A Kendall Square biopharmaceutical company will move next year into a new headquarters at Alexandria Real Estate Equities' massive new Watertown campus.

Constellation Pharmaceuticals signed a 10-year lease with Alexandria for 79K SF at 100 Talcott Ave. beginning next December, it disclosed in a Securities and Exchange Commission filing this week. Constellation, which works on novel therapeutics including myelofibrosis cancer research, currently leases 35K SF at 215 First St. in Cambridge's Kendall Square from Alexandria, it said in a separate SEC filing.

Representatives for Alexandria didn't respond to calls for comment. While 100 Talcott Ave. was not listed in South Middlesex County public land records, the site is part of the 11-building, 1M SF campus the life sciences real estate investment trust purchased for $526M from Athenahealth last year.

Constellation will pay a base rent of $70.98 per SF in Watertown, escalating 3% each year, for a total expected base rent cost of $64.4M. It paid a base rent of $65 per SF at 215 First St. per a lease amendment filed with the SEC in 2018.

Alexandria frees Constellation's Kendall Square space next fall as current lab vacancy in East Cambridge sits at just 1.1% and average rents are $104.93, according to a Q3 2020 lab report by CBRE.

Constellation CEO Jigar Raythatha said in a statement the benefits of relocating to Watertown include close proximity to Cambridge and Boston and the ability for expansion.

“As Constellation enters its next phase of growth to support the development of CPI-0610, our lead candidate for the treatment of myelofibrosis and a pipeline of other earlier staged oncology targeted therapies, we are excited with our new expanded footprint in Watertown,” Raythatha said.

Alexandria has a massive footprint across Watertown, Cambridge and Boston, including near its Watertown campus, a 141K office and lab building at 480 Arsenal St.

Last month, Alexandria scooped up two Seaport plots on E Street for a combined $168M, and it is also planning a 12-story, 316K SF life sciences facility with National Development at General Electric property in the Seaport’s Fort Point neighborhood. On nearby A Street in the Seaport, ARE is also planning a six-story, 99K SF building in a joint venture with Anchor Line Partners.