New emerging targets in cancer immunotherapy: the role of LAG3

The success of immunotherapy in many disease entities is limited to a specific subpopulation of patients. To overcome this problem, dual blockade treatments mainly against cytotoxic T-lymphocyte-associated protein 4 (CTLA4) and programmed cell death receptor (ligand) 1 (PD-(L)1) axis were developed. However, due to high toxicity rates and treatment resistance, alternative pathways and novel strategies were desperately needed. Lymphocyte-associated gene 3 (LAG3) represents an inhibitory receptor, which is mainly found on activated immune cells and involved in the exhaustion of T cells in malignant diseases. Its co-expression with other inhibitory receptors, particularly with PD-1 leads to an extensive research on the blockade of LAG3 and PD-1 in preclinical settings. Interestingly, several in-vivo approaches demonstrated a highly significant clinical benefit under dual blockade, whereas the efficacy was very low in case of single agent targeting. Moreover, human tumour tissues showed co-expression of LAG3 and PD-1 in infiltrated lymphocytes, which again generated a rationale for blocking these both molecules in clinical settings. The ongoing clinical studies mainly use dual blockage of LAG3/PD-1, which demonstrated promising survival benefits and long duration of response rates. The following review focuses on the biological background and rationale of combining LAG3 with other agents and serves as an update on the state of clinical research on LAG3 targeting.