The pro-tumor effect of CD200 expression is not mimicked by agonistic CD200R antibodies

Abstract

Tumor-infiltrating immune cells can impact tumor growth and progression. The inhibitory CD200 receptor (CD200R) suppresses the activation of myeloid cells and lack of this pathway results in a reduction of tumor growth, conversely a tumorigenic effect of CD200R triggering was also described. Here we investigated the role of CD200R activation in syngeneic mouse tumor models. We showed that agonistic CD200R antibody reached tumors, but had no significant impact on tumor growth and minor effect on infiltration of immune myeloid cells. These effects were reproduced using two different anti-CD200R clones. In contrast, we showed that CD200-deficiency did decrease melanoma tumor burden. The presence of either endogenous or tumor-expressed CD200 restored the growth of metastatic melanoma foci. On the basis of these findings, we conclude that blockade of the endogenous ligand CD200 prevented the tumorigenic effect of CD200R-expressing myeloid cells in the tumor microenvironment, whereas agonistic anti-CD200R has no effect on tumor development.

Fig 1. Impact of anti-CD200R antibodies (clone OX110) on the growth of EMT6 tumors.

(A) EMT6 tumor growth measured as a tumor volume. (B) Example of the gating strategy in flow cytometric analysis of the intratumoral immune cells. (C) Percentage of intratumoral myeloid cells (CD11b⁺) without neutrophils (Ly6G⁺). (D) Expression of CD200R in intratumoral immune cells. (E) Percentage of splenic myeloid cells from mice with EMT6 tumors, gating as in the tumors. (F) Expression of CD200R in splenic immune cells. Mice were treated with control or anti-CD200R antibodies (clone OX110). N = 7–8 / group, data are presented as mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001.

Fig 2. Impact of anti-CD200R antibodies (clone OX131) on the growth of EMT6 tumors.

(A) EMT6 tumor growth measured as a tumor volume. (B) Percentage of intratumoral myeloid cells (in immune gate CD45⁺). (C) Percentage of intratumoral myeloid cells—subpopulations in CD11b⁺ cells. (D) Percentage of intratumoral CD8⁺ T lymphocytes. Expression of IFN-γ and TNF-α in the intratumoral CD8⁺ T lymphocytes (E) (F) respectively. Mice were treated with control or anti-CD200R (clone OX131). N = 7–10 / group, data are presented as mean ± SEM. *P < 0.05.

Fig 3. Impact of anti-CD200R antibodies on the growth of LLC and B16F10 tumors.

(A) Tumor growth depicted as tumor surface of LLC, N = 5 / group. (B) Tumor burden quantified as luminescence of the luciferase expressed by tumor cells in lungs (B16F10), N = 10 / group. (C) Percentage of intratumoral myeloid cells (CD11b⁺) in LLC. (D) Percentage of myeloid cells in lungs with B16F10 tumor foci. (E) Expression of CD200R in intratumoral immune cells of LLC tumors. Mice were treated with control or anti-CD200R (clone OX110). Data are presented as mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001.

Fig 4. Impact of CD200-CD200R signaling on the growth of subcutaneous B16F10 melanoma.

(A) Tumor (B16F10) growth expressed as a tumor surface measured by caliper in Cd200^-/- and control (WT) mice inoculated subcutaneously, N = 5–8 / group. (B) Bioluminescence intensity from each of the tumors shown in (A) on day 18 after tumor cells inoculation. (C) Total body bioluminescence of mice inoculated intravenously with B16F10 cells. (D) Bioluminescence from chest areas of mice shown in (C) on day 20 after tumor cells inoculation, N = 6–10 / group. Data are presented as mean ± SEM, significance was calculated with t-test (A,B) or Mann-Whitney test (D) *P < 0.05, ***P < 0.001.