Abstract 4053: A mesothelin targeting chimeric antigen receptor macrophage (CAR-M) for solid tumor immunotherapy: pre-clinical development of CT-1119

While adoptive cell therapies have seen significant success in the treatment of hematological malignancies, solid tumors remain challenging for the field. A significant obstacle is the exclusion of T cells from the tumor microenvironment (TME). In contrast, monocytes/macrophages are naturally recruited to the TME. These cells then have the potential to phagocytose tumor cells, activate the TME, and prime a broad anti-tumor adaptive immune response via T cell recruitment and activation. We have previously developed CT-0508, a chimeric antigen receptor macrophage (CAR-M) targeting HER2 which showed efficacy in a variety of pre-clinical models and is currently in a Phase I clinical trial for patients with HER2+ solid tumors. Mesothelin is overexpressed in a variety of solid tumors, including mesothelioma, lung, pancreatic, and ovarian cancers. To leverage tumor biology with myeloid cells, we engineered primary human macrophages using the chimeric adenoviral vector Ad5f35 to express a CAR containing a human scFv against human mesothelin. We used both in vitro cell based assays and in vivo xenograft models to assess the activity of CT-1119. CAR-M engineered with an Ad5f35 vector demonstrated high CAR expression, high viability, upregulated M1 (anti-tumor) macrophage markers, and downregulated M2 (pro-tumor) macrophage markers. CT-1119 specifically phagocytosed multiple mesothelin expressing tumor cell lines in a CAR-dependent and antigen-dependent manner. CT-1119 demonstrated robust in vitro killing of the relevant tumor cell lines A549 and MES-OV expressing mesothelin. CAR engagement also induced the release of pro-inflammatory cytokines such as TNFα following stimulation with mesothelin in both cell-free and cell-based contexts in a dose-dependent manner. In vivo, CT-1119 significantly reduced tumor burden in a murine xenograft model of lung cancer. Similarly, human monocytes targeting mesothelin were successfully generated using the same Ad5f35 vector and demonstrated specific activity against mesothelin positive tumor cells. The presented results demonstrate that CT-1119, an autologous human anti-mesothelin CAR-M, can cause phagocytosis, tumor cell killing, and pro-inflammatory cytokine release in response to stimulation with mesothelin. These results show that CAR-M is a feasible approach for the treatment of mesothelin expressing sold tumors via the potential for induction of a systemic anti-tumor response.

Citation Format: Nicholas R. Anderson, Brinda Shah, Alison Worth, Rashid Gabbasov, Brett Menchel, Kerri Ciccaglione, Daniel Blumenthal, Stefano Pierini, Sabrina Ceeraz DeLong, Sascha Abramson, Thomas Condamine, Michael Klichinsky. A mesothelin targeting chimeric antigen receptor macrophage (CAR-M) for solid tumor immunotherapy: pre-clinical development of CT-1119. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4053.

Abstract 4054: Macrophages engineered with cytokine switch receptors: Development of a modular platform for rebalancing inflammation in microenvironments

Motivation: Cytokines in tissue microenvironments regulate the balance between pro- and anti-inflammatory signals. Dysregulated cytokines cause deleterious immunosuppression or inflammation, which underpins the pathophysiology of solid tumors, chronic kidney disease, and more. Rebalancing inflammation/immunosuppression by rectifying cytokine signals offers a generalizable approach for treating numerous diseases. While doing so through cytokine blockade carries risks due to systemic administration, cellular immunotherapies offer a localized approach that could detect pathogenic cytokines then proportionately rebalance inflammation as needed. Specifically, macrophages are homeostatic regulators responsible for initiating and resolving inflammation. Here, we leveraged macrophages’ ability to regulate inflammation by equipping them with synthetic cytokine switch receptors (SR) that convert immunosuppressive M2 signals into pro-inflammatory M1 responses for solid tumor microenvironment conversion, or vice versa for inflammatory disease. We termed this platform “Engineered Microenvironment Converters” (EM-C) and evaluated its modular ability to target disease-associated cytokines.

Methods: EM-Cs targeting IL10, TGFβ, IFNγ and IL17A were generated by expressing SR in primary human macrophages. M2-to-M1 SR were designed to convert IL10 or TGF-β into pro-inflammatory stimuli, and M1-to-M2 SR were designed to IFNγ or IL17A into immunosuppressive signals. The in vitro response of EM-Cs to their target cytokine was monitored using phenotypic characterization of surface molecules, measurement of cytokine production, mRNA sequencing, and biochemical analysis of downstream signaling. Co-culture assays with bystander cells were used to assess the ability of EM-Cs to alter their microenvironment.

Results: Pro-inflammatory EM-Cs converted IL10 and TGFβ, two prevalent immunosuppressive cytokines in the TME, into pro-inflammatory signals. Unlike wildtype macrophages, these EM-Cs responded to IL10 or TGFβ with upregulated M1 markers and cytokines in a dose-dependent manner. Furthermore, EM-Cs repolarized bystander M2 macrophages towards a pro-inflammatory phenotype following co-culture. Similarly, anti-inflammatory EM-Cs responded IFNγ and IL17A, two cytokines canonically overexpressed in inflammatory disease, by upregulating M2 markers and inducing an anti-inflammatory environment.

Conclusion: We present for the first time a novel immunotherapy platform that harnesses macrophages as “living converters” to locally regulate inflammation for oncology and inflammatory applications. By demonstrating EM-Cs in the M2-to-M1 and M1-to-M2 direction, this platform offers modularity in controlling the inflammatory status of tissue microenvironments without systemic cytokine antagonism.

Citation Format: Chris Sloas, Yuhao Huangfu, Rehman Qureshi, Michael Ball, Thomas Condamine, Michael Klichinsky, Yumi Ohtani. Macrophages engineered with cytokine switch receptors: Development of a modular platform for rebalancing inflammation in microenvironments. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4054.

Expression of inducible factors reprograms CAR-T cells for enhanced function and safety

Despite the success of CAR-T cell cancer immunotherapy, challenges in efficacy and safety remain. Investigators have begun to enhance CAR-T cells with the expression of accessory molecules to address these challenges. Current systems rely on constitutive transgene expression or multiple viral vectors, resulting in unregulated response and product heterogeneity. Here, we develop a genetic platform that combines autonomous antigen-induced production of an accessory molecule with constitutive CAR expression in a single lentiviral vector called Uni-Vect. The broad therapeutic application of Uni-Vect is demonstrated in vivo by activation-dependent expression of (1) an immunostimulatory cytokine that improves efficacy, (2) an antibody that ameliorates cytokine-release syndrome, and (3) transcription factors that modulate T cell biology. Uni-Vect is also implemented as a platform to characterize immune receptors. Overall, we demonstrate that Uni-Vect provides a foundation for a more clinically actionable next-generation cellular immunotherapy.

Abstract CT524: A phase 1, first in human (FIH) study of autologous anti-HER2 chimeric antigen receptor macrophages (CAR-M) in HER2-overexpressing solid tumors (ST)

Background: Adoptive T cell therapies have led to remarkable advances in hematologic cancers but with less effect in ST. Actively recruited tumor associated macrophages (TAM) are abundant in the ST microenvironment (TME) and typically display immunosuppressive behavior. Macrophages engineered to be proinflammatory may be an ideal vector for adoptive ST cellular therapy. Engineered CAR-M selectively recognize and phagocytose antigen overexpressing cancer cells, reprogram TME and present neoantigens to T cells, leading to epitope spreading and immune memory. Human Epidermal Growth Factor Receptor 2 (HER2) overexpression promotes tumorigenesis in many cancers (Table 1). CT-0508 is a cell product comprised of autologous monocyte-derived proinflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies show that CT-0508 induces targeted cancer cell phagocytosis while sparing normal cells, decreases tumor burden and prolongs survival, and was safe and effective in a semi-immunocompetent mouse model of human HER2-overexpressing ovarian cancer.

Methods: This FIH Phase 1 study is evaluating safety, tolerability, cell manufacturing feasibility, trafficking, and preliminary efficacy in 18 subjects with locally advanced/unresectable or metastatic ST overexpressing HER2, with progression on available therapies, including anti-HER2 therapies. Filgrastim is used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis prior to CT-0508 CAR macrophage infusion. Group 1 subjects receive CT-0508 on D1, 3, & 5. Group 2 subjects will receive full dose on D1. A Safety Review Committee will review dose limiting toxicities. Pre/post-treatment biopsies and blood samples will be collected for correlative analysis of immunogenicity, trafficking (PCR, RNA scope), CT-0508 persistence in blood and tumor, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others.

Table 1. Her2 Overexpression Across Tumor Types Tumor HER2 Overexpression (%) Bladder 8–70 Salivary duct 30–40 Gastric 7–34 Ovarian 26 Breast 11–25 Salivary mucoepidermoid 17.6 Esophageal 12–14 Gallbladder 9.8–12.8 Cholangiocarcinoma 6.3–9 Colorectal 1.6–5 Cervical 2.8–3.9 Uterine 3 Testicular 2.4

Citation Format: Kim A. Reiss, Yuan Yuan, Naoto T. Ueno, Yara Abdou, Debora Barton, Ramona F. Swaby, Amy Ronczka, Daniel J. Cushing, Sascha Abramson, Thomas Condamine, Michael Klichinsky, E. Claire Dees. A phase 1, first in human (FIH) study of autologous anti-HER2 chimeric antigen receptor macrophages (CAR-M) in HER2-overexpressing solid tumors (ST) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT524.

Abstract 2112: Chimeric antigen receptor macrophages (CAR-M) sensitize solid tumors to anti-PD1 immunotherapy

Despite the remarkable efficacy achieved by CAR-T cell therapy in hematologic malignancies, achieving efficacy against solid tumors has been challenging. We previously developed human CAR-M and demonstrated that adoptive cell transfer of CAR-M into xenograft models of human cancer controls tumor progression and improves overall survival1. Given that CAR-M are M1-polarized macrophages with the potential to remodel the tumor microenvironment (TME) and act as professional antigen presenting cells, we developed an immunocompetent animal model to evaluate the interaction of CAR-M with the endogenous immune system and to study the combinatorial approach of CAR-M with blockade of the PD1/PDL1 T cell checkpoint axis. Murine bone marrow-derived macrophages were engineered to express an anti-HER2 CAR using the chimeric adenoviral vector Ad5f35. In addition to efficient gene delivery, Ad5f35 transduction promoted a pro-inflammatory (M1) phenotype in murine macrophages. Anti-HER2 CAR-M, but not control macrophages, phagocytosed and killed HER2-overexpressing tumor cell lines. CAR-M induced MHC-I expression on tumor cells and enhanced the cytotoxicity of CD8+ T cells. To evaluate the safety and efficacy of CAR-M therapy, immunocompetent mice were engrafted with HER2+ tumors and treated with syngeneic HER2-CAR or untransduced (UTD) macrophages. CAR-M treated mice showed significant tumor control and improved survival compared to control groups. Analysis of the TME showed increased intratumoral immune infiltration - as well as an increase in T cell responsiveness to tumor-associated antigens, indicating enhanced epitope spreading. Given the impact of CAR-M on the endogenous adaptive immune system, we evaluated the combination of CAR-M with anti-PD1 in tumors resistant to anti-PD1 monotherapy and found that the combination further reprogrammed the TME, significantly enhanced tumor control, and improved overall survival compared to monotherapy with either agent. Mice that achieved complete responses (CRs) after CAR-M therapy were protected against antigen-negative relapse in a HER2-negative rechallenge model, indicating long-term anti-tumor immunity. Finally, the combination of CAR-M with anti-PD1 did not trigger sustained elevations of serum analytes associated with cytokine release syndrome (CRS) and was well tolerated across numerous safety assessments. These results demonstrate that CAR-M reprogram the TME, induce epitope spreading, and orchestrate a systemic immune response against solid tumors. Moreover, our findings provide rationale for the combination of CAR-M with immune checkpoint inhibitors. The anti-HER2 CAR-M, CT-0508, is under evaluation in a phase I clinical trial for patients with HER2 overexpressing solid tumors.

Citation Format: Stefano Pierini, Rashid Gabbasov, Alison Worth, Ilyssa Ramos, Daniel Blumenthal, Yumi Ohtani, Linara Gabitova, Michael Ball, Sascha Abramson, Thomas Condamine, Michael Klichinsky. Chimeric antigen receptor macrophages (CAR-M) sensitize solid tumors to anti-PD1 immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2112.

Abstract 582: Pre-clinical development of CAR Monocytes (CAR Mono) for solid tumor immunotherapy

Introduction: Engineered cell therapies have demonstrated significant clinical activity against hematologic malignancies, but responses have been rare in solid tumors. Our previously developed human chimeric antigen receptor macrophage (CAR-M) platform has shown potent anti-tumor activity in pre-clinical solid tumor models1, and the anti-HER2 CAR-M CT-0508 is currently being evaluated in a Phase I trial. The use of myeloid cells as a platform for cell therapy provides the tools to overcome critical solid tumor challenges such as infiltration, immunosuppression within the tumor microenvironment, lymphocyte exclusion, and target antigen heterogeneity. Currently, CAR-M are generated in a week-long ex-vivo process in which peripheral blood monocytes are differentiated into macrophages prior to genetic manipulation. Here, we demonstrate the production feasibility, phenotype, pharmacokinetics, cellular fate, specificity, and anti-tumor activity of human CD14+ CAR monocytes.

Experimental: Using the chimeric adenoviral vector Ad5f35, we engineered primary human CD14+ monocytes to express a CAR (CAR-mono) targeted against HER2. We established a process that allowed for same day manufacturing (from Leukopak to cryopreserved CAR-mono cell product).

Results: CAR-mono showed high CAR expression and viability (>90%), and efficiently differentiated into CAR-expressing macrophages. Adenoviral transduction led to pre-conditioning of CAR-mono, resulting in a strong M1 phenotype upon differentiation into CAR-M. CAR-mono derived macrophages demonstrated potent anti-tumor activity regardless of exposure to GM-CSF or M-CSF, and were protected against M2 switching by immunosuppressive factors. Treating CAR-mono with GM-CSF and IL-4 resulted in their differentiation to monocyte-derived CAR-DCs with an activated phenotype, indicating that these cells retained their myeloid differentiation potential. In vivo, CAR-mono induced anti-tumor activity in various HER2+ solid tumor xenograft models. Following IV administration, CAR-mono demonstrated the ability to traffic to both GM-CSFhigh and GM-CSFlow expressing tumors. Notably, CAR-mono showed long-term CAR expression and persistence (>180 days) in both NSG and NSG-S mouse models, demonstrating lasting persistence irrespective of human cytokine support.

Conclusions: The CAR-mono platform enables an automated, same-day manufacturing process while maintaining the key characteristics of CAR-M therapy. The use of Ad5f35 for human monocyte transduction primes the cells toward M1 macrophage differentiation and produces a cell population phenotypically and functionally similar to our established CAR-M platform. These data provide strong pre-clinical support to advance the CAR-mono platform into clinical testing.1Klichinsky M, et al. Human chimeric antigen receptor macrophages for cancer immunotherapy. Nature Biotechnology. March 2020.

Citation Format: Daniel Blumenthal, Linara Gabitova, Brett Menchel, Patricia Reyes-Uribe, Sabrina Ceeraz DeLong, Sascha Abramson, Michael Klichinsky. Pre-clinical development of CAR Monocytes (CAR Mono) for solid tumor immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 582.

A phase 1, first-in-human (FIH) study of the anti-HER2 CAR macrophage CT-0508 in subjects with HER2 overexpressing solid tumors

2533

Background: Most solid tumors are resistant to immunotherapy. In pre-clinical studies, CAR-M infiltrate tumors, phagocytose tumor cells, activate the tumor micro environment (TME), recruit T cells, and present tumor antigens to T cells leading to robust anti-tumor immunity. CT-0508 is a first in class CAR-M, comprised of autologous monocyte derived macrophages expressing an anti-HER2 CAR. Here we present preliminary clinical results from the CT-0508 Phase 1 FIH study. Methods: This multi-center, open-label study is evaluating CT-0508’s safety, tolerability, and manufacturing feasibility in 18 participants (pts) with advanced solid tumors overexpressing HER2 who have progressed on prior therapies. Monocytes are isolated from mobilized apheresis products, differentiated into macrophages and engineered with an anti-HER2 CAR. Group 1 pts (n = 9) receive a fractionated dose (D1, D3, D5) and Group 2 pts (n = 9) receive the full dose on D1. CT-0508 is administered without preparative chemotherapy (bridging is permitted). Serial blood samples, 1 pre and 2 post-treatment biopsies are collected to investigate safety, pharmacokinetics and mechanism of action. Results: Seven pts (4F/3M), median age 64 (49-73), have been treated [breast (2), esophageal (2), cholangiocarcinoma, ovarian and parotid gland cancers]. A median of 3 (2-10) prior lines of therapy have been administered, most pts (85.7%) received prior anti HER2 therapy. CT-0508 was successfully manufactured with high viability, purity and CAR expression, and was well tolerated with no dose limiting toxicities or AEs leading to discontinuation or dose modification. Two related SAEs were reported in the same pt (Grade 1 CRS, hospitalized for monitoring and Grade 2 infusion reaction, resolved within 1h). Three other pts had Grade 1-2 CRS; resolved within 4d with no use of tocilizumab needed. There were no major organ toxicities and no on-target off-tumor toxicities. Post-infusion cytokines were transiently elevated in most pts and were self-limiting. Among the 4 pts who reached week 8, the best overall response was stable disease (n = 3) and 1 pt progressed, with a median follow up of 8w. CT-0508 rapidly egressed from peripheral blood. CT-0508 CAR mRNA was detected in all tumor biopsies of the first 2 pts. CT-0508 activated the TME, with increased myeloid cell activation, T cell infiltration, activation and proliferation. TCR sequencing demonstrated peripherally expanding T cells enriched for tumor infiltrating lymphocyte clones, suggesting expansion of tumor reactive T cells. Correlative data from additional pts will be presented. Conclusions: In 7 pts, CT-0508 was safe and feasible to manufacture. Early correlative data demonstrate trafficking, TME modulation, and potential induction of anti-tumor T cell immunity. The study is actively enrolling. Clinical trial information: NCT04660929.

A phase 1, first-in-human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in participants with HER2 overexpressing solid tumors

TPS2677

Background: Adoptive T cell therapies have led to remarkable advances among patients with hematologic malignancies, but have had less success in those with solid tumors. Macrophages are actively recruited and abundantly present in the solid tumor microenvironment (sTME). Tumor associated macrophages are predominantly immunosuppressive and support tumor growth (M2), while a subset of proinflammatory macrophages enhance anti-tumor immunogenicity (M1). M1 macrophage function can be augmented by CAR expression to selectively recognize and phagocytose antigen overexpressing cancer cells. Moreover, CAR macrophages can reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and anti-tumor immune memory. Human Epidermal Growth Factor Receptor 2 (HER2) overexpression promotes tumorigenesis in many solid tumors (Table). CT-0508 is a cell product comprised of autologous monocyte-derived proinflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies have shown that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreased tumor burden, prolonged survival, and were safe and effective in a semi-immunocompetent mouse model of human HER2 overexpressing ovarian cancer. Methods: This Phase 1, FIH study is evaluating safety, tolerability, cell manufacturing feasibility, trafficking, and preliminary evidence of efficacy of investigational product CT-0508 in 18 participants (pt) with locally advanced (unresectable) or metastatic solid tumors overexpressing HER2. Pt previously treated with available therapies, including anti-HER2 therapies, as indicated, and subsequent progression are permitted. Filgrastim is used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis. CT-0508 is manufactured, prepared, and cryopreserved from mobilized peripheral blood monocytes. Group 1 pt (n=9) receive CT-0508 infusion split over D1, 3, and 5. A Safety Review Committee will review dose limiting toxicities. Group 2 pt (n=9) will receive the full CT-0508 infusion on D1. Pre- and post-treatment biopsies and blood samples will be collected to investigate correlates of safety (immunogenicity), trafficking (RNA scope), CT-0508 persistence in blood and in the tumor, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others. Radiographic imaging is also being conducted to assess preliminary tumor activity. Clinical trial information: NCT04660929. [Table: see text]

Abstract OT1-03-01: A phase 1, first in human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in subjects with HER2 overexpressing solid tumors

Adoptive T cell therapies have led to remarkable advances among patients with hematologic malignancies, but not in those with solid tumors. Macrophages are actively recruited into, and abundantly present in the solid tumor microenvironment (sTME). Tumor- associated macrophages typically evince immunosuppressive behavior, but when engineered to be proinflammatory, may be an ideal vector to administer adoptive cellular therapy in solid tumors. Furthermore, insertion of a CAR on the macrophages confers the ability to selectively recognize and phagocytose antigen overexpressing cancer cells. Additionally, CAR macrophages reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and immune memory. Human Epidermal Growth Factor Receptor 2 (HER2) overexpression promotes tumorigenesis and is seen in many cancers, including but not limited to breast and gastroesophageal cancers (Table 1). CT-0508 is a cell product comprised of autologous monocyte-derived pro-inflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies have shown that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreasing tumor burden and prolonging survival in relevant models. CT-0508 cells were safe and effective in a semi-immunocompetent mouse model of human HER2 overexpressing ovarian cancer. This is a FIH Phase 1 study to evaluate safety, tolerability, cell manufacturing feasibility, trafficking, and preliminary evidence of efficacy of investigational product CT-0508 in approximately 18 subjects with locally advanced (unresectable) or metastatic solid tumors overexpressing HER2, who have failed available therapies including anti-HER2 therapies where indicated.Filgrastim is being used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis. The CT-0508 CAR macrophage product is manufactured, prepared and cryopreserved from mobilized peripheral blood monocytes. The study is enrolling Group 1 subjects, who receive CT-0508 infusion split over D1, 3 and 5. Subjects will be continually assessed for acute and cumulative toxicity. Dose limiting toxicities will be observed and addressed by a Safety Review Committee. Group 2 subjects will follow, and will receive the full CT-0508 infusion on D1. Pre and post treatment biopsies and blood samples will be collected to investigate correlates of safety (immunogenicity), trafficking (PCR, RNA scope), CT-0508 persistence in blood and in the tumor, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others. Clinical trial registry number: NCT04660929

Table 1.HER2 Positivity Frequencies Across Tumor TypesTumor typeHER2 positivity (%)ReferenceBladder cancer8-70Gandour-Edwards et al, 2002;Caner et al, 2008;Laé et al, 2010; Fleischmann et al, 2011;Charfi et al, 2013;Yan et al, 2015Breast cancer11.0-25.0Varga et al, 2013;Stenehjem et al, 2014Cervical cancer2.8-3.9Chavez-Blanco et al, 2004;Yan et al, 2015Colorectal cancer1.6-5.0Schuell et al, 2006;Ingold Heppner et al, 2014;Seo et al, 2014Esophageal cancer12.0-14.0König et al, 2013;Yoon et al, 2013;Wang et al, 2014Extrahepatic Cholangiocarcinoma6.3-9.0Yoshikawa et al, 2008;Yan et al, 2015Gallbladder cancer9.8-12.8Roa et al, 2014;Yan et al, 2015Gastric adenocarcinoma7.0-34.0Rüschoff et al, 2012;Hofmann et al, 2008Ovarian cancer26Slamon et al, 1989Salivary mucoepidermoid carcinomas17.6Glisson et al, 2004Salivary duct carcinoma30-40Skálová et al, 2003; Cornolti et al, 2007; Nardi et al, 2013Testicular cancer2.4Yan et al, 2015Uterine cancer3.0Yan et al, 2015

Citation Format: Yara George Abdou, Debora Barton, Amy Ronczka, Daniel Cushing, Michael Klichinsky, Kim Reiss Binder. A phase 1, first in human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in subjects with HER2 overexpressing solid tumors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-03-01.

A phase 1, first-in-human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in subjects with HER2 overexpressing solid tumors

TPS668

Background: Adoptive T cell therapies have led to remarkable advances among patients with hematologic malignancies, but not in those with solid tumors. Macrophages are actively recruited into, and are abundantly present in the solid tumor microenvironment (sTME). Tumor- associated macrophages typically display immunosuppressive behavior, but when engineered to be proinflammatory, may be an ideal vector to administer adoptive cellular therapy in solid tumors. Furthermore, insertion of a CAR on the macrophages allow them to selectively recognize and phagocytose antigen overexpressing cancer cells. CAR macrophages reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and immune memory. Human Epidermal Growth Factor Receptor 2 (HER2) overexpression promotes tumorigenesis in many cancers (Table). CT-0508 is a cell product comprised of autologous monocyte-derived pro-inflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies have shown that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreased tumor burden and prolonged survival in relevant models. CT-0508 cells were safe and effective in a semi-immunocompetent mouse model of human HER2 overexpressing ovarian cancer. Methods: This is a FIH Phase 1 study to evaluate safety, tolerability, cell manufacturing feasibility, trafficking and preliminary evidence of efficacy of investigational product CT-0508 in 18 subjects with locally advanced (unresectable) or metastatic solid tumors overexpressing HER2, who have failed available therapies, including anti-HER2 therapies when indicated. Filgrastim is being used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis. The CT-0508 CAR macrophage product is manufactured, prepared and cryopreserved from mobilized peripheral blood monocytes. Group 1 subjects receive CT-0508 infusion split over D1, 3 and 5. Dose limiting toxicities will be observed and addressed by a Safety Review Committee. Group 2 subjects will receive the full CT-0508 infusion on D1. Pre and post treatment biopsies and blood samples will be collected to investigate correlates of safety (immunogenicity), trafficking (PCR, RNA scope), CT-0508 persistence in blood and in the tumor, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others. Clinical trial information: NCT04660929. [Table: see text]

Engineered CAR-Macrophages as Adoptive Immunotherapies for Solid Tumors

Cellular immunotherapies represent a promising approach for the treatment of cancer. Engineered adoptive cell therapies redirect and augment a leukocyte’s inherent ability to mount an immune response by introducing novel anti-tumor capabilities and targeting moieties. A prominent example of this approach is the use of T cells engineered to express chimeric antigen receptors (CARs), which have demonstrated significant efficacy against some hematologic malignancies. Despite increasingly sophisticated strategies to harness immune cell function, efficacy against solid tumors has remained elusive for adoptive cell therapies. Amongst cell types used in immunotherapies, however, macrophages have recently emerged as prominent candidates for the treatment of solid tumors. In this review, we discuss the use of monocytes and macrophages as adoptive cell therapies. Macrophages are innate immune cells that are intrinsically equipped with broad therapeutic effector functions, including active trafficking to tumor sites, direct tumor phagocytosis, activation of the tumor microenvironment and professional antigen presentation. We focus on engineering strategies for manipulating macrophages, with a specific focus on CAR macrophages (CAR-M). We highlight CAR design for macrophages, the production of CAR-M for adoptive cell transfer, and clinical considerations for their use in treating solid malignancies. We then outline recent progress and results in applying CAR-M as immunotherapies. The recent development of engineered macrophage-based therapies holds promise as a key weapon in the immune cell therapy armamentarium.

951 A phase 1 first in human study of adenovirally transduced anti-HER2 CAR macrophages in subjects with HER2 overexpressing solid tumors: preliminary safety, pharmacokinetics, and TME reprogramming data

Background

CT-0508 is an autologous monocyte-derived pro-inflammatory macrophage cell product engineered with Ad5f35 to express an anti-HER2 CAR. In pre-clinical studies CT-0508 was safe and effective. This abstract contains preliminary results from the first-in-human experience with CAR macrophages (CAR-M).

Methods

This First-In-Human Phase 1, multi-center, open-label study is evaluating the safety, tolerability, manufacturing feasibility, pharmacokinetics and mechanism of action of CT-0508 in 18 subjects with advanced solid tumors overexpressing HER2 who have progressed on prior therapies, including HER2 targeted therapies if indicated.

Patients receive four doses of filgrastim for monocyte mobilization prior to apheresis. CT-0508 CAR-M is manufactured from autologous apheresis products and delivered as a cryopreserved cell product. Group 1 subjects enter an intra-patient fractionated dose escalation regimen, receiving CT-0508 on D1, D3 and D5, followed by Group 2 subjects who receive CT-0508 on D1. There is no preparative chemotherapy prior to CT-0508 infusion.

Pre and post treatment biopsies and blood samples are collected to investigate correlates of safety, serum cytokines and chemokines, pharmacokinetics, TME modulation, and induction of an adaptive anti-tumor immune response.

Results

To date, two subjects have been treated with CT-0508 (esophageal adenocarcinoma and extrahepatic cholangiocarcinoma). Patient product was successfully manufactured, CT-0508 treatment was well tolerated, with no dose limiting and no major organ toxicities observed.

One subject experienced Grade 2 CRS on Day 3 which resolved on the same day.

Grade 3 AEs included anemia (present at baseline for both subjects) and lymphopenia (present at baseline in one subject). One subject experienced one SAE of Grade 4 tumor bleeding which was unrelated to CT-0508, 88 days after the last infusion.

CAR-M were transiently detected in the peripheral blood following each infusion, demonstrating rapid egress from the periphery into tissues within hours. Transient cytokine/chemokine elevations were observed (peak: 2 hours, back to baseline at 48 hours). Single cell RNAseq analysis of dissociated tumor tissue samples (pre-treatment, day 8 and week 4) demonstrated dynamic TME reprogramming, with recruitment of inflammatory innate immune cells and naïve T cells at day 8, and significant CD8+ T cell infiltration, activation, and proliferation at week 4.

Conclusions

CT-0508 has been administered to two subjects thus far, exhibiting safety, good tolerability, T cell repertoire modulation, and reprogramming of the TME consistent with the induction of anti-tumor immunity. The study continues to recruit patients and updated data will be presented.

Trial Registration

NCT04660929

Reference

Klichinsky M, Ruella M, Shestova O, et al. Human chimeric antigen receptor macrophages for cancer immunotherapy. Nat Biotechnol 2020;38(8):947–953.

Ethics Approval

Ethics approvals have been obtained from the clinical sites enrolling patients: the University of Pennsylvania (844106/IORG0000029), the University of North Carolina and City of Hope Comprehensive Cancer Center (20201732/IORG0000432).

144 SIRPα deficient CAR-Macrophages exhibit enhanced anti-tumor function and bypass the CD47 immune checkpoint

Background

Adoptive macrophage cell therapy represents a novel approach for cancer immunotherapy. Macrophages engineered to express chimeric antigen receptors (CAR-M) have shown promising pre-clinical results against solid tumors by improving tumor clearance, overall survival and facilitating the remodeling of the tumor microenvironment to induce a potent adaptive immune response. CD47 is a well-established macrophage immune checkpoint molecule that is over-expressed on tumor cells. CD47 binds to the macrophage signal regulatory protein α (SIRPα) to limit phagocytosis and macrophage effector functions. In this study we evaluated the impact of CD47 on CAR-M activity and showed that CD47-resistant targeted macrophage cell therapy mediates enhanced anti-tumor activity.

Methods

CRISPR/Cas9 was used to deplete the cognate receptor SIRPα from primary human macrophages (>90% efficiency and >90% viability) to increase CAR-M function. To assess anti-tumor activity of CAR-M, < i >in vitro</i > co-culture assays were established with an anti- human epidermal growth factor receptor 2 (HER2) CAR and HER2+ tumor cell lines. Macrophage killing and phagocytosis of target cells were quantified in real-time using a genetically encoded fluorophore (to monitor tumor cell growth) or a pH-sensitive dye (to monitor phagocytic acidification). In parallel, phenotypic characterization of surface molecules, cytokine secretion levels, biochemical analysis of downstream signaling molecules and response to purified HER2 and CD47 protein stimulation were evaluated.

Results

SIRPα knockout (KO) alone failed to induce tumor phagocytosis and cytotoxicity but enhanced targeted CAR-M anti-tumor activity. This was demonstrated by a reduced time required to kill 50% of tumor cells and a 2-fold increase in phagocytic activity, indicating synergy between SIRPα KO and CAR stimulation. Furthermore, in the absence of SIRPα, enhanced cytokine/chemokine secretion, macrophage polarization, and downstream signaling were observed.

Conclusions

We show for the first time the feasibility of generating gene edited primary human CAR macrophages for therapeutic purposes, and demonstrate that SIRPα deletion enhances the targeted anti-tumor activity of CAR-M.

139 Chimeric antigen receptor macrophages (CAR-M) elicit a systemic anti-tumor immune response and synergize with PD1 blockade in immunocompetent mouse models of HER2+ solid tumors

Background

Despite the remarkable efficacy achieved by CAR-T therapy in hematologic malignancies, application in solid tumors has been challenging. We previously developed human CAR-M and demonstrated that adoptive transfer of CAR-M into xenograft models of human cancer controls tumor progression and improves overall survival.1 Given that CAR-M are M1-polarized macrophages with the potential to remodel the tumor microenvironment (TME) and act as professional antigen presenting cells, we developed an immunocompetent animal model to evaluate the interaction of CAR-M with the TME and the adaptive immune system.

Methods

Murine bone marrow-derived macrophages were engineered to express an anti-HER2 CAR using the chimeric adenoviral vector Ad5f35. To evaluate the safety and efficacy of CAR-M therapy, immunocompetent mice were engrafted with HER2+ tumors and treated with syngeneic CAR-M monotherapy or in combination with a PD1 blocking antibody. Tumors were collected at various time points and dynamic changes in the TME were assessed using flow cytometry, immunohistochemistry, and gene expression analysis.

Results

In addition to efficient gene delivery, Ad5f35 transduction promoted a pro-inflammatory (M1) phenotype in murine macrophages. CAR-M, but not control macrophages, phagocytosed and killed HER2-overexpressing tumor cell lines. CAR-M induced MHC-I expression on tumor cells and enhanced the cytotoxicity of CD8+ T cells. In vivo, CAR-M led to significant tumor regression and improved overall survival in multiple syngeneic models. Analysis of the TME showed that CAR-M led to increased infiltration of intratumoral CD4+ and CD8+ T, NK, and dendritic cells – as well as an increase in T cell responsiveness to tumor-associated antigens, indicating enhanced epitope spreading. Given the impact of CAR-M on the endogenous adaptive immune system, we evaluated the combination of CAR-M with anti-PD1 in the CT26-HER2 model, which is resistant to anti-PD1 monotherapy, and found that the combination further reprogrammed the TME, enhanced tumor control, and improved overall survival compared to monotherapy with either agent. Mice that achieved complete responses (CRs) after CAR-M therapy were protected against antigen-negative relapse, indicating long-term anti-tumor immunity. Finally, the combination of CAR-M with anti-PD1 did not trigger sustained elevations of any serum analyte associated with cytokine release syndrome (CRS) and was well tolerated across numerous safety assessments

Conclusions

These results demonstrate that CAR-M reprogram the TME, induce epitope spreading, and orchestrate a systemic immune response against solid tumors. Moreover, our findings provide rationale for the combination of CAR-M with immune checkpoint inhibitors for the treatment of solid tumors.

Reference

Klichinsky M, Ruella M, Shestova O, et al. Human chimeric antigen receptor macrophages for cancer immunotherapy. Nat Biotechnol 2020;38(8):947–953

104 Development and characterization of human chimeric antigen receptor monocytes (CAR-Mono), a novel cell therapy platform

Background

Engineered cell therapies have demonstrated significant clinical activity against hematologic malignancies, but solid tumors remain an intractable challenge. We have previously developed a human chimeric antigen receptor macrophage (CAR-M) platform for adoptive cell therapy and shown potent anti-tumor activity in pre-clinical solid tumor models.1 CAR-M overcome critical solid tumor challenges such as tumor infiltration, immunosuppression within the tumor microenvironment, lymphocyte exclusion, and target antigen heterogeneity. Currently, CAR-M are generated in a week-long ex-vivo process in which peripheral blood monocytes are differentiated into macrophages prior to genetic manipulation. Here, we demonstrate the production feasibility, phenotype, pharmacokinetics, cellular fate, specificity, and anti-tumor activity of human CD14+ CAR monocytes.

Methods

Using the chimeric adenoviral vector Ad5f35, we engineered primary human CD14+ monocytes to express a CAR targeted against human epidermal growth factor receptor 2 (HER2) (CAR-mono). Using a partially automated approach, we established a process that allowed for same day manufacturing (from Leukopak to cryopreserved CAR-mono cell product).

Results

CAR expression and cell viability exceeded 90%, and cells efficiently differentiated into CAR-expressing macrophages. The adenoviral based gene modification method led to pre-conditioning of CAR-mono cells resulting in a strong M1 phenotype upon differentiation, and potent anti-tumor activity regardless of exposure to GM-CSF, M-CSF, or immunosuppressive factors. Treating CAR-mono cells with GM-CSF and IL-4 resulted in their differentiation to monocyte-derived CAR-DCs, indicating that these cells retain their myeloid differentiation potential. In vivo, CAR-mono treatment induced anti-tumor activity in various HER2+ solid tumor xenograft models. Following intravenous administration, CAR-mono demonstrated the ability to traffic to both GM-CSF < sup >high</sup > and GM-CSF< sup >low</sup >expressing tumors. Notably, CAR-mono showed long-term CAR expression and persistence (>100 days) in both NSG and NSG-S mouse models, demonstrating lasting persistence irrespective of human cytokine support.

Conclusions

The CAR-mono platform allows for a rapid, same-day manufacturing process while maintaining the key characteristics of CAR-M therapy. Ad5f35 engineered human monocytes are primed toward M1 macrophage differentiation and produce a cell population highly similar to our established CAR-M platform. Collectively, these findings provide strong pre-clinical support to advance the CAR-mono platform into clinical testing.

Reference

Klichinsky M, et al. Human chimeric antigen receptor macrophages for cancer immunotherapy. Nature Biotechnology March 2020.

Abstract 1530: Anti-HER2 CAR monocytes demonstrate targeted anti-tumor activity and enable a single day cell manufacturing process

Recent advances in cell therapy have led to significant efficacy in hematologic malignancies, but solid tumors remain an intractable challenge. We have previously developed a CAR macrophage (CAR-M) adoptive cell therapy platform and demonstrated potent anti-tumor activity in pre-clinical models. CAR-M overcome several of the barriers to efficacy in the solid tumor setting - trafficking, immunosuppression, lymphocyte exclusion, and antigen heterogeneity. Currently, CAR-M are generated via ex vivo differentiation of peripheral blood monocytes into macrophages prior to genetic manipulation. In order to streamline the manufacturing process, improve cell yields, and potentially improve tumor infiltration, we sought to evaluate the feasibility of directly engineering CD14+ monocytes to express CAR. Using the chimeric adenoviral vector Ad5f35, we engineered primary human CAR-monocytes to target tumors overexpressing HER2. CAR expression and viability both exceeded 90%. Anti-HER2 CAR-monocytes produced pro-inflammatory cytokines in response to antigen, specifically phagocytosed HER2 overexpressing target cells, and eradicated HER2-overexpressing tumor cells in a time and dose-dependent manner. CAR-monocytes efficiently differentiated into CAR-expressing macrophages in response to various maturation factors and cytokines within 3-5 days. Adenoviral based gene modification resulted in the upregulation of several pro-inflammatory markers on CAR-monocytes and pre-conditioned these cells to differentiate into M1 macrophages in the absence of exogenous M1 polarization factors. The M1 phenotype was maintained when CAR-monocytes were challenged with immunosuppressive cytokines in vitro. These cells demonstrated potent effector function after differentiation into macrophages, regardless of exposure to GM-CSF, M-CSF, or immunosuppressive factors. Anti-HER2 CAR monocytes carried broadly expressed myeloid chemokine receptors and responded to a panel of chemotactic factors. In order to optimize the cell manufacturing process associated with CAR-M, we established a closed-system, ultra-rapid CAR monocyte process. This process enabled same day manufacturing of the final CAR monocyte cell product, significantly reducing the cost of goods associated with autologous cell therapy as well as “vein to vein” time. This study demonstrated the successful development of CAR-monocytes with direct anti-tumor activity and capacity to differentiate into M1 polarized CAR-M. In addition, we established an ultra-rapid same-day CAR monocyte manufacturing process. The CAR-monocyte platform represents an advance in the field of adoptive cell therapy.

Citation Format: Linara Gabitova, Brett Menchel, Rashid Gabbasov, Stefano Pierini, Andrew Best, Kayleigh Ross, Yumi Ohtani, Daniel Blumenthal, Sascha Abramson, Thomas Condamine, Michael Klichinsky. Anti-HER2 CAR monocytes demonstrate targeted anti-tumor activity and enable a single day cell manufacturing process [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 1530.

Abstract CT204: A phase 1, first in human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in subjects with HER2 overexpressing solid tumors

Background: Adoptive T cell therapies have led to remarkable advances among patients with hematologic malignancies, but not in those with solid tumors. Macrophages are actively recruited into, and abundantly present in the solid tumor microenvironment (sTME). Tumor- associated macrophages typically evince immunosuppressive behavior, but when engineered to be proinflammatory, may be an ideal vector to administer adoptive cellular therapy in solid tumors. Furthermore, insertion of a CAR confers on the macrophages the ability to selectively recognize and phagocytose antigen overexpressing cancer cells. Additionally, CAR macrophages reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and immune memory.

Human Epidermal Growth Factor Receptor 2 (HER2) is overexpressed in many cancers, including but not limited to breast and gastroesophageal cancers.

CT-0508 is a cell product comprised of autologous monocyte-derived pro-inflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies have shown that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreased tumor burden and prolonged survival in relevant models. CT-0508 cells were safe in a semi-immunocompetent mouse model of human HER2 overexpressing ovarian cancer.

Methods: This is a FIH Phase 1 study to evaluate safety, tolerability, cell manufacturing feasibility, trafficking, and preliminary evidence of efficacy of investigational product CT-0508 in approximately 18 subjects with locally advanced (unresectable) or metastatic solid tumors overexpressing HER2 who have failed available therapies including anti-HER2 therapies when indicated.

Filgrastim will be used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis. The CT-0508 CAR macrophage product will be manufactured, prepared and cryopreserved from mobilized peripheral blood monocytes.

Group 1 subjects will receive CT-0508 infusion split over D1, 3 and 5. Subjects will be continually assessed for acute and cumulative toxicity. Dose limiting toxicities will be observed and addressed by a Safety Review Committee.

Group 2 subjects will receive the full CT-0508 infusion on D1.

Pre and post treatment biopsies and blood samples will be collected to investigate correlates of safety (immunogenicity), trafficking (PCR, RNA scope), persistence, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others.

Clinical trial registry number: NCT04660929

Citation Format: Joshua Bauml, Debora Barton, Amy Ronczka, Daniel Cushing, Michael Klichinsky, Elizabeth C. Dees. A phase 1, first in human (FIH) study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in subjects with HER2 overexpressing solid tumors [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 CT204.

A phase 1, first in human study of adenovirally transduced autologous macrophages engineered to contain an anti-HER2 chimeric antigen receptor (CAR) in subjects with HER2 overexpressing solid tumors

TPS2660

Background: Adoptive T cell therapies have led to remarkable advances among patients with hematologic malignancies, but not in those with solid tumors. Macrophages are actively recruited into, and abundantly present in the solid tumor microenvironment (sTME). Tumor- associated macrophages typically evince immunosuppressive behavior, but when engineered to be proinflammatory, may be an ideal vector to administer adoptive cellular therapy in solid tumors. Furthermore, insertion of a CAR confers on the macrophages the ability to selectively recognize and phagocytose antigen overexpressing cancer cells. Additionally, CAR macrophages reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and immune memory. Human Epidermal Growth Factor Receptor 2 (HER2) is overexpressed in many cancers, including but not limited to breast and gastroesophageal cancers (Table). CT-0508 is a cell product comprised of autologous monocyte-derived pro-inflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies have shown that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreased tumor burden and prolonged survival in relevant models. CT-0508 cells were safe and effective in a semi-immunocompetent mouse model of human HER2 overexpressing ovarian cancer. Methods: This is a FIH phase 1 study to evaluate safety, tolerability, cell manufacturing feasibility, trafficking, and preliminary evidence of efficacy of investigational product CT-0508 in approximately 18 subjects with locally advanced (unresectable) or metastatic solid tumors overexpressing HER2 who have failed available therapies including anti-HER2 therapies when indicated. Filgrastim will be used to mobilize autologous hematopoietic progenitor cells for monocyte collection by apheresis. The CT-0508 CAR macrophage product will be manufactured, prepared and cryopreserved from mobilized peripheral blood monocytes. The study is enrolling Group 1 subjects, who will receive CT-0508 infusion split over D1, 3 and 5. Subjects will be continually assessed for acute and cumulative toxicity. Dose limiting toxicities will be observed and addressed by a Safety Review Committee. Group 2 subjects will follow, and will receive the full CT-0508 infusion on D1. Pre and post treatment biopsies and blood samples will be collected to investigate correlates of trafficking, persistence, TME modulation, immune response and safety. Clinical trial information: NCT04660929. [Table: see text]

Macrophage-Based Approaches for Cancer Immunotherapy

Adoptive cell therapy with genetically modified T cells has generated exciting outcomes in hematologic malignancies, but its application to solid tumors has proven challenging. This gap has spurred the investigation of alternative immune cells as therapeutics. Macrophages are potent immune effector cells whose functional plasticity leads to antitumor as well as protumor function in different settings, and this plasticity has led to notable efforts to deplete or repolarize tumor-associated macrophages. Alternatively, macrophages could be adoptively transferred after ex vivo genetic modification. In this review, we highlight the role of macrophages in solid tumors, the progress made with macrophage-focused immunotherapeutic modalities, and the emergence of chimeric antigen receptor macrophage cell therapy.

Abstract 2180: Genetically engineered chimeric antigen receptor (CAR) monocytes demonstrate targeted anti-tumor activity and differentiate into M1-polarized CAR macrophages

Despite rapid advances in cancer immunotherapy, clinical responses in metastatic solid tumors have been limited. Macrophages are the most abundant immune cell in the solid tumor microenvironment (TME) and are primarily recruited as monocytes by TME-derived chemokines. When not under the control of the TME, macrophages are potent immune effector cells capable of phagocytosis, T cell recruitment, and antigen presentation. We have previously demonstrated that CAR macrophages (CAR-M) have potent anti-tumor activity and overcome several of the barriers to success in solid tumor immunotherapy - trafficking, immunosuppression, and antigen heterogeneity.

Currently, CAR-M are generated via ex vivo differentiation of peripheral blood monocytes into macrophages prior to genetic manipulation. To more closely recapitulate normal biologic behavior, we attempted to create CAR monocytes that could traffic and differentiate into CAR macrophages upon tumor penetration. Toward that goal, we genetically engineered CD14+ human monocytes without ex vivo differentiation and with minimal cell culture. Using the chimeric adenoviral vector Ad5f35, we engineered human CAR-monocytes targeted against HER2. CAR expression and viability both exceeded 90%. Ad5f35 transduced CAR monocytes survived and maintained CAR expression ex vivo for at least 21 days. CAR monocytes efficiently differentiated into CAR-expressing macrophages when treated with GM-CSF as determined by FACS-based phenotypic characterization and Wright-Giemsa staining. Anti-HER2 CAR monocytes eradicated HER2 expressing tumor cells in a time and dose-dependent manner, and had comparable potency to anti-HER2 CAR-M. Additionally, the CAR monocyte manufacturing process offered the logistical advantage of a short manufacturing process (approximately two days).

We have previously demonstrated that CAR-M are polarized toward a pro-inflammatory M1 phenotype after transduction with Ad5f35. Similarly, CAR monocytes demonstrated elevated expression of M1 markers, and intriguingly after differentiation into CAR-expressing macrophages, HLA-DR, CD80, CD86, and other M1 markers remained elevated - suggesting that transduction prior to differentiation does not impact the pro-inflammatory impact of adenoviral vectors on myeloid cells.

Taken together, this abstract describes the successful development of CAR-monocytes with the potential for a rapid manufacturing process. In addition to direct anti-tumor activity while in the monocyte phase, CAR monocytes have the capacity to differentiate into CAR macrophages in situ, which are in turn capable of phagocytosis, T cell recruitment, TME activation, and antigen presentation. Given the previously demonstrated pre-clinical efficacy of CT-0508 (an anti-HER2 CAR macrophage), the CAR monocyte platform described herein offers a shortened manufacturing process and a potential advantage in tumor penetration, which will be directly evaluated in upcoming studies.

Citation Format: Konrad Gabrusiewicz, Maggie Schmierer, Andrew Best, Martha Zeeman, Yumi Ohtani, Linara Gabitova, Daniel Cushing, Saar Gill, Michael Klichinsky. Genetically engineered chimeric antigen receptor (CAR) monocytes demonstrate targeted anti-tumor activity and differentiate into M1-polarized CAR macrophages [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2180.

Abstract PR07: Human chimeric antigen receptor (CAR) macrophages for cancer immunotherapy

Despite recent landmark advances in T-cell immunotherapy for the treatment of human cancer, metastatic solid tumors remain an intractable challenge. Macrophages are often the most abundant immune cell in the tumor microenvironment (TME), where they may convert into immunosuppressive (M2) tumor-associated macrophages (TAMs) and participate in disease progression. Currently, macrophage-orientated immunotherapeutic approaches under clinical development in oncology seek to reduce TAM infiltration (CSF-1 antagonists) or enhance TAM phagocytosis (CD47 antagonists). Transfer of autologous, activated, but nontargeted macrophages failed to demonstrate antitumor efficacy in past clinical trials. We hypothesized that genetically engineering human macrophages with CARs against tumor-associated antigens could redirect their phagocytic activity and lead to therapeutic efficacy with the potential for the induction of an antitumor T-cell response. We first demonstrate that CD3-zeta-based CARs are capable of inducing phagocytosis in human THP-1 macrophages, while truncated intracellular-domain deficient CARs were not. Targeted phagocytosis and clearance of CD19+, mesothelin +, and HER2+ cells by CARs targeted against each respective antigen was significantly superior to that by control untransduced (UTD) macrophages. We demonstrate that primary human macrophages, which are resistant to most viral vectors, are efficiently transduced by the chimeric fiber adenoviral vector Ad5f35 (~70% in 10 normal donors). Using Ad5f35, we engineered primary human macrophages with a CD3-zeta-based CAR against HER2. Anti-HER2 primary human CAR macrophages demonstrated targeted phagocytosis against HER2+ but not HER2- cell lines, with phagocytic activity dependent on both the CAR and antigen densities. Furthermore, CAR, but not UTD, macrophages led to potent dose-dependent killing of three distinct HER2-high cell lines in vitro. We sought to test the efficacy of anti-HER2 primary human macrophages in xenograft models of human HER2+ ovarian cancer. A single dose of CAR, but not UTD macrophages, led to tumor regression and improved overall survival in both intraperitoneal and disseminated models of disease. We show that macrophage transduction with Ad5f35, a double-stranded DNA virus, leads to a broad gene expression change, an interferon signaling signature, and phenotypic clustering toward classically activated M1 macrophages. CAR macrophages upregulated co-stimulatory ligand and antigen processing/presentation genes and led to enhanced T-cell stimulation in vitro and in vivo. Lastly, CAR, but not UTD, macrophages showed a broad resistance for M2 conversion in response to immunosuppressive cytokines. In conclusion, we show that primary human CAR macrophages are capable of targeted tumor phagocytosis, lead to improved overall survival in xenograft models, and demonstrate enhanced T-cell stimulation. CAR macrophages are a novel cell therapy platform for the treatment of human cancer.

This abstract is also being presented as Poster B29.

Citation Format: Michael Klichinsky, Marco Ruella, Olga Shestova, Andrew Best, Kristin Blouch, Xueqing M. Lu, Saad S. Kenderian, Miriam Y. Kim, Roddy O'Connor, Stephen Wallace, Miroslaw Kozlowski, Dylan M. Marchione, Maksim Shestov, Benjamin A. Garcia, Carl June, Saar Gill. Human chimeric antigen receptor (CAR) macrophages for cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr PR07.

Human chimeric antigen receptor macrophages for cancer immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has shown promise in hematologic malignancies, but its application to solid tumors has been challenging^1-4. Given the unique effector functions of macrophages and their capacity to penetrate tumors⁵, we genetically engineered human macrophages with CARs to direct their phagocytic activity against tumors. We found that a chimeric adenoviral vector overcame the inherent resistance of primary human macrophages to genetic manipulation and imparted a sustained pro-inflammatory (M1) phenotype. CAR macrophages (CAR-Ms) demonstrated antigen-specific phagocytosis and tumor clearance in vitro. In two solid tumor xenograft mouse models, a single infusion of human CAR-Ms decreased tumor burden and prolonged overall survival. Characterization of CAR-M activity showed that CAR-Ms expressed pro-inflammatory cytokines and chemokines, converted bystander M2 macrophages to M1, upregulated antigen presentation machinery, recruited and presented antigen to T cells and resisted the effects of immunosuppressive cytokines. In humanized mouse models, CAR-Ms were further shown to induce a pro-inflammatory tumor microenvironment and boost anti-tumor T cell activity.

Abstract B65: CT-0508, a novel CAR macrophage product directed against HER2, promotes a proinflammatory tumor microenvironment

Despite recent advances in T cell immunotherapy for the treatment of human cancer, metastatic solid tumors remain an intractable challenge. Macrophages are usually the most abundant immune cell in the tumor microenvironment (TME) where, as immunosuppressive tumor-associated macrophages (TAMs), they participate in disease progression. The current goals of macrophage-based immunotherapies are to reduce TAM infiltration or enhance TAM phagocytosis. In contrast, we have developed a new paradigm based on the adoptive transfer of genetically engineered chimeric antigen receptor (CAR) macrophages (CAR-M) for the treatment of human cancer. CAR-M can only be produced using a unique adenoviral vector, since human macrophages are highly resistant to other methods of gene transfer. We have previously shown that the primary mechanism of action of CAR-M is phagocytosis, and that a single dose of primary human anti-HER2 CAR-M led to significantly improved overall survival in multiple xenograft models. We now establish that Ad5f35-transduced anti-HER2 CAR-M (CT-0508) adopt a unique proinflammatory and antitumor M1 phenotype. Functional evaluation and RNA sequencing revealed that CT-0508 maintain a proinflammatory M1 phenotype despite challenge with immunosuppressive environments in vitro, highlighting their resistance to subversion. By engrafting immunodeficient mice with human hematopoietic cells and human cancer cells, we established a novel xenografted human TME model. We demonstrate with single-cell resolution that CT-0508 maintain their phenotype within the human TME. Additionally, CT-0508 activated the human TME and generated an activated human dendritic cell signature. To further investigate the potential of CT-0508 for TME activation, we modeled the interaction of CT-0508 with immunosuppressive macrophages, dendritic cells, and T cells. CT-0508 shifted bystander macrophages toward a proinflammatory phenotype, induced activation and maturation markers on DCs, and recruited resting as well as activated T cells in chemotaxis assays. Lastly, CT-0508 demonstrated enhanced antigen presentation when compared to control human macrophages. These results show that in addition to direct antitumor activity, the anti-HER2 CAR macrophage cell product CT-0508 is capable of activating the solid cancer TME and promoting a proinflammatory phenotype. The safety of CT-0508 will be evaluated in an upcoming first-in-human phase I clinical trial.

Citation Format: Konrad Gabrusiewicz, Nicholas Anderson, Xueqing Lu, Xinhe Shan, Olga Shestova, Nicholas Petty, Feng Shen, Maggie Schmierer, Andrew Best, Martha Zeeman, Yumi Ohtani, Katherine Cummins, Saar Gill, Michael Klichinsky. CT-0508, a novel CAR macrophage product directed against HER2, promotes a proinflammatory tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B65.

Induction of resistance to chimeric antigen receptor T cell therapy by transduction of a single leukemic B cell

We report a patient relapsing 9 months after CD19-targeted CAR T cell (CTL019) infusion with CD19^- leukemia that aberrantly expressed the anti-CD19 CAR. The CAR gene was unintentionally introduced into a single leukemic B cell during T cell manufacturing, and its product bound in cis to the CD19 epitope on the surface of leukemic cells, masking it from recognition by and conferring resistance to CTL019.

Genetic Inactivation of CD33 in Hematopoietic Stem Cells to Enable CAR T Cell Immunotherapy for Acute Myeloid Leukemia

The absence of cancer-restricted surface markers is a major impediment to antigen-specific immunotherapy using chimeric antigen receptor (CAR) T cells. For example, targeting the canonical myeloid marker CD33 in acute myeloid leukemia (AML) results in toxicity from destruction of normal myeloid cells. We hypothesized that a leukemia-specific antigen could be created by deleting CD33 from normal hematopoietic stem and progenitor cells (HSPCs), thereby generating a hematopoietic system resistant to CD33-targeted therapy and enabling specific targeting of AML with CAR T cells. We generated CD33-deficient human HSPCs and demonstrated normal engraftment and differentiation in immunodeficient mice. Autologous CD33 KO HSPC transplantation in rhesus macaques demonstrated long-term multilineage engraftment of gene-edited cells with normal myeloid function. CD33-deficient cells were impervious to CD33-targeting CAR T cells, allowing for efficient elimination of leukemia without myelotoxicity. These studies illuminate a novel approach to antigen-specific immunotherapy by genetically engineering the host to avoid on-target, off-tumor toxicity.

Overcoming the Immunosuppressive Tumor Microenvironment of Hodgkin Lymphoma Using Chimeric Antigen Receptor T Cells

Patients with otherwise treatment-resistant Hodgkin lymphoma could benefit from chimeric antigen receptor T-cell (CART) therapy. However, Hodgkin lymphoma lacks CD19 and contains a highly immunosuppressive tumor microenvironment (TME). We hypothesized that in Hodgkin lymphoma, CART should target both malignant cells and the TME. We demonstrated CD123 on both Hodgkin lymphoma cells and TME, including tumor-associated macrophages (TAM). In vitro, Hodgkin lymphoma cells convert macrophages toward immunosuppressive TAMs that inhibit T-cell proliferation. In contrast, anti-CD123 CART recognized and killed TAMs, thus overcoming immunosuppression. Finally, we showed in immunodeficient mouse models that CART123 eradicated Hodgkin lymphoma and established long-term immune memory. A novel platform that targets malignant cells and the microenvironment may be needed to successfully treat malignancies with an immunosuppressive milieu.Significance: Anti-CD123 chimeric antigen receptor T cells target both the malignant cells and TAMs in Hodgkin lymphoma, thereby eliminating an important immunosuppressive component of the tumor microenvironment. Cancer Discov; 7(10); 1154-67. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 1047.

Dual CD19 and CD123 targeting prevents antigen-loss relapses after CD19-directed immunotherapies

Potent CD19-directed immunotherapies, such as chimeric antigen receptor T cells (CART) and blinatumomab, have drastically changed the outcome of patients with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL). However, CD19-negative relapses have emerged as a major problem that is observed in approximately 30% of treated patients. Developing approaches to preventing and treating antigen-loss escapes would therefore represent a vertical advance in the field. Here, we found that in primary patient samples, the IL-3 receptor α chain CD123 was highly expressed on leukemia-initiating cells and CD19-negative blasts in bulk B-ALL at baseline and at relapse after CART19 administration. Using intravital imaging in an antigen-loss CD19-negative relapse xenograft model, we determined that CART123, but not CART19, recognized leukemic blasts, established protracted synapses, and eradicated CD19-negative leukemia, leading to prolonged survival. Furthermore, combining CART19 and CART123 prevented antigen-loss relapses in xenograft models. Finally, we devised a dual CAR-expressing construct that combined CD19- and CD123-mediated T cell activation and demonstrated that it provides superior in vivo activity against B-ALL compared with single-expressing CART or pooled combination CART. In conclusion, these findings indicate that targeting CD19 and CD123 on leukemic blasts represents an effective strategy for treating and preventing antigen-loss relapses occurring after CD19-directed therapies.

The Addition of the BTK Inhibitor Ibrutinib to Anti-CD19 Chimeric Antigen Receptor T Cells (CART19) Improves Responses against Mantle Cell Lymphoma

PURPOSE

Responses to therapy with chimeric antigen receptor T cells recognizing CD19 (CART19, CTL019) may vary by histology. Mantle cell lymphoma (MCL) represents a B-cell malignancy that remains incurable despite novel therapies such as the BTK inhibitor ibrutinib, and where data from CTL019 therapy are scant. Using MCL as a model, we sought to build upon the outcomes from CTL019 and from ibrutinib therapy by combining these in a rational manner.

EXPERIMENTAL DESIGN

MCL cell lines and primary MCL samples were combined with autologous or normal donor-derived anti-CD19 CAR T cells along with ibrutinib. The effect of the combination was studied in vitro and in mouse xenograft models.

RESULTS

MCL cells strongly activated multiple CTL019 effector functions, and MCL killing by CTL019 was further enhanced in the presence of ibrutinib. In a xenograft MCL model, we showed superior disease control in the CTL019- as compared with ibrutinib-treated mice (median survival not reached vs. 95 days, P < 0.005) but most mice receiving CTL019 monotherapy eventually relapsed. Therefore, we added ibrutinib to CTL019 and showed that 80% to 100% of mice in the CTL019 + ibrutinib arm and 0% to 20% of mice in the CTL019 arm, respectively, remained in long-term remission (P < 0.05).

CONCLUSIONS

Combining CTL019 with ibrutinib represents a rational way to incorporate two of the most recent therapies in MCL. Our findings pave the way to a two-pronged therapeutic strategy in patients with MCL and other types of B-cell lymphoma. Clin Cancer Res; 22(11); 2684-96. ©2016 AACR.

Abstract 3139: CD33 directed chimeric antigen receptor T cell therapy as a novel regimen prior to allogeneic stem cell transplantation in acute myeloid leukemia

Allogeneic stem cell transplantation is the only option in relapsed acute myeloid leukemia (AML). However, patients are often excluded due to refractory disease. The successful translation of Chimeric Antigen Receptor (CAR) T cell therapy to AML would constitute a vertical advance in the field. We developed a 2nd generation CAR using the anti CD33 scFv of Gemtuzumab ozogamicin, 41BB costimulation, CD3ζ signaling domain, and a lentiviral (LV) vector.

In vitro, CART33 resulted in robust functions when incubated with the CD33+ cell line MOLM14. In NSGS mice (NOD SCID γc-/-(NSG), transgenic for stem cell factor, IL3 and GM-CSF) engrafted with primary AML, CART33 eradicated AML and led to a long term disease free survival (Table 1).

Activity of CART33, compared to control untransduced T cellsCART33UTDP-value% Degranulation (4 hr incubation with MOLM14)98%1.3%&lt;0.0001% Specific Lysis, 24 hr incubation with MOLM14 (E:T 0.625:1)65.7%30%&lt;0.0001CFSE based proliferation (5-day incubation with MOLM14)91.6%3%&lt;0.0001IL-6 (24-hour incubation with MOLM14, median, pg/ml)22.655.73&lt;0.0001GM-CSF (24-hour incubation with MOLM14, median, pg/ml)1324816.9&lt;0.0001MIP-1b (24-hour incubation with MOLM14, median, pg/ml)81809.15&lt;0.0001IFN-g (24-hour incubation with MOLM14, median, pg/ml)249890.35&lt;0.0001IL-2 (24-hour incubation with MOLM14, median, pg/ml)93000.39&lt;0.0001Overall survival at 200 days (NSG-S mice engrafted with primary AML blasts and treated with CART-33 or UTD)100%0%&lt;0.0001Median AML burden, measured by bioluminescence (photons/sec) in NSG mice engrafted with MOLM14, 6 weeks after treatment7×10(7)2×10(9)0.01

Since CD33 is also expressed on normal myeloid progenitors, we assessed the potential myelotoxicity of CART33 in humanized immune system (HIS) mice (NSG mice engrafted with human fetal liver CD34+ cells). CART33 resulted in human lineage cytopenias and in a significant reduction of CD34+CD38- hematopoietic stem cells and CD34+CD38+ myeloid progenitors.

Both the anti-leukemic activity and myeloablative potential of CART33 could be used as a novel conditioning regimen in refractory AML. However, the effect of the CAR T cells needs to be terminated to avoid engraftment failure. We therefore designed a “biodegradable” mRNA modified CAR33. T cells were electroporated with this construct and expressed CAR for up to six days. When compared with LV-CART33, RNA-CART33 resulted in comparable in vitro functions that declined over time post electroporation. In NSG mice engrafted with MOLM14, treatment with cyclophosphamide (for lymphodepletion) plus RNA-CART33 resulted in deeper and longer leukemic response compared to cyclophosphamide plus control T cells.

In conclusion, our preclinical studies show potent activity of CART33 in AML. Biodegradable CART33 could be used as a novel anti-leukemic cellular conditioning in patients with relapsed AML

Note: This abstract was not presented at the meeting.

Citation Format: Saad S. Kenderian, Marco Ruella, Olga Shestova, Michael Klichinsky, John Scholler, Decheng Song, David L. Porter, Martin Carroll, Carl H. June, Saar Gill. CD33 directed chimeric antigen receptor T cell therapy as a novel regimen prior to allogeneic stem cell transplantation in acute myeloid leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3139. doi:10.1158/1538-7445.AM2015-3139

An atlas of the Epstein-Barr virus transcriptome and epigenome reveals host-virus regulatory interactions

Epstein-Barr virus (EBV), which is associated with multiple human tumors, persists as a minichromosome in the nucleus of B lymphocytes and induces malignancies through incompletely understood mechanisms. Here, we present a large-scale functional genomic analysis of EBV. Our experimentally generated nucleosome positioning maps and viral protein binding data were integrated with over 700 publicly available high-throughput sequencing data sets for human lymphoblastoid cell lines mapped to the EBV genome. We found that viral lytic genes are coexpressed with cellular cancer-associated pathways, suggesting that the lytic cycle may play an unexpected role in virus-mediated oncogenesis. Host regulators of viral oncogene expression and chromosome structure were identified and validated, revealing a role for the B cell-specific protein Pax5 in viral gene regulation and the cohesin complex in regulating higher order chromatin structure. Our findings provide a deeper understanding of latent viral persistence in oncogenesis and establish a valuable viral genomics resource for future exploration.

EBV latency types adopt alternative chromatin conformations

Epstein-Barr Virus (EBV) can establish latent infections with distinct gene expression patterns referred to as latency types. These different latency types are epigenetically stable and correspond to different promoter utilization. Here we explore the three-dimensional conformations of the EBV genome in different latency types. We employed Chromosome Conformation Capture (3C) assay to investigate chromatin loop formation between the OriP enhancer and the promoters that determine type I (Qp) or type III (Cp) gene expression. We show that OriP is in close physical proximity to Qp in type I latency, and to Cp in type III latency. The cellular chromatin insulator and boundary factor CTCF was implicated in EBV chromatin loop formation. Combining 3C and ChIP assays we found that CTCF is physically associated with OriP-Qp loop formation in type I and OriP-Cp loop formation in type III latency. Mutations in the CTCF binding site located at Qp disrupt loop formation between Qp and OriP, and lead to the activation of Cp transcription. Mutation of the CTCF binding site at Cp, as well as siRNA depletion of CTCF eliminates both OriP-associated loops, indicating that CTCF plays an integral role in loop formation. These data indicate that epigenetically stable EBV latency types adopt distinct chromatin architectures that depend on CTCF and mediate alternative promoter targeting by the OriP enhancer.

Epstein-Barr Virus (EBV) latent infection is associated with several human malignancies. The viral genes expressed during latent infection can vary depending on host cell or tumor type. The different gene expression programs, referred to as latency types, are determined by alternative viral promoter usage. In this work, we investigate how differential DNA loop formation regulates viral promoter selection in different latency types. We use chromatin conformation capture methods to demonstrate that the transcriptional enhancer at OriP forms a stable loop with one of two different promoters, depending on the latency type. In type I latency, OriP forms a loop with the active Q promoter (Qp). In type III latency, OriP forms a loop with the active C promoter (Cp). Loop formation was mediated, in part, by CTCF binding sites located within the loops. Mutation in the CTCF binding site located at Qp caused a loss of OriP-Qp loop formation, a loss of Qp transcription, and a reactivation of Cp transcription from an alternative loop formed with OriP-Cp. These findings indicate that OriP loop formation is an integral component of promoter selection, and that chromatin conformation may determine EBV latency type.