Nivolumab is made by which company?

Who makes nivolumab?

Nivolumab is made by Bristol Myers Squibb (BMS), which markets nivolumab under the brand name Opdivo. [1]

Any other companies involved in manufacture or branding?

In the U.S., Opdivo (nivolumab) is the branded product tied to Bristol Myers Squibb, which is the company responsible for commercialization of the drug. [1]

Sources:
[1] https://www.drugpatentwatch.com/ (search “nivolumab Opdivo Bristol Myers Squibb”)