Abstract 3203: EVOcells Oncology: Tailored genetic engineering of iPSC-derived immune effector cells and combination with the right biologic therapeutics result in optimal killing of primary tumor cells from patients

Current autologous cell therapies, with blockbuster products on the market, have been leading for a decade to unprecedented clinical successes in patients with hematological malignancies. However, these patient-derived T-cell therapies are facing many challenges. The use of GMP iPSC lines to produce immune effector cells will reduce the complexity of the manufacturing process and will provide an unlimited source of starting material. The goal of the EVOcells Oncology platform is to offer a truly allogeneic cell therapy platform to treat a broad number of cancer patients with consistent quality and scalability of the final product. Besides, the versatility of our platform to produce different immune cell types combined to customized genetic engineering strategies will bring cell therapy to the level of personalized medicine. Our “off-the-shelf” cell therapy platform has already validated two pillars: iPSC-derived NK cells (iNK) and iPSC-derived Macrophages (iMACs). Through multiple genetic engineering strategies specific to each immune cell type, we are developing a comprehensive portfolio of cell therapy products to address specific tumor escape mechanism in liquid and solid tumors. Our initial effort aimed to develop these two innate immune cell types to propose efficacious cell therapies with an increased safety profile as they have low risk of graft-versus-host disease (GvHD) or CRS (Cytokine Release Syndrome). Thanks to the expression of a broad pattern of activatory receptors, iNK cells form Immunological Synapses with tumor cells leading in turn to efficient killing with and without addition of a CAR construct. Besides, we demonstrated the possibility to combine “naked” iNK cells with marketed therapeutic monoclonal antibodies (mAb) to further improve their efficacy. At the end of the differentiation process, iMACs are showing a M0 like phenotype with high plasticity allowing the in vitro differentiation of the cells towards either a M1 or a M2 polarization in response to the appropriate stimulations. iMACs produce key macrophages cytokines and are able to kill tumor cells via ADCP (Antibody-Dependent-Cell-Phagocytosis) mechanism when combined to a therapeutic mAb. Thanks to our collaboration with clinicians at the IUCT-Oncopole (Toulouse Cancer Hospital), we were able to identify appropriate cancer indications and further demonstrate in a translational fashion that both iNK and iMACs are able to kill primary resistant tumor cells which were isolated from patient’ samples. Taken together, these results are showing the versatility and the breadth of our EVOcells Oncology platform to produce a true arsenal of cell therapies and its potential for future clinical development.

Citation Format: Michael Esquerré, Audrey Holtzinger, Nadja Wagner, Monika Braun, Mélanie Pichery, Stefanie Pfaender, Stephanie Sontag, Kathrin Haake, Michela Mirenda, Michael Paillasse, Davide Grandolfo, Chloé Beuraud, Mandy Richter, Philip Hublitz, Julien Bousquet, Marion Fabre, Mylène Gador, Daniel Sommermeyer, Tanja Schneider, Oriane Bombarde, Camille Esquerré, Loic Ysebaert, Fabien Despas, Matthias Austen, Andreas Scheel, Markus Dangl. EVOcells Oncology: Tailored genetic engineering of iPSC-derived immune effector cells and combination with the right biologic therapeutics result in optimal killing of primary tumor cells from patients [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 3203.

T-Cells Expressing a Highly Potent PRAME-Specific T-Cell Receptor in Combination with a Chimeric PD1-41BB Co-Stimulatory Receptor Show a Favorable Preclinical Safety Profile and Strong Anti-Tumor Reactivity

Simple Summary

The development of effective adoptive T-cell therapies (ATCs) to treat solid tumors has several challenges: the choice of a suitable target antigen, the generation of a specific T-cell receptor (TCR) directed against this target, and the hostile tumor microenvironment (TME). The cancer/testis antigen Preferentially Expressed Antigen in Melanoma (PRAME) is a promising target for ATCs since it is highly expressed in several solid tumor indications, while its expression in normal tissues is mainly restricted to the testis. Using our well-established high throughput TCR generation and characterization process, we identified a highly potent PRAME-specific TCR. To convert the inhibitory PD-1 signal in T-cells to an activating signal, we designed a chimeric receptor consisting of the extracellular domain of PD-1 and the signaling domain of 4-1BB. Combining this PD1-41BB receptor with our lead PRAME-TCR generated a very promising T-cell product with a favorable preclinical in vitro safety profile and enhanced in vitro and in vivo anti-tumor efficacy.

Abstract

The hostile tumor microenvironment (TME) is a major challenge for the treatment of solid tumors with T-cell receptor (TCR)-modified T-cells (TCR-Ts), as it negatively influences T-cell efficacy, fitness, and persistence. These negative influences are caused, among others, by the inhibitory checkpoint PD-1/PD-L1 axis. The Preferentially Expressed Antigen in Melanoma (PRAME) is a highly relevant cancer/testis antigen for TCR-T immunotherapy due to broad expression in multiple solid cancer indications. A TCR with high specificity and sensitivity for PRAME was isolated from non-tolerized T-cell repertoires and introduced into T-cells alongside a chimeric PD1-41BB receptor, consisting of the natural extracellular domain of PD-1 and the intracellular signaling domain of 4-1BB, turning an inhibitory pathway into a T-cell co-stimulatory pathway. The addition of PD1-41BB to CD8+ T-cells expressing the transgenic PRAME-TCR enhanced IFN-γ secretion, improved cytotoxic capacity, and prevented exhaustion upon repetitive re-challenge with tumor cells in vitro without altering the in vitro safety profile. Furthermore, a single dose of TCR-Ts co-expressing PD1-41BB was sufficient to clear a hard-to-treat melanoma xenograft in a mouse model, whereas TCR-Ts without PD1-41BB could not eradicate the PD-L1-positive tumors. This cutting-edge strategy supports development efforts to provide more effective TCR-T immunotherapies for the treatment of solid tumors.

189 Targeting a novel shared tumor-specific antigen with T cell receptor transduced T cells for the treatment of ovarian cancer

Background

Transgenic T cell receptor (TCR)-based T cell therapies are a powerful treatment for cancer. However, one of the greatest remaining challenges is the successful identification of tumor-specific antigens (TSAs) that are shared between patients and tumor entities and elicit strong T cell responses. The non-coding region of the genome has become a promising source of such novel TSAs. Previously, we have identified ten immunogenic shared TSAs, derived from the translation in canonical and non-canonical reading frames of non-mutated non-coding genomic regions like introns, intergenic regions and 5’-untranslated regions. In the following process, we identified several TCRs specific for these TSAs. Here we aimed at the validation of two TSA-specific TCRs in a model of ovarian cancer-derived organoids.

Methods

Freshly collected ovarian tumor and normal ovarian tissue expressing the HLA of interest were mechanically disrupted, enzymatically digested and cryopreserved. Expression of the TSA of interest in the primary tumor tissue was confirmed with RNA sequencing and mass spectrometry. Thawed single cell suspensions were used to generate tumor organoids and 2D-growing normal ovarian cell lines. To validate the generated cell lines, the presence or absence of two previously identified tumor-specific mutations was investigated by targeted Sanger sequencing in the genome of the tumor organoids, normal cell lines and primary tissues. Two TSA-specific TCRs were retrovirally transduced into CD8+ T cells of three healthy donors. Expanded TSA-specific CD8+T cells were co-cultured 24 hours with single cell suspensions of IFN-γ pre-stimulated, tumor organoids or the 2D-growing normal ovarian cell line. IFN-γ ELISA was used to assess activation of TSA-specific T cells upon co-culture.

Results

The TSA of interest was detected both at the transcriptomic and proteomic level in the primary ovarian tumor tissue. Using frozen single cell suspensions of this tumor and corresponding normal tissue, tumor organoids and 2D-growing normal cell lines were successfully established and their integrity was confirmed. Both TSA-specific TCRs were efficiently expressed on CD8+ T cells from three donors. TCR-transgenic T cells showed activation upon co-culture with tumor organoids without recognition of normal ovarian cell lines. Normal cells were only recognized after loading with the specific target peptide.

Conclusions

In conclusion, the high relevance of two TCRs identified to be specific for a novel shared tumor-specific antigen was confirmed in a model of ovarian cancer organoids. The findings support further development of these TCRs for cancer immunotherapy and implementation of tumor organoids as a relevant tool for the characterization of TSA-specific TCRs.

Ethics Approval

‘The tumor and normal tissue samples were purchased at a Biobank, collected in compliance with all applicable EU regulations and were pseudonymized.’

Comparative analysis of TCR and CAR signaling informs CAR designs with superior antigen sensitivity and in vivo function

Chimeric antigen receptor (CAR)-modified T cell therapy is effective in treating lymphomas, leukemias, and multiple myeloma in which the tumor cells express high amounts of target antigen. However, achieving durable remission for these hematological malignancies and extending CAR T cell therapy to patients with solid tumors will require receptors that can recognize and eliminate tumor cells with a low density of target antigen. Although CARs were designed to mimic T cell receptor (TCR) signaling, TCRs are at least 100-fold more sensitive to antigen. To design a CAR with improved antigen sensitivity, we directly compared TCR and CAR signaling in primary human T cells. Global phosphoproteomic analysis revealed that key T cell signaling proteins-such as CD3δ, CD3ε, and CD3γ, which comprise a portion of the T cell co-receptor, as well as the TCR adaptor protein LAT-were either not phosphorylated or were only weakly phosphorylated by CAR stimulation. Modifying a commonplace 4-1BB/CD3ζ CAR sequence to better engage CD3ε and LAT using embedded CD3ε or GRB2 domains resulted in enhanced T cell activation in vitro in settings of a low density of antigen, and improved efficacy in in vivo models of lymphoma, leukemia, and breast cancer. These CARs represent examples of alterations in receptor design that were guided by in-depth interrogation of T cell signaling.

Abstract 1520: Targetable immunogenic tumor specific antigens can be identified in non-coding regions of the genome

CD8+ cytotoxic T cells are the main mediators of immune responses during cancer immunotherapy. Effective T cell functionality depends on the specific interaction with major histocompatibility (MHC) class I-bound peptide antigens. Significant efforts are being dedicated to the identification of novel tumor specific antigens (TSAs), investigating not only the known proteome, but also non-coding regions of the genome, that would allow for improved discrimination between cancer cells and healthy tissues. Through extensive comparisons of tumor and healthy tissues at the transcriptional and MHC-presented peptidome levels, TSAs were identified that derived from the translation in canonical and non-canonical reading frames of non-mutated non-coding genomic regions, including 5'- and 3'-untranslated regions (UTRs), introns and intergenic regions. A remarkable feature of these TSAs is that they are shared among patients and solid tumor types, thus representing ideal targets for cancer immunotherapies, including vaccines and adoptive cell therapies. To identify TSAs that can elicit T cell responses, a high throughput screening procedure was used to investigate the immunogenicity of 47 TSAs in the context of five common HLA types. Constructs harboring the TSA sequences were developed and transfected into HLA-matched monocyte-derived dendritic cells (mDCs) that were used to stimulate autologous CD8+ T cells. TSA-reactive T cells were enriched upon stimulation with antigen-positive and -negative cells using the T cell activation marker CD137 and sorted as single cells. Reactivity of individual T cell clones towards specific TSAs was confirmed by measuring cytokine release upon co-culture with HLA-matched TSA-positive and negative cell lines. Ten immunogenic TSAs were identified with this procedure, including at least one immunogenic TSA for each of the five analyzed HLAs. For some of these antigens, specific T cells were found in multiple healthy donors. The identified immunogenic TSAs derive from a variety of non-coding regions, such as introns, 5'-UTRs and non-coding RNAs. The T cell receptor (TCR) α and β chain sequences of TSA-reactive T cell clones were identified by NGS, engineered into a retroviral expression construct and transduced into CD8+ T cells. The reactivity of TCR-transgenic T cells against TSA-positive target cells was confirmed by recognition of TSA-peptide-loaded cell lines and target cells internally processing and presenting the TSAs. In conclusion, our high throughput screening approach successfully detected immunogenic TSAs. Furthermore, it can be used for the identification of TSA-reactive TCRs, thus representing a key tool in the development of novel TCR-based cancer immunotherapies targeting this novel class of TSAs.

Citation Format: Tiziana Franceschetti, Qingchuan Zhao, Krystel Vincent, Claude Perreault, Slavoljub Milosevic, Daniel Sommermeyer. Targetable immunogenic tumor specific antigens can be identified in non-coding regions of the genome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1520.

Abstract 1521: Combining a PRAME-specific TCR showing potent in vitro and in vivo anti-tumor reactivity and a favorable preclinical safety profile with a PD1-41BB switch receptor results in highly efficient T cells

The development of effective adoptive T cell therapies to treat cancer patients has two main challenges. The first is identifying an antigen that is highly expressed in tumors with limited or no expression in normal tissues. The second is to develop a receptor that specifically binds to this antigen inducing potent anti-tumor activity without cross-reactivity to healthy cells. An additional challenge in the treatment of solid tumors is the hostile tumor microenvironment (TME) including the T cell inhibitory PD-1/PD-L1 axis. The cancer/testis antigen PRAME is an attractive target for immunotherapies of solid tumors using TCR-modified T cells as it is highly expressed in several solid tumor indications while its expression in normal tissues is mainly restricted to the testis. TCR candidates with high specificity for a PRAME-derived peptide presented on HLA-A2 were isolated from a non-tolerized T cell repertoire using our well-established high-throughput TCR generation process. Based on multi-parameter screening a lead TCR candidate was selected from more than 30 analyzed specific TCRs. T cells genetically modified to express the lead TCR (MDG1014) were characterized using a dedicated set of multi-parameter in vitro assays to evaluate specificity and activity. Favorable preclinical specificity was confirmed by analysis of the potential cross-recognition of partially homologous peptides presented on HLA-A2 and the allo-cross-recognition of common HLAs. In addition, no off-target toxicity was observed when testing a set of normal cells. Specific effector functions were confirmed by cytotoxicity and cytokine release assays using a panel of PRAME-positive tumor cell lines from various solid tumor types. Furthermore, the efficacy of MDG1014 was corroborated in a xenograft melanoma mouse model. To prevent the inhibition of T cells via the PD1-PD-L1 axis in the TME, we developed a switch receptor fusing the extracellular domain of PD1 with the intracellular signaling domain of 4-1BB. Co-expressing the switch receptor on MDG1014 in vitro led to enhanced proliferation and increased effector function against PRAME/PD-L1-positive tumor cell lines, including after repeated exposure, suggesting increased T cell fitness under chronic antigen stimulation. To confirm this effect in vivo, we have established a xenograft mouse model with tumor cells expressing PRAME and high PD-L1 levels, mimicking the TME of hard to treat solid tumors. In summary, we developed a TCR specific for an HLA-A2-restricted PRAME-epitope with high natural anti-tumor reactivity and specificity. Its favorable preclinical profile qualifies the TCR for evaluation in clinical trials. Combining this potent TCR with our PD1-41BB switch receptor results in a very promising T cell product, especially for the treatment of solid tumors.

Citation Format: Ina Fetzer, Nadja Sailer, Melanie Salvermoser, Manon Weis, Christian Krendl, Maja Bürdek, Doris Brechtefeld, Isabella Rampp, Julian Rydzek-Wiesner, Monika Braun, Christian Ellinger, Christiane Geiger, Daniel Sommermeyer, Susanne Wilde. Combining a PRAME-specific TCR showing potent in vitro and in vivo anti-tumor reactivity and a favorable preclinical safety profile with a PD1-41BB switch receptor results in highly efficient T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1521.

Development of a CD8 co-receptor independent T-cell receptor specific for tumor-associated antigen MAGE-A4 for next generation T-cell-based immunotherapy

BACKGROUND

The cancer-testis antigen MAGE-A4 is an attractive target for T-cell-based immunotherapy, especially for indications with unmet clinical need like non-small cell lung or triple-negative breast cancer.

METHODS

An unbiased CD137-based sorting approach was first used to identify an immunogenic MAGE-A4-derived epitope (GVYDGREHTV) that was properly processed and presented on human leukocyte antigen (HLA)-A2 molecules encoded by the HLA-A*02:01 allele. To isolate high-avidity T cells via subsequent multimer sorting, an in vitro priming approach using HLA-A2-negative donors was conducted to bypass central tolerance to this self-antigen. Pre-clinical parameters of safety and activity were assessed in a comprehensive set of in vitro and in vivo studies.

RESULTS

A MAGE-A4-reactive, HLA-A2-restricted T-cell receptor (TCR) was isolated from primed T cells of an HLA-A2-negative donor. The respective TCR-T-cell (TCR-T) product bbT485 was demonstrated pre-clinically to have a favorable safety profile and superior in vivo potency compared with TCR-Ts expressing a TCR derived from a tolerized T-cell repertoire to self-antigens. This natural high-avidity TCR was found to be CD8 co-receptor independent, allowing effector functions to be elicited in transgenic CD4+ T helper cells. These CD4+ TCR-Ts supported an anti-tumor response by direct killing of MAGE-A4-positive tumor cells and upregulated hallmarks associated with helper function, such as CD154 expression and release of key cytokines on tumor-specific stimulation.

CONCLUSION

The extensive pre-clinical assessment of safety and in vivo potency of bbT485 provide the basis for its use in TCR-T immunotherapy studies. The ability of this non-mutated high-avidity, co-receptor-independent TCR to activate CD8+ and CD4+ T cells could potentially provide enhanced cellular responses in the clinical setting through the induction of functionally diverse T-cell subsets that goes beyond what is currently tested in the clinic.

Phosphoproteomic analysis of chimeric antigen receptor signaling reveals kinetic and quantitative differences that affect cell function

Chimeric antigen receptors (CARs) link an antigen recognition domain to intracellular signaling domains to redirect T cell specificity and function. T cells expressing CARs with CD28/CD3ζ or 4-1BB/CD3ζ signaling domains are effective at treating refractory B cell malignancies but exhibit differences in effector function, clinical efficacy, and toxicity that are assumed to result from the activation of divergent signaling cascades. We analyzed stimulation-induced phosphorylation events in primary human CD8⁺ CD28/CD3ζ and 4-1BB/CD3ζ CAR T cells by mass spectrometry and found that both CAR constructs activated similar signaling intermediates. Stimulation of CD28/CD3ζ CARs activated faster and larger-magnitude changes in protein phosphorylation, which correlated with an effector T cell-like phenotype and function. In contrast, 4-1BB/CD3ζ CAR T cells preferentially expressed T cell memory-associated genes and exhibited sustained antitumor activity against established tumors in vivo. Mutagenesis of the CAR CD28 signaling domain demonstrated that the increased CD28/CD3ζ CAR signal intensity was partly related to constitutive association of Lck with this domain in CAR complexes. Our data show that CAR signaling pathways cannot be predicted solely by the domains used to construct the receptor and that signal strength is a key determinant of T cell fate. Thus, tailoring CAR design based on signal strength may lead to improved clinical efficacy and reduced toxicity.

Tumour ischaemia by interferon-γ resembles physiological blood vessel regression

The relative contribution of the effector molecules produced by T cells to tumour rejection is unclear, but interferon-γ (IFNγ) is critical in most of the analysed models. Although IFNγ can impede tumour growth by acting directly on cancer cells, it must also act on the tumour stroma for effective rejection of large, established tumours. However, which stroma cells respond to IFNγ and by which mechanism IFNγ contributes to tumour rejection through stromal targeting have remained unknown. Here we use a model of IFNγ induction and an IFNγ-GFP fusion protein in large, vascularized tumours growing in mice that express the IFNγ receptor exclusively in defined cell types. Responsiveness to IFNγ by myeloid cells and other haematopoietic cells, including T cells or fibroblasts, was not sufficient for IFNγ-induced tumour regression, whereas responsiveness of endothelial cells to IFNγ was necessary and sufficient. Intravital microscopy revealed IFNγ-induced regression of the tumour vasculature, resulting in arrest of blood flow and subsequent collapse of tumours, similar to non-haemorrhagic necrosis in ischaemia and unlike haemorrhagic necrosis induced by tumour necrosis factor. The early events of IFNγ-induced tumour ischaemia resemble non-apoptotic blood vessel regression during development, wound healing or IFNγ-mediated, pregnancy-induced remodelling of uterine arteries. A better mechanistic understanding of how solid tumours are rejected may aid the design of more effective protocols for adoptive T-cell therapy.

Analysis of ROR1 Protein Expression in Human Cancer and Normal Tissues

Purpose: This study examines cell surface ROR1 expression in human tumors and normal tissues. ROR1 is considered a promising target for cancer therapy due to putative tumor-specific expression, and multiple groups are developing antibodies and/or chimeric antigen receptor-modified T cells to target ROR1. On-target, off-tumor toxicity is a challenge for most nonmutated tumor antigens; however, prior studies suggest that ROR1 is absent on most normal tissues.Experimental Design: Our studies show that published antibodies lack sensitivity to detect endogenous levels of cell surface ROR1 by immunohistochemistry (IHC) in formalin-fixed, paraffin-embedded tissues. We developed a ROR1-specific monoclonal antibody (mAb) targeting the carboxy-terminus of ROR1 and evaluated its specificity and sensitivity in IHC.Results: The 6D4 mAb is a sensitive and specific reagent to detect cell surface ROR1 by IHC. The data show that ROR1 is homogenously expressed on a subset of ovarian cancer, triple-negative breast cancer, and lung adenocarcinomas. Contrary to previous findings, we found ROR1 is expressed on several normal tissues, including parathyroid; pancreatic islets; and regions of the esophagus, stomach, and duodenum. The 6D4 mAb recognizes rhesus ROR1, and ROR1 expression was similar in human and macaque tissues, suggesting that the macaque is a suitable model to evaluate safety of ROR1-targeted therapies.Conclusions: ROR1 is a promising immunotherapeutic target in many epithelial tumors; however, high cell surface ROR1 expression in multiple normal tissues raises concerns for on-target off-tumor toxicities. Clinical translation of ROR1-targeted therapies warrants careful monitoring of toxicities to normal organs and may require strategies to ensure patient safety. Clin Cancer Res; 23(12); 3061-71. ©2016 AACR.

Targeted antibody-mediated depletion of murine CD19 CAR T cells permanently reverses B cell aplasia

The adoptive transfer of T cells that have been genetically modified to express a CD19-specific chimeric antigen receptor (CAR) is effective for treating human B cell malignancies. However, the persistence of functional CD19 CAR T cells causes sustained depletion of endogenous CD19+ B cells and hypogammaglobulinemia. Thus, there is a need for a mechanism to ablate transferred T cells after tumor eradication is complete to allow recovery of normal B cells. Previously, we developed a truncated version of the epidermal growth factor receptor (EGFRt) that is coexpressed with the CAR on the T cell surface. Here, we show that targeting EGFRt with the IgG1 monoclonal antibody cetuximab eliminates CD19 CAR T cells both early and late after adoptive transfer in mice, resulting in complete and permanent recovery of normal functional B cells, without tumor relapse. EGFRt can be incorporated into many clinical applications to regulate the survival of gene-engineered cells. These results support the concept that EGFRt represents a promising approach to improve safety of cell-based therapies.

CD19 CAR-T cells of defined CD4+:CD8+ composition in adult B cell ALL patients

BACKGROUND

T cells that have been modified to express a CD19-specific chimeric antigen receptor (CAR) have antitumor activity in B cell malignancies; however, identification of the factors that determine toxicity and efficacy of these T cells has been challenging in prior studies in which phenotypically heterogeneous CAR-T cell products were prepared from unselected T cells.

METHODS

We conducted a clinical trial to evaluate CD19 CAR-T cells that were manufactured from defined CD4+ and CD8+ T cell subsets and administered in a defined CD4+:CD8+ composition to adults with B cell acute lymphoblastic leukemia after lymphodepletion chemotherapy.

RESULTS

The defined composition product was remarkably potent, as 27 of 29 patients (93%) achieved BM remission, as determined by flow cytometry. We established that high CAR-T cell doses and tumor burden increase the risks of severe cytokine release syndrome and neurotoxicity. Moreover, we identified serum biomarkers that allow testing of early intervention strategies in patients at the highest risk of toxicity. Risk-stratified CAR-T cell dosing based on BM disease burden decreased toxicity. CD8+ T cell-mediated anti-CAR transgene product immune responses developed after CAR-T cell infusion in some patients, limited CAR-T cell persistence, and increased relapse risk. Addition of fludarabine to the lymphodepletion regimen improved CAR-T cell persistence and disease-free survival.

CONCLUSION

Immunotherapy with a CAR-T cell product of defined composition enabled identification of factors that correlated with CAR-T cell expansion, persistence, and toxicity and facilitated design of lymphodepletion and CAR-T cell dosing strategies that mitigated toxicity and improved disease-free survival.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01865617.

FUNDING

R01-CA136551; Life Science Development Fund; Juno Therapeutics; Bezos Family Foundation.

Role of memory T cell subsets for adoptive immunotherapy

Adoptive transfer of primary (unmodified) or genetically engineered antigen-specific T cells has demonstrated astonishing clinical results in the treatment of infections and some malignancies. Besides the definition of optimal targets and antigen receptors, the differentiation status of transferred T cells is emerging as a crucial parameter for generating cell products with optimal efficacy and safety profiles. Long-living memory T cells subdivide into phenotypically as well as functionally different subsets (e.g. central memory, effector memory, tissue-resident memory T cells). This diversification process is crucial for effective immune protection, with probably distinct dependencies on the presence of individual subsets dependent on the disease to which the immune response is directed as well as its organ location. Adoptive T cell therapy intends to therapeutically transfer defined T cell immunity into patients. Efficacy of this approach often requires long-term maintenance of transferred cells, which depends on the presence and persistence of memory T cells. However, engraftment and survival of highly differentiated memory T cell subsets upon adoptive transfer is still difficult to achieve. Therefore, the recent observation that a distinct subset of weakly differentiated memory T cells shows all characteristics of adult tissue stem cells and can reconstitute all types of effector and memory T cell subsets, became highly relevant. We here review our current understanding of memory subset formation and T cell subset purification, and its implications for adoptive immunotherapy.

Inclusion of Strep-tag II in design of antigen receptors for T-cell immunotherapy

The tactical introduction of Strep-tag II into synthetic antigen receptors provides engineered T cells with a marker for identification and rapid purification, and a functional element for selective antibody coated microbead-driven large-scale expansion. Such receptor designs can be applied to chimeric antigen receptors of different ligand specificities and costimulatory domains, and to T cell receptors to facilitate cGMP manufacturing of adoptive T cell therapies to treat cancer and other diseases.

Chimeric antigen receptor-modified T cells derived from defined CD8+ and CD4+ subsets confer superior antitumor reactivity in vivo

Adoptive T-cell therapy with gene-modified T-cells expressing a tumor-reactive T-cell receptor (TCR) or chimeric antigen receptor (CAR) is a rapidly growing field of translational medicine and has shown success in the treatment of B-cell malignancies and solid tumors. In all reported trials, patients have received T-cell products comprised of random compositions of CD4⁺ and CD8⁺ naïve and memory T-cells, meaning that each patient received a different therapeutic agent. This variation might have influenced the efficacy of T-cell therapy, and complicates comparison of outcomes between different patients and across trials. We analyzed CD19 CAR-expressing effector T-cells derived from different subsets (CD4⁺/CD8⁺ naïve, central memory, effector memory). T-cells derived from each of the subsets were efficiently transduced and expanded, but showed clear differences in effector function and proliferation in vitro and in vivo. Combining the most potent CD4⁺ and CD8⁺ CAR-expressing subsets resulted in synergistic antitumor effects in vivo. We show that CAR-T-cell products generated from defined T-cell subsets can provide uniform potency compared with products derived from unselected T-cells that vary in phenotypic composition. These findings have important implications for the formulation of T-cell products for adoptive therapies.

Safety of targeting ROR1 in primates with chimeric antigen receptor-modified T cells

Genetic engineering of T cells for adoptive transfer by introducing a tumor-targeting chimeric antigen receptor (CAR) is a new approach to cancer immunotherapy. A challenge for the field is to define cell surface molecules that are both preferentially expressed on tumor cells and can be safely targeted with T cells. The orphan tyrosine kinase receptor ROR1 is a candidate target for T-cell therapy with CAR-modified T cells (CAR-T cells) because it is expressed on the surface of many lymphatic and epithelial malignancies and has a putative role in tumor cell survival. The cell surface isoform of ROR1 is expressed in embryogenesis but absent in adult tissues except for B-cell precursors and low levels of transcripts in adipocytes, pancreas, and lung. ROR1 is highly conserved between humans and macaques and has a similar pattern of tissue expression. To determine if low-level ROR1 expression on normal cells would result in toxicity or adversely affect CAR-T cell survival and/or function, we adoptively transferred autologous ROR1 CAR-T cells into nonhuman primates. ROR1 CAR-T cells did not cause overt toxicity to normal organs and accumulated in bone marrow and lymph node sites, where ROR1-positive B cells were present. The findings support the clinical evaluation of ROR1 CAR-T cells for ROR1(+) malignancies and demonstrate the utility of nonhuman primates for evaluating the safety of immunotherapy with engineered T cells specific for tumor-associated molecules that are homologous between humans and nonhuman primates.

The nonsignaling extracellular spacer domain of chimeric antigen receptors is decisive for in vivo antitumor activity

The use of synthetic chimeric antigen receptors (CAR) to redirect T cells to recognize tumor provides a powerful new approach to cancer immunotherapy; however, the attributes of CARs that ensure optimal in vivo tumor recognition remain to be defined. Here, we analyze the influence of length and composition of IgG-derived extracellular spacer domains on the function of CARs. Our studies demonstrate that CD19-CARs with a long spacer from IgG4 hinge-CH2-CH3 are functional in vitro but lack antitumor activity in vivo due to interaction between the Fc domain within the spacer and the Fc receptor-bearing myeloid cells, leading to activation-induced T-cell death. We demonstrate that in vivo persistence and antitumor effects of CAR-T cells with a long spacer can be restored by modifying distinct regions in the CH2 domain that are essential for Fc receptor binding. Our studies demonstrate that modifications that abrogate binding to Fc receptors are crucial for CARs in which a long spacer is obligatory for tumor recognition as shown here for a ROR1-specific CAR. These results demonstrate that the length and composition of the extracellular spacer domain that lacks intrinsic signaling function can be decisive in the design of CARs for optimal in vivo activity.

Misinitiation of intrathymic MART-1 transcription and biased TCR usage explain the high frequency of MART-1-specific T cells

Immunity to tumor differentiation antigens, such as melanoma antigen recognized by T cells 1 (MART-1), has been comprehensively studied. Intriguingly, CD8(+) T cells specific for the MART-1(26(27)-35) epitope in the context of HLA-A0201 are about 100 times more abundant compared with T cells specific for other tumor-associated antigens. Moreover, MART-1-specific CD8(+) T cells show a highly biased usage of the Vα-region gene TRAV12-2. Here, we provide independent support for this notion, by showing that the combinatorial pairing of different TCRα- and TCRβ- chains derived from HLA-A2-MART-1(26-35) -specific CD8(+) T-cell clones is unusually permissive in conferring MART-1 specificity, provided the CDR1α TRAV12-2 region is used. Whether TCR bias alone accounts for the unusual abundance of HLA-A2-MART-1(26-35) -specific CD8(+) T cells has remained conjectural. Here, we provide an alternative explanation: misinitiated transcription of the MART-1 gene resulting in truncated mRNA isoforms leads to lack of promiscuous transcription of the MART-1(26-35) epitope in human medullary thymic epithelial cells and, consequently, evasion of central self-tolerance toward this epitope. Thus, biased TCR usage and leaky central tolerance might act in an independent and additive manner to confer high frequency of MART-1(26-35) -specific CD8(+) T cells.

Plasticity in the contribution of T cell receptor variable region residues to binding of peptide-HLA-A2 complexes

One hypothesis accounting for major histocompatibility complex (MHC) restriction by T cell receptors (TCRs) holds that there are several evolutionary conserved residues in TCR variable regions that contact MHC. While this "germline codon" hypothesis is supported by various lines of evidence, it has been difficult to test. The difficulty stems in part from the fact that TCRs exhibit low affinities for pep/MHC, thus limiting the range of binding energies that can be assigned to these key interactions using mutational analyses. To measure the magnitude of binding energies involved, here we used high-affinity TCRs engineered by mutagenesis of CDR3. The TCRs included a high-affinity, MART-1/HLA-A2-specific single-chain TCR and two other high-affinity TCRs that all contain the same Vα region and recognize the same MHC allele (HLA-A2), with different peptides and Vβ regions. Mutational analysis of residues in CDR1 and CDR2 of the three Vα2 regions showed the importance of the key germline codon residue Y51. However, two other proposed key residues showed significant differences among the TCRs in their relative contributions to binding. With the use of single-position, yeast-display libraries in two of the key residues, MART-1/HLA-A2 selections also revealed strong preferences for wild-type germline codon residues, but several alternative residues could also accommodate binding and, hence, MHC restriction. Thus, although a single residue (Y51) could account for a proportion of the energy associated with positive selection (i.e., MHC restriction), there is significant plasticity in requirements for particular side chains in CDR1 and CDR2 and in their relative binding contributions among different TCRs.

Receptor affinity and extracellular domain modifications affect tumor recognition by ROR1-specific chimeric antigen receptor T cells

PURPOSE

The adoptive transfer of T cells modified to express a chimeric antigen receptor (CAR) comprised of an extracellular single-chain antibody (scFV) fragment specific for a tumor cell surface molecule, and linked to an intracellular signaling module, has activity in advanced malignancies. The receptor tyrosine kinase-like orphan receptor 1 (ROR1) is a tumor-associated molecule expressed in prevalent B-lymphoid and epithelial cancers and is absent on normal mature B cells and vital tissues, making it a candidate for CAR T-cell therapy.

EXPERIMENTAL DESIGN

We constructed ROR1-CARs from scFVs with different affinities and containing extracellular IgG4-Fc spacer domains of different lengths, and evaluated the ability of T cells expressing each CAR to recognize ROR1(+) hematopoietic and epithelial tumors in vitro, and to eliminate human mantle cell lymphoma (MCL) engrafted into immunodeficient mice.

RESULTS

ROR1-CARs containing a short "Hinge-only" extracellular spacer conferred superior lysis of ROR1(+) tumor cells and induction of T-cell effector functions compared with CARs with long "Hinge-CH2-CH3" spacers. CARs derived from a higher affinity scFV conferred maximum T-cell effector function against primary CLL and ROR1(+) epithelial cancer lines in vitro without inducing activation-induced T-cell death. T cells modified with an optimal ROR1-CAR were equivalently effective as CD19-CAR-modified T cells in mediating regression of JeKo-1 MCL in immunodeficient mice.

CONCLUSIONS

Our results show that customizing spacer design and increasing affinity of ROR1-CARs enhances T-cell effector function and recognition of ROR1(+) tumors. T cells modified with an optimized ROR1-CAR have significant antitumor efficacy in a preclinical model in vivo, suggesting they may be useful to treat ROR1(+) tumors in clinical applications.

NY-ESO-1 antigen-reactive T cell receptors exhibit diverse therapeutic capability

The cancer-testis antigen NY-ESO-1 has been used as a target for different immunotherapies like vaccinations and adoptive transfer of antigen-specific cytotoxic T cells, as it is expressed in various tumor types and has limited expression in normal cells. The in vitro generation of T cells with defined antigen specificity by T cell receptor (TCR) gene transfer is an established method to create cells for immunotherapy. However, an extensive characterization of TCR which are candidates for treatment of patients is crucial for successful therapies. The TCR has to be efficiently expressed, their affinity to the desired antigen should be high enough to recognize low amounts of endogenously processed peptides on tumor cells, and the TCR should not be cross-reactive to other antigens. We characterized three NY-ESO-1 antigen-reactive cytotoxic T lymphocyte clones which were generated by different approaches of T cell priming (autologous, allogeneic), and transferred their TCR into donor T cells for more extensive evaluations. Although one TCR most efficiently bound MHC-multimers loaded with NY-ESO-1 peptide, T cells expressing this transgenic TCR were not able to recognize endogenously processed antigen. A second TCR recognized HLA-A2 independent of the bound peptide beside its much stronger recognition of NY-ESO-1 bound to HLA-A2. A third TCR displayed an intermediate but peptide-specific performance in all functional assays and, therefore, is the most promising candidate TCR for further clinical development. Our data indicate that multiple parameters of TCR gene-modified T cells have to be evaluated to identify an optimal TCR candidate for adoptive therapy.

Human antitumor CD8+ T cells producing Th1 polycytokines show superior antigen sensitivity and tumor recognition

Adoptive transfer of T cells expressing transgenic TCR with antitumor specificity provides a hopeful new therapy for patients with advanced cancer. To fulfill a large need for TCR with high affinity and specificity for various tumor entities, we sought to identify parameters for rapid selection of CTL clones with suitable characteristics. Twelve CTL clones displaying different Ag sensitivities for the same peptide-MHC epitope of the melanoma-associated Ag tyrosinase were analyzed in detail. Better MHC-multimer binding and slower multimer release are thought to reflect stronger TCR-peptide-MHC interactions; thus, these parameters would seem well suited to identify higher avidity CTL. However, large disparities were found comparing CTL multimer binding with peptide sensitivity. In contrast, CD8(+) CTL with superior Ag sensitivity mediated good tumor cytotoxicity and also secreted the triple combination of IFN-γ, IL-2, and TNF-α, representing a Th1 pattern often missing in lower avidity CTL. Furthermore, recipient lymphocytes were imbued with high Ag sensitivity, superior tumor recognition, as well as capacity for Th1 polycytokine secretion after transduction with the TCR of a high-avidity CTL. Thus, Th1 polycytokine secretion served as a suitable parameter to rapidly demark cytotoxic CD8(+) T cell clones for further TCR evaluation.

Minimal amino acid exchange in human TCR constant regions fosters improved function of TCR gene-modified T cells

TCR gene therapy using adoptive transfer of TCR gene-modified T cells is a new strategy for treatment of cancer. One critical prerequisite for TCR gene therapy is sufficient expression of transferred TCRs. Several strategies to achieve optimal expression were developed, including "murinization," which replaces the human TCRalpha and TCRbeta constant regions by their murine counterparts. Using a series of mouse-human hybrid constructs, we have identified nine amino acids responsible for the improved expression of murinized TCRs. Five essential amino acid exchanges were identified in the TCRbeta C region, with exchange of a glutamic acid (human) for a basic lysine (mouse) at position 18 of the C region, being most important. For the TCRalpha C region, an area of four amino acids was sufficient for improved expression. The minimally murinized TCR variants (harboring only nine residues of the mouse sequence) enhanced expression of human TCRs by supporting preferential pairing of transferred TCR chains and a more stable association with the CD3 proteins. Most important, usage of minimally murinized TCR chains improved the function of transduced primary human T cells in comparison with cells transduced with wild-type TCRs. For TCR gene therapy, the utilization of minimally instead of completely murinized constant regions dramatically reduces the number of foreign residues and thereby the risk for immunogenicity of therapeutic TCRs.

Tumor rejection by local interferon gamma induction in established tumors is associated with blood vessel destruction and necrosis

It has been shown that injecting a suspension of IFN-γ-secreting tumor cells results in their rejection. This effect has been attributed to IFN-γ preventing tumor stroma formation but not to a direct effect on the cancer cells. However, it is not known, which influence IFN-γ has on tumors with an established stroma. To address this question, the plasmacytoma cell line J558L was transduced with a vector allowing doxycycline-inducible IFN-γ gene expression. After the injection of the tumor cells into mice, IFN-γ was induced at different time points. Tumors did not grow when inducing IFN-γ immediately after tumor cell inoculation, while approximately half of the tumors were rejected when IFN-γ was induced in early established tumors within 2 weeks. Induction of IFN-γ 2-3 weeks after tumor cell inoculation was less efficient (0-17% rejection). IFN-γ induction in established tumors led to a reduction of CD146(+) endothelial cells and massive necrosis. Together, we show that vascularized tumors can be rejected by local IFN-γ expression, but that rejection of established tumors was less efficient over time. This suggests that transplanted tumors became less susceptible to local IFN-γ treatment the better they are established.

Enhanced functionality of T cell receptor-redirected T cells is defined by the transgene cassette

The transfer of T cell receptor (TCR) genes allows to endow T cells with a new antigen specificity. For clinical applications of TCR-redirected T cells, efficient functional expression of the transgenic TCR is a key prerequisite. Here, we compared the influence of the transgene cassette on the expression and function of the murine TCR P14 (recognizing a LCMV gp33 epitope) and the human TCR WT-1 (recognizing an epitope of the tumor-associated antigen WT-1). We constructed different vectors, in which TCRalpha- and beta-chain genes were either (a) linked by an internal ribosomal entry site (IRES), (b) combined by a 2A peptide, or (c) introduced into two individual retroviral constructs. While in a TCR-deficient T cell line TCR P14 was expressed equally well by all constructs, we found that IRES- but not 2A-employing TCR expression is hampered in a TCR-bearing cell line and in primary murine T cells where the transgenic TCR has to compete with endogenous TCR chains. Similarly, 2A-linked TCR WT-1 genes yielded highest expression and function as measured by tetramer binding and peptide-specific IFN-gamma secretion. Differences in expression were independent of copy number integration as shown by real-time PCR. Thus, linking TCRalpha- and beta-chain genes by a 2A peptide is superior to an IRES for TCR expression and T cell function.

Dual T cell receptor expressing CD8+ T cells with tumor- and self-specificity can inhibit tumor growth without causing severe autoimmunity

The engineering of Ag-specific T cells by expression of TCR genes is a convenient method for adoptive T cell immunotherapy. A potential problem is the TCR gene transfer into self-reactive T cells that survived tolerance mechanisms. We have developed an experimental system with T cells that express two TCRs with defined Ag-specificities, one recognizing a tumor-specific Ag (LCMV-gp(33)), the other recognizing a self-Ag in the pancreas (OVA). By using tumor cells expressing high and low amounts of Ag and mice expressing high and low levels of self-Ag in the pancreas (RIP-OVA-Hi and RIP-OVA-Lo), we show that 1) tumor rejection requires high amount of tumor Ag, 2) severe autoimmunity requires high amount of self-Ag, and 3) if Ag expression on tumor cells is sufficient and low in the pancreas, successful adoptive T cell therapy can be obtained in the absence of severe autoimmunity. These results are shown with T cells from dual TCR transgenic mice or T cells that were redirected by TCR gene transfer. Our data demonstrate that the approach of adoptively transferring TCR redirected T cells can be effective without severe side effects, even when high numbers of T cells with self-reactivity were transferred.

Designer T cells by T cell receptor replacement

T cell receptor (TCR) gene transfer is a convenient method to produce antigen-specific T cells for adoptive therapy. However, the expression of two TCR in T cells could impair their function or cause unwanted effects by mixed TCR heterodimers. With five different TCR and four different T cells, either mouse or human, we show that some TCR are strong--in terms of cell surface expression--and replace weak TCR on the cell surface, resulting in exchange of antigen specificity. Two strong TCR are co-expressed. A mouse TCR replaces human TCR on human T cells. Even though it is still poorly understood why some TCRalpha/beta combinations are preferentially expressed on T cells, our data suggest that, in the future, designer T cells with exclusive tumor reactivity can be generated by T cell engineering.