Merck KGaA and Pfizer have drafted in Danish group Dako to work on a companion diagnostic for their investigational anti-PD-L1 antibody avelumab.

The three-party agreement is focused on development of CDx to assess PD-L1 protein expression levels in tumour tissue and its microenvironment.

Avelumab is a checkpoint inhibitor that blocks the interaction of PD-L1 with its receptor PD-1, potentially restoring effective anti-tumour T-cell responses and thereby to inhibiting cancer growth.

The drug is being assessed my Pfizer and Merck under a deal allowing up to 20 immuno-oncology clinical development programmes, and entered a Phase III trial earlier this year in patients with non-small cell lung cancer.

An effective test would help determine which patients would most likely respond to treatment.

Financial terms of the deal weren’t disclosed.