Intrathecal bivalent CAR T cells targeting EGFR and IL13Rα2 in recurrent glioblastoma: phase 1 trial interim results

Recurrent glioblastoma (rGBM) remains a major unmet medical need, with a median overall survival of less than 1 year. Here we report the first six patients with rGBM treated in a phase 1 trial of intrathecally delivered bivalent chimeric antigen receptor (CAR) T cells targeting epidermal growth factor receptor (EGFR) and interleukin-13 receptor alpha 2 (IL13Rα2). The study's primary endpoints were safety and determination of the maximum tolerated dose. Secondary endpoints reported in this interim analysis include the frequency of manufacturing failures and objective radiographic response (ORR) according to modified Response Assessment in Neuro-Oncology criteria. All six patients had progressive, multifocal disease at the time of treatment. In both dose level 1 (1 ×107 cells; n = 3) and dose level 2 (2.5 × 107 cells; n = 3), administration of CART-EGFR-IL13Rα2 cells was associated with early-onset neurotoxicity, most consistent with immune effector cell-associated neurotoxicity syndrome (ICANS), and managed with high-dose dexamethasone and anakinra (anti-IL1R). One patient in dose level 2 experienced a dose-limiting toxicity (grade 3 anorexia, generalized muscle weakness and fatigue). Reductions in enhancement and tumor size at early magnetic resonance imaging timepoints were observed in all six patients; however, none met criteria for ORR. In exploratory endpoint analyses, substantial CAR T cell abundance and cytokine release in the cerebrospinal fluid were detected in all six patients. Taken together, these first-in-human data demonstrate the preliminary safety and bioactivity of CART-EGFR-IL13Rα2 cells in rGBM. An encouraging early efficacy signal was also detected and requires confirmation with additional patients and longer follow-up time. ClinicalTrials.gov identifier: NCT05168423 .

Long-term stability of clinical-grade lentiviral vectors for cell therapy

The use of lentiviral vectors in cell and gene therapy is steadily increasing, both in commercial and investigational therapies. Although existing data increasingly support the usefulness and safety of clinical-grade lentiviral vectors used in cell manufacturing, comprehensive studies specifically addressing their long-term stability are currently lacking. This is significant considering the high cost of producing and testing GMP-grade vectors, the limited number of production facilities, and lengthy queue for production slots. Therefore, an extended shelf life is a critical attribute to justify the investment in large vector lots for investigational cell therapies. This study offers a thorough examination of essential stability attributes, including vector titer, transduction efficiency, and potency for a series of clinical-grade vector lots, each assessed at a minimum of 36 months following their date of manufacture. The 13 vector lots included in this study were used for cell product manufacturing in 16 different clinical trials, and at the time of the analysis had a maximum storage time at -80°C of up to 8 years. The results emphasize the long-term durability and efficacy of GMP-grade lentiviral vectors for use in ex vivo cell therapy manufacturing.

Deletion of the inhibitory co-receptor CTLA-4 enhances and invigorates chimeric antigen receptor T cells

Chimeric antigen receptor (CAR) T cell therapy targeting CD19 has achieved tremendous success treating B cell malignancies; however, some patients fail to respond due to poor autologous T cell fitness. To improve response rates, we investigated whether disruption of the co-inhibitory receptors CTLA4 or PD-1 could restore CART function. CRISPR-Cas9-mediated deletion of CTLA4 in preclinical models of leukemia and myeloma improved CAR T cell proliferation and anti-tumor efficacy. Importantly, this effect was specific to CTLA4 and not seen upon deletion of CTLA4 and/or PDCD1 in CAR T cells. Mechanistically, CTLA4 deficiency permitted unopposed CD28 signaling and maintenance of CAR expression on the T cell surface under conditions of high antigen load. In clinical studies, deletion of CTLA4 rescued the function of T cells from patients with leukemia that previously failed CAR T cell treatment. Thus, selective deletion of CTLA4 reinvigorates dysfunctional chronic lymphocytic leukemia (CLL) patient T cells, providing a strategy for increasing patient responses to CAR T cell therapy.

Two cases of severe pulmonary toxicity from highly active mesothelin-directed CAR T cells

Multiple clinical studies have treated mesothelin (MSLN)-positive solid tumors by administering MSLN-directed chimeric antigen receptor (CAR) T cells. Although these products are generally safe, efficacy is limited. Therefore, we generated and characterized a potent, fully human anti-MSLN CAR. In a phase 1 dose-escalation study of patients with solid tumors, we observed two cases of severe pulmonary toxicity following intravenous infusion of this product in the high-dose cohort (1-3 × 108 T cells per m2). Both patients demonstrated progressive hypoxemia within 48 h of infusion with clinical and laboratory findings consistent with cytokine release syndrome. One patient ultimately progressed to grade 5 respiratory failure. An autopsy revealed acute lung injury, extensive T cell infiltration, and accumulation of CAR T cells in the lungs. RNA and protein detection techniques confirmed low levels of MSLN expression by benign pulmonary epithelial cells in affected lung and lung samples obtained from other inflammatory or fibrotic conditions, indicating that pulmonary pneumocyte and not pleural expression of mesothelin may lead to dose-limiting toxicity. We suggest patient enrollment criteria and dosing regimens of MSLN-directed therapies consider the possibility of dynamic expression of mesothelin in benign lung with a special concern for patients with underlying inflammatory or fibrotic conditions.

Type I Interferon Signaling via the EGR2 Transcriptional Regulator Potentiates CAR T Cell-Intrinsic Dysfunction

Chimeric antigen receptor (CAR) T cell therapy has shown promise in treating hematologic cancers, but resistance is common and efficacy is limited in solid tumors. We found that CAR T cells autonomously propagate epigenetically programmed type I interferon signaling through chronic stimulation, which hampers antitumor function. EGR2 transcriptional regulator knockout not only blocks this type I interferon-mediated inhibitory program but also independently expands early memory CAR T cells with improved efficacy against liquid and solid tumors. The protective effect of EGR2 deletion in CAR T cells against chronic antigen-induced exhaustion can be overridden by interferon-β exposure, suggesting that EGR2 ablation suppresses dysfunction by inhibiting type I interferon signaling. Finally, a refined EGR2 gene signature is a biomarker for type I interferon-associated CAR T cell failure and shorter patient survival. These findings connect prolonged CAR T cell activation with deleterious immunoinflammatory signaling and point to an EGR2-type I interferon axis as a therapeutically amenable biological system.

SIGNIFICANCE

To improve CAR T cell therapy outcomes, modulating molecular determinants of CAR T cell-intrinsic resistance is crucial. Editing the gene encoding the EGR2 transcriptional regulator renders CAR T cells impervious to type I interferon pathway-induced dysfunction and improves memory differentiation, thereby addressing major barriers to progress for this emerging class of cancer immunotherapies. This article is highlighted in the In This Issue feature, p. 1501.

Tissue-resident memory CAR T cells with stem-like characteristics display enhanced efficacy against solid and liquid tumors

Chimeric antigen receptor (CAR) T cells demonstrate remarkable success in treating hematological malignancies, but their effectiveness in non-hematopoietic cancers remains limited. This study proposes enhancing CAR T cell function and localization in solid tumors by modifying the epigenome governing tissue-residency adaptation and early memory differentiation. We identify that a key factor in human tissue-resident memory CAR T cell (CAR-T_RM) formation is activation in the presence of the pleotropic cytokine, transforming growth factor β (TGF-β), which enforces a core program of both "stemness" and sustained tissue residency by mediating chromatin remodeling and concurrent transcriptional changes. This approach leads to a practical and clinically actionable in vitro production method for engineering peripheral blood T cells into a large number of "stem-like" CAR-T_RM cells resistant to tumor-associated dysfunction, possessing an enhanced ability to accumulate in situ and rapidly eliminate cancer cells for more effective immunotherapy.

Phase I Trial of Autologous RNA-electroporated cMET-directed CAR T Cells Administered Intravenously in Patients with Melanoma and Breast Carcinoma

Purpose

Treatments are limited for metastatic melanoma and metastatic triple-negative breast cancer (mTNBC). This pilot phase I trial (NCT03060356) examined the safety and feasibility of intravenous RNA-electroporated chimeric antigen receptor (CAR) T cells targeting the cell-surface antigen cMET.

Experimental Design

Metastatic melanoma or mTNBC subjects had at least 30% tumor expression of cMET, measurable disease and progression on prior therapy. Patients received up to six infusions (1 × 10e8 T cells/dose) of CAR T cells without lymphodepleting chemotherapy. Forty-eight percent of prescreened subjects met the cMET expression threshold. Seven (3 metastatic melanoma, 4 mTNBC) were treated.

Results

Mean age was 50 years (35-64); median Eastern Cooperative Oncology Group 0 (0-1); median prior lines of chemotherapy/immunotherapy were 4/0 for TNBC and 1/3 for melanoma subjects. Six patients experienced grade 1 or 2 toxicity. Toxicities in at least 1 patient included anemia, fatigue, and malaise. One subject had grade 1 cytokine release syndrome. No grade 3 or higher toxicity, neurotoxicity, or treatment discontinuation occurred. Best response was stable disease in 4 and disease progression in 3 subjects. mRNA signals corresponding to CAR T cells were detected by RT-PCR in all patients' blood including in 3 subjects on day +1 (no infusion administered on this day). Five subjects underwent postinfusion biopsy with no CAR T-cell signals seen in tumor. Three subjects had paired tumor tissue; IHC showed increases in CD8 and CD3 and decreases in pS6 and Ki67.

Conclusions

Intravenous administration of RNA-electroporated cMET-directed CAR T cells is safe and feasible.

Significance

Data evaluating CAR T therapy in patients with solid tumors are limited. This pilot clinical trial demonstrates that intravenous cMET-directed CAR T-cell therapy is safe and feasible in patients with metastatic melanoma and metastatic breast cancer, supporting the continued evaluation of cellular therapy for patients with these malignancies.

Anti-BCMA/CD19 CAR T Cells with Early Immunomodulatory Maintenance for Multiple Myeloma Responding to Initial or Later-Line Therapy

We conducted a phase I clinical trial of anti-BCMA chimeric antigen receptor T cells (CART-BCMA) with or without anti-CD19 CAR T cells (huCART19) in multiple myeloma (MM) patients responding to third- or later-line therapy (phase A, N = 10) or high-risk patients responding to first-line therapy (phase B, N = 20), followed by early lenalidomide or pomalidomide maintenance. We observed no high-grade cytokine release syndrome (CRS) and only one instance of low-grade neurologic toxicity. Among 15 subjects with measurable disease, 10 exhibited partial response (PR) or better; among 26 subjects responding to prior therapy, 9 improved their response category and 4 converted to minimal residual disease (MRD)-negative complete response/stringent complete response. Early maintenance therapy was safe, feasible, and coincided in some patients with CAR T-cell reexpansion and late-onset, durable clinical response. Outcomes with CART-BCMA + huCART19 were similar to CART-BCMA alone. Collectively, our results demonstrate favorable safety, pharmacokinetics, and antimyeloma activity of dual-target CAR T-cell therapy in early lines of MM treatment.

SIGNIFICANCE

CAR T cells in early lines of MM therapy could be safer and more effective than in the advanced setting, where prior studies have focused. We evaluated the safety, pharmacokinetics, and efficacy of CAR T cells in patients with low disease burden, responding to current therapy, combined with standard maintenance therapy. This article is highlighted in the In This Issue feature, p. 101.

BLIMP1 and NR4A3 transcription factors reciprocally regulate antitumor CAR T cell stemness and exhaustion

Chimeric antigen receptor (CAR) T cells have not induced meaningful clinical responses in solid tumors. Loss of T cell stemness, poor expansion capacity, and exhaustion during prolonged tumor antigen exposure are major causes of CAR T cell therapeutic resistance. Single-cell RNA-sequencing analysis of CAR T cells from a first-in-human trial in metastatic prostate cancer identified two independently validated cell states associated with antitumor potency or lack of efficacy. Low expression of PRDM1, encoding the BLIMP1 transcription factor, defined highly potent TCF7 [encoding T cell factor 1 (TCF1)]-expressing CD8⁺ CAR T cells, whereas enrichment of HAVCR2 [encoding T cell immunoglobulin and mucin-domain containing-3 (TIM-3)]-expressing CD8⁺ T cells with elevated PRDM1 was associated with poor outcomes. PRDM1 knockout promoted TCF7-dependent CAR T cell stemness and proliferation, resulting in marginally enhanced leukemia control in mice. However, in the setting of PRDM1 deficiency, a negative epigenetic feedback program of nuclear factor of activated T cells (NFAT)-driven T cell dysfunction was identified. This program was characterized by compensatory up-regulation of NR4A3 and other genes encoding exhaustion-related transcription factors that hampered T cell effector function in solid tumors. Dual knockout of PRDM1 and NR4A3 skewed CAR T cell phenotypes away from TIM-3⁺CD8⁺ and toward TCF1⁺CD8⁺ to counter exhaustion of tumor-infiltrating CAR T cells and improve antitumor responses, effects that were not achieved with PRDM1 and NR4A3 single knockout alone. These data underscore dual targeting of PRDM1 and NR4A3 as a promising approach to advance adoptive cell immuno-oncotherapy.

Abstract 5571: Disruption of cell-intrinsic checkpoint regulator CTLA-4 in CD19 directed CAR T cells provides clinical efficacy in CLL patients

The field of cancer immunotherapy has led to successful treatments such as monoclonal antibodies (MAb), inhibitory receptor (IR) blockade, and adoptive cell transfer (ACT). ACT modified to express chimeric antigen receptors (CARs) can redirect T cells to tumor antigens and has shown remarkable clinical efficacy in patients with relapse and refractory leukemia and lymphoma. 90% of pediatric patients with acute lymphoblastic leukemia (ALL) respond to CD19 CAR T cell therapy (CAR T19), although only 26-35% of patients with chronic lymphocytic leukemia (CLL) show complete responses (CR). It is unclear why responses are less frequent in CLL compared to ALL. The heavy pre-treatment received by CLL patients likely contributes to lower response rates with CAR T cell therapy, and disease progression is worsened due to profound T cell defects characterized by elevated expression of IRs such as PD-1 and CTLA-4. Fraietta et. al. assessed CLL patient apheresis samples and CART19 products to show that CR was associated with elevated levels of CD27+PD1-CD8+ T memory cells whereas the non-responders (NR) showed an exhausted phenotype with high levels of multiple IRs. We studied 14 patients with advanced, heavily pretreated CLL who received at least one dose of CART19. Patients with CRs exhibited high in vivo expansion and persistence of infused CAR T cells, as opposed to NR’s. Importantly, at peak levels of in vivo CAR expansion, NR’s had elevated levels of CTLA-4 expression which correlated with poor CLL patient responses to CART19 therapy. In summary, these data suggest that eliminating CTLA-4 mediated T cell inhibition can be clinically beneficial. Thus, we tested the hypothesis that disruption of CTLA4 would improve CAR T cell efficacy in CLL based on numerous observations. Our data demonstrate that knockout (KO) of CTLA-4 in T cells from healthy donors using CRISPR Cas9 technology leads to maintenance of surface CAR expression and higher tumor clearance in a chronic re-stimulation model using CART19 cells against NALM6 tumor cells. In xenograft models of ALL, KO of CTLA-4 increases the anti-tumor efficacy of CART19 cells. We then performed CTLA4 disruption in T cells banked from CLL patients that did not respond to CAR T cell therapy to determine whether dysfunctional CAR T infusion products can be invigorated by CTLA-4 KO. In both chronic re-stimulation model and xenograft models of NALM6, CTLA-4 KO CD19 CAR T cells from CLL patients maintained surface CAR expression, exhibited enhanced tumor clearance, and higher survival rates relative to subject-matched unedited CAR T cells. Thus, suggesting that CTLA4 disrupted CAR T cell products may enhance the success rate of CAR T cell therapy for CLL patients. This technology can be feasibly expanded to other tumor indications to increase the overall efficacy of CAR T cells. These IND-enabling studies will support the translation of this therapy to the clinic.

Citation Format: Sangya Agarwal, Angela Aznar Gomez, Tong Da, Shunichiro Kuramitsu, Weimin Kong, Pranali Ravikumar, Mercy Gohil, Megan M. Davis, Joseph A. Fraietta, Gabriela Plesa, David L. Porter, Regina M. Young, Carl H. June. Disruption of cell-intrinsic checkpoint regulator CTLA-4 in CD19 directed CAR T cells provides clinical efficacy in CLL patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5571.

431 First-in-human phase I clinical trial evaluating intraperitoneal administration of MOv19-BBz CAR T cells in patients with alpha folate receptor-expressing recurrent high grade serous ovarian cancer

Background

Most women with epithelial ovarian cancer develop uniformly incurable disease recurrence. Chimeric antigen receptor (CAR) T cells pair the MHC-independent tumor-recognition capabilities of monoclonal antibodies with the cytotoxicity of effector T cells. The success of CAR T cell therapy in solid tumors has been hindered by (1) difficulty identifying highly expressed, tumor-specific, cell surface target antigens; (2) limited trafficking and infiltration; and (3) suboptimal cytotoxic activity. Alpha folate receptor (FRα) is a transmembrane protein involved in cellular folate transport; expression has been reported in 80% of ovarian cancer, with limited physiologic expression on epithelial cells including bronchial, renal, and intestinal tissue. We hypothesize that intraperitoneal administration of alpha folate receptor (FRα) directed CAR T cells with dual 4-1BB and TCRzeta signaling domains will circumvent the above challenges and be safe, feasible, and elicit anti-tumor responses.

Methods

We initiated a first-in-human phase I clinical trial to evaluate the feasibility, safety and preliminary efficacy of intraperitoneal administration of FRα directed CAR T cells with and without antecedent lymphodepleting chemotherapy (LDC) in women with recurrent high grade serous ovarian cancer. The lentivirally-transduced CAR is composed of a MOv19 anti-FRα-specific single chain variable fragment fused to 4-1BB and TCRzeta signaling domains. Eligible patients have persistent or recurrent high grade serous epithelial ovarian, fallopian tube, or primary peritoneal carcinoma that is not platinum refractory and expresses ≥2+ FRα staining in ≥70% of tumor cells. Subjects must have an ECOG performance status 0–1, measurable disease, adequate hematologic and organ function, and must have progressed on at least two prior chemotherapy regimens for advanced disease. Patients undergo biopsy pre-infusion and Day +14 after infusion. After same-day placement of an intraperitoneal catheter by Interventional Radiology, CAR T cells are administered via a single infusion on three dose cohorts: Cohort 1 (starting cohort), 1–3x107/m2 cells without LDC; Cohort 2, 1–3x107/m2 CAR T cells after LDC; Cohort 3, 1–3x108/m2 cells after LDC. Catheter is removed after infusion. A 3+3 dose escalation design to determine maximum tolerated dose (MTD) yields approximately 9 to 18 subjects. The primary objective is safety and feasibility, and secondary objectives are anti-tumor response (endpoints: overall response rate based on RECIST v 1.1 and irRECIST when feasible, progression-free survival and overall survival). Correlative endpoints include CAR T cell engraftment and persistence in peripheral blood and body fluids examined via quantitative PCR of CAR T DNA, and bioactivity of CAR T cells. Enrollment is ongoing.

Trial Registration

This trial is registered at ClinicalTrials.gov (NCT03585764).

Ethics Approval

This study was approved by the Institutional Review Board at the University of Pennsylvania (IRB 830111). All subjects provided written informed consent prior to any study-related procedures.

A phase I clinical trial of PSMA-directed/TGFβ-insensitive CAR-T cells in metastatic castration-resistant prostate cancer

125

Background: Prostate specific membrane antigen (PSMA) is a highly expressed tumor-associated antigen potentially amenable to chimeric antigen receptor-modified T (CAR-T) cell therapy for castration-resistant prostate cancer (CRPC). However, a primary challenge to the success of CAR-T therapy in CRPC is the immunosuppressive microenvironment, characterized by high levels of TGFβ. The immunosuppressive functions of TGFβ can be inhibited in T cells using a dominant negative TGFβ receptor (TGFβRdn), thereby enhancing antitumor immunity. Methods: We conducted a first-in-human phase 1 clinical trial to evaluate the feasibility, safety and preliminary efficacy of PSMA-directed/TGFβ-insensitive CAR-T cells (CART-PSMA-TGFβRdn) in patients with metastatic CRPC (NCT03089203). In a 3+3 dose-escalation design, patients received a single dose of 1-3 x 107/m2 (Cohort 1) or 1-3 x 108/m2 (Cohort 2) CART-PSMA-TGFβRdn cells without lymphodepleting (LD) chemotherapy. In Cohort 3, one patient received 1-3 x 108/m2 CART-PSMA-TGFβRdn cells following a LD chemotherapy regimen of cyclophosphamide and fludarabine (Cy/Flu). In Cohort -3, three patients received 1-3 x 107/m2 CART-PSMA-TGFβRdn cells following Cy/Flu. Patients underwent metastatic tumor biopsies at baseline and on day 10 following treatment. Quantitative PCR of CART-PSMA-TGFβRdn DNA was performed at serial timepoints to evaluate for CAR-T expansion and persistence in peripheral blood and trafficking to target tissues. Multiplex cytokine analysis assessed CART-PSMA-TGFβRdn bioactivity. Results: Ten patients received CART-PSMA-TGFβRdn therapy across dose-level cohorts. All CART-PSMA-TGFβRdn infusion products met target transduction efficiency. Evaluation of CAR-T cellular kinetics demonstrated dose-dependent peripheral blood T cell expansion, as well as tumor tissue trafficking in post-treatment tumor biopsies. At Cohort 2 and above, 5 of 7 treated patients developed grade ≥2 cytokine release syndrome (CRS). Marked increases in inflammatory cytokines (IL-6, IL-15, IL-2, IFNγ) correlated with high-grade CRS events. One grade 5 adverse event (sepsis) occurred in Cohort 3. PSA decline was observed in 6 of 10 patients (median decline -33.2%, range -11.6% to -98.3%), and PSA30 response occurred in 4 of 10 patients (including one patient achieving PSA < 0.1 ng/mL). Conclusions: Adoptive cellular therapy with CART-PSMA-TGFβRdn is safe and feasible in patients with metastatic CRPC. A dose-dependent and lymphodepletion chemotherapy-dependent relationship was observed with CART-PSMA-TGFβRdn cell expansion, cytokine expression, CRS, and anti-tumor effect. Correlative cell trafficking and paired tumor Nanostring analyses will be presented. Future clinical investigations seek to enhance anti-tumor efficacy, while optimizing the therapeutic window. Clinical trial information: NCT03089203.

Autologous CD4 T Lymphocytes Modified with a Tat-Dependent, Virus-Specific Endoribonuclease Gene in HIV-Infected Individuals

MazF is an Escherichia coli-derived endoribonuclease that selectively cleaves ACA sequences of mRNA prevalent in HIV. We administered a single infusion of autologous CD4 T lymphocytes modified to express a Tat-dependent MazF transgene to 10 HIV-infected individuals (six remaining on antiretroviral therapy [ART]; four undergoing treatment interruption post-infusion) in order to provide a population of HIV-resistant immune cells. In participants who remained on ART, increases in CD4 and CD8 T cell counts of ~200 cells/mm3 each occurred within 2 weeks of infusion and persisted for at least 6 months. Modified cells were detectable for several months in the blood and trafficked to gastrointestinal lymph tissue. HIV-1 Tat introduced ex vivo to the modified CD4+ T cells induced MazF expression in both pre- and post-infusion samples, and MazF expression was detected in vivo post-viral-rebound during ATI. One participant experienced mild cytokine release syndrome. In sum, this study of a single infusion of MazF-modified CD4 T lymphocytes demonstrated safety of these cells, distribution to lymph tissue and maintenance of Tat-inducible MazF endoribonuclease activity, as well as sustained elevation of blood CD4 and CD8 T cell counts. Future studies to assess effects on viremia and latent proviral reservoir are warranted.

Phase I trial of autologous cMET-directed CAR-t cells administered intravenously in patients with melanoma & breast carcinoma

10035

Background: Advanced relapsed/refractory melanoma and metastatic triple-negative breast cancer are lethal diseases for which effective therapies are limited. We conducted a pilot phase I clinical trial (NCT03060356) to establish the safety and feasibility of intravenous autologous chimeric antigen receptor (CAR) T cell immunotherapy targeting cMET, a cell-surface antigen that is highly expressed in these cancers. Methods: Subjects had metastatic or unresectable melanoma (Mel) or triple-negative breast cancer (BC) with ≥30% expression of cMET on archival tissue or screening biopsy. Eligible subjects had measurable disease and progression on at least 1 prior therapy. Patients (pts) received up to 6 doses (1x108 total T-cells per dose) of RNA electroporated anti-cMET CAR T cells over a 2-week period without antecedent lymphodepleting chemotherapy. Subjects underwent pre- and post-infusion biopsies. The primary objective was to determine feasibility and safety of treatment. Results: 77 subjects (39 mel, 38 BC) were prescreened for tumor cMET expression and 37 (17 mel, 20 BC) met the eligibility threshold. Seven pts (4 BC, 3 Mel) received cMET-directed CAR T infusions on study. Mean age was 50 years (35-64); median (M) ECOG 0 (0-1); M prior lines of chemotherapy/immunotherapy were 4/0 for BC pts and 1/3 for Mel pts. 6 of 7 pts received all planned CAR T cell infusions, and 1 received 5 infusions. 5 pts experienced grade (G) 1 or G 2 toxicity that was possibly or definitely related to study. Toxicities occurring in ≥1 pt included: anemia (n = 3), fatigue (n = 2), and malaise (n = 2). No G ≥3 toxicities or cytokine release syndrome were observed. No pts discontinued therapy due to toxicity. Best response was stable disease in 4 pts (2 BC, 2 Mel) and PD in 3 pts (2 BC, 1 Mel). Messenger RNA signals corresponding to CAR T cells were detected by RT-PCR in the peripheral blood of all pts during the infusion period and in 2 pts after the infusion period. 6 pts underwent baseline biopsy and 4 pts underwent post-infusion biopsy. Immunohistochemical stains of CD3, CD4, CD8, CD163, L26, PD1, PDL1, Foxp3, Ki67, Granzyme B and Phospho-S6 were performed on pre- and post-treatment tissue biopsies and are being evaluated. Conclusions: Intravenous administration of RNA-electroporated cMET-directed CAR T cells was safe and feasible. Future directions include examination of this target using a lentiviral construct in combination with lymphodepleting chemotherapy. Clinical trial information: NCT03060356.

A phase I clinical trial of PSMA-directed/TGFβ-insensitive CAR-T cells in metastatic castration-resistant prostate cancer

TPS269

Background: Adoptive immunotherapy with Chimeric Antigen Receptor (CAR)-T cells is a novel approach for the treatment of prostate cancer. However, the prostate cancer immunosuppressive microenvironment, including high levels of TGFβ, may limit the therapeutic potential of re-directed T cells upon tumor infiltration. The inhibition of TGFβ signaling via co-expression of a dominant negative TGFβ receptor (TGFβRdn) can enhance antitumor immunity. Co-expression of TGFβRdn on PSMA-redirected CAR-T cells in in vivo disseminated tumor models led to increased T cell proliferation, enhanced cytokine secretion, resistance to exhaustion, long-term persistence, and greater induction of tumor eradication. Methods: We are conducting a first-in-human phase 1 clinical trial evaluating the safety and preliminary efficacy of lentivirally-transduced PSMA-redirected/TGFβ-insensitive CAR-T cells (CART-PSMA-TGFβRdn) in metastatic CRPC (NCT03089203). In a 3+3 dose-escalation design, patients received a single dose of 1-3 x 107/m2 (Cohort 1) or 1-3 x 108/m2 (Cohort 2) CART-PSMA-TGFβRdn cells without lymphodepleting chemotherapy. In Cohort 3, 1-3 x 108/m2 CART-PSMA-TGFβRdn cells are administered following a lymphodepleting chemotherapy regimen of cyclophosphamide and fludarabine (cy/flu). A currently accruing modified protocol seeks to optimize the therapeutic window with CART-PSMA-TGFβRdn (CAR-T dose of 1-3 x 107/m2 following lymphodepleting cy/flu). Eight patients have received a single dose of CART-PSMA-TGFβRdn. CAR-T expansion and persistence in peripheral blood and trafficking to target tissues is evaluated via quantitative PCR of CART-PSMA-TGFβRdn DNA. Bioactivity of CAR-T cells in peripheral blood is evaluated via multiplex immunoassays. Additional correlative analyses will interrogate the therapeutic contribution of TGFβRdn, as well as early markers of response and resistance to CART-PSMA-TGFβRdn therapy. Clinical trial information: NCT03089203.

CRISPR-engineered T cells in patients with refractory cancer

CRISPR-Cas9 gene editing provides a powerful tool to enhance the natural ability of human T cells to fight cancer. We report a first-in-human phase 1 clinical trial to test the safety and feasibility of multiplex CRISPR-Cas9 editing to engineer T cells in three patients with refractory cancer. Two genes encoding the endogenous T cell receptor (TCR) chains, TCRα (TRAC) and TCRβ (TRBC), were deleted in T cells to reduce TCR mispairing and to enhance the expression of a synthetic, cancer-specific TCR transgene (NY-ESO-1). Removal of a third gene encoding programmed cell death protein 1 (PD-1; PDCD1), was performed to improve antitumor immunity. Adoptive transfer of engineered T cells into patients resulted in durable engraftment with edits at all three genomic loci. Although chromosomal translocations were detected, the frequency decreased over time. Modified T cells persisted for up to 9 months, suggesting that immunogenicity is minimal under these conditions and demonstrating the feasibility of CRISPR gene editing for cancer immunotherapy.

Phase I Study of Lentiviral-Transduced Chimeric Antigen Receptor-Modified T Cells Recognizing Mesothelin in Advanced Solid Cancers

This phase I study investigated the safety and activity of lentiviral-transduced chimeric antigen receptor (CAR)-modified autologous T cells redirected against mesothelin (CART-meso) in patients with malignant pleural mesothelioma, ovarian carcinoma, and pancreatic ductal adenocarcinoma. Fifteen patients with chemotherapy-refractory cancer (n = 5 per indication) were treated with a single CART-meso cell infusion. CART-meso cells were engineered by lentiviral transduction with a construct composed of the anti-mesothelin single-chain variable fragment derived from the mouse monoclonal antibody SS1 fused to intracellular signaling domains of 4-1BB and CD3zeta. Patients received 1-3 × 10⁷ or 1-3 × 10⁸ CART-meso cells/m² with or without 1.5 g/m² cyclophosphamide. Lentiviral-transduced CART-meso cells were well tolerated; one dose-limiting toxicity (grade 4, sepsis) occurred at 1-3 × 10⁷/m² CART-meso without cyclophosphamide. The best overall response was stable disease (11/15 patients). CART-meso cells expanded in the blood and reached peak levels by days 6-14 but persisted transiently. Cyclophosphamide pre-treatment enhanced CART-meso expansion but did not improve persistence beyond 28 days. CART-meso DNA was detected in 7/10 tumor biopsies. Human anti-chimeric antibodies (HACA) were detected in the blood of 8/14 patients. CART-meso cells were well tolerated and expanded in the blood of all patients but showed limited clinical activity. Studies evaluating a fully human anti-mesothelin CAR are ongoing.

CRISPR/Cas9-based genome editing in the era of CAR T cell immunotherapy

The advent of engineered T cells as a form of immunotherapy marks the beginning of a new era in medicine, providing a transformative way to combat complex diseases such as cancer. Following FDA approval of CAR T cells directed against the CD19 protein for the treatment of acute lymphoblastic leukemia and diffuse large B cell lymphoma, CAR T cells are poised to enter mainstream oncology. Despite this success, a number of patients are unable to receive this therapy due to inadequate T cell numbers or rapid disease progression. Furthermore, lack of response to CAR T cell treatment is due in some cases to intrinsic autologous T cell defects and/or the inability of these cells to function optimally in a strongly immunosuppressive tumor microenvironment. We describe recent efforts to overcome these limitations using CRISPR/Cas9 technology, with the goal of enhancing potency and increasing the availability of CAR-based therapies. We further discuss issues related to the efficiency/scalability of CRISPR/Cas9-mediated genome editing in CAR T cells and safety considerations. By combining the tools of synthetic biology such as CARs and CRISPR/Cas9, we have an unprecedented opportunity to optimally program T cells and improve adoptive immunotherapy for most, if not all future patients.

B cell maturation antigen-specific CAR T cells are clinically active in multiple myeloma

BACKGROUND

Chimeric antigen receptor (CAR) T cells are a promising therapy for hematologic malignancies. B-cell maturation antigen (BCMA) is a rational target in multiple myeloma (MM).

METHODS

We conducted a phase I study of autologous T cells lentivirally-transduced with a fully-human, BCMA-specific CAR containing CD3ζ and 4-1BB signaling domains (CART-BCMA), in subjects with relapsed/refractory MM. Twenty-five subjects were treated in 3 cohorts: 1) 1-5 x 108 CART-BCMA cells alone; 2) Cyclophosphamide (Cy) 1.5 g/m2 + 1-5 x 107 CART-BCMA cells; and 3) Cy 1.5 g/m2 + 1-5 x 108 CART-BCMA cells. No pre-specified BCMA expression level was required.

RESULTS

CART-BCMA cells were manufactured and expanded in all subjects. Toxicities included cytokine release syndrome and neurotoxicity, which were grade 3-4 in 8 (32%) and 3 (12%) subjects, respectively, and reversible. One subject died at day 24 from candidemia and progressive myeloma, following treatment for severe CRS and encephalopathy. Responses (based on treated subjects) were seen in 4/9 (44%) in cohort 1, 1/5 (20%) in cohort 2, and 7/11 (64%) in cohort 3, including 5 partial, 5 very good partial, and 2 complete responses, 3 of which were ongoing at 11, 14, and 32 months. Decreased BCMA expression on residual MM cells was noted in responders; expression increased at progression in most. Responses and CART-BCMA expansion were associated with CD4:CD8 T cell ratio and frequency of CD45RO-CD27+CD8+ T cells in the pre-manufacturing leukapheresis product.

CONCLUSION

CART-BCMA infusions with or without lymphodepleting chemotherapy are clinically active in heavily-pretreated MM patients.

TRIAL REGISTRATION

NCT02546167.

FUNDING

University of Pennsylvania-Novartis Alliance and NIH.

A phase I clinical trial of PSMA-directed/TGFβ-insensitive CAR-T cells in metastatic castration-resistant prostate cancer

TPS347

Background: Adoptive immunotherapy with Chimeric Antigen Receptor (CAR)-T cells has transformative potential for the treatment of cancer. However, a primary challenge to the success of these therapies in prostate cancer is the immunosuppressive microenvironment, including high levels of Transforming Growth Factor-beta (TGFβ), encountered by re-directed T cells upon tumor infiltration. Importantly, these immunosuppressive functions of TGFβ can be abrogated in T cells using a dominant negative TGFβ receptor (TGFβRdn), thereby enhancing antitumor immunity. In in vivo disseminated prostate cancer models, co-expression of TGFβRdn on PSMA-redirected CAR-T cells led to increased T cell proliferation, enhanced cytokine secretion, resistance to exhaustion, long-term persistence, and greater tumor eradication. Methods: We initiated a first-in-human phase 1 clinical trial to evaluate the safety and preliminary efficacy of lentivirally-transduced PSMA-directed/TGFβ-insensitive CAR-T cells (CART-PSMA-TGFβRdn) in men with metastatic CRPC. In preliminary dose-escalation cohorts, patients received a single dose of 1-3 x 107/m2 (Cohort 1) or 1-3 x 108/m2 (Cohort 2) CART-PSMA-TGFβRdn cells without lymphodepleting chemotherapy in a 3+3 design. In Cohort 3, patients will receive the MTD of CART-PSMA-TGFβRdn following a lymphodepleting regimen of cyclophosphamide and fludarabine. All patients provide newly obtained metastatic tumor biopsies at baseline, as well as on day +10 following the CAR-T cell infusion and at disease progression. CAR-T expansion and persistence in peripheral blood and trafficking to target tissues is evaluated via quantitative PCR of CART-PSMA-TGFβRdn DNA. Bioactivity of CART-PSMA-TGFβRdn cells is evaluated via multiplex immunoassays. Additional correlative studies include enumeration and phenotyping of circulating tumor cells and DNA. Cohorts 1 and 2 have been completed without observed DLT. Interestingly, a reversible cytokine release syndrome has been observed that is responsive to tocilizumab. Enrollment in Cohort 3 began in September 2018. Cohort expansions will examine serial CART-PSMA-TGFβRdn re-treatment strategies. Clinical trial information: NCT03089203.

Multiparametric magnetic resonance imaging in the assessment of anti-EGFRvIII chimeric antigen receptor T cell therapy in patients with recurrent glioblastoma

EGFRvIII targeted chimeric antigen receptor T (CAR-T) cell therapy has recently been reported for treating glioblastomas (GBMs); however, physiology-based MRI parameters have not been evaluated in this setting. Ten patients underwent multiparametric MRI at baseline, 1, 2 and 3 months after CAR-T therapy. Logistic regression model derived progression probabilities (PP) using imaging parameters were used to assess treatment response. Four lesions from "early surgery" group demonstrated high PP at baseline suggestive of progression, which was confirmed histologically. Out of eight lesions from remaining six patients, three lesions with low PP at baseline remained stable. Two lesions with high PP at baseline were associated with large decreases in PP reflecting treatment response, whereas other two lesions with high PP at baseline continued to demonstrate progression. One patient didn't have baseline data but demonstrated progression on follow-up. Our findings indicate that multiparametric MRI may be helpful in monitoring CAR-T related early therapeutic changes in GBM patients.

Activity of Mesothelin-Specific Chimeric Antigen Receptor T Cells Against Pancreatic Carcinoma Metastases in a Phase 1 Trial

Pancreatic ductal adenocarcinoma (PDAC) is resistant to T-cell-mediated immunotherapy. We engineered T cells to transiently express a messenger RNA encoding a chimeric antigen receptor (CAR) specific for mesothelin, a protein that is overexpressed by PDAC cells. We performed a phase I study to evaluate the safety and efficacy of adoptive cell therapy with autologous mesothelin-specific CAR T cells (CARTmeso cells) in 6 patients with chemotherapy-refractory metastatic PDAC. Patients were given intravenous CARTmeso cells 3 times weekly for 3 weeks. None of the patients developed cytokine release syndrome or neurologic symptoms and there were no dose-limiting toxicities. Disease stabilized in 2 patients, with progression-free survival times of 3.8 and 5.4 months. We used ¹⁸F-2-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography/computed tomography imaging to monitor the metabolic active volume (MAV) of individual tumor lesions. The total MAV remained stable in 3 patients and decreased by 69.2% in 1 patient with biopsy-proven mesothelin expression; in this patient, all liver lesions had a complete reduction in FDG uptake at 1 month compared with baseline, although there was no effect on the primary PDAC. Transient CAR expression was detected in patients' blood after infusion and led to expansion of new immunoglobulin G proteins. Our results provide evidence for the potential antitumor activity of messenger RNA CARTmeso cells, as well as PDAC resistance to the immune response.

A single dose of peripherally infused EGFRvIII-directed CAR T cells mediates antigen loss and induces adaptive resistance in patients with recurrent glioblastoma

We conducted a first-in-human study of intravenous delivery of a single dose of autologous T cells redirected to the epidermal growth factor receptor variant III (EGFRvIII) mutation by a chimeric antigen receptor (CAR). We report our findings on the first 10 recurrent glioblastoma (GBM) patients treated. We found that manufacturing and infusion of CAR-modified T cell (CART)-EGFRvIII cells are feasible and safe, without evidence of off-tumor toxicity or cytokine release syndrome. One patient has had residual stable disease for over 18 months of follow-up. All patients demonstrated detectable transient expansion of CART-EGFRvIII cells in peripheral blood. Seven patients had post-CART-EGFRvIII surgical intervention, which allowed for tissue-specific analysis of CART-EGFRvIII trafficking to the tumor, phenotyping of tumor-infiltrating T cells and the tumor microenvironment in situ, and analysis of post-therapy EGFRvIII target antigen expression. Imaging findings after CART immunotherapy were complex to interpret, further reinforcing the need for pathologic sampling in infused patients. We found trafficking of CART-EGFRvIII cells to regions of active GBM, with antigen decrease in five of these seven patients. In situ evaluation of the tumor environment demonstrated increased and robust expression of inhibitory molecules and infiltration by regulatory T cells after CART-EGFRvIII infusion, compared to pre-CART-EGFRvIII infusion tumor specimens. Our initial experience with CAR T cells in recurrent GBM suggests that although intravenous infusion results in on-target activity in the brain, overcoming the adaptive changes in the local tumor microenvironment and addressing the antigen heterogeneity may improve the efficacy of EGFRvIII-directed strategies in GBM.

Safety and Efficacy of Intratumoral Injections of Chimeric Antigen Receptor (CAR) T Cells in Metastatic Breast Cancer

Chimeric antigen receptors (CAR) are synthetic molecules that provide new specificities to T cells. Although successful in treatment of hematologic malignancies, CAR T cells are ineffective for solid tumors to date. We found that the cell-surface molecule c-Met was expressed in ∼50% of breast tumors, prompting the construction of a CAR T cell specific for c-Met, which halted tumor growth in immune-incompetent mice with tumor xenografts. We then evaluated the safety and feasibility of treating metastatic breast cancer with intratumoral administration of mRNA-transfected c-Met-CAR T cells in a phase 0 clinical trial (NCT01837602). Introducing the CAR construct via mRNA ensured safety by limiting the nontumor cell effects (on-target/off-tumor) of targeting c-Met. Patients with metastatic breast cancer with accessible cutaneous or lymph node metastases received a single intratumoral injection of 3 × 10⁷ or 3 × 10⁸ cells. CAR T mRNA was detectable in peripheral blood and in the injected tumor tissues after intratumoral injection in 2 and 4 patients, respectively. mRNA c-Met-CAR T cell injections were well tolerated, as none of the patients had study drug-related adverse effects greater than grade 1. Tumors treated with intratumoral injected mRNA c-Met-CAR T cells were excised and analyzed by immunohistochemistry, revealing extensive tumor necrosis at the injection site, cellular debris, loss of c-Met immunoreactivity, all surrounded by macrophages at the leading edges and within necrotic zones. We conclude that intratumoral injections of mRNA c-Met-CAR T cells are well tolerated and evoke an inflammatory response within tumors. Cancer Immunol Res; 5(12); 1152-61. ©2017 AACR.

Overcoming barriers of car T-cell therapy in patients with mesothelin-expressing cancers

One obstacle to the application of immunotherapy to solid malignancies is to overcome the existing tolerance to self-antigens. Vaccine strategies aimed at harnessing endogenous antitumor T cells are limited by the T-cell receptor repertoire, which can be detected within the thymus as central tolerance or rendered nonfunctional by post-thymic mechanisms of peripheral tolerance. Adoptive immunotherapy can overcome these obstacles, since therapeutically effective T cells can be engineered to recognize tumors. Continued advancements in novel treatments, including immunotherapy, in solid malignancies are imperative. While mesothelin is an attractive target for cancer immunotherapy given its normal expression is limited to mesothelial cells, the breakthrough for chimeric antigen receptor T-cell treatment against this antigen is still forthcoming.

Effect of chimeric antigen receptor (CAR) T cells on clonal expansion of endogenous non-CAR T cells in patients (pts) with advanced solid cancer

3011

Background: CAR T cells have produced remarkable responses in heme malignancies, but efficacy in solid cancers is limited. Poor in vivo persistence and heterogeneous expression of the CAR target on tumors are potential barriers to the success of CAR T cell therapy. However, even with transient persistence, CAR T cells may elicit a “vaccine” effect by inducing cancer cell death and subsequent release of tumor antigens that could stimulate tumor-specific T cell activity. Methods: 6 pts with pancreatic ductal adenocarcinoma (PDAC) received repeated 3x per week intravenous (iv) infusions of mRNA-transfected mesothelin-redirected CAR T cells (CARTmeso). Pts with PDAC (n = 5), ovarian carcinoma (n = 5), and mesothelioma (n = 5) received iv infusion of lentiviral-transduced (lenti) CARTmeso with or without cyclophosphamide (Cy) preconditioning. Peripheral blood samples were collected from pts at baseline and defined time points after treatment. Genomic DNA from these samples or from pre-infused CAR T cell product was used for deep sequencing of the TCRbeta chain using the ImmunoSEQ platform. A TCRbeta clone was considered to have expanded from baseline to defined time points after treatment if it showed a two-fold change from baseline and met statistical significance by Fisher’s exact test (p < 0.05). Results: mRNA CARTmeso cells persisted in vivo for < 24 hrs. Unexpectedly, therapy induced clonal T cell expansion detected in the blood by day 14 in all 6 pts. Expanded clones underwent contraction by day 28 in 3 pts. In one pt, peripherally expanded clones were also detected in a tumor biopsy, but without significant intratumoral clonal expansion. Lenti CARTmeso therapy also induced peripheral expansion of T cell clones both present and not present in the infused CAR T cell product. However, with Cy preconditioning, clonal expansion seen after lenti CARTmeso therapy was predominately restricted to clones detected in the CAR T cell product. Conclusions: In pts with advanced solid cancers, CARTmeso stimulates clonal expansion of endogenous T cells, which is lost with Cy conditioning. Findings suggest that CAR T cells may elicit a “vaccine” effect with potential therapeutic implications.

Abstract P6-10-08: Preliminary results of a first in human Phase 1 clinical trial to demonstrate safety and feasibility of chimeric antigen receptor T (CART) cells directed against c-Met in the treatment of breast cancer

This abstract was withdrawn by the authors.

Rational development and characterization of humanized anti-EGFR variant III chimeric antigen receptor T cells for glioblastoma

Chimeric antigen receptors (CARs) are synthetic molecules designed to redirect T cells to specific antigens. CAR-modified T cells can mediate long-term durable remissions in B cell malignancies, but expanding this platform to solid tumors requires the discovery of surface targets with limited expression in normal tissues. The variant III mutation of the epidermal growth factor receptor (EGFRvIII) results from an in-frame deletion of a portion of the extracellular domain, creating a neoepitope. We chose a vector backbone encoding a second-generation CAR based on efficacy of a murine scFv-based CAR in a xenograft model of glioblastoma. Next, we generated a panel of humanized scFvs and tested their specificity and function as soluble proteins and in the form of CAR-transduced T cells; a low-affinity scFv was selected on the basis of its specificity for EGFRvIII over wild-type EGFR. The lead candidate scFv was tested in vitro for its ability to direct CAR-transduced T cells to specifically lyse, proliferate, and secrete cytokines in response to antigen-bearing targets. We further evaluated the specificity of the lead CAR candidate in vitro against EGFR-expressing keratinocytes and in vivo in a model of mice grafted with normal human skin. EGFRvIII-directed CAR T cells were also able to control tumor growth in xenogeneic subcutaneous and orthotopic models of human EGFRvIII(+) glioblastoma. On the basis of these results, we have designed a phase 1 clinical study of CAR T cells transduced with humanized scFv directed to EGFRvIII in patients with either residual or recurrent glioblastoma (NCT02209376).

Mesothelin-specific chimeric antigen receptor mRNA-engineered T cells induce anti-tumor activity in solid malignancies

Off-target toxicity due to the expression of target antigens in normal tissue represents a major obstacle to the use of chimeric antigen receptor (CAR)-engineered T cells for treatment of solid malignancies. To circumvent this issue, we established a clinical platform for engineering T cells with transient CAR expression by using in vitro transcribed mRNA encoding a CAR that includes both the CD3-ζ and 4-1BB co-stimulatory domains. We present two case reports from ongoing trials indicating that adoptive transfer of mRNA CAR T cells that target mesothelin (CARTmeso cells) is feasible and safe without overt evidence of off-tumor on-target toxicity against normal tissues. CARTmeso cells persisted transiently within the peripheral blood after intravenous administration and migrated to primary and metastatic tumor sites. Clinical and laboratory evidence of antitumor activity was demonstrated in both patients and the CARTmeso cells elicited an antitumor immune response revealed by the development of novel anti-self antibodies. These data demonstrate the potential of utilizing mRNA engineered T cells to evaluate, in a controlled manner, potential off-tumor on-target toxicities and show that short-lived CAR T cells can induce epitope-spreading and mediate antitumor activity in patients with advanced cancer. Thus, these findings support the development of mRNA CAR-based strategies for carcinoma and other solid tumors.

Identification of a Titin-derived HLA-A1-presented peptide as a cross-reactive target for engineered MAGE A3-directed T cells

MAGE A3, which belongs to the family of cancer-testis antigens, is an attractive target for adoptive therapy given its reactivation in various tumors and limited expression in normal tissues. We developed an affinity-enhanced T cell receptor (TCR) directed to a human leukocyte antigen (HLA)-A*01-restricted MAGE A3 antigen (EVDPIGHLY) for use in adoptive therapy. Extensive preclinical investigations revealed no off-target antigen recognition concerns; nonetheless, administration to patients of T cells expressing the affinity-enhanced MAGE A3 TCR resulted in a serious adverse event (SAE) and fatal toxicity against cardiac tissue. We present a description of the preclinical in vitro functional analysis of the MAGE A3 TCR, which failed to reveal any evidence of off-target activity, and a full analysis of the post-SAE in vitro investigations, which reveal cross-recognition of an off-target peptide. Using an amino acid scanning approach, a peptide from the muscle protein Titin (ESDPIVAQY) was identified as an alternative target for the MAGE A3 TCR and the most likely cause of in vivo toxicity. These results demonstrate that affinity-enhanced TCRs have considerable effector functions in vivo and highlight the potential safety concerns for TCR-engineered T cells. Strategies such as peptide scanning and the use of more complex cell cultures are recommended in preclinical studies to mitigate the risk of off-target toxicity in future clinical investigations.

Gene editing of CCR5 in autologous CD4 T cells of persons infected with HIV

BACKGROUND

CCR5 is the major coreceptor for human immunodeficiency virus (HIV). We investigated whether site-specific modification of the gene ("gene editing")--in this case, the infusion of autologous CD4 T cells in which the CCR5 gene was rendered permanently dysfunctional by a zinc-finger nuclease (ZFN)--is safe.

METHODS

We enrolled 12 patients in an open-label, nonrandomized, uncontrolled study of a single dose of ZFN-modified autologous CD4 T cells. The patients had chronic aviremic HIV infection while they were receiving highly active antiretroviral therapy. Six of them underwent an interruption in antiretroviral treatment 4 weeks after the infusion of 10 billion autologous CD4 T cells, 11 to 28% of which were genetically modified with the ZFN. The primary outcome was safety as assessed by treatment-related adverse events. Secondary outcomes included measures of immune reconstitution and HIV resistance.

RESULTS

One serious adverse event was associated with infusion of the ZFN-modified autologous CD4 T cells and was attributed to a transfusion reaction. The median CD4 T-cell count was 1517 per cubic millimeter at week 1, a significant increase from the preinfusion count of 448 per cubic millimeter (P<0.001). The median concentration of CCR5-modified CD4 T cells at 1 week was 250 cells per cubic millimeter. This constituted 8.8% of circulating peripheral-blood mononuclear cells and 13.9% of circulating CD4 T cells. Modified cells had an estimated mean half-life of 48 weeks. During treatment interruption and the resultant viremia, the decline in circulating CCR5-modified cells (-1.81 cells per day) was significantly less than the decline in unmodified cells (-7.25 cells per day) (P=0.02). HIV RNA became undetectable in one of four patients who could be evaluated. The blood level of HIV DNA decreased in most patients.

CONCLUSIONS

CCR5-modified autologous CD4 T-cell infusions are safe within the limits of this study. (Funded by the National Institute of Allergy and Infectious Diseases and others; ClinicalTrials.gov number, NCT00842634.).

Efficient clinical scale gene modification via zinc finger nuclease-targeted disruption of the HIV co-receptor CCR5

Since HIV requires CD4 and a co-receptor, most commonly C-C chemokine receptor 5 (CCR5), for cellular entry, targeting CCR5 expression is an attractive approach for therapy of HIV infection. Treatment of CD4(+) T cells with zinc-finger protein nucleases (ZFNs) specifically disrupting chemokine receptor CCR5 coding sequences induces resistance to HIV infection in vitro and in vivo. A chimeric Ad5/F35 adenoviral vector encoding CCR5-ZFNs permitted efficient delivery and transient expression following anti-CD3/anti-CD28 costimulation of T lymphocytes. We present data showing CD3/CD28 costimulation substantially improved transduction efficiency over reported methods for Ad5/F35 transduction of T lymphocytes. Modifications to the laboratory scale process, incorporating clinically compatible reagents and methods, resulted in a robust ex vivo manufacturing process capable of generating >10(10) CCR5 gene-edited CD4+ T cells from healthy and HIV+ donors. CD4+ T-cell phenotype, cytokine production, and repertoire were comparable between ZFN-modified and control cells. Following consultation with regulatory authorities, we conducted in vivo toxicity studies that showed no detectable ZFN-specific toxicity or T-cell transformation. Based on these findings, we initiated a clinical trial testing the safety and feasibility of CCR5 gene-edited CD4+ T-cell transfer in study subjects with HIV-1 infection.

Decade-long safety and function of retroviral-modified chimeric antigen receptor T cells

The success of adoptive T cell gene transfer for treatment of cancer and HIV is predicated on generating a response that is both durable and safe. We report long-term results from three clinical trials to evaluate gammaretroviral vector-engineered T cells for HIV. The vector encoded a chimeric antigen receptor (CAR) composed of CD4 linked to the CD3ζ signaling chain (CD4ζ). CAR T cells were detected in 98% of samples tested for at least 11 years after infusion at frequencies that exceeded average T cell levels after most vaccine approaches. The CD4ζ transgene retained expression and function. There was no evidence of vector-induced immortalization of cells; integration site distributions showed no evidence of persistent clonal expansion or enrichment for integration sites near genes implicated in growth control or transformation. The CD4ζ T cells had stable levels of engraftment, with decay half-lives that exceeded 16 years, in marked contrast to previous trials testing engineered T cells. These findings indicate that host immunosuppression before T cell transfer is not required to achieve long-term persistence of gene-modified T cells. Further, our results emphasize the safety of T cells modified by retroviral gene transfer in clinical application, as measured in >500 patient-years of follow-up. Thus, previous safety issues with integrating viral vectors are hematopoietic stem cell or transgene intrinsic, and not a general feature of retroviral vectors. Engineered T cells are a promising form of synthetic biology for long-term delivery of protein-based therapeutics. These results provide a framework to guide the therapy of a wide spectrum of human diseases.

Naturally occurring MHC class I restricted TCRs effectively redirect human T regulatory cells to suppress high affinity, polyfunctional CD8 T cell responses (52.8)

Because most autoimmune diseases exist in the periphery, we investigated whether MHC class I restricted TCRs could be used to re-direct expanded human Tregs in order to better target engineered Tregs to the site of the aberrant immune response. By taking advantage of a series of HLA-A2 restricted TCRs that recognize the same peptide-MHC class I (pMHC) with varying affinities, we observed augmenting TCR affinity had no effect on the ability of Tregs to function. In fact, MHC class I restricted TCRs that had limited activity in CD4+ T effector cells (Teff) were fully able to suppress the expansion of highly functional CD8 T cells expressing a high affinity TCR. These studies demonstrate that Tregs expressing naturally occurring, introduced MHC class I restricted TCRs have potent suppressive activity and further highlight the fundamental differences that exist between effector and regulatory T cells.

The inducible costimulator (ICOS) is critical for the development of human T(H)17 cells

Human T helper 17 (T(H)17) cells regulate host defense, autoimmunity, and tumor immunity. Although cytokines that control human T(H)17 cell development have been identified, the costimulatory molecules important for T(H)17 cell generation are unknown. Here, we found that the inducible costimulator (ICOS) was critical for the differentiation and expansion of human T(H)17 cells. Human cord blood contained a subset of CD161(+)CD4(+) T cells that were recent emigrants from the thymus, expressed ICOS constitutively, and were imprinted as T(H)17 cells through ICOS signaling. ICOS stimulation induced c-MAF, RORC2, and T-bet expression in these cells, leading to increased secretion of interleukin-21 (IL-21), IL-17, and interferon-γ (IFN-γ) compared with cells stimulated with CD28. Conversely, CD28 ligation abrogated ICOS costimulation, dampening RORC2 expression while promoting the expression of the aryl hydrocarbon receptor, which led to reduced secretion of IL-17 and enhanced production of IL-22 compared with cells stimulated with ICOS. Moreover, ICOS promoted the robust expansion of IL-17(+)IFN-γ(+) human T cells, and the antitumor activity of these cells after adoptive transfer into mice bearing large human tumors was superior to that of cells expanded with CD28. The therapeutic effectiveness of ICOS-expanded cells was associated with enhanced functionality and engraftment in vivo. These findings reveal a vital role for ICOS signaling in the generation and maintenance of human T(H)17 cells and suggest that components of this pathway could be therapeutically targeted to treat cancer or chronic infection and, conversely, that interruption of this pathway may have utility in multiple sclerosis and other autoimmune syndromes. These findings have provided the rationale for designing new clinical trials for tumor immunotherapy.

Steric shielding of surface epitopes and impaired immune recognition induced by the ebola virus glycoprotein

Many viruses alter expression of proteins on the surface of infected cells including molecules important for immune recognition, such as the major histocompatibility complex (MHC) class I and II molecules. Virus-induced downregulation of surface proteins has been observed to occur by a variety of mechanisms including impaired transcription, blocks to synthesis, and increased turnover. Viral infection or transient expression of the Ebola virus (EBOV) glycoprotein (GP) was previously shown to result in loss of staining of various host cell surface proteins including MHC1 and β1 integrin; however, the mechanism responsible for this effect has not been delineated. In the present study we demonstrate that EBOV GP does not decrease surface levels of β1 integrin or MHC1, but rather impedes recognition by steric occlusion of these proteins on the cell surface. Furthermore, steric occlusion also occurs for epitopes on the EBOV glycoprotein itself. The occluded epitopes in host proteins and EBOV GP can be revealed by removal of the surface subunit of GP or by removal of surface N- and O- linked glycans, resulting in increased surface staining by flow cytometry. Importantly, expression of EBOV GP impairs CD8 T-cell recognition of MHC1 on antigen presenting cells. Glycan-mediated steric shielding of host cell surface proteins by EBOV GP represents a novel mechanism for a virus to affect host cell function, thereby escaping immune detection.

The Ebola virus (EBOV) is a highly pathogenic virus that infects humans and non-human primates, causing severe disease or death in the majority of these cases. The interaction of this virus with its host on a cellular level is only just beginning to be understood. EBOV, like many viruses, affects the expression or function of several cell surface proteins, including adhesion factors and protein complexes responsible for allowing the immune system to recognize infected cells. Our group and others have previously shown that expression of the main viral glycoprotein of EBOV in cultured cells is sufficient to cause this disruption. Here we have identified the mechanism by which this disruption occurs. Heavily glycosylated domains of the EBOV glycoprotein form a steric shield over proteins at the cell surface. This steric interference blocks the detection of affected surface proteins using antibody reagents, but also has the functional effect of abrogating cell adhesion and preventing interactions with CD8 T cells. The results from this study highlight a novel mechanism for viral disruption of host cell surface protein functions and give insight to interactions between the Ebola virus and its host.

Abstract 5616: Soluble, high affinity TCRs fused to anti-CD3 redirect T cells to kill cancer cells presenting MAGE-A3 and NY-ESO antigens

In the last decade, major efforts in the fight against cancer have focussed on galvanising the adaptive immune system to kill tumours. Many of these endeavours are based on the development and clinical use of monoclonal antibodies (mAb) which are the most successful class of immune modulating agent identified to date. However, while mAbs show promise against certain cancers, their specificity is limited to integral membrane proteins; this hinders their extensive development for the purposes of targeting cancer cells.

In contrast to mAbs, T cell receptors (TCRs) recognise peptides bound to major histocompatibility complex class I (MHC I) molecules. These peptides are derived from endogenously processed proteins, and therefore represent a different repertoire of targets to those recognised by mAbs. This alternate spectrum of antigens provides the potential to target cancers using an untapped source of well-validated epitopes. Naturally occurring TCRs, however, have relatively low affinities for their antigen compared to antibody binding. Advances in engineering techniques have allowed the generation of high affinity monoclonal TCRs (mTCRs) with picomolar affinities for their antigen. Using targeted mutagenesis and phage display, we have generated a number of soluble, high affinity mTCRs specific for several reported tumour-associated antigens. Through mTCR fusion to an anti-CD3 single chain variable fragment (scfv), we produced bifunctional proteins that redirect T cell immune specificity. These novel proteins are termed ImmTACs (Immune-mobilising mTCRs Against Cancer). We present data demonstrating the potential of two such ImmTAC molecules, NY-ESO-ImmTAC and MAGE-A3-ImmTAC, to treat certain cancers. NY-ESO1 and MAGE-A3 are both cancer testes antigens and therefore represent potentially very clean molecular targets. We demonstrate that both NY-ESO-ImmTAC and MAGE-A3-ImmTAC are capable of potently redirecting unstimulated peripheral blood mononuclear cells (PBMC) or CD8+ T cells against multiple myeloma, colorectal carcinoma and non-small cell lung cancer cell lines despite the presentation of extremely low antigen numbers (&lt;100 epitopes/cell) on the surface of these cells. ImmTAC-redirected T cells respond with multiple effector functions including the production of granzyme B, IFNγ and IL-2, resulting in a high level of antigen-specific cancer cell killing over the course of 24 hours. The mechanism of killing is at least partly contributed by the caspase-3/7 apoptotic pathway. We also show that NY-ESO-ImmTAC and MAGE-A3-ImmTAC were inert by all our measures in the presence of normal primary cells including melanocytes, hepatocytes and astrocytes. Thus both MAGE-A3 and NY-ESO-ImmTACs possess the potential to be highly specific, potent cancer immunotherapies offering a targeting and therapeutic approach distinct from any other biologic in development.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5616.

HIV sequence variation associated with env antisense adoptive T-cell therapy in the hNSG mouse model

The first use of lentiviral vectors in humans involved transduction of mature T-cells with an human immunodeficiency virus (HIV)-derived env antisense (envAS) vector to protect cells from HIV infection. In that study, only a minority of the patient T-cell population could be gene-modified, raising the question of whether the altered cells could affect replicating HIV populations. We investigated this using humanized NOD/SCID IL-2Rgamma(null) (hNSG) mice reconstituted with approximately 4-11% envAS-modified human T-cells. Mice were challenged with HIV-1(NL4-3), which has an env perfectly complementary to envAS, or with HIV-1(BaL), which has a divergent env. No differences were seen in viral titer between mice that received envAS-modified cells and control mice that did not. Using 454/Roche pyrosequencing, we analyzed the mutational spectrum in HIV populations in serum-from 33 mice we recovered 84,074 total reads comprising 31,290 unique sequence variants. We found enrichment of A-to-G transitions and deletions in envAS-treated mice, paralleling a previous tissue culture study where most target cells contained envAS, even though minority of cells were envAS-modified here. Unexpectedly, this enrichment was only detected after the challenge with HIV-1(BaL), where the viral genome would form an imperfect duplex with envAS, and not HIV-1(NL4-3), where a perfectly matched duplex would form.

Derivation and fluidity of acutely induced dysfunctional CD8+ T cells

Dysfunctional CD8(+) T (T(CD8(+))) cells lacking cytokine production have been identified in many viral infections, but their genesis is not well understood. Established results indicate that such cells could be either high avidity that enter a refractory state due to overstimulation or low avidity that are only partially stimulated. Using an acute, resolving infection model that results in rapid production of dysfunctional cells, we show that this IL2 unresponsive phenotype emerges from the low end of the avidity spectrum and is characterized by broad TCR usage and a reduced proliferation rate. Furthermore, the dysfunctional population is extremely fluid, being sustained by high Ag dose but virtually eliminated following low dose boosting. Together, these results suggest that persistence of dysfunctional cells generated in this manner depends upon continual exposure to high Ag levels and that such cells may ultimately predominate if functional cells become exhausted.

Adoptive immunotherapy: good habits instilled at youth have long-term benefits

Many recent advances in basic cell biology and immunology are a harbinger of progress in adoptive cell therapy (ACT) including (1) the finding that host lymphodepletion enhances engraftment and efficacy, (2) the recognition that in vitro T cell functions may not correlate with in vivo efficacy, and (3) the development of advanced ex vivo culture methods to expand lymphocytes to therapeutically effective numbers. In this article, we focus on the development of artificial antigen presenting cells (aAPCs) in our laboratory and their applicability to augment ACT protocols. We also describe how aAPCs can be used to broaden ACT to treat patients with a wide variety of cancers, chronic infectious diseases, and autoimmune manifestations.

Immunogenicity of cytopathic and noncytopathic viral vectors

The impact of cytolytic versus noncytolytic viral infections on host responses is not well understood, due to limitations of the systems that have been used to address this issue. Using paired cytopathic and noncytopathic rabies viruses that differ by only two amino acids, we investigated several fundamental aspects of the immune response to these viral vectors. Greater cytopathic capacity translated into a greater degree of cross-priming to CD8(+) T cells (T(CD8)(+)) and more-robust short-term humoral and cellular responses. However, long-term responses to the two viruses were similar, suggesting that direct priming drives the bulk of the T(CD8)(+) antirabies response and that enhanced acute responses associated with greater virally mediated cellular destruction were balanced by other factors, such as prolonged antigen expression associated with noncytopathic virus. Such compensatory mechanisms may be in place to ensure comparable immunologic memories to various pathogens.