Prothena Prices 5.91M Share Offering at $22.00/Share

Prothena Corporation plc.

announced that it has priced an underwritten public offering of 5,910,000 of its ordinary shares at a price of $22.00 per ordinary share, before underwriting discounts and commissions. Of these ordinary shares, Prothena is offering 3,500,000 ordinary shares and Janssen Pharmaceutical, a wholly owned subsidiary of Johnson & Johnson, as selling shareholder, is offering 2,410,000 ordinary shares. In addition, the underwriters have been granted a 30-day option to purchase up to an additional 886,500 ordinary shares. If the option is exercised in full, Prothena will issue and sell an additional 677,079 ordinary shares and Janssen Pharmaceutical will sell an additional 209,421 ordinary shares, which represents all of Janssen's shareholdings in Prothena. Net proceeds to Prothena from the ordinary shares to be sold by Prothena in the offering are expected to be $70.8 million, after deducting the underwriting discount and estimated offering expenses, but excluding any exercise of the underwriters' option to purchase additional ordinary shares. Prothena will not receive any proceeds from the sale