CpG oligodeoxynucleotides potentiate the antitumor activity of anti-BST2 antibody

Abstract

Numerous monoclonal antibodies (mAb) targeting tumor antigens have recently been developed. Antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) via effector cells such as tumor-infiltrating natural killer (NK) cells and macrophages are often involved in mediating the antitumor activity of mAb. CpG oligodeoxynucleotides (ODN) have a potent antitumor activity and are considered to increase tumor infiltration of NK cells and macrophages. Our group previously reported significant antitumor activity of anti-bone marrow stromal antigen 2 (BST2) mAb against BST2-positive endometrial cancer cells through ADCC. In this study, we evaluated the synergistic antitumor activity of combination therapy with anti-BST-2 mAb and CpG ODN using SCID mice and elucidated the mechanisms underlying this activity. Anti-BST2 mAb and CpG ODN monotherapy had a significant dose-dependent antitumor activity (P = 0.0135 and P = 0.0196, respectively). Combination therapy with anti-BST2 mAb and CpG ODN had a significant antitumor activity in SCID mice (P < 0.01), but not in NOG mice. FACS analysis revealed significantly increased numbers of NK cells and macrophages in tumors treated with a combination of anti-BST2 mAb and CpG ODN and with CpG ODN alone in SCID mice (P < 0.05 and P < 0.01, respectively). These results suggested that the combination therapy with anti-BST2 mAb and CpG ODN has a significant antitumor activity and induces tumor infiltration of NK cells and macrophages. Combination therapy with CpG ODN and anti-BST2 mAb or other antitumor mAb depending on ADCC may represent a new treatment option for cancer.

Keywords: Antitumor antibody; CpG oligodeoxynucleotides; bone marrow stromal antigen 2; macrophage; natural killer cell.

Figure 1

Anti-bone marrow stromal antigen 2 (BST2) monoclonal antibodies (mAb) and CpG oligodeoxynucleotides (ODN) monotherapy have dose-dependent antitumor activity in SCID mice: (a) xenografted SCID mice treated with 400 μL of PBS or anti-BST2 mAb (12.5, 50 and 200 μg in 400 μL of PBS/mouse) by i.p. injection. Anti-BST2 mAb caused significant dose-dependent decrease in tumor weight (P = 0.0135) and a trend toward reduced tumor volume (P = 0.0552). (b) Xenografted SCID mice treated with PBS or CpG ODN (10, 20 and 40 μg in 10 μL of PBS/mouse) by i.t. injection. CpG ODN caused a significant dose-dependent reduction in tumor volume and weight (P = 0.0319 and P = 0.0196, respectively).

Figure 2

Combination therapy with anti-bone marrow stromal antigen 2 (BST2) monoclonal antibodies (mAb) and CpG oligodeoxynucleotides (ODN) reveals synergistic antitumor activity. Xenografted SCID (a, b) and NOG (c, d) mice were treated by i.p./i.t. injection of (A) PBS/PBS, (B) anti-BST2 mAb (12.5 μg/mouse)/PBS, (C) anti-BST2 mAb (200 μg/mouse)/PBS, (D) PBS/CpG ODN (10 μg/mouse) and (E) anti-BST2 mAb (12.5 μg/mouse)/CpG ODN (10 μg/mouse), respectively. Treatment with regimen (E) caused a significant decrease in tumor volume compared with that of other regimens in SCID mice (P < 0.01).

Figure 3

CpG oligodeoxynucleotides (ODN) increases tumor infiltration of natural killer (NK) cells and macrophages. Xenografted SCID mice were treated by i.p./i.t. injection of (A) PBS/PBS, (B) anti-bone marrow stromal antigen 2 (BST2) monoclonal antibodies (mAb) (12.5 μg/mouse)/PBS, (C) PBS/CpG ODN (10 μg/mouse) or (D) anti-BST2 mAb (12.5 μg/mouse)/CpG ODN (10 μg/mouse). (a) FACS analysis of the tumor-infiltrated macrophages and NK cells. Tumor-infiltrated cells were isolated and gated on CD45⁺ cells. Representative dot plot data of F4/80⁺ macrophages and CD49b⁺ NK cells in tumors treated with regimens (A) to (D) were shown. (b) Significantly higher numbers of NK cells in tumors treated with regimens (C) and (D) than in those treated with regimens (A) and (B) (P < 0.05). (c) Significantly higher numbers of macrophages in tumors treated with regimens (C) and (D) than in those treated with regimens (A) and (B) (P < 0.01).