Compugen study identifies key TIGIT family immune checkpoint pair

Antibodies blocking the PVRIG/PVLRL2 interaction now in pre-clinical development

Leading predictive drug discovery company Compugen presented exciting results from their immune checkpoint program at the 2016 Annual Meeting of the Society for the Immunotherapy of Cancer (SITC) conference in National Harbor, MD. The presentation focused on the in silico discovery of PVRIG, its functional characterisation as a novel immune checkpoint, the identification– using the Retrogenix technology – of PVRL2 as a PVRIG binding partner and the subsequent investigation of a novel immunotherapy strategy via antibody blockade.

 

Identifying immune checkpoint receptors using the Retrogenix technology

Following Compugen’s identification and confirmation of PVRIG as a novel immune checkpoint on T cells, the Retrogenix cell microarray technology was used to screen for human cell surface binding partners. Scientists at Retrogenix were blinded to the identity of the test ligand and had no knowledge of any putative receptor targets prior to the study.

Background screen

A PVRIG Fc-fusion protein was supplied to Retrogenix and applied to slides of fixed untransfected HEK293 cells at various doses to assess the levels of background binding. Binding was detected using an AlexaFluor647-labelled anti Fc antibody and the dose with the most favourable background level was selected for full screening.

Primary screen

Over 4,500 expression vectors, each encoding an individual full-length human plasma membrane protein, were arrayed in duplicate across 13 specialised microarray slides. Expression vectors that act as transfection controls were also spotted. Human HEK293 cells grown over the slides were reverse transfected resulting in distinct clusters of cells, each over-expressing an individual plasma membrane protein.

PVRIG-Fc was applied to all 13 slide sets in duplicate and binding was detected.

Confirmation screen

Vectors encoding all the hits identified in one or both of the two primary screens were sequenced to double-check their identities. These were then respotted on fresh slides and expressed in HEK cells, along with appropriate positive and negative controls. PVRIG-Fc was again applied to the arrays and binding detected to confirm the specificity and reproducibility of the hits (Figure 1). The study identified PVRL2 as a specific cell surface binding partner for PVRIG. The results were returned to Compugen as part of a full data package.

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Impact

The work on PVRIG undertaken by Compugen, along with their colleagues at Johns Hopkins University, has presented a new opportunity for the development of cancer immunotherapy treatments including the potential for drug combination with current immune checkpoint blockers. The group noted that binding of PVRIG to PVRL2 is of particular therapeutic interest as it links PVRIG to the axis of a second immune checkpoint, TIGIT, which is gaining traction in the field of immuno-oncology.

The abstract for the oral presentation has been published in the Journal for the Immunotherapy of Cancer and is entitled “Computational identification, functional characterization, and antibody blockade of a new immune checkpoint in the TIGIT family of interacting molecules”.

 

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