Bahram Valamehr

Platform for Induction and Maintenance of Transgene-free hiPSCs Resembling Ground State Pluripotent Stem Cells

Summary Cell banking, disease modeling, and cell therapy applications have placed increasing demands on hiPSC technology. Specifically, the high-throughput derivation of footprint-free hiPSCs and their expansion in systems that allow scaled production remains technically challenging. Here, we describe a platform for the rapid, parallel generation, selection, and expansion of hiPSCs using small molecule pathway inhibitors in stage-specific media compositions. The platform supported efficient and expedited episomal reprogramming using just OCT4/SOX2/SV40LT combination (0.5%–4.0%, between days 12 and 16) in a completely feeder-free environment. The resulting hiPSCs are transgene-free, readily cultured, and expanded as single cells while maintaining a homogeneous and genomically stable pluripotent population. hiPSCs generated or maintained in the media compositions described exhibit properties associated with the ground state of pluripotency. The simplicity and robustness of the system allow for the high-throughput generation and rapid expansion of a uniform hiPSC product that is applicable to industrial and clinical-grade use.

Myogenic Differentiation of Muscular Dystrophy-Specific Induced Pluripotent Stem Cells for Use in Drug Discovery

Human induced pluripotent stem cells (iPSCs) represent a scalable source of potentially any cell type for disease modeling and therapeutic screening. We have a particular interest in modeling skeletal muscle from various genetic backgrounds; however, efficient and reproducible methods for the myogenic differentiation of iPSCs have not previously been demonstrated. Ectopic myogenic differentiation 1 (MyoD) expression has been shown to induce myogenesis in primary cell types, but the same effect has been unexpectedly challenging to reproduce in human iPSCs. In this study, we report that optimization of culture conditions enabled direct MyoD‐mediated differentiation of iPSCs into myoblasts without the need for an intermediate step or cell sorting. MyoD induction mediated efficient cell fusion of mature myocytes yielding multinucleated myosin heavy chain‐positive myotubes. We applied the same approach to dystrophic iPSCs, generating 16 iPSC lines from fibroblasts of four patients with Duchenne and Becker muscular dystrophies. As seen with iPSCs from healthy donors, within 36 hours from MyoD induction there was a clear commitment toward the myogenic identity by the majority of iPSCs in culture (50%–70%). The patient iPSC‐derived myotubes successfully adopted the skeletal muscle program, as determined by global gene expression profiling, and were functionally responsive to treatment with hypertrophic proteins insulin‐like growth factor 1 (IGF‐1) and wingless‐type MMTV integration site family, member 7A (Wnt7a), which are being investigated as potential treatments for muscular dystrophy in clinical and preclinical studies, respectively. Our results demonstrate that iPSCs have no intrinsic barriers preventing MyoD from inducing efficient and rapid myogenesis and thus providing a scalable source of normal and dystrophic myoblasts for use in disease modeling and drug discovery.

A novel platform to enable the high-throughput derivation and characterization of feeder-free human iPSCs

Human induced pluripotent stem cells (hiPSCs) hold enormous potential, however several obstacles impede their translation to industrial and clinical applications. Here we describe a platform to efficiently generate, characterize and maintain single cell and feeder-free (FF) cultured hiPSCs by means of a small molecule cocktail media additive. Using this strategy we have developed an effective multiplex sorting and high-throughput selection platform where individual clonal hiPSC lines are readily obtained from a pool of candidate clones, expanded and thoroughly characterized. By promoting survival and self-renewal, the selected hiPSC clones can be rapidly expanded over multiple FF, single-cell passages while maintaining their pluripotency and genomic stability as demonstrated by trilineage differentiation, karyotype and copy number variation analysis. This study provides a robust platform that increases efficiency, throughput, scale and quality of hiPSC generation and facilitates the industrial and clinical use of iPSC technology.

Optimized Surface Markers for the Prospective Isolation of High-Quality hiPSCs using Flow Cytometry Selection

hiPSC derivation and selection remains inefficient; with selection of high quality clones dependent on extensive characterization which is not amenable to high-throughput (HTP) approaches. We recently described the use of a cocktail of small molecules to enhance hiPSC survival and stability in single cell culture and the use of flow cytometry cell sorting in the HTP-derivation of hiPSCs. Here we report an enhanced protocol for the isolation of bona fide hiPSCs in FACS-based selection using an optimized combination of cell surface markers including CD30. Depletion of CD30+ cells from reprogramming cultures almost completely abolished the NANOG and OCT4 positive sub-population, suggesting it is a pivotal marker of pluripotent cells. Combining CD30 to SSEA4 and TRA-1-81 in FACS greatly enhanced specificity and efficiency of hiPSC selection and derivation. The current method allows for the efficient and automated, prospective isolation of high-quality hiPSC from the reprogramming cell milieu.

GSK3 inhibition drives maturation of NK cells and enhances their antitumor activity

Maturation of human natural killer (NK) cells as defined by accumulation of cell-surface expression of CD57 is associated with increased cytotoxic character and TNF and IFNγ production upon target-cell recognition. Notably, multiple studies point to a unique role for CD57+ NK cells in cancer immunosurveillance, yet there is scant information about how they mature. In this study, we show that pharmacologic inhibition of GSK3 kinase in peripheral blood NK cells expanded ex vivo with IL15 greatly enhances CD57 upregulation and late-stage maturation. GSK3 inhibition elevated the expression of several transcription factors associated with late-stage NK-cell maturation including T-BET, ZEB2, and BLIMP-1 without affecting viability or proliferation. When exposed to human cancer cells, NK cell expanded ex vivo in the presence of a GSK3 inhibitor exhibited significantly higher production of TNF and IFNγ, elevated natural cytotoxicity, and increased antibody-dependent cellular cytotoxicity. In an established mouse xenograft model of ovarian cancer, adoptive transfer of NK cells conditioned in the same way also displayed more robust and durable tumor control. Our findings show how GSK3 kinase inhibition can greatly enhance the mature character of NK cells most desired for effective cancer immunotherapy. Cancer Res; 77(20); 5664-75. ©2017 AACR.

Generation of skeletal muscle cells from pluripotent stem cells: advances and challenges.

Human pluripotent stem cells (hPSCs) possess unlimited proliferative potential while maintaining the ability to differentiate into any cell type including skeletal muscle cells (SMCs). hPSCs are amenable to genetic editing and can be derived from patient somatic cells, and thus represent a promising option for cell therapies for the treatment of degenerative diseases such as muscular dystrophies. There are unresolved challenges however associated with the derivation and scale-up of hPSCs and generation of differentiated cells in large quantity and high purity. Reported myogenic differentiation protocols are long, require cell sorting and/or rely on ectopic expression of myogenic master regulators. More recent advances have been made with the application of small molecules to enhance the myogenic differentiation efficiency and the identification of more selective markers for the enrichment of myogenic progenitors with enhanced regenerative potential. Here we review the field of myogenic differentiation and highlight areas requiring further research.

Off-the-shelf cell therapy with induced pluripotent stem cell-derived natural killer cells

Cell therapy is emerging as a very promising therapeutic modality against cancer, spearheaded by the clinical success of chimeric antigen receptor (CAR) modified T cells for B cell malignancies. Currently, FDA-approved CAR-T cell products are based on engineering of autologous T cells harvested from the patient, typically using a central manufacturing facility for gene editing before the product can be delivered to the clinic and infused to the patients. For a broader implementation of advanced cell therapy and to reduce costs, it would be advantageous to use allogeneic “universal” cell therapy products that can be stored in cell banks and provided upon request, in a manner analogous to biopharmaceutical drug products. In this review, we outline a roadmap for development of off-the-shelf cell therapy based on natural killer (NK) cells derived from induced pluripotent stem cells (iPSCs). We discuss strategies to engineer iPSC-derived NK (iPSC-NK) cells for enhanced functional potential, persistence, and homing.

Abstract 3576: FT500, an off-the-shelf NK cell cancer immunotherapy derived from a master pluripotent cell line, enhances T-cell activation and recruitment to overcome checkpoint blockade resistance

The development of PD1/PDL1 targeting checkpoint inhibitors (CI) has transformed the oncology landscape, providing long term remissions in multiple indications. However, many tumor subtypes are resistant to checkpoint blockade therapy, and relapse remains a significant concern. Novel therapeutic approaches with the ability to overcome CI resistance are needed, and there is significant opportunity for therapies capable of additively or synergistically enhancing T-cell activation and recruitment when combined with CI. Adoptive transfer of NK cells from healthy donors has the potential to recruit T cells to the tumor microenvironment and augment T-cell activation at the tumor site. NK cells have both direct anti-tumor activity and the capacity to secrete inflammatory cytokines and chemokines upon activation, enabling the cells to play a unique and critical role in regulating anti-tumor T cell activity. We sought to determine whether FT500, an off-the-shelf NK cell product derived from a clonal master pluripotent cell line, could synergize with CI to relieve local immunosuppression and enhance T-cell activation and recruitment to the tumor site. FT500 is universally negative for cell surface PD1, and expression of PDL1 on tumor lines had no discernable effect on FT500 cytotoxicity. Similarly, addition of PDL1 blocking antibody had no effect on FT500 cytotoxicity or degranulation, suggesting that FT500 is inherently resistant to PDL1-PD1 mediated inhibition. Additionally, activation of FT500 induced the secretion of soluble factors capable of enhancing T-cell activation, as evidenced by increased upregulation of CD69. We hypothesized that FT500 might also enhance CI by promoting recruitment of T cells to the tumor site. Using conventional in vitro transwell migration assays, we found that FT500 produced soluble factors that promoted the migration of activated T cells. Additional profiling confirmed FT500 production of a range of chemokines, including CCL3, CCL4, CXCL10 and CCL22. Furthermore, using an in vivo recruitment model, FT500 was able to recruit T cells out of the circulation and into the peritoneal cavity. Similarly, utilizing a three-dimensional tumor spheroid model in vitro, infiltration of T cells into tumor spheroids was significantly enhanced when combined with FT500, suggesting that FT500 can enhance tumor infiltration of T cells. Our data suggest that FT500 is a potent producer of chemokines and can facilitate the recruitment of T cells to the tumor site. In addition to its direct cytotoxic potential, FT500 is also able to enhance T-cell activation, suggesting an ability to synergize with CI to reduce tumor burden. Together, our data provide evidence supporting the combination of FT500, an off-the-shelf NK cell cancer immunotherapy, with CI to overcome checkpoint blockade resistance. Citation Format: Ryan Bjordahl, Sajid Mahmood, Svetlana Gaidarova, Ramzey Abujarour, Raedun Clarke, Laurel Stokely, Paul Rogers, Moyar Ge, Megan Robinson, Betsy Rezner, Tom Tong Lee, Bahram Valamehr. FT500, an off-the-shelf NK cell cancer immunotherapy derived from a master pluripotent cell line, enhances T-cell activation and recruitment to overcome checkpoint blockade resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3576.

Abstract 3755: Renewable and genetically engineered natural killer cells for off-the-shelf adoptive cellular immunotherapy

The unique attributes of a combinatorial tumor recognition system, diminished off-tumor cytotoxicity, and multifaceted effector function make natural killer (NK) cells a prime candidate for a universal approach to cancer immunotherapy. In addition, NK cells are the principal mediator of antibody-directed cellular cytotoxicity (ADCC). However, NK cell function is often impaired in the setting of cancer, reducing the effectiveness of the endogenous immune system and the therapeutic efficacy of monoclonal antibodies. To address the need for advanced and combinatorial cancer therapies, we developed a unique and effective strategy to create a renewable source of engineered “off-the-shelf” NK cells with augmented function, including enhanced ADCC and persistence. Key challenges associated with genetic editing, limited expansion, persistence and variability of peripheral blood (PB)-derived NK cells were overcome by utilizing our induced pluripotent stem cell (iPSC) technology as the unlimited starting material for the reproducible and consistent derivation of engineered NK cells. Through targeted transgene integration, we produced a clonal iPSC master cell line to continuously produce NK cells engineered to uniformly express a high affinity, non-cleavable version of CD16 (hnCD16-NK). In directed differentiation, the hnCD16-NK cells displayed homogeneous expression of CD16 (>95%) and a mature CD56+ NK cell phenotype, as exhibited by expression of KIR, NCRs, DNAM-1, and NKG2D. In contrast to endogenous CD16 expression, the engineered hnCD16 molecule was shown to be cleavage resistant upon NK cell activation (>95% CD16+ hnCD16-NK vs. Citation Format: Ryan Bjordahl, Frank Cichocki, Raedun Clarke, Svetlana Gaidarova, Brian Groff, Paul Rogers, Stacey Moreno, Ramzey Abujarour, Greg Bonello, Tom Lee, Weijie Lan, Matthieu Bauer, Dave Robbins, Betsy Rezner, Sarah Cooley, Bruce Walcheck, Stewart Abbot, Bruce Blazar, Scott Wolchko, Daniel Shoemaker, Jeffrey S. Miller, Bahram Valamehr. Renewable and genetically engineered natural killer cells for off-the-shelf adoptive cellular immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3755. doi:10.1158/1538-7445.AM2017-3755