ALBERT

Description: The remissions achieved using autologous T-cells expressing chimeric antigen receptors (CARs) in patients with advanced B cell leukemia and lymphomas have encouraged the use of CAR technology to treat different types of cancers by targeting distinct tumor-specific antigens. Since the current autologous approach utilizes CAR T-cells manufactured on a "per patient" basis, we propose an alternative approach based on the use of a standardized platform for manufacturing T-cells from third-party healthy donors to generate allogeneic "off-the-shelf" CAR T-cell-based frozen products. In the present work we have adapted this allogeneic platform to the production of T-cells targeting CD123, the transmembrane alpha chain of the interleukin-3 receptor, which is expressed on tumor cells from the majority of patients with Acute Myeloid Leukemia (AML). Multiple antigen recognition domains were screened in the context of different CAR architectures to identify candidates displaying activity against cells expressing variable levels of the CD123 antigen. The three lead candidates were tested in an orthotopic human AML cell line xenograft mouse model. From the three candidates that displayed comparable activity in vitro, we found two candidates capable of eradicating tumor cells in vivo with high efficiency. Subsequently, Transcription Activator-Like Effector Nuclease (TALEN) gene editing technology was used to inactivate the TCRα constant (TRAC) gene, eliminating the potential for engineered T-cells to mediate Graft versus Host Disease (GvHD). Editing of the TRAC gene can be achieved at high frequencies, and allows efficient amplification of TCR-deficient T-cells that no longer mediate alloreactivity in a xeno-GvHD mouse model. In addition, we show that TCR-deficient T-cells display equivalent in vitro and in vivo activity to non-edited T-cells expressing the same CAR. We have performed an initial evaluation of the expression of CD123 in AML patients and found an average cell surface expression of CD123 was of 67% in leukemic blasts (95% CI 48-82), 71% in CD34+CD38+ cells (95% CI 56-86), and 64% in CD34+CD38- (95% CI 41-87). Importantly, we have found that CD123 surface expression persists in CD34+CD38-CD90- cells after therapy in at least 20% of patients in remission (n=25), thus emphasizing the relevance of the target. Currently, the sensitivity of primary AML cells to CAR T-cells is being tested. Finally, we will also present our large scale manufacturing process of allogeneic CD123 specific T-cells from healthy donors, showing the feasibility for this off-the-shelf T-cell product that could be available for administration to a large number of AML patients. Disclosures Galetto: Cellectis SA: Employment. Lebuhotel:Cellectis SA: Employment. Gouble:Cellectis SA: Employment. Smith:Cellectis: Employment, Patents & Royalties.

Description: Adoptive immunotherapy with autologous T-cells expressing chimeric antigen receptors (CARs) targeting CD19 has achieved long-term remissions in patients with B cell leukemia, pointing out that CAR technology may become a new alternative in cancer treatment. In this work we assessed the feasibility of targeting the CS1 antigen (SLAMF7) for the treatment of Multiple Myeloma (MM). MM is a B-cell neoplasia characterized by clonal expansion of malignant plasma cells in the bone marrow. Even if currently available therapies can improve overall survival, MM still remains incurable in most patients. Immunotherapy against MM is therefore an area in which extensive research is being made, with novel antigenic targets being considered. Among these is the CS1 glycoprotein, which is highly expressed on tumor cells from most patients with MM. However, CS1 is also expressed on normal CD8+ T-cells, which may be problematic for a CAR-based approach as antigen-expressing T cells will be targeted, impacting both the number and the phenotype of the final CAR T cell population. To circumvent this issue we have used our highly-efficient transcription activator-like effector nuclease (TALEN) gene-editing technology to inactivate CS1 in T-cells prior to transduction with a viral vector encoding an anti-CS1 CAR. Our results demonstrate that while non-gene-edited T-cells expressing an anti-CS1 CAR display limited cytolytic activity against MM cell lines, and resulted in a progressive loss of CD8+ T-cells. CS1-gene-edited CAR cells display significantly increased cytotoxic activity, with the percentage of CD8+ T-cells remaining unaffected. In addition, experiments in an orthotopic MM mouse model showed that CS1 disrupted T-cells were able to mediate an in vivo anti-tumoral activity. Subsequently, we have utilized this strategy for CS1 in the context of our allogeneic "off-the-shelf" engineered CAR+ T-cell platform. This allogenic platform utilizes TALEN gene editing technology to inactivate the TCRα constant (TRAC) gene, eliminating their potential to mediate Graft versus Host Disease (GvHD). We have previously shown that editing of the TRAC gene can be achieved at high frequencies, allowing efficient production of TCR-deficient T-cells that no longer mediate alloreactivity in a xeno-GvHD mouse model. Our results also show that multiplex genome editing is possible and can lead to the production of double KO (TRAC and CS1) T-cells, allowing large scale manufacturing of allogeneic, non alloreactive CS1 specific T-cells with enhanced antitumor activity. Moreover, these allogenic T-cells could be easily available for administration to a large number of MM patients. Disclosures Galetto: Cellectis SA: Employment. Chion-Sotinel:Cellectis SA: Employment. Gouble:Cellectis SA: Employment. Smith:Cellectis: Employment, Patents & Royalties.

Description: Chimeric antigen receptor (CAR)-redirected T-cells have given rise to long-term durable remissions and remarkable objective response rates in patients with refractory leukemia, raising hopes that a wider application of CAR technology may lead to a new paradigm in cancer treatment. A limitation of the current autologous approach is that CAR T-cells must be manufactured on a "per patient basis". We have developed a standardized platform for manufacturing T-cells from third-party healthy donors to generate allogeneic "off-the-shelf" engineered CD19-CAR+ T-cell–based frozen products. Our platform involves the use of transcription activator-like effector nucleases (TALEN™), which mediate the simultaneous inactivation of two genes through genome editing. The knockout of the TCR alpha gene eliminates TCR expression and is intended to abrogate the donor T-cell’s potential for graft-versus-host disease (GvHD), while knocking out the CD52 gene makes donor T-cells resistant to the lymphodepleting agent alemtuzumab. In addition, our T-cells are engineered to coexpress the RQR8 gene as a safety feature, with the aim of rendering them sensitive to the monoclonal antibody rituximab. We previously provided proof-of-concept for the application of this approach by manufacturing TCR/CD52-deficient RQR8+ and CD19-CAR+ T-cells (UCART19) using a good manufacturing practice–compatible process, and we also demonstrated that the resulting UCART19 cells were functional using in vitro assays. Here we report the ability of UCART19 cells to engraft into an orthotopic human CD19+ lymphoma xenograft immunodeficient mouse model. UCART19 cells exhibited antitumor activity equivalent to that of standard CD19 CAR T-cells. We also demonstrated that UCART19 cells did not mediate alloreactivity in a xeno-GvHD mouse model. Furthermore, the effectiveness of the rituximab-induced depletion mechanism of RQR8+ cells was shown in an immunocompetent mouse model. In conclusion, our work significantly enlarges upon previous results by showing in vivo that (1) concomitant inactivation of a second gene has no deleterious effects on T-cells, (2) the antitumor potency of manufactured TCR/CD52-deficient CD19–CAR+ T-cells is similar to that of standard CD19-CAR+ T-cells, (3) TCR gene inactivation is efficient at preventing potential graft-versus-host reaction, and (4) allogeneic T-cells can be depleted by the use of rituximab. This valuable dataset supports the development of allogeneic CAR T-cells, and UCART19 will be investigated in an exploratory, first-in-human, clinical trial where refractory/relapsed CD19+ B-cell leukemia patients are to be enrolled. Disclosures Gouble: Cellectis SA: Employment. Poirot:Cellectis SA: Employment. Schiffer-Mannioui:Cellectis SA: Employment. Galetto:Cellectis SA: Employment. Derniame:Cellectis SA: Employment. Arnould:Cellectis SA: Employment. Desseaux:Cellectis SA: Employment. Smith:Cellectis SA: Employment.

Description: Acute myeloid leukemia (AML) is a disease with a high incidence of relapse and mortality. Relapse is attributed to the inability of current chemotherapeutic agents to eliminate leukemia stem cells (LSCs). Thus, to improve leukemia therapy, it is critical to identify agents that effectively target LSCs, e.g. via unique cell surface antigens. A target of major interest is CD123, the transmembrane alpha chain of the interleukin-3 receptor, expressed on blasts, leukemic progenitor and LSCs in the majority of AML patients. We have developed an allogeneic chimeric antigen receptor (CAR) T-cell platform using T-cells from third-party healthy donors to generate engineered T-cells targeting CD123 (UCART123). UCART123 cells no longer express a TCR, having undergone a disruption of the TCRα gene using TALEN¨ gene editing technology followed by elimination of TCRα/β-positive cells, thus minimizing the potential for engineered T-cells to cause graft versus host disease (GvHD). We tested the activity of UCART123 cells in vitro using primary AML samples, normal bone marrow (nBM) and cord blood (CB) cells. Additionally, we established patient derived xenograft (PDX), nBM- or CB- humanized xenografts (HuX) and a competitive nBM/AML xenograft model to evaluate the in vivo potential of UCART123 cells to preferentially eliminate AML over normal BM cells. In vitro studies reveled that UCART123 cells eliminate AML cells and had minimum effect on normal cells at effector:target ratios as low as 0.5:1. Next, we evaluated the in vivo activity of UCART123 against PDX (AML37, TP53 mutant relapsed AML and AML20, FLT3-ITD+ and TP53 mutant AML) and normal-HuX mice (n=3). At 3 weeks post T-cell injection we found that UCART123 treatment eliminated the leukemic cells when using 10M or 3M UCART123 cells per mouse and no significant difference between PBS or TCR-deficient T-cells (TCRkoT; 10M/mouse). Toxicity to normal cells was dose dependent, doses of 2.5M UCART123 cells did not significantly affect hematopoietic cells. T-cells were detected in the BM at day 14 after treatment, without evidence of GvHD. Since we found complete elimination of human AML cells in the BM of the PDX precluding serial transplantation to evaluate LSC activity, we initiated two new sets of PDX-AML mice [AML2 (NPM1+FLT3-ITD+) and AML37 (TP53 mutant)] to evaluate long-term survival, and time to relapse. Animals were treated with PBS, UCART123 (2.5M or 1M), TCRkoT (2.5M), or Ara-C (60mg/kg 5 days). Animal weight and peripheral blood (PB) was monitored. Cytokines changes were evaluated at day 2. We found that the cytokine release and the kinetics of AML targeting by UCART123 were dose dependent. We found a significant overall survival (OS) benefit with UCART123 in both PDX tested. For example, all PDX-AML2 mice treated with UCART123 are alive to date (day 167; updates will be presented). All other cohorts were lost (PBS day124, TCRkoT day126, AraC day144) (Figure 1A). Finally, to determine selectivity of UCART123 cells for AML cells over nBM cells, we generated a competitive model bearing both nBM and AML (NPM1+FLT3-ITD+). With PB monitoring, treatment with 1M UCAR123 cells resulted in selective elimination of AML cells. Untreated and TCRkoT treated mice showed a rapid progression of AML, while treated mice showed normal hematopoiesis (Figure 1B). NPM1 transcripts were also monitored in the mice and confirmed molecular remission in mice. Taken together, our data show that UCART123, an "off-the-shelf" allogeneic engineered CAR-T product targeting CD123 potently eliminates AML cells in vivo, prevents relapse, and improves OS in PDX mice. Also, UCART123 cells preferentially targets AML cells in a competitive BM/AML model. A phase I trial of UCART123 in AML is under development. Disclosures Guzman: Cellectis: Research Funding. Sugita:Cellectis: Research Funding. Galetto:Cellectis SA: Employment. Gouble:Cellectis: Employment. Smith:Cellectis SA: Employment. Roboz:Agios, Amgen, Amphivena, Astex, AstraZeneca, Boehringer Ingelheim, Celator, Celgene, Genoptix, Janssen, Juno, MEI Pharma, MedImmune, Novartis, Onconova, Pfizer, Roche/Genentech, Sunesis, Teva: Consultancy; Cellectis: Research Funding.

Description: Adoptive immunotherapy using autologous T-cells endowed with chimeric antigen receptors (CARs) has emerged as a promising new approach to treating cancer. However, a limitation of this approach is that CAR T-cells must be generated on a bespoke basis. To overcome this limitation, we have developed an allogeneic based platform for large scale production of “off-the-shelf” CAR T-cells from unrelated 3rd party donors. This platform utilizes Transcription Activator-Like Effector Nuclease (TALENTM) gene editing technology to inactivate the TCRα constant (TRAC) gene, eliminating the potential for T-cells bearing alloreactive TCR’s to mediate Graft versus Host Disease (GvHD). We have previously demonstrated that editing of the TRAC gene can be achieved at high frequencies, obtaining up to 80% of TCRαβ negative cells. This allows us to efficiently produce TCR-deficient T-cells that have been shown to no longer mediate alloreactivity in a xeno-GvHD mouse model. Furthermore, the capacity to perform efficient multiplex genome editing using TALENTM offers the possibility of simultaneously rendering cells resistant to standard chemotherapy or to tumor evasion mechanisms. In this work we present the adaptation of this allogeneic platform to the production of T cells targeting CD123, the transmembrane alpha chain of the interleukin-3 receptor, which is expressed in tumor cells from the majority of patients with Acute Myeloid Leukemia (AML). In a first step, we have screened human primary T-cells harboring CARs with different antigen recognition domains in the context of multiple CAR architectures in order to identify candidates displaying specific activity against cell lines expressing variable levels of the CD123 antigen. To provide proof of concept for the general applicability of the allogeneic approach we have manufactured a TCR-deficient CD123 CAR T-cell (UCART123) and demonstrated that this product maintains a potent anti-tumoral activity in vitro. Experiments in an orthotopic AML mouse model using UCART123 cells are currently ongoing, in order to establish the absence of alloreactivity and the anti-tumoral activity in vivo. The ability to carry out large scale manufacturing of allogeneic, non alloreactive CD123 specific T Cells from a single healthy donor could thus offer the possibility of an off-the-shelf treatment that would be immediately available for administration to a large number of AML patients. Disclosures Galetto: Cellectis SA: Employment. Lebuhotel:Cellectis SA: Employment. Gouble:Cellectis SA: Employment. Schiffer-Mannioui:Cellectis SA: Employment. Smith:Cellectis SA: Employment.

Description: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive hematologic malignancy with historically poor outcomes and no established standard of care. Nearly 100% of patients with BPDCN overexpress CD123, and targeting CD123 has therefore emerged as an attractive therapeutic target. UCART123v1 is an allogeneic "off the shelf" product composed of genetically modified T-cells expressing an anti-CD123 CAR and a RQR8 depletion ligand, which confers susceptibility to rituximab. The expression of the T-cell receptor αβ (TCRαβ) is abrogated through the inactivation of the TRAC gene, using Cellectis' TALEN® gene-editing technology. We have previously reported the selective in vitro anti-tumor activity of UCART123v1 cells against primary BPDCN samples using cytotoxicity and T-cell degranulation assays, as well as the secretion of IFNγ and other cytokines (IL2, IL5, IL6, IL-13 and TNF-α) by UCART123v1 cells when cultured in the presence of BPDCN cells (Cai et al, 2017 ASH). To evaluate anti-tumor activity of UCART123v1 cells in vivo, we established two relapsed BPDCN patient-derived xenografts (PDX1 and 2) in NSG-SGM3 mice. In PDX-1 model, mice were randomized upon tumour engraftment (D21 after primary BPDCN injection) into 4 groups and received an IV injection of either vehicle, 10×106 TCRαβ KO control T-cells, or UCART123v1 cells (3×106 or 10×106 cells). Mice from vehicle group died by D53 after BPDCN injection with high tumor burden in PB, spleen and BM. 3 out of 9 (33%) mice treated with 3×106 and 6 out of 9 (67%) mice treated with 10×106 UCART123v1 were alive and disease-free at the end of the study (D299 after primary BPDCN injection). In PDX-2 model, which received the same treatment as PDX-1 (at D19 after primary BPDCN cell injection), all vehicle-treated mice died by D49. UCART123v1 therapy extended survival of treated mice to 104-241 days, but tumors relapsed at 90-155 days (Fig. 1A). The relapses in UCART123v1 treated mice were associated with the emergence of CD123-, CD56+CD45+ BPDCN cells infiltrating spleens and BMs (Fig. 1B). To understand the molecular basis for CD123 loss, we isolated RNA from CD123+ cells from two of the vehicle-treated mice and CD123- cells from four of the UCART123v1-treated mice and performed RT-PCR and RNA-sequencing. The cells from all samples were hCD45+ and hCD56+, indicating leukemic origin. These analyses detected the presence of full-length transcripts (exons 2-12) in both CD123+ control samples (Sample 1 and 2in Fig. 1C). In 2 of the 4 CD123- samples, CD123 transcripts were absent, as were transcripts of neighbouring genes (samples 3 and 9 in Fig. 1C). RNA-sequencing reads aligned to Genome Browser tracks for CD123 and housekeeping gene GPI showed no reads present for CD123 but reads present for GPI in the two samples with CD123 loss. The aCGH (Array‐Based Comparative Genomic Hybridization) results showed that samples 3 and 9 (CD123-) had large regional deletions on chromosome X, which includes the CD123 gene. In another sample (sample 5), the splicing analysis algorithm MAJIQ detected CD123 transcripts containing only exons 2-9, indicating premature transcription termination. If translated, this truncated transcript would produce a protein isoform lacking the transmembrane domain in exon 10. Finally, MAJIQ also revealed canonical splicing of exon 2 to exon 3 in all CD123+ samples but a sharp increase in skipping from exon 2 to exon 5 in sample 16 (Fig. 1D). This exon-skipping event preserves the open-reading frame and yields the previously reported transcript variant 2. Per UniProt, the resultant protein will retain the ligand-binding domain but lack several glycosylation sites and two beta sheets in the extracellular domain, potentially compromising recognition by UCART123v1 cells. The aCGH and FISH results further showed that this patient sample harbored TP53 deletion, which could have contributed to DNA instability observed in different mice engrafted with these tumor cells. In summary, allogeneic anti-CD123 CAR T therapy resulted in eradication of BPDCN in vitro and in increased disease-free survival in primary BPDCN PDX models. However, CD123 loss was observed in one PDX model harboring a TP53 deletion. These results provide preclinical proof-of-principle that UCART123v1 cells have potent anti-BPDCN activity, and indicate potential mechanisms leading to antigen loss and disease relapse. Disclosures Galetto: Cellectis Inc: Employment. Gouble:Cellectis: Employment. Zhang:The University of Texas M.D.Anderson Cancer Center: Employment. Kuruvilla:The University of Texas M.D.Anderson Cancer Center: Employment. Neelapu:Cellectis: Research Funding; Celgene: Consultancy, Research Funding; Kite, a Gilead Company: Consultancy, Research Funding; BMS: Research Funding; Poseida: Research Funding; Novartis: Consultancy; Karus: Research Funding; Acerta: Research Funding; Incyte: Consultancy; Pfizer: Consultancy; Merck: Consultancy, Research Funding; Unum Therapeutics: Consultancy, Research Funding; Precision Biosciences: Consultancy; Cell Medica: Consultancy; Allogene: Consultancy. Lane:AbbVie: Research Funding; Stemline Therapeutics: Research Funding; N-of-One: Consultancy. Kantarjian:BMS: Research Funding; Amgen: Honoraria, Research Funding; Cyclacel: Research Funding; Agios: Honoraria, Research Funding; Novartis: Research Funding; Immunogen: Research Funding; Jazz Pharma: Research Funding; Pfizer: Honoraria, Research Funding; Ariad: Research Funding; Takeda: Honoraria; Astex: Research Funding; Daiichi-Sankyo: Research Funding; Actinium: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Research Funding. Guzman:Cellectis: Research Funding; Samus Therapeutics: Patents & Royalties: intellectual rights to the PU-FITC assay; SeqRx: Consultancy. Pemmaraju:Stemline Therapeutics: Consultancy, Honoraria, Research Funding; samus: Research Funding; plexxikon: Research Funding; incyte: Consultancy, Research Funding; affymetrix: Research Funding; sagerstrong: Research Funding; Daiichi-Sankyo: Research Funding; cellectis: Research Funding; celgene: Consultancy, Honoraria; abbvie: Consultancy, Honoraria, Research Funding; novartis: Consultancy, Research Funding; mustangbio: Consultancy, Research Funding. Konopleva:Genentech: Honoraria, Research Funding; Ablynx: Research Funding; Astra Zeneca: Research Funding; Agios: Research Funding; Eli Lilly: Research Funding; Forty-Seven: Consultancy, Honoraria; Calithera: Research Funding; Stemline Therapeutics: Consultancy, Honoraria, Research Funding; F. Hoffman La-Roche: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Cellectis: Research Funding; Amgen: Consultancy, Honoraria; Ascentage: Research Funding; Kisoji: Consultancy, Honoraria; Reata Pharmaceuticals: Equity Ownership, Patents & Royalties.

Description: Adoptive T-cell therapies, where exogenous expression of a chimeric antigen receptor (CAR) confers cancer recognition, have shown significant promise in initial clinical trials. However, present adoptive immunotherapy Methods are limited by the need for manipulation of autologous patient T-cells. To permit such an approach in an allogeneic context, Transcription Activator-Like Effector Nucleases (TALENTM) have been used to simultaneously inactivate the endogenous T cell receptor and CD52, a cellular target for a lymphodepleting treatment. This approach reduces the risk of GVHD while permitting proliferation and activity of the introduced T lymphocytes in the presence of the immunosuppressive drug alemtuzumab. Electroporation of primary T cells with mRNA coding for the appropriate TALENTM result in double knock-out (dKO) frequencies of up to 70%. Furthermore, functional characterization demonstrates that the dKO cells are resistant to complement dependent lysis or in vivo depletion by alemtuzumab, and show no apparent potential for TCR-mediated activation. Finally, endowing the dKO cells with a CD19 CAR supports their capacity to kill CD19+ tumor targets as efficiently as unedited T-cells both in vitro and in vivo. Disclosures: Poirot: CELLECTIS THERAPEUTICS: Employment. Schiffer-Mannioui:CELLECTIS THERAPEUTICS: Employment. Philip:UCL Cancer Institute, London, United Kingdom: Employment. Derniame:CELLECTIS THERAPEUTICS: Employment. Gouble:CELLECTIS THERAPEUTICS: Employment. Chion-Sotinel:CELLECTIS THERAPEUTICS: Employment. Le Clerre:CELLECTIS THERAPEUTICS: Employment. Lemaire:CELLECTIS THERAPEUTICS: Employment. Grosse:CELLECTIS THERAPEUTICS: Employment. Cheung:UCL Cancer Institute, London, United Kingdom: Employment. Arnould:CELLECTIS THERAPEUTICS: Employment. Smith:CELLECTIS THERAPEUTICS: Employment. Pule:UCL Cancer Institute, London, United Kingdom: Employment. Scharenberg:CELLECTIS THERAPEUTICS: Employment.