Photo courtesy of Jonathan Azize Photography

Cambridge-based biotech investor Flagship Pioneering has picked Somerville’s Boynton Yards to establish a new life science research cluster, leasing 208,000-square-foot lease for a group of its companies at Leggat McCall Properties’ 101 South St. development.

Tessera Therapeutics, Cellarity and Laronde are among the Flagship platform companies that will take occupancy of the 300,000-square-foot tower, which is scheduled for completion in October. Flagship has an option to lease the remaining 70,000 square feet and another 300,000 square feet in an adjacent master-planned lab complex, Leggat McCall announced. Leggat McCall plans an additional two office-lab buildings in a life science campus totaling 1.3 million square feet.

Flagship has raised more than $4.4 billion over the past two decades and invested more than $1.9 billion in life science companies, including COVID-19 vaccine creator Moderna of Cambridge.

Boston-based Leggat McCall broke ground in 2019 on the speculative project, with $140 million in construction from Bank OKZ, as lab developers look for growth opportunities in the Union Square and Boynton Yards neighborhoods near the Cambridge line.

Union Square master developer US2 received financing from Bank OZK in February for a 194,000-square-foot life science tower along with a 450-unit multifamily building in the first phase of its 2.4 million-square-foot project.

“Flagship’s expansion into Somerville gives a number of our companies the space they need for their critical growth trajectories while remaining close to Flagship’s wider ecosystem of 40-plus companies within Cambridge,” Christine Heenan, senior partner at Flagship Pioneering, said in a statement.