Efficacy and pharmacodynamic effect of anti-CD73 and anti-PD-L1 monoclonal antibodies in combination with cytotoxic therapy: observations from mouse tumor models

CD73 is a cell surface 5'nucleotidase (NT5E) and key node in the catabolic process generating immunosuppressive adenosine in cancer. Using a murine monoclonal antibody surrogate of Oleclumab, we investigated the effect of CD73 inhibition in concert with cytotoxic therapies (chemotherapies as well as fractionated radiotherapy) and PD-L1 blockade. Our results highlight improved survival in syngeneic tumor models of colorectal cancer (CT26 and MC38) and sarcoma (MCA205). This therapeutic outcome was in part driven by cytotoxic CD8 T-cells, as evidenced by the detrimental effect of CD8 depleting antibody treatment of MCA205 tumor bearing mice treated with anti-CD73, anti-PD-L1 and 5-Fluorouracil+Oxaliplatin (5FU+OHP). We hypothesize that the improved responses are tumor microenvironment (TME)-driven, as suggested by the lack of anti-CD73 enhanced cytopathic effects mediated by 5FU+OHP on cell lines in vitro. Pharmacodynamic analysis, using imaging mass cytometry and RNA-sequencing, revealed noteworthy changes in specific cell populations like cytotoxic T cells, B cells and NK cells in the CT26 TME. Transcriptomic analysis highlighted treatment-related modulation of gene profiles associated with an immune response, NK and T-cell activation, T cell receptor signaling and interferon (types 1 & 2) pathways. Inclusion of comparator groups representing the various components of the combination allowed deconvolution of contribution of the individual therapeutic elements; highlighting specific effects mediated by the anti-CD73 antibody with respect to immune-cell representation, chemotaxis and myeloid biology. These pre-clinical data reflect complementarity of adenosine blockade with cytotoxic therapy, and T-cell checkpoint inhibition, and provides new mechanistic insights in support of combination therapy.

Abstract 1695: Activation of B cells by CD73 blocking antibodies

The catabolism of ATP into immunosuppressive adenosine contributes to the dysfunction of tumor infiltrating leukocytes (TIL). CD73 is an ectonucleotidase which catabolizes conversion of AMP to adenosine and is expressed on a range of immune cells including B cells. Oleclumab (MEDI9447) is a monoclonal antibody specific for human CD73 and is currently in clinical development for the treatment of cancer. B cells constitute a significant proportion of human TIL; however, their importance to Immuno-Oncology (IO) treatments remains unclear. Recent publications demonstrate that B cells sustain inflammation and predict response to immune checkpoint blockade in human melanoma, their presence within the tumor microenvironment is correlated with improved prognosis in several human tumor types, and CD73 expression has been shown to vary on different human B cell subtypes. Further investigations into the role of CD73 in control of human B cell function are therefore warranted. We show that blockade of CD73 by oleclumab and other monoclonal antibodies on peripheral blood B cells from healthy human donors upregulates expression of CD69, CD83 and CD86, and induces secretion of IL-6, MIP-1α and MIP-1β. Activation is mediated by antibodies that block and internalize CD73 and is reduced by pharmacological inhibition of BTK, thus highlighting involvement of the canonical B-cell receptor signaling pathway. Furthermore, our analyses highlight a differential effect of CD73 blockade on individual B-cell populations, with the most robust increases in activation marker expression being observed on naïve subsets that retain expression of IgD. Our research has identified that oleclumab activates human peripheral blood B cells. Given the renewed interest in B-cell biology in IO, this is an area we believe warrants further clinical investigation.

Citation Format: James Hair, Fabien Garcon, Michelle Hsueh, Laura Dallaway, Elena Bibikova, Maria Letizia Giardino Torchia, Gordon Moody, Alwin Schuller, Simon J. Dovedi, Zachary A. Cooper, Kris Sachsenmeier, Rakesh Kumar, Jim Eyles, Robert W. Wilkinson. Activation of B cells by CD73 blocking antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1695.

Abstract 1584: Efficacy and pharmacodynamic effect of anti-CD73/PD-L1 monoclonal antibodies in combination with chemotherapy: Observations from mouse tumor models

Intratumoral adenosine is a key immunosuppressive factor linked to poor prognosis and reduced efficacy of T cell checkpoint inhibitors. CD73 is an ectoenzyme and key node in the catabolic pathway responsible for sequential hydrolysis of extracellular ATP to adenosine. ATP is released from necrotic and damaged tumor cells; a phenomenon enhanced as consequence of cytotoxic chemotherapy or radiotherapy. A CD73 inhibiting human monoclonal IgG1-TM antibody, Oleclumab, is currently in phase 2 clinical development for treatment of patients with various solid tumors. The combination of CD73 inhibition with chemotherapy and T cell checkpoint inhibition was tested using two murine cancer models, CT26 (colorectal) or MCA205 (fibrosarcoma) implanted subcutaneously in BALB/c mice or C57BL/6 mice, respectively. Tumor bearing mice were treated with combinations of oxaliplatin and 5-fluorouracil and murine surrogate monoclonal antibodies for Oleclumab and Durvalumab (anti-PD-L1). CT26 implanted mice were also treated with the murine surrogate antibodies in the presence and absence of Docetaxel. In an attempt to define contribution of components, comparator groups received monotherapies and other iterations of the combination. Treatment with anti-CD73 and anti-PD-L1 antibodies, concomitantly with chemotherapy, resulted in improved tumor growth inhibition, plus increased proportions of complete tumor regression (P<0.05). FACS analysis of CT26 tumors highlighted elevated frequencies of intratumoral IFN-gamma secreting T and NK cells in the chemotherapy plus double IO combination group (P<0.05). Consistent with this, selective depletion of CD8 T cells significantly diminished tumor control and long term survival (P<0.05). RNAseq and Mass spectrometry based imaging techniques were utilized as tools to explore biomarker changes and mechanism.

Citation Format: Jim Eyles, Amanda Watkins, Kristina Ilieva, Stef Mullins, Jude Anderton, Elena Galvani, Fabien Garcon, Kelli Ryan, Brajesh P. Kaistha, Andreas Dannhorn, Stephanie Ling, Tim Slidel, Gozde Kar, Alwin Schuller, Zachary A. Cooper, Kris Sachsenmeier, Nadia Luheshi, Rakesh Kumar, Robert W. Wilkinson. Efficacy and pharmacodynamic effect of anti-CD73/PD-L1 monoclonal antibodies in combination with chemotherapy: Observations from mouse tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1584.

Intratumoral IL12 mRNA Therapy Promotes TH1 Transformation of the Tumor Microenvironment

PURPOSE

While immune checkpoint inhibitors such as anti-PD-L1 are rapidly becoming the standard of care in the treatment of many cancers, only a subset of treated patients have long-term responses. IL12 promotes antitumor immunity in mouse models; however, systemic recombinant IL12 had significant toxicity and limited efficacy in early clinical trials.

EXPERIMENTAL DESIGN

We therefore designed a novel intratumoral IL12 mRNA therapy to promote local IL12 tumor production while mitigating systemic effects.

RESULTS

A single intratumoral dose of mouse (m)IL12 mRNA induced IFNγ and CD8⁺ T-cell-dependent tumor regression in multiple syngeneic mouse models, and animals with a complete response demonstrated immunity to rechallenge. Antitumor activity of mIL12 mRNA did not require NK and NKT cells. mIL12 mRNA antitumor activity correlated with TH1 tumor microenvironment (TME) transformation. In a PD-L1 blockade monotherapy-resistant model, antitumor immunity induced by mIL12 mRNA was enhanced by anti-PD-L1. mIL12 mRNA also drove regression of uninjected distal lesions, and anti-PD-L1 potentiated this response. Importantly, intratumoral delivery of mRNA encoding membrane-tethered mIL12 also drove rejection of uninjected lesions with very limited circulating IL12p70, supporting the hypothesis that local IL12 could induce a systemic antitumor immune response against distal lesions. Furthermore, in ex vivo patient tumor slice cultures, human IL12 mRNA (MEDI1191) induced dose-dependent IL12 production, downstream IFNγ expression and TH1 gene expression.

CONCLUSIONS

These data demonstrate the potential for intratumorally delivered IL12 mRNA to promote TH1 TME transformation and robust antitumor immunity.See related commentary by Cirella et al., p. 6080.

Abstract 1190: Tissue slice culture platform: A slice of reality in drug development

Immuno-oncology (IO) therapies for cancer have recently delivered step-change improvements in patient outcomes, but the major proportion of patients remain unresponsive or become refractory to IO treatment. Because IO-based approaches necessarily rely on the interplay of multiple cell types, including immune cells, and other elements that constitute the tumor microenvironment (TME), innovative assays are critical to generate further translational insight. Indeed, results from in vivo mouse models and in vitro assays with human cell lines often do not correlate with clinical efficacy and as such, do not always represent relevant avatars. We have leveraged recent advances in tumor slice culture (TSC) techniques to enable in vitro mechanistic and novel biomarker testing/identification studies. TSC involves the in vitro culture of thick slices (200-300 μm) of fresh tissue prepared using a vibratome and is currently the only in vitro assay system which retains the 3-dimensional tissue architecture, complete with cell-cell and cell-matrix interactions. We are now regularly using the TSC together with tumor samples derived from patients and human cancer cell line derived xenograft or syngeneic mouse cancer models, to generate exciting pre-clinical data for several Oncology programs, including oncolytic viruses, modified RNA, bispecific antibodies and antibody-drug conjugates. For instance, the TSC platform has allowed us to analyse the strong type I IFN-driven inflammatory response initiated by infection of tumor nests within patient samples and demonstrate the consequent infiltration of immune cells from the surrounding stroma. Thus, using a tissue phenomics approach incorporating a range of endpoint assays, including multiplex whole-mount imaging, transcriptomics and cytokine expression, the data generated using the TSC platform will inform the underlying biology and translational strategies of multiple therapeutic candidates.

Citation Format: Shannon Burke, Fabien Garcon, Kelli Ryan, James Harper, Robert W. Wilkinson. Tissue slice culture platform: A slice of reality in drug development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1190.

Abstract 5017: MEDI1191, a novel IL-12 mRNA therapy for intratumoral injection to promote TH1 transformation of the patient tumor microenvironment

Patients who respond to PD-L1 / PD-1 immune checkpoint blockade tend to have an inflamed, TH1 polarised tumor microenvironment (TME), characterised by expression of interferon-γ (IFNγ) and PD-L1. Novel therapies that induce TH1 transformation of the patient TME therefore have the potential to enhance anti-tumor immunity. As a central mediator of TH1 immune responses, interleukin 12 (IL-12) directly induces IFNγ release from activated NK, NKT and T cells, and is known to play a key role in driving anti-tumor responses. However systemic recombinant IL-12 was poorly tolerated in early clinical trials. We therefore designed MEDI1191 as a novel IL-12-based therapy designed for injection directly into tumors, composed of a lipid nanoparticle (LNP)-formulated mRNA encoding human IL-12.

We previously reported that intratumoral (IT) mouse (m) IL-12 mRNA, the surrogate for MEDI1191, promotes cytotoxic T cell-dependent anti-tumor immunity and enhances responses to PD-L1 blockade in pre-clinical models. Here, we demonstrate that IFNγ is also required for the anti-tumor activity of mIL-12 mRNA. A single dose of mIL-12 mRNA significantly increased expression of IFNγ and TH1 genes in MC38 tumor-bearing mice. Treatment with an IFNγ neutralising antibody blocked mIL-12 mRNA anti-tumor activity in this model. In addition, we report here that MC38 tumor rejection in response mIL-12 mRNA / anti-PD-L1 combination therapy correlates with increased cytotoxic T cell infiltration into tumors, and expansion of tumor-reactive T cells in the periphery.

We next investigated the pharmocodynamic activity of MEDI1191 in patient tumor-derived models. A single IT dose of MEDI1191 induced human IL-12p70 expression in mice bearing four different patient-derived xenograft tumors. Furthermore, in an ex vivo patient tumor slice culture assay, MEDI1191 induced dose-dependent IL-12 release, IFNγ expression and upregulation of TH1-signature gene expression. IL-12 protein secretion was induced in slices of all patient tumors tested. However, the magnitude of the IFNγ response to MEDI1191 varied between patient tumors. Quantification of the tumoral T cell and NK cell numbers within the patient tumor samples revealed a positive correlation between MEDI1191-induced IFNγ release and baseline tumor NK infiltrate.

These preclinical data demonstrate the potential for MEDI1191 to induce IFNγ-dependent TH1 transformation of the TME, and support the development of MEDI1191 as a potential treatment for patients with solid tumors, alone and in combination with inhibitors of the PD-1/PD-L1 T cell checkpoint.

Citation Format: Nadia Luheshi, Susannah Hewitt, Fabien Garcon, Shannon Burke, Amanda Watkins, Kristen Arnold, John Zielinski, Philip Martin, Michael Sulikowski, Christopher Bagnall, Jean-Martin Lapointe, Gordon Moody, Han Si, Christopher Morehouse, Robert W. Wilkinson, Ronald Herbst, Joshua Frederick. MEDI1191, a novel IL-12 mRNA therapy for intratumoral injection to promote TH1 transformation of the patient tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5017.

Non-Invasive Multiphoton Imaging of Islets Transplanted Into the Pinna of the NOD Mouse Ear Reveals the Immediate Effect of Anti-CD3 Treatment in Autoimmune Diabetes

We present a novel and readily accessible method facilitating cellular time-resolved imaging of transplanted pancreatic islets. Grafting of islets to the mouse ear pinna allows non-invasive, in vivo longitudinal imaging of events in the islets and enables improved acquisition of experimental data and use of fewer experimental animals than is possible using invasive techniques, as the same mouse can be assessed for the presence of islet infiltrating cells before and after immune intervention. We have applied this method to investigating therapeutic protection of beta cells through the well-established use of anti-CD3 injection, and have acquired unprecedented data on the nature and rapidity of the effect on the islet infiltrating T cells. We demonstrate that infusion of anti-CD3 antibody leads to immediate effects on islet infiltrating T cells in islet grafts in the pinna of the ear, and causes them to increase their speed and displacement within 20 min of infusion. This technique overcomes several technical challenges associated with intravital imaging of pancreatic immune responses and facilitates routine study of beta islet cell development, differentiation, and function in health and disease.

The PI3K isoforms p110alpha and p110delta are essential for pre-B cell receptor signaling and B cell development

B cell development is controlled by a series of checkpoints that ensure that the immunoglobulin (Ig)-encoding genes produce a functional B cell receptor (BCR) and antibodies. As part of this process, recombination-activating gene (Rag) proteins regulate the in-frame assembly of the Ig-encoding genes. The BCR consists of Ig proteins in complex with the immunoreceptor tyrosine-based activation motif (ITAM)-containing Igalpha and Igbeta chains. Whereas the activation of the tyrosine kinases Src and Syk is essential for BCR signaling, the pathways that act downstream of these kinases are incompletely defined. Previous work has revealed a key role for the p110delta isoform of phosphatidylinositol 3-kinase (PI3K) in agonist-induced BCR signaling; however, early B cell development and mature B cell survival, which depend on agonist-independent or "tonic" BCR signaling, are not substantially affected by a deficiency in p110delta. Here, we show that p110alpha, but not p110beta, compensated in the absence of p110delta to promote early B cell development in the bone marrow and B cell survival in the spleen. In the absence of both p110alpha and p110delta activities, pre-BCR signaling failed to suppress the production of Rag proteins and to promote developmental progression of B cell progenitors. Unlike p110delta, however, p110alpha did not contribute to agonist-induced BCR signaling. These studies indicate that either p110alpha or p110delta can mediate tonic signaling from the BCR, but only p110delta can contribute to antigen-dependent activation of B cells.