Co-Stimulatory Bispecific Antibodies Induce Enhanced T Cell Activation and Tumor Cell Killing in Breast Cancer Models

Although T cell-recruiting CD3-binding bispecific antibodies (BiMAb) have been proven to be clinically effective for hematologic malignancies, the success of BiMAb targeting solid tumor-associated antigens (TAA) in carcinomas so far remains poor. We reasoned that provision of co-stimulatory BiMAb in combination with αTAA-αCD3 BiMAb would boost T cell activation and proliferative capacity, and thereby facilitate the targeting of weakly or heterogeneously expressed tumor antigens. Various αTAA-αCD3 and αTAA-αCD28 BiMAb in a tetravalent IgG1-Fc based format have been analyzed, targeting multiple breast cancer antigens including HER2, EGFR, CEA, and EpCAM. Moreover, bifunctional fusion proteins of αTAA-tumor necrosis factor ligand (TNFL) superfamily members including 4-1BBL, OX40L, CD70 and TL1A have been tested. The functional activity of BiMAb was assessed using co-cultures of tumor cell lines and purified T cells in monolayer and tumor spheroid models. Only in the presence of tumor cells, αTAA-αCD3 BiMAb activated T cells and induced cytotoxicity in vitro, indicating a strict dependence on cross-linking. Combination treatment of αTAA-αCD3 BiMAb and co-stimulatory αTAA-αCD28 or αTAA-TNFL fusion proteins drastically enhanced T cell activation in terms of proliferation, activation marker expression, cytokine secretion and tumor cytotoxicity. Furthermore, BiMAb providing co-stimulation were shown to reduce the minimally required dose to achieve T cell activation by at least tenfold. Immuno-suppressive effects of TGF-β and IL-10 on T cell activation and memory cell formation could be overcome by co-stimulation. BiMAb-mediated co-stimulation was further augmented by immune checkpoint-inhibiting antibodies. Effective co-stimulation could be achieved by targeting a second breast cancer antigen, or by targeting fibroblast activation protein (FAP) expressed on another target cell. In tumor spheroids derived from pleural effusions of breast cancer patients, co-stimulatory BiMAb were essential for the activation tumor-infiltrating lymphocytes and cytotoxic anti-tumor responses against breast cancer cells. Taken together we showed that co-stimulation significantly potentiated the tumoricidal activity of T cell-activating BiMAb while preserving the dependence on TAA recognition. This approach could provide for a more localized activation of the immune system with higher efficacy and reduced peripheral toxicities.

Abstract 3573: Novel DNA vectors encoding a chimeric antigen receptor mediate long term expression without genomic integration

Adoptive immunotherapy is one of the most encouraging therapeutic strategies for the treatment of a range of cancers. One particularly promising avenue of research is the functional introduction of Chimeric Antigen Receptors (CARs) into naive Human T-Cells for autologous-immunotherapy. Currently, the genetic engineering of these cells is achieved through the use of proprietary integrating vector systems such as lentiviruses or the sleeping beauty transposon system which present a risk of genotoxicity associated with their random genomic integration.

We have invented a novel DNA Vector platform for the safe and efficient generation of genetically engineered T-Cells for Human Immunotherapy. This DNA vector system contains no viral components and comprises only clinically approved sequences, it does not integrate into the target cell's genome but it can replicate autonomously and extrachromosomally in the nucleus of dividing human primary cells. These DNA Vectors offer several advantages over currently used vector systems; they are not subject to commercial licences, they are cheaper and easier to produce, and they can more quickly genetically modify human cells without the inherent risk of integrative mutagenesis.

In preclinical experiments we have successfully generated genetically engineered human T-Cells expressing the CAR receptor against several epitopes and have demonstrated their viability and capability in targeting and killing human cancer cells which express these epitopes. The long term anti-tumor activity of our DNA-CAR-T cells has been confirmed in vivo using xenotransplanted cell lines in immunodeficient mice.

We believe that this novel DNA Vector system provides a unique and innovative approach to this exciting therapeutic strategy for cancer therapy. We estimate that this novel methodology will provide a simpler method of CAR T-cell manufacturing, resulting in a 10-fold reduction in the cost of the CART-product.

Citation Format: Patrick Schmidt, Matthias Bozza, Aileen Berger, Claudia Luckner-Minden, Alexandra Tuch, Inka Zörnig, Dirk Jäger, Richard Harbottle. Novel DNA vectors encoding a chimeric antigen receptor mediate long term expression without genomic integration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3573.

Reconstitution of T Cell Proliferation under Arginine Limitation: Activated Human T Cells Take Up Citrulline via L-Type Amino Acid Transporter 1 and Use It to Regenerate Arginine after Induction of Argininosuccinate Synthase Expression

In the tumor microenvironment, arginine is metabolized by arginase-expressing myeloid cells. This arginine depletion profoundly inhibits T cell functions and is crucially involved in tumor-induced immunosuppression. Reconstitution of adaptive immune functions in the context of arginase-mediated tumor immune escape is a promising therapeutic strategy to boost the immunological antitumor response. Arginine can be recycled in certain mammalian tissues from citrulline via argininosuccinate (ASA) in a two-step enzymatic process involving the enzymes argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL). Here, we demonstrate that anti-CD3/anti-CD28-activated human primary CD4⁺ and CD8⁺ T cells upregulate ASS expression in response to low extracellular arginine concentrations, while ASL is expressed constitutively. ASS expression peaked under moderate arginine restriction (20 µM), but no relevant induction was detectable in the complete absence of extracellular arginine. The upregulated ASS correlated with a reconstitution of T cell proliferation upon supplementation of citrulline, while the suppressed production of IFN-γ was refractory to citrulline substitution. In contrast, ASA reconstituted proliferation and cytokine synthesis even in the complete absence of arginine. By direct quantification of intracellular metabolites we show that activated primary human T cells import citrulline but only metabolize it further to ASA and arginine when ASS is expressed in the context of low amounts of extracellular arginine. We then clarify that citrulline transport is largely mediated by the L-type amino acid transporter 1 (LAT1), induced upon human T cell activation. Upon siRNA-mediated knockdown of LAT1, activated T cells lost the ability to import citrulline. These data underline the potential of citrulline substitution as a promising pharmacological way to treat immunosuppression in settings of arginine deprivation.

Abstract B037: Macrophage repolarization therapy in metastatic colorectal cancer: CCR5 inhibition

The influence of the local immune response on the clinical course of colorectal cancer (CRC) has been analyzed extensively. Analyzing the invasive margin of human CRC liver metastases, we identified a protumoral mechanism of T-cell-derived CCL5 that leads to immune cell exploitation by tumor cells. Two distinct subsets of myeloid cells produce CXCL9/CXCL10, which induce an influx of T cells into the invasive margin. CCL5 is produced by these exhausted T cells and stimulates tumor cell proliferation and invasive behavior via CCR5 on tumor cells and macrophages. CCR5 inhibition in patient-derived functional in vitro organotypic culture models induced macrophage repolarization with anti-tumoral effects. These immunomodulatory and anti-tumoral effects of CCR5 blockade then could be confirmed in a phase I trial with a CCR5 antagonist in advanced refractory CRC patients with liver metastases. Amelioration of tumor-promoting inflammation on the tumor tissue level and objective tumor responses in advanced metastatic CRC patients were observed.

Citation Format: Niels Halama, Inka Zoernig, Anna Berthel, Christoph Kahlert, Fee Klupp, Meggy Suarez-Carmona, Juergen Krauss, Karsten Brand, Felix Lasitschka, Tina Lerchl, Claudia Luckner-Minden, Alexis Ulrich, Juergen Weitz, Martin Schneider, Markus W. Buechler, Laurence Zitvogel, Thomas Herrmann, Axel Benner, Christina Kunz, Stephan Luecke, Christoph Springfeld, Christine Falk, Dirk Jaeger. Macrophage repolarization therapy in metastatic colorectal cancer: CCR5 inhibition [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B037.

Tumoral Immune Cell Exploitation in Colorectal Cancer Metastases Can Be Targeted Effectively by Anti-CCR5 Therapy in Cancer Patients

The immune response influences the clinical course of colorectal cancer (CRC). Analyzing the invasive margin of human CRC liver metastases, we identified a mechanism of immune cell exploitation by tumor cells. While two distinct subsets of myeloid cells induce an influx of T cells into the invasive margin via CXCL9/CXCL10, CCL5 is produced by these T cells and stimulates pro-tumoral effects via CCR5. CCR5 blockade in patient-derived functional in vitro organotypic culture models showed a macrophage repolarization with anti-tumoral effects. These anti-tumoral effects were then confirmed in a phase I trial with a CCR5 antagonist in patients with liver metastases of advanced refractory CRC. Mitigation of tumor-promoting inflammation within the tumor tissue and objective tumor responses in CRC were observed.

Mcl-1 confers protection of Her2-positive breast cancer cells to hypoxia: therapeutic implications

BACKGROUND

Molecular mechanisms leading to the adaptation of breast cancer (BC) cells to hypoxia are largely unknown. The anti-apoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) is frequently amplified in BC; and elevated Mcl-1 levels have been correlated with poor prognosis. Here we investigated the pathophysiologic role of Mcl-1 in Her2-positive BC cells under hypoxic conditions.

METHODS

RNA interference and a novel small molecule inhibitor, EU-5346, were used to examine the role of Mcl-1 in Her2-positive BC cell lines and primary BC cells (sensitive or intrinsically resistant to Her2 inhibitors) under hypoxic conditions (using a hypoxic incubation chamber). Mechanisms-of-action were investigated by RT-PCR, mitochondrial isolation, as well as immunoprecipitation/blotting analysis, and microscopy. The specificity against Mcl-1 of the novel small molecule inhibitor EU5346 was verified in Mcl-1(Δ/null) versus Mcl-1(wt/wt) Murine Embryonic Fibroblasts (MEFs). Proliferation, survival, and spheroid formation were assessed in response to Mcl-1 and Her2 inhibition.

RESULTS

We demonstrate for a strong correlation between high Mcl-1 protein levels and hypoxia, predominantly in Her2-positive BC cells. Surprisingly, genetic depletion of Mcl-1 decreased Her2 and Hif-1α levels followed by inhibition of BC cell survival. In contrast, Mcl-1 protein levels were not downregulated after genetic depletion of Her2 indicating a regulatory role of Mcl-1 upstream of Her2. Indeed, Mcl-1 and Her2 co-localize within the mitochondrial fraction and form a Mcl-1/Her2- protein complex. Similar to genetically targeting Mcl-1 the novel small molecule Mcl-1 inhibitor EU-5346 induced cell death and decreased spheroid formation in Her2-positive BC cells. Of interest, EU-5346 induced ubiquitination of Mcl-1- bound Her2 demonstrating a previously unknown role for Mcl-1 to stabilize Her2 protein levels. Importantly, targeting Mcl-1 was also active in Her2-positive BC cells resistant to Her2 inhibitors, including a brain-primed Her2-positive cell line.

CONCLUSION

Our data demonstrate a critical role of Mcl-1 in Her2-positive BC cell survival under hypoxic conditions and provide the preclinical framework for the therapeutic use of novel Mcl-1- targeting agents to improve patient outcome in BC.

Induced arginine transport via cationic amino acid transporter-1 is necessary for human T-cell proliferation

Availability of the semiessential amino acid arginine is fundamental for the efficient function of human T lymphocytes. Tumor-associated arginine deprivation, mainly induced by myeloid-derived suppressor cells, is a central mechanism of tumor immune escape from T-cell-mediated antitumor immune responses. We thus assumed that transmembranous transport of arginine must be crucial for T-cell function and studied which transporters are responsible for arginine influx into primary human T lymphocytes. Here, we show that activation via CD3 and CD28 induces arginine transport into primary human T cells. Both naïve and memory CD4(+) T cells as well as CD8(+) T cells specifically upregulated the human cationic amino acid transporter-1 (hCAT-1), with an enhanced and persistent expression under arginine starvation. When hCAT-1 induction was suppressed via siRNA transfection, arginine uptake, and cellular proliferation were impaired. In summary, our results demonstrate that hCAT-1 is a key component of efficient T-cell activation and a novel potential target structure to modulate adaptive immune responses in tumor immunity or inflammation.

Granulocyte functions are independent of arginine availability

Arginine depletion via myeloid cell arginase is critically involved in suppression of the adaptive immune system during cancer or chronic inflammation. On the other hand, arginine depletion is being developed as a novel anti-tumor metabolic strategy to deprive arginine-auxotrophic cancer cells of this amino acid. In human immune cells, arginase is mainly expressed constitutively in PMNs. We therefore purified human primary PMNs from healthy donors and analyzed PMN function as the main innate effector cell and arginase producer in the context of arginine deficiency. We demonstrate that human PMN viability, activation-induced IL-8 synthesis, chemotaxis, phagocytosis, generation of ROS, and fungicidal activity are not impaired by the absence of arginine in vitro. Also, profound pharmacological arginine depletion in vivo via ADI-PEG20 did not inhibit PMN functions in a mouse model of pulmonary invasive aspergillosis; PMN invasion into the lung, activation, and successful PMN-dependent clearance of Aspergillus fumigatus and survival of mice were not impaired. These novel findings add to a better understanding of immunity during inflammation-associated arginine depletion and are also important for the development of therapeutic arginine depletion as anti-metabolic tumor therapy.

Cytotoxicity of tumor antigen specific human T cells is unimpaired by arginine depletion

Tumor-growth is often associated with the expansion of myeloid derived suppressor cells that lead to local or systemic arginine depletion via the enzyme arginase. It is generally assumed that this arginine deficiency induces a global shut-down of T cell activation with ensuing tumor immune escape. While the impact of arginine depletion on polyclonal T cell proliferation and cytokine secretion is well documented, its influence on chemotaxis, cytotoxicity and antigen specific activation of human T cells has not been demonstrated so far. We show here that chemotaxis and early calcium signaling of human T cells are unimpaired in the absence of arginine. We then analyzed CD8⁺ T cell activation in a tumor peptide as well as a viral peptide antigen specific system: (i) CD8⁺ T cells with specificity against the MART-1_{aa26–35*A27L} tumor antigen expanded with in vitro generated dendritic cells, and (ii) clonal CMV pp65_aa495–503 specific T cells and T cells retrovirally transduced with a CMV pp65_aa495–503 specific T cell receptor were analyzed. Our data demonstrate that human CD8⁺ T cell antigen specific cytotoxicity and perforin secretion are completely preserved in the absence of arginine, while antigen specific proliferation as well as IFN-γ and granzyme B secretion are severely compromised. These novel results highlight the complexity of antigen specific T cell activation and demonstrate that human T cells can preserve important activation-induced effector functions in the context of arginine deficiency.

Human eosinophil granulocytes do not express the enzyme arginase

Human polymorphonuclear PMN constitutively express the enzyme arginase I, which hydrolyzes arginine to ornithine and urea. This arginine consumption has been recognized as a key pathway of myeloid cell-mediated suppression of the adaptive immune system during inflammation, infection, and tumor growth. Eos granulocytes are crucial immunoregulatory and effector cells of allergic inflammation and infections with parasites and helminths and in a variety of tumors. Here, we analyzed if human Eos also express arginase with its potential immunosuppressive consequences. We show that human peripheral blood Eos do not express arginase I or II protein or arginase enzymatic activity. Correspondingly, no metabolism of arginine to ornithine can be detected in Eos-S. Neither Eos apoptosis nor cytokine-mediated cellular activation induces arginase in human Eos in vitro. Finally, we show that arginase activity and protein are also undetectable in Eos of allergic patients from peripheral blood or from BALF activated in vivo during allergic pulmonary inflammation. This work demonstrates a fundamental difference between neutrophil and Eos granulocytes. As Eos are not equipped with the immunosuppressive enzyme arginase, they cannot participate, via arginine limitation, in the suppression of the evolving adaptive immune response in allergy, infections, or tumor immunity.