ALBERT

Description: Chimeric-antigen receptor (CAR)-T cell immunotherapies have been remarkably effective in treating acute lymphoblastic leukemia. However, current strategies generally suffer from difficult, inefficient and costly manufacturing processes, significant patient side effects and poor durability of response in some patients. Here, we report for the first time a CAR-T cell therapeutic comprising a non-immunoglobulin alternative scaffold Centyrin molecule (a "CARTyrin") manufactured with a novel non-viral piggyBacTM (PB) transposon-based system. Our lead candidate, P-BCMA-101, encodes a CARTyrin that targets the B cell maturation antigen (BCMA) for the treatment of multiple myeloma (MM) and has several unique aspects that improve upon earlier CAR-T products. First, P-BCMA-101 is manufactured using only in vitro transcribed mRNA and plasmid DNA without the need for lentivirus or g-retrovirus, resulting in time and cost savings. Importantly, PB is also safer than viral systems due to a less mutagenic insertional profile and is non-oncogenic. Furthermore, PB can efficiently deliver transgenes as large as several hundred kilobases, and, once inserted, transgenes demonstrate more stable, prolonged and higher expression when compared to those delivered by virus. Second, a mutein of the dihydrofolate reductase (DHFR) gene is included in the P-BCMA-101 transgene that can be used in combination with the non-genotoxic drug methotrexate (MTX) to provide a simple and effective method of CARTyrin+ cell enrichment and reduces variability in patient product material. Third, P-BCMA-101 incorporates a safety switch for optional depletion in vivo in case of adverse events. Lastly, the CARTyrin is comprised of a BCMA-specific Centyrin, which are based on a human tenascin fibronectin type III (FN3) consensus sequence. Centyrins have similar binding affinities to the antibody-derived single chain variable fragments (scFv), but are smaller, more thermostable and predicted to be less immunogenic. Importantly, no signs of tonic signaling leading to T cell exhaustion have been observed with CARTyrins unlike scFv-based CAR molecules, which can interact with each other on the surface causing non-specific CAR signaling. The manufacture process of P-BCMA-101 from primary human T cells is straightforward, employs no cytokines, and easily produces enough CARTyrin+ cells to treat patients. Within 18 days of electroporation of purified T cells, we demonstrate 〉 95% of the cell product is positive for CARTyrin expression and ready to be administered. Notably, our manufacturing process results in 〉 60% of CARTyrin+ T cells exhibiting a stem-cell memory phenotype (i.e. CD45RA+ CD62L+). P-BCMA-101 cells exhibit specific and robust in vitro activity against BCMA+ tumor targets, ranging from high to very low levels of BCMA, as measured by target-cell killing and CARTyrin-T cell proliferation. Importantly, proliferating P-BCMA-101 cells were highly sensitive in vitro to activation of the safety switch. Finally, we have evaluated the anti-tumor efficacy of P-BCMA-101 in a model of human MM. NSG™ mice were injected IV with 1.5x106 luciferase+ MM.1S cells, an aggressive human MM-derived cell line. After the tumor cells were allowed to grow for 21 days, animals received a single IV administration of 5x106 P-BCMA-101 cells. All untreated control animals demonstrated a marked increase in serum M-protein levels, rapid growth of tumor cells demonstrated by bioluminescent imaging (BLI), and death within four weeks. In stark contrast, 100% of animals that received P-BCMA-101 rapidly eliminated tumors within 7 days as measured by BLI and serum M-protein levels and improved survival out to at least 60 days post-treatment. P-BCMA-101 is the first-in-class of Centyrin-based CAR therapeutics. The CARTyrin, combined with our advanced manufacturing processes, represents a significant improvement over first generation, immunoglobulin-based and virally-transduced CAR-T products. P-BCMA-101 exhibited an advantageous stem-cell memory phenotype and demonstrated specific and potent anti-tumor efficacy against BCMA+ myeloma cells both in vitro and in vivo. Based on these results, we plan to initiate a phase I clinical trial of P-BCMA-101 for the treatment of patients with relapsed and/or refractory MM. Disclosures Hermanson: Poseida Therapeutics: Employment. Barnett:Poseida Therapeutics: Employment. Rengarajan:Poseida Therapeutics: Employment. Codde:Poseida Therapeutics: Employment. Wang:Poseida Therapeutics: Employment. Tan:Poseida Therapeutics: Employment. Martin:Poseida Therapeutics: Employment. Smith:Poseida Therapeutics: Employment. Osertag:Poseida Therapeutics: Employment, Equity Ownership. Shedlock:Poseida Therapeutics: Employment.

Description: Chimeric-antigen receptor (CAR)-T cell immunotherapy is a promising type of cancer therapy and substantial progress has been made in developing adoptive T cell approaches for B cell malignancies. B cell maturation antigen (BCMA) is an attractive target for patients with multiple myeloma (MM) due to its high level of expression on tumor cells and restricted expression on normal tissues. Traditionally, the antigen-binding domain of a CAR is a single chain variable fragment (scFv) comprised of heavy chain (HC) and light chain (LC) variable fragments joined by a flexible linker that has been derived from a non-human monoclonal Ab (mAb). However, there are a number of disadvantages to scFv-based CARs including the limited availability of scFv, their potential to elicit antibody responses, and their association with tonic signaling due, in part, to inherent instability and flexibility of the structure and the potential for both HC/LC domain swapping and multimer formation through framework region interactions. Thus, replacement with alternative binding technologies may improve CAR-T efficacy in the clinic. Centyrins are alternative scaffold molecules that bind protein targets with high affinity and specificity, similar to scFv molecules. However, unlike scFv, Centyrins are smaller, derived from human consensus tenascin FN3 domains and are predicted to have decreased immunogenicity. Additionally, a monomeric Centryin in CAR format (i.e. CARTyrin molecule) is less likely to engage in domain swapping or interact with other Centyrins at the cell surface, thereby limiting the potential for the tonic signaling that drives the functional exhaustion of CAR T cells. Centyrins can be isolated against virtually any antigen through ex vivo panning of an extensive Centyrin library, yielding many distinct binders with a range of affinities and target epitopes. Panning with soluble BCMA protein yielded a large pool of BCMA-specific Centyrins, from which 11 distinct monomeric binders and 1 non-monomeric binder were selected for further study in CAR format. In addition, we tested numerous signal peptides, linkers, transmembrane domains and signaling domains to determine optimal configuration. We then created all CARTyrins by fusing each Centyrin with a CD8a leader peptide, spacer and transmembrane domain, as well as an intracellular signaling domain derived from both 4-1BB and CD3ζ. High quality mRNA of each CARTyrin construct was produced in order to rapidly screen CARTyrin cell surface expression and functionality in human pan T cells against BCMA+ targets. We also constructed scFv-based CARs against CD19 and BCMA for comparison. Previously CD3/CD28-stimulated T cells were electroporated (EP) with mRNA encoding each of the 12 anti-BCMA CARTyrins and, the following day, analyzed for surface expression of CARTyrin and their ability to degranulate against BCMA+ tumor cells. All 12 CARTyrins were detected on the cell surface and the 11 monomeric CARTyrins imparted BCMA-specific killing capacity to T cells. Notably, in these assays, CARTyrins were functionally comparable to scFv-based CARs against BCMA or to CD19-specific scFv-based CARs in a parallel assay with CD19+ tumor cells. The 11 functional anti-BCMA CARTyrins were further characterized for functional avidity by determining their activity against a panel of target cells with titrated levels of surface BCMA expression. To create this panel, various amounts of high quality BCMA mRNA were electroporated into BCMA- K562 tumor cells. After 4 hours of co-culture with the panel of BCMA expressing cells, CARTyrin+ T cell activity was measured as a function of CD107a expression. We observed a range of activities by each CARTyrin and show that this assay can be utilized to determine the minimal effective dose of BCMA needed to induce killing by CARTyrin+ cells. Furthermore, we establish that certain BCMA-specific CARTyrins are responsive to target cells with extremely low levels of surface BCMA expression. These results confirm that Centyrins are viable replacements for scFv in the construction of functional CARs and establish their potential utility in generating novel BCMA-specific CAR molecules, as well as other novel targetable tumor antigens. Disclosures Barnett: Poseida Therapeutics: Employment. Wang:Poseida Therapeutics: Employment. Hermanson:Poseida Therapeutics: Employment. Tan:Poseida Therapeutics: Employment. Osertag:Poseida Therapeutics: Employment, Equity Ownership. Shedlock:Poseida Therapeutics: Employment.

Description: Immunotherapy using chimeric-antigen receptor (CAR)-T cells is emerging as an exciting therapeutic approach for cancer therapies. Autologous CAR-modified T cells targeting a tumor-associated antigen (Ag) can result in robust tumor killing, in some cases resulting in complete remission of CD19+ hematological malignancies. Unlike traditional biologics and chemotherapeutics, CAR-T cells possess the capacity to rapidly reproduce upon Ag recognition, thereby potentially obviating the need for repeat treatments. To achieve this, CAR-T cells must not only drive tumor destruction initially, but must also persist in the patient as a stable population of viable memory T cells to prevent potential cancer relapses. Thus, intensive efforts have been focused on the development of CAR molecules that do not cause T cell exhaustion through Ag-independent (tonic) signaling, as well as of a CAR-T product containing early memory cells, especially stem cell memory (TSCM). It is hypothesized that a stem cell-like CAR-T would exhibit the greatest capacity for self-renewal and multipotent capacity to derive central memory (TCM), effector memory (TEM) and effector T cells (TE), thereby producing better tumor eradication and long-term CAR-T engraftment. We developed a novel Centyrin-based CAR, referred to as a CARTyrin, that is specific for human B cell maturation antigen (BCMA). Centyrins are alternative scaffold molecules based on human consensus tenascin FN3 domain, are smaller than scFv molecules, and can be selected for monomeric properties that favor stability and decrease the likelihood of tonic signaling in CAR molecules. We produced a plasmid DNA transposon encoding the CARTyrin that was flanked by two cis-regulatory insulator elements to help stabilize CARTyrin expression by blocking improper gene activation or silencing. The piggyBac™ (PB) Transposon System was used for stable integration of anti-BCMA CARTyrin into resting pan T cells, whereby the transposon was co-delivered along with an mRNA transposase enzyme, called Super piggyBac™ (SPB), in a single electroporation reaction. Delivery of piggyBac™ transposon into untouched, resting primary human pan T cells resulted in 20-30% of cells with stable integration and expression of PB-delivered genes. Surprisingly, we observed that a majority of these cells were positive for expression of CD62L and CD45RA, markers commonly associated with TSCM cells. To see if this phenotype was retained upon CAR-T cell stimulation and expansion, we activated the cells via stimulation of CD3 and CD28, and later show that 〉 60% of CARTyrin+ T cells exhibited a stem-cell memory phenotype. Furthermore, these cells were fully capable of expressing potent anti-tumor effector function. To determine whether or not the PB system directly contributed to enhancing the expression of stem-like markers, we compared the phenotype of CAR-T cells generated either by PB transposition or lentiviral (LV) transduction. To do this, we constructed a new vector by subcloning the CARTyrin transgene into a common LV construct for production of virus. Following introduction of the CARTyrin to untouched resting T cells either by PB-transposition or LV-transduction, we expanded the CARTyrin+ cells and then allowed them to return to a resting state. A variety of phenotypic and functional characteristics were measured including kinetic analysis of memory and exhaustion-associated markers, secondary proliferation in response to homeostatic cytokine or tumor-associated Ag, cytokine production, and lytic capability in response to BCMA+ tumor cells. Unlike the PB-transposed CARTyrin+ T cells, we found that the LV-transduced CARTyrin+ T cells did not exhibit an augmented memory phenotype. In addition, PB-transposed cells exhibited a comparable or greater capability for secondary proliferation and killing of BCMA+ tumor cells. Together, these data demonstrate that CAR-T cells produced by PB transposition are predominantly TSCM cells, a highly desirable product phenotype in the CAR-T field. Furthermore, these CARTyrin+ T cells exhibit strong anti-tumor activity and may give rise to cells that persist longer in vivo due to the use of a Centyrin-based CAR, which may be less prone to tonic signaling and functional exhaustion. Disclosures Barnett: Poseida Therapeutics: Employment. Hermanson:Poseida Therapeutics: Employment. Smith:Poseida Therapeutics: Employment. Wang:Poseida Therapeutics: Employment. Tan:Poseida Therapeutics: Employment. Martin:Poseida Therapeutics: Employment. Osertag:Poseida Therapeutics: Employment, Equity Ownership. Shedlock:Poseida Therapeutics: Employment.

Description: Natural killer (NK) cells are a key part in the innate immune system and have the ability to recognize diverse types of tumors and virally-infected targets. NK cells represent an attractive cell population for adoptive immunotherapy due to their ability to kill target cells in a human leukocyte antigen (HLA) non-restricted manner and without prior sensitization. Clinical studies using IL-2 activated NK cells demonstrate significant anti-tumor effects when adoptively transferred into patients with refractory leukemia (mainly AML). However, there has been a more limited response observed in clinical trials for the treatment of ovarian cancer and other solid malignancies. Chimeric antigen receptors (CARs) consist of an antigen-specific single chain antibody variable fragment fused to intracellular signaling domains derived from receptors involved in lymphocyte activation. CARs targeting various tumor-associated antigens have been developed and tested via expression in primary T cells with promising clinical results. However, engineering these T cells must be done on a patient-specific basis, thus limiting the number of patients who can be treated. In order to produce a potential targeted, “off-the-shelf” product suitable to treat patients with diverse tumors or chronic infections, we have generated human pluripotent stem cells with stable CAR expression. Previous studies by our group demonstrate that human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) provide an accessible, genetically tractable, and homogenous starting cell population to develop NK cells. We use a combined approach using “Spin-EB”- mediated differentiation of hESCs/iPSCs, followed by co-culture with artificial antigen presenting cells (aAPCs) that express mbIL-21. Using this strategy, we can generate 109 NK cells from a population of approximately 106 undifferentiated hESCs or iPSCs. This GMP compatible method is fully defined, without xenogeneic stromal cells or serum. Here, we have expressed both an anti-CD19 (targeting B cell malignancies) and an anti-mesothelin CAR (targeting ovarian cancer cells and other adenocarcinomas) in both hESCs and iPSCs. Using the Sleeping Beauty transposon system, both hESCs and iPSCs have been genetically engineered to express 3rd generation CARs, which express a single chain antibody fragment recognizing either CD19 or mesothelin, a CD8α hinge region, the transmembrane protein CD28, a co-stimulatory protein 4-1BB, and the activating domain CD3ζ. NK cells derived from hESCs/iPSCs with or without CAR expression are phenotypically similar to NK cells isolated from peripheral blood. These NK cells are CD56+, CD94+/CD117-, Nkp44+, Nkp46+, NKG2A+, NKG2D+, and KIR+. In 51Cr release assays against tumor targets expressing either CD19 or mesothelin, NK cells expressing the corresponding CAR show an enhanced killing ability. In cell lines lacking CD19 or mesothelin expression, the engineered cell lines exhibit equal activity compared to their non-engineered counterparts. Specifically, at a 10:1 effector:target ratio, anti-CD19 CAR+ iPSC-NK cells kill 58% of Lax7R cells (a CD19+ ALL cell line) compared to just 5% cell killing by CAR- iPSC-NK cells. Anti-CD19 CAR+ iPSC-NK cells also killed 2 other CD19+ ALL cell lines (018Z and Raji) better than CAR- iPSC-NK cells killing 63% vs 18% and 61% vs 8%, respectively. Similar results are seen against the mesothelin+ ovarian tumor line A1847. Here, anti-mesothelin CAR+ iPSC-NK cells kill 39% vs 14% for CAR- iPSC-NK cells. Currently, CAR-expressing NK cells derived from hESCs and iPSCs are being tested in vivo against both mesothelin+ ovarian tumor lines and CD19+ leukemia cells. Together, these studies demonstrate engineering hESCs and iPSCs with tumor-specific receptors provides a novel strategy to produce targeted NK cells suitable for immune therapies against refractory malignancies. Disclosures: No relevant conflicts of interest to declare.