The goal of this observational study is to identify risk factors associated with the absence of CMV-specific cellular immune response in low-risk CMV-seropositive kidney transplant recipients in the early post-transplant period. The participant population includes adult CMV-seropositive kidney transplant recipients who did not receive antithymocyte globulin (ATG) induction therapy and underwent QuantiFERON-CMV testing within the first 45 days after transplantation.

The main question it aims to answer is:

- Is it possible to predict which patients will fail to develop a CMV-specific cellular immune response before day 45 post-transplant in the absence of directly available immune assessment techniques?

Researchers will compare patients with reactive QuantiFERON-CMV results to patients with non-reactive or indeterminate results to identify factors associated with the absence of CMV-specific cellular immune response.

Participants will have retrospective clinical and laboratory data collected from medical records.

Study Hypothesis: In the absence of available techniques to assess CMV-specific cellular immunity, it may be possible to predict which patients will fail to develop a CMV-specific cellular immune response before day 45 post-transplant.

Objective:

Primary objective:

• Derivation Cohort: To evaluate the risk factors associated with a non-reactive or indeterminate QF-CMV result before day 45 post-transplant in CMV-seropositive (R⁺) recipients who did not receive ATG prophylaxis.
• Validation Cohort: To validate these risk factors in an independent validation cohort.

Secondary Objectives:

• To confirm whether patients with a non-reactive or indeterminate QF-CMV result before day 45 post-transplant and without ATG induction develop a higher rate of clinically significant CMV infection compared with those with a reactive QF-CMV result during the first 6 months post-transplant.
• To confirm whether these same patients present a higher rate of viral replication during the first 6 months post-transplant.

Study Population: The study will include adult patients (>18 years) who are CMV-seropositive (R⁺), received a kidney transplant during the study period, did not receive ATG prophylaxis, and underwent QF-CMV testing on day 45 post-transplant (with a window period between day 30 and day 60 post-transplant).

Inclusion Criteria:

• Age >18 years
• Kidney or pancreas-kidney transplant recipients with positive CMV serology
• QF-CMV test performed on day 45 post-transplant (window period between day 30 and day 60 post-transplant)
• CMV PCR testing performed at least every two weeks during the first three months post-transplant

Exclusion Criteria:

• HIV-infected patients
• Multivisceral transplant recipients
• Patients scheduled to receive universal prophylaxis despite having a reactive QF-CMV result
• Patients who received ATG induction therapy
• Less than 6 months of post-transplant follow-up

We will conduct a retrospective, observational, multicenter cohort study of CMV-seropositive (R⁺) kidney transplant recipients who did not receive ATG induction, between 1 January, 2019 and 30 April, 2025.