Synergism between GM-CSF and IFNgamma: enhanced immunotherapy in mice with glioma

Old drug, new use: Recent advances for G-CSF

Granulocyte colony-stimulating factor (G-CSF), also known as colony-stimulating factor 3 (CSF3), is a proinflammatory cytokine that primarily stimulates the survival, proliferation, differentiation and function of neutrophil granulocyte progenitor cells and mature neutrophils. Over the past years, G-CSF has mainly been used to cure patients with neutropenia and as a part of chemotherapy to induct the remission for refractory/relapse leukemia. Recent studies showed that C-CSF can been used as condition regimens and as a part of preventive methods after allogeneic transplantation to improve the survival of patients and also has immunoregulation, and has promote or inhibit the proliferation of solid tumors. Therefore, in this review, we firstly describe the structure for G-CSF. Then its functions and mechanism were reviewed including the neutrophil mobilization, differentiation, migration, and inhibiting apoptosis of neutrophils, and its immunoregulation. Finally, the clinical applications were further discussed.

Convection-enhanced delivery of temozolomide and whole cell tumor immunizations in GL261 and KR158 experimental mouse gliomas

Background

Glioblastomas (GBM) are therapy-resistant tumors with a profoundly immunosuppressive tumor microenvironment. Chemotherapy has shown limited efficacy against GBM. Systemic delivery of chemotherapeutic drugs is hampered by the difficulty of achieving intratumoral levels as systemic toxicity is a dose-limiting factor. Although some of its effects might be mediated by immune reactivity, systemic chemotherapy can also inhibit induced or spontaneous antitumor immune reactivity. Convection-enhanced delivery of temozolomide (CED-TMZ) can tentatively increase intratumoral drug concentration while reducing systemic side effects. The objective of this study was to evaluate the therapeutic effect of intratumorally delivered temozolomide in combination with immunotherapy and whether such therapy can generate a cellular antitumor immune response.

Methods

Single bolus intratumoral injection and 3-day mini-osmotic pumps (Alzet®) were used to deliver intratumoral TMZ in C57BL6 mice bearing orthotopic gliomas. Immunotherapy consisted of subcutaneous injections of irradiated GL261 or KR158 glioma cells. Tumor size and intratumoral immune cell populations were analyzed by immunohistochemistry.

Results

Combined CED-TMZ and immunotherapy had a synergistic antitumor effect in the GL261 model, compared to CED-TMZ or immunotherapy as monotherapies. In the KR158 model, immunization cured a small proportion of the mice whereas addition of CED-TMZ did not have a synergistic effect. However, CED-TMZ as monotherapy prolonged the median survival. Moreover, TMZ bolus injection in the GL261 model induced neurotoxicity and lower cure rate than its equivalent dose delivered by CED. In addition, we found that T-cells were the predominant cells responsible for the TMZ antitumor effect in the GL261 model. Finally, CED-TMZ combined with immunotherapy significantly reduced tumor volume and increased the intratumoral influx of T-cells in both models.

Conclusions

We show that immunotherapy synergized with CED-TMZ in the GL261 model and cured animals in the KR158 model. Single bolus administration of TMZ was effective with a narrower therapeutic window than CED-TMZ. Combined CED-TMZ and immunotherapy led to an increase in the intratumoral influx of T-cells. These results form part of the basis for the translation of the therapy to patients with GBM but the dosing and timing of delivery will have to be explored in depth both experimentally and clinically.

The effect of locally delivered cisplatin is dependent on an intact immune function in an experimental glioma model

Several chemotherapeutic drugs are now considered to exert anti-tumour effects, by inducing an immune-promoting inflammatory response. Cisplatin is a potent chemotherapeutic agent used in standard medulloblastoma but not glioblastoma protocols. There is no clear explanation for the differences in clinical efficacy of cisplatin between medulloblastomas and glioblastomas, despite the fact that cisplatin is effective in vitro against the latter. Systemic toxicity is often dose limiting but could tentatively be reduced by intratumoral administration. We found that intratumoral cisplatin can cure GL261 glioma-bearing C57BL/6 mice and this effect was abolished in GL261-bearing NOD-scid IL2rγnull (NSG) mice. Contrary to previous results with intratumoral temozolomide cisplatin had no additive or synergistic effect with whole cell either GL261 wild-type or GM-CSF-transfected GL261 cells whole cell vaccine-based immunotherapy. While whole tumour cell immunizations increased CD8+ T-cells and decreased F4/80+ macrophages intratumorally, cisplatin had no effect on these cell populations. Taken together, our results demonstrate that intratumoral cisplatin treatment was effective with a narrow therapeutic window and may be an efficient approach for glioma or other brain tumour treatment.

Overcoming the resistance of pancreatic cancer to immune checkpoint inhibitors

Immunotherapy has become a new modality of cancer treatment, but has had a limited success in treating PDAC. A combination approach to immunotherapy, using both immune checkpoint inhibitors and immune activating agonists, is needed, as PDAC does not respond to single-agent checkpoint inhibitors. Studies have also supported using vaccine-based therapies to prime the tumor microenvironment of PDAC with effector T-cells. Other therapeutic strategies including epigenetic agents, stroma modulators, radiotherapy, and T-cell transfer therapies may also prime the tumor microenvironment to overcome resistance to immune checkpoint inhibitors.

A standardized and reproducible protocol for serum-free monolayer culturing of primary paediatric brain tumours to be utilized for therapeutic assays

In vitro cultured brain tumour cells are indispensable tools for drug screening and therapeutic development. Serum-free culture conditions tentatively preserve the features of the original tumour, but commonly comprise neurosphere propagation, which is a technically challenging procedure. Here, we define a simple, non-expensive and reproducible serum-free cell culture protocol for establishment and propagation of primary paediatric brain tumour cultures as adherent monolayers. The success rates for establishment of primary cultures (including medulloblastomas, atypical rhabdoid tumour, ependymomas and astrocytomas) were 65% (11/17) and 78% (14/18) for sphere cultures and monolayers respectively. Monolayer culturing was particularly feasible for less aggressive tumour subsets, where neurosphere cultures could not be generated. We show by immunofluorescent labelling that monolayers display phenotypic similarities with corresponding sphere cultures and primary tumours, and secrete clinically relevant inflammatory factors, including PGE₂, VEGF, IL-6, IL-8 and IL-15. Moreover, secretion of PGE₂ was considerably reduced by treatment with the COX-2 inhibitor Valdecoxib, demonstrating the functional utility of our newly established monolayer for preclinical therapeutic assays. Our findings suggest that this culture method could increase the availability and comparability of clinically representative in vitro models of paediatric brain tumours, and encourages further molecular evaluation of serum-free monolayer cultures.

Cytokines: shifting the balance between glioma cells and tumor microenvironment after irradiation

Malignant gliomas invariably recur after irradiation, showing radioresistance. Meanwhile, cranial irradiation can bring some risk for developing cognitive dysfunction. There is increasing evidence that cytokines play their peculiar roles in these processes. On the one hand, cytokines directly influence the progression of malignant glioma, promoting or suppressing tumor progression. On the other hand, cytokines indirectly contribute to the immunologic response against gliomas, exhibiting pro-inflammatory or immunosuppressive activities. We propose that cytokines are not simply unregulated products from tumor cells or immune cells, but mediators finely adjust the balance between glioma cells and tumor microenvironment after irradiation. The paper, therefore, focuses on the changes of cytokines after irradiation, analyzing how these mediate the response of tumor cells and normal cells to irradiation. In addition, cytokine-based immunotherapeutic strategies, accompanied with irradiation, for the treatment of gliomas are also discussed.

Immunizations with unmodified tumor cells and simultaneous COX-2 inhibition eradicate malignant rat brain tumors and induce a long-lasting CD8(+) T cell memory

Malignant brain tumors induce pronounced immunosuppression, which diminishes immune responses generated by immunotherapy. Here we report that peripheral immunotherapy, using irradiated unmodified whole tumor cells, and systemic cyclooxygenase-2 inhibition induce cure in glioma-bearing rats (60% cure rate), whereas neither monotherapy was sufficient to cure any animal. Moreover, the combined therapy protected against secondary tumor challenges (89% cure rate) and the secondary immune response was correlated with increased plasma interferon-gamma levels and CD8(+) T cells systemically and intratumorally. In conclusion, we demonstrate that cyclooxygenase-2 inhibition is sufficient to render unmodified tumor cells immunogenic in immunotherapy of experimental brain tumors.

Antibody-based immunotherapy for malignant glioma

Conventional therapy for malignant glioma (MG) fails to specifically eliminate tumor cells, resulting in toxicity that limits therapeutic efficacy. In contrast, antibody-based immunotherapy uses the immune system to eliminate tumor cells with exquisite specificity. Increased understanding of the pathobiology of MG and the profound immunosuppression present among patients with MG has revealed several biologic targets amenable to antibody-based immunotherapy. Novel antibody engineering techniques allow for the production of fully human antibodies or antibody fragments with vastly reduced antigen-binding dissociation constants, increasing safety when used clinically as therapeutics. In this report, we summarize the use of antibody-based immunotherapy for MG. Approaches currently under investigation include the use of antibodies or antibody fragments to: (1) redirect immune effector cells to target tumor mutations, (2) inhibit immunosuppressive signals and thereby stimulate an immunological response against tumor cells, and (3) provide costimulatory signals to evoke immunologic targeting of tumor cells. These approaches demonstrate highly compelling safety and efficacy for the treatment of MG, providing a viable adjunct to current standard-of-care therapy for MG.

A role for G-CSF and GM-CSF in nonmyeloid cancers

Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) modulate progression of certain solid tumors. The G-CSF- or GM-CSF-secreting cancers, albeit not very common are, however, among the most rapidly advancing ones due to a cytokine-mediated immune suppression and angiogenesis. Similarly, de novo angiogenesis and vasculogenesis may complicate adjuvant use of recombinant G-CSF or GM-CSF thus possibly contributing to a cancer relapse. Rapid diagnostic tools to differentiate G-CSF- or GM-CSF-secreting cancers are not well developed therefore hindering efforts to individualize treatments for these patients. Given an increasing utilization of adjuvant G-/GM-CSF in cancer therapy, we aimed to summarize recent studies exploring their roles in pathophysiology of solid tumors and to provide insights into some complexities of their therapeutic applications.

Intratumoral temozolomide synergizes with immunotherapy in a T cell-dependent fashion

Despite temozolomide (TMZ) treatment, the prognosis for patients with glioblastoma multiforme is still dismal. As dose escalation of TMZ is limited by systemic toxicity, intratumoral delivery emerges as an attractive treatment modality, which may sustain cytotoxic drug concentrations intratumorally and induce immunogenic cell death. Both clinical and experimental gliomas have responded to immunotherapy, but the benefit of simultaneous chemo- and immunotherapy is inadequately studied. Here, we monitored survival of GL261-bearing C57BL/6 mice following a 3-day treatment with either intratumoral TMZ (micro-osmotic pump, 4.2 mg/kg/day) or systemic TMZ (i.p. injections, 50 mg/kg/day) alone, or combined with immunization using GM-CSF secreting GL261 cells. Peripheral and intratumoral leukocytes were analyzed by flow cytometry and immunohistochemistry. Intratumoral TMZ induced higher survival rate than systemic TMZ (45 vs. 8%). When T cells were depleted following intratumoral TMZ, the therapeutic effect was completely abrogated (0 % survival). Intratumoral TMZ synergistically increased survival rate of immunized mice (from 25 to 83%), while systemic TMZ failed (0%). While systemic TMZ induced a transient leukopenia, intratumoral TMZ and immunotherapy sustained the proliferation of CD8+ T cells and decreased the number of intratumoral immunosuppressive cells. In conclusion, intratumoral TMZ alone or in combination with immunotherapy could cure glioma-bearing mice, due to attenuation of local immunosuppression and increase in potential effector immune cells.

In vitro synthesis of primary specific anti-breast cancer antibodies by normal human peripheral blood mononuclear cells

In this study, we developed a unique in vitro model to mimic the endogenous tumor microenvironment to understand the effect of immunotherapy with activated T-cells (ATC) armed with anti-CD3 × anti-Her2 bispecific antibody (aATC) on antibody response by naive immune cells. This model contained a co-culture of naïve peripheral blood mononuclear cells (PBMC), breast cancer cells (SK-BR-3), ATC or aATC and CpG ODNs. Culture supernatants were tested at various time points for anti-SK-BR-3 antibodies by ELISA, Western blot and flow cytometry. PBMC cocultured with non-irradiated aATC or irradiated (*) aATC showed significant increases in anti-tumor antibody production at day 14 (P < 0.0001) in the presence of CpG-ODN compared to unstimulated PBMC cultures (n = 9). Antibody specificity was confirmed by ELISA, Western blot and flow cytometry. Co-cultures containing *aATC and CpG showed significantly enhanced levels of IgG(2) (P < 0.001) and cytokines that promote IgG(2) synthesis including IL-13 (P < 0.02), IFNγ (P < 0.01) and GM-CSF (P < 0.05) compared to unstimulated PBMC control (n = 3). We show that aATC targeting and lysis of tumor cells induces an anti-tumor antibody response in our in vitro model. This model provides a unique opportunity to evaluate the interactions of T-cells, B-cells, and antigen-presenting cells leading to specific anti-tumor antibody responses.

Experimental immunotherapy for malignant glioma: lessons from two decades of research in the GL261 model

Nearly twenty years of experimental immunotherapy for malignant glioma yielded important insights in the mechanisms governing glioma immunology. Still considered promising, it is clear that immunotherapy does not on its own represent the magic bullet in glioma therapy. In this review, we summarize the major immunotherapeutic achievements in the mouse GL261 glioma model, which has emerged as the gold standard syngeneic model for experimental glioma therapy. Gene therapy, monoclonal antibody treatment, cytokine therapy, cell transfer strategies and dendritic cell therapy were hereby considered. Apart from the considerable progress made in understanding glioma immunology in this model, we also addressed its most pertinent issues and shortcomings. Despite these, the GL261 model will remain indispensable in glioma research since it is a fast, highly reproducible and easy-to-establish model system.

Mitigation of ionizing radiation-induced bone marrow suppression by p38 inhibition and G-CSF administration

p38 mitogen-activated protein kinases (p38) has been shown to be activated in hematopoietic stem and progenitors cells after exposure to ionizing radiation (IR) and its activation has been implicated in bone marrow (BM) suppression under various pathological conditions. Therefore, in the present study we investigated whether inhibition of p38 activity alone with SB203580 (SB, a specific p38 inhibitor) or in combination with granulocyte colony-stimulating factor (G-CSF) can mitigate total body irradiation (TBI)-induced BM damage and lethality. Our results showed that p38 inhibition with SB had no significant effect on the 30-day survival rates of the mice exposed to 7.2 Gy TBI when it was used alone but increased the survival of the mice when it was combined with G-CSF. This combined effect may be attributable to a better preservation or stimulation of hematopoietic stem and progenitor cells, because BM cells from SB and G-CSF-treated mice produced more colony forming units-granulocyte-macrophage (CFU-GM) and 4-week cobblestone area forming cells (CAFCs) than the cells from either SB or G-CSF-treated mice after TBI in a colony forming cell assay and a CAFC assay, respectively. These findings suggest that the combined therapy with SB and G-GSF is more effective in mitigating TBI-induced acute BM injury than either agent alone.

Targeting HSV-1 virions for specific binding to epidermal growth factor receptor-vIII-bearing tumor cells

Oncolytic herpes simplex virus (HSV) vectors have been used in early phase human clinical trials as a therapy for recurrent malignant glioblastoma. This treatment proved safe but limited improvements in patient survival were observed. The potency of these vectors might be enhanced by targeting vector infectivity to tumor cells. Glioma tumors often express a mutant form (vIII) of the epidermal growth factor receptor (EGFR) resulting in the presence of a novel epitope on the cell surface. This epitope is specifically recognized by a single chain antibody designated MR1-1. HSV-1 infection involves initial binding to heparan sulfate (HS) on the cell surface mediated primarily by the viral envelope, glycoprotein C (gC). Here we joined the MR1-1 single chain antibody (scFv) to the gC sequence deleted for the HS binding domain (HSBD) as a means of targeting viral attachment to EGFRvIII on glial tumor cells. Virions bearing MR1-1-modified-gC had 5-fold increased infectivity for EGFRvIII-bearing human glioma U87 cells compared to mutant receptor-deficient cells. Further, MR1-1/EGFRvIII mediated infection was more efficient for EGFRvIII-positive cells than was wild-type virus for either positive or negative cells. Sustained infection of EGFRvIII+ glioma cells by MR1-1-modified-gC bearing oncolytic virus, as compared to wild-type gC oncolytic virus, was also shown in subcutaneous tumors in vivo using firefly luciferase as a reporter of infection. These data demonstrate that HSV tropism can be manipulated so that virions recognize a cell specific binding site with increased infectivity for the target cell. The retargeting of HSV infection to tumor cells should enhance vector specificity, tumor cell killing and vector safety.

Intratumoral IL-7 delivery by mesenchymal stromal cells potentiates IFNgamma-transduced tumor cell immunotherapy of experimental glioma

The present study reports regression of pre-established experimental rat gliomas as a result of combining peripheral immunization using interferon gamma (IFNgamma) transduced autologous tumor cells with local intratumoral delivery of interleukin 7 (IL-7) by mesenchymal stromal cells. IL-7 alone significantly decreased the tumor area and this effect was enhanced with IFNgamma immunization. A higher density of intratumoral T-cells was observed in animals receiving combined therapies compared to rats receiving either cytokine alone suggesting that the therapeutic effect is dependent on a T-cell response.

Cure of established GL261 mouse gliomas after combined immunotherapy with GM-CSF and IFNgamma is mediated by both CD8+ and CD4+ T-cells

We were the first to demonstrate that combined immunotherapy with GM-CSF producing GL261 cells and recombinant IFNgamma of preestablished GL261 gliomas could cure 90% of immunized mice. To extend these findings and to uncover the underlying mechanisms, the ensuing experiments were undertaken. We hypothesized that immunizations combining both GM-CSF and IFNgamma systemically would increase the number of immature myeloid cells, which then would mature and differentiate into dendritic cells (DCs) and macrophages, thereby augmenting tumor antigen presentation and T-cell activation. Indeed, the combined therapy induced a systemic increase of both immature and mature myeloid cells but also an increase in T regulatory cells (T-regs). Cytotoxic anti-tumor responses, mirrored by an increase in Granzyme B-positive cells as well as IFNgamma-producing T-cells, were augmented after immunizations with GM-CSF and IFNgamma. We also show that the combined therapy induced a long-term memory with rejection of intracerebral (i.c.) rechallenges. Depletion of T-cells showed that both CD4+ and CD8+ T-cells were essential for the combined GM-CSF and IFNgamma effect. Finally, when immunizations were delayed until day 5 after tumor inoculation, only mice receiving immunotherapy with both GM-CSF and IFNgamma survived. We conclude that the addition of recombinant IFNgamma to immunizations with GM-CSF producing tumor cells increased the number of activated tumoricidal T-cells, which could eradicate established intracerebral tumors. These results clearly demonstrate that the combination of cytokines in immunotherapy of brain tumors have synergistic effects that have implications for clinical immunotherapy of human malignant brain tumors.