Chemokines and their receptors are important for the migration of various cell types into the inflammatory sites. CCR8 is a chemokine receptor that belongs to the β chemokine receptor family. The crystal structure has not been deciphered, but is predicted to be a seven-transmembrane protein, similar to G-protein-coupled receptors. CCR8 expression is low or absent on Tregs in normal tissues (e.g.thymus, spleen) and peripheral blood, but is highly expressed in tumor-infiltrating Treg cells. In human peripheral blood cells, over 30% of Tregs upregulate CCR8 in response to CCL1. This interaction induces stat3-dependent upregulation of FOXp3, CD39, IL-10, and granzyme B, which enhances the immunosuppressive activity of these Treg cells. There are currently four known human CCR8 ligands, CCL1, CCL8, CCL16, and CCL18, of which CCR8 is a specific receptor for CCL1, which has a more significant role in enhancing Treg cell immunosuppression. Targeting CCR8 may selectively and specifically modulate a subpopulation of tumor-resident Tregs in the TME to augment antitumor immunity. Therefore, CCR8 is a promising new target for cancer immunotherapy.
mRNA expression analysis
CCR8 gene expression in C57BL/6 and B-hCCR8 mice by RT-PCR. Mouse Ccr8 mRNA was detectable in thymocytes of wild-type mice (+/+) . Human CCR8 mRNA was detectable only in homozygous B-hCCR8 mice (H/H) but not in wild-type mice (+/+).
Protein expression analysis
Human CCR8 expression in B-hCCR8 mice. MC38 tumor cells were inoculated into wild-type C57BL/6 (+/+) and homozygous B-hCCR8 mice (H/H). Tumors were harvested at the endpoint of experiment, and tumor-infiltrating lymphocytes were analyzed by flow cytometry. Human CCR8 was detected on CD4+ T cells and Treg cells in tumors from homozygous B-hCCR8 mice, while mouse CCR8 was detected only in wild-type mice.
Tissue distribution of CCR8+ T lymphocytes in wildtype and B-hCCR8 mice bearing tumors. Human CCR8 was detected on CD4+ T cells and Treg cells in tumors isolated from homozygous B-hCCR8 mice, but not those T cells isolated from spleen or blood. Similarly, mouse CCR8 was detected in tumors and expressed on some T cells isolated from wild-type mice, but not on blood cells.
In vivo efficacy
Antitumor activity of anti-human CCR8 antibody in male B-hCCR8 mice
(A) Murine colon cancer MC38 cells were subcutaneously implanted into homozygous B-hCCR8 mice (male, 6-7 week-old, n=6). Mice were grouped when tumor volume reached approximately 100 mm3, at which time they were treated with anti-human CCR8 antibodies as indicated. (B) Body weight changes during treatment. As shown in panel A, anti-human CCR8 antibodies blunted tumor growth. Values are expressed as mean ± SEM.
Antitumor activity of anti-human CCR8 antibody in female B-hCCR8 mice
(A) Anti-human CCR8 antibody inhibited MC38 tumor growth in B-hCCR8 mice. Murine colon cancer MC38 cells were subcutaneously implanted into homozygous B-hCCR8 mice (female, 8 week-old, n=8). Mice were grouped when tumor volume reached approximately 100 mm3, at which time they were treated with anti-human CCR8 antibody as indicated. (B) Body weight changes during treatment. As shown in panel A, anti-human CCR8 antibody blunted tumor growth in B-hCCR8 mice. Values are expressed as mean ± SEM.