Cytomegalovirus-specific T-cell Reconstitution following Letermovir Prophylaxis after Hematopoietic Cell Transplantation.

Abstract Decreased cytomegalovirus (CMV)-specific immunity after hematopoietic cell transplantation (HCT) is associated with late CMV reactivation and increased mortality. Whether letermovir prophylaxis-associated reduction in viral exposure influences CMV-specific immune reconstitution is unknown. We compared polyfunctional CMV-specific T-cell responses in a prospective cohort of allogeneic HCT recipients who received letermovir to controls who received PCR-guided preemptive therapy prior to the introduction of letermovir. Thirteen-color flow cytometry was used to assess T-cell responses at three months post-HCT following stimulation with CMV immediate early-1 (IE-1) antigen and phosphoprotein 65 (pp65) antigens. Polyfunctionality was characterized by combinatorial polyfunctionality analysis of antigen specific T-cell subsets (COMPASS). Letermovir use and reduction in viral exposure were assessed for their association with CMV-specific T-cell immunity. Polyfunctional T-cell responses to IE-1 and pp65 were decreased in letermovir recipients and remained diminished after adjusting for donor CMV serostatus, absolute lymphocyte count, and steroid use. Among letermovir recipients, greater peak CMV DNAemia and increased viral shedding were associated with stronger CD8+ responses to pp65; whereas CMV shedding rate was associated with greater CD4+ responses to IE-1. In conclusion, our study provides initial evidence that letermovir may delay CMV-specific cellular reconstitution, possibly due to decreased CMV antigen exposure. Evaluating T-cell polyfunctionality may identify patients at risk for late CMV infection after HCT.