Factors impacting the efficacy of the in-situ vaccine with CpG and OX40 agonist.

BACKGROUND: The in-situ vaccine using CpG oligodeoxynucleotide combined with OX40 agonist antibody (CpG + OX40) has been shown to be an effective therapy activating an anti-tumor T cell response in certain settings. The roles of tumor volume, tumor model, and the addition of checkpoint blockade in the efficacy of CpG + OX40 in-situ vaccination remains unknown. METHODS: Mice bearing flank tumors (B78 melanoma or A20 lymphoma) were treated with combinations of CpG, OX40, and anti-CTLA-4. Tumor growth and survival were monitored. In vivo T cell depletion, tumor cell phenotype, and tumor infiltrating lymphocyte (TIL) studies were performed. Tumor cell sensitivity to CpG and macrophages were evaluated in vitro. RESULTS: As tumor volumes increased in the B78 (one-tumor) and A20 (one-tumor or two-tumor) models, the anti-tumor efficacy of the in-situ vaccine decreased. In vitro, CpG had a direct effect on A20 proliferation and phenotype and an indirect effect on B78 proliferation via macrophage activation. As A20 tumors progressed in vivo, tumor cell phenotype changed, and T cells became more involved in the local CpG + OX40 mediated anti-tumor response. In mice with larger tumors that were poorly responsive to CpG + OX40, the addition of anti-CTLA-4 enhanced the anti-tumor efficacy in the A20 but not B78 models. CONCLUSIONS: Increased tumor volume negatively impacts the anti-tumor capability of CpG + OX40 in-situ vaccine. The addition of checkpoint blockade augmented the efficacy of CpG + OX40 in the A20 but not B78 model. These results highlight the importance of considering multiple preclinical model conditions when assessing the efficacy of cancer immunotherapy regimens and their translation to clinical testing.

Tumor-associated myeloid cells can be activated in vitro and in vivo to mediate antitumor effects.

Tumor growth is often accompanied by the accumulation of myeloid cells in the tumors and lymphoid organs. These cells can suppress T cell immunity, thereby posing an obstacle to T cell-targeted cancer immunotherapy. In this study, we tested the possibility of activating tumor-associated myeloid cells to mediate antitumor effects. Using the peritoneal model of B16 melanoma, we show that peritoneal cells (PEC) in tumor-bearing mice (TBM) had reduced ability to secrete nitric oxide (NO) following in vitro stimulation with interferon gamma and lipopolysaccharide, as compared to PEC from control mice. This reduced function of PEC was accompanied by the influx of CD11b(+) Gr-1(+) myeloid cells to the peritoneal cavity. Nonadherent PEC were responsible for most of the NO production in TBM, whereas in naïve mice NO was mainly secreted by adherent CD11b(+) F4/80(+) macrophages. Sorted CD11b(+) Gr-1(-) monocytic and CD11b(+) Gr-1(+) granulocytic PEC from TBM had a reduced ability to secrete NO following in vitro stimulation (compared to naïve PEC), but effectively suppressed proliferation of tumor cells in vitro. In vivo, treatment of mice bearing established peritoneal B16 tumors with anti-CD40 and CpG resulted in activation of tumor-associated PEC, reduction in local tumor burden and prolongation of mouse survival. Inhibition of NO did not abrogate the antitumor effects of stimulated myeloid cells. Taken together, the results indicate that in tumor-bearing hosts, tumor-associated myeloid cells can be activated to mediate antitumor effects.

Synergy of anti-CD40, CpG and MPL in activation of mouse macrophages.

Activation of macrophages is a prerequisite for their antitumor effects. Several reagents, including agonistic anti-CD40 monoclonal antibody (anti-CD40), CpG oligodeoxynucleotides (CpG) and monophosphoryl lipid A (MPL), can stimulate activation of macrophages. Our previous studies showed synergy between anti-CD40 and CpG and between anti-CD40 and MPL in macrophage activation and antitumor efficacy in mice. In the present study, we asked whether there was synergy among these three reagents. The activation of adherent peritoneal exudate cells (PEC) obtained from mice injected with anti-CD40 and then treated with CpG and/or MPL in vitro was determined by their ability to suppress proliferation of tumor cells and to produce various cytokines and chemokines in vitro. Cell sorting and histology followed by functional testing showed that macrophages were the main cell population in PEC activated by CD40 ligation in vivo. A combination of anti-CD40, CpG or MPL activated PEC to suppress proliferation of B16 cells and produce nitric oxide far greater than the single reagents or any of the double combinations of these reagents. In addition, the combination of all three reagents activated PEC to secrete IL-12, IFN-γ and MCP-1 to a greater degree than any single reagent or any two combined reagents. These results demonstrate that macrophages can be synergistically activated by anti-CD40, CpG and MPL, suggesting that this novel combined approach might be further investigated as potential cancer therapy.

Antitumor effects of anti-CD40/CpG immunotherapy combined with gemcitabine or 5-fluorouracil chemotherapy in the B16 melanoma model.

Our previous studies demonstrated that anti-CD40 mAb (anti-CD40) can synergize with CpG oligodeoxynucleotides (CpG) to mediate antitumor effects by activating myeloid cells, such as macrophages in tumor-bearing mice. Separate teams have shown that chemotherapy with gemcitabine (GEM) or 5-fluorouracil (5-FU) can reduce tumor-induced myeloid-derived suppressor cells (MDSC) in mice. In this study we asked if the same chemotherapy regimens with GEM or 5-FU will enhance the antitumor effect of anti-CD40 and CpG. Using the model of B16 melanoma growing intraperitoneally in syngeneic C57BL/6 mice, we show that these GEM or 5-FU treatment regimens reduced MDSC in the peritoneal cavity of tumor-bearing mice. Treatment of mice with GEM or 5-FU did not significantly affect the antitumor function of macrophages as assessed in vitro. In vivo, treatment with these GEM or 5-FU regimens followed by anti-CD40/CpG resulted in antitumor effects similar to those of anti-CD40/CpG in the absence of GEM or 5-FU. Likewise, reduction of MDSC by in vivo anti-Gr-1 mAb treatment did not significantly affect anti-CD40/CpG antitumor responses. Together, the results show that the GEM or 5-FU chemotherapy regimens did not substantially affect the antitumor effects induced by anti-CD40/CpG immunotherapy.

Intratumoral delivery of low doses of anti-CD40 mAb combined with monophosphoryl lipid a induces local and systemic antitumor effects in immunocompetent and T cell-deficient mice.

In this study, an agonistic anti-CD40 monoclonal antibody was combined with monophosphoryl lipid A (MPL), a nontoxic derivative of lipopolysaccharide and agonist of toll-like receptor-4, to assess the immunomodulatory and antitumor synergy between the 2 agents in mice. Anti-CD40 was capable of priming macrophages to subsequent ex vivo activation by MPL in immunocompetent and T-cell-depleted mice. Intraperitoneal injections of anti-CD40+MPL induced additive to synergistic suppression of poorly immunogenic B16-F10 melanoma growing subcutaneously in syngeneic mice. When anti-CD40+MPL were injected directly into the subcutaneous tumor, the combination treatment was more effective, even with a 25-fold reduction in dose. Low-dose intratumoral treatment also slowed the growth of a secondary tumor growing simultaneously at a distant, untreated site. Antitumor effects were also induced in severe combined immunodeficiency mice and in T-cell-depleted C57BL/6 mice. Taken together, our results show that the antitumor effects of anti-CD40 are enhanced by subsequent treatment with MPL, even in T-cell-deficient hosts. These preclinical data suggest that an anti-CD40+MPL combined regimen is appropriate for clinical testing in human patients, including cancer patients who may be immunosuppressed from prior chemotherapy.

Enhanced T-cell-independent antitumor effect of cyclophosphamide combined with anti-CD40 mAb and CpG in mice.

We have earlier demonstrated T-cell-independent antitumor effects of a combination of anti-CD40 monoclonal antibody (mAb) and CpG oligodeoxynucleotides (CpG) which involved macrophages. As some immunotherapeutic treatments can be potentiated by chemotherapy, we tested if cyclophosphamide (CY) would enhance the antitumor effect of anti-CD40 mAb+CpG. Treatment of B16 melanoma-bearing mice with CY and anti-CD40 mAb+CpG resulted in a significant reduction in tumor growth in immunocompetent mice compared with either CY alone or anti-CD40 mAb with CpG. This enhanced antitumor effect was maintained in severe combined immunodeficiency mice, as measured by both tumor growth and overall survival. Natural killer cells were not required for this antitumor effect as it was also observed in severe combined immunodeficiency/beige mice. Moreover, although CY treatment of immunocompetent mice suppressed natural killer cell activity, it did not negatively affect the antitumor activity of their macrophages when assayed in vitro. Depletion of macrophages in vivo reduced the antitumor effect of CY and anti-CD40 mAb+CpG. These results suggest that therapeutic strategies to activate macrophages may have potential for clinical application in cancer patients receiving chemotherapy.