In accordance with the PNG national expanded Ivacaftor manufacturer program on immunisation, all study children received BCG (birth); oral polio vaccine (neonatal, 1, 2 and 3 months), Hepatitis B (neonatal, 1 and 3 months), a combined Haemophilus influenzae type b, diphtheria, tetanus, whole cell pertussis vaccine (TETRActHib) (1, 2 and 3 months), and measles vaccine (6 and 9 months). A data safety monitoring board (DSMB) was established and was immediately advised of any serious adverse events

and of all adverse events 3-monthly. This trial is registered at ClinicalTrials.gov under registration number NCT00219401 (http://clinicaltrials.gov/ct2/show/NCT00219401). Assent was sought from women and check details their partners at the time of recruitment. Written informed consent was obtained after delivery and before enrolment of the newborn child. Ethical approval was obtained from the PNG Medical Research Advisory Committee and the Princess Margaret Hospital Ethics Committee in Perth, Australia. At 3 and 9 months of

age, venous blood samples (1–2.5 ml) were collected into empty 2-ml tubes (serum) and 10-ml sterile tubes containing 100 IU preservative-free heparin (PBMC). Samples were centrifuged within 2 h to separate serum/plasma and aliquots were stored at −20 °C. PBMC were isolated from the remaining heparin tube cell pellet by centrifugation over a Ficoll-Hypaque gradient (Lymphoprep, Alexis-Shield, Oslo, Norway) and cryo-preserved in 50% heat-inactivated (HI) foetal calf serum (FCS) and 7.5% DMSO. Cells were kept under liquid nitrogen vapour phase conditions during storage at IMR, transport to and storage at the Telethon Institute of Child Health Research (ICHR). PBMC were cultured in duplicate in 96-wells plates (1 × 106 cells/ml) MTMR9 in medium (RPMI/5% HI-inactivated human AB serum) (Pharmacia Australia Pty. Ltd., Sydney, Australia) or stimulated with CRM197 (kindly provided by former Wyeth Pharmaceuticals, USA) (2.5 μg/ml), Tetanus Toxoid (TT; CSL, Victoria,

Australia) (0.5 lf/ml), measles lysate (kindly provided by Steven Wesselingh and Diane Webster, Macfarlane Burnet Institute for Medical Research, Melbourne, Australia) (4 × 105 particles/ml) and phytohemagglutinin (PHA; Remel Europe Ltd., Kent, UK) (positive control, 1 μg/ml). Supernatants were collected after 96 h (48 h for PHA). Due to low blood volumes, sufficient PBMC for in vitro CRM197 experiments (including negative and positive controls) were available for 198 children at 3 months (neonatal 68; infant 68; control 62) [18] and 222 children at 9 months (neonatal 74; infant 76; control 72); 132 children (neonatal 48; infant 46; control 38) had in vitro CRM197 data available for both time points.