B7.1/NHS76: a new costimulator fusion protein for the immunotherapy of solid tumors

CD80 Expression on Tumor Cells Alters Tumor Microenvironment and Efficacy of Cancer Immunotherapy by CTLA-4 Blockade

Cluster of differentiation (CD) 80 is mainly expressed in immune cells but can also be found in several types of cancer cells. This molecule may either activate or inhibit immune reactions. Here, we determined the immunosuppressive role of CD80 in the tumor microenvironment by CRISPR/Cas9-mediated deactivation of the corresponding gene in the mouse oncogenic TC-1 cell line. The tumor cells with deactivated CD80 (TC-1/dCD80-1) were more immunogenic than parental cells and induced tumors that gained sensitivity to cytotoxic T-lymphocyte antigen 4 (CTLA-4) blockade, as compared with the TC-1 cells. In vivo depletion experiments showed that the deactivation of CD80 switched the pro-tumorigenic effect of macrophages observed in TC-1-induced tumors into an anti-tumorigenic effect in TC-1/dCD80-1 tumors and induced the pro-tumorigenic activity of CD4⁺ cells. Moreover, the frequency of lymphoid and myeloid cells and the CTLA-4 expression by T helper (Th)17 cells were increased in TC-1/dCD80-1- compared with that in the TC-1-induced tumors. CTLA-4 blockade downregulated the frequencies of most immune cell types and upregulated the frequency of M2 macrophages in the TC-1 tumors, while it increased the frequency of lymphoid cells in TC-1/dCD80-1-induced tumors. Furthermore, the anti-CTLA-4 therapy enhanced the frequency of CD8⁺ T cells as well as CD4⁺ T cells, especially for a Th1 subset. Regulatory T cells (Treg) formed the most abundant CD4⁺ T cell subset in untreated tumors. The anti-CTLA-4 treatment downregulated the frequency of Treg cells with limited immunosuppressive potential in the TC-1 tumors, whereas it enriched this type of Treg cells and decreased the Treg cells with high immunosuppressive potential in TC-1/dCD80-1-induced tumors. The immunosuppressive role of tumor-cell-expressed CD80 should be considered in research into biomarkers for the prediction of cancer patients' sensitivity to immune checkpoint inhibitors and for the development of a tumor-cell-specific CD80 blockade.

Antibody-cytokine fusion proteins: Biopharmaceuticals with immunomodulatory properties for cancer therapy

Cytokines have long been used for therapeutic applications in cancer patients. Substantial side effects and unfavorable pharmacokinetics limit their application and may prevent dose escalation to therapeutically active regimens. Antibody-cytokine fusion proteins (often referred to as immunocytokines) may help localize immunomodulatory cytokine payloads to the tumor, thereby activating anticancer immune responses. A variety of formats (e.g., intact IgGs or antibody fragments), molecular targets (e.g., extracellular matrix components and cell membrane antigens) and cytokine payloads have been considered for the development of this novel class of biopharmaceuticals. This review presents the basic concepts on the design and engineering of immunocytokines, reviews their potential limitations, points out emerging opportunities and summarizes key features of preclinical and clinical-stage products.

Enhanced binding of necrosis-targeting immunocytokine NHS-IL12 after local tumour irradiation in murine xenograft models

PURPOSE

NHS-IL12 is an immunocytokine targeting necrotic tumour areas. IL12 shows anti-tumour activity. As local irradiation might induce additional necrosis in solid tumours, we aimed to evaluate the increase in intratumoural accumulation of NHS-IL12 after irradiation and correlate the findings with diffusion-weighted MRI studies in two xenograft models.

METHODS

Human rhabdomyosarcoma (A204) and prostate cancer (PC3) cells were studied in vitro and as subcutaneous xenografts. Radiation sensitivity of the cell lines was assessed in vitro by colony formation assays. In vivo tumour necrosis was assessed based on apparent diffusion coefficients (ADC). Biodistribution of NHS-IL12 was evaluated with and without tumour irradiation using in vivo small-animal PET and ex vivo biodistribution.

RESULTS

A204 and PC3 differed in their intrinsic radiation sensitivity. Accordingly, radiation-induced tumour necrosis was found only in A204 xenografts. In comparison with control, ADC was significantly increased after irradiation of A204 tumours with 1 × 8.0 Gy and 5 × 2.0 Gy, whereas no change in ADC was observed in PC3 xenografts in all irradiation regimes. ADC correlated with histology. An enhanced uptake of radiolabelled NHS-IL12 in A204 tumours was detected by PET and ex vivo biodistribution after tumour irradiation. In PC3 tumours, no increase in NHS-IL12 uptake was observed.

CONCLUSIONS

In dependence of the tumour model, tumour irradiation enhanced tumour necrosis measured in MRI and histology. In vivo PET and ex vivo biodistribution showed enhanced binding of NHS-IL12 in rhabdomyosarcoma xenografts. Thus, enhanced binding of necrosis-targeting immunocytokines might be a novel mechanism of additive effects in combination with irradiation.

Antibody fusions with immunomodulatory proteins for cancer therapy

The potential of immunomodulatory proteins, in particular cytokines, for cancer therapy is well recognized, but hampered by the toxicity associated with their systemic application. In order to address this problem, targeted delivery by antibody fusion proteins has been early proposed and their development intensively pursued over the last decade. Here, factors influencing the selection and modification of cytokines and antibody formats for this approach are being discussed, indicating current developments and translational advances in the field.

Evaluating combinations of costimulatory antibody-ligand fusion proteins for targeted cancer immunotherapy

Combinatory strategies are becoming of increasing interest in cancer immunotherapy. Costimulation by individual members of the immunoglobulin-like (Ig)- and TNF superfamily have already shown promising antitumor potential, thus prompting the exploration of their synergistic abilities in combinatorial approaches. Here, we pursued a targeted strategy with antibody-fusion proteins composed of a tumor-directed antibody and the extracellular domain of the costimulatory ligand B7.1, 4-1BBL, OX40L, GITRL or LIGHT, respectively. Costimulatory activity was assessed in an experimental setting where initial T cell activation was induced by a bispecific antibody (tumor-related antigen × CD3). Advantage of combined targeted costimulation was shown for either B7.1 or 4-1BBL with OX40L, GITRL, LIGHT and 4-1BBL in terms of T cell proliferation and IFN-γ release. Since encouraging results were obtained by the combination of B7.1 and 4-1BBL, we adapted the model system for a time-shift setting. Here, enhanced proliferation and granzyme B expression as well as reduced PD-1 expression on the T cell population demonstrated the benefit of costimulation-assisted restimulation. Finally, the antitumor potential of this combinatorial setting was confirmed in vivo in a lung metastasis mouse model. Thus, combinatorial approaches with costimulatory antibody-ligand fusion proteins seem a promising strategy to be further investigated for cancer immunotherapy.

Chemokines, costimulatory molecules and fusion proteins for the immunotherapy of solid tumors

In this article, the role of chemokines and costimulatory molecules in the immunotherapy of experimental murine solid tumors and immunotherapy used in ongoing clinical trials are presented. Chemokine networks regulate physiologic cell migration that may be disrupted to inhibit antitumor immune responses or co-opted to promote tumor growth and metastasis in cancer. Recent studies highlight the potential use of chemokines in cancer immunotherapy to improve innate and adaptive cell interactions and to recruit immune effector cells into the tumor microenvironment. Another critical component of antitumor immune responses is antigen priming and activation of effector cells. Reciprocal expression and binding of costimulatory molecules and their ligands by antigen-presenting cells and naive lymphocytes ensures robust expansion, activity and survival of tumor-specific effector cells in vivo. Immunotherapy approaches using agonist antibodies or fusion proteins of immunomodulatory molecules significantly inhibit tumor growth and boost cell-mediated immunity. To localize immune stimulation to the tumor site, a series of fusion proteins consisting of a tumor-targeting monoclonal antibody directed against tumor necrosis and chemokines or costimulatory molecules were generated and tested in tumor-bearing mice. While several of these reagents were initially shown to have therapeutic value, combination therapies with methods to delete suppressor cells had the greatest effect on tumor growth. In conclusion, a key conclusion that has emerged from these studies is that successful immunotherapy will require both advanced methods of immunostimulation and the removal of immunosuppression in the host.

Construction and preclinical characterization of Fc-mGITRL for the immunotherapy of cancer

PURPOSE

To provide proper costimulation required for effective cancer T-cell immunity, Fc-GITRL fusion proteins were generated for use in immunotherapy protocols.

EXPERIMENTAL DESIGN

Soluble fusion proteins consisting of the Fc fragment of immunoglobulin and the murine glucocorticoid-induced tumor necrosis factor-related receptor ligand (mGITRL) connected with different linkers were genetically engineered and tested for their potency in two BALB/c solid tumor models.

RESULTS

In vivo, construct #178-14 (-5aa, -linker) showed the best activity (>90% tumor reduction) at doses ranging from 5 to 25 microg and was found to be intact by gel electrophoresis. Similar doses used with construct #175-2 (-linker) produced good but not as high tumor regression. Construct #5-1 (+linker), which was found to be relatively unstable by SDS gel electrophoresis, produced <60% tumor regression and required a higher dose (100 microg) to produce optimal results. Survival curves showed that Fc-mGITRL treatment extended the life of 80% of tumor-bearing mice to >3 months compared with controls that died by day 40. T-cell depletion studies showed that CD8(+) T cells play a major role in Fc-mGITRL immunotherapy, and tumors removed from Fc-mGITRL- and DTA-1-treated mice showed a significant influx of granzyme B(+) lymphocytes compared with controls. Finally, T regulatory (Treg) cell assays showed that, unlike other Fc fusion proteins, all three Fc-mGITRL constructs profoundly suppressed Treg activity.

CONCLUSIONS

These studies suggest that a stable, intact Fc-mGITRL fusion protein can provide missing costimulation for the immunotherapy of solid tumors. In addition, Fc-mGITRL may alter Treg activity to enhance its effectiveness for tumor immunotherapy.

Cytokine, chemokine, and co-stimulatory fusion proteins for the immunotherapy of solid tumors

This chapter describes the generation of novel reagents for the treatment of cancer using fusion proteins constructed with natural ligands of the immune system. Immunotherapy is a powerful therapeutic modality that has not been fully harnessed for the treatment of cancer. We and others have hypothesized that if the proper immunoregulatory ligands can be targeted to the tumor, an effective immune response can be mounted to treat both established primary tumors and distant metastatic lesions. Though it is generally believed that immunotherapy has the potential to treat only residual disease, we offer evidence that this approach can, by itself, destroy large tumor masses and produce lasting remissions of experimental solid tumors. From these studies, three major classes of immune activators, namely, cytokines, chemokines, and costimulatory molecules, have been shown to generate antitumor responses in animal models. In addition, the reversal of immune tolerance by the deletion of T regulatory (Treg) cells has been shown to be equally important for effective immunotherapy. In an attempt to identify reagents that can provide an enhanced immune stimulation and treatment of cancer, our laboratory has developed a novel monoclonal antibody targeting approach, designated Tumor Necrosis Therapy (TNT), which utilizes stable intracellular antigens present in all cell types but which are only accessible in dead and/or dying cells. Since tumors contain necrotic and degenerating regions that account for 30-80% of the tumor mass, this targeting approach can be used to deliver therapeutic reagents to the core of tumors, a site abundant in tumor antigens. In our first set of reagents, a panel of cytokine fusion proteins was genetically engineered using monoclonal antibody chimeric TNT-3 (chTNT-3) directed against necrotic regions of tumors (single-stranded DNA) fused with IL-2, or GM-CSF, or TNFalphaa, or IFNgamma. Tested against different solid tumors, these reagents were found to mount an effective although transient immune response to tumor especially when used in combination. To improve upon these results, additional chTNT-3 fusion proteins using the liver-expression chemokine (LEC) and the costimulatory molecule B7.1 were constructed. Both of these reagents were found to work significantly better than the above cytokine fusion proteins due to their ability to stimulate multiple arms of the immune system deemed useful for cancer immunotherapy. Finally, the Tumor Necrosis Factor Superfamily (TNFSF) gene DC137L was used to generate chTNT-3 antibody (targeted) and soluble Fc (untargeted) fusion proteins. When used alone, both forms of costimulatory fusion proteins were found to produce in a s dose-dependent manner, complete regression of murine solid tumors. Evidence is presented to show that Treg cells play an important role in suppressing antitumor immunity since the deletion of these cells, when used in combination with LEC or costimulatory fusion proteins, produced profound and effective treatment with sustained memory. It is hoped that these data will further the preclinical development of soluble Fc and antibody based fusion proteins fro the immunotherapy of cancer.

RA8, a human anti-CD25 antibody against human Treg cells

Although anti-CD25 antibodies exist for clinical use in patients, there is a need for the development of a human Treg antibody that will abrogate the immunosuppressive function of this small but critical T cell subtype. Based upon mounting evidence that the level of Treg cells in the tumor microenvironment correlates with clinical prognosis and stage in man, it appears that Treg cells play an important role in the tumor's ability to overcome host immune responses. In mice, the rat anti-mouse CD25 antibody PC61 causes depletion of CD25-bearing Treg cells both peripherally in lymphatic tissues and in the tumor microenvironment, without inducing symptoms of autoimmunity. A similar antibody, though with the ability to delete Treg cells specifically, would be an important new tool for reversing tumor escape associated with Treg immunosuppression in man. To begin to generate such a reagent, we now describe the development of a human anti-CD25 antibody using a novel yeast display library. The target antigen CD25-Fc was constructed and used for five rounds of selection using a non-immune yeast display library that contained as many as 10(9) single chain variable fragments (scFv). Two unique clones with low K(D) values (RA4 and RA8) were then selected to construct fully human anti-CD25 antibodies (IgG1/kappa) for stable expression. One antibody, RA8, showed excellent binding to human CD25(+) cell lines and to human Treg cells and appears to be an excellent candidate for the generation of a human reagent that may be used in man for the immunotherapy of cancer.

Engineering antibodies for clinical applications

Molecular engineering has contributed immensely to the clinical success of antibodies in recent years. The modular structure of antibodies has permitted their modification in numerous ways, to meet various clinical requirements. With the help of antibody engineering, it has been possible to modify the molecular size, pharmacokinetics, immunogenicity, binding affinity, specificity and effector function of antibodies. In addition, fusion proteins of antibodies with various proteins and peptides have yielded targeted biological modifiers, toxins and imaging agents. This review focuses on the recent trends in antibody engineering for improving their clinical utility.