Sean Harper and Beth Seidenberg add $500M to their new VC, betting on the LA biotech ecosystem

When Arsenal Bio launched last year, the headline name was Napster billionaire Sean Parker, who, after funding an immunotherapy institute, decided to back a bold bet on cell therapy 2.0.

The first investor named on the press release for Arsenal’s $85 million launch, though, wasn’t Parker; it was Westlake Village Biopartners, an LA-based VC firm founded just the year prior by longtime Amgen R&D chief Sean Harper and the longtime life sciences chief at the legendary Silicon Valley firm Kleiner Perkins, Beth Seidenberg.

Arsenal marked Westlake’s first public investment, and while 8 of the 11 companies they’ve backed remain under wraps, the duo has already raised a new fund — two, actually. One fund, worth $430 million, will continue their original goal, allowing them to back about a dozen early-stage startups. Another, worth $70 million, will let the firm join Series B and other mid-rounds for the companies they helped launch.

The new funds bring Westlake to $820 million in capital in the two-plus years since their launch. They had always intended to raise the second fund. The third, they said, arose out of some strong suggestions they received as they were fundraising.

“Our limited partners were looking at my returns for my [Kleiner Perkins] biotech companies and said, ‘Beth, do you know how much money you left on the table?’” Seidenberg told Endpoints News.

So far, the companies they’ve announced have focused on high profile cell therapy efforts. In addition to Arsenal, they also backed TMunity, a Carl June-founded effort to use CRISPR to engineer CAR-Ts. And they invested in Kyverna Therapeutics, Jeffrey Bluestone’s effort to use cell therapy for auto-immune and neurodegenerative conditions.

Harper, though, says that amounts to a sampling error, as most of the companies they’ve backed remain in stealth mode.

“We have cell-based therapies, gene therapies, small molecules and antibodies,” he told Endpoints. “We’re pretty agnostic in the modality and we’re pretty opportunistic and broad in the disease areas we’re working in.”

The duo said they look for one of three things to build a biotech around, bringing to each firsthand technical knowledge of early drug development: A proven collection of drug discovery veterans, to whom they can provide money and lab space and let them do their thing; a promising technology coming out of the university level; or shelved drugs in other companies that they can offer a focused development.

The fund’s latest company, also announced Tuesday, amounts to a heavy bet on the first model.

Known as Acelyrin, the company so far consists only of Shao-Lee Lin and Bob Carey, the former R&D chief and CBO of Horizon Therapeutics, respectively.  The plan, they say, is to partner and license assets in immunology, but they haven’t disclosed what assets or intellectual property they have — or even if they have licensed any intellectual property. They also haven’t disclosed the size of the Series A, if they have lab space, or if they have any other employees.

Harper notes, though, that the duo has succeeded before, building Horizon’s pipeline, including a handful of approved immunology drugs. And Lin says they can offer future partners a unique acumen and experience.

“There’s a lot of funding out there,” she told Endpoints. “The gap we believe we feel, is that in addition to the access to capital, we believe we bring expertise to the table. We have track records of building multi-billion dollar therapeutics.”