Abstract 2142: Immune determinants of CAR-T expansion in solid tumor patients receiving GD2 CAR-T cell therapy

Chimeric antigen receptor T cells (CAR-Ts) have demonstrated remarkable efficacy in leukemia and lymphomas but limited responses in solid tumors. We conducted a phase I trial (NCT02107963) of GD2 CAR-Ts (GD2-CAR.OX40.28.z.ICD9), demonstrating feasibility and safety of administering GD2 CAR-Ts in children and young adults with neuroblastoma and, for the first time, osteosarcoma. 15 patients aged 8-28 years were enrolled on four dose levels, of which 13 patients were infused. No dose-limiting toxicities were observed, and administration of up to 1x107 GD2-CAR-T/kg was feasible and safe for children and young adults with neuroblastoma and osteosarcoma. At Day 28 following GD2 CAR-T infusion, 23.1% (3/13) of evaluable patients had progressive disease and 76.9% (10/13) had stable disease (SD). 3/10 SD patients remained stable at 60 days post-infusion of GD2 CAR-T, but all patients eventually progressed. Since a major barrier to CAR-T efficacy is inadequate CAR-T expansion, we evaluated CAR-T levels and found that patients stratified into good and poor expander groups, observed across dose levels and associated with pro-inflammatory cytokine signatures in patients. To understand the immune cell contributors to CAR-T expansion, patient pre-treatment apheresis, CAR-T product, and post-infusion samples were evaluated by high-dimensional proteomic (CyTOF), transcriptomic (RNAseq), and epigenetic (ATACseq) analyses. In patient apheresis, good CAR-T expansion associated with more open chromatin and with both proteomic and transcriptomic enrichment of naïve T cells, while poor CAR-T expansion associated with increased levels of T effector memory (TEMRA) cells and enrichment of myeloid derived suppressor cell (MDSC) transcriptomic signatures. CAR-T products across patients, regardless of CAR-T expansion, demonstrated increased T cell activation proteomic signatures, with enhanced exhaustion transcriptomic signatures in poor expanders compared to good. The most robust cellular correlate to good CAR-T expansion was a population of CXCR3-expressing monocytes in pre-treatment apheresis. Interestingly, this CXCR3+ monocyte population reduced in post-infusion timepoints of good expanders, resembling levels found in poor expanders. Our findings were validated in TARGET-OS patient data in The Cancer Genome Atlas, where high CXCR3 expression was found to be associated with survival benefit in osteosarcoma patients. CXCR3 has been extensively studied on T cells, but its function on myeloid populations is yet to be fully explored. These results are the first to demonstrate that the peripheral immune environment prior to CAR-T administration may effectively predict and modulate CAR-T expansion in patients.

Citation Format: Tara Murty, Sabina Kaczanowska, Ahmad Alimadadi, Cristina Contreras, Caroline Duault, Priyanka Balasubrahmanyan, Warren Reynolds, Norma Gutierrez, Reema Baskar, Catherine Wu, Franziska Michor, Jennifer Altreuter, Yang Liu, Aashna Jhaveri, Vandon Duong, Hima Anbunathan, Radim Moravec, Joyce Hong, Roshni Biswas, Stephen Van Nostrand, James Lindsay, Mina Pichavant, Elena Sotillo, Bita Sahaf, Sean Bendall, Holden Maecker, Steven Highfill, David Stroncek, Melinda Merchant, John Glod, Catherine Hedrick, Crystal Mackall, Sneha Ramakrishna, Rosandra Kaplan. Immune determinants of CAR-T expansion in solid tumor patients receiving GD2 CAR-T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2142.

A phase I study of GPC3 targeted CAR-T cell therapy in advanced GPC3-expressing hepatocellular carcinoma (HCC)

TPS624

Background: The mortality of hepatocellular carcinoma (HCC) is increasing worldwide, but outcome of systemic treatments in advanced HCC is suboptimal. Adoptive T-cell transfer therapy represents a promising field that exploits the ability of T-cells to recognize and eliminate their target. Targeting the tumor-associated antigen glypican- 3 (GPC3) through chimeric antigen receptors (CAR) engineered T cells is a mechanistically rational novel treatment for advanced HCC. This study aims to determine the dose and early signals of GPC3 targeted (CAR)-T cells in advanced GPC3 expressing HCC (NCT05003895). Methods: This phase I first in human dose escalation trial will study the safety and feasibility of CAR (hYP7)- T cells in advanced HCC patients expressing GPC3. Eligibility criteria includes advanced HCC, not candidates for curative interventions, progressed on first line systemic treatment, tumor GPC3 positivity of ³ 25% by IHC, Child-Pugh Class A, ³1 measurable lesion, ECOG 0 or 1, adequate organ and marrow function. ParticipantsÕ T cells collected through leukapheresis will be transduced with a lentivirus encoding the CAR construct to generate CAR expressing T cells. Patients receive a conditioning chemotherapy regimen of cyclophosphamide and fludarabine prior to the infusion of the GPC3 directed CAR-T cells (Table). The trial has a 4-level modified Fibonacci dose escalation with a minimum of 3 patients at each level and a 28-day interval between the first three patients. Response will be assessed by imaging every two months during the first year. Patients undergo close monitoring with safety assessments during the first year and are followed for life. The primary objective is to determine the MTD, DLT, safety and feasibility of anti-GPC3 CAR expressing T- cells in patients with GPC3-expressing advanced HCC. Secondary objectives include best overall response and overall survival. Exploratory objectives are multiple and include studies to evaluate the persistence and peak levels of anti-GPC3 CAR-T cells after infusion. Recruitment began in December 2021 and the two patients at dose level -1 has been treated; the planned sample size is 38 patients. Table 1 Dose Level Anti-GPC3 CAR-T Cyclophosphamide (mg/m2) Fludarabine (mg/m2) Level -1 0.3x106 CAR-T per kg bw 200 30 Level 1 0.3x106 CAR-T per kg bw 300 30 Level 2 1x106 CAR-T per kg bw 300 30 Level 3 3x106 CAR-T per kg bw 300 30. Clinical trial information: NCT05003895 .

Abstract CT142: GD2.Ox40.CD28.z CAR T cell trial in neuroblastoma and osteosarcoma

Background: Chimeric antigen receptor T cells (CARTs) hold promising therapeutic potential for refractory tumors. GD2 is a tumor antigen expressed on neuroblastoma and osteosarcoma. In initial studies, T cells expressing 1st generation GD2-CARTs were shown to be safe and mediated modest antitumor activity in some patients with refractory neuroblastoma.

Methods: We developed a 3rd generation GD2-CART (GD2-CAR.OX40.28.z.ICD9) and conducted a phase I trial (NCT02107963) to determine the feasibility of producing and safety of administering escalating doses of GD2-CARTs in children and young adults with GD2+ solid tumors, including neuroblastoma and osteosarcoma, following cyclophosphamide-based lymphodepletion. Patient samples were evaluated for cytokine profile kinetics, immune phenotype analysis with mass cytometry (CyTOF), transcriptomic evaluation with RNA-sequencing (RNA-seq), epigenetic determination with Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq), and functional studies with flow cytometry.

Results: 15 patients aged 8-28 years were enrolled on four dose levels, of which 13 patients were infused. No dose-limiting toxicities were observed and administration of up to 1x107 GD2-CART/kg was feasible and safe for children and young adults with neuroblastoma and osteosarcoma. 15.4% (2/13) of patients experienced grade-1 cytokine release syndrome (CRS) and no neurological toxicity was observed. We measured the expansion and persistence of adoptively transferred GD2-CARTs in the peripheral blood. GD2-CARTs expanded in all patients receiving treatment, half of whom had expansion similar to that seen in clinically active CD19 and CD22 CARTs, but the GD2-CARTs had limited persistence. At Day 28 following GD2-CART infusion, 23.1% (3/13) of evaluable patients had progressive disease and 76.9% (10/13) had stable disease (SD). 3/10 SD patients remained stable at 60 days post-GD2-CART, but all patients eventually progressed. Since a major barrier to CART efficacy is inadequate CART expansion, we comprehensively evaluated for phenotypic, transcriptomic, and epigenetic immune profiles of patient apheresis, CART product, and post-treatment peripheral blood samples to identify determinants of CART expansion. GD2-CART expansion is significantly correlated with several T cell markers, and a larger baseline naïve and central memory T cell pool. Unique myeloid populations are associated with CART expansion. ATACseq identifies epigenetic differences in pre-treatment apheresis that may predict good CAR expansion in patients.

Conclusions: GD2-CART therapy following cyclophosphamide conditioning was well tolerated at all four dose levels in pediatric and young adult patients with neuroblastoma and osteosarcoma. Subsequent multi-dimensional analyses suggest key mechanisms underlying CART biology and function and highlight the potential of defining and applying molecular signatures in apheresis and CART product as biomarkers and prognostic indicators of CART expansion, with promise for advancing immunotherapies for solid tumor patients in the future.

Citation Format: Sneha Ramakrishna, Sabina Kaczanowska, Tara Murty, Cristina F. Contreras, Melinda Merchant, John Glod, Norma Gutierrez, Ahmad Alimadadi, David Stroncek, Steven Highfill, Caroline Duault, Priyanka B. Subrahmanyam, Tyson Holmes, Warren Reynolds, Reema Baskar, Antoine Barge, Hayley Lyon, Radim Moravec, Srinika Ranasinghe, Joyce Yu, Roshni Biswas, Samuel Pollack, Stephen Van Nostrand, James Lindsay, Mina Pichavant, Bita Sahaf, Sean C. Bendall, Andrew J. Gentles, Holden Maecker, Catherine C. Hedrick, Crystal Mackall, Rosandra Kaplan. GD2.Ox40.CD28.z CAR T cell trial in neuroblastoma and osteosarcoma [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 CT142.

Abstract LB213: Potent antitumor activity of a FGFR4 CAR-T in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive soft tissue sarcoma originating from skeletal muscle in children and adolescent young adults. Despite multi-modal aggressive therapies, relapsed, refractory or metastatic rhabdomyosarcoma remains a lethal disease with no significant improvement in outcome over decades of clinical trials. Therefore novel therapies are needed. FGFR4 is a developmentally regulated cell surface receptor tyrosine kinase that is overexpressed in RMS when compared with normal tissues, and mutationally activated in about 7.5% of RMS. Recently we showed that PAX3-FOXO1 establishes a super-enhancer in the FGFR4 genomic locus driving its high expression in fusion positive RMS. CAR T-cell therapy is effective in treating refractory and relapsed B-cell leukemia and lymphoma, with three CARs targeting CD19 approved by the FDA. Multiple CART trials are currently underway for solid tumors. Since FGFR4 is a cell surface protein, we hypothesized that FGFR4 will provide a rational target for immunotherapy in RMS. We confirmed by immunohistochemistry staining, western analysis, and Meso Scale Discovery that FGFR4 protein is highly differentially expressed in RMS samples. We developed a murine anti-FGFR4 antibody, 3A11, by immunizing mouse with FGFR4-IG fusion protein. 3A11 showed high affinity and specificity of binding to FGFR4. We then developed a second-generation CAR using the VL and VH domain of 3A11 antibody and found that the scFvFc retained its specificity and high affinity at nanomolar range. Human T cells transduced with 3A11 CAR construct were found to be highly potent at inducing IFN-γ, TNF-α, IL-2 and cytotoxicity when the FGFR4-CART was co-cultured with RMS cells, but not with RMS cells with FGFR4 knocked out or FGFR4 negative cells. 3A11 CART incubated with human primary cells obtained from liver, kidney, heart, and pancreas, did not elicit a cytokine response, indicating a low potential for “on-target off-tumor” toxicity. In vivo testing also found that 3A11 CART eliminated RMS cells in both murine xenograft metastatic and localized subcutaneous models. Therefore we have developed a CART targeting FGFR4 that shows high potency for treating RMS. A phase 1 FGFR4-CART clinical trial is planned for children and adolescent young adults with relapsed/refractory rhabdomyosarcoma.

Citation Format: Adam Tai Chi Cheuk, Meijie Tian, Nityashree Shivaprasad, Steven Highfill, David Milewski, G Tom Brown, Peter Azorsa, Dina Schneider, Berkley Gryder, Jun S Wei, Young Kwok Song, Hsien-Chao Chou, Jerry Wu, Joon-Yong Chung, Brian Belyea, Corinne Linardic, Stephen M Hewitt, Boro Dropulic, Rimas Orentas, Javed Khan. Potent antitumor activity of a FGFR4 CAR-T in rhabdomyosarcoma [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 LB213.

A phase I trial of T-cell receptor gene therapy targeting KK-LC-1 for gastric, breast, cervical, lung and other KK-LC-1 positive epithelial cancers

TPS2678

Background: T cell receptor (TCR)-T cell therapy is an emerging cancer treatment strategy. Thus far, demonstration of clinical activity has been limited to a subset of solid tumors including melanoma, synovial cell sarcoma and HPV-associated cancer. It is estimated that metastatic epithelial cancers are responsible for approximately 90% of cancer deaths in the United States. The estimated 600,000 cancer deaths each year is driven largely by lung adeno- and squamous cell carcinoma and invasive breast cancer, which account for approximately 30% of all cancer-related deaths. Kita-Kyushu Lung Cancer Antigen 1 (KK-LC-1) is a cancer germline antigen with expression restricted to germ cells in adults and certain epithelial cancers including lung, breast, gastric and cervical. We identified a KK-LC-1 TCR from the tumor-infiltrating lymphocytes (TIL) of a patient with cervical cancer who had a complete tumor response to TIL therapy. The KK-LC-1 TCR was the most dominate clonotype in the infused TIL product and persisted in the peripheral blood following infusion, suggesting that it may have contributed to cancer regression in this patient. Methods: We are conducting a phase I cell dose escalation trial to test the safety and efficacy of KK-LC-1 TCR-T cell therapy in patients with metastatic KK-LC-1 positive epithelial cancer. Patients receive a lymphocyte depleting conditioning regimen followed by a one-time infusion of genetically engineered T cells expressing the KK-LC-1 TCR (KK-LC-1 TCR-T cells) and high-dose systemic aldesleukin. KK-LC-1 positivity is determined by RNAscope assay measuring the percentage of cancer cells expressing CT83 (gene encoding KK-LC-1) with a percentage of 25 or greater considered positive. Main inclusion criteria include HLA-A*01:01 allele, prior first-line therapy, ECOG of 0 or 1 and adequate organ and hematologic function. Main exclusion criteria include active major medical illness of the cardiovascular, respiratory or immune system, primary or secondary immunodeficiency and autoimmune disease. Participants will be entered in sequential dose levels and receive escalating doses of cells beginning at 1x108 and ending with 6x1010. Dose-limiting toxicities will be assessed during the first 30 days of cell infusion. The primary objective is to determine the maximally tolerated dose of KK-LC-1 TCR-T cells. Exploratory objectives include assessing the safety and efficacy of KK-LC-1 TCR-T cells and to conduct immunologic studies to understand and improve the administered treatment. Clinical trial information: NCT05035407.

CAR T-cells effective for post-CART relapse: A new treatment paradigm

e19508

Background: Chimeric antigen receptor T-cells (CART) induce remarkable responses in B-cell acute lymphoblastic leukemia (B-ALL), but relapse remains a challenge. Effective therapies for post-CART relapse are limited but may include infusion of a unique CART construct, a strategy distinct from reinfusion of the same CART product. Given limited data evaluating outcomes of a unique CART as salvage therapy for post-CART relapse, we report on the impact of prior CART constructs on subsequent CART responses. Methods: This was a retrospective review (NCT03827343) of children and young adults receiving CD19 and/or CD22 CART therapy for B-ALL between 7/1/12-12/30/21 at our center. Patients included received at least 2 unique CART constructs at some point in therapy, excluding interim CART reinfusions. CART-A was the first CART construct ever received and CART-B the second unique CART. The primary objective was to evaluate complete remission (CR) rates following CART-A versus CART-B. Results: Of 135 heavily pretreated patients, 54 (40%) received at least one prior CART. The majority (n=37, 68.5%) were male. Median age at CART-A and CART-B was 12.5 (range, 3.3-30.4) and 13.7 years (range, 4.5-30.7), respectively. In 42 (77.8%) patients, CART-B targeted a different antigen than CART-A, primarily due to loss of antigen target after CART-A. CR rate was substantially lower with CART-B (n=35, 64.8%) than with CART-A (n=48, 88.9%, p=0.006) (Table). Still, two (3.7%) patients with CART-A nonresponse attained CR with CART-B. Most CART-B responders (n=31, 88.6%) had CART-B targeting a different antigen than CART-A, suggesting limitations of same antigen targeting even with a unique CART construct. CART-B responses amongst 10 patients with interim hematopoietic stem cell transplantation (HSCT) after CART-A were similar to CART-B responses in those without interim HSCT (5 of 10, 50% vs. 30 of 44, 68.2%, p=0.3). In those where CRS grade was known for both CART infusions (n=40), CRS severity was milder with CART-B (≥grade 3, n=1, 2.5%) than with CART-A (≥grade 3, n=15, 37.5%, p=0.0001). Conclusions: Using an alternative CART for post-CART relapse is effective in a substantial proportion of patients, particularly when targeting a unique antigen. As post-CART relapse occurs more frequently and patients receive multiple CARTs, identifying optimization strategies for CART-B will be critical. Further investigation of indication for CART-B, role of interim HSCT, and optimal timing for sequential CART infusions is underway.[Table: see text]

Efficacy of second CAR-T (CART2) infusion limited by poor CART expansion and antigen modulation

Chimeric antigen receptor T-cells (CART) are active in relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL), but relapse remains a substantial challenge. Reinfusion with the same CART product (CART2) in patients with suboptimal response or antigen positive relapse following first infusion (CART1) represents a potential treatment strategy, though early experiences suggest limited efficacy of CART2 with CD19 targeting. We report on our experience with CART2 across a host of novel CAR T-cell trials. This was a retrospective review of children and young adults with B-ALL who received reinfusion with an anti-CD19, anti-CD22, or anti-CD19/22 CART construct on one of 3 CAR T-cells trials at the National Cancer Institute (NCT01593696, NCT02315612, NCT0344839) between July 2012 and January 2021. All patients received lymphodepletion (LD) pre-CART (standard LD: 75 mg/m² fludarabine, 900 mg/m² cyclophosphamide; or intensified LD: 120 mg/m² fludarabine, 1200 mg/m² cyclophosphamide). Primary objectives were to describe response to and toxicity of CART2. Indication for CART2, impact of LD intensity, and CAR T-cell expansion and leukemia antigen expression between CART infusions was additionally evaluated. Eighteen patients proceeded to CART2 due to persistent (n=7) or relapsed antigen positive disease (n=11) following CART1. Seven of 18 (38.9%) demonstrated objective response (responders) to CART2: 5 achieved a minimal residual disease (MRD) negative CR, 1 had persistent MRD level disease, and 1 showed a partial remission, the latter with eradication of antigen positive disease and emergence of antigen negative B-ALL. Responders included four patients who had not achieved a CR with CART1. Limited cytokine release syndrome was seen following CART2. Peripheral blood CART1 expansion was higher than CART2 expansion (p=0.03). Emergence of antigen negative/dim B-ALL in 6 (33.3%) patients following CART2 contributed to lack of CR. Five of seven (71.4%) responders received intensified LD pre-CART2, which corresponded with higher CART2 expansion than in those receiving standard LD (p=0.029). Diminished CAR T-cell expansion and antigen downregulation/loss impeded robust responses to CART2. A subset of patients, however, may derive benefit from CART2 despite suboptimal response to CART1. Intensified LD may be one strategy to augment CART2 responses, though further study of factors associated with CART2 response, including serial monitoring of antigen expression, is warranted.

145 Comparison of CAR-T cell manufacturing platforms reveals distinct phenotypic and transcriptional profiles

Background

With the clinical success of chimeric antigen receptor (CAR)-T cells against hematological malignancies, investigators are looking to expand CAR-T therapies to new tumor targets and patient populations. To support translation to the clinic, a variety of cell manufacturing platforms have been developed to scale manufacturing capacity while using closed and/or automated systems. Such platforms are particularly useful for solid tumor targets, which typically require higher CAR-T cell doses that can number in the billions. Although T cell phenotype and function are key attributes that often correlate with therapeutic efficacy, it is currently unknown whether the manufacturing platform itself significantly influences the output T cell phenotype and function.

Methods

Static bag culture was compared with 3 widely-used commercial CAR-T manufacturing platforms (Miltenyi CliniMACS Prodigy, Cytiva Xuri W25 rocking platform, and Wilson-Wolf G-Rex gas-permeable bioreactor) to generate CAR-T cells against FGFR4, a promising target for pediatric sarcoma. Selected CD4+CD8+ cells were stimulated with Miltenyi TransAct, transduced with lentiviral vector, and cultured out to 14 days in TexMACS media with serum and IL2.

Results

As expected, there were significant differences in overall expansion, with bag cultures yielding the greatest fold-expansion while the Prodigy had the lowest (481-fold vs. 84-fold, respectively; G-Rex=175-fold; Xuri=127-fold; average of N=4 donors). Interestingly, we also observed considerable differences in CAR-T phenotype. The Prodigy had the highest percentage of CD45RA+CCR7+ stem/central memory (Tscm)-like cells at 46%, while the bag and G-Rex cultures had the lowest at 16% and 13%, respectively (average N=4 donors). In contrast, the bag, G-Rex, and Xuri cultures were enriched for CD45RO+CCR7- effector memory cells and also had higher expression of exhaustion markers PD1 and LAG3. Gene clustering analysis using a CAR-T panel of 780 genes revealed clusters of genes enriched in Prodigy/de-enriched in bag, and vice versa. We are currently in the process of evaluating T cell function.

Conclusions

This is the first study to our knowledge to benchmark these widely-used bioreactor systems in terms of cellular output, demonstrating that variables inherent to each platform (such as such as nutrient availability, gas exchange, and shear force) significantly influence the final CAR-T cell product. Whether enrichment of Tscm-like cells in the final infusion product correlates with response rate, as has been demonstrated in the setting of CD19 CAR-Ts, remains to be seen and may differ for FGFR4 CAR-Ts and other solid tumors. Overall, our study outlines methods to identify the optimal manufacturing process for future CAR-T cell therapies.

610 Technical challenges in monocyte-derived dendritic cell vaccine manufacturing; a QI project

Background

With the explosive growth of cancer immunotherapies, cancer vaccines have been in the spotlight for their ability to turn cold tumors hot. Particularly, dendritic cell vaccines (DCV) are capable of harnessing the immune system to recognize single or multiple epitopes as they are professional antigen presenting cells. However, DCVs have not been recognized as the platform of choice in many studies due to relatively high cost, difficulty in standardizing manufacturing methods and risk of product inconsistency. We have been using monocyte-derived DCs transduced with an adenovirus vector expressing HER2/neu in a clinical trial to treat HER2-expressing cancers. The vaccine was administered on weeks 0, 4, 8, 16 and 24 at 4 different dose-levels; 5 × 10E6, 10 × 10E6, 20 × 10E6 and 40 × 10E6 viable cells. The clinical outcome of the study is under analysis.1 To further optimize the safety and consistency of DCV, we reviewed the issues encountered in a first-in-human clinical trial during the manufacture of these cells at the NIH Clinical Center.

Methods

Manufacturing records of NCT01730118 A Phase I Study of an Autologous DCV Targeting HER2 in Solid Tumors were reviewed to identify any complications or deviations encountered during manufacturing from apheresis to delivery of the fresh DCVs (figure 1).

Results

Between April 2013 and October 2019, 134 vaccines were manufactured for 33 patients. A total of 113 (84%) DCVs were administered, with 103 (91%) of those meeting release criteria, and the remaining administered under authorized medical exception (AME). All patients underwent a single apheresis collection with 18 (median, range 15–20) liters processed and a goal of 6 aliquots (333 × 10E6 monocytes/vial). Dual lumen catheterization was required in 23 (70%) patients, and all procedural reactions required no or minimal intervention. Summaries enumerate aberrancies encountered during the manufacturing process (table 1). Overall, interpatient variabilities may have contributed to 92 (78%) events, while 26 (22%) events arose in a ‘controllable’, patient-unrelated environment.

Abstract 610 Figure 1

Autologous DC vaccine manufacturing at the NIH clinical center

Abstract 610 Table 1

Conclusions

In spite of the variable events encountered during the manufacturing process, the majority of products were administered successfully. Patient-related variabilities were linked to most of the events. Future studies should be designed to minimize the impact of such variabilities on DCVs to provide high-quality personalized therapies. Manufacturing one large lot of DCs and cryopreserving enough aliquots for the entire study and the incorporation of an automated, closed cell culture system may reduce the aforementioned incidents and improve product quality.

Acknowledgements

This study was supported by the NIH Clinical Center and Center for Cancer Research, the National Cancer Institute. The authors are indebted to the staffs at NIH Clinical Center and the patients.

Ethics Approval

The study was approved by NCI/NIH Institutional Review Board (#534360, 13C0016).

References

Maeng, H.M., et al., Preliminary results of a phase I clinical trial using an autologous dendritic cell cancer vaccine targeting HER2 in patients with metastatic cancer or operated high-risk bladder cancer (NCT01730118). Journal of Clinical Oncology 2019. 37(15_suppl): p. 2639–2639.

Jin, P., et al., Plasma from some cancer patients inhibits adenoviral Ad5f35 vector transduction of dendritic cells. Cytotherapy 2018;20(5): p. 728–739.

Safety and clinical activity of gene-engineered T-cell therapy targeting HPV-16 E7 for epithelial cancers

101

Background: Genetically engineered T-cell therapy has shown remarkable clinical activity in hematologic malignancies. It is not known if this type of treatment can be applied effectively to epithelial cancers, which account for 80% to 90% of human malignancies. Methods: We conducted a phase I clinical trial with a 3 + 3 dose escalation in which patients with metastatic HPV-16+ epithelial cancers were treated with a one-time infusion of genetically engineered T cells expressing a T-cell receptor targeting an HLA-A*02:01-restricted epitope of HPV-16 E7 (E7 TCR-T cells). A lymphocyte-depleting conditioning regimen was administered before cell infusion, and high-dose systemic aldesleukin was administered after cell infusion. Results: Twelve patients, previously treated with a median of 4 (range, 3 to 7) anticancer agents, were treated. The cell dose was not limited by toxicity. Six patients demonstrated objective clinical responses, which included regression of bulky tumors and complete elimination of some tumors. Responses occurred in patients with vulvar, anal, head and neck, and cervical cancer. Four patients who previously received PD-1-based therapy responded. Response duration ranged from 3 to 9 months. Sustained, high-level engraftment of E7 TCR-T cells in peripheral blood was observed (median after approximately 6 weeks, 66% of total T cells, range 1% to 88%) and correlated with cell dose but not with clinical response. Infused T cell characteristics did not correlate strongly with response. Of the 4 resistant tumors that were studied, 3 demonstrated genetic defects in HLA-A*02:01 or B2M (necessary components of the target complex) and 1 demonstrated copy loss with decreased expression of antigen presentation and interferon response molecules (i.e. TAP1, TAP2, IFNGR1, IFNGR2). Of the 3 sensitive tumors studied, 0 showed genetic defects in these molecules. Conclusions: E7 TCR-T cells demonstrated safety and clinical activity in the treatment of highly refractory metastatic HPV-16+ cancers. Treatment resistance was linked to definitive genetic defects in the targeted peptide-HLA complex and to manifold defects in antigen processing and interferon response. Clinical trial information: NCT02858310.

Robust Selections of Various Hematopoietic Cell Fractions on the CliniMACS Plus Instrument

Cell separation technologies play a vital role in the graft engineering of hematopoietic cellular fractions, particularly with the rapid expansion of the field of cellular therapeutics. The CliniMACS Plus Instrument (Miltenyi Biotec) utilizes immunomagnetic techniques to isolate hematopoietic progenitor cells (HPCs), T cells, NK cells, and monocytes. These products are ultimately used for HPC transplantation and for the manufacture of adoptive immunotherapies. We evaluated the viable cell recovery and cell purity of selections and depletions performed on the CliniMACS Plus over a 10-year period at our facility, specifically assessing for the isolation of CD34+, CD4+, CD3+/CD56+, CD4+/CD8+, and CD25+ cells. Additionally, patient- and instrument-related factors affecting these parameters were examined. Viable cell recovery ranged from 32.3 ± 10.2% to 65.4 ± 15.4%, and was the highest for CD34+ selections. Cell purity ranged from 86.3 ± 7.2% to 99.0 ± 1.1%, and was the highest for CD4+ selections. Undesired cell fractions demonstrated a range of 1.2 ± 0.45 to 5.1 ± 0.4 log reductions. Red cell depletions averaged 2.12 ± 0.68 logs, while platelets were reduced by an average of 4.01 ± 1.57 logs. Donor characteristics did not impact viable cell recovery or cell purity for CD34+ or CD4+ cell enrichments; however, these were affected by manufacturing variables, including tubing size, bead quantity, and whether preselection platelet washes were performed. Our data demonstrate the efficient recovery of hematopoietic cellular fractions on the CliniMACS Plus that may be optimized by adjusting manufacturing variables.

Plasma from some cancer patients inhibits adenoviral Ad5f35 vector transduction of dendritic cells

BACKGROUND

Pooled AB serum is often used as a media supplement for cell culture but it has the potential to transmit infectious diseases. To avoid this risk, we used autologous plasma as a media supplement for manufacturing dendritic cells (DCs) for cancer immunotherapy. We noticed inconsistencies in the DCs and investigated their nature and cause.

METHODS

Adenovirus human epidural growth factor receptor 2 (adHER2/neu) DCs for 21 patients were manufactured from autologous peripheral blood monocytes that were treated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4 for 3 days, transduced with Ad5f35HER2ECTM and then treated with lipopolysaccharide and interferon (IFN)-γ for 1 day. The cells were cultured in RPMI-1640 supplemented with either 10% heat inactivated autologous or AB plasma.

RESULTS

Twenty-eight adHER2/neu DCs were manufactured for 21 patients using autologous plasma and 68 were manufactured for 20 of those patients using AB plasma. The expression of human epidural growth factor receptor 2 (HER2/neu) was less for DCs manufactured with autologous plasma (70.3 ± 33.3% versus 86.1 ± 22.8%; P <0.01). Manufacturing adHER2/neu DCs using monocytes from three healthy subjects and plasma from one patient with low HER2/neu expression (18%) resulted in low HER2/neu expression by all three DCs (13%, 16% and 23%). Analysis of the levels of 1322 proteins in eight plasma samples associated with low HER2/neu expression and in 12 associated with high HER2/neu expression revealed that the levels of 14 predicted HER2/neu transduction efficiency.

CONCLUSION

The manufacture of adHER2/neu DC using autologous plasma as a media supplement resulted in inconsistent HER2/neu expression. It is likely that variability in the levels of multiple proteins in autologous plasma contributed to low HER2/neu expression.

Elutriated lymphocytes for manufacturing chimeric antigen receptor T cells

BACKGROUND

Clinical trials of Chimeric Antigen Receptor (CAR) T cells manufactured from autologous peripheral blood mononuclear cell (PBMC) concentrates for the treatment of hematologic malignancies have been promising, but CAR T cell yields have been variable. This variability is due in part to the contamination of the PBMC concentrates with monocytes and granulocytes.

METHODS

Counter-flow elutriation allows for the closed system separation of lymphocytes from monocytes and granulocytes. We investigated the use of PBMC concentrates enriched for lymphocytes using elutriation for manufacturing 8 CD19- and 5 GD2-CAR T cell products.

RESULTS

When compared to PBMC concentrates, lymphocyte-enriched elutriation fractions contained greater proportions of CD3+ and CD56+ cells and reduced proportions of CD14+ and CD15+ cells. All 13 CAR T cell products manufactured using the elutriated lymphocytes yielded sufficient quantities of transduced CAR T cells to meet clinical dose criteria. The GD2-CAR T cell products contained significantly more T cells and transduced T cells than the CD19-CAR T cell products. A comparison of the yields of CAR T cells produced from elutriated lymphocytes with the yields of CAR T cells previous produced from cells isolated from PBMC concentrates by anti-CD3/CD28 bead selection or by anti-CD3/CD28 bead selection plus plastic adherence found that greater quantities of GD2-CAR T cells were produced from elutriated lymphocytes, but not CD19-CAR T cells.

CONCLUSIONS

Enrichment of PBMC concentrates for lymphocytes using elutriation increased the quantity of GD2-CAR T cells produced. These results provide further evidence that CAR T cell expansion is inhibited by monocytes and granulocytes.

Abstract 4725: Hematopoietic stem cell niche activation and progenitor mobilization mediate cancer-associated immunosuppression and metastasis

Metastatic tumors have been shown to establish microenvironments in distant tissues that are permissive to disseminated tumor cells. Hematopoietic cells are essential components of this microenvironment, yet the events that initiate the hematopoietic response remain unclear. Further, the functional contribution of hematopoietic stem and progenitor cells (HSPCs) to metastatic progression has not been addressed. Here, we utilized two highly metastatic C57bl/6 murine cell lines capable of spontaneous metastasis following orthotopic injection to study how the hematopoietic response is initiated and can function to promote metastatic progression in immune competent tumor-bearing mice. In both the E0771 breast carcinoma model and M3-9-M rhabdomyosarcoma model we found that a primary tumor drove expansion of HSPCs within the bone marrow prior to establishment of metastatic lesions. To detect changes within the bone marrow microenvironment that accounted for the observed HSPC expansion in tumor-bearing mice, we performed qPCR analysis of whole femur lysate from control or pre-metastatic tumor-bearing mice. We found the bone marrow microenvironment of tumor-bearing mice expressed a transcriptional program of hematopoietic niche activation that promoted expansion as well as mobilization of hematopoietic progenitors, including downregulation of the HSPC homing cytokine CXCR4. Consistent with this, we detected elevated HSPCs in the circulation of newly diagnosed cancer patients as well as pre-metastatic tumor-bearing mice. By using a pharmacological antagonist of CXCR4 to mobilize HSPCs as seen in the tumor bearing setting, we demonstrated that circulating HSPCs were functionally capable of significantly enhancing metastasis in mice. To determine the mechanisms by which circulating HSPCs can promote metastatic progression, we tracked the developmental fate of flow cytometry-sorted HSPCs injected into the circulation of control or tumor-bearing pre-metastatic mice. We found that HSPCs localized within pre-metastatic tissues preferentially differentiated into the myeloid lineage. Further, depletion of these myeloid cells abrogated the metastasis-promoting effects of HSPC mobilization. Together, these data establish bone marrow niche activation as one of the earliest steps of the metastatic process and identify circulating HSPCs as a potential indicator of metastatic niche initiation.

Citation Format: Amber J. Giles, Meera Murgai, Yorleny Vicioso, Steven Highfill, Miki Kasai, Linda Vahdat, Leonard Wexler, Crystal Mackall, David Lyden, Rosandra Kaplan. Hematopoietic stem cell niche activation and progenitor mobilization mediate cancer-associated immunosuppression and metastasis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4725. doi:10.1158/1538-7445.AM2015-4725

Neutralization of murine myeloid suppressor cells enhances the efficacy of GD2-specific CAR T cells directed against human sarcoma in a xenograft model (VAC11P.1010)

Genetically engineered T-cells expressing chimeric antigen receptors directly target cell surface antigens on tumor cells. CARs have shown remarkable activity in clinical trials for hematologic malignancies but remain unproven for the treatment of solid tumors. The disialoganglioside GD2 is considered a tumor-associated antigen for neuroblastoma and we have found that GD2 is expressed on pediatric sarcomas. Analysis of primary human tumor tissue samples taken from 18/18 patients with osteosarcoma and alveolar rhabdomyosarcoma (2/15) demonstrate robust expression of GD2 on the cell surface. Based on this finding, we developed assays to test the ability of GD2-CAR T-cells to target human sarcomas. We find that GD2-CAR T-cells specifically lyse GD2-expressing solid tumors in vitro even at low E:T, but fail to induce a response in vivo. In studying these xenografted tumors we discovered an expansion of murine CD11b+Gr1+ MDSC that inhibit human T-cell responses in vitro. This lead us to adopt a combinatorial therapeutic strategy in which we inhibited the suppressive potential of MDSC by administration of all-trans retinoic acid followed by the infusion of GD2-specific CAR T-cells. This resulted in significant improvements in overall survival and tumor growth. The results presented here suggest that ATRA coadministration with CAR T-cell therapy for solid tumors may yield a beneficial additive effect through the modulation of myeloid derived suppressor cells.

Abstract LB-284: Bone marrow-derived progenitor cells develop into myeloid-derived suppressor cells at metastatic sites

The ability of tumor cells to metastasize to distant tissues is the most lethal aspect of cancer. Prior to detectable metastasis tumors elicit distant changes within the bone marrow and future sites of metastasis, including formation of the pre-metastatic niche. We have found that prior to detectable spontaneous metastasis, a primary tumor causes enhanced production and mobilization of progenitor cells from the bone marrow into the blood. We find in cancer patients that increased circulating progenitors are associated with metastatic disease progression. By utilizing bone marrow transplant models and a novel ex vivo lung culture, we demonstrate that bone marrow-derived progenitor cells accumulate at the primary tumor as well as metastatic lesions. As our cancer models approach detectable spontaneous metastases, we observe a loss of progenitor cells in pre-metastatic sites and an increase in myeloid-derived suppressor cells (MDSCs). We further traced adoptively transferred bone marrow-derived progenitors in tumor-bearing mice and demonstrate that these cells contribute to the MDSC population. Together, these data suggest that circulating progenitor cells provide a prognostic tool to predict metastatic dissemination. Furthermore, these cells likely contribute to metastatic progression by developing into MDSCs within the primary tumor and at metastatic sites.

Citation Format: Amber Giles, Yorleny Vicioso, Christianne Persenaire, Miki Kasai, Steven Highfill, Arnulfo Mendoza, Rosandra Kaplan. Bone marrow-derived progenitor cells develop into myeloid-derived suppressor cells at metastatic sites. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-284. doi:10.1158/1538-7445.AM2013-LB-284

NFATc2 is an intrinsic negative regulator of proliferation in effector T cells and is necessary for extrinsic control by regulatory T cells (49.17)

In addition to its effect to limit the number of cell division cycles and the accumulation of memory T cells, recent data suggest NFATc2 may be required to enable development and function of regulatory T cells (Tregs). Here, we verified loss of NFATc2 relieved intrinsic negative regulation: effector T cells (CD4+ /CD25-) from NFATc2 knockout (KO) mice showed more facile in vitro proliferation than effector T cells from WT or heterozygous mice and, in vivo had significantly more activated (CD69+ ) and memory phenotype (CD44hi ) T cells. In contrast, we found no differences in the number of Tregs (CD4+ /CD25+ /FoxP3+ ) between NFATc2 KO and WT mice. However, NFATc2 KO Tregs were less able to functionally suppress NFATc2 KO and WT effector cells in vitro. In contrast to NFATc2 KO Tregs, WT Tregs effectively suppressed proliferation of NFATc2 KO T cells, indicating that NFATc2 KO Tregs are hypofunctional. The reduced suppressive capacity of NFATc2 KO vs WT Tregs was not due to global T cell hyperproliferation since Tregs from Tob1 KO mice, that also have hyperproliferative T cells, were more potent suppressors than Tregs from WTs or NFATc2 KOs. The functional deficit of NFATc2 Tregs could not be replicated by treating WT Tregs with the NFAT inhibitor, cyclosporin A. Instead, Treg function was directly correlated with reduced expression of CTLA4 in NFATc2 vs WT Tregs. Our data support the premise that NFATc2 is required for Treg function, possibly by controlling CTLA4 expression.

Expansion of myeloid suppressor cells in SHIP-deficient mice represses allogeneic T cell responses

Previously we demonstrated that SHIP(-/-) mice accept allogeneic bone marrow transplants (BMT) without significant acute graft-vs-host disease (GvHD). In this study we show that SHIP(-/-) splenocytes and lymph node cells are poor stimulators of allogeneic T cell responses that cause GvHD. Intriguingly, SHIP(-/-) splenocytes prime naive T cell responses to peptide epitopes, but, conversely, are partially impaired for priming T cell responses to whole Ag. However, dendritic cells (DC) purified from SHIP(-/-) splenocytes prime T cell responses to allogeneic targets, peptide epitopes, and whole Ag as effectively as SHIP(+/+) DC. These findings point to an extrinsic effect on SHIP(-/-) DC that impairs priming of allogeneic T cell responses. Consistent with this extrinsic effect, we found that a dramatic expansion of myeloid suppressor cells in SHIP(-/-) mice impairs priming of allogeneic T cells. These findings suggest that SHIP expression or its activity could be targeted to selectively compromise T cell responses that mediate GvHD and graft rejection.