In recent years, immune checkpoint inhibitors (ICIs) have revolutionized cancer treatment. One of the potential therapeutic targets that seems increasingly attractive is LAG-3 (Lymphocyte activation gene 3, CD223), a human protein encoded by the LAG3 gene. LAG-3 can be found on activated T cells, NK cells, B cells and plasmacytoid DCs and serves as a negative regulator of immunity. Inhibition of LAG-3 enhances the antitumor effect of specific CD8+ T cells, which is an observation pursued by several pharmaceutical companies with their products in pre-clinical or early clinical development. Therefore, it is clear there is a need for suitable preclinical models able to accurately reflect the relevant physiological processes to evaluate the safety and efficacy of LAG3-targeted therapeutics.