New Insights Into Factors Shaping <scp>CMV</scp> ‐Specific T‐Cell Polyfunctionality After Hematopoietic Cell Transplantation

Polyfunctional cytomegalovirus (CMV)-specific T cells are critical for antiviral immunity in allogeneic hematopoietic cell transplantation (HCT) recipients. However, gaps remain in managing refractory CMV and optimizing virus-specific cellular therapy (VST). We conducted a comparative analysis of how timing and dosing of immunosuppressive agents, including post-transplant cyclophosphamide (PT-Cy), corticosteroids, mycophenolate mofetil (MMF), and calcineurin inhibitors (CNIs), shape CMV-specific T-cell polyfunctionality. CD4⁺ and CD8⁺ T-cell responses (IFN-γ plus ≥ 1 functional marker) were assessed following pp65 stimulation within 100 days post-HCT in the pre- and post-letermovir era. Among 243 patients, 31% exhibited polyfunctional CD4⁺ and CD8⁺ responses. PT-Cy did not significantly impair T-cell functionality. Cyclosporine was associated with higher frequencies of polyfunctional T cells compared to tacrolimus, even at concentrations above the therapeutic range. Intermediate (≥ 0.5 mg/kg) and high-dose (≥ 1 mg/kg) corticosteroids, especially within 2-4 weeks before testing, significantly suppressed T-cell responses, though rapid tapering preserved function. Prolonged administration of MMF (≥ 2000 mg) diminished T-cell polyfunctionality. These findings provide novel insights into the importance of timing and dosing of the immunosuppressive effects of PT-Cy, corticosteroids, MMF and CNIs on CMV-specific immunity. Adjusting immunosuppression in specific time windows may improve the management of refractory CMV infections and optimize VST in HCT recipients.