Rubius Therapeutics Inc. sold 12,055,450 common shares priced at $23 apiece in its IPO, raising $277.3 million in gross proceeds.

The shares sold include the underwriters' full exercise of their option to buy up to an additional 1,572,450 common shares in the offering.

The Cambridge, Mass.-based company's shares started trading on the Nasdaq Global Select Market under the RUBY ticker on July 18.

Rubius Therapeutics is engaged in the development of a new class of medicines known as red cell therapeutics, which have the potential to treat rare diseases, cancer and autoimmune diseases.

J.P. Morgan, Morgan Stanley, Jefferies and Leerink Partners acted as joint book-running managers in the IPO.