Immunizations and Sample Collection

This animal study was approved by the Local Ethical Committee on Animal Experiments. Chinese rhesus macaques were housed in the Astrid Fagraeus laboratory at Karolinska Institutet according to guidelines of the Association for Assessment and Accreditation of Laboratory Animal Care, and all procedures were performed abiding to the provisions and general guidelines of the Swedish Animal Welfare Agency. Animals were divided into three groups (n = 4/group) receiving H10 mRNA/LNP (50 µg) either by IM or ID delivery or H10 mRNA/LNP co-formulated with GLA adjuvant (5 µg) delivered IM. Prime and boost immunizations were delivered at week 0 and 4, respectively. Animals receiving H10 mRNA/LNP with GLA received an additional boost at week 15. The animals were sedated with ketamine 10–15 mg/kg given IM (Ketaminol 100 mg/ml, Intervet, Sweden) during the immunizations, blood and bone marrow sampling. Bone marrow was sampled before immunization and at 2, 6, and 25 weeks from the humerus as previously described (22).

An axillary LN was collected before vaccination, opposite from the planned vaccination site, and a collateral axillary LN after boost. The animals were anesthetized by IM injection of 10–15 mg/kg of ketamine and 0.05 mg/kg of medetomidine. Carprofen (4 mg/kg) was given IM as analgesia. LNs were removed in an aseptic manner using minimal entry holes with the aim of removing a singular LN in each procedure. The anesthesia was reversed with atipamezole, 0.25 mg/kg IM after suturing.