X0306 4 2018-04-20 0 0001390478 SELLAS Life Sciences Group, Inc. SLS 0001737979 Mack Gene C/O SELLAS LIFE SCIENCES GROUP, INC. 315 MADISON AVENUE, 4TH FLOOR NEW YORK NY 10017 0 1 0 0 CFO and Treasurer Stock Option (Right to Buy) 5.38 2018-04-20 4 A 0 40000 0.00 A 2028-04-19 Common Stock 40000 40000 D One-quarter (1/4) of the option shares will vest and became exercisable one year from the April 20, 2018 grant date, and the remainder will vest and become exercisable in equal monthly installments for thirty-six (36) months thereafter, provided that the Reporting Person remains in service with the Issuer through each such monthly vesting date. Gene C. Mack, by /s/ Ron A. Metzger, Attorney-in-Fact 2018-04-24