Westlake Village BioPartners

Investment decisions are made by co-founders and managing directors Beth Seidenberg and Sean Harper. Seidenberg spent 15 years as a general partner at Kleiner Perkins before launching the firm; Harper was previously chief scientific officer at Amgen and head of R&D at Merck. The firm has not publicly named additional managing directors or investment committee members, suggesting a tightly held decision-making structure.

The firm's sourcing advantage stems from its physical location in the Greater Los Angeles area, specifically Westlake Village. This sits adjacent to Thousand Oaks, the global headquarters of Amgen. The density of Amgen alumni and life sciences talent in the region creates a pipeline of new company formation that Westlake Village BioPartners is positioned to access before coastal venture capital firms.

The firm leads or co-leads seed and Series A rounds, with a stated intent to reserve capital for follow-on investments through clinical proof-of-concept. Fund I was $320 million; Fund II, announced in 2022, totaled $450 million. The stage focus is early, but the firm's reserve strategy allows it to maintain meaningful ownership positions as companies advance toward clinical data readouts.

Westlake Village BioPartners operates exclusively as a direct investor, taking equity positions in early-stage life sciences companies. There is no public evidence of fund-of-funds activity, special-purpose vehicles for LP co-investment, or secondary market participation. The firm's model is structured entirely around building and backing new companies from formation through clinical milestones.

Acelyrin, an inflammation-focused biotech, was a named portfolio company of Westlake Village BioPartners. The company priced a $540 million initial public offering in May 2023 (per Reuters, May 2023), which was one of the largest biotech IPOs of that year. Acelyrin's lead asset, izokibep, subsequently missed a Phase 2b/3 endpoint in hidradenitis suppurativa in September 2023, resulting in a significant share price decline.

The firm does not publicly disclose fund-level performance metrics, including internal rates of return, multiples on invested capital, or distributions to paid-in capital. Fund I is sufficiently mature to have returned capital through exits including the Acelyrin IPO, but formal performance data has not been released to media or public filings.

The firm has not publicly communicated a succession plan. Seidenberg and Harper remain the sole named managing directors, and no junior investment partners have been elevated to managing director or added to the firm's leadership filings. For institutional allocators considering a commitment, this concentration of decision-making authority is a due-diligence item.