Conventional Chimeric Antigen Receptor Research Articles

Scrutiny of chimeric antigen receptor activation by the extracellular domain: experience with single domain antibodies targeting multiple myeloma cells highlights the need for case-by-case optimization.

Multiple myeloma (MM) remains incurable, despite the advent of chimeric antigen receptor (CAR)-T cell therapy. This unfulfilled potential can be attributed to two untackled issues: the lack of suitable CAR targets and formats. In relation to the former, the target should be highly expressed and reluctant to shedding; two characteristics that are attributed to the CS1-antigen. Furthermore, conventional CARs rely on scFvs for antigen recognition, yet this withholds disadvantages, mainly caused by the intrinsic instability of this format. VHHs have been proposed as valid scFv alternatives. We therefore intended to develop VHH-based CAR-T cells, targeting CS1, and to identify VHHs that induce optimal CAR-T cell activation together with the VHH parameters required to achieve this. CS1-specific VHHs were generated, identified and fully characterized, in vitro and in vivo. Next, they were incorporated into second-generation CARs that only differ in their antigen-binding moiety. Reporter T-cell lines were lentivirally transduced with the different VHH-CARs and CAR-T cell activation kinetics were evaluated side-by-side. Affinity, cell-binding capacity, epitope location, in vivo behavior, binding distance, and orientation of the CAR-T:MM cell interaction pair were investigated as predictive parameters for CAR-T cell activation. Our data show that the VHHs affinity for its target antigen is relatively predictive for its in vivo tumor-tracing capacity, as tumor uptake generally decreased with decreasing affinity in an in vivo model of MM. This does not hold true for their CAR-T cell activation potential, as some intermediate affinity-binding VHHs proved surprisingly potent, while some higher affinity VHHs failed to induce equal levels of T-cell activation. This could not be attributed to cell-binding capacity, in vivo VHH behavior, epitope location, cell-to-cell distance or binding orientation. Hence, none of the investigated parameters proved to have significant predictive value for the extent of CAR-T cell activation. We gained insight into the predictive parameters of VHHs in the CAR-context using a VHH library against CS1, a highly relevant MM antigen. As none of the studied VHH parameters had predictive value, defining VHHs for optimal CAR-T cell activation remains bound to serendipity. These findings highlight the importance of screening multiple candidates.

Implantable CAR T cell factories enhance solid tumor treatment

Chimeric Antigen Receptor (CAR) T cell therapy has produced revolutionary success in hematological cancers such as leukemia and lymphoma. Nonetheless, its translation to solid tumors faces challenges due to manufacturing complexities, short-lived in vivo persistence, and transient therapeutic impact. We introduce 'Drydux' - an innovative macroporous biomaterial scaffold designed for rapid, efficient in-situ generation of tumor-specific CAR T cells. Drydux expedites CAR T cell preparation with a mere three-day turnaround from patient blood collection, presenting a cost-effective, streamlined alternative to conventional methodologies. Notably, Drydux-enabled CAR T cells provide prolonged in vivo release, functionality, and enhanced persistence exceeding 150 days, with cells transitioning to memory phenotypes. Unlike conventional CAR T cell therapy, which offered only temporary tumor control, equivalent Drydux cell doses induced lasting tumor remission in various animal tumor models, including systemic lymphoma, peritoneal ovarian cancer, metastatic lung cancer, and orthotopic pancreatic cancer. Drydux's approach holds promise in revolutionizing solid tumor CAR T cell therapy by delivering durable, rapid, and cost-effective treatments and broadening patient accessibility to this groundbreaking therapy.

Controlling CAR-T cell activity and specificity with synthetic SparX adapters

While conventional chimeric antigen-receptor (CAR)-T therapies have shown remarkable clinical activity in some settings, they can induce severe toxicities and are rarely curative. To address these challenges, we developed a controllable cell therapy where synthetic D-domain-containing proteins (soluble protein antigen-receptor X-linker [SparX]) bind one or more tumor antigens and mark those cells for elimination by genetically modified Tcells (antigen-receptor complex [ARC]-T). The chimeric antigen receptor was engineered with a D-domain that specifically binds to the SparX protein via a unique TAG, derived from human alpha-fetoprotein. The interaction is mediated through an epitope on the TAG that is occluded in the native alpha-fetoprotein molecule. Invitro and invivo data demonstrate that the activation and cytolytic activity of ARC-T cells is dependent on the dose of SparX protein and only occurs when ARC-T cells are engaged with SparX proteins bound to antigen-positive cells. ARC-T cell specificity was also redirected invivo by changing SparX proteins that recognized different tumor antigens to combat inherent or acquired tumor heterogeneity. The ARC-SparX platform is designed to expand patient and physician access to cell therapy by controlling potential toxicities through SparX dosing regimens and enhancing tumor elimination through sequential or simultaneous administration of SparX proteins engineered to bind different tumor antigens.

Abstract 5231: NK and T cells armed with EVE16, a novel synthetic immune receptor, mediate robust anti-tumor responses through dual direct cytotoxicity and ADCC with minimal trogocytosis and exhaustion

Abstract Despite the major advances, cancer patients treated with targeted chimeric antigen receptor (CAR)- based T and NK cell therapies often face the challenge of frequent disease relapse, and their efficacy in solid tumors is low. This is attributed to the inherent potency of the starting cell material, unique characteristics of CAR engineering resulting in trogocytosis and tonic signaling, and the notable absence of homogenously expressed surface markers, particularly in solid tumors. To address these limitations, we engineered a novel synthetic immune receptor termed Enhanced-Valency Engineered CD16A (EVE16) and evaluated it in memory-like NK cells and T cells against liquid and solid tumors. We hypothesized that post-activation cleavage of CD16A by ADAM17 plays a crucial role in reducing trogocytosis and tonic signaling. EVE16 utilizes the inherent potential of CD16A to trigger an activation signaling cascade through the endogenous CD3ζ adaptor signaling protein. Unexpectedly, we discovered that, aside from the CD16A transmembrane domain, the Fc-binding domain is essential for proper surface expression. After multiple rounds of optimization, we developed a receptor that surpassed the activation potency of endogenous CD16A and allowed both direct binding to the tumor targets and retained antibody-dependent cellular cytotoxicity (ADCC), and this dual 'CAR-like' and ADCC function opens the potential for combination with clinically approved antibodies to prevent immune escape. Furthermore, in contrast to the conventional CAR(BBζ), the optimized EVE16 receptor exhibited minimal tonic signaling in both T and NK cells. This translated to enhanced sensitivity towards low antigen-density targets, as demonstrated by a cytotoxicity assay performed on polyclonal cancer cells engineered with target antigen knock-down. Additionally, EVE16, but not CAR transduced, protected T and NK cells from trogocytosis and allowed for the efficient disengagement of cytotoxic lymphocytes from cancer targets due to CD16A cleavage by ADAM17 upon immune cell activation. In in vivo mouse xenograft models, CD19-targeted EVE16 memory-like NK cells, rapidly manufactured using our approach, demonstrate outstanding performance in terms of robust expansion, prolonged persistence, and effective leukemic clearance, underscoring the effectiveness of our method. In summary, we here describe a novel synthetic immune receptor called EVE16 which enables both direct (CAR-like) and ADCC functionality while preventing trogocytosis and exhaustion. Clinical trials are being planned for the near future. Citation Format: Alaa Ali, James D. Ham, Faten Zairi, Vaishvi Patel, Mubin Tarannum, Khanhlinh Dinh, Yasmin Abdulhamid, Juliana Vergara, Robert Soiffer, Jerome Ritz, John Beadle, Nikola A. Ivica, Jianzhu Chen, Rizwan Romee. NK and T cells armed with EVE16, a novel synthetic immune receptor, mediate robust anti-tumor responses through dual direct cytotoxicity and ADCC with minimal trogocytosis and exhaustion [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 5231.

Abstract 6319: Characterization of AB-1015 logic-gated CAR induction (ON kinetics), receptor turnover (OFF kinetics), and logic gate sensitivity to ALPG/P and MSLN

Abstract CAR T cell activity in solid tumors is limited, in part, by off-tumor toxicity. To address this obstacle, AB-1015 contains an “AND” logic gate, consisting of a priming receptor (PrimeR) and an inducible chimeric antigen receptor (CAR) that is upregulated by PrimeR activation. The AB-1015 logic gate targets ALPG/P and MSLN, which are coexpressed in ovarian tumors but not normal tissues. AB-1015 CAR induction within the tumor is expected to be a dynamic process influenced by multiple factors, including antigen density, target cell abundance, as well as tumor microenvironmental factors. To characterize CAR induction and receptor turnover, we developed an in vitro assay with plate-bound ALPG to induce CAR. CAR induction occurred quickly in response to ALPG priming, with most ICT cells expressing CAR within 24 hrs, and plateaued by 72 hrs. Once removed from ALPG, CAR expression returned to baseline within 96 hrs. Similar to conventional CAR T cells, the presence of the cytolytic target antigen (MSLN) was expected to increase the rate of CAR turnover on AB-1015. To assess this, we measured the CAR functional half-life of AB-1015 cells once removed from ALPG priming. The cytotoxic activity of AB-1015 cells rapidly decreased in the absence of ALPG, reaching baseline within 24 hrs. Of note, our in vitro assay did not result in 100% CAR induction from all PrimeR+ AB-1015 cells. To understand whether this reflected biology versus a limitation of our in vitro assay, we conducted a CAR induction, sorted the CAR- cells, then performed a second induction. ICT cells that did not express CAR after the first induction were shown to be able to induce CAR during the second induction assay, thereby demonstrating that all PrimeR+ ICT cells have the potential to induce CAR. To assess the sensitivity of AB-1015 for low density ALPG/P and MSLN, isogenic cell lines were engineered to express each antigen at variable levels. In co-culture, AB-1015 was able to prime and kill targets expressing ALPG and MSLN at or below the limit of detection using immunohistochemistry. In light of these observations, the specificity of AB-1015 was verified using a dual flank in vivo model where one tumor expressed both ALPG and MSLN, and the contralateral tumor expressed MSLN alone. While robust anti-tumor activity was observed against the ALPG+/MSLN+ tumor, no activity was detected against the MSLN+ tumor. In summary, AB-1015 CAR induction and receptor turnover kinetics is a dynamic process. A reductionist in vitro model system was developed, enabling analysis of CAR induction and receptor turnover. Importantly, we demonstrated that all PrimeR+ ICT cells have the potential to induce CAR. Finally, the in vivo specificity of AB-1015 for ALPG+/MSLN+ tumors was established using a dual flank specificity model. Together, these data support the continued development of AB-1015 in a phase I clinical trial (NCT05617755). Citation Format: Xinyan Tang, Marvin Chew, Rakesh Sudhakar, Hongruo Yun, Doreen Sakamoto, Vibhavari Sail, Amanda Fearon, Jasper Williams, Jun Feng, Stephen Santoro. Characterization of AB-1015 logic-gated CAR induction (ON kinetics), receptor turnover (OFF kinetics), and logic gate sensitivity to ALPG/P and MSLN [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 6319.

Early induction of cytokine release syndrome by rapidly generated CAR T cells in preclinical models

Cytokine release syndrome (CRS) is a significant side-effect of conventional chimeric antigen receptor (CAR) T-cell therapy. To facilitate patient accessibility, short-term (st) CAR T cells, which are administered to patients only 24 h after vector exposure, are in focus of current investigations. Their impact on the incidence and severity of CRS has been poorly explored. Here, we evaluated CD19-specific stCAR T cells in preclinical models. In co-culture with tumor cells and monocytes, stCAR T cells exhibited anti-tumoral activity and potent release of CRS-related cytokines (IL-6, IFN-γ, TNF-α, GM-CSF, IL-2, IL-10). When administered to NSG-SGM3 mice, stCAR T cells, but not conventional CAR T cells, induced severe acute adverse events within 24 h, including hypothermia and weight loss, as well as high body scores, independent of the presence of tumor target cells. Human (IFN-γ, TNF-α, IL-2, IL-10) and murine (MCP-1, IL-6, G-CSF) cytokines, typical for severe CRS, were systemically elevated. Our data highlight potential safety risks of rapidly manufactured CAR T cells and suggest NSG-SGM3 mice as sensitive model for their preclinical safety evaluation.

The SpyCatcher-SpyTag interaction mediates tunable anti-tumor cytotoxicity of NK cells

Chimeric antigen receptor (CAR)-modified T and NK cell immunotherapy is a promising approach for cancer treatment. Due to the lack of tunability in anti-tumor activity, conventional CAR therapies have limited efficacy at low tumor antigen densities. To tune the CAR response to tumor cell surface antigens, we have developed a split CAR using the SpyCatcher-SpyTag system. The SpyCatcher serves as the ectodomain to constitute a SpyCatcher-CAR (SpyCAR), while SpyTag is attached to the antibodies that recognize tumor antigens. With dimerization mediated by SpyCatcher and SpyTag, the number and activation level of SpyCARs recruited by tumor antigens depends on the SpyTag number in the “antibody-SpyTag” fusion protein. The results demonstrated that the increasing number of SpyTags effectively enhanced the cytotoxicity of SpyCAR-NK92 cells against target cells. The development of SpyCAR with tunable cytotoxicity provides a novel strategy for CAR-based tumor immunotherapies.

Abstract C028: A phase 1/2 study investigating the safety and efficacy of autologous TAC T cells in subjects with unresectable, locally advanced or metastatic claudin 18.2+ solid tumors

Abstract CLDN18.2 is a tight junction protein found in differentiated gastric epithelial cells which can become abnormally expressed in a number of solid malignancies. This exposure profile illustrates the potential of CLDN18.2 as a candidate for targeted therapy. To date, there are no approved therapeutic agents directed against this target but promising data exist using monoclonal antibodies and conventional chimeric antigen receptor (CAR) T therapy. The T cell antigen coupler (TAC) technology is an approach to modifying T cells ex vivo, which allows recognition and cytotoxicity of tumor cells by co-opting the natural T cell receptor.  TAC T cells demonstrate a safer profile than CAR T treatments. TAC01-CLDN18.2 is an autologous T-cell product comprising T cells expressing CLDN18.2 TAC. This is a first-in-human study (NCT05862324) to investigate the safety and preliminary anti-tumor activity of TAC01-CLDN18.2 in CLDN18.2+/HER2- solid tumors. Subjects will undergo leukapheresis and may receive bridging anticancer therapy as appropriate during cell manufacturing. Prior to TAC01-CLDN18.2 infusion, subjects will undergo low-intensity lymphodepletion chemotherapy. In phase I dose escalation, TAC01-CLDN18.2 will be administered at increasing doses (Cohorts 1-3) in adult subjects after ≥2 lines of therapy using the classic 3+3 dose escalation study design. Subjects with pancreatic ductal adenocarcinoma (PDAC) may have been treated with 1 line of prior therapy. CLDN18.2 expression levels will be determined centrally using a clinical trial assay validated across relevant indications. Dose limiting toxicities will be assessed up to 28 days from TAC01-CLDN18.2 infusion. A second dose may be administered, according to preidentified clinical and safety criteria. In Phase II, dose expansion groups will further evaluate the efficacy, safety, and pharmacokinetics of the optimal TAC01-CLDN18.2 dose, with the option of redosing. Indications will include gastric and esophageal adenocarcinoma (group A), PDAC (group B) and ovarian and non-small cell lung cancer (group C) in subjects after ≥2 and <4 lines of prior therapy (subjects with PDAC may have been exposed to 1 therapy). Definitions of eligible CLDN18.2 expression levels will be based on retrospective analysis of data from Phase 1 in association with clinical efficacy. A Simon 2-stage design will be used to enroll ≤57 subjects in Group A and ≤22 subjects in Group C. Group B will be exploratory and will enroll ≤10 subjects with an opportunity of cohort enrichment based on clinical efficacy data. Citation Format: Benjamin Schlechter, Ecaterina Dumbrava, Samuel Saibil, Martin Gutierez, Syma Iqbal, Davendra Sohal, Maria Apostolopoulou, Kara Moss, Deyaa Adib, Daniel Olson. A phase 1/2 study investigating the safety and efficacy of autologous TAC T cells in subjects with unresectable, locally advanced or metastatic claudin 18.2+ solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C028.

T lymphocytes expressing the switchable chimeric Fc receptor CD64 exhibit augmented persistence and antitumor activity

Chimeric antigen receptor (CAR) Tcell therapy lacks persistent efficacy with "on-target, off-tumor" toxicities for treating solid tumors. Thus, an antibody-guided switchable CAR vector, the chimeric Fc receptor CD64 (CFR64), composed of a CD64 extracellular domain, is designed. Tcells expressing CFR64 exert more robust cytotoxicity against cancer cells than CFR Tcells with high-affinity CD16 variant (CD16v) or CD32A as their extracellular domains. CFR64 Tcells also exhibit better long-term cytotoxicity and resistance to Tcell exhaustion compared with conventional CAR Tcells. With trastuzumab, the immunological synapse (IS) established by CFR64 is more stable with lower intensity induction of downstream signaling than anti-HER2 CAR Tcells. Moreover, CFR64 Tcells exhibit fused mitochondria in response to stimulation, while CARH2 Tcells contain predominantly punctate mitochondria. These results show that CFR64 Tcells may serve as a controllable engineered Tcell therapy with prolonged persistence and long-term antitumor activity.

IRF4 downregulation improves sensitivity and endurance of CAR T cell functional capacities.

Chimeric antigen receptor (CAR) modified T cells can induce complete remissions in patients with advanced hematological malignancies. Nevertheless, the efficacy is mostly transient and remains so far poor in the treatment of solid tumors. Crucial barriers to long-term CAR T cell success encompass loss of functional capacities known as "exhaustion", among others. To extend CAR T cell functionality, we reduced interferon regulatory factor 4 (IRF4) levels in CAR T cells using a one-vector system encoding a specific short-hairpin (sh) RNA along with constitutive CAR expression. At baseline, CAR T cells with downregulated IRF4 showed equal cytotoxicity and cytokine release compared to conventional CAR T cells. However, under conditions of repetitive antigen encounter, IRF4low CAR T cells displayed enhanced functionality with superior cancer cell control in the long-term compared with conventional CAR T cells. Mechanistically, the downregulation of IRF4 in CAR T cells resulted in prolonged functional capacities and upregulation of CD27. Moreover, IRF4low CAR T cells were more sensitive to cancer cells with low levels of target antigen. Overall, IRF4 downregulation capacitates CAR T cells to recognize and respond to target cells with improved sensitivity and endurance.

Abstract LB095: Hybrid TCR-CAR design surpasses conventional CARs and patient-derived TCRs in targeting an ultra-low-density neoantigen

Abstract Mutation-associated neoantigens (MANAs) are exquisitely cancer-specific therapeutic targets. However, MANAs are present at ultra-low densities on the cancer cell surface (as few as 1-2 copies per cell), leading to the challenge of eliciting a sufficiently robust therapeutic effect. We combined components of both T cell receptors (TCRs) and chimeric antigen receptors (CARs) to create a new receptor with improved potency against an ultra-low-density MANA. From CARs, we utilized the antibody-based antigen recognition domain (i.e. the single chain variable fragment, scFv) and the integrated co-stimulation that amplifies T cell activation. From TCRs, we utilized the multi-chain signaling platform that facilitates high antigen sensitivity. This new receptor, termed a TCR Embedded ScFv for Long-term Activation (TESLA), showed promising characteristics when tested with the H2-scFv which targets the p53 R175H mutation presented on HLA-A*02:01 (R175H/A2). Using CRISPR-based homology directed repair in primary human T cells, we tested 15 configurations of appending the H2-scFv to subunits of the TCR complex to identify a design that maximized T cell cytotoxicity and interferon gamma release in co-cultures with cancer cells expressing endogenous levels of the R175H/A2 antigen. In this system, we showed that the optimal TCR-embedded configuration of the H2-scFv produced similar levels of cytotoxicity and interferon gamma secretion as patient-derived TCRs targeting the same R175H/A2 MANA, while conventional H2-CARs were unable to produce any T-cell activation. We then used a multiple stimulation co-culture system to identify a co-stimulation domain combination (MyD88 and CD40) that improved serial cytotoxicity and proliferation of H2-TESLAs when incorporated on the intracellular side of the TCRbeta chain. Finally, we compared the H2-TESLA receptor to patient-derived TCRs modified with the same MyD88 and CD40 co-stimulation domains. In vivo, H2-TESLAs cured all mice in a tumor model, while co-stimulation-modified TCRs produced only temporary tumor control. Moreover, in vivo, H2-TESLAs elicited 100-fold greater T cell expansion than co-stimulation-modified TCRs. In conclusion, we demonstrated that by combining aspects of both CARs and TCRs, the TESLA receptor improved T cell reactivity against an ultra-low-density neoantigen compared to conventional CARs and patient-derived TCRs. Citation Format: Brian J. Mog, Sarah R. DiNapoli, Michael S. Hwang, Tushar D. Nichakawade, Jacqueline Douglass, Emily Han-Chung Hsiue, Katharine M. Wright, Alexander H. Pearlman, Maximilian F. Konig, Suman Paul, Nicolas Wyhs, Nikita Marcou, Stephanie Glavaris, Jiaxin Ge, Michelle S. Miller, P. Aitana Azurmendi, Evangeline Watson, Drew M. Pardoll, Sandra B. Gabelli, Chetan Bettegowda, Nickolas Papadopoulos, Kenneth W. Kinzler, Bert Vogelstein, Shibin Zhou. Hybrid TCR-CAR design surpasses conventional CARs and patient-derived TCRs in targeting an ultra-low-density neoantigen [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 LB095.

IL7 and IL7 Flt3L co-expressing CAR T cells improve therapeutic efficacy in mouse EGFRvIII heterogeneous glioblastoma.

Chimeric antigen receptor (CAR) T cell therapy in glioblastoma faces many challenges including insufficient CAR T cell abundance and antigen-negative tumor cells evading targeting. Unfortunately, preclinical studies evaluating CAR T cells in glioblastoma focus on tumor models that express a single antigen, use immunocompromised animals, and/or pre-treat with lymphodepleting agents. While lymphodepletion enhances CAR T cell efficacy, it diminishes the endogenous immune system that has the potential for tumor eradication. Here, we engineered CAR T cells to express IL7 and/or Flt3L in 50% EGFRvIII-positive and -negative orthotopic tumors pre-conditioned with non-lymphodepleting irradiation. IL7 and IL7 Flt3L CAR T cells increased intratumoral CAR T cell abundance seven days after treatment. IL7 co-expression with Flt3L modestly increased conventional dendritic cells as well as the CD103+XCR1+ population known to have migratory and antigen cross-presenting capabilities. Treatment with IL7 or IL7 Flt3L CAR T cells improved overall survival to 67% and 50%, respectively, compared to 9% survival with conventional or Flt3L CAR T cells. We concluded that CAR T cells modified to express IL7 enhanced CAR T cell abundance and improved overall survival in EGFRvIII heterogeneous tumors pre-conditioned with non-lymphodepleting irradiation. Potentially IL7 or IL7 Flt3L CAR T cells can provide new opportunities to combine CAR T cells with other immunotherapies for the treatment of glioblastoma.

Interleukin-15 and chemokine ligand 19 enhance cytotoxic effects of chimeric antigen receptor T cells using zebrafish xenograft model of gastric cancer.

Chimeric antigen receptor (CAR) T cells have been proven effective for the treatment of B-cell-mediated malignancies. Currently, the development of efficient tools that supply CAR T cells for the treatment of other malignancies would have great impact. In this study, interleukin (IL)-15 and C-C motif chemokine ligand 19 (CCL19) were introduced into natural killer group 2D (NKG2D)-based CARs to generate 15×19 CAR T cells, which remarkably increased T-cell expansion and promoted the production of central memory T (Tcm) cells. 15×19 CAR T cells showed greater cytotoxicity to gastric cell lines than conventional CAR T cells and produced higher levels of IL-15 and CCL-19, which resulted in increased responder T cell chemotaxis and reduced expression of T cell exhaustion markers. A live zebrafish model was used for single-cell visualization of local cytotoxicity and metastatic cancers. Administration of 15×19 CAR T cells resulted in significant shrinking of gastric cancer xenograft tumors and expansion of 15×19 CAR T cells in zebrafish models. Taken together, these findings demonstrate that 15×19 CAR T cells are highly efficient in killing gastric cancer cells, are effective to avoid off-target effects, and migrate to local and metastatic sites for long-term surveillance of cancers.

Glyco-binding domain chimeric antigen receptors as a new option for cancer immunotherapy

In the last decade, treatment using Chimeric Antigen Receptor (CAR) are largely studied and demonstrate the potential of immunotherapeutic strategies, as seen mainly for blood related cancers. Still, efficient CAR-T cell approaches especially for the treatment of solid tumors are needed. Tn- and Sialyl-Tn antigens are tumor associated carbohydrate antigens correlating with poor prognosis and tumor metastasis on a variety of tumor entities. These glycans can be recognized by CD301 (CLEC10A, MGL), which is a surface receptor found primarily on immune cells. In the present study, we hypothesized, that it is possible to use newly generated CD301-bearing CARs, enabling cytotoxic effector cells to recognize and eliminate breast cancer cells. Thus, we genetically modified human NK92 cells with different chimeric receptors based on the carbohydrate recognition domain (CRD) of human CD301. We assessed their cytotoxic activity in vitro demonstrating the specific recognition of CD301 ligand positive cell lines. These results were confirmed by degranulation assays and in cytokine release assays. Overall, this study demonstrates CD301-CARs represent a cost-effective and fast alternative to conventional scFv CARs for cancer immunotherapy.

Hyperstabilization of T cell microvilli contacts by chimeric antigen receptors.

T cells typically recognize their ligands using a defined cell biology-the scanning of their membrane microvilli (MV) to palpate their environment-while that same membrane scaffolds T cell receptors (TCRs) that can signal upon ligand binding. Chimeric antigen receptors (CARs) present both a therapeutic promise and a tractable means to study the interplay between receptor affinity, MV dynamics and T cell function. CARs are often built using single-chain variable fragments (scFvs) with far greater affinity than that of natural TCRs. We used high-resolution lattice lightsheet (LLS) and total internal reflection fluorescence (TIRF) imaging to visualize MV scanning in the context of variations in CAR design. This demonstrated that conventional CARs hyper-stabilized microvillar contacts relative to TCRs. Reducing receptor affinity, antigen density, and/or multiplicity of receptor binding sites normalized microvillar dynamics and synapse resolution, and effector functions improved with reduced affinity and/or antigen density, highlighting the importance of understanding the underlying cell biology when designing receptors for optimal antigen engagement.

45P The RevCAR T cell platform: A switchable and combinatorial therapeutic strategy for glioblastoma

Glioblastoma (GBM) is a very aggressive brain tumor, associated with poor prognosis and survival. So far, the efficiency of available therapies is limited. After proving their effectiveness in targeting hematological malignancies, chimeric antigen receptor (CAR) T cells might provide a promising therapeutic approach for GBM. Here, we present our switchable Reverse CAR technology (RevCAR). Unlike conventional CAR T cells, RevCAR T cells contain an epitope in their extracellular receptor domain, and can only be activated via bispecific target modules (RevTM) which recognize the RevCAR T cells on one side and tumor cells on the other side.

CAR Triggered Release of Type-1 Interferon Limits CAR T-Cell Activities by an Artificial Negative Autocrine Loop

The advent of chimeric antigen receptor (CAR) T cells expedited the field of cancer immunotherapy enabling durable remissions in patients with refractory hematological malignancies. T cells redirected for universal cytokine-mediated killing (TRUCKs), commonly referred to as "fourth generation" CAR T-cells, are designed to release engineered payloads upon CAR-induced T-cell activation. Building on the TRUCK technology, we aimed to generate CAR T-cells with a CAR-inducible artificial, self-limiting autocrine loop. To this end, we engineered CAR T-cells with CAR triggered secretion of type-1 interferons (IFNs). At baseline, IFNα and IFNβ CAR T-cells showed similar capacities in cytotoxicity and cytokine secretion compared to conventional CAR T-cells. However, under "stress" conditions of repetitive rounds of antigen stimulation using BxPC-3 pancreas carcinoma cells as targets, anti-tumor activity faded in later rounds while being fully active in destructing carcinoma cells during first rounds of stimulation. Mechanistically, the decline in activity was primarily based on type-1 IFN augmented CAR T-cell apoptosis, which was far less the case for CAR T-cells without IFN release. Such autocrine self-limiting loops can be used for applications where transient CAR T-cell activity and persistence upon target recognition is desired to avoid lasting toxicities.

LigandCD70.CAR As a Platform for Dual-Targeting CAR T Cells for Acute Myeloid Leukemia

Chimeric antigen receptor (CAR) T cells have demonstrated remarkable potency in acute lymphoblastic leukemia (ALL), but similar success has yet to be seen in acute myeloid leukemia (AML). Due to the variable expression of targetable antigens on AML blasts and leukemic stem cells, treatment with single-antigen targeting immunotherapy may select for antigen-negative clones that ultimately cause disease progression or relapse. An appropriate combination of two different CAR-binders and co-stimulatory domains could both increase tumor control and reduce antigen escape. We utilized a binder derived from human CD27 protein, the only known ligand of CD70, to generate the LigandCD70.CAR, which demonstrated superior in vivo activity against AML compared to conventional antibody-derived CARs (Sauer et al 2021). As the LigandCD70.CAR consists of a full length CD27 fused with CD3-zeta, this design takes advantage of the physiologic receptor-ligand interaction of CD70/CD27 to bind with high affinity to CD70+ cells and provides CD27-mediated costimulation to the T cells. These characteristics combined with the high expression of CD70 on more than 80% of AML make the LigandCD70.CAR a promising candidate for combination with other CARs to target AML. We evaluated the LigandCD70.CAR in combination with a CLL-1.CAR and a CD123.CAR, as both have shown preclinical efficacy and are currently being tested in clinical trials. We co-transduced activated T cells with LigandD70.CAR and CLL-1 CAR to generate LigandCD70/CLL-1 bispecific CAR (CLL-1.BiCAR) T cells. CLL-1.BiCAR T cells had comparable in vitro expansion to single-CAR expressing T cells but with enhanced cytotoxicity against CLL-1+ AML cell lines compared to single CLL-1.CARs, even if CD70 expression on tumor cells was low. In xenograft AML models of CD70-low CLL-1-high tumors (HL60), CLL-1.BiCAR T cells enhanced tumor control, survival and T cell persistence compared to single CLL-1.CAR T Cells (Figure 1). In order to determine whether the LigandC70.CAR can enhance other CARs, we co-transduced ligandCD70.CAR with CD123.CAR (Riberdy et al 2020) to generate a Ligand.CD70/CD123 bispecific CAR (CD123.BiCAR). The in vitro expansion and cytotoxicity was comparable to single-CAR expressing T cells. Treatment with CD123.BiCAR T cells significantly improved in vivo survival and tumor control in a xenograft model of AML with CD70-low/CD123-high target cells. In summary, LigandCD70.CAR co-expressed with either CLL-1.CAR or CD123.CAR demonstrate enhanced anti-tumor efficacy compared to single-targeting CLL-1.CAR and CD123.CAR, even in CD70-low tumors. The simultaneous targeting of two AML antigens may thus mitigate the risk of antigen-negative relapse. These data indicate that the Ligand70.CAR combined with other AML targeting CARs could be an effective therapeutic option for AML. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Highly Parallel Discovery of Synthetic Knockin Sequences for Enhanced Cancer Immunotherapies

Introduction T cells engineered to express transgenic T cell receptors (TCRs) or chimeric antigen receptors (CARs) have emerged as powerful treatment options for some malignancies. However, while CAR T cells have induced impressive initial response rates in patients with B-precursor acute lymphoblastic leukemia (ALL) and lymphoma, they fail to mediate long-term relapse-free survival in 40-60% of patients and have not been successful in most solid tumors. For both TCR- and CAR-based approaches, T cell persistence and long-term functionality can be diminished by chronic antigen stimulation or tonic signaling. One approach to enhance the efficacy of cell therapies that has been explored by several groups is the overexpression of specific transcription factors (e.g. AP-1/ATF transcription factors such as c-JUN or BATF); however, more systematic gain-of-function screens in human CAR T cells have not yet been done. Methods and Results Here, we introduce CRISPR-based modular pooled knockin (ModPoKI) screens to evaluate hundreds to thousands of different constructs in human T cells and their potential to overcome TCR or CAR T cell dysfunction. We generated two barcoded ModPoKI libraries of 100 transcription factors (TFs) and 129 natural and synthetic surface receptors (SRs) to identify those that confer a fitness advantage to TCR or CAR T cells. The libraries were combined with either an NY-ESO-1-specific TCR, an anti-CD19 CAR or a high affinity anti-GD2 CAR that is known to induce tonic signaling-based dysfunction. The libraries and the TCR/CAR were engineered as polycistronic sequences that were non-virally integrated into the TRAC (T cell receptor alpha chain constant) locus of primary human T cells. We performed >20 unique ModPoKI screens including bead-based single stimulation, repetitive stimulation with target cells and tonic stimulation (GD2 CAR model). While constructs containing known AP-1/ATF transcription factors BATF and BATF3 showed increased abundance across multiple screens, transcription factor AP4 (TFAP4) knockin (KI) constructs were more clearly enriched after repetitive stimulation and tonic signaling, suggesting potentially undescribed benefits in exhaustion-prone environments. We next validated single knockins of TFAP4 or a control construct (truncated nerve growth factor receptor, tNGFR) in combination with the GD2 or the CD19 CAR. TFAP4 KI led to increased levels of cytokine release, proliferation and target cell killing compared to conventional CAR T cells. Moreover, TFAP4 KI mediated increased tumor control and survival in an in vivo model. Interestingly, we observed elevated levels of CD25 (IL2RA) expression on TFAP4 KI T cells and enrichment of genes related to IL2/STAT5 pathways which could hint at a potential benefit in situations of IL-2 competition/presence of regulatory T cells. Lastly, we aimed to discover specific combinations of TFs that work in concert to enhance T cell fitness in the setting of tonic CAR signaling. We created a ~10,000-member library (102 x 102 - pairwise combinations of 100 transcription factors plus two controls) cloned into constructs with the GD2 CAR and performed a tonic signaling ModPoKI screen. Analysis of the constructs that increased the most in relative abundance highlighted that several of the top performing constructs included either TFAP4, BATF, BATF3 or a combination of TFAP4 and BATF(3), suggesting that TFAP4 and BATF(3) are key transcription factors that can coordinately drive increased T cell fitness upon repetitive stimulation. Validation analyses confirmed that the combinatorial KI of a BATF-TFAP4 construct confers highest cytotoxic capacity in vitro and in vivo compared to single knockin (BATF-RFP or RFP-TFAP4) or control knockin (RFP-tNGFR) GD2 CAR constructs. Conclusions In conclusion, ModPoKI screens allow for customizable parallel evaluation and functional characterization of hundreds to thousands of different T cell constructs. Using clinically relevant screening modalities, we nominated candidate genes that can synthetically re-write the T cell response to repetitive antigen exposure or tonic signaling and thus have the potential to program more effective TCR or CAR T cell therapies for cancer. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Safety and Feasibility of Anti-CD19 CAR-T Expressing IL-7 and CCL19 in Patients with Relapsed or Refractory Large B-Cell Lymphoma

Chimeric antigen receptor (CAR) T cell therapy provides a potential curative option for patients with relapsed or refractory large B-cell lymphoma (R/R LBCL). However, there are major limitations of this therapy which result in treatment resistance in B-cell malignancies, including inadequate CAR-T persistence, poor trafficking and tumor infiltration, the immunosuppressive microenvironment and frequent tumor antigen escape. Recently, several armored CAR T-cells are being developed for potential improved efficacy relative to conventional CAR T cells. Here, we engineered a CD19-spectific CAR-T cell capable of constitutive secretion of interleukin (IL)-7 and chemokine (C-C motif) ligand (CCL)-19 (7 × 19 CAR-T) and performed a multicenter phase 1b clinical trial of 7 × 19 CAR-T cell therapy in patients with R/R LBCL (NCT03929107 and NCT04833504). The 7 × 19 CAR-T cells showed that a favorable safety profile, with grade 3 cytokine release syndrome occurred in 5 (12.8%) patients and grade 3 or higher neurotoxicity occurred in 4 (10.3%) patients. The overall response rate evaluated at 3 months post-single infusion was 79.5% (complete remission, 56.4%; partial response, 23.1%). With a median follow-up of 32 months, the median progression free survival was 13 months and median overall survival was not reached, with the estimated rate of 53.8% (95% CI, 40.3% to 72.0%) at two years. Together, this long-term follow-up data from a multicenter study suggests that 7 × 19 CAR-T cells can induce durable responses with a median overall survival of greater than 2 years, and has a manageable safety profile in patients with R/R LBCL.