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NEW YORK, New York — OrbiMed Advisors, which has invested in Ohio companies Athersys Inc. and ViewRay, has raised $550 million for its latest health venture capital fund.

The company’s Caduceus Private Investments IV fund will be its largest-ever, surpassing its predecessor by $20 million, VentureWire reported.

OrbiMed plans to invest 60 percent of the fund in biotechnology, 30 percent in medical devices and 10 percent in diagnostics, and will back a total of 25 to 30 companies, according to VentureWire.

Last year, OrbiMed led a $25 million Series B round for Oakwood-based ViewRay, which is developing a device that uses MRIs to guide gamma rays to target cancerous tumors. OrbiMed lists Cleveland-based stem cell developer Athersys as one of its portfolio companies and OrbiMed General Partner Michael Sheffery sits on Athersys’ board.

Along with Frazier Healthcare Ventures‘ $600 million sixth fund and Essex Woodlands Health Ventures‘ $900 million eighth fund, OrbiMed’s latest fund is among the largest health care-only venture funds, VentureWire reported.

OrbiMed is headquartered in New York with offices in San Francisco, Shanghai and Mumbai.

A string of successful exits helped draw investors to OrbiMed’s latest fund, VentureWire said. Those exits include CoGenesys Inc., which sold to Teva Pharmaceutical Industries Ltd. in 2008; Cerexa Inc., acquired by Forest Laboratories Inc. in 2007; and Peninsula Pharmaceuticals Inc., bought by Johnson & Johnson in 2005.