Immune checkpoint inhibitor therapy in kidney transplant recipients: Real-world outcomes of antitumor activity and graft rejection risk

Background: Kidney transplant recipients (KTRs) have a markedly elevated risk of aggressive malignancies, yet the use of immune checkpoint inhibitors (ICIs) in this population remains limited by concerns for allograft rejection and the absence of prospective evidence. We evaluated real-world antitumor activity, graft safety, and immunosuppression-related outcomes of ICI therapy in KTRs with advanced cancers. Methods: We retrospectively analyzed 57 KTRs with locally advanced unresectable or metastatic malignancies treated between 2018-2025 at a single tertiary center. Thirty-three received ICIs and 24 received non-ICI systemic therapy. Outcomes included objective response rate (ORR), clinical benefit rate (CBR), progression-free survival (PFS), overall survival from diagnosis (OSd), overall survival from treatment initiation (OSt), acute allograft rejection, and immune-related adverse events (irAEs). Tumor response was assessed by RECIST v1.1. Results: ICI-treated patients achieved higher ORR (40.0% vs 26.1%) and CBR (60.0% vs 33.3%) compared with non-ICI therapy. Median OSd was 35.8 vs 23.3 months, and median PFS was 4.3 vs 3.5 months (both not statistically significant). Median OSt was significantly longer with ICIs (15.1 vs 7.9 months; p=0.012). Acute rejection occurred in 12.1% of ICI-treated patients (3% irreversible) versus 4.2% with systemic therapy; rejection events were heterogeneous in timing (3 weeks-14 months) and largely responsive to pulse-dose corticosteroids. IrAEs occurred in 27.3% of ICI patients, with grade ≥2 events in 12.1%, and no treatment-related deaths. In the cutaneous squamous cell carcinoma (cSCC) subgroup (n=33), ICI therapy produced an ORR of 47.4% and CBR of 63.2%, with trends toward improved survival relative to controls. Conclusions: ICIs produced clinically meaningful antitumor activity in KTRs, particularly in cSCC, with a manageable rate of allograft rejection under carefully tailored immunosuppression. Despite higher historical concerns, irreversible graft loss was uncommon. These findings support the feasibility of ICI therapy in selected transplant recipients and highlight the importance of immunosuppression strategy in balancing antitumor efficacy and graft safety. Prospective, biomarker-integrated studies are needed to define optimal immunosuppression during PD-1 blockade in this high-risk population.