Data are lacking for lung evaluation after hematopoietic cell stem transplantation (HSCT) in children under the age of six, as this population cannot be included in respiratory function monitoring protocols.

The RESPPEDHEM cohort included individuals under the age of 18 who underwent HSCT between January 2014 and November 2017. The eligible population for this study consisted of children from the RESPEDHEM cohort, who underwent HSCT before the age of 6, were still alive in October 2023 and had pulmonary function tests (PFTs) performed more than 3 years after HSCT. The primary objective of our multicenter study was to describe long-term PFT outcomes in children who received HSCT before the age of six, as included in the RESPEDDHEM cohort. The secondary objective was to identify clinical, radiological and transplant-related factors associated with abnormal lung function. Pulmonary abnormalities were defined according to the guidelines of the American Thoracic Society (ATS), the European Respiratory Society (ERS), and Global Lung Initiative (GLI).

Among the 40 children, the mean (SD) age at transplantation was 3.7 ± 1.4 years; 50 % had undergone PFT before HSCT. The last follow-up lung function test was performed at 10.2 ± 2.2 years. Twelve individuals (30 %; 95 %CI: 17-47 %) had abnormal lung function at the end of the study, based on the recent ERS/ATS technical standard on interpretive strategies for routine lung function tests. The main anomalies were obstructive defect (n=4) and restrictive defect (n=4).

This study is the first lung function analysis of children undergoing HSCT before the age of six. Abnormalities persist in about one-third of the population, and 42 % of these children were asymptomatic. Therefore, systematic and long-term respiratory monitoring is needed even if the absence of clinical symptoms. However, half of the cohort did not undergo pre-HSCT pulmonary function testing, which limits the ability to attribute abnormalities solely to the transplant.