Cytomegalovirus (CMV) reactivation is a common and serious complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT), and the reconstitution of CMV-specific cell-mediated immunity (CMV-CMI) plays a key role in viral control.

This prospective, exploratory study will enroll 40 adult CMV-seropositive patients who experience their first CMV reactivation after allo-HSCT. CMV-specific T cell levels (IFN-γ-producing T cells stimulated by IE-1 and pp65 antigens) will be measured using ELISPOT at four time points: at diagnosis of CMV viremia, 3 weeks after initiating preemptive therapy, at anti-CMV drug withdrawal, and 4 weeks after treatment discontinuation. Patients will be followed for 12 weeks after stopping treatment.

The primary objective is to describe the changes in CMV-specific T cell levels over the therapy. Secondary objectives are to explore the relationship between these levels and the occurrence of refractory CMV infection, recurrent CMV infection, and CMV disease. Findings may help identify patients at high risk of progressing to severe or persistent CMV infection at an early stage of preemptive therapy, enabling personalized intervention strategies.

Inclusion Criteria:

1. ≥18 years old and underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT);
2. First CMV reactivation after transplantation;
3. Life expectancy of ≥8 weeks;
4. The participant (or legally acceptable representative, if applicable) has provided written informed consent for the trial.

Exclusion Criteria:

1. Recurrence of CMV infection;
2. primary CMV infection in CMV-seronegative recipients (R-);
3. Resistance to known anti-CMV drugs (ganciclovir, valganciclovir, foscarnet, maribavir, etc.);
4. Currently receiving CMV-CTL treatment or lymphocyte infusion.

The study population consists of CMV-seropositive adults (≥18 years of age) who have undergone allogeneic hematopoietic stem cell transplantation (allo-HSCT) and experience their first CMV reactivation after transplantation.

De-identified individual participant data (IPD) for the primary and secondary outcome measures will be made available upon reasonable request to the principal investigator. Data will be shared after publication of the primary study results, for research purposes only, under a data transfer agreement that ensures compliance with ethical and confidentiality requirements. Supporting documents (study protocol, statistical analysis plan, and informed consent form) will be available as supplementary files.