A soluble LAG-3 protein as an immunopotentiator for therapeutic vaccines: Preclinical evaluation of IMP321

A soluble LAG-3 (CD223) molecule (sLAG-3) is a natural high affinity ligand for MHC class II. It is known to induce maturation of monocyte-derived dendritic cells in vitro and is used as a vaccine adjuvant to induce CD4 Th1 and CD8 T cell responses in vivo. The work presented herein was performed to study the biological activity of a preclinical grade human sLAG-3 protein, called IMP321: (i) binding on murine APC, (ii) induction of dendritic cell maturation, (iii) safety of repeated injections in mice. The results show that IMP321 binds MHC class II+ murine APC, induces the maturation of dendritic cells and is well tolerated either injected alone or as an adjuvant with strongly immunogenic antigens.