Having initially targeted $115m in proceeds, the genome sequencing spinout of Stanford has closed its offering at $140m after a full exercise of the overallotment option.

Personalis, a US-based genome sequencing platform for cancer research spun out of Stanford University, has completed a $140m initial public offering on the Nasdaq Global Market.

The spinout had initially targeted $115m in proceeds, but ended up selling more than 9.1 million shares priced at $17 each while convincing underwriters to exercise their overallotment option in full, resulting in an additional 1.18 million shares sold.

Shares opened at $25.01 on Friday, reaching a peak of $31.38 on Monday before closing at $27.80 yesterday, giving Personalis a market cap of more than $860m.

Founded in 2011, Personalis has created a genome sequencing and analytics platform to enable personalised cancer vaccines and immunotherapies.

The spinout’s accuracy and content enhanced (Ace) technology helps biopharmaceutical firms drive immuno-oncological clinical and biomarker discovery programs.

Personalis was co-founded by Euan Ashley, associate professor of medicine, and Russ Altman, professor of bioengineering, genetics and medicine at Stanford University, together with chief executive John West, former CEO of diabetes cell therapy developer ViaCyte.

Michael Snyder, the Stanford Ascherman professor and chair of genetics and director of the Center of Genomics and Personalized Medicine, is also a co-founder, as is Atul Butte, the Priscilla Chan and Mark Zuckerberg distinguished professor at University of California, San Francisco.

Personalis will use the proceeds to bolster its research and development efforts, expand its infrastructure and facilities, hire additional staff and support sales and marketing activities.

Personalis secured $75m in funding ahead of the offering. Lightspeed Venture Partners led a $33m series C round in 2015 that also featured Stanford University, Abingworth, Mohr Davidow Ventrues and assorted angel investors.

Abingworth led a $22m series B round in 2013, with participation from Lightspeed, Mohr Davidow and Wellington Shields, after Stanford, Abingworth, Lightspeed, Mohr Davidow and several private investors had injected $20m in series A capital in 2011.

Stanford University owned a 6.5% stake in Personalis ahead of the IPO, which has been diluted to 5%.

Lightspeed remains the largest shareholder with 21.3% (down from 27.8%), while Abingworth’s 25% stake has dropped to 19.1% and Mohr Davidow Ventures now owns 9.1% (down from 11.9%).

Morgan Stanley, BofA Merrill Lynch and Cowen acted as joint book-running managers for the offering, while Oppenheimer & Co acted as co-manager.