An antibody or antigen-binding fragment thereof that specifically binds programmed death 1 (PD-1) for use in a method of treating B-cell non-Hodgkin's lymphoma in combination with a bispecific antibody comprising a first antigen-binding arm that specifically binds CD20 and a second antigen-binding arm that specifically binds CD3, said method comprising administering to a subject in need thereof a therapeutically effective amount of each antibody or fragment, wherein: the anti-PD-1 antibody or antigen-binding fragment thereof comprises three heavy chain complementarity determining regions (CDRs) (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO: 3; HCDR2 comprises the amino acid sequence of SEQ ID NO: 4; HCDR3 comprises the amino acid sequence of SEQ ID NO: 5; LCDR1 comprises the amino acid sequence of SEQ ID NO: 6; LCDR2 comprises the amino acid sequence of SEQ ID NO: 7; and LCDR3 comprises the amino acid sequence of SEQ ID NO: 8; the first antigen-binding arm of the bispecific antibody comprises three heavy chain complementarity determining regions (CDRs) (A-HCDR1, A-HCDR2 and A-HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein A-HCDR1 comprises the amino acid sequence of SEQ ID NO: 14; A-HCDR2 comprises the amino acid sequence of SEQ ID NO: 15; A-HCDR3 comprises the amino acid sequence of SEQ ID NO: 16; LCDR1 comprises the amino acid sequence of SEQ ID NO: 17; LCDR2 comprises the amino acid sequence of SEQ ID NO: 18; and LCDR3 comprises the amino acid sequence of SEQ ID NO: 19; the second antigen-binding arm of the bispecific antibody comprises three heavy chain CDRs (B-HCDR1, B-HCDR2 and B-HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein B-HCDR1 comprises the amino acid sequence of SEQ ID NO: 20; B-HCDR2 comprises the amino acid sequence of SEQ ID NO: 21; B-HCDR3 comprises the amino acid sequence of SEQ ID NO: 22; LCDR1 comprises the amino acid sequence of SEQ ID NO: 17; LCDR2 comprises the amino acid sequence of SEQ ID NO: 18; and LCDR3 comprises the amino acid sequence of SEQ ID NO: 19; and each dose of the anti-PD-1 antibody comprises 0.1 to 20 mg/kg of the subject's body weight. the anti-PD-1 antibody or antigen-binding fragment thereof comprises three heavy chain complementarity determining regions (CDRs) (HCDR1, HCDR2 and HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein HCDR1 comprises the amino acid sequence of SEQ ID NO: 3; HCDR2 comprises the amino acid sequence of SEQ ID NO: 4; HCDR3 comprises the amino acid sequence of SEQ ID NO: 5; LCDR1 comprises the amino acid sequence of SEQ ID NO: 6; LCDR2 comprises the amino acid sequence of SEQ ID NO: 7; and LCDR3 comprises the amino acid sequence of SEQ ID NO: 8; the first antigen-binding arm of the bispecific antibody comprises three heavy chain complementarity determining regions (CDRs) (A-HCDR1, A-HCDR2 and A-HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein A-HCDR1 comprises the amino acid sequence of SEQ ID NO: 14; A-HCDR2 comprises the amino acid sequence of SEQ ID NO: 15; A-HCDR3 comprises the amino acid sequence of SEQ ID NO: 16; LCDR1 comprises the amino acid sequence of SEQ ID NO: 17; LCDR2 comprises the amino acid sequence of SEQ ID NO: 18; and LCDR3 comprises the amino acid sequence of SEQ ID NO: 19; the second antigen-binding arm of the bispecific antibody comprises three heavy chain CDRs (B-HCDR1, B-HCDR2 and B-HCDR3) and three light chain CDRs (LCDR1, LCDR2 and LCDR3), wherein B-HCDR1 comprises the amino acid sequence of SEQ ID NO: 20; B-HCDR2 comprises the amino acid sequence of SEQ ID NO: 21; B-HCDR3 comprises the amino acid sequence of SEQ ID NO: 22; LCDR1 comprises the amino acid sequence of SEQ ID NO: 17; LCDR2 comprises the amino acid sequence of SEQ ID NO: 18; and LCDR3 comprises the amino acid sequence of SEQ ID NO: 19; and each dose of the anti-PD-1 antibody comprises 0.1 to 20 mg/kg of the subject's body weight.