We previously developed human CAR macrophages (CAR-M) and demonstrated redirection of macrophage anti-tumor function leading to tumor control in immunodeficient xenograft models. Here, we develop clinically relevant fully immunocompetent syngeneic models to evaluate the potential for CAR-M to remodel the tumor microenvironment (TME), induce T cell anti-tumor immunity, and sensitize solid tumors to PD1/PDL1 checkpoint inhibition. In vivo, anti-HER2 CAR-M significantly reduce tumor burden, prolong survival, remodel the TME, increase intratumoral T cell and natural killer (NK) cell infiltration, and induce antigen spreading. CAR-M therapy protects against antigen-negative relapses in a T cell dependent fashion, confirming long-term anti-tumor immunity. In HER2+ solid tumors with limited sensitivity to anti-PD1 (aPD1) monotherapy, the combination of CAR-M and aPD1 significantly improves tumor growth control, survival, and remodeling of the TME in pre-clinical models. These results demonstrate synergy between CAR-M and T cell checkpoint blockade and provide a strategy to potentially enhance response to aPD1 therapy for patients with non-responsive tumors. Anti-PD1 monotherapy shows limited efficacy against HER2+ tumors. Here, the authors show that murine CAR macrophages (CAR-M) induce tumor microenvironment remodeling, T-cell mediated immunity and synergy with PD1 blockade, improving survival in immunocompetent female-mouse models of HER2+ solid tumors.

Background: Myeloid cells are actively recruited to the solid tumor microenvironment (TME) and have the potential to mediate tumor control via phagocytosis, TME remodeling, and T cell activation. We previously developed human chimeric antigen receptor macrophages (CAR-Macrophage) and have shown potent anti-tumor activity in pre-clinical solid tumor models1. The anti-HER2 CAR-Macrophage cell therapy product, CT-0508, was evaluated in a Phase 1 trial as a monotherapy and in combination with pembrolizumab. Clinical data have demonstrated preliminary safety, feasibility, and validated the mechanism of action. We have developed a next-generation CAR monocyte (CAR-Monocyte) platform to increase the available dose, improve tumor trafficking and engraftment, and shorten the manufacturing and vein-to-vein time as compared to CAR-Macrophage therapy. CT-0525 is an autologous anti-HER2 CAR-Monocyte cell therapy based on CD14+ monocytes engineered with an Ad5f35 adenoviral vector to express an anti-HER2 CAR. Pre-clinical studies have demonstrated the feasibility, phenotype, pharmacokinetics, durable CAR expression, cellular fate, antigen specificity, and anti-tumor activity of CT-0525. Pre-clinical studies have shown that CT-0525 differentiated into pro-inflammatory CAR-Macrophages in vivo and controlled tumor growth. The CT-0525 manufacturing process takes one day and enables the production of up to 10 billion cells from a single apheresis. CT-0525 is being investigated in a first-in-human, open-label, multi-center, Phase 1 study in participants (pts) with HER2 overexpressing solid tumors. Methods: This Phase 1, first-in-human study evaluates the preliminary safety, feasibility, tolerability, trafficking, TME activation, and initial evidence of efficacy of the investigational CAR-Monocyte product, CT-0525, in pts with locally advanced unresectable/metastatic solid tumors overexpressing HER2. Pts previously treated with anti-HER2 therapies are eligible for this dose escalation study. Filgrastim mobilized autologous CD14+ monocytes are collected by apheresis, followed by manufacturing and cryopreservation. CT-0525 will be administered without conditioning chemotherapy. The 1st cohort of pts will receive 3 x 109 CT-0525 CAR positive monocytes administered in one infusion intravenously. If tolerated as per the modified toxicity probability interval algorithm (mTPI), the 2nd cohort of pts will receive up to 10 x 109 CT-0525 CAR positive monocytes in one infusion. A minimum of 3 evaluable pts is required at each dose level. Primary endpoints include assessment of safety and tolerability, as well as manufacturing feasibility. Secondary endpoints include initial evidence of efficacy. Correlative assessments include pre- and post-treatment biopsies and blood samples for safety, immunogenicity, pharmacokinetics, tumor trafficking, TME modulation, epitope spreading, and other translational biomarkers. This clinical trial (NCT06254807) is currently enrolling at multiple sites across the United States. 1. Klichinsky M, et al. Human chimeric antigen receptor macrophages for cancer immunotherapy. Nature Biotechnology. 2020; 38: 947-953 Citation Format: Yara Abdou, Felicia Cao, Paula Pohlman, Richard Maziarz, Hemant Murthy, Yuan Yuan, Anuradha Krishnamurthy, Kim Reiss Binder, James Isaacs, Aiwu He, Pooja Advani, Daniel Blumenthal, Kenneth Locke, Jeanette Wetzel, Michael Klichinsky, Thomas Condamine, Eugene Kennedy, Davendra Sohal. A Phase 1, First-in-Human study of autologous monocytes engineered to express an anti-HER2 chimeric antigen receptor (CAR) in participants with HER2 overexpressing solid tumors [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-12-17.

TPS2682 Background: Myeloid cells are actively recruited to the solid tumor microenvironment (TME) and have the potential to mediate tumor control via phagocytosis, TME remodeling, and T cell activation. We previously developed human chimeric antigen receptor macrophages (CAR-M) and have shown potent anti-tumor activity in pre-clinical solid tumor models. The anti-HER2 CAR-M cell therapy product, CT-0508, is currently being evaluated in a Phase I trial as a monotherapy and in combination with pembrolizumab. Early clinical data have shown feasibility, safety, and validated the mechanism of action. We have developed a next-generation CAR monocyte (CAR-Mono) platform to increase the dose, improve tumor trafficking and engraftment, and shorten the manufacturing and vein-to-vein time as compared to CAR-M therapy. CT-0525 is an autologous anti-HER2 CAR-Mono cell therapy based on CD14+ monocytes engineered with an Ad5f35 adenoviral vector to express an anti-HER2 CAR. Pre-clinical studies have demonstrated the feasibility, phenotype, pharmacokinetics, durable CAR expression, cellular fate, antigen specificity, and anti-tumor activity of CT-0525. Pre-clinical studies have shown that CT-0525 differentiated into pro-inflammatory CAR-M in vivo and controlled tumor growth. The CT-0525 manufacturing process takes one day and enables the production of up to 10 billion cells from a single apheresis. CT-0525 is being investigated in a first-in-human, open-label, multi-center, Phase I study in patients with HER2 overexpressing solid tumors. Methods: This Phase 1, first-in-human study evaluates the feasibility, safety, tolerability, trafficking, TME activation, and preliminary evidence of efficacy of the investigational CAR-Mono product CT-0525 in 6 participants (pts) with locally advanced unresectable/metastatic solid tumors overexpressing HER2. Pts previously treated with anti-HER2 therapies are eligible. Filgrastim mobilized autologous CD14+ monocytes are collected by apheresis, followed by manufacturing and cryopreservation. The 1st cohort of pts (n=3) will receive 3 x 109 CT-0525 CAR positive monocytes administered IV in one infusion. If tolerated as per the modified toxicity probability interval algorithm (mTPI), the 2nd cohort of pts (n=3) will receive up to 10 x 109 CT-0525 CAR positive monocytes in one infusion. CT-0525 will be administered without conditioning chemotherapy. Primary endpoints include assessment of safety and tolerability, as well as manufacture feasibility. Correlative assessments include pre- and post-treatment biopsies and blood samples for safety, immunogenicity, pharmacokinetics, tumor trafficking, TME modulation, epitope spreading, and other translational biomarkers. Clinical trial information: NCT06254807 .

Chimeric antigen receptor (CAR) macrophages (CAR-Ms) mediate antitumor immunity via phagocytosis, cytokine release, activation of the tumor microenvironment and antigen presentation. We report results from a non-prespecified interim analysis of a first-in-human, phase 1 clinical trial of CT-0508, an anti-human epidermal growth factor receptor 2 (HER2) CAR-M in patients with advanced HER2-overexpressing tumors. Fourteen patients were treated across two different regimens. Patients with breast cancer and gastroesophageal cancer were primarily enrolled and had to have demonstrated overexpression of HER2 according to the American Society of Clinical Oncology/College of American Pathologists guidelines (HER2 immunohistochemistry 3+ or immunohistochemistry 2+/in situ hybridization-amplified). No lymphodepletion chemotherapy was used before infusion. The primary endpoints were safety and CAR-M manufacturability. Secondary endpoints included cellular kinetics and efficacy using objective response rate, overall survival, progression-free survival and duration of response. No dose-limiting toxicities, severe cytokine release syndrome (>= grade 3) or immune effector cell-associated neurotoxicity syndrome were observed; 44% (n = 4 of 9, 95% confidence interval = 14-79%) of HER2 3+ tumors achieved stable disease as best overall response 8 weeks after treatment. No meaningful activity was observed in the HER2 2+ population (n = 5). Correlative analyses of serial biopsies confirmed that CT-0508 traffics to and remodels the tumor microenvironment, resulting in expansion of CD8+ T cells. These findings demonstrate the preliminary safety, tolerability and manufacturing feasibility of CT-0508 for HER2+ tumors. ClinicalTrials.gov registration: NCT04660929.

Abstract Motivation: In solid tumors, anti-inflammatory cytokines such as IL10 and TGFβ support an immunosuppressive tumor microenvironment (TME) and inhibit anti-tumor immunity. Many therapeutic approaches to overcome immunosuppression have used monoclonal antibodies to block cytokine signaling. Instead of silencing TME-associated cytokines, a more powerful strategy may be to leverage them as disease markers and convert them into anti-tumor signals, using a logic-gated cell-based immunotherapy. Here, we engineered macrophages with synthetic cytokine switch receptors (SR) that convert IL10 or TGFβ into pro-inflammatory signals. Macrophages are homeostatic regulators capable of both infiltrating solid tumors and initiating inflammation, and we harnessed this proficiency using SRs that convert prevalent cytokines in the TME into pro-inflammatory responses for TME modulation. We termed this engineered myeloid cell platform “Engineered Microenvironment Converters” (EM-C) and evaluated its ability to overcome cytokine-mediated immunosuppression in solid tumors. Methods: EM-C were produced by transducing primary macrophages or monocytes with a SR that converts IL10 into an interferon-based signal. The response of EM-C to IL10 was monitored in vitro using phenotypic characterization of surface molecules, measurement of secreted factors, and mRNA profiling. The in vivo activity of EM-C was evaluated using a subcutaneous tumor model in immunocompetent mice. Murine EM-C were administered to tumor-bearing mice, and their ability to modulate the TME was monitored via immunophenotyping, secretome analysis, and single cell transcriptomics. To demonstrate modularity of the EM-C platform, additional SR were designed to convert TGFβ into interferon or toll-like receptor signals. Results: EM-C efficiently sequestered IL10 or TGFβ and upregulated pro-inflammatory markers, cytokines, and pathways in a dose-dependent manner in vitro. EM-C administered to tumor-bearing mice remodeled the TME immune compartment by increasing the abundance of CD8 T cells and reducing the presence of immunosuppressive Tregs. EM-C furthermore augmented the cytokine/chemokine profile of the TME in a manner that correlated with anti-tumor response. TME modulation by EM-C improved tumor control, as compared to non-engineered macrophages, and had additive efficacy with checkpoint blockade. Conclusion: We present a versatile immunotherapy platform that harnesses macrophages as “living converters” to locally augment inflammation in solid tumors. EM-C exhibit a modular ability to locally convert IL10 or TGFβ into pro-inflammatory signals without systemic cytokine antagonism. The EM-C platform enables development of target antigen-agnostic myeloid cell immunotherapies for overcoming immunosuppression in diverse solid tumors. Citation Format: Chris Sloas, Silvia Beghi, Yuhao Huangfu, Rehman Qureshi, Benjamin Schott, Michael Ball, Daniel Blumenthal, Thomas Condamine, Michael Klichinsky, Yumi Ohtani. Macrophages expressing synthetic cytokine receptors reverse IL10-mediated immunosuppression within solid tumors and promote adaptive immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5249.

Abstract Background: In pre-clinical studies, CAR macrophages (CAR-M) phagocytose tumor cells, activate the tumor microenvironment (TME), recruit T cells, and induce anti-tumor T cell immunity. CT-0508 is a first-in-class CAR-M product comprised of autologous monocyte-derived macrophages expressing an anti-HER2 CAR. In pre-clinical models, anti-HER2 CAR-M was able to control the growth of syngeneic metastatic HER2+ breast cancer. Here we present preliminary clinical results and translational data from Group 1 of 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 with advanced solid tumors overexpressing HER2 with progression on prior therapies. Monocytes are isolated from mobilized apheresis products, differentiated into macrophages, and engineered with an anti-HER2 CAR. Group 1 participants (n = 9) receive a fractionated dose on days 1, 3, 5 and Group 2 participants (n = 9) receive the full dose on day 1. CT-0508 is administered without preparative chemotherapy. Serial blood samples and biopsies (baseline and 2 post-treatment) are collected to investigate safety, pharmacokinetics, and mechanism of action. AU565 and 4T1-HER2 cell lines were utilized to model human and murine breast cancer, respectively, in vitro and in vivo. Results: Nine participants (6F/3M) have been treated in Group 1, comprising breast (4), esophageal (2), cholangiocarcinoma, ovarian, and parotid gland cancers, with a median age of 58. Participants had received a median of 3 (range, 2-11) prior lines of therapy; 8 had received prior anti-HER2 therapy. CT-0508 was successfully manufactured and well tolerated with no dose-limiting toxicities. Three related SAEs occurred in 2 participants: grade 1 CRS with hospitalization for monitoring and grade 2 infusion reaction that resolved within 1 hour were reported in one participant. Grade 2 CRS with fever and hypoxia occurred in another participant and resolved within ~ 72 hours. Five additional participants experienced Grade 1-2 CRS and/or infusion reactions with rapid resolution. There were no cases of Grade 3 or 4 CRS. There were no major organ toxicities. Post-infusion cytokines were transiently elevated in most participants enrolled in group 1 and were self-limiting. Four of the 7 participants evaluated had stable disease. CT-0508 was transiently detectable in the blood and was detected in the TME of 8/9 participants. CT-0508 modulated the TME, leading to myeloid cell activation, effector T cell infiltration, activation, and proliferation. TCR sequencing demonstrated newly expanding T cell clones in the blood post-treatment that accumulated within the TME, suggesting expansion of tumor-reactive T cells upon CT-0508 infusion. Data from participants enrolled in Group 1 will be presented. Most of these patients were breast cancer patients with HER2 overexpressing metastatic disease. Conclusions: CT-0508 was feasible to manufacture and had acceptable safety and tolerability. Early correlative data demonstrate trafficking, TME modulation, and induction of anti-tumor T cell immunity in participants with HER2 overexpressing solid tumors including metastatic breast cancer. The study is actively enrolling (NCT04660929). Citation Format: Yara Abdou, Joanne Mortimer, Paula Pohlmann, Melissa Johnson, Richard Maziarz, Jennifer M. Specht, Claire Dees, Naoto Ueno, Yuan Yuan, Mathew Angelos, Saar Gill, Olga Shestova, Jonathon Serody, Saul Priceman, Rehman Qureshi, Poonam Sonawane, Stefano Pierini, Maria Cecilia Oliveira-Nunes, Daniel Cushing, Michael Klichinsky, Thomas Condamine, Ramona Swaby, Kim Reiss. Translational insights from a phase 1, first-in-human (FIH) clinical trial of the anti-HER2 CAR macrophage CT-0508 in participants with HER2 positive metastatic breast cancer and other HER2 overexpressing solid tumors [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-04-08.

Background: Macrophages are abundant in the solid tumor microenvironment (sTME) and can exhibit both pro- and anti-tumor functions. Macrophages can be redirected by CAR expression to phagocytose cancer cells in an antigen-specific manner. CAR-M can reprogram the sTME and present neoantigens to T cells, leading to epitope spreading and anti-tumor immunity. CT-0508 is comprised of autologous monocyte-derived proinflammatory macrophages expressing an anti-HER2 CAR. Pre-clinical studies showed that CT-0508 induced targeted cancer cell phagocytosis while sparing normal cells, decreased tumor burden, prolonged survival, and was safe and effective. Notably, anti-HER2 CAR-M treatment led to activation of the sTME, with infiltration of CD8+ and CD4+ T cells, NK cells, dendritic cells, and increased activated CD8+ tumor infiltrating lymphocytes. In a pre-clinical model of advanced solid tumor resistant to PD1 blockade, mice treated with anti-HER2 CAR-M combined with a PD1 blocking antibody demonstrated improved tumor control, overall survival, and TME activation compared to either treatment alone, indicating synergy and capacity for CAR-M to sensitize solid tumors to checkpoint blockade. Methods: This Phase 1, FIH study is evaluating safety, tolerability, cell manufacturing feasibility, trafficking, TME activation, and preliminary evidence of efficacy of investigational product CT-0508 in 18 pt with locally advanced (unresectable)/metastatic solid tumors overexpressing HER2. Pt previously treated with anti-HER2 therapies are eligible. Filgrastim mobilized autologous CD14+ monocytes are collected by apheresis, followed by manufacturing and cryopreservation. Group 1 pt (n = 9; enrollment complete) received fractionated doses over Days 1, 3, and 5. Group 2 pt (n = 9) receive CT-0508 as a single infusion on D1. Additional cohorts include: CT-0508 co-administered with pembrolizumab and CT-0508 monotherapy administered intraperitoneally in pt with peritoneal predominant disease. Correlative assessments include pre- and post-treatment biopsies and blood samples for safety (immunogenicity), trafficking (qPCR, RNA in situ hybridization), CT-0508 persistence in blood and tumor, target antigen engagement, TME modulation (single cell RNA sequencing), immune response (TCR sequencing) and others. Citation Format: Yara Abdou, E. Claire Dees, Joanne Mortimer, Naoto Ueno, Melissa Johnson, Richard Maziarz, Jennifer Specht, Yuan Yuan, Paula Puhlman, Mathew Angelos, Saar Gill, Amy Ronczka, Thomas Condamine, Daniel J. Cushing, Michael Klichinsky, Debora Barton, Ramona F. Swaby, Kim Reiss Binder. A phase 1, first-in-human (FIH) study of autologous anti-HER2 chimeric antigen receptor macrophage (CAR-M) in participants (pt) with HER2 overexpressing solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT241.

Background Immune homeostasis is regulated by a balance of pro- and anti-inflammatory cytokine signals. Dysregulated cytokine expression can cause deleterious immunosuppression or inflammation, which drives disease pathology. In solid tumors, cytokines such as IL10 and TGFβ induce an immunosuppressive tumor microenvironment (TME) that blunts endogenous and therapeutic anti-tumor immunity. Therapeutic strategies to block immunosuppressive cytokines have primarily focused on monoclonal antibodies targeting cytokines/cytokine receptors. While this approach can reduce immunosuppressive signaling, it fails to provide an inflammatory signal that could initiate anti-tumor immunity. Here, we engineered macrophages with synthetic cytokine switch receptors (SR) to develop a cell therapy platform for modulation of pro-/anti-inflammatory signals. Macrophages are homeostatic regulators capable of both initiating inflammation and infiltrating solid tumors, and we leveraged this natural proficiency using SRs that convert tumor-related immunosuppressive (M2) signals into pro-inflammatory (M1) responses for tumor microenvironment (TME) modulation. We termed this engineered myeloid cell platform 'Engineered Microenvironment Converters' (EM-C) and evaluated its modular ability to target several tumor-associated cytokines. Methods EM-Cs targeting IL10 or TGFβ were generated by expressing SR in primary human macrophages and monocytes. M2-to-M1 SR were designed to convert IL10 or TGF-β into pro-inflammatory signals based on interferon or toll-like receptor (TLR) signaling pathways. The response of EM-Cs to target cytokines was monitored using phenotypic characterization of surface molecules, measurement of cytokine release, mRNA profiling, and biochemical analysis of downstream signaling. Co-culture assays with bystander immunosuppressive cells were used to assess the ability of EM-Cs to alter their microenvironment. Additionally, combinatorial EM-C were designed to target both IL10 and TGFβ for multiplexed TME conversion. Results Pro-inflammatory EM-Cs efficiently sequestered IL10 and TGFβ, two prevalent immunosuppressive cytokines in the TME, and converted them into pro-inflammatory signals by upregulating M1 markers, cytokines, and pathways in a dose-dependent manner. EM-Cs furthermore repolarized bystander M2 macrophages towards a pro-inflammatory phenotype following co-culture. Conclusions We present a novel immunotherapy platform that harnesses macrophages as 'living converters' to locally regulate inflammation in solid tumors. We establish EM-C that convert IL10 or TGFβ into pro-inflammatory signals, showcasing a modular ability to control the inflammatory status of microenvironments without systemic cytokine antagonism. EM-Cs enable the development of target antigen agnostic myeloid cell immunotherapies for solid tumors.

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Background Pathologic response assessment after neoadjuvant treatment is the potential analog to radiographic response for advanced disease, with regard to study design, clinical care, and accelerated regulatory approvals. A standardized system for assessing degree of pathologic response in the primary tumor (PT) and lymph nodes (LNs) as a survival surrogate is an unmet need. It is also a prerequisite for determining whether patients with versus without LN involvement benefit from neoadjuvant therapy. Here, in a pre-specified exploratory analysis from CheckMate 816, we report the first in-depth assessment of the full spectrum of percent residual viable tumor (RVT; beyond pathologic complete response) in both the PT and LNs and its association with event-free survival (EFS). This study represents the first prospective use of such a pan-tumor scoring system in a phase 3 registrational trial. Methods Pathologic response was prospectively assessed in the randomized phase 3 study of neoadjuvant nivolumab plus chemotherapy versus chemotherapy alone in patients with resectable non-small cell lung carcinoma. Percentages of RVT, regression, and necrosis were quantified (0%-100%) in the PT and LNs using pan-tumor immune-related pathologic response criteria (irPRC). Pathologic features scored using this system were tested for association with EFS. An exploratory comparison between pathologic response, radiographic response, and circulating tumor DNA (ctDNA) clearance was performed. Results In both treatment arms and regardless of pathologic evidence of LN involvement, EFS was improved in patients with 0% versus >0% RVT-PT (HR=0.18). RVT-PT predicted EFS for nivolumab plus chemotherapy (AUC=0.74); 2-year EFS rates were 90%, 60%, 57%, and 39% for patients with 0%-5%, >5%-30%, >30%-80%, and >80% RVT, respectively. Each 1% increase in RVT associated with a 0.017 increase in HR for EFS. Combining pathologic response from PT+LNs helped differentiate outcomes. An increase in%necrosis was not observed in paired pre- and on-treatment specimens in either treatment arm. Further, necrosis within the on-treatment specimens was associated with lower EFS rates, arguing against necrosis as a histologic feature of treatment effect. When pathologic response was compared to radiographic response and ctDNA clearance, pathologic response best approximated EFS. Conclusions Percent RVT associates with improved EFS, supporting pathologic response as an emerging survival surrogate. Given the prognostic value of%RVT, its assessment using routine surgical pathology workflows, and a scoring system generalizable to any solid tumor type, it is also anticipated to become a biomarker for guiding subsequent adjuvant therapy. Further assessment of clinically-relevant%RVT cutoffs in PT+LN is warranted. Acknowledgements Funding for this study was provided by Bristol Myers Squibb and Ono Pharmaceutical Company Ltd. Trial Registration NCT02998528 Ethics Approval This study was approved by the Johns Hopkins University Institutional Review Board.

Background Macrophages expressing chimeric antigen receptors (CAR-M) have been shown to reduce tumor burden, remodel the tumor microenvironment (TME), and coordinate a systemic immune response in pre-clinical solid tumor models. Solid tumors overexpress immunosuppressive molecules, such as CD47, which reduces macrophage tumor phagocytosis. We have previously demonstrated that CD47 is a checkpoint that reduces CAR-M function, and have shown that CRISPR-mediated SIRPα knockout (KO) CAR-M are refractory to the anti-phagocytic checkpoint protein CD47.1 Here, we have enhanced our ability to control gene expression in CAR-M by creating a single vector system that incorporates synthetic shRNA into the CAR intron, enabling simultaneous CAR expression with knockdown of SIRPα. The intronic shRNA platform allows gene-silenced CAR-M and CAR-Monocytes to be manufactured using a single vector in a streamlined single-day process. Methods To generate gene-silenced CAR-M, we transduced primary human macrophages or monocytes with a novel adenoviral vector comprising a CAR transgene with custom intronic shRNA expressed under a shared promoter. We characterized shRNA-modified CAR-M using a model anti- human epidermal growth factor receptor 2 (HER2) CAR paired with shRNA targeting SIRPα. CAR-M phenotype was characterized using flow cytometry. The anti-tumor efficacy of CAR-M in vitro was monitored by quantifying killing, phagocytosis, and cytokine production in co-culture assays with HER2+ tumor cell lines. The in vivo efficacy of CAR-M was characterized using metastatic solid tumor xenograft models. Results Intronic shRNA enabled concomitant CAR expression with target SIRPα knockdown. Reduction in SIRPα expression by shRNA was comparable to that achieved by CRISPR/Cas9 ribonucleoprotein. Additionally, the inclusion of an intron significantly augmented expression of the neighboring CAR transgene. Compared to unmodified CAR-M, SIRPα-knockdown CAR-M exhibited enhanced killing, phagocytosis, and cytokine production against HER2+ tumor cells in vitro. Furthermore, SIRPα-knockdown CAR-M significantly delayed tumor growth and prolonged survival in vivo. Conclusions We show the feasibility of generating gene-silenced primary CAR-M in a single transduction step by integrating CAR delivery with custom intronic shRNA, and we demonstrate that targeted gene knockdown of SIRPα can enhance the anti-tumor activity of CAR-M in vivo. The intronic shRNA design is a generalizable platform that will be valuable for future CAR designs, target tumor antigens, and gene knockout targets. Reference Sloas C, Gabbasov R, Anderson N, Abramson S, Klichinsky M, Ohtani Y. 144 SIRPα deficient CAR-Macrophages exhibit enhanced anti-tumor function and bypass the CD47 immune checkpoint. J Immunother Cancer. 2021;9:A152-A152.