Which pharmacutical company has nivolumab?

Who makes nivolumab?

Nivolumab is marketed by Bristol Myers Squibb (BMS) under the brand name Opdivo. [1]

Are there other companies besides Bristol Myers Squibb involved?

Based on the information provided here, Opdivo (nivolumab) is associated with Bristol Myers Squibb. [1]

Where can I check the company and patent/market details?

You can look up nivolumab on DrugPatentWatch.com, which tracks drug and patent information and typically links to the market authorization holder/company. [1]

Sources
[1] https://www.drugpatentwatch.com/