The Lymphatic Immune Response Induced by the Adjuvant AS01: A Comparison of Intramuscular and Subcutaneous Immunization Routes.

The liposome-based adjuvant AS01 incorporates two immune stimulants, 3-O-desacyl-4'-monophosphoryl lipid A and the saponin QS-21. AS01 is under investigation for use in several vaccines in clinical development. i.m. injection of AS01 enhances immune cell activation and dendritic cell (DC) Ag presentation in the local muscle-draining lymph node. However, cellular and Ag trafficking in the lymphatic vessels that connect an i.m. injection site with the local lymph node has not been investigated. The objectives of this study were: 1) to quantify the in vivo cellular immune response induced by AS01 in an outbred ovine model, 2) to develop a lymphatic cannulation model that directly collects lymphatic fluid draining the muscle, and 3) to investigate the function of immune cells entering and exiting the lymphatic compartments after s.c. or i.m. vaccination with AS01 administered with hepatitis B surface Ag (HBsAg). We show that HBsAg-AS01 induces a distinct immunogenic cellular signature within the blood and draining lymphatics following both immunization routes. We reveal that MHCII(high) migratory DCs, neutrophils, and monocytes can acquire Ag within muscle and s.c. afferent lymph, and that HBsAg-AS01 uniquely induces the selective migration of Ag-positive neutrophils, monocytes, and an MHCII(high) DC-like cell type out of the lymph node via the efferent lymphatics that may enhance Ag-specific immunity. We report the characterization of the immune response in the lymphatic network after i.m. and s.c. injection of a clinically relevant vaccine, all in real time using a dose and volume comparable with that administered in humans.