Activity Of Chimeric Antigen Receptor Research Articles

Modular Chimeric Antigen Receptor Systems for Universal CAR T Cell Retargeting.

The engineering of T cells through expression of chimeric antigen receptors (CARs) against tumor-associated antigens (TAAs) has shown significant potential for use as an anti-cancer therapeutic. The development of strategies for flexible and modular CAR T systems is accelerating, allowing for multiple antigen targeting, precise programming, and adaptable solutions in the field of cellular immunotherapy. Moving beyond the fixed antigen specificity of traditional CAR T systems, the modular CAR T technology splits the T cell signaling domains and the targeting elements through use of a switch molecule. The activity of CAR T cells depends on the presence of the switch, offering dose-titratable response and precise control over CAR T cells. In this review, we summarize developments in universal or modular CAR T strategies that expand on current CAR T systems and open the door for more customizable T cell activity.

Designed Ankyrin Repeat Protein (DARPin) to target chimeric antigen receptor (CAR)-redirected T cells towards CD4+ T cells to reduce the latent HIV+ cell reservoir

Chimeric Antigen Receptor (CAR)-redirected T cells show great efficacy in the patient-specific therapy of hematologic malignancies. Here, we demonstrate that a DARPin with specificity for CD4 specifically redirects and triggers the activation of CAR engineered T cells resulting in the depletion of CD4+ target cells aiming for elimination of the human immunodeficiency virus (HIV) reservoir.

Abstract 2193: Small molecule inducible MyD88/CD40 (iMC) in CAR-T cells can repolarize M2 macrophage to an anti-tumor M1 phenotype

Abstract Background: Effective chimeric antigen receptor (CAR) T cell therapy against solid tumors must overcome a hostile, tumor microenvironment that includes tumor-associated macrophages (TAM). Pancreatic adenocarcinomas (PDAC) are commonly infiltrated with TAMs polarized to a tumor-promoting M2 phenotype rather than a T cell-stimulatory and tumor-inhibitory M1 phenotype. The GoCAR platform combines an inducible MyD88/CD40 (iMC) costimulation protein with a 1st generation CAR. Our previously published results demonstrated that iMC costimulation, activated by the small molecule dimerizer, rimiducid (Rim), enhanced CAR-T proliferation and anti-tumor efficacy. Here, we examined the extrinsic effects of iMC signaling on CAR-T cell immune-activating ligands, cytokine production and their ability to polarize M2 macrophage to an anti-tumor phenotype. Methods: Macrophages were prepared from peripheral blood monocytes of four or more random blood donors from the Gulf Coast Regional Blood Center (Houston, TX) and differentiated in vitro to an M2 phenotype with TGF-β and IL-10, or an M1 phenotype (as a positive control). GoCAR-T cells targeting prostate stem cell antigen (PSCA) were prepared by retroviral transduction from the autologous donors. To test the effects of iMC activation on macrophage polarization, contact-dependent or independent (i.e., separation of cell populations with transwell inserts) coculture assays were performed with and without activation of iMC with 1 nM Rim and/or surface-bound PSCA. Anti-tumor cytotoxicity was measured by coculture with PSCA+ Panc1-GFP cells. Results: CAR activation by PSCA antigen recognition or iMC activation with Rim decreased CD163, an M2 macrophage marker, and increased CD80, expressed on M1 macrophage. Full activation of the GoCAR-T cells with both Rim and the target antigen fully repolarized M2 macrophage to an M1 marked phenotype (CD163lowCD80high). This repolarization could be directed partially in the absence of cell-cell contact by diffusion of soluble factors through Transwell membranes. M2 macrophages repolarized by conditioning media from activated GoCAR-T cells also exhibited the functionality of M1 macrophages and acquired cytotoxicity against tumor cells. Furthermore, cultures of conditioned macrophages and limiting dilutions of GoCAR-T cells demonstrated a cooperative enhancement of the cytotoxicity of PSCA GoCAR-T cells toward Panc-1 targets. This cooperation was more effective for GoCAR-T cells than CD28- or 4-1BB-enhanced 2nd generation PSCA CAR-T cells. Conclusions: These results predict that GoCAR-T activation with Rim will convert TAMs within a solid tumor microenvironment from T cell inhibitors to tumor-caustic agents. Citation Format: Xiaohong Wang, Konrad Gabrusiewicz, David M. Spencer, Aaron E. Foster, J. Henri Bayle. Small molecule inducible MyD88/CD40 (iMC) in CAR-T cells can repolarize M2 macrophage to an anti-tumor M1 phenotype [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 2193.

Abstract 2173: CRISPR-Cas9 gene editing of inhibitory receptor signaling pathways improves CAR T cell activity against glioblastoma

Abstract Early clinical trials have demonstrated the therapeutic potential of chimeric antigen receptor (CAR) T cells against glioblastoma (GBM), but also highlighted the obstacles that need to be addressed to improve their anti-tumor activity. GBM is highly immunosuppressive and thus necessitates endowing adoptively transferred CAR T cells with resistance mechanisms to achieve sustained treatment responses. This is, in part, due to the effect of immune-inhibitory receptors, including PD1, CTLA4, LAG3 and BTLA, that antagonize the tumor-directed T cells. A common mechanism of T cell inhibition involves the recruitment of Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2) to the immune synapse upon engagement of multiple co-inhibitory receptors. SHP2, in turn, de-phosphorylates key signaling proteins involved in T cell activation. We hypothesized that disrupting SHP2 expression will offset multiple co-inhibitory pathways, thereby improving the anti-tumor activity of CAR T cells. Using CRISPR/Cas9 gene editing, we disrupted the SHP2-encoding gene locus, PTPN11, in primary human T cells by generating and testing a library of single-guide RNA (sgRNA). We selected the top candidate that reproducibly reduced the SHP2 protein expression to <10%. A HER2-targeting second-generation CAR (HER2-CAR) was then expressed in SHP2 knock-out (SHP2KO) T cells via gamma retroviral vector transduction. SHP2KO CAR T cell manufacturing following a single round of stimulation was optimized to minimize ex vivo manipulation of the cells. The phenotypic profiles of SHP2KO and wild-type HER2-CAR T cells were comparable at baseline. Loss of SHP2 did not alter the CAR T cell viability, expansion or proliferative capacity in comparison to the wild-type CAR T cells. Mass cytometry (CyTOF)-based analysis of SHP2KO CAR T cells after encountering GBM cells demonstrated the preservation of the central memory (CCR7+CD45RA-) T cell subset. The majority of PD1+ SHP2KO CAR T cells co-expressed functional activation markers such as ICOS and CD107a. The PD1+ T cell subset was comprised of mostly T-betHi progenitor population and only a smaller percentage of EomesHi terminally exhausted population. Functionally, HER2-specific SHP2KO CAR T cells from different donors (n=4) exhibited improved anti-tumor activity that was sustained in long-term cytotoxicity assays. In an experimental orthotopic LN229-GBM mouse model, SHP2KO HER2-CAR T cells better controlled the growth of established xenografts and improved survival in comparison to wild-type HER2-CAR T cells. In conclusion, our results show that disrupting SHP2 expression using a CRISPR/Cas9 gene editing strategy could improve the CAR T cell function against GBM and warrants further clinical testing. Citation Format: Khaled Sanber, Zeid Nawas, Vita Salsman, Ahmed Gad, Pretty Rose Matthew, Daniel Landi, Ciaran Lee, Amel Sengal, Rikhia Chakraborty, Sujith Joseph, Ahmed Nabil, Meenakshi Hegde. CRISPR-Cas9 gene editing of inhibitory receptor signaling pathways improves CAR T cell activity against glioblastoma [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 2173.

Abstract 2216: Combinational strategy targeting B cell malignancy using iPSC engineered CAR-NK (FT596) and CAR-T cell (FT819) platforms with therapeutic antibody to achieve an effective deep and durable response

Abstract The use of induced pluripotent stem cells (iPSCs) to derive immune effector cells offers distinct advantages for immune therapy over existing patient- or donor- derived platforms, not only in terms of scalable manufacturing and precision genetic engineering at the clonal level, but also in allowing the generation and combinational use of multiple effector cell types each with distinct characteristics. Taking cues from the natural propagation of innate to adaptive effector responses, here we describe the combined use of multi-engineered iPSC derived Natural Killer (iNK) and T (iT) cell platforms in order to exploit the unique properties of each cell type to achieve both depth and durability of response for hematological malignancies. As innate cells, NK cells are characterized by the capacity for spontaneous reactivity, either in response to cell surface antigen or downregulation of class I MHC, and the rapid kinetic under which NK cells operate make them an ideal candidate to achieve a depth of response that outpaces the limiting effects of cytokine support. FT596 was developed as a dual-targeted iNK cell platform engineered to express both a CD19-directed, NK cell-optimized (NKG2D-2B4-CD3ζ) chimeric antigen receptor (CAR) and a high-affinity, non-cleavable Fc receptor (hnCD16), enabling multi-targeting through combination with therapeutic antibodies. The activity of each receptor is further enhanced by the expression of an IL15-IL15Ra fusion receptor, which also allows the cells to expand in the absence of exogenous cytokine support and prolongs cell survival in vitro and in vivo. T cells are exquisitely specific and undergo rapid clonal expansion and differentiation in response to target antigen, and antigen driven persistence has been demonstrated as a key determinant in efficacy in primary CAR-T cell immune therapy. FT819 is an iT cell platform engineered to express a functionally optimized CD19-CAR (1XX) that has been genome edited into the T cell receptor (TCR) alpha constant (TRAC) locus to provide ideal CAR activity and to prevent TCR expression, thereby avoiding the complications of GVH reactivity in an allogeneic setting. In vivo, both FT596 and FT819 showed stable levels of tumor cell clearance against the CD19+ acute lymphoblastic leukemia cell line NALM6, comparable to that of primary CAR19 T cells (p*<0.0001 for FT596, FT819 or Primary CART vs NALM6 alone). FT596 also shows enhanced clearance of CD19+CD20+ Burkitts lymphoma cell line RAJI when used in combination with rituximab (p=0.0002 vs rituximab alone). Collectively, these studies suggest a compounded anti-tumor effect can be achieved utilizing the inherent properties of engineered CAR-iNK cells together with therapeutic antibody combined with engineered CAR-iT cells which will be highlighted in this presentation. Citation Format: Jode P. Goodridge, John W. Reiser, Ryan Bjordahl, Milli Mandal, Chia-wei Chang, Raedun Clarck, Sajid Mahmood, Huang Zhu, Svetlana Gaidarova, Robert Blum, Frank Cichocki, Hui-ting Hsu, Greg Bonello, Tom Lee, Brian Groff, Karl-Johan Mamlberg, Bruce Walcheck, Jeffrey S. Miller, Dan Kaufman, Bahram Valamehr. Combinational strategy targeting B cell malignancy using iPSC engineered CAR-NK (FT596) and CAR-T cell (FT819) platforms with therapeutic antibody to achieve an effective deep and durable response [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 2216.

Lactate Dehydrogenase A Depletion Alters MyC-CaP Tumor Metabolism, Microenvironment, and CAR T Cell Therapy

To enhance human prostate-specific membrane antigen (hPSMA)-specific chimeric antigen receptor (CAR) T cell therapy in a hPSMA+ MyC-CaP tumor model, we studied and imaged the effect of lactate dehydrogenase A (LDH-A) depletion on the tumor microenvironment (TME) and tumor progression. Effective LDH-A short hairpin RNA (shRNA) knockdown (KD) was achieved in MyC-CaP:hPSMA+ Renilla luciferase (RLuc)-internal ribosome entry site (IRES)-GFP tumor cells, and changes in tumor cell metabolism and in the TME were monitored. LDH-A downregulation significantly inhibited cell proliferation and subcutaneous tumor growth compared to control cells and tumors. However, total tumor lactate concentration did not differ significantly between LDH-A knockdown and control tumors, reflecting the lower vascularity, blood flow, and clearance of lactate from LDH-A knockdown tumors. Comparing treatment responses of MyC-CaP tumors with LDH-A depletion and/or anti-hPSMA CAR T cells showed that the dominant effect on tumor growth was LDH-A depletion. With anti-hPSMA CAR T cell treatment, tumor growth was significantly slower when combined with tumor LDH-A depletion and compared to control tumor growth (p < 0.0001). The lack of a complete tumor response in our animal model can be explained in part by (1) the lower activity of human CAR T cells against hPSMA-expressing murine tumors in a murine host, and (2) a loss of hPSMA antigen from the tumor cell surface in progressive generations of tumor cells.

Rewired signaling network in T cells expressing the chimeric antigen receptor (CAR).

The chimeric antigen receptor (CAR) directs T cells to target and kill specific cancer cells. Despite the success of CAR T therapy in clinics, the intracellular signaling pathways that lead to CAR T cell activation remain unclear. Using CD19 CAR as a model, we report that, similar to the endogenous T cell receptor (TCR), antigen engagement triggers the formation of CAR microclusters that transduce downstream signaling. However, CAR microclusters do not coalesce into a stable central supramolecular activation cluster (cSMAC). Moreover, LAT, an essential scaffold protein for TCR signaling, is not required for microcluster formation, immunological synapse formation, nor actin remodeling following CAR activation. However, CAR T cells still require LAT for an optimal production of the cytokine IL-2. Together, these data show that CAR T cells can bypass LAT for a subset of downstream signaling outputs, thus revealing a rewired signaling pathway as compared to native T cells.

Activation of CAR and non-CAR T cells within the tumor microenvironment following CAR T cell therapy.

Mechanisms of chimeric antigen receptor (CAR) T cell-mediated antitumor immunity and toxicity remain poorly characterized because few studies examine the intact tumor microenvironment (TME) following CAR T cell infusion. Axicabtagene ciloleucel is an autologous anti-CD19 CAR T cell therapy approved for patients with large B cell lymphoma. We devised multiplex immunostaining and ISH assays to interrogate CAR T cells and other immune cell infiltrates in biopsies of diffuse large B cell lymphoma following axicabtagene ciloleucel infusion. We found that a majority of intratumoral CAR T cells expressed markers of T cell activation but, unexpectedly, constituted ≤5% of all T cells within the TME 5 days or more after therapy. Large numbers of T cells without CAR were also activated within the TME after axicabtagene ciloleucel infusion; these cells were positive for Ki-67, IFN-γ, granzyme B (GzmB), and/or PD-1 and were found at the highest levels in biopsies with CAR T cells. Additionally, non-CAR immune cells were the exclusive source of IL-6, a cytokine associated with cytokine release syndrome, and were found at their highest numbers in biopsies with CAR T cells. These data suggest that intratumoral CAR T cells are associated with non-CAR immune cell activation within the TME with both beneficial and pathological effects.

Ligand-Induced Degradation of a CAR Permits Reversible Remote Control of CAR T Cell Activity In Vitro and In Vivo

Chimeric antigen receptor (CAR)-modified Tcells are endowed with novel antigen specificity and are most often administered to patients without an engineered mechanism to control the CAR Tcells once infused. "Suicide switches" such as the small molecule-controlled, inducible caspase-9 (iCas9) system afford the ability to selectively eliminate engineered Tcells; however, these approaches are designed for all-or-none, irreversible termination of an ongoing immune response. In order to permit reversible and adjustable modulation, we have created a CAR that is capable of on-demand downregulation by fusing the CAR to a previously developed ligand-induced degradation (LID) domain. Addition of a small molecule ligand triggers exposure of a cryptic degron within the LID domain, resulting in proteasomal degradation of the CAR-LID fusion protein andloss of CAR on the surface of Tcells. This fusion construct allowed for reversible and "tunable" inhibition of CAR Tcell activity invitro. Delivery of the triggering molecule in CAR-LID-treated tumor-bearing mice temporarily reduced CAR activity through modulation of CAR surface expression. The ability to more flexibly modulate CAR Tcell expression through a small molecule provides a platform for controlling possible adverse side effects, as well as preclinical investigations of CAR Tcell biology.

Enhancing Chimeric Antigen Receptor T-Cell Efficacy in Solid Tumors.

Chimeric antigen receptor (CAR) T-cell therapy has been acclaimed as a revolution in cancer treatment following the impressive results in hematologic malignancies. Unfortunately, in patients with solid tumors, objectives responses to CAR T cells are still anecdotal, and important issues are driven by on-target but off-tumor activity of CAR T cells and by the extremely complex biology of solid tumors. Here, we will review the recent attempts to challenge the therapeutic impediments to CAR T-cell therapy in solid tumors. We will focus on the most promising strategies of antigen targeting to improve tumor specificity and address the tumor heterogeneity, efforts to circumvent the physical barriers of the tumor architecture such as subverted tumor vasculature, impediments of CAR T-cell trafficking and immune suppressive microenvironment.

Modulation of inhibitory signals in CAR T cells leads to improved activity against glioblastoma.

3031 Background: Early clinical trials have demonstrated the safety of chimeric antigen receptor (CAR) T cells targeting glioblastoma (GBM), however, their efficacy remains limited by multiple obstacles including the immunosuppressive tumor microenvironment. Adoptively transferred CAR T cells remain susceptible to inhibition via the engagement of co-inhibitory receptors on their surface such as PD1, BTLA, CTLA4 and LAG3. The subsequent recruitment of Src homology region 2 containing protein tyrosine phosphatase 2 (SHP2) by these receptors to the immune synapse may represent a common mechanism of T cell inhibition, as SHP2 can de-phosphorylate key signaling molecules that mediate T cell activation (including CD28 and CD3ζ). We hypothesized that SHP2 deletion will simultaneously offset the effects of multiple co-inhibitory receptors, thereby improving the anti-tumor activity of CAR T cells. Methods: Electroporation of sgRNA/Cas9 ribonucleoprotein complexes into human T cells was used to knockout (KO) SHP2. Retroviral vector transduction was used to express a clinically-utilized second generation CAR (with a CD28 endodomain) targeting HER2. The phenotype of wild-type (WT) and SHP2KO CAR T cells was evaluated with mass cytometry and flow cytometry. Their anti-tumor function was tested in vitro using the xCELLigence assay (an impedance-based cytotoxicity assay), and in vivo, in an orthotopic xenograft mouse model of GBM. Results: Efficient and reproducible depletion of the SHP2 protein in human T cells was verified using western blotting. The Inference of CRISPR Efficiency (ICE) Assay confirmed efficient editing of the PTPN11 gene encoding SHP2. An anti-HER2 CAR was efficiently expressed in the SHP2KO T cells. SHP2 deletion did not significantly affect CAR T cell expansion, proliferation or baseline phenotype. However, following co-culture with HER2+ LN229-GBM cells, the CD8+ central memory (CCR7+ CD45RA-) and effector memory (CCR7- CD45RA-) subsets were enriched to a greater extent in the SHP2KO CAR T cells. The pattern of cytokine co-expression varied between donors in a single-cell analysis comparing SHP2KO to WT CAR T cells after encountering LN229 cells. Functionally, SHP2KO CAR T cells derived from the majority of healthy donor and patient peripheral blood eliminated LN229 cells more rapidly in vitro. In an orthotopic mouse model of GBM, SHP2KO CAR T cells showed better early control of established LN229 xenografts and improved survival in comparison to WT CAR T cells. Conclusions: SHP2 deletion in CD28ζ.CAR T cells improves their anti-tumor activity.

Modulation of inhibitory receptor signaling pathways improves CAR T cell activity against glioblastoma

Background & Aim Early clinical trials have demonstrated the safety of chimeric antigen receptor (CAR) T cells targeting glioblastoma (GBM), however, their efficacy remains limited by multiple obstacles including the highly immunosuppressive tumor microenvironment. These adoptively transferred CAR T cells are susceptible to inhibition via the engagement of inhibitory receptors on their surface including PD1, CTLA4, LAG3 and BTLA. The recruitment of Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2) to the immune synapse upon engagement of these co-inhibitory receptors may represent a common mechanism of T cell inhibition. Upon its recruitment and activation, SHP2 dephosphorylates key stimulatory signaling molecules, thus limiting T cell activation. We hypothesized that disrupting SHP2 expression will simultaneously offset multiple co-inhibitory pathways, thereby improving the anti-tumor activity of CAR T cells. Methods, Results & Conclusion CRISPR/Cas9 technology was used to knockout (KO) SHP2 from human T cells. Retroviral vector transduction was used to express a clinically-utilized second generation CAR (with a CD28 signaling endodomain) targeting HER2. The phenotype of wild-type and edited CAR T cells was investigated using mass cytometry and confirmed with flow cytometry. Their function was tested in vitro using xcelligence (an electrical impedance-based long-term cytotoxicity assay) and in vivo in an orthotopic xenograft mouse model of GBM. Efficient SHP2 KO in human T cells was verified using western blotting. The Inference of CRISPR Efficiency (ICE) Assay confirmed efficient editing of the PTPN11 gene encoding SHP2. An anti-HER2 CAR was efficiently expressed in the SHP2KO T cells. SHP2 deletion did not significantly affect T cell expansion, proliferation or phenotypic profile. However, SHP2KO CAR T cells eliminated LN229 cells (a GBM cell line) in vitro more efficiently compared to wild-type CAR T cells. In vivo, SHP2KO CAR T cells showed better control of engrafted LN229 tumor cells and improved the survival of treated mice in comparison to wild-type CAR T cells. In conclusion, these results suggest that SHP2 may limit the function of CAR T cells and that SHP2 deletion may improve their anti-GBM activity.

Tuning the Antigen Density Requirement for CAR T-cell Activity.

Insufficient reactivity against cells with low antigen density has emerged as an important cause of chimeric antigen receptor (CAR) T-cell resistance. Little is known about factors that modulate the threshold for antigen recognition. We demonstrate that CD19 CAR activity is dependent upon antigen density and that the CAR construct in axicabtagene ciloleucel (CD19-CD28ζ) outperforms that in tisagenlecleucel (CD19-4-1BBζ) against antigen-low tumors. Enhancing signal strength by including additional immunoreceptor tyrosine-based activation motifs (ITAM) in the CAR enables recognition of low-antigen-density cells, whereas ITAM deletions blunt signal and increase the antigen density threshold. Furthermore, replacement of the CD8 hinge-transmembrane (H/T) region of a 4-1BBζ CAR with a CD28-H/T lowers the threshold for CAR reactivity despite identical signaling molecules. CARs incorporating a CD28-H/T demonstrate a more stable and efficient immunologic synapse. Precise design of CARs can tune the threshold for antigen recognition and endow 4-1BBζ-CARs with enhanced capacity to recognize antigen-low targets while retaining a superior capacity for persistence. SIGNIFICANCE: Optimal CAR T-cell activity is dependent on antigen density, which is variable in many cancers, including lymphoma and solid tumors. CD28ζ-CARs outperform 4-1BBζ-CARs when antigen density is low. However, 4-1BBζ-CARs can be reengineered to enhance activity against low-antigen-density tumors while maintaining their unique capacity for persistence.This article is highlighted in the In This Issue feature, p. 627.

A VHH-Based Anti-MUC1 Chimeric Antigen Receptor for Specific Retargeting of Human Primary T Cells to MUC1-Positive Cancer Cells.

Objective Immunotherapy with redirected T cells that express a chimeric antigen receptor (CAR) is a promising prospect in cancer treatment. Most CARs use murine-derived single-chain variable fragments (scFvs) as an antigen targeting moiety, which may lead to host immunogenic responses and engineered T cell disappearance. It seems that development of less immunogenic CARs, such as CARs composed of the camelid variable domain of heavy chain antibodies (VHHs) may likely overcome this obstacle. Here, we improved the expression of the VHH-based anti-MUC1 CAR gene construct using a third generation lentiviral vector in primary human T cells and assessed its effect on antigen specific targeting, activation and cytotoxicity of redirected human T cells. Materials and Methods In this experimental study, we established a second generation novel CAR (VHH-based anti- MUC1 CAR) that contained a camelid-derived anti-MUC1 VHH followed by an IgG3 hinge, a CD28 transmembrane domain and signalling endodomains of CD28 and CD3+. Next, we constructed lentiviral vectors that contained this CAR gene construct using an optimized transiently virus production method and transduced it into human T cells. Cell surface expression of CAR, cytokine secretion and cytotoxic activity were assessed in the transduced CD3+T cells. Results The transduced T cells had high levels of surface expression of CAR. T cells that expressed anti-MUC1 CAR showed significantly increased secretion of Th1 cytokines, including IL-2, TNF alpha and IFN-γ, as well as cytotoxic activity upon recognition of MUC1 on tumour cells after co-incubation with T47D or MCF-7 (MUC1-positive) compared with A431 (MUC1-negative) or untransduced T cells. ConclusionOur results suggested that, given the unique properties of VHHs to prevent immunogenic responses and tonic signalling, our novel VHH-based anti-MUC1 CAR might be effective for clinical purposes in cancer immunotherapy.

Pharmacological targeting of immune checkpoint A2aR improves function of anti-CD19 CAR T cells in vitro

In spite of impressive results in the treatment of acute lymphoblastic B cell leukemia (B-ALL) with chimeric antigen receptor (CAR) T cells, the clinical outcome of some hematological cancers like follicular lymphoma (FL) and chronic lymphocytic leukemia (CLL) has not been very promising likely due to immunosuppressive networks within tumor microenvironment. Hypoxia in the microenvironment of hematological malignancies and consequently generation of adenosine molecule is appeared to be correlated with immunosuppression, tumor progression, and relapse. Herein, we hypothesized that whether pharmacological targeting of adenosine 2a receptor (A2aR) can enhance antitumor activity of anti-CD19 CAR T cells in vitro. Prior to functional assays, A2aR expression was assessed in CAR-expressing T cells. Our results showed that A2aR was not only up-regulated in the fully human anti-CD19 CAR T cells (hereafter referred to as huCAR19 T cells) but also was further overexpressed following re-stimulation with target cells. Although pharmacological inhibition of A2aR could significantly increase proliferation capacity and cytokine production of huCAR19 T cells following treatment with an adenosine analog, cytotoxic activity of huCAR19 T cells was not significantly improved. Considering A2aR overexpression in huCAR19 T cells in the tumor microenvironment, our results indicated that pharmacological targeting of A2aR could not only improve huCAR19 T cells functionality in a hostile tumor microenvironment but also could have a therapeutic advantage, and sought to assess the possibility in a pre-clinical setting.

4-1BB costimulation promotes CAR T cell survival through noncanonical NF-κB signaling.

Clinical response to chimeric antigen receptor (CAR) T cell therapy is correlated with CAR T cell persistence, especially for CAR T cells that target CD19+ hematologic malignancies. 4-1BB-costimulated CAR (BBζ) T cells exhibit longer persistence after adoptive transfer than do CD28-costimulated CAR (28ζ) T cells. 4-1BB signaling improves T cell persistence even in the context of 28ζ CAR activation, which indicates distinct prosurvival signals mediated by the 4-1BB cytoplasmic domain. To specifically study signal transduction by CARs, we developed a cell-free, ligand-based activation and ex vivo culture system for CD19-specific CAR T cells. We observed greater ex vivo survival and subsequent expansion of BBζ CAR T cells when compared to 28ζ CAR T cells. We showed that only BBζ CARs activated noncanonical nuclear factor κB (ncNF-κB) signaling in T cells basally and that the anti-CD19 BBζ CAR further enhanced ncNF-κB signaling after ligand engagement. Reducing ncNF-κB signaling reduced the expansion and survival of anti-CD19 BBζ T cells and was associated with a substantial increase in the abundance of the most pro-apoptotic isoforms of Bim. Although our findings do not exclude the importance of other signaling differences between BBζ and 28ζ CARs, they demonstrate the necessary and nonredundant role of ncNF-κB signaling in promoting the survival of BBζ CAR T cells, which likely underlies the engraftment persistence observed with this CAR design.

Abstract A52: Systemic anti-PD-1 immunotherapy results in PD-1 blockade on T cells in the cerebrospinal fluid

Abstract Immune checkpoint inhibitors have shown promising clinical efficacy in many types of cancers, including some with metastasis into the central neural system (CNS). However, little is known about the CNS penetration of immune checkpoint inhibitors and their bioactivity on the locoregional T cells. Here, we analyzed the CNS and systemic concentration of pembrolizumab (Pembro) in high-grade glioma patients, who were concurrently treated with intravenously administered Pembro and locoregionally delivered chimeric antigen receptor (CAR) T cells. A total of 99 paired cerebrospinal fluid (CSF) and serum samples were collected from 10 patients during multicycle treatment of CAR T cell and Pembro. We discovered that after the first Pembro infusion, CSF antibody concentrations were increased slower than serum concentrations. However, CSF antibody concentrations reached steady-state 24 hours after Pembro infusion and were maintained stable over the 21-day infusion cycles. Although average CSF Pembro concentrations (3.2nM) were only 1% of serum levels (329nM), we observed effective PD-1 blockade on the T cells in CSF samples of all analyzed patients. The blocking effect was found on both endogenous T cells and locoregionally administered CAR T cells. Further, PD-1 on CD3/CD28 beads-activated T cells was completely blocked after incubation with cell-depleted CSF samples, suggesting the bioactivity of Pembro that penetrated into the CSF. Using a dose-titration assay, we also confirmed that CSF Pembro concentrations were sufficient to ameliorate the cytotoxic activity of CAR T cells against repetitive tumor challenges. Together, for the first time, we showed the dynamic Pembro levels in the CSF throughout multiple treatment cycles and confirmed that systemically administered immune checkpoint inhibitors can penetrate into the CNS and elicit blocking effect on T cells. Our findings add strength to the rationale for combining immune checkpoint inhibitors with locoregionally delivered CAR T cells and other types of immunotherapy for the treatment of brain tumors. Citation Format: Dongrui Wang, Jana Portnow, Vivi Tran, Vivian Chiu, Alfonso Brito, Darya Alizadeh, Renate Starr, Julie Kilpatrick, Paige McNamara, Stephen J. Forman, Behnam Badie, Timothy W. Synold, Christine E. Brown. Systemic anti-PD-1 immunotherapy results in PD-1 blockade on T cells in the cerebrospinal fluid [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 A52.

A Bump in the Road: How the Hostile AML Microenvironment Affects CAR T Cell Therapy.

Chimeric antigen receptor (CAR) T cells targeting CD19 have been successful treating patients with relapsed/refractory B cell acute lymphoblastic leukemia (ALL) and B cell lymphomas. However, relapse after CAR T cell therapy is still a challenge. In addition, preclinical and early clinical studies targeting acute myeloid leukemia (AML) have not been as successful. This can be attributed in part to the presence of an AML microenvironment that has a dampening effect on the antitumor activity of CAR T cells. The AML microenvironment includes cellular interactions, soluble environmental factors, and structural components. Suppressive immune cells including myeloid derived suppressor cells and regulatory T cells are known to inhibit T cell function. Environmental factors contributing to T cell exhaustion, including immune checkpoints, anti-inflammatory cytokines, chemokines, and metabolic alterations, impact T cell activity, persistence, and localization. Lastly, structural factors of the bone marrow niche, secondary lymphoid organs, and extramedullary sites provide opportunities for CAR T cell evasion by AML blasts, contributing to treatment resistance and relapse. In this review we discuss the effect of the AML microenvironment on CAR T cell function. We highlight opportunities to enhance CAR T cell efficacy for AML through manipulating, targeting, and evading the anti-inflammatory leukemic microenvironment.

Oncolytic Adenovirus Armed with BiTE, Cytokine, and Checkpoint Inhibitor Enables CAR T Cells to Control the Growth of Heterogeneous Tumors.

No single cancer immunotherapy will likely defeat all evasion mechanisms of solid tumors, including plasticity of tumor antigen expression and active immune suppression by the tumor environment. In this study, we increase the breadth, potency, and duration of anti-tumor activity of chimeric antigen receptor (CAR) Tcells using an oncolytic virus (OV) that produces cytokine, checkpoint blockade, and a bispecific tumor-targeted Tcell engager (BiTE) molecule. First, we constructed a BiTE molecule specific for CD44 variant 6 (CD44v6), since CD44v6 is widely expressed on tumor but not normal tissue, and a CD44v6 antibody has been safely administered to cancer patients. We then incorporated this BiTE sequence into an oncolytic-helper binary adenovirus (CAdDuo) encoding an immunostimulatory cytokine (interleukin [IL]-12) and an immune checkpoint blocker (PD-L1Ab) to form CAdTrio. CD44v6 BiTE from CAdTrio enabled HER2-specific CAR Tcells to kill multiple CD44v6+ cancer cell lines and to produce more rapid and sustained disease control of orthotopic HER2+ and HER2-/- CD44v6+ tumors than any component alone. Thus, the combination of CAdTrio with HER2.CAR Tcells ensures dual targeting of two tumor antigens by engagement of distinct classes of receptor (CAR and native Tcell receptor [TCR]), and significantly improves tumor control and survival.

Interleukin-23 engineering improves CAR T cell function in solid tumors.

Cytokines that stimulate T cell proliferation, such as interleukin (IL)-15, have been explored as a means of boosting the antitumor activity of chimeric antigen receptor (CAR) T cells. However, constitutive cytokine signaling in T cells and activation of bystander cells may cause toxicity. IL-23 is a two-subunit cytokine known to promote proliferation of memory T cells and T helper type 17 cells. We found that, upon T cell antigen receptor (TCR) stimulation, T cells upregulated the IL-23 receptor and the IL-23α p19 subunit, but not the p40 subunit. We engineered expression of the p40 subunit in T cells (p40-Td cells) and obtained selective proliferative activity in activated T cells via autocrine IL-23 signaling. In comparison to CAR T cells, p40-Td CAR T cells showed improved antitumor capacity in vitro, with increased granzyme B and decreased PD-1 expression. In two xenograft and two syngeneic solid tumor mouse models, p40-Td CAR T cells showed superior efficacy in comparison to CAR T cells and attenuated side effects in comparison to CAR T cells expressing IL-18 or IL-15.