144 0001753224 XXXXXXXX LIVE 0001722964 Y-mAbs Therapeutics, Inc. 001-38650 230 Park Avenue Suite3350 New York NY 10169 6468858505 Gad Enterprises LLC (Thomas Gad) Officer Common Stock J.P. Morgan Securities LLC

390 Madison Avenue 6th Floor New York NY 10017

150000 1015500 43621618 12/13/2023 Nasdaq Common 08/15/2015 Private Investment Issuer N 150000 08/15/2015 Cash N Gad Enterprises (Thomas Gad)

230 Park Avenue New York NY 10169

Common 11/20/2023 75000 392432 Gad Enterprises (Thomas Gad)

230 Park Avenue New York NY 10169

Common 11/21/2023 75000 393010 12/13/2023 /s/ J.P. Morgan Securities LLC as agent and attorney-in-fact for Gad Enterprises LLC