Locoregional delivery of IL-13Rα2-targeting CAR-T cells in recurrent high-grade glioma: a phase 1 trial

Chimeric antigen receptor T cell (CAR-T) therapy is an emerging strategy to improve treatment outcomes for recurrent high-grade glioma, a cancer that responds poorly to current therapies. Here we report a completed phase I trial evaluating IL-13Rα2-targeted CAR-T cells in 65 patients with recurrent high-grade glioma, the majority being recurrent glioblastoma (rGBM). Primary objectives were safety and feasibility, maximum tolerated dose/maximum feasible dose and a recommended phase 2 dose plan. Secondary objectives included overall survival, disease response, cytokine dynamics and tumor immune contexture biomarkers. This trial evolved to evaluate three routes of locoregional T cell administration (intratumoral (ICT), intraventricular (ICV) and dual ICT/ICV) and two manufacturing platforms, culminating in arm 5, which utilized dual ICT/ICV delivery and an optimized manufacturing process. Locoregional CAR-T cell administration was feasible and well tolerated, and as there were no dose-limiting toxicities across all arms, a maximum tolerated dose was not determined. Probable treatment-related grade 3+ toxicities were one grade 3 encephalopathy and one grade 3 ataxia. A clinical maximum feasible dose of 200 × 106 CAR-T cells per infusion cycle was achieved for arm 5; however, other arms either did not test or achieve this dose due to manufacturing feasibility. A recommended phase 2 dose will be refined in future studies based on data from this trial. Stable disease or better was achieved in 50% (29/58) of patients, with two partial responses, one complete response and a second complete response after additional CAR-T cycles off protocol. For rGBM, median overall survival for all patients was 7.7 months and for arm 5 was 10.2 months. Central nervous system increases in inflammatory cytokines, including IFNγ, CXCL9 and CXCL10, were associated with CAR-T cell administration and bioactivity. Pretreatment intratumoral CD3 T cell levels were positively associated with survival. These findings demonstrate that locoregional IL-13Rα2-targeted CAR-T therapy is safe with promising clinical activity in a subset of patients. ClinicalTrials.gov Identifier: NCT02208362 .

Targeting Wnt signaling for improved glioma immunotherapy

Introduction

Despite aggressive standard-of-care therapy, including surgery, radiation, and chemotherapy, glioblastoma recurrence is almost inevitable and uniformly lethal. Activation of glioma-intrinsic Wnt/β-catenin signaling is associated with a poor prognosis and the proliferation of glioma stem-like cells, leading to malignant transformation and tumor progression. Impressive results in a subset of cancers have been obtained using immunotherapies including anti-CTLA4, anti-PD-1, and anti-PD-L1 or chimeric antigen receptor (CAR) T cell therapies. However, the heterogeneity of tumors, low mutational burden, single antigen targeting, and associated antigen escape contribute to non-responsiveness and potential tumor recurrence despite these therapeutic efforts. In the current study, we determined the effects of the small molecule, highly specific Wnt/CBP (CREB Binding Protein)/β-catenin antagonist ICG-001, on glioma tumor cells and the tumor microenvironment (TME)-including its effect on immune cell infiltration, blood vessel decompression, and metabolic changes.

Methods

Using multiple glioma patient-derived xenografts cell lines and murine tumors (GL261, K-Luc), we demonstrated in vitro cytostatic effects and a switch from proliferation to differentiation after treatment with ICG-001.

Results

In these glioma cell lines, we further demonstrated that ICG-001 downregulated the CBP/β-catenin target gene Survivin/BIRC5-a hallmark of Wnt/CBP/β-catenin inhibition. We found that in a syngeneic mouse model of glioma (K-luc), ICG-001 treatment enhanced tumor infiltration by CD3+ and CD8+ cells with increased expression of the vascular endothelial marker CD31 (PECAM-1). We also observed differential gene expression and induced immune cell infiltration in tumors pretreated with ICG-001 and then treated with CAR T cells as compared with single treatment groups or when ICG-001 treatment was administered after CAR T cell therapy.

Discussion

We conclude that specific Wnt/CBP/β-catenin antagonism results in pleotropic changes in the glioma TME, including glioma stem cell differentiation, modulation of the stroma, and immune cell activation and recruitment, thereby suggesting a possible role for enhancing immunotherapy in glioma patients.

Inclusion of 4-1BB Costimulation Enhances Selectivity and Functionality of IL13Rα2-Targeted Chimeric Antigen Receptor T Cells

Chimeric antigen receptor (CAR) T cell immunotherapy is emerging as a powerful strategy for cancer therapy; however, an important safety consideration is the potential for off-tumor recognition of normal tissue. This is particularly important as ligand-based CARs are optimized for clinical translation. Our group has developed and clinically translated an IL13(E12Y) ligand-based CAR targeting the cancer antigen IL13Rα2 for treatment of glioblastoma (GBM). There remains limited understanding of how IL13-ligand CAR design impacts the activity and selectivity for the intended tumor-associated target IL13Rα2 versus the more ubiquitous unintended target IL13Rα1. In this study, we functionally compared IL13(E12Y)-CARs incorporating different intracellular signaling domains, including first-generation CD3ζ-containing CARs (IL13ζ), second-generation 4-1BB (CD137)-containing or CD28-containing CARs (IL13-BBζ or IL13-28ζ), and third-generation CARs containing both 4-1BB and CD28 (IL13-28BBζ). In vitro coculture assays at high tumor burden establish that second-generation IL13-BBζ or IL13-28ζ outperform first-generation IL13ζ and third-generation IL13-28BBζ CAR designs, with IL13-BBζ providing superior CAR proliferation and in vivo antitumor potency in human xenograft mouse models. IL13-28ζ displayed a lower threshold for antigen recognition, resulting in higher off-target IL13Rα1 reactivity both in vitro and in vivo. Syngeneic mouse models of GBM also demonstrate safety and antitumor potency of murine IL13-BBζ CAR T cells delivered systemically after lymphodepletion. These findings support the use of IL13-BBζ CARs for greater selective recognition of IL13Rα2 over IL13Rα1, higher proliferative potential, and superior antitumor responsiveness. This study exemplifies the potential of modulating factors outside the antigen targeting domain of a CAR to improve selective tumor recognition.

Significance

This study reveals how modulating CAR design outside the antigen targeting domain improves selective tumor recognition. Specifically, this work shows improved specificity, persistence, and efficacy of 4-1BB-based IL13-ligand CARs. Human clinical trials evaluating IL13-41BB-CAR T cells are ongoing, supporting the clinical significance of these findings.

Engineered IL13 variants direct specificity of IL13Rα2-targeted CAR T cell therapy

IL13Rα2 is an attractive target due to its overexpression in a variety of cancers and rare expression in healthy tissue, motivating expansion of interleukin 13 (IL13)-based chimeric antigen receptor (CAR) T cell therapy from glioblastoma into systemic malignancies. IL13Rα1, the other binding partner of IL13, is ubiquitously expressed in healthy tissue, raising concerns about the therapeutic window of systemic administration. IL13 mutants with diminished binding affinity to IL13Rα1 were previously generated by structure-guided protein engineering. In this study, two such variants, termed C4 and D7, are characterized for their ability to mediate IL13Rα2-specific response as binding domains for CAR T cells. Despite IL13Rα1 and IL13Rα2 sharing similar binding interfaces on IL13, mutations to IL13 that decrease binding affinity for IL13Rα1 did not drastically change binding affinity for IL13Rα2. Micromolar affinity to IL13Rα1 was sufficient to pacify IL13-mutein CAR T cells in the presence of IL13Rα1-overexpressing cells in vitro. Interestingly, effector activity of D7 CAR T cells, but not C4 CAR T cells, was demonstrated when cocultured with IL13Rα1/IL4Rα-coexpressing cancer cells. While low-affinity interactions with IL13Rα1 did not result in observable toxicities in mice, in vivo biodistribution studies demonstrated that C4 and D7 CAR T cells were better able to traffic away from IL13Rα1+ lung tissue than were wild-type (WT) CAR T cells. These results demonstrate the utility of structure-guided engineering of ligand-based binding domains with appropriate selectivity while validating IL13-mutein CARs with improved selectivity for application to systemic IL13Rα2-expressing malignancies.

Spatial organization of heterogeneous immunotherapy target antigen expression in high-grade glioma

High-grade (WHO grades III-IV) glioma remains one of the most lethal human cancers. Adoptive transfer of tumor-targeting chimeric antigen receptor (CAR)-redirected T cells for high-grade glioma has revealed promising indications of anti-tumor activity, but objective clinical responses remain elusive for most patients. A significant challenge to effective immunotherapy is the highly heterogeneous structure of these tumors, including large variations in the magnitudes and distributions of target antigen expression, observed both within individual tumors and between patients. To obtain a more detailed understanding of immunotherapy target antigens within patient tumors, we immunochemically mapped at single cell resolution three clinically-relevant targets, IL13Rα2, HER2 and EGFR, on tumor samples drawn from a 43-patient cohort. We observed that within individual tumor samples, expression of these antigens was neither random nor uniform, but rather that they mapped into local neighborhoods - phenotypically similar cells within regions of cellular tumor - reflecting not well understood properties of tumor cells and their milieu. Notably, tumor cell neighborhoods of high antigen expression were not arranged independently within regions. For example, in cellular tumor regions, neighborhoods of high IL13Rα2 and HER2 expression appeared to be reciprocal to those of EGFR, while in areas of pseudopalisading necrosis, expression of IL13Rα2 and HER2, but not EGFR, appeared to reflect the radial organization of tumor cells around hypoxic cores. Other structural features affecting expression of immunotherapy target antigens remain to be elucidated. This structured but heterogeneous organization of antigen expression in high grade glioma is highly permissive for antigen escape, and combinatorial antigen targeting is a commonly suggested potential mitigating strategy. Deeper understanding of antigen expression within and between patient tumors will enhance optimization of combination immunotherapies, the most immediate clinical application of the observations presented here being the importance of including (wild-type) EGFR as a target antigen.

Antibody-based redirection of universal Fabrack-CAR T cells selectively kill antigen bearing tumor cells

Background

Chimeric antigen receptor (CAR) T cells engineered to recognize and target tumor associated antigens have made a profound impact on the quality of life for many patients with cancer. However, tumor heterogeneity and intratumoral immune suppression reduce the efficacy of this approach, allowing for tumor cells devoid of the target antigen to seed disease recurrence. Here, we address the complexity of tumor heterogeneity by developing a universal CAR.

Method

We constructed a universal Fabrack-CAR with an extracellular domain composed of the non-tumor targeted, cyclic, twelve residue meditope peptide that binds specifically to an engineered binding pocket within the Fab arm of monoclonal antibodies (mAbs). As this site is readily grafted onto therapeutic mAbs, the antigen specificity of these universal Fabrack-CAR T cells is simply conferred by administering mAbs with specificity to the heterogeneous tumor.

Results

Using in vitro and in vivo studies with multiple meditope-engineered mAbs, we show the feasibility, specificity, and robustness of this approach. These studies demonstrate antigen- and antibody-specific T cell activation, proliferation, and IFNγ production, selective killing of target cells in a mixed population, and tumor regression in animal models.

Conclusion

Collectively, these findings support the feasibility of this universal Fabrack-CAR T cell approach and provide the rationale for future clinical use in cancer immunotherapy.

3D-organoid culture supports differentiation of human CAR+ iPSCs into highly functional CAR T cells

Unlimited generation of chimeric antigen receptor (CAR) T cells from human-induced pluripotent stem cells (iPSCs) is an attractive approach for "off-the-shelf" CAR T cell immunotherapy. Approaches to efficiently differentiate iPSCs into canonical αβ T cell lineages, while maintaining CAR expression and functionality, however, have been challenging. We report that iPSCs reprogramed from CD62L⁺ naive and memory T cells followed by CD19-CAR engineering and 3D-organoid system differentiation confers products with conventional CD8αβ-positive CAR T cell characteristics. Expanded iPSC CD19-CAR T cells showed comparable antigen-specific activation, degranulation, cytotoxicity, and cytokine secretion compared with conventional CD19-CAR T cells and maintained homogeneous expression of the TCR derived from the initial clone. iPSC CD19-CAR T cells also mediated potent antitumor activity in vivo, prolonging survival of mice with CD19⁺ human tumor xenografts. Our study establishes feasible methodologies to generate highly functional CAR T cells from iPSCs to support the development of "off-the-shelf" manufacturing strategies.

Off-the-shelf, steroid-resistant, IL13Rα2-specific CAR T cells for treatment of glioblastoma

BACKGROUND

Wide-spread application of chimeric antigen receptor (CAR) T cell therapy for cancer is limited by the current use of autologous CAR T cells necessitating the manufacture of individualized therapeutic products for each patient. To address this challenge, we have generated an off-the-shelf, allogeneic CAR T cell product for the treatment of glioblastoma (GBM), and present here the feasibility, safety, and therapeutic potential of this approach.

METHODS

We generated for clinical use a healthy-donor derived IL13Rα2-targeted CAR+ (IL13-zetakine+) cytolytic T-lymphocyte (CTL) product genetically engineered using zinc finger nucleases (ZFNs) to permanently disrupt the glucocorticoid receptor (GR) (GRm13Z40-2) and endow resistance to glucocorticoid treatment. In a phase I safety and feasibility trial we evaluated these allogeneic GRm13Z40-2 T cells in combination with intracranial administration of recombinant human IL-2 (rhIL-2; aldesleukin) in six patients with unresectable recurrent GBM that were maintained on systemic dexamethasone (4-12 mg/day).

RESULTS

The GRm13Z40-2 product displayed dexamethasone-resistant effector activity without evidence for in vitro alloreactivity. Intracranial administration of GRm13Z40-2 in four doses of 108 cells over a two-week period with aldesleukin (9 infusions ranging from 2500-5000 IU) was well tolerated, with indications of transient tumor reduction and/or tumor necrosis at the site of T cell infusion in four of the six treated research subjects. Antibody reactivity against GRm13Z40-2 cells was detected in the serum of only one of the four tested subjects.

CONCLUSIONS

This first-in-human experience establishes a foundation for future adoptive therapy studies using off-the-shelf, zinc-finger modified, and/or glucocorticoid resistant CAR T cells.

CTIM-29. CLINICAL EVALUATION OF CHLOROTOXIN-DIRECTED CAR T CELLS FOR PATIENTS WITH RECURRENT GLIOBLASTOMA

Chlorotoxin (CLTX), a peptide component of scorpion venom, exhibits selective and broad binding to glioblastoma (GBM) and other tumors with minimal activity against non-malignant cells. We have developed a novel CAR that utilizes CLTX as the tumor targeting domain. Preclinical studies established that CLTX-CAR T cells target GBM through recognition of a receptor complex incorporating membrane-bound matrix metalloprotease-2 (MMP-2). Here, we report initial clinical findings for our phase I trial evaluating safety and bioactivity of CLTX-CAR T cells in patients with MMP2+ recurrent GBM (NCT04214392). Weekly infusions of CLTX-CAR T cells are delivered locoregionally, either directly into the tumor cavity (ICT; Arm 1), or in combination with intracerebroventricular (ICV) delivery (dual ICT/ICV; Arm 2). At this interim analysis, four participants have received at least three cycles of CLTX-CAR T cells ICT (Arm 1; 3-8 cycles) at dose level 1 (DL1; 4M, 20M, 20M CAR T cells per cycle). None of the participants experienced dose limiting toxicity (DLT) during the DLT evaluation period of 28-days, although one participant experienced a serious adverse event of grade 3 cerebral edema, possibly attributed to CAR T cells. Overall, Arm 1-DL1 was well-tolerated, and the next patient cohort will be treated on Arm 2-DL1 (dual ICT/ICV; 8M, 40M, 40M CAR T cells per cycle), as per protocol design. Disease response was assessed by RANO, overall survival, and time to progression; three of four participants achieved a best response of stable disease. Liquid biopsy detected persistent CAR T cells in the tumor cavity throughout treatment, suggesting that the therapeutic cells are not immunogenic. Ongoing studies are evaluating biomarkers of response and resistance, including CAR T cell activation and inflammatory cytokines. This clinical study provides first-in-human evidence for the safety and feasibility of CLTX-CAR T cells as a new class of toxin-based CARs for treatment of GBM.

Abstract 59: CAR T cell therapy reshapes the tumor microenvironment to promote host antitumor immune repsonses in glioblastoma

CAR T cell therapy is emerging as a promising strategy to treat cancer and may offer new therapeutic options for individuals diagnosed with glioblastoma (GBM) and other solid tumors. While early clinical studies evaluating CAR T cell therapy in GBM have established evidence of safety and bioactivity, objective clinical responses have been limited. It remains unclear whether productive CAR T cell therapy for solid tumors requires solely CAR T cell engagement with tumor antigen, or if it also necessitates the stimulation of a patient's endogenous immune response. Focusing on our preclinical and clinical program evaluating IL13Rα2-targeted CAR-T cells for the treatment of IL13Rα2-positive glioblastoma (GBM), we set out to mechanistically interrogate the interplay between CAR T cell therapy and the host tumor microenvironment. We designed a murine CAR T cell syngeneic platform in C57BL/6 immunocompetent mice and demonstrate that single intratumoral infusion of IL13Rα2-CAR T cells mediate potent antitumor activity against established KR158 tumors, a highly invasive and poorly immunogenic murine glioma model. We demonstrate that CAR T cell treatment of mouse syngeneic GBM alters the tumor immune landscape, activates intratumoral myeloid cells and induces endogenous T cell memory responses coupled with feed forward propagation of CAR T responses. IFNγ production by CAR T cells and IFNγ-responsiveness of host immune cells is critical for tumor immune landscape remodeling to promote a more activated and less suppressive tumor microenvironment. The clinical relevance of these findings was explored in patient samples from our on-going IL13Rα2-CAR T cell phase I clinical trial [NCT02208362]. Consistent with our preclinical findings, we show that locoregional CAR T cell infusions result in spikes in inflammatory cytokines and an influx of endogenous immune cells into the cerebrospinal fluid (CSF) and resected tumor cavity. Single cell RNA-sequencing revealed unique genes upregulated in immune cells from blood and CSF samples after treatment. One patient of particular interest, who presented with recurrent multifocal GBM, remarkably achieved a complete response (CR) following locoregional delivery of IL13Rα2-CAR T cells, despite heterogeneous IL13Rα2 tumor expression (PMID: 28029927). In this responding patient, we now show the induction of endogenous tumor-specific T cell reactivity and T cell clones whose dynamics contracted with tumor volume following IL13Rα2-targeted CAR T therapy. These studies establish that CAR T cell therapy has the potential to re-shape the tumor microenvironment, creating a context permissible for eliciting endogenous antitumor immunity and emphasize the importance of the host innate and adaptive immunity in productive CAR T cell therapy of solid tumors.

Citation Format: Christine E. Brown, Darya Alizadeh, Vanessa Jonsson, Jonathan Hibbard, Stephanie Yahn, Robyn A. Wong, Xin Yang, Rachel Ng, Natalie Dullerud, Madeleine Maker, Sharahreh Gholamin, Renate Starr, Nicholas Banovich, Stephen J. Forman, Behnam Badie. CAR T cell therapy reshapes the tumor microenvironment to promote host antitumor immune repsonses in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 59.

Chlorotoxin-directed CAR T cells for specific and effective targeting of glioblastoma

Although chimeric antigen receptor (CAR) T cells have demonstrated signs of antitumor activity against glioblastoma (GBM), tumor heterogeneity remains a critical challenge. To achieve broader and more effective GBM targeting, we developed a peptide-bearing CAR exploiting the GBM-binding potential of chlorotoxin (CLTX). We find that CLTX peptide binds a great proportion of tumors and constituent tumor cells. CAR T cells using CLTX as the targeting domain (CLTX-CAR T cells) mediate potent anti-GBM activity and efficiently target tumors lacking expression of other GBM-associated antigens. Treatment with CLTX-CAR T cells resulted in tumor regression in orthotopic xenograft GBM tumor models. CLTX-CAR T cells do not exhibit observable off-target effector activity against normal cells or after adoptive transfer into mice. Effective targeting by CLTX-CAR T cells requires cell surface expression of matrix metalloproteinase-2. Our results pioneer a peptide toxin in CAR design, expanding the repertoire of tumor-selective CAR T cells with the potential to reduce antigen escape.

IFNγ Is Critical for CAR T Cell-Mediated Myeloid Activation and Induction of Endogenous Immunity

Chimeric antigen receptor (CAR) T cells mediate potent antigen-specific antitumor activity; however, their indirect effects on the endogenous immune system are not well characterized. Remarkably, we demonstrate that CAR T-cell treatment of mouse syngeneic glioblastoma (GBM) activates intratumoral myeloid cells and induces endogenous T-cell memory responses coupled with feed-forward propagation of CAR T-cell responses. IFNγ production by CAR T cells and IFNγ responsiveness of host immune cells are critical for tumor immune landscape remodeling to promote a more activated and less suppressive tumor microenvironment. The clinical relevance of these observations is supported by studies showing that human IL13Rα2-CAR T cells activate patient-derived endogenous T cells and monocytes/macrophages through IFNγ signaling and induce the generation of tumor-specific T-cell responses in a responding patient with GBM. These studies establish that CAR T-cell therapy has the potential to shape the tumor microenvironment, creating a context permissible for eliciting endogenous antitumor immunity. SIGNIFICANCE: Our findings highlight the critical role of IFNγ signaling for a productive CAR T-cell therapy in GBM. We establish that CAR T cells can activate resident myeloid populations and promote endogenous T-cell immunity, emphasizing the importance of host innate and adaptive immunity for CAR T-cell therapy of solid tumors.This article is highlighted in the In This Issue feature, p. 2113.

CRISPR Screening of CAR T Cells and Cancer Stem Cells Reveals Critical Dependencies for Cell-Based Therapies

Glioblastoma (GBM) contains self-renewing GBM stem cells (GSC) potentially amenable to immunologic targeting, but chimeric antigen receptor (CAR) T-cell therapy has demonstrated limited clinical responses in GBM. Here, we interrogated molecular determinants of CAR-mediated GBM killing through whole-genome CRISPR screens in both CAR T cells and patient-derived GSCs. Screening of CAR T cells identified dependencies for effector functions, including TLE4 and IKZF2. Targeted knockout of these genes enhanced CAR antitumor efficacy. Bulk and single-cell RNA sequencing of edited CAR T cells revealed transcriptional profiles of superior effector function and inhibited exhaustion responses. Reciprocal screening of GSCs identified genes essential for susceptibility to CAR-mediated killing, including RELA and NPLOC4, the knockout of which altered tumor-immune signaling and increased responsiveness of CAR therapy. Overall, CRISPR screening of CAR T cells and GSCs discovered avenues for enhancing CAR therapeutic efficacy against GBM, with the potential to be extended to other solid tumors. SIGNIFICANCE: Reciprocal CRISPR screening identified genes in both CAR T cells and tumor cells regulating the potency of CAR T-cell cytotoxicity, informing molecular targeting strategies to potentiate CAR T-cell antitumor efficacy and elucidate genetic modifications of tumor cells in combination with CAR T cells to advance immuno-oncotherapy.This article is highlighted in the In This Issue feature, p. 995.

Systemic Anti-PD-1 Immunotherapy Results in PD-1 Blockade on T Cells in the Cerebrospinal Fluid

Question

Are systemically administered programmed cell death 1–blocking antibodies able to penetrate and maintain bioactivity in the central nervous system?

Findings

In this case series study of 10 adult patients with high-grade gliomas, intravenous administration of pembrolizumab yielded cerebrospinal fluid (CSF) concentrations that were approximately 1% of that in serum but were sufficient for blocking programmed cell death 1 on T cells in the CSF.

Meaning

Systemically administered immune checkpoint blockade is able to reinvigorate T cells within the CSF compartment, supporting its bioavailability for treatment of tumors in the central nervous system and its use in combination with locoregionally delivered cellular therapies.

Importance

Little is known about the penetration and bioactivity of systemically administered programmed cell death 1 (PD-1) antibodies in the central nervous system. Such information is critical for advancing checkpoint antibody therapies for treatment of brain tumors.

Objective

To evaluate pembrolizumab concentrations and PD-1 blockade on T cells in the cerebrospinal fluid (CSF) after intravenous administration.

Design, Setting, and Participants

Cerebrospinal fluid and blood samples were collected from 10 adult patients with high-grade gliomas who were participating in clinical trials of intracranially administered chimeric antigen receptor (CAR) T cells and intravenous pembrolizumab at City of Hope in Duarte, California, from 2017 through 2019. Neuropharmacokinetic and immunologic correlative studies were performed on CSF and serum samples.

Interventions or Exposures

Pembrolizumab, 200 mg, was given intravenously every 3 weeks with a median of 2 cycles (range, 1-8). CAR T cells were administered intracranially every 1 to 4 weeks. Cerebrospinal fluid and blood samples were collected on the day of CAR T-cell administration and then 24 hours later for a total of 100 paired samples.

Main Outcomes and Measures

Pembrolizumab concentrations were measured by enzyme-linked immunosorbent assay, PD-1 blocking on T cells by flow cytometry, and results of PD-1 blockade on CAR T-cell function by in vitro tumor rechallenge assays.

Results

Of the 10 patients included in this study, the mean (SD) age was 45.7 (11.0) years, and 6 (60%) were women. Steady-state pembrolizumab concentrations in the CSF were achieved by 24 hours after initial intravenous administration, with a mean CSF:serum ratio of 0.009 (95% CI, 0.004-0.014). The CSF concentrations of pembrolizumab effectively blocked PD-1 on both endogenous T cells and intracranially administered CAR T cells in the CSF, with flow cytometric detection of surface PD-1 on the T cells decreasing from a mean (SD) of 39.3% (20.2%) before pembrolizumab to a mean (SD) of 3.8% (5.8%) 24 hours after pembrolizumab infusion. Steady-state concentrations in the CSF were maintained throughout the 21-day cycle of pembrolizumab, as was the PD-1 blocking effect, evidenced by no increase in detectable surface PD-1 on T cells in the CSF during that time period. Incubation of PD-1–expressing T cells with CSF samples from patients treated with pembrolizumab also resulted in PD-1 blockade.

Conclusions and Relevance

Results of this study demonstrate steady-state concentrations of pembrolizumab in CSF after intravenous administration as well as CSF concentrations that are sufficient for blocking PD-1 on endogenous and adoptively transferred T cells. This provides mechanistic insight regarding the ability of systemically administered PD-1 blocking antibodies to modulate T-cell activity in the brain.

EPCO-18. MULTI-MODAL AND MULTI-TISSUE PROFILING OF GBM PATIENTS TREATED WITH CAR T CELL THERAPY TO ELUCIDATE MOLECULAR MECHANISMS OF VARIATION IN TREATMENT RESPONSE

Recent advances in immunotherapy, particularly chimeric antigen receptor (CAR)-engineered T cell therapy, have shown promise for the treatment of many tumor types including progressive recurrent glioblastoma (GBM). While early phase clinical trials have illuminated the potential for CAR T cell therapy to effectively treat GBM, they have also highlighted the unique challenges regarding the efficacy and safety of immunotherapy for brain tumors, and many patients continue to progress during therapy. We seek to overcome these challenges and ultimately extend the time of survival for patients diagnosed with GBM by investigating the immune- and tumor-mediated mechanisms driving variation in response to CAR T cell therapy. We generated the first multi-omics time-series dataset of CAR T cells, endogenous immune cells, and tumor cells from 59 GBM patients treated with CAR T cell therapy. Using single cell RNA-sequencing and simultaneous quantification of nearly 200 cell surface proteins, we comprehensively profiled the cellular phenotypes and signaling pathways within tumor and circulating immune cells that are associated with treatment response. The combination of mRNA and protein expression allowed us to resolve cell states beyond what either modality was capable of alone. Additionally, we found differentially expressed genes and proteins between tumor biopsies collected before and after CAR T cell therapy as well as differential expression between pre-infusion CAR T cells and those identified within the tumor following infusion. By evaluating the CAR T cell phenotypes prior to and during treatment we sought to address the outstanding question of how intrinsic variability impacts the activity and persistence of CAR T cells and to determine the phenotypes that confer the greatest therapeutic benefit for patients with GBM. Our results have direct implications for precision medicine and future clinical trials investigating the use of CAR T cell therapy for GBM as well as other solid tumors.

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

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.

Massively-Parallelized, Deterministic Mechanoporation for Intracellular Delivery

Microfluidic intracellular delivery approaches based on plasma membrane poration have shown promise for addressing the limitations of conventional cellular engineering techniques in a wide range of applications in biology and medicine. However, the inherent stochasticity of the poration process in many of these approaches often results in a trade-off between delivery efficiency and cellular viability, thus potentially limiting their utility. Herein, we present a novel microfluidic device concept that mitigates this trade-off by providing opportunity for deterministic mechanoporation (DMP) of cells en masse. This is achieved by the impingement of each cell upon a single needle-like penetrator during aspiration-based capture, followed by diffusive influx of exogenous cargo through the resulting membrane pore, once the cells are released by reversal of flow. Massive parallelization enables high throughput operation, while single-site poration allows for delivery of small and large-molecule cargos in difficult-to-transfect cells with efficiencies and viabilities that exceed both conventional and emerging transfection techniques. As such, DMP shows promise for advancing cellular engineering practice in general and engineered cell product manufacturing in particular.

Abstract 2321: Dual-function of CD27-CD70 costimulatory signal in CAR T cell therapy

Purpose: To investigate the function of co-stimulatory molecule CD27 on the antitumor efficacy of chimeric antigen receptor (CAR) T cells.

Experimental Design: IL13 receptor α2 (IL13Rα2)-targeted CAR T cell products from glioblastoma (GBM) patients were characterized for CD27 surface expression and proliferation potential against recursive tumor challenge. Isolated CD27+ and CD27- fractions of CAR T cells were then evaluated for their antitumor potency against orthotopic GBM xenografts, as well as their molecular characteristics before and after tumor stimulation. Further, T cells were engineered to express a CAR construct together with a constitutively-expressed CD27 to investigate the role of continuous CD27 costimulation on CAR T cell maintenance and effector potency.

Results: CD27 expression on CAR T cell products was correlated with their proliferation capacity against recursive tumor stimulation. Isolated CD27+ CAR T cells outperformed CD27- and unsorted cells in mediating long-term tumor eradication. CD27+ CAR T cells exhibited memory-associated genetic signatures, and were less exhausted following in vitro and in vivo tumor stimulation, both phenotypically and functionally. Moreover, CD27 also sensitized CAR T cells to target low antigen-expressing tumors. When targeting tumor cells expressing CD70 (CD27 ligand), CD27 on CAR T cells became rapidly down-regulated, suggesting a transient CD27-CD70 interaction. The advantageous effector function of CD27+ CAR T cells was diminished by blocking the CD27-CD70 interaction with CD70-targeting antibodies. CD70 is also expressed on CAR T cells, displaying a mutually exclusive expression pattern with CD27. Extended in vitro culture resulted in a phenotypic switch of CAR T cells from CD27+CD70- to CD27-CD70+. Surprisingly, constitutive expression of CD27 (CD27-cons) greatly impaired the effector activity of CAR T cells. These cells were able to eliminate tumor cells in vitro, but failed to mediate potent antitumor effect in vivo. Further characterization showed an early exhaustion phenotype for CD27-cons CAR T cells during in vitro expansion. Additionally, CD27-cons CAR T cells were also prone to activation-induced T cell apoptosis especially against high antigen-expressing targets.

Conclusion: These studies demonstrate a dual-function of CD27 costimulation for CAR T cell antitumor activity. In the enriched CD27+ CAR T cell subset, the transient CD27-CD70 interaction with tumor cells resulted in enhanced antitumor potency. By contrast, constitutively expressed CD27 drove CAR T cell exhaustion and induced apoptosis. These results illustrate the critical role of CD27 in mediating potent CAR T cell therapeutic efficacy, and suggest the potential of CD27 as a marker for the functional quality of CAR T cell products.

Citation Format: Dongrui Wang, Alfonso Brito, Darya Alizadeh, Renate Starr, Brenda Aguilar, Behnam Badie, Stephen J. Forman, Christine E. Brown. Dual-function of CD27-CD70 costimulatory signal in CAR T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2321.

IL15 Enhances CAR-T Cell Antitumor Activity by Reducing mTORC1 Activity and Preserving Their Stem Cell Memory Phenotype

Improvements in the quality and fitness of chimeric antigen receptor (CAR)-engineered T cells, through CAR design or manufacturing optimizations, could enhance the therapeutic potential of CAR-T cells. One parameter influencing the effectiveness of CAR-T cell therapy is the differentiation status of the final product: CAR-T cells that are less-differentiated and less exhausted are more therapeutically effective. In the current study, we demonstrate that CAR-T cells expanded in IL15 (CAR-T/IL15) preserve a less-differentiated stem cell memory (Tscm) phenotype, defined by expression of CD62L⁺CD45RA⁺ CCR7⁺, as compared with cells cultured in IL2 (CAR-T/IL2). CAR-T/IL15 cells exhibited reduced expression of exhaustion markers, higher antiapoptotic properties, and increased proliferative capacity upon antigen challenge. Furthermore, CAR-T/IL15 cells exhibited decreased mTORC1 activity, reduced expression of glycolytic enzymes and improved mitochondrial fitness. CAR-T/IL2 cells cultured in rapamycin (mTORC1 inhibitor) shared phenotypic features with CAR-T/IL15 cells, suggesting that IL15-mediated reduction of mTORC1 activity is responsible for preserving the Tscm phenotype. CAR-T/IL15 cells promoted superior antitumor responses in vivo in comparison with CAR-T/IL2 cells. Inclusion of cytokines IL7 and/or IL21 in addition to IL15 reduced the beneficial effects of IL15 on CAR-T phenotype and antitumor potency. Our findings show that IL15 preserves the CAR-T cell Tscm phenotype and improves their metabolic fitness, which results in superior in vivo antitumor activity, thus opening an avenue that may improve future adoptive T-cell therapies.

In Vitro Tumor Cell Rechallenge For Predictive Evaluation of Chimeric Antigen Receptor T Cell Antitumor Function

The field of chimeric antigen receptor (CAR) T cell therapy is rapidly advancing with improvements in CAR design, gene-engineering approaches and manufacturing optimizations. One challenge for these development efforts, however, has been the establishment of in vitro assays that can robustly inform selection of the optimal CAR T cell products for in vivo therapeutic success. Standard in vitro tumor-lysis assays often fail to reflect the true antitumor potential of the CAR T cells due to the relatively short co-culture time and high T cell to tumor ratio. Here, we describe an in vitro co-culture method to evaluate CAR T cell recursive killing potential at high tumor cell loads. In this assay, long-term cytotoxic function and proliferative capacity of CAR T cells is examined in vitro over 7 days with additional tumor targets administered to the co-culture every other day. This assay can be coupled with profiling T cell activation, exhaustion and memory phenotypes. Using this assay, we have successfully distinguished the functional and phenotypic differences between CD4⁺ and CD8⁺ CAR T cells against glioblastoma (GBM) cells, reflecting their differential in vivo antitumor activity in orthotopic xenograft models. This method provides a facile approach to assess CAR T cell potency and to elucidate the functional variations across different CAR T cell products.

Abstract A045: Chlorotoxin redirects T-cells for specific and effective targeting against glioblastomas

Glioblastoma (GBM) is the most common type of primary brain tumor, with the standard therapy only modestly improving the prognosis, highlighting the necessity to develop advanced treatments. We and others have established the platform to potentiate immune response against GBMs using chimeric antigen receptor (CAR) engineered T-cells. Specifically, we have shown that intracranial administration of CAR T-cells can be well tolerated in patients with recurrent GBMs, together with some early clinical evidence of antitumor response. However, CAR T-cell therapy against GBMs is complicated by the inter- and intratumoral heterogeneity, while the single-targeting therapies only respond to a subset of tumor cells. The development of new CAR therapy would thus aim for targeting a wider range of tumor cells and bypassing antigen escape. Here, we took an approach different from conventional strategies of tumor antigen discovery, exploiting the tumor-binding potential of a natural peptide to develop CAR T-cells that broadly target GBMs. Chlorotoxin (CLTX) is a 36-amino acid peptide with demonstrated GBM-binding capability. Inspired by the utilization of CLTX in GBM tumor imaging, we used a fluorescence-conjugated CLTX to screen the freshly-dispersed primary GBM cells and patient-derived GBM neurospheres, and found that CLTX binding was more homogeneous than the expression of other GBM-associated antigens including EGFR, HER2 and IL13Rα2. Although CLTX has limited inhibitory effect on GBM growth, its broad binding to GBM cells illustrates the potential to be conjugated with a cytotoxic agent. Therefore, we generated CAR T-cells bearing CLTX as the antigen targeting domain. CLTX-CAR T-cells were able to get activated after stimulating with GBM cells, as indicated by their degranulation, cytokine production and immuno-synapse formation. Modification of CAR constructs revealed that CLTX-CAR T-cells with CD28 costimulatory signal exhibited potent effector activity, while the 4-1BB costimulation resulted in inadequate CAR activation. In both in vitro and in vivo models, CLTX-CAR T-cells effectively eliminated GBM cells and tumors, including the ones with no/low expression of EGFR, HER2 and IL13Rα2. Importantly, CLTX peptide exhibited negligible binding to a panel of normal cells from neural and other tissues, and CLTX-CAR T-cells showed no off-target effect against normal organs in tumor-bearing mouse models. Screening on patient-derived GBM neurospheres, we discovered that the expression of metalloproteinase (MMP)-2 on targeT-cells was correlated with the effector function of CLTX-CAR T-cells. Further, the antitumor function of CLTX-CAR T-cells was severely diminished against GBMs with MMP-2 knockdown. Consistent with the cytotoxicity of CLTX-CAR T-cells, MMP-2 expression was also present in a subgroup of GBM cells with undetectable levels of EGFR, HER2 and IL13Rα2 expression. Our results demonstrate for the first time that a peptide toxin can be successfully used as the tumor targeting domain of a CAR, which eliminates GBMs with high efficiency and selectivity. The CLTX-CAR has the potential to limit GBM heterogeneity and compensate current CAR T-cell therapies against solid tumors.

Citation Format: Dongrui Wang, Vanessa Jonsson, Sarah Wright, Wen-Chung Chang, Xin Yang, Renate Starr, Alfonso Brito, Brenda Aguilar, Aniee Sarkissian, Lihong Weng, Stephen J Forman, Michael E Barish, Christine E. Brown. Chlorotoxin redirects T-cells for specific and effective targeting against glioblastomas [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A045.

Glioblastoma-targeted CD4+ CAR T cells mediate superior antitumor activity

Chimeric antigen receptor-modified (CAR-modified) T cells have shown promising therapeutic effects for hematological malignancies, yet limited and inconsistent efficacy against solid tumors. The refinement of CAR therapy requires an understanding of the optimal characteristics of the cellular products, including the appropriate composition of CD4+ and CD8+ subsets. Here, we investigated the differential antitumor effect of CD4+ and CD8+ CAR T cells targeting glioblastoma-associated (GBM-associated) antigen IL-13 receptor α2 (IL13Rα2). Upon stimulation with IL13Rα2+ GBM cells, the CD8+ CAR T cells exhibited robust short-term effector function but became rapidly exhausted. By comparison, the CD4+ CAR T cells persisted after tumor challenge and sustained their effector potency. Mixing with CD4+ CAR T cells failed to ameliorate the effector dysfunction of CD8+ CAR T cells, while surprisingly, CD4+ CAR T cell effector potency was impaired when coapplied with CD8+ T cells. In orthotopic GBM models, CD4+ outperformed CD8+ CAR T cells, especially for long-term antitumor response. Further, maintenance of the CD4+ subset was positively correlated with the recursive killing ability of CAR T cell products derived from GBM patients. These findings identify CD4+ CAR T cells as a highly potent and clinically important T cell subset for effective CAR therapy.

PET of Adoptively Transferred Chimeric Antigen Receptor T Cells with 89Zr-Oxine

Chimeric antigen receptor (CAR) T cell therapy is a promising clinical approach for reducing tumor progression and prolonging patient survival. However, improvements in both the safety and the potency of CAR T cell therapy demand quantitative imaging techniques to determine the distribution of cells after adoptive transfer. The purpose of this study was to optimize ⁸⁹Zr-oxine labeling of CAR T cells and evaluate PET as a platform for imaging adoptively transferred CAR T cells. Methods: CAR T cells were labeled with 0-1.4 MBq of ⁸⁹Zr-oxine per 10⁶ cells and assessed for radioactivity retention, viability, and functionality. In vivo trafficking of ⁸⁹Zr-oxine-labeled CAR T cells was evaluated in 2 murine xenograft tumor models: glioblastoma brain tumors with intracranially delivered IL13Rα2-targeted CAR T cells, and subcutaneous prostate tumors with intravenously delivered prostate stem cell antigen (PSCA)-targeted CAR T cells. Results: CAR T cells were efficiently labeled (75%) and retained more than 60% of the ⁸⁹Zr over 6 d. In vitro cytokine production, migration, and tumor cytotoxicity, as well as in vivo antitumor activity, were not significantly reduced when labeled with 70 kBq/10⁶ cells. IL13Rα2-CAR T cells delivered intraventricularly were detectable by PET for at least 6 d throughout the central nervous system and within intracranial tumors. When intravenously administered, PSCA-CAR T cells also showed tumor tropism, with a 9-fold greater tumor-to-muscle ratio than for CAR-negative T cells. Conclusion: ⁸⁹Zr-oxine can be used for labeling and imaging CAR T cells while maintaining cell viability and function. On the basis of these studies, we conclude that ⁸⁹Zr-oxine is a clinically translatable platform for real-time assessment of cell therapies.

Optimization of IL13Rα2-Targeted Chimeric Antigen Receptor T Cells for Improved Anti-tumor Efficacy against Glioblastoma

T cell immunotherapy is emerging as a powerful strategy to treat cancer and may improve outcomes for patients with glioblastoma (GBM). We have developed a chimeric antigen receptor (CAR) T cell immunotherapy targeting IL-13 receptor α2 (IL13Rα2) for the treatment of GBM. Here, we describe the optimization of IL13Rα2-targeted CAR T cells, including the design of a 4-1BB (CD137) co-stimulatory CAR (IL13BBζ) and a manufacturing platform using enriched central memory T cells. Utilizing orthotopic human GBM models with patient-derived tumor sphere lines in NSG mice, we found that IL13BBζ-CAR T cells improved anti-tumor activity and T cell persistence as compared to first-generation IL13ζ-CAR CD8⁺ T cells that had shown evidence for bioactivity in patients. Investigating the impact of corticosteroids, given their frequent use in the clinical management of GBM, we demonstrate that low-dose dexamethasone does not diminish CAR T cell anti-tumor activity in vivo. Furthermore, we found that local intracranial delivery of CAR T cells elicits superior anti-tumor efficacy as compared to intravenous administration, with intraventricular infusions exhibiting possible benefit over intracranial tumor infusions in a multifocal disease model. Overall, these findings help define parameters for the clinical translation of CAR T cell therapy for the treatment of brain tumors.

Abstract 3024: CD4+ outperform CD8+ central memory-derived CAR T cells, mediating persistent antitumor responses and long-term eradication of glioblastoma

Purpose: To compare antitumor effector function mediated by CD4+ and CD8+ chimeric antigen receptor (CAR)-T cells targeting IL13 receptor α2 (IL13Rα2) for treatment of glioblastoma (GBM).

Experimental Design: CD4+ and CD8+ IL13Rα2-specific CAR-T cells, derived from enriched central memory T cells (Tcm), were evaluated for their antitumor potential both in vitro by recursive challenge with GBM cells and in vivo in established orthotopic GBM xenograft models. Further, GBM-stimulated CD4+ and CD8+ CAR-T cells were examined for their exhaustion- and memory-associated phenotypes at transcriptional and protein levels, which would account for their differential antitumor activity.

Results: While CD8+ CAR-T cells mediated robust short-term cytolytic effector function, they became rapidly exhausted and lost antitumor potential after repeated stimulation with tumor cells. CD4+ CAR-T cells, by contrast, persisted and retained effector potency even after repetitive tumor challenge. CD4-mediated cytotoxicity acted through the granzyme B/perforin pathway and was independent of the CD8+ cells. Activated CD4+ CAR-T cells augmented the proliferation of CD8+ cells, but failed to protect the CD8+ cells against stimulation-induced exhaustion. In NSG mice bearing GBM xenografts, CD4+ CAR-T cell treatment led to long-term tumor-free survival, while CD8+ CAR-T cell treated mice showed short-term tumor regression followed by antigen-positive relapse and associated T cell exhaustion. Upon GBM stimulation, CD4+ cells expressed less co-inhibitory receptors and more memory-associated markers than the CD8+ T cell subset. Further, a comprehensive transcriptional analysis revealed that when activated, CD4+ cells retained expression of genes involved in survival- and self-renewal-related pathways, indicating a less exhausted status and a better functional persistence in comparison to the CD8+ cells.

Conclusion: We observed a superior anti-GBM activity mediated by CD4+ CAR-T cells over the CD8+ subset, featured by their ability to maintain long-term immune response and reduce stimulation-induced exhaustion. It is thus inferred that the frequency of CD4+ cells could be an important criteria for evaluating the efficacy of CAR-T cells as immunotherapeutic products.

Citation Format: Dongrui Wang, Renate Starr, Brenda Aguilar, Alfonso Brito, Brenda Chang, Aniee Sarkissian, Behnam Badie, Michael E. Barish, Stephen J. Forman, Christine E. Brown. CD4+ outperform CD8+ central memory-derived CAR T cells, mediating persistent antitumor responses and long-term eradication of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3024. doi:10.1158/1538-7445.AM2017-3024

Regression of Glioblastoma after Chimeric Antigen Receptor T-Cell Therapy

A patient with recurrent multifocal glioblastoma received chimeric antigen receptor (CAR)-engineered T cells targeting the tumor-associated antigen interleukin-13 receptor alpha 2 (IL13Rα2). Multiple infusions of CAR T cells were administered over 220 days through two intracranial delivery routes - infusions into the resected tumor cavity followed by infusions into the ventricular system. Intracranial infusions of IL13Rα2-targeted CAR T cells were not associated with any toxic effects of grade 3 or higher. After CAR T-cell treatment, regression of all intracranial and spinal tumors was observed, along with corresponding increases in levels of cytokines and immune cells in the cerebrospinal fluid. This clinical response continued for 7.5 months after the initiation of CAR T-cell therapy. (Funded by Gateway for Cancer Research and others; ClinicalTrials.gov number, NCT02208362 .).

Bioactivity and Safety of IL13Rα2-Redirected Chimeric Antigen Receptor CD8+ T Cells in Patients with Recurrent Glioblastoma

PURPOSE

A first-in-human pilot safety and feasibility trial evaluating chimeric antigen receptor (CAR)-engineered, autologous primary human CD8(+) cytotoxic T lymphocytes (CTL) targeting IL13Rα2 for the treatment of recurrent glioblastoma (GBM).

EXPERIMENTAL DESIGN

Three patients with recurrent GBM were treated with IL13(E13Y)-zetakine CD8(+) CTL targeting IL13Rα2. Patients received up to 12 local infusions at a maximum dose of 10(8) CAR-engineered T cells via a catheter/reservoir system.

RESULTS

We demonstrate the feasibility of manufacturing sufficient numbers of autologous CTL clones expressing an IL13(E13Y)-zetakine CAR for redirected HLA-independent IL13Rα2-specific effector function for a cohort of patients diagnosed with GBM. Intracranial delivery of the IL13-zetakine(+) CTL clones into the resection cavity of 3 patients with recurrent disease was well-tolerated, with manageable temporary brain inflammation. Following infusion of IL13-zetakine(+) CTLs, evidence for transient anti-glioma responses was observed in 2 of the patients. Analysis of tumor tissue from 1 patient before and after T-cell therapy suggested reduced overall IL13Rα2 expression within the tumor following treatment. MRI analysis of another patient indicated an increase in tumor necrotic volume at the site of IL13-zetakine(+) T-cell administration.

CONCLUSIONS

These findings provide promising first-in-human clinical experience for intracranial administration of IL13Rα2-specific CAR T cells for the treatment of GBM, establishing a foundation on which future refinements of adoptive CAR T-cell therapies can be applied.

Chimeric antigen receptors with mutated IgG4 Fc spacer avoid fc receptor binding and improve T cell persistence and antitumor efficacy

The success of adoptive therapy using chimeric antigen receptor (CAR)-expressing T cells partly depends on optimal CAR design. CARs frequently incorporate a spacer/linker region based on the constant region of either IgG1 or IgG4 to connect extracellular ligand-binding with intracellular signaling domains. Here, we evaluated the potential for the IgG4-Fc linker to result in off-target interactions with Fc gamma receptors (FcγRs). As proof-of-principle, we focused on a CD19-specific scFv-IgG4-CD28-zeta CAR and found that, in contrast to CAR-negative cells, CAR+ T cells bound soluble FcγRs in vitro and did not engraft in NSG mice. We hypothesized that mutations to avoid FcγR binding would improve CAR+ T cell engraftment and antitumor efficacy. Thus, we generated CD19-specific CARs with IgG4-Fc spacers that had either been mutated at two sites (L235E; N297Q) within the CH2 region (CD19R(EQ)) or incorporated a CH2 deletion (CD19Rch2Δ). These mutations reduced binding to soluble FcγRs without altering the ability of the CAR to mediate antigen-specific lysis. Importantly, CD19R(EQ) and CD19Rch2Δ T cells exhibited improved persistence and more potent CD19-specific antilymphoma efficacy in NSG mice. Together, these studies suggest that optimal CAR function may require the elimination of cellular FcγR interactions to improve T cell persistence and antitumor responses.

Cytokine induction of VCAM-1 but not IL13Rα2 on glioma cells: a tale of two antibodies

The interleukin-13 receptor alpha2 (IL13Rα2) is a cell surface receptor that is over-expressed by a subset of high-grade gliomas, but not expressed at significant levels by normal brain tissue. For both malignant and non-malignant cells, IL13Rα2 surface expression is reported to be induced by various cytokines such as IL-4 or IL-13 and tumor necrosis factor (TNF). Our group has developed a therapeutic platform to target IL13Rα2-positive brain tumors by engineering human cytotoxic T lymphocytes (CTLs) to express the IL13-zetakine chimeric antigen receptor. We therefore sought to investigate the potential of cytokine stimulation to induce IL13Rα2 cell surface expression, and thereby increase susceptibility to IL13Rα2-specific T cell killing. In the course of these experiments, we unexpectedly found that the commercially available putative IL13Rα2-specific monoclonal antibody B-D13 recognizes cytokine-induced VCAM-1 on glioblastoma. We provide evidence that the induced receptor is not IL13Rα2, because its expression does not consistently correlate with IL13Rα2 mRNA levels, it does not bind IL-13, and it is not recognized by IL13-zetakine CTL. Instead we demonstrate by immunoprecipitation experiments and mass spectrometry that the antigen recognized by the B-D13 antibody following cytokine stimulation is VCAM-1, and that VCAM-1, but not IL13Rα2, is induced on glioma cells by TNF alone or in combination with IL-13 or IL-4. Further evaluation of several commercial B-D13 antibodies revealed that B-D13 is bi-specific, recognizing both IL13Rα2 and VCAM-1. This binding is non-overlapping based on soluble receptor competition experiments, and mass spectrometry identifies two distinct heavy and light chain species, providing evidence that the B-D13 reagent is di-clonal. PE-conjugation of the B-D13 antibody appears to disrupt IL13Rα2 recognition, while maintaining VCAM-1 specificity. While this work calls into question previous studies that have used the B-D13 antibody to assess IL13Rα2 expression, it also suggests that TNF may have significant effects on glioma biology by up-regulating VCAM-1.

Glioma IL13Rα2 is associated with mesenchymal signature gene expression and poor patient prognosis

A major challenge for successful immunotherapy against glioma is the identification and characterization of validated targets. We have taken a bioinformatics approach towards understanding the biological context of IL-13 receptor α2 (IL13Rα2) expression in brain tumors, and its functional significance for patient survival. Querying multiple gene expression databases, we show that IL13Rα2 expression increases with glioma malignancy grade, and expression for high-grade tumors is bimodal, with approximately 58% of WHO grade IV gliomas over-expressing this receptor. By several measures, IL13Rα2 expression in patient samples and low-passage primary glioma lines most consistently correlates with the expression of signature genes defining mesenchymal subclass tumors and negatively correlates with proneural signature genes as defined by two studies. Positive associations were also noted with proliferative signature genes, whereas no consistent associations were found with either classical or neural signature genes. Probing the potential functional consequences of this mesenchymal association through IPA analysis suggests that IL13Rα2 expression is associated with activation of proinflammatory and immune pathways characteristic of mesenchymal subclass tumors. In addition, survival analyses indicate that IL13Rα2 over-expression is associated with poor patient prognosis, a single gene correlation ranking IL13Rα2 in the top ~1% of total gene expression probes with regard to survival association with WHO IV gliomas. This study better defines the functional consequences of IL13Rα2 expression by demonstrating association with mesenchymal signature gene expression and poor patient prognosis. It thus highlights the utility of IL13Rα2 as a therapeutic target, and helps define patient populations most likely to respond to immunotherapy in present and future clinical trials.

Stem-like tumor-initiating cells isolated from IL13Rα2 expressing gliomas are targeted and killed by IL13-zetakine-redirected T Cells

PURPOSE

To evaluate IL13Rα2 as an immunotherapeutic target for eliminating glioma stem-like cancer initiating cells (GSC) of high-grade gliomas, with particular focus on the potential of genetically engineered IL13Rα2-specific primary human CD8(+) CTLs (IL13-zetakine(+) CTL) to target this therapeutically resistant glioma subpopulation.

EXPERIMENTAL DESIGN

A panel of low-passage GSC tumor sphere (TS) and serum-differentiated glioma lines were expanded from patient glioblastoma specimens. These glioblastoma lines were evaluated for expression of IL13Rα2 and for susceptibility to IL13-zetakine(+) CTL-mediated killing in vitro and in vivo.

RESULTS

We observed that although glioma IL13Rα2 expression varies between patients, for IL13Rα2(pos) cases this antigen was detected on both GSCs and more differentiated tumor cell populations. IL13-zetakine(+) CTL were capable of efficient recognition and killing of both IL13Rα2(pos) GSCs and IL13Rα2(pos) differentiated cells in vitro, as well as eliminating glioma-initiating activity in an orthotopic mouse tumor model. Furthermore, intracranial administration of IL13-zetakine(+) CTL displayed robust antitumor activity against established IL13Rα2(pos) GSC TS-initiated orthotopic tumors in mice.

CONCLUSIONS

Within IL13Rα2 expressing high-grade gliomas, this receptor is expressed by GSCs and differentiated tumor populations, rendering both targetable by IL13-zetakine(+) CTLs. Thus, our results support the potential usefullness of IL13Rα2-directed immunotherapeutic approaches for eradicating therapeutically resistant GSC populations.

Hydrogen mapping of the lunar south pole using the LRO neutron detector experiment LEND

Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon's south polar region from the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) spacecraft were used to select the optimal impact site for LCROSS. LEND data show several regions where the epithermal neutron flux from the surface is suppressed, which is indicative of enhanced hydrogen content. These regions are not spatially coincident with permanently shadowed regions of the Moon. The LCROSS impact site inside the Cabeus crater demonstrates the highest hydrogen concentration in the lunar south polar region, corresponding to an estimated content of 0.5 to 4.0% water ice by weight, depending on the thickness of any overlying dry regolith layer. The distribution of hydrogen across the region is consistent with buried water ice from cometary impacts, hydrogen implantation from the solar wind, and/or other as yet unknown sources.