Cetuximab-mediated tumor regression depends on innate and adaptive immune responses

Abstract

Epidermal growth factor receptor (EGFR) over-signaling leads to more aggressive tumor growth. The antitumor effect of Cetuximab, an anti-EGFR antibody, depends on oncogenic-signal blockade leading to tumor cell apoptosis and antibody dependent cell-mediated cytotoxicity (ADCC). However, whether adaptive immunity plays a role in Cetuximab-mediated tumor inhibition is unclear, as current xenograft models lack adaptive immunity and human-EGFR-dependent mouse tumor cell lines are unavailable. Using a newly developed xenograft model with reconstituted immune cells, we demonstrate that the Cetuximab effect becomes more pronounced and reduces the EGFR(+) human tumor burden when adaptive immunity is present. To further study this in a mouse tumor model, we created a novel EGFR(+) mouse tumor cell line and demonstrated that Cetuximab-induced tumor regression depends on both innate and adaptive immunity components, including CD8(+) T cells, MyD88, and FcγR. To test whether strong innate signals inside tumor tissues amplifies the Cetuximab-mediated therapeutic effect, Cetuximab was conjugated to CpG. This conjugate is more potent than Cetuximab alone for complete tumor regression and resistance to tumor rechallenge. Furthermore, Cetuximab-CpG conjugates can activate tumor-reactive T cells for tumor regression by increasing dendritic cell (DC) cross-presentation. Therefore, this study establishes new models to evaluate immune responses induced by antibody-based treatment, defines molecular mechanisms, and provides new tumor-regression strategies.

Figures

Figure 1

The antitumor effect of Cetuximab depends on adaptive immunity in a human A431 tumor xenograft model. (a) Rag1 knockout (KO) mice (n = 5/group) were injected subcutaneously with 6 × 106 A431 cells, and 2 × 106 OTI lymph node (LN) cells were adoptively transferred on day 13. Two hundred micrograms of Cetuximab or control human immunoglobulin G (IgG) was administered on days 14, 21, and 28. The growth of tumor was measured and compared twice a week. (b) Draining LN cells were collected for fluorescence-activated cell sorting (FACS) analysis on day 35 after treatment. *P < 0.05 compared with control treated group. One of three experiments is shown. (c) Rag1 KO mice (n = 5/group) were injected subcutaneously with 6 × 106 A431 cells, and 2 × 106 OTI LN cells were adoptively transferred on day 13. Two hundred micrograms of Cetuximab or control human IgG was administered on days 14, 21, and 28. Draining LN cells were collected 9 days after the last treatment and were stimulated with 1 × 104 A431 cells in an interferon-γ (IFNγ) enzyme-linked immunosorbent spot (ELISPOT) assay. *P < 0.05 compared with control group. One representative experiment of three is depicted.

Figure 2

Adaptive immunity is essential for the therapeutic effect of Cetuximab treatment in mouse epidermal growth factor receptor (EGFR) tumor model. (a) TUBO and TUBO-EGFR cells were stained with Cetuximab and antihuman–IgG-PE. (b) Wild type (Wt) BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR cells and treated with 200 µg of Cetuximab or control human immunoglobulin G (IgG) on days 14, 21, and 28. The growth of tumor was measured and compared twice a week. *P < 0.05 compared with control group. (c) TUBO-bearing Rag1 knockout (KO) mice (n = 5/group) were treated with 200 µg of Cetuximab or control human IgG on days 14, 21, and 28. One of three representative experiments is shown.

Figure 3

Anti-EGFR Ab induced a tumor-specific CTL response, which is required for the therapeutic effect. (a) Wild type (Wt) BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR and treated with 200 µg of Cetuximab on days 14, 21, and 28. A CD8-depleting antibody (200 µg/mouse) was administered on the same day as Cetuximab. The tumor growth was measured and compared twice a week. *P < 0.05, compared to Cetuximab-treated Wt mice. One of three representative experiments is shown. (b) TUBO-EGFR-HA–bearing Wt mice received an adoptive transfer of 6 × 106 carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled clone 4 (CL4) T cells on day 10 after tumor inoculation. Six hours later, mice were treated with 500 µg of Cetuximab or control human immunoglobulin G (IgG). Draining lymph node (LN) cells were collected 3 days later and analyzed for CFSE dilution. Data is gated on the Thy1.1+CD8+Vβ8+ population. *P < 0.05 compared to control group. One of two similar experiments is represented. (c) TUBO-EGFR-HA–bearing Wt BALB/c mice received an adoptive transfer of 2 × 103 CL4 splenocytes on day 10 after tumor inoculation. Six hours later, mice were treated with 500 µg of Cetuximab or control human IgG. Draining LN cells were collected 9 days later and stimulated with hemagglutinin (HA) peptide in an interferon-γ (IFNγ) enzyme-linked immunosorbent spot (ELISPOT) assay. *P < 0.05 compared with control group. One representative experiment of three is depicted.

Figure 4

The MyD88 signaling pathway and FcγR contribute to the therapeutic effect of Cetuximab. (a) Wild type (Wt) and MyD88 knockout (KO) BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR cells and treated with 200 µg of Cetuximab or control human immunoglobulin G (IgG) on days 14, 21, and 28. *P < 0.05 compared to control treated mice. One of three experiments is shown. (b) Wt and FcγR KO BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR cells and were treated with 200 µg of Cetuximab or control human IgG on days 14, 21, and 28. *P < 0.05 compared to control treated mice. One of two experiments is shown. EGFR, epidermal growth factor receptor.

Figure 5

CpG conjugation improves the antitumor effect of Cetuximab. (a) Approximately 1 × 104 TUBO-EGFR cells were plated in 96-well plate and incubated with 10, 3, or 0.3 µg/ml Cetuximab or anti-neu antibodies. Cell viability was measured by an MTT assay at 24, 36, and 72 hours after incubation. Cell growth rate was normalized to control cell growth. (b) Wild type (Wt) BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR and treated with 40 µg of human Ig (hIg), Cetuximab, Cetuximab-CpG, or 10 µg of CpG on days 14, 18, and 22. Tumor growth was measured and compared twice a week. *P < 0.05 compared to Cetuximab-treated Wt mice. One of three representative experiments is shown. (c) Wt BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR and treated with 40 µg of hIg or Cetuximab-CpG on days 14, 18, and 22. A CD8-depleting antibody (200 µg/mouse) was administered on days 14, 21, and 28. Tumor growth was measured and compared twice a week. *P < 0.05, compared to Cetuximab-CpG-treated Wt mice. One of three representative experiments is shown. (d) Wt BALB/c mice or cured Cetuximab-CpG treated mice (n = 5/group) were injected subcutaneously with 2 × 106 TUBO-EGFR, and the growth of tumor was measured and compared twice a week. *P < 0.05, compared to naive Wt mice. One of three representative experiments is shown. EGFR, epidermal growth factor receptor.

Figure 6

The TLR-MyD88 signal pathway and FcγR contribute to the therapeutic effect of Cetuximab-CpG conjugates. (a) A431 cells were stained with human Ig (hIg), Cetuximab, or Cetuximab-CpG, and antihuman immunoglobulin G (IgG) Fcγ-PE. (b). Approximately 1 × 105 purified dendritic cells (DCs) from splenocytes were incubated with 3 µg/ml of hIg or Cetuximab-CpG. Supernatants were collected and CBA assay was performed to detect the tumor necrosis factor (TNF) and interleukin-6 (IL-6) levels 48 hours later. (c) Wild type (Wt) and MyD88 knockout (KO) BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR cells and treated with 40 µg of hIg or Cetuximab-CpG on days 14, 18, and 22. The growth of tumor was measured and compared twice a week. *P < 0.05 compared to control-treated mice. One of three experiments is shown. (d) Wt and FcγR KO BALB/c mice (n = 5/group) were injected subcutaneously with 5 × 105 TUBO-EGFR cells and treated with 40 µg of hIg or Cetuximab-CpG on days 14, 18, and 22. The growth of tumor was measured and compared twice a week. *P < 0.05 compared to control treated mice. One of two experiments is shown. EGFR, epidermal growth factor receptor.

Figure 7

Cetuximab-CpG conjugate treatment activates dendritic cells (DCs) to enhance the antitumor CTL response through cross-presentation. (a) TUBO-EGFR-HA bearing mice were treated with 40 µg of human Ig (hIg), Cetuximab, or Cetuximab-CpG on days 14 and 17. Approximately 1 × 105 draining lymph node (LN) DC were purified and incubated with 2 × 105 purified clone 4 (CL4) T cells on day 18. Hemagglutinin (HA) peptides were supplied at concentration of 10 µg/ml. Supernatants were collected 48 hours later and interferon-γ (IFNγ) and interleukin-2 (IL-2) concentration was determined by CBA assay. (b) Approximately 1 × 105 purified DCs from splenocytes were incubated with 2 × 105 purified CL4 T cells and 1 × 104 TUBO-EGFR-HA. The mixture was stimulated with 3 µg/ml hIg, Cetuximab, or Cetuximab-CpG. Supernatants were collected 48 hours later and IFNγ concentration was determined by CBA assay. EGFR, epidermal growth factor receptor.