NantWorks LLC, a West L.A. health care and technology company backed by Patrick Soon-Shiong, said last week that its subsidiary has accepted a $125 million investment from private-equity giant Blackstone Group.

But why would a company run by L.A.’s wealthiest man need to take on a partner? After all, that amount is practically pocket change for Soon-Shiong, whose personal fortune is estimated at $8 billion.

In an interview with the Business Journal last week, the biotech entrepreneur said bringing a respected investor like New York’s Blackstone on board increases the visibility and lends legitimacy to his young company. Additionally, it strengthens the company’s expertise since Blackstone directors will join the board.

“They bring a lot of expertise in building and scaling up this type of manufacturing, which is highly capital intensive,” Soon-Shiong said. “This (deal) is a strategic one for us.”

Under the agreement, Blackstone will invest in NantPharma, a West L.A. startup that is developing blood-based therapies and makes specialized ingredients that are sold to other drug companies. NantPharma operates three drug manufacturing and research facilities in other states, and it employs 250 people, including about 50 in Los Angeles.

Blackstone will appoint two of its senior managing directors, Chinh Chu and Anjan Mukherjee, to NantPharma’s board, as well as Arthur Higgins from the firm’s health care group.

Blackstone could not be reached for comment, but said in a statement that it is open to working with Soon-Shiong “both in this exciting venture and in other initiatives.”

It’s the first time that NantWorks, Soon-Shiong’s holding company, has accepted a large outside investment in one of its startups, but it will likely not be the last. Soon-Shiong said at least one other investment is in the works and he is open to other types of partnerships.

Earlier this month, NantWorks announced a joint venture with Malibu toymaker Jakks Pacific Inc. to develop a line of interactive toys using NantWorks’ proprietary image-recognition technology.

Steven Mednick, a startup expert and professor at the USC Marshall School of Business, said creating these partnerships validates the business and could provide access to additional suppliers or customers. What’s more, just because Soon-Shiong could fund the businesses by himself, he might not want to.

“Regardless of how much money you have, you will have a ceiling on your financial appetite for any particular business,” Mednick said. “There are good reasons to bring in others.”