Sanofi (SNY) said Thursday it plans to purchase Dren Bio's experimental autoimmune treatment DR-0201 for $600 million.

The deal, which is expected to close in Q2, also includes up to $1.3 billion in milestone-based payments tied to development progress and potential product launches, the company said.

DR-0201 is a bispecific antibody meant to engage myeloid cells and remove B cells, a mechanism believed to help reset the immune system in hard-to-treat autoimmune disorders.

The drug is currently being tested in two phase 1 trials and has shown early signals of effectiveness in both lab and clinical research, Sanofi said.

The company's shares were down almost 0.5% in recent Thursday premarket activity.