5.0]
Length of stay, days	9.0 [8.0-12.0]
Creatinine - 4 months, µmol/L	92.0 [73.5-113.5]
Creatinine - 1 year, µmol/L	89.0 [73.0-111.0]
Creatinine - 2 years, µmol/L	90.5 [71.2-107.8]
eGFR - 4 months, mL/minute/1.73 m2	80.0 [64.0-94.0]
eGFR - 1 year, mL/minute/1.73 m2	83.0 [66.0-98.0]
eGFR - 2 years, mL/minute/1.73 m2	85.0 [71.5-97.0]

DSA: Donor-specific antibody; ATG: Antithymocyte globulin; FK: Tacrolimus; MMF: Mycophenolate mofetil; Pred: Prednisolone; CSA: Cyclosporine; IVIG: Intravenous immunoglobulin; CMV: Cytomegalovirus; BKV: BK virus; eGFR: Estimated glomerular filtration rate.

Pretransplant DSA were common and frequently involved multiple HLA loci. Anti-HLA-C was the most frequent Class I DSA (n = 50, 32.9%), while anti-HLA-DR was the most common Class II DSA (n = 32, 21.1%). A high proportion of patients demonstrated multi-locus sensitization rather than isolated antibody specificity.

Fourteen patients (9.2%) had both anti-HLA-A and anti-HLA-C, nine (5.9%) had antibodies against all Class I loci (A, B, C), 29 (19.1%) had antibodies against all Class II loci (DR, DQ, DP), and 15 (9.8%) had dual Class II sensitization patterns (e.g., DR + DQ). Overall, 30 patients (19.9%) had Class I DSA only, 50 (33.1%) had Class II DSA only, and 69 (45.7%) had both Class I and Class II DSA, highlighting the high prevalence of dual-class sensitization.

All DSA with MFI ≥ 500 were included in the analysis to ensure capture of clinically relevant low-level sensitization and to reflect the full spectrum of immunologic reactivity within the cohort. This approach was chosen to avoid exclusion of low-intensity antibodies that may represent early or subclinical sensitization, although their clinical significance may vary depending on antibody strength and complement-binding capacity. The Venn diagram (Figure 1) illustrates the distribution and overlap of DSA, while UpSet analysis (Figure 2) confirmed that sensitization most commonly involved multiple HLA loci rather than isolated reactivity.

Figure 1 Venn diagrams illustrating the prevalence and overlap of donor-specific antibodies. A: Distribution of anti-human leukocyte antigen (HLA)-A, -B, and -C antibodies (class I); B: Overlap between Class I and Class II antibodies; C: Distribution of anti-HLA-DR, -DQ, and -DP antibodies (Class II).

Figure 2 UpSet plot showing the distribution of pretransplant human leukocyte antigen antibody class combinations (human leukocyte antigen-A, -B, -C, -DR, -DQ, -DP) among kidney transplant candidates. Each vertical bar quantifies the number of patients with a specific antibody combination.

Longitudinal analysis of graft function (Figure 3) showed no significant differences in eGFR between DSA-positive and DSA-negative recipients at four months, one year, or two years (P > 0.05), suggesting that pretransplant DSA alone did not significantly influence short- to intermediate-term graft function in this cohort.

Figure 3 Longitudinal trends in estimated glomerular filtration rate by donor-specific antibodies status. A: Medians with interquartile ranges; B: Means with standard deviations. Measurements were obtained at 4 months, 1 year, and 2 years post-transplant. DSA: Donor-specific antibodies.

Recipient characteristics differed between groups. DSA-positive recipients were older at transplantation [47.0 (35.0-61.0) vs 38.0 (29.0-58.0) years, P = 0.0121] and had a higher HLA mismatch burden [7.0 (5.0-9.0) vs 5.0 (2.0-7.0), P < 0.001].

DSA-positive patients more frequently received ATG-based induction (96.0% vs 63.3%), whereas basiliximab use was higher in DSA-negative recipients (33.9% vs 4.0%, P < 0.0001). IVIG use was also significantly higher in the DSA-positive group (54.0% vs 11.9%, P < 0.0001).

Although not statistically significant, graft loss showed a numerical increase in DSA-positive recipients (6.6% vs 1.8%, P = 0.0796), while acute rejection rates were comparable between groups (4.6% vs 2.8%, P = 0.5274). Table 2 presents the univariate comparison.

Table 2 Univariate comparison between donor-specific antibody-positive and donor-specific antibody-negative kidney transplant recipients, n (%)/median (interquartile range).

Group and variable	DSA-negative	DSA-positive	Univariate
Recipient
Age	38.0 [29.0-58.0]	47.0 [35.0-61.0]	0.0121
Gender			0.8942
Male	66 (60.6)	89 (58.9)
Female	43 (39.4)	62 (41.1)
Donor
Age	33.0 [28.0-42.0]	34.0 [28.0-41.0]	0.7858
Gender			0.7613
Male	73 (67.0)	105 (69.5)
Female	36 (33.0)	46 (30.5)
Type			0.3038
Living donor	97 (89.0)	141 (93.4)
Deceased donor	12 (11.0)	10 (6.6)
DSA & HLA matching
HLA mismatches	5.0 [2.0-7.0]	7.0 [5.0-9.0]	0.0000
DSA strength			-
< 1000 MFI	-	71 (47.0)
≥ 1000 MFI	-	80 (53.0)
DSA type	-		-
Class I only	-	30 (19.9)
Class II only	-	52 (34.4)
Both	-	69 (45.7)
Number of DSAs		3.0 [1.0-6.0]	-
Cumulative MFI		2145.0 [895.5-4235.0]	-
Treatment & sensitization
ATG dose	4.0 [4.0-5.0]	5.0 [4.0-5.0]	0.1388
Sensitizing events			1.0000
Yes	7 (6.4)	10 (6.6)
No	102 (93.6)	141(93.4)
Induction therapy			0.0000
ATG-based	69 (63.3)	145 (96.0)
Basiliximab-based	37 (33.9)	6 (4.0)
Mixed	3 (2.8)	0 (0.0)
Maintenance therapy			1.0000
FK MMF Pred	107(98.2)	149 (98.7)
CSA MMF Pred	2 (1.8)	2 (1.3)
Diabetes pre-transplant			0.1624
Yes	40 (36.7)	69 (45.7)
No	69 (63.3)	82 (54.3)
Use of IVIG			0.0000
Yes	0 (0)	94 (57.6)
No	96 (100)	69 (42.3)
Previous transplant			0.1429
Yes	0 (0.0)	4 (2.6)
No	108 (100.0)	147 (97.4)
Graft function & outcomes
Acute rejection			0.5274
Yes	3 (2.8)	7 (4.6)
No	106 (97.2)	144 (95.4)
Graft loss			0.0796
Yes	2 (1.8)	10 (6.6)
No	10 (98.2)	141 (93.4)
Delayed graft function			1.0000
Yes	5 (4.6)	7 (4.6)
No	104 (95.4)	144 (95.4)
Death (mortality)			0.1442
Yes	1 (0.9)	7 (4.6)
No	108 (99.1)	144 (95.4)
CMV infection			1.0000
Yes	2 (1.8)	3 (2.0)
No	107 (98.2)	148 (98.0)
BKV infection			0.4066
Yes	1 (1.0)	4 (2.9)
No	98 (99.0)	136 (97.1)
Length of stay (days)	9.0 [8.0-12.0]	9.0 [7.0-12.0]	0.9488
Creatinine - 4 months	91.0 [74.0-110.0]	93.5 [73.2-114.0]	0.8153
Creatinine - 1 year	93.0 [73.5-111.5]	89.0 [73.0-109.0]	0.7218
Creatinine - 2 years	94.0 [72.0-103.0]	88.0 [71.0-110.0]	0.7605
eGFR - 4 months	83.0 [65.0-95.0]	77.5 [64.0-92.5]	0.2258
eGFR - 1 year	83.0 [67.0-97.0]	82.5 [65.0-99.0]	0.8518
eGFR - 2 years	83.0 [72.5-95.8]	86.0 [71.0-97.0]	0.9898

Statistical comparisons were conducted using the Mann-Whitney U test for continuous variables and χ² or Fisher’s exact test for categorical variables, depending on expected cell counts. A P value < 0.05 was considered statistically significant. Analyses were performed using listwise deletion to account for missing data. DSA: Donor-specific antibody; MFI: Mean fluorescence intensity; HLA: Human leukocyte antigen; ATG: Antithymocyte globulin; FK: Tacrolimus; MMF: Mycophenolate mofetil; Pred: Prednisolone; CSA: Cyclosporine; IVIG: Intravenous immunoglobulin; CMV: Cytomegalovirus; BKV: BK virus; eGFR: Estimated glomerular filtration rate.

Multivariable logistic regression identified recipient age and HLA mismatch burden as independent predictors of DSA positivity. Each additional year of age was associated with a small but significant increase in DSA risk (OR: 1.02, 95%CI: 1.01-1.04, P = 0.006). HLA mismatch burden emerged as the strongest predictor, with each additional mismatch increasing odds of DSA positivity by approximately 31% (OR: 1.31, 95%CI: 1.18-1.44, P < 0.001). These findings highlight the dominant role of immunologic disparity in sensitization. Table 3 shows the multivariable logistic regression for factors associated with DSA positivity.

Table 3 Multivariable logistic regression for factors associated with donor-specific antibody positivity.

Predictor	OR	95%CI	P value	Significance
Recipient age	1.02	1.01-1.04	0.009	Significant
HLA mismatches	1.31	1.18-1.44	0.0000	Significant
eGFR < 60 at 4 months	1.70	0.82-3.54	0.156	Not significant
Any sensitizing event	0.68	0.26-1.82	0.448	Not significant

eGFR: Estimated glomerular filtration rate; HLA: Human leukocyte antigen; OR: Odds ratio.

Acute rejection and associated factors

Acute rejection occurred in 10 patients during follow-up, with a median time to first episode of six months (range: 2 weeks-3.5 years). Of these, five were TCMR, two were AMR, and three were mixed TCMR/AMR.

On univariate analysis, higher HLA mismatches (9.0 vs 6.0, P = 0.0048) and prior sensitizing events (30.0% vs 7.2%, P = 0.0378) were associated with acute rejection. In contrast, DSA status, antibody patterns, and induction regimen were not significantly associated with rejection.

Acute rejection was strongly associated with early graft dysfunction, reflected by higher creatinine at four months (136.5 μmol/L vs 92.0 μmol/L, P = 0.0217) and increased graft loss (30.0% vs 3.6%, P = 0.0076). Table 4 summarizes these findings.

Table 4 Univariate analysis of factors associated with acute rejection after kidney transplantation, n (%)/median (interquartile range).

Group and variable	AR-negative	AR-positive	Univariate
Recipient
Age	43.5 [31.2-60.0]	40.0 [30.8-45.2]	0.2584
Recipient gender			0.3243
Male	147 (58.8)	8 (80.0)
Female	103 (41.2)	2 (20.0)
Donor
Donor age	33.5 [28.0-42.0]	34.5 [31.2-36.8]	0.8586
Donor gender			0.7296
Male	172 (68.8)	6 (60.0)
Female	78 (31.2)	4 (40.0)
Donor type			0.5936
Living donor	229 (91.6)	9 (90.0)
Deceased donor	21 (8.4)	1 (10.0)
DSA & HLA matching
HLA mismatches	6.0 [5.0-8.0]	9.0 [7.2-9.0]	0.0048
DSA presence			0.5274
Yes	144 (57.6)	7 (70.0)
No	106 (42.4)	3 (30.0)
DSA strength			1.0000
< 1000 MFI	68 (47.2)	3 (42.9)
≥ 1000 MFI	76 (52.8)	4 (57.1)
DSA type			0.3598
Class I only	29 (20.1)	1 (14.3)
Class II only	51 (35.4)	1 (14.3)
Both	64 (44.4)	5 (71.4)
Number of DSAs	3.0 [2.0-6.0]	1.0 [1.0-2.0]	0.0698
Cumulative MFI	2205.0 [901.2-4195.0]	2010.0 [1191.5-5216.5]	0.9330
Treatment & sensitization
ATG dose	4.0 [4.0-5.0]	4.0 [4.0-6.0]	0.4704
Sensitizing events			0.0378
Yes	15 (6.1)	2 (18.2)
No	234 (93.9)	9 (81.8)
Induction therapy			0.6758
ATG-based	206 (82.4)	8 (80.0)
Basiliximab-based	41 (16.4)	2 (20.0)
Mixed	3 (1.2)	0 (0.0)
Maintenance therapy			1.0000
FK MMF ST	246 (98.4)	10 (100.0)
CSA MMF ST	4 (1.6)	0 (0.0)
Use of IVIG			0.1764
Yes	88 (35.3)	6 (60.0)
No	161 (64.7)	4 (40.0)
Previous transplant			1.0000
Yes	4 (1.6)	0 (0.0)
No	245 (98.4)	10 (100.0)
Pre-transplant diabetes			0.7463
Yes	104 (41.6)	5 (50.0)
No	146 (58.4)	5 (50.0)
Graft function & outcomes
Graft loss			0.0076
Yes	9 (3.6)	3 (30.0)
No	241 (96.4)	7 (70.0)
DGF			0.0716
Yes	10 (4.0)	2 (20.0)
No	240 (96.0)	8 (80.0)
Mortality			0.2725
Yes	7 (2.8)	1 (10.0)
No	243 (97.2)	9 (90.0)
CMV infection			1.0000
Yes	5 (2.0)	0 (0.0)
No	245 (98.0)	10 (100.0)
BKV infection			1.0000
Yes	5 (2.2)	0 (0.0)
No	225 (97.8)	9 (100.0)
Length of stay (days)	9.0 [8.0-12.0]	8.0 [7.0-9.0]	0.1376
Creatinine - 4 months	92.0 [73.0-112.0]	136.5 [106.5-148.0]	0.0217
Creatinine - 1 year	89.0 [73.0-109.0]	122.0 [95.0-126.0]	0.0649
Creatinine - 2 year	89.5 [71.8-104.5]	118.0 [79.2-129.8]	0.2531
eGFR - 4 months	80.0 [64.5-95.0]	57.5 [51.5-87.2]	0.1032
eGFR - 1 year	83.0 [66.8-98.0]	69.0 [62.0-93.0]	0.3210
eGFR - 2 years	85.0 [72.0-97.0]	75.5 [68.8-84.5]	0.4011
Class I antibody profile
Anti-A presence			0.6287
Yes	33 (13.2)	2 (20.0)
No	217 (86.8)	8 (80.0)
Anti-B presence			1.0000
Yes	25 (10.0)	1 (10.0)
No	225 (90.0)	9 (90.0)
Anti-C presence			0.2936
Yes	76 (30.4)	5 (50.0)
No	174 (69.6)	5 (50.0)
Class II antibody profile
Anti-DR presence			0.3975
Yes	80 (32.0)	5 (50.0)
No	170 (68.0)	5 (50.0)
Anti-DP presence			1.0000
Yes	52 (20.8)	2 (20.0)
No	198 (79.2)	8 (80.0)
Anti-DQ presence			0.7317
Yes	67 (26.8)	3 (30.0)
No	183 (73.2)	7 (70.0)

The Mann-Whitney U test was used for continuous variables, and the χ² or Fisher’s exact test was applied for categorical variables, depending on cell sizes. Statistical significance was defined as P < 0.05. AR: Acute rejection; ATG: Antithymocyte globulin; BKV: BK virus; CMV: Cytomegalovirus; CSA: Cyclosporine; DGF: Delayed graft function; DSA: Donor-specific antibody; eGFR: Estimated glomerular filtration rate; FK: Tacrolimus; HLA: Human leukocyte antigen; IQR: Interquartile range; IVIG: Intravenous immunoglobulin; MFI: Mean fluorescence intensity; MMF: Mycophenolate mofetil; OR: Odds ratio; Pred: Prednisolone; ST: Steroid; TCMR: T cell-mediated rejection.

Given the low number of acute rejection events (n = 10), multivariable analysis was considered exploratory. In this context, higher HLA mismatch burden (OR: 1.44, 95%CI: 1.03-2.01, P = 0.0333) and reduced early graft function [eGFR < 60 mL/minute/1.73 m² at four months (OR: 7.75, 95%CI: 1.69-35.63, P = 0.0085)] were associated with acute rejection (Table 5). However, given the limited number of events, these findings are hypothesis-generating and should be interpreted with caution. After adjustment, neither pretransplant DSA nor sensitizing history remained a significant predictor. Tables 6 and 7 show a detailed summary of rejections.

Table 5 Multivariable logistic regression for acute rejection.

Predictor	OR	95%CI	P value	Significance
HLA mismatches	1.44	1.03-2.01	0.0333	Significant
eGFR < 60 at 4 months	7.75	1.69-35.63	0.0085	Significant
Sensitizing events	4.18	0.68-25.64	0.1227	Borderline
ATG dose (mg/kg)	1.36	0.59-3.12	0.4721	Not significant
DSA presence	1.09	0.18-6.48	0.9252	Not significant

The model included five clinically relevant variables: Human leukocyte antigen mismatches (continuous), glomerular filtration rate < 60 at 4 months, sensitizing events prior to transplantation, antithymocyte globulin dose, and donor-specific antibody (DSA) presence. ATG: Antithymocyte globulin; DSA: Donor-specific antibody; eGFR: Estimated glomerular filtration rate; HLA: Human leukocyte antigen; OR: Odds ratio.

Table 6 Kidney transplant rejection summary.

ID.	Tx type	Tx date	Rejection type(s)	Rejection date(s)	Time post-Tx	Banff grade	C4d status	SV40	Primary disease	DSA	HLA mismatch	Class I antibodies	Class II antibodies
29	LRRT	April 26, 2021	Acute AMR	May 12, 2021	2 weeks	-	Inconclusive	Negative	Unknown	Positive	7	AntiC (1091.0)	AntiDR (615)
41	LRRT	June 13, 2021	Acute TCMR/Acute AMR	July 5, 2021/July 19, 2021	3 weeks/1 month	Type IIB	Negative	Negative	Unknown	Positive	11	AntiA (879.0) | AntiC (985.0)	AntiDR (905+561) | AntiDQ (567.0)
47	ERRT	September 20, 2021	Mixed acute TCMR/CAAMR	April 27, 2023/April 8, 2024	1.5 years	Type IB	Positive	Negative	Unknown	Positive	9	AntiC (1290.0)	AntiDQ (720.0)
118	LRRT	September 29, 2022	Acute TCMR	September 18, 2024	2 years	Type IB	Negative	Negative	Unknown	Negative	9	-	-
113	LURT	November 5, 2022	Acute TCMR	November 29, 2022	3 weeks	Type IIB	Negative	Negative	Unknown	Positive	8	AntiB (647.0) | AntiC (3027.0)	AntiDR (1022+699+902) | AntiDP (1227)
161	LRRT	June 12, 2023	Acute TCMR	August 13, 2023	2 months	Borderline	Negative	Negative	Unknown	Positive	9	AntiC (677.0)	-
171	LRRT	July 15, 2023	Acute TCMR	January 25, 2024	6 months	Type IA	Negative	Negative	Unknown	Negative	11	-	-
225	DDRT	May 11, 2024	Acute AMR	June 5, 2024	1 month	-	Focally positive	Not done	FSGS	Positive	9	AntiA (4641.0)	AntiDR (707) | AntiDP (559.0) | AntiDQ (629.0)
44	LRRT	June 28, 2021	Acute TCMR	January 28, 2025	3.5 years	-	Negative	Negative	Lupus Nephritis	Negative	6	-	-
104	LRRT	October 6, 2022	Mixed Acute TCMR/AMR	May 27, 2025	2.5 years	Type IB, ptc 2-3	Negative	Negative	FSGS/SCD	Positive	7	-	AntiDR (616)

AMR: Antibody-mediated rejection; ATG: Antithymocyte globulin; CAAMR: Chronic active antibody-mediated rejection; DSA: Donor-specific antibody; DDRT: Deceased donor renal transplant; eGFR: Estimated glomerular filtration rate; ERRT: Emotionally related renal transplant; FSGS: Focal segmental glomerulosclerosis; HLA: Human leukocyte antigen; IQR: Interquartile range; IVIG: Intravenous immunoglobulin; LRRT: Living related renal transplant; LURT: Living unrelated renal transplant; MFI: Mean fluorescence intensity; MMF: Mycophenolate mofetil; OR: Odds ratio; Pred: Prednisolone; SCD: Sickle cell disease; SV40: Simian virus 40; TCMR: T-cell-mediated rejection.

Table 7 Clinical and immunological profiles by rejection group.

Group	n	Median HLA mismatches	Median LOS	DSA class profile	Median DSA count	Median DSA MFI	Sensitizing events (%)	Graft loss (%)
DSA+ AMR	2	8.0	8.5 days	Both	3.5	4121.0	50.0	0.0
DSA+ mixed	3	9.0	8.0 days	Both, Class II	1.0	2010.0	33.3	100.0
DSA+ TCMR	2	8.5	8.5 days	Both, Class I	1.0	4100.5	50.0	0.0
DSA- TCMR	3	9.0	9.0 days	-	-	-	0.0	0.0

AMR: Antibody-mediated rejection; DSA: Donor-specific antibody; HLA: Human leukocyte antigen; LOS: Length of stay; MFI: Mean fluorescence intensity; TCMR: T cell-mediated rejection.

Composite outcome predictors (Cox regression)

Event counts for the individual components of the composite outcome were acute rejection (n = 10), graft loss (n = 12), and death (n = 8). These events occurred during follow-up in the study cohort. A multivariable Cox proportional hazards model was used to evaluate predictors of the composite outcome (acute rejection, graft loss, or death). HLA mismatch burden ≥ 7 was associated with a significantly increased risk of the composite outcome (HR: 1.95, 95%CI: 1.42-2.66, P < 0.001). Early graft dysfunction (eGFR < 60 at four months) further increased risk (HR: 2.71, 95%CI: 1.52-4.84, P < 0.001). Prior sensitizing events were also independently associated with higher risk (HR: 2.91, 95%CI: 1.22-6.90, P = 0.02). DSA status did not reach statistical significance in the adjusted model. The model demonstrated strong discrimination (C-index = 0.89), indicating good predictive performance for post-transplant outcomes. Table 8 shows the multivariable Cox regression and identifies predictors of the composite outcome.

Table 8 Multivariable Cox regression identifying predictors of the composite outcome.

Predictor	HR	95%CI	P value	Significance
HLA mismatches ≥ 7	1.95	1.42-2.66	< 0.005	Significant
DSA present	1.23	0.84-1.80	0.29	Not significant
eGFR < 60 at 4 months	2.71	1.52-4.84	< 0.005	Significant
ATG dose (mg/kg)	1.24	0.93-1.64	0.14	Borderline
Sensitizing events	2.91	1.22-6.90	0.02	Significant
Gender male (vs female)	1.33	0.92-1.92	0.13	Borderline

Cox proportional hazards model was used to evaluate independent risk factors for a composite outcome comprising acute rejection, graft loss, or patient mortality in a cohort of 260 kidney transplant recipients. Six clinically relevant variables were selected a priori: HLA mismatches (≥ 7), donor-specific antibody presence, estimated glomerular filtration rate at 4 months (glomerular filtration rate < 60), ATG dose, sensitizing events, and recipient gender. ATG: Antithymocyte globulin; DSA: Donor-specific antibody; eGFR: Estimated glomerular filtration rate; HR: Hazard ratio; HLA: Human leukocyte antigen.

Kaplan-Meier analysis of the composite outcome

Kaplan-Meier survival analysis (Figure 4) was performed for the composite endpoint of acute rejection, graft loss, or death. Figure 5 illustrates the distribution of pretransplant donor-specific antibody MFI across HLA loci (A, B, C, DR, DQ, and DP), together with the individual patient follow-up timeline and recorded outcomes, including acute rejection, graft loss, death, and censoring.

Figure 4 Kaplan-Meier survival analysis of post-transplant outcomes. Patients with ≥ 7 human leukocyte antigen mismatches had worse composite event-free survival. No statistically significant survival differences were observed by donor-specific antibodies (DSA) status, although DSA-positive patients showed numerically lower survival. DSA: Donor-specific antibodies; GFR: Glomerular filtration rate.

Figure 5 Distribution of pretransplant donor-specific antibodies mean fluorescence intensity across human leukocyte antigen loci (A, B, C, DR, DQ, DP) and patient follow-up timeline. A: Box plots show locus-specific mean fluorescence intensity values; B: Horizontal timeline plot illustrates individual follow-up duration and outcomes, with markers for death, graft loss, acute rejection, and censoring. HLA: Human leukocyte antigen.

Recipients with ≥ 7 HLA mismatches had significantly worse event-free survival compared with those with fewer mismatches (log-rank P = 0.0336). Reduced eGFR at four months was associated with poorer survival (P = 0.0506). No significant difference in event-free survival was observed between DSA-positive and DSA-negative groups (P = 0.1138), although a numerically lower survival trend was observed in the DSA-positive group.

DISCUSSION

Our cohort is the largest single-center cohort from the Middle East. We identified several pertinent findings, among them being that pretransplant DSA were common and often broad, with frequent dual- and multi-locus sensitization patterns. In addition, anti-HLA-C was found to be the most frequent Class I DSA, and anti-HLA-DR the most frequent Class II DSA. Despite this high immunologic burden, however, pretransplant DSA was not independently associated with short- to intermediate-term graft function or rejection. Instead, HLA mismatch burden and early post-transplant graft dysfunction emerged as the dominant determinants of outcomes. Acute rejection occurred in 3.8% of recipients, predominantly within the first six months, and was independently associated with HLA mismatches and reduced eGFR at four months. Multivariable Cox regression analysis confirmed that HLA mismatch ≥ 7, early graft dysfunction, and prior sensitizing events were significant predictors of a composite outcome (rejection, graft loss, or death), with excellent model discrimination. These findings highlight the central role of immunologic mismatch and early graft performance. In our cohort, however, the impact of pretransplant DSA appeared to be less pronounced. This may have been mitigated by the predominant use of ATG-based induction, administered to more than 80% of recipients, along with IVIG in about one-third of patients. Importantly, although DSA is a well-established immunologic risk factor in kidney transplantation, its effect in the present study should be interpreted in the context of potent induction therapy and relatively low event rates, which may have attenuated its measurable impact on early outcomes. Overall, contemporary induction strategies likely attenuated antibody-mediated risk, shifting outcome determination toward structural immunologic disparity (HLA mismatch) and early graft recovery. This does not imply that DSA lacks clinical relevance, but rather that its effect may be partially modulated by ATG-based immunosuppression and early post-transplant immune control. Moreover, short- to intermediate-term follow-up may not detect the long-term sequelae of DSA. This is particularly relevant for Class II DSA, which have been associated with chronic AMR, progressive allograft injury, and late graft loss. Consequently, the lack of a significant association between pretransplant DSA and clinical outcomes in the present study may reflect the timing of assessment rather than the absence of long-term immunological risk.

Previous studies from the region have provided essential but limited insights into the role of DSA in kidney transplantation. A Turkish cohort of 211 kidney transplant recipients found no significant differences among patients with preformed DSA, non-DSA, or without anti-HLA antibodies in terms of rejection, graft survival, or patient survival[14]. Another smaller single-center study, of 44 cases from Saudi Arabia, highlighted the prevalence of de novo DQ-DSA in AMR[15] whereas a Kuwaiti study of 111 kidney transplants found that pretransplant DSAs with negative CDC crossmatch posed minimal risk when optimized immunosuppression and desensitization protocols were used, with no difference in graft or patient survival over 24 months[16]. In contrast, our study is more extensive, analyzing a larger and more sensitized cohort. We examined a detailed profile of DSA and the factors associated with its development. Induction strategies were incorporated into the analysis and we also discussed how DSA characteristics relate to rejection, graft loss, and mortality. This broader approach offers a more comprehensive and generalizable understanding of DSA-related risks in the Middle Eastern transplant population. Importantly, our findings suggest that, in the era of potent induction therapy, traditional antibody-centric risk models may underestimate the relative contribution of HLA-mismatch burden.

The prevalence of DSA has been reported to be 18%-25%[19-21]. However, we found preformed DSA in 58% of cases, suggesting that our cohort was highly sensitized. This higher prevalence may reflect regional differences, more sensitizing events, and the inclusion of multi-locus and low-level DSAs detected by sensitive single-antigen bead assays. Our cohort showed a broad and heterogeneous DSA profile, with approximately half of the patients harboring both Class I and Class II antibodies with anti-HLA-C and anti-HLA-DR emerging as the most prevalent individual antibodies. Class I antibodies may contribute to acute antibody-mediated injury[22], whereas Class II antibodies are more often associated with chronic graft injury[23]. We also observed frequent multi-locus and overlapping reactivity, indicating a high cumulative alloimmune burden. This supports a model of repeated immune sensitization rather than isolated antibody formation.

We found HLA mismatches and a median age of 47 years as predictors of DSA development with HLA mismatches usually linked to de novo DSA after transplantation. Sensitizing events such as pregnancy, transfusion, or prior transplantation can lead to preformed antibodies[24]. In such patients, a higher mismatch burden increases the likelihood that existing antibodies will become donor-specific. Direct clinical evidence remains limited; however, retransplant studies demonstrate that preformed DSA against repeated mismatches is strongly associated with AMR and poor graft survival[25]. This likely explains the broad DSA profile observed in our cohort. These findings reinforce that antigenic exposure history and mismatch burden act synergistically in shaping pretransplant sensitization.

Immunosenescence usually begins after the sixth decade of life and is associated with reduced immune responsiveness and lower rejection risk[26]. In our cohort, increasing age was associated with DSA, but recipients were relatively young (median 47 years vs 40 years). This suggests that age-related immune decline was not the driver; instead, cumulative sensitizing exposure was more relevant. Thus, even middle-aged recipients can mount strong alloimmune responses.

Despite a highly sensitized cohort, our rejection rate was only 3.8%, compared to the 7.7%-11.3% reported in the literature[27]. This could be attributed to extensive use of ATG induction (82.3%) and IVIG in about one-third of patients. This aligns with prior reports showing that ATG and IVIG reduce the risk of rejection in recipients with low-level preformed DSA[28]. Nearly half of DSA-positive patients had low-level antibodies with MFI < 1000, which are generally associated with modest and often non-significant risk of AMR[29]. However, DSA were analyzed as a binary variable in the present study, and outcomes were not formally stratified according to antibody strength. Therefore, we cannot exclude the possibility that higher-MFI DSA may confer a different level of risk than low-level antibodies. Given the small number of adverse events, meaningful MFI-based subgroup analyses were not feasible. In our analysis, HLA mismatches emerged as a primary predictor of rejection, and rejection episodes were associated with a significant reduction in graft function. These findings indicate that effective immunosuppression may neutralize much of the short-term risk from preformed antibodies, whereas structural mismatch remains unaffected.

Our analysis showed that HLA mismatches, early post-transplant graft dysfunction, and prior sensitizing events were the main predictors of adverse outcomes (acute rejection, graft loss, or mortality). These findings are consistent with previous reports showing that HLA mismatches[30], sensitizing events[31], and early graft function[32] influence long-term outcomes. Kaplan-Meier analysis confirmed worse event-free survival in patients with higher HLA mismatches and lower early eGFR. Preformed DSA did not significantly impact survival, although a trend toward worse outcomes was observed. Notably, early graft function and HLA mismatch burden consistently outweighed baseline immunologic antibody status in predictive strength. These findings emphasize that immunologic compatibility and early graft performance are central determinants of transplant success, even in a highly sensitized population.

Another factor that could have affected our results is that most of our patients received kidneys from living donors, making up over 90% of all transplants. Kidneys from living donors usually have shorter ischemia times[33], fewer cases of delayed graft function[34], and better early graft performance compared to those from deceased donors[35]. These benefits may reduce the impact of ischemia-reperfusion injury and make it less likely that preformed DSA will cause noticeable graft injury. As a result, the positive outcomes seen in DSA-positive recipients in our study may not be due only to immunological reasons, but could also be linked to the advantages of living-donor transplantation. Because of this, our findings should be interpreted carefully when considering transplant programs with more deceased-donor recipients, where the effects of preformed DSA might be stronger.

Our findings highlight the need to balance aggressive induction strategies with careful donor-recipient selection. ATG and IVIG may mitigate early immunologic risk, but HLA mismatches and early graft dysfunction continue to determine long-term outcomes. Therefore, donor selection optimization remains as important as immunosuppressive intensity in modern transplant practice.

A major strength of our study is the large, single-center cohort with detailed immunologic profiling, which allows assessment of the interplay among DSA, HLA mismatch, and induction strategies. Standardized surgical techniques and immunosuppression protocols improved internal consistency, while the predominance of living donors further reduced confounding related to donor quality and ischemia time. Unlike prior regional studies, our data demonstrate that mismatch burden and early graft performance are stronger determinants of outcome than preformed DSA. This supports a paradigm shift toward prioritizing immunologic compatibility over antibody detection alone in risk stratification.

Our study has several limitations. Being a single-center, retrospective study, generalizability is limited. Follow-up was restricted to short- to medium-term outcomes, potentially missing long-term effects. The adverse effects of preformed DSAs, particularly Class II antibodies, are often more pronounced in the late post-transplant period, where they are associated with chronic antibody-mediated injury and progressive graft dysfunction. Therefore, the absence of a significant association between pretransplant DSA and adverse outcomes in our cohort should be interpreted cautiously, as longer follow-up may reveal effects that were not yet clinically apparent at the time of analysis. Variations in induction protocols may have influenced associations. The SAB assay may overestimate the levels of clinically relevant antibodies by detecting non-complement-binding or denatured epitope reactivity. All DSAs, including low MFI (> 500), were included, which may have inflated prevalence estimates. Additionally, causal inference cannot be established, and unmeasured confounders such as adherence and socioeconomic factors may have influenced outcomes. The study did not evaluate HLA locus-specific mismatch effects, Class I vs Class II mismatch stratification, or the impact of DSA strength using MFI-based categories. Because of the limited number of rejection, graft loss, and mortality events, meaningful MFI-stratified analyses were not feasible, and potential differences between low-level and high-level DSA may therefore have been missed. Given the relatively low number of rejection events, the multivariable logistic regression analysis should be interpreted as exploratory and hypothesis-generating rather than confirmatory. Consequently, some clinically relevant associations may not have been detected because of limited statistical power. The cohort comprised 91.5% living-donor transplants, which is unusually high and typically associated with better outcomes and reduced immunological burden. This may have attenuated the observed impact of HLA-DSA on outcomes and limits the generalizability of the findings to settings where deceased-donor transplantation predominates.

CONCLUSION

In conclusion, pretransplant DSA are common in kidney transplant recipients. Higher HLA mismatch burden, lower early post-transplant eGFR, and prior sensitizing events were associated with adverse outcomes. However, given the low number of rejection events, findings from the multivariable acute rejection analysis should be considered exploratory and hypothesis-generating rather than confirmatory. Patients with ≥ 7 HLA mismatches showed reduced event-free survival, whereas pretransplant DSA was not independently associated with survival outcomes in multivariable analysis in this cohort, although this may reflect limited event numbers and lack of long-term follow-up rather than absence of biological effect. These findings highlight the role of HLA mismatch burden, early graft function, and sensitization history in post-transplant risk stratification. However, given the retrospective design, the low number of outcome events, and the potential effects of intensive immunosuppression and the predominance of living donors, the multivariable findings should be interpreted as exploratory and hypothesis-generating. A longer follow-up is needed to clarify the long-term impact of preformed DSA.

ACKNOWLEDGEMENTS

We acknowledge the help of the transplant team involved in the care of these patients.