REGN3767 is an immune checkpoint inhibitor that Regeneron Pharmaceuticals and Sanofi are developing as a treatment for both solid tumors and blood cancers.

How REGN3767 works

The immune system destroys infected or abnormal cells, including cancer cells, by activating specialized T-cells.

Several immune system checkpoints are in place to turn off an immune response so that T-cells don’t accidentally attack healthy tissue, however. This can lead to T-cells being inactivated before they can rein in a tumor.

Immunotherapies like REGN3767 turn off immune system checkpoints. This boosts immune response, increasing the body’s ability to fight cancer.

Regeneron and Sanofi designed REGN3767 to interact with an immune checkpoint protein called LAG-3 — for lymphocyte activation gene 3. LAG-3 is found on the surface of activated T-cells. Its interaction with MHC class 2 proteins turns off T-cells’ cell-killing ability and prevents them from multiplying. This leads to a buildup of inactivated T-cells around a tumor, further reducing immune response.

By binding to LAG-3, REGN3767 blocks its ability to interact with MHC class 2 proteins. This prevents LAG-3 from inactivating T-cells. The result is an increase in the number of T-cells capable of killing cancer cells, reducing tumor growth.

REGN3767 in clinical trials

Regeneron is recruiting people for a Phase 1 clinical trial (NCT03005782) of REGN3767’s ability to fight advanced cases of cancer. The trial will test REGN3767 by itself and in combination with REGN2810, a monoclonal antibody that targets the immune checkpoint protein PD-1.

The study will consist of a dose escalation stage and a dose expansion stage. The escalation stage will determine the dose used in the expansion stage.

Regeneron said the primary objective of the dose expansion stage is to obtain a preliminary assessment of REGN3767’s ability to fight cancer, either alone or combined with REGN2810. The effectiveness yardstick that researchers will use is objective response rate, or the percentage of patients who respond either fully or partially to treatment. The team will use RECIST 1.1 criteria to determine the response rate for solid tumors and Lugano criteria to determine it for blood cancers known as lymphomas.

In addition to response rate, researchers will look at how long REGN3767 alone, or in combination with REGN2810, stays in and acts on the body.

Regeneron hopes to recruit 283 participants for the trial in Texas and Michigan, and to  complete the study by July 2020.


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