Anti-metabolite chemotherapy increases LAG-3 expressing tumor-infiltrating lymphocytes which can be targeted by combination immune checkpoint blockade.

Background: Antibodies that target immune checkpoints such as cytotoxic T lymphocyte antigen 4 (CTLA-4), programmed cell death protein/ligand 1 (PD-1/PD-L1) are approved for treatment of multiple cancer types. Chemotherapy is often administered with immune checkpoint blockade (ICB) therapies that target CTLA-4 and/or PD-(L)1. ICB targeting other immune checkpoints such as lymphocyte activating gene-3 (LAG-3) has the potential to improve antitumor responses when combined with chemotherapy. Response to anti-PD-1 ICB is dependent on progenitor exhausted CD8 T cells (T) in the tumor, but it is unclear how chemotherapy alters T proportions and phenotype.

Methods: Here we investigated whether sequential chemotherapy altered T frequency and immune checkpoint expression in multiple murine tumor models.

Results: Two doses of two different anti-metabolite chemotherapies increased tumor infiltrating CD4, and CD8 T expressing LAG-3 in multiple mouse models, which was not restricted to tumor antigen specific CD8 T cells. To determine if LAG-3tumor infiltrating lymphocytes (TILs) could be targeted to improve tumor control, we administered anti-LAG-3 and anti-PD-1 ICB after two doses of chemotherapy and found combination therapy generated robust antitumor responses compared with each agent alone. Both anti-LAG-3 and anti-PD-1 ICB with chemotherapy were required for the complete tumor regression observed.

Conclusions: Changes in immune checkpoint expression on TILs during chemotherapy administration informs selection of ICB therapies to combine with.