Real-life use of letermovir in paediatric recipients of haematopoietic stem cell transplant (HSCT) is generally safe and prevents the development of cytomegalovirus (CMV) disease, as shown in a study presented at ESPID 2026.
“In this large real-world multicentre cohort, letermovir demonstrated a favourable safety profile and was associated with low rates of CMV disease in paediatric HSCT recipients,” said lead study author Dr Cristina Rivera Perez, Hospital Sant Joan de Déu Bacelona, Oncology and HSCT Unit, Barcelona, Spain.
Perez and her team conducted this retrospective, observational, multicentric study from August 2020 to December 2024 in six hospitals in Spain. They assessed the safety and outcomes of letermovir use in 144 seropositive children (mean age 10.6 years, 60 percent male) undergoing HSCT.
Of the patients, 108 (75 percent) used letermovir as primary prophylaxis, initiated on day 0, 1, or 5 post-transplant, with a median duration of 132 days. Thirty-six patients (25 percent) were administered letermovir as secondary prophylaxis, with a median duration of 135 days. [ESPID 2026, abstract OP-062]
More than half of the paediatric HSCT recipients (n=82, 57 percent) developed acute graft-versus-host disease (grade I: 27; grade II: 24; grade III: 16; grade IV: 15).
Notably, 37 patients (26 percent) had CMV reactivation, but only three (2 percent) had CMV disease (two gastrointestinal grade 4 and one pulmonary grade 5). Among those with CMV reactivation, 25 were administered letermovir as primary prophylaxis and 12 (33 percent) as secondary prophylaxis.
Furthermore, 51 paediatric and young adult patients (35.4 percent) experienced CMV blips during treatment with letermovir. CMV blips were characterized by viral brief and self-limited replication <1,000 IU/mL with no clinically relevant reactivation.
With regard to safety, eight HSCT recipients (5.5 percent) experienced adverse events potentially related to letermovir use, and these events were predominantly mild gastrointestinal symptoms (grade 1 or 2).
“These findings support the use of letermovir as an effective and well-tolerated CMV prophylactic strategy in this population,” Perez and colleagues said.
Transplant characteristics
More than half of the patients underwent HSCT due to acute leukaemia (n=84, 58.3 percent), followed by inborn errors of immunity (n=19, 13.2 percent) and aplastic anaemia (n=15, 10.4 percent). Other indications were constitutional bone marrow failure syndromes, haemoglobinopathies, myelodysplastic syndrome, lymphoma, inborn errors of metabolism, eosinophilic syndrome, and telomeropathy.
Stem cells used in the transplant were mostly derived from the peripheral blood (n=79, 54.9 percent) and bone marrow (n=60, 41.7 percent), while the rest were sourced from cord blood (n=5, 3.5 percent).
Donor types were primarily haploidentical (n=60, 41.7 percent), followed by matched unrelated (n=34, 23.6 percent), mismatched unrelated (n=29, 20.1 percent), matched related (n=19, 13.2 percent), and mismatched related (n=2, 1.4 percent).
In terms of conditioning intensity, 103 patients (71.5 percent) had myeloablative, 19 (13.2 percent) non-myeloablative, and 22 (15.3 percent) reduced intensity.
“CMV may cause severe and potentially life-threatening complications following HSCT,” according to Perez and colleagues.
“Letermovir is an antiviral approved for CMV prophylaxis after HSCT and has recently been approved for use in the paediatric population,” they added.