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

A combined radio-immunotherapy regimen eradicates late-stage tumors in mice

Background

The majority of experimental approaches for cancer immunotherapy are tested against relatively small tumors in tumor-bearing mice, because in most cases advanced cancers are resistant to the treatments. In this study, we asked if even late-stage mouse tumors can be eradicated by a rationally designed combined radio-immunotherapy (CRI) regimen.

Methods

CRI consisted of local radiotherapy, intratumoral IL-12, slow-release systemic IL-2 and anti- CTLA-4 antibody. Therapeutic effects of CRI against several weakly immunogenic and immunogenic mouse tumors including B78 melanoma, MC38 and CT26 colon carcinomas and 9464D neuroblastoma were evaluated. Immune cell depletion and flow cytometric analysis were performed to determine the mechanisms of the antitumor effects.

Results

Tumors with volumes of 2,000 mm3 or larger were eradicated by CRI. Flow analyses of the tumors revealed reduction of T regulatory (Treg) cells and increase of CD8/Treg ratios following CRI. Rapid shrinkage of the treated tumors did not require T cells, whereas T cells were involved in the systemic effect against the distant tumors. Cured mice developed immunological memory.

Conclusions

These findings underscore that rationally designed combination immunotherapy regimens can be effective even against large, late-stage tumors.

Higher postoperative plasma EV PD-L1 predicts poor survival in patients with gastric cancer

Background

The satisfactory prognostic indicator of gastric cancer (GC) patients after surgery is still lacking. Perioperative plasma extracellular vesicular programmed cell death ligand-1 (ePD-L1) has been demonstrated as a potential prognosis biomarker in many types of cancers. The prognostic value of postoperative plasma ePD-L1 has not been characterized.

Methods

We evaluated the prognostic value of preoperative, postoperative and change in plasma ePD-L1, as well as plasma soluble PD-L1, in short-term survival of GC patients after surgery. The Kaplan-Meier survival model and Cox proportional hazards models for both univariate and multivariate analyzes were used. And the comparison between postoperative ePD-L1 and conventional serum biomarkers (carcinoembryonic antigen (CEA), cancer antigen 19–9 (CA19-9) and CA72-4) in prognostic of GC patients was made.

Results

The prognostic value of postoperative ePD-L1 is superior to that of preoperative ePD-L1 on GC patients after resection, and also superior to that of conventional serum biomarkers (CEA, CA19-9 and CA72-4). The levels of postoperative ePD-L1 and ePD-L1 change are independent prognostic factors for overall survival and recurrence free survival of GC patients. High plasma level of postoperative ePD-L1 correlates significantly with poor survival, while high change in ePD-L1 level brings the significant survival benefit.

Conclusions

The level of plasma postoperative ePD-L1 could be considered as a candidate prognostic biomarker of GC patients after resection.

MUC16 suppresses human and murine innate immune responses

OBJECTIVE

MUC16, the mucin that contains the CA125 epitopes, suppresses the cytolytic responses of human NK cells and inhibits the efficacy of therapeutic antibodies. Here, we provide further evidence of the regulatory role of MUC16 on human and murine NK cells and macrophages.

METHODS

Target cell cytolysis and doublet formation assays were performed to assess effects of MUC16 on human NK cells. The effect of MUC16 on ovarian tumor growth was determined in a mouse model by monitoring survival and ascites formation. Innate immune cells from spleens and peritoneal cavities of mice were isolated and stimulated in vitro with anti-CD40 antibody, lipopolysaccharide and IFN-γ and their ability to cytolyse MUC16 expressing and non-expressing cells was determined.

RESULTS

We confirm that MUC16 inhibits cytolysis by human NK cells as well as the formation of NK-tumor conjugates. Mice implanted with MUC16-knockdown OVCAR-3 show >2-fold increase in survival compared to controls. Murine NK cells and macrophages are more efficient at lysing MUC16-knockdown cells. In vitro cytotoxicity assays with NK cells and macrophages isolated from mice stimulated with anti-CD40 antibody showed 2-3-fold increased activity against the MUC16-knockdown cells as compared to matching target cells expressing this mucin. Finally, knockdown of MUC16 increased the susceptibility of cancer cells to ADCC by murine splenocytes.

CONCLUSIONS

For the first time, we demonstrate the immunoregulatory effects of MUC16 on murine NK cells and macrophages. Our study implies that the immunoregulatory role of MUC16 on murine NK cells and macrophages should be considered when examining the biology of MUC16 in mouse models.

PD-L1 and immune infiltrates are differentially expressed in distinct subgroups of gastric cancer

This study investigates the association of PD-L1 expression and immune cell infiltrates and their impact on clinical outcome, in addition to their overlap with microsatellite instability (MSI), HER2 and ATM molecular subgroups of gastric cancer (GC). PD-L1 membrane expression on tumour cells (TC) and infiltrating immune cells (IC), CD3 + T-lymphocytes, CD8+ cytotoxic T-cells, ATM and HER2 were assessed by immunohistochemistry (IHC) in the ACRG (Asian Cancer Research Group) GC cohort (N = 380). EBV status was determined using in situ hybridization and MSI status was performed using PCR and MLH1 IHC. The PD-L1 segment was associated with increased T-cell infiltrates, while the MSI-high segment was enriched for PD-L1, CD3, and CD8. Multivariate analysis confirmed PD-L1 positivity, high CD3 and high CD8 as independent prognostic factors for both disease-free survival and overall survival (all p < 0.05). Patients with MSI-high tumours had better overall survival by both univariate and multivariate analysis. The ATM-low and HER2-high subgroups differed markedly in their immune profile; the ATM-low subgroups enriched for MSI, PD-L1 positivity and CD8 + T-cells, while the HER2 segment was enriched for MSS, with no enrichment for immune markers. Hence, we demonstrate a molecular profiling approach that can divide GC into four molecular subgroups, namely ATM-low, HER2-high, PD-L1 positive and MSI-high with differing levels of immune infiltrates and prognostic significance which may help to stratify patients for response to targeted therapies.

Experimental Combined Immunotherapy of Tumours with Major Histocompatibility Complex Class I Downregulation

Combined immunotherapy constitutes a novel, advanced strategy in cancer treatment. In this study, we investigated immunotherapy in the mouse TC-1/A9 model of human papillomavirus type 16 (HPV16)-associated tumors characterized by major histocompatibility complex class I (MHC-I) downregulation. We found that the induction of a significant anti-tumor response required a combination of DNA vaccination with the administration of an adjuvant, either the synthetic oligodeoxynucleotide ODN1826, carrying immunostimulatory CpG motifs, or α-galactosylceramide (α-GalCer). The most profound anti-tumor effect was achieved when these adjuvants were applied in a mix with a one-week delay relative to DNA immunization. Combined immunotherapy induced tumor infiltration with various subsets of immune cells contributing to tumor regression, of which cluster of differentiation (CD) 8⁺ T cells were the predominant subpopulation. In contrast, the numbers of tumor-associated macrophages (TAMs) were not markedly increased after immunotherapy but in vivo and in vitro results showed that they could be repolarized to an anti-tumor M1 phenotype. A blockade of T cell immunoglobulin and mucin-domain containing-3 (Tim-3) immune checkpoint had a negligible effect on anti-tumor immunity and TAMs repolarization. Our results demonstrate a benefit of combined immunotherapy comprising the activation of both adaptive and innate immunity in the treatment of tumors with reduced MHC-I expression.

CSF1R-dependent myeloid cells are required for NK‑mediated control of metastasis

Myeloid leukocytes are essentially involved in both tumor progression and control. We show that neo-adjuvant treatment of mice with an inhibitor of CSF1 receptor (CSF1R), a drug that is used to deplete tumor-associated macrophages, unexpectedly promoted metastasis. CSF1R blockade indirectly diminished the number of NK cells due to a paucity of myeloid cells that provide the survival factor IL-15 to NK cells. Reduction of the number of NK cells resulted in increased seeding of metastatic tumor cells to the lungs but did not impact on progression of established metastases. Supplementation of mice treated with CSF1R-inhibitor with IL-15 restored numbers of NK cells and diminished metastasis. Our data suggest that CSF1R blockade should be combined with administration of IL-15 to reduce the risk of metastasis.

Toll-Like Receptor Ligands and Interferon-γ Synergize for Induction of Antitumor M1 Macrophages

Tumor-associated macrophages may either promote or suppress tumor growth depending on their activation status. Interferon-γ (IFN-γ) has been identified as a key factor for inducing tumoricidal M1 phenotype in macrophages. However, it remains unclear whether IFN-γ is sufficient or if additional stimuli are required. Here, we tested IFN-γ and a panel of toll-like receptor (TLR) agonists for the ability to activate murine macrophages toward a tumoricidal M1 phenotype. The following TLR ligands were used: TLR1/TLR2 agonist Pam3CSK4, TLR2/TLR6 agonist lipotechoic acid, TLR3 agonist poly(I:C), TLR4 agonist lipopolysaccharide (LPS), TLR5 agonist flagellin, TLR7 agonist CL264, and TLR9 agonist CpG. We used an in vitro growth inhibition assay to measure both cytotoxic and cytostatic activity of mouse macrophages against Lewis lung carcinoma (LLC) and MOPC315 plasmacytoma tumor cells. Production of nitric oxide (NO) and cytokines by activated macrophages was quantified. We found that IFN-γ alone was not able to render macrophages tumoricidal. Similarly, macrophage activation with single TLR agonists was inefficient. In sharp contrast, IFN-γ was shown to synergize with TLR agonists for induction of macrophage tumoricidal activity and production of both NO and pro-inflammatory cytokines (TNF-α, IL-12p40, and IL-12p70). Furthermore, IFN-γ was shown to suppress macrophage IL-10 secretion induced by TLR agonists. NO production was necessary for macrophage tumoricidal activity. We conclude that two signals from the microenvironment are required for optimal induction of antitumor M1 macrophage phenotype. Combination treatment with IFN-γ and TLR agonists may offer new avenues for macrophage-based cancer immunotherapy.

Efficacy of Juzentaihoto for Tumor Immunotherapy in B16 Melanoma Metastasis Model

Introduction. Medical care for Japanese cancer patients includes Western and Kampo medicines, and treatments with juzentaihoto (JTT) reportedly prevent cancer metastasis and recurrence. In this study, we examined the effects of JTT on natural killer (NK) cell activity and metastasis in combined treatments with anti-PD-1 antibody in a mouse model of melanoma metastasis. Methods. C57BL/6 male mice were intravenously injected with B16 melanoma cells (B16 cell) and were given chow containing 3% JTT. In subsequent in vivo experiments, we assessed serum cytokine levels and tumor colony formation in the lungs. Additionally, we assessed NK cell activity in ex vivo experiments. Results. JTT significantly suppressed B16 cell metastasis, whereas injection of anti-asialo-GM1 antibody into mice abrogated the inhibitory actions of JTT. JTT significantly increased interleukin- (IL-) 12 and interferon- (IFN-) γ levels in serum and induced NK cell activity. It increased the inhibitory actions of the anti-PD-1 antibody on B16 cell metastasis. Discussion. These data suggest that JTT inhibits B16 cell metastasis by inducing NK cell activity. Additionally, combination therapy with JTT and anti-PD-1 antibody increased treatment response rates for B16 melanoma.

Tumoricidal Effects of Macrophage-Activating Immunotherapy in a Murine Model of Relapsed/Refractory Multiple Myeloma

Myeloma remains a virtually incurable malignancy. The inevitable evolution of multidrug-resistant clones and widespread clonal heterogeneity limit the potential of traditional and novel therapies to eliminate minimal residual disease (MRD), a reliable harbinger of relapse. Here, we show potent anti-myeloma activity of macrophage-activating immunotherapy (αCD40+CpG) that resulted in prolongation of progression-free survival (PFS) and overall survival (OS) in an immunocompetent, preclinically validated, transplant-based model of multidrug-resistant, relapsed/refractory myeloma (t-Vκ*MYC). αCD40+CpG was effective in vivo in the absence of cytolytic natural killer, T, or B cells and resulted in expansion of M1-polarized (cytolytic/tumoricidal) macrophages in the bone marrow. Moreover, we show that concurrent loss/inhibition of Tpl2 kinase (Cot, Map3k8), a MAP3K that is recruited to activated CD40 complex and regulates macrophage activation/cytokine production, potentiated direct, ex vivo anti-myeloma tumoricidal activity of αCD40+CpG-activated macrophages, promoted production of antitumor cytokine IL12 in vitro and in vivo, and synergized with αCD40+CpG to further prolong PFS and OS in vivo. Our results support the combination of αCD40-based macrophage activation and TPL2 inhibition for myeloma immunotherapy. We propose that αCD40-mediated activation of innate antitumor immunity may be a promising approach to control/eradicate MRD following cytoreduction with traditional or novel anti-myeloma therapies.

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.

Macrophages in multiple myeloma: emerging concepts and therapeutic implications

Multiple myeloma, a clonal plasma cell malignancy, has long provided a prototypic model to study regulatory interactions between malignant cells and their microenvironment. Myeloma-associated macrophages have historically received limited scrutiny, but recent work points to central and non-redundant roles in myeloma niche homeostasis. The evidence supports a paradigm of complex, dynamic and often mutable interactions between macrophages and other cellular constituents of the niche. We and others have shown that macrophages support myeloma cell growth, viability and drug resistance through both contact-mediated and non-contact-mediated mechanisms. These tumor-beneficial roles have evolved in opposition to, or in parallel with, intrinsic pro-inflammatory and tumoricidal properties. Thus, simple blockade of protective "don't eat me" signals on the surface of myeloma cells leads to macrophage-mediated myeloma cell killing. Macrophages also enhance the tumor-supportive role of mesenchymal stem/stromal cells (MSCs) in the niche: importantly, this interaction is bidirectional, producing a distinct state of macrophage polarization that we termed "MSC-educated macrophages." The intriguing pattern of cross-talk between macrophages, MSCs and tumor cells highlights the myeloma niche as a dynamic multi-cellular structure. Targeted reprogramming of these interactions harbors significant untapped therapeutic potential, particularly in the setting of minimal residual disease, the main obstacle toward a cure.

Enhancement of the anti-melanoma response of Hu14.18K322A by αCD40 + CpG

Targeted monoclonal antibodies (mAb) can be used therapeutically for tumors with identifiable antigens such as disialoganglioside GD2, expressed on neuroblastoma and melanoma tumors. Anti-GD2 mAbs (αGD2) can provide clinical benefit in patients with neuroblastoma. An important mechanism of mAb therapy is antibody-dependent cellular cytotoxicity (ADCC). Combinatorial therapeutic strategies can dramatically increase the anti-tumor response elicited by mAbs. We combined a novel αGD2 mAb, hu14.18K322A, with an immunostimulatory regimen of agonist CD40 mAb and class B CpG-ODN 1826 (CpG). Combination immunotherapy was more effective than the single therapeutic components in a syngeneic model of GD2-expressing B16 melanoma with minimal tumor burden. NK cell depletion in B6 mice showed that NK cells were required for the anti-tumor effect; however, anti-tumor responses were also observed in tumor-bearing SCID/beige mice. Thus, NK cell cytotoxicity did not appear to be essential. Peritoneal macrophages from anti-CD40 + CpG-treated mice inhibited tumor cells in vitro in an hu14.18K322A antibody-dependent manner. These data highlight the importance of myeloid cells as potential effectors in immunotherapy regimens utilizing tumor-specific mAb and suggest that further studies are needed to investigate the therapeutic potential of activated myeloid cells and their interaction with NK cells.