A T-cell immunostimulatory factor, derived from the soluble form of the lymphocyte-activation gene 3 (LAG-3) protein, with potential antineoplastic activity. Upon administration, alone or in combination with tumor antigens, eftilagimod alpha binds with high affinity to MHC class II molecules expressed by dendritic cells (DC), potentially resulting in DC maturation, DC migration to lymph nodes, enhanced DC cross-presentation of antigens to T cells, and antitumor cytotoxic T cell responses.