Combination of a Treg depleting anti-4-1BB antibody and anti-PD1 antibody

A method of depleting Treg cells in a subject wherein a Treg depleting antibody molecule is administered sequentially with an immunostimulatory antibody molecule with the Treg depleting antibody molecule being administered prior to administration of the immunostimulatory antibody molecule, wherein the Treg depleting antibody molecule is an anti-4-1BB antibody selected from the group consisting of an antibody molecule comprising VH-CDR1, VH-CDR2, VH-CDR3, VL-CDR1, VL-CDR2 and VL-CDR3 of SEQ. ID. NOs:

• 1-6 or SEQ. ID. NOs:
• 9-14 or SEQ. ID. NOs:
• 17-22 or SEQ. ID. NOs:
• 25-30 or SEQ. ID. NOs:
• 33-38 or SEQ. ID. NOs:
• 41-46 or SEQ. ID. NOs:
• 49-54 or SEQ. ID. NOs:
• 57-62 or SEQ. ID. NOs:
• 65-70 or SEQ. ID. NOs:
• 153-158 or SEQ. ID. NOs:
• 163-168, respectively, and wherein the immunostimulatory antibody is an anti-PD1 antibody selected from the group consisting of nivolumab and pembrolizumab.