Animals were housed in standard cages, in groups of maximal 8 animals during the pre-immunization phase and in study groups of 6 animals during the immunization phase. The study groups were transferred to negatively pressurized glovebox isolator cages on the day of challenge. During

the whole study animals were provided with commercial food pellets and water ad libitum. The experimental protocol was approved before start of the experiments by an independent institutional animal ethics committee according to the Dutch law. Five groups of six ferrets received three intranasal immunizations (droplets: 100 μl in each nostril, using a pipet with filtertip) under anesthesia with ketamine and domitor at days 0, 21 and 42. Groups 3, 4 and 5 were intranasally immunized with 200 μl Endocine™ formulated H1N1/California/2009 Akt inhibitor split antigen containing 5, 15 and 30 μg HA, respectively. Group 6 was intranasally immunized with 200 μl Endocine™ formulated H1N1/California/2009 whole virus antigen containing 15 μg

HA. Control group 1 received 200 μl of saline intranasally. One group Epacadostat of six ferrets (group 2) received two subcutaneous immunizations (days 21 and 42 using 25Gx5/8” needles) with 0.5 ml Fluarix®, season 2010/2011, a non-adjuvanted trivalent influenza vaccine (TIV) that also contains the pH1N1 (15 μg HA) component. Blood samples for serum preparation were collected prior immunization on days 0, 21 and 42 and before challenge on study days 64 and 70. Four weeks after the last immunization (day 70), all ferrets were challenged with wild-type influenza A/Netherlands/602/2009 (wt-pH1N1) virus as previously described [30]. Briefly, 106 50% tissue culture infective doses (TCID50) of wt-pH1N1 virus was diluted in 3 ml of PBS and administered via the intratracheal route under anesthesia with a cocktail of ketamine and domitor. Several procedures were performed on the ferrets over the

course of the experiment. For implantation of temperature sensors, immunizations, viral challenge and computed tomography (CT) imaging the animals were anesthetized with a cocktail of ketamine (4-8 mg/kg: i.m.; Alfasan, Woerden, The Netherlands) and domitor (0.1 mg/kg: i.m.; Orion Pharma, Espoo, Finland). For sampling (blood, swabs and nasal washes) and euthanasia by exsanguination, the animals were anesthetized with ketamin. Two weeks prior to the start of enough the experiment, a temperature logger (DST micro-T ultrasmall temperature logger; Star-Oddi, Reykjavik, Iceland) was placed in the peritoneal cavity of the ferrets. This device recorded body temperature of the animals every 10 min. Ferrets were weighed prior to each immunization (days 0, 21 and 42) and on the days of challenge and euthanasia (days 70 and 74). Animals of groups 1, 2 and 4 were monitored by CT imaging on days 64, 71, 72, 73 and 74. Blood samples were collected prior to the immunization on days 0, 21 and 42, on day 64 and before challenge on day 70.