Therapeutic strategies to target cancer stem cells

T cell receptor (TCR) engineered T cellsPhilip Greenberg, Fred Hutchinson Cancer Research Center• Three major elements must be considered to design safe and effective T cell therapies: 1) an appropriate antigenic target; 2) generation of a high avidity and high magnitude T cell response; and 3) the ability of tumor-reactive T cells to infiltrate and retain their function within the tumor microenvironment
• Efforts to manipulate the TCR affinity and avidity by substituting amino acid residues within the complementary determining region 3 (CDR3) of the TCR chains, could lead to greatly improved TCR-engineered T cells from the point of view of efficacy
• However, appropriate safeguards need to be pursued to pre-empt toxicities due to cross-reactivity against unintended targets. This represents a hurdle for utilization of affinity enhanced TCRs and of TCRs generated in preclinical models
• Other aspects of adoptive cell transfer with TCR-engineered T cells were also discussed: utilization of cytokines in the manufacturing process, T cell subsets and vaccines to enhance the effectiveness of adoptive T cell therapy and T cell subsets for enhanced adoptive T cell therapy
• Cautionary note was provided on using central memory T cells, as there is emerging preclinical evidence that the effectiveness of T cell subsets could be dependent on the type of targeted tumor
Chimeric antibody receptor (CAR)-engineered T cellsRichard Morgan, National Cancer Institute• Presented efforts to design and test genetically engineered T cells encompassing chimeric antigen receptors (CARs) against antigens such as EGFRvIII and CSPG4
• Such CARs are endowed with co-stimulatory signalling domains that provide the engineered T cells with supra-physiological capabilities• Discussed results obtained in a glioblastoma model, with cancer stem cells in the neurosphere assay as targets for an EGFRvIII-directed CAR engineered T cell approach
• A third generation CAR against EGFRvIII, encompassing 4-1BB, CD28, CD3z as signalling domains, is currently undergoing phase 1 clinical testing in patients with glioblastoma multiformae
Daniel Powell, University of Pennsylvania• Introduced an innovative design of an engineered T cell that could be armed ex vivo with the desired ligand for a specific tumor target or targeted against pre-labelled tumor cells in vivo (universal therapeutic platform)
• Such universal immune receptor bearing T cells can target multiple and diverse tumor antigens, including those expressed by cancer stem cells
• The limitation of the approach could be the dilution of the receptor as the engineered T cells divide. However, this might also be viewed as a built in safety switch to prevent long term toxic effects of redirected T cells
• Also discussed approaches to increase on-tumor immunity but limit off-tumor toxicity, by utilizing newer CAR T cell designs based on simultaneous recognition of multiple antigens
• As an example, a dual CAR engineered T cell product co-recognizing mesothelin and folate receptor is being considered for testing in patients with ovarian carcinoma
• Discussed the significance of signalling domains selected for CAR design, and provided compelling preclinical evidence that the CD27 costimulatory domain is a viable option
Adoptive T + NKT/NK cell therapyDr. Masoud Manjili, Virginia Commonwealth University School of Medicine, Massey Cancer Center• Presented data relevant to the mechanism and applicability of adoptive cellular therapy (ACT) in preclinical models of breast carcinoma.
• Showed evidence that reprogramming tumor-sensitized immune cells in the presence of bryostatin 1/ionomycin and common gamma chain cytokines, generated memory T cells and activated NKT/NK cell populations
• Presence of activated NKT/NK cells within the T cell product could have a major role, through interfering with immune inhibition by the myeloid derived suppressor cells (MDSCs)
• The use of activated NKT/NK cells along with canonical long-lasting memory T cells could prolong the functionality of T cells and overcome inhibiting mechanisms
Stem cell like memory T cells for adoptive T cell therapyNicholas Restifo, National Cancer Institute• Described his group’s pioneering efforts in this area that led to discovery of stem cell-like memory T cells
• Utilization of these cells for adoptive T cell therapy could overcome current limitations, such as reduced engraftment, limited persistence of T cells and need to preservation their functional capabilities over a longer timeframe
• Outlined several approaches to increase the yield of stem cell-like T cells in the manufacturing process of T cells for adoptive T cell therapy, by manipulating the Wnt signalling pathway or by utilizing certain cytokines that maintain the T cells in a juvenile state
• Shared late-breaking information on transcriptional and epigenetic programming of T cell stemness, which could be utilized to design approaches to de-differentiate such cells with in vivo renewable capabilities, from effector T cells isolated from tumors and other sources
Hematopoietic stem cellsRichard Koya, University of California Los Angeles• Presented generation and testing of hematopoietic stem cells engineered with a TCR that recognizes NY-ESO-1
• Showed successful differentiation of functional CD8+ T cells in humanized mice, from transduced human CD34+ cells with an average transduction efficiency of 50%
• At three months post-transplant, CD8+ T cells harvested from spleens could expand in vitro and recognize NY-ESO-1 expressing targets, specifically killing melanoma cells
• Also confirmed that a co-expressed PET reporter gene sr39TK was functional in vivo, as demonstrated by micro-PET imaging; ganciclovir administration could efficiently eliminate these cells
• Outlined plans to translate these findings to a clinical trial that integrates 1) stem cell transplantation with TCR-engineered hematopietic stem cells, 2) adoptive cell therapy with TCR-engineered differentiated T cells, and 3) vaccination
• In this trial, purified CD34+ cells from mobilized peripheral progenitor cells are transduced with a codon-optimized lentiviral vector to induce expression of NY-ESO-1 TCR alpha and beta chains together with the PET marker/suicide gene
Lili Yang, University of California Los Angeles• Discussed her team’s efforts to engineer immunity through the utilization of genetically engineered hematopoietic stem cells
• Presented results of an innovative imaging technology applied to T cells differentiated from TCR-engineered stem cells engrafted into mice. Showed evidence that in this model, while differentiated CD8+ T cells migrate to lymph nodes where they expand and persist, the CD4+ T cells traffic to and persist within the lymphoid tissue associated with the intestinal tract
• Discussed the roles of IL-15 and IL-7 in the homeostasis and survival of genetically engineered T cells that differentiate from TCR-engineered hematopoietic stem cells, to CD8+ and CD4+ T cells respectively
Human induced pluripotent stem cells (iPS)Raul Vizcardo, RIKEN Research Center for Allergy and Immunology, Japan• In the current era of generation and manipulation of, there is significant and legitimate interest in understanding whether one can utilize re-programmed iPS as a renewable source of T cells for adoptive T cell therapy
• Presented pioneering efforts to generate high numbers of tumor-antigen specific T cells from iPS de-differentiated from specific CD8+ T cells with proven anti-cancerous activity. Facilitated by techniques to separate the most desirable T cells from tumors, this approach can revolutionize TIL-based adoptive T cell therapy
• Much more needs to be done to fully understand and appropriately tap into this technology as a renewable source of T cells with therapeutic potential, as well as to understand its safety profile influenced by the presence of undifferentiated cells
CaspaCIDe™ system (applicable to adoptive cell therapy)David Spencer, Bellicum Pharmaceuticals Inc.• Genetic cell engineering especially at the level of lymphoid, hematopoietic or pluripotent stem cells carries an inherent risk of oncogenesis
• CaspaCIDe™ system is a rapid, cell cycle-independent and non-immunogenic suicide gene that is triggered by the membrane-permeable, synthetic dimerizer ligand, AP1903
• Clinical proof of principle has been demonstrated in a Phase I/II trial in the allogeneic, hematopoietic stem cell therapy setting
• Potential use of CaspaCIDe to enable emerging stem cell therapies and tumor-targeting T cells was also discussed
• CaspaCIDe comprises an FK506-binding protein 12 (FKBP12)-based, high affinity (Kd ~ 0.1 nM) ligand-binding domain fused to a truncated human Caspase-9 domain, lacking its Caspase-recruitment domain (CARD). In the presence of pM levels of AP1903, dimerization leads to its processing and initiation of apoptosis within 30 minutes
• In the clinical setting symptoms of
• GVHD were alleviated in less than 24 hours after administration of AP1903
• Outside of FKBP12v36 binding, the ligand is bio-inert and is currently delivered as a single intravenous infusion
• This contrasts with the virally derived HSV-thymidine kinase (tk)/, ganciclovir (GCV) system that is immunogenic, inappropriate for immune competent hosts, and relatively slow, requiring multiple infusions over several days for maximum efficacy on cycling cells
• The other major suicide gene therapy class, cell surface proteins, like CD20 or truncated EGFRt coupled with clinically approved antibodies, would be more limited by the diffusion characteristics of MoAbs and possible co-targeting of normal cells
Monoclonal antibodies and antibody drug conjugatesElaine Hurt, Medimmune• Described some of her company’s efforts to discover cancer stem cell-associated targets suitable for antibody therapy
Soldano Ferrone, Harvard Medical School• Presented efforts on design, research and develop antibodies against CSPG4 for treatment of various solid tumours
Kenneth Geles, Pfizer Inc.• Described his team’s efforts to develop an antibody drug conjugate (ADC) against 5T4, comprising the tubulin inhibitor monomethylauristatin F, backed up by preclinical results in a lung cancer model that lead to a phase 1 clinical trial
Therapeutic cancer vaccinesBrian Czerniecki, University of Pennsylvania• Described his group’s activities to develop a HER-2 pulsed DC1 vaccine that is effective in inducing CD4, CD8 T cell responses of T1 phenotype in 1) HER-2 high expressing ductal carcinoma in situ (DCIS) and early invasive breast cancer and 2) as well as intermediate expressing HER-2 early luminal cancers
• Such a DC1 vaccine could eliminate HER-2 expressing DCIS cells in the HER-2 2+ population, compared with HER-2 high expressing early breast cancers
• DC1 vaccines against HER-2 may be useful to eliminate HER-2 expressing breast cancer stem cells that may be responsible for many late recurrences in patients with ER + luminal breast cancers
• A trial to assess the DC1 vaccines in such patients after adjuvant therapy is being currently conducted
Andrew Cornforth, of California Stem Cell, Inc.• Discussed the company’s progress utilizing their autologous stem cell based immunotherapy. This integrates an innovative method to generate stem cell-like cells from primary tumours, and utilization of autologous DC that are pulsed with cancer stem cell antigens
• Also discussed how the manufacturing challenges of autologous cell therapy products involving whole tumor cells as an antigen source have been overcome by utilizing proprietary techniques to purify and expand cancer stem cells
• Presented two phase II clinical trials which demonstrated 5-year overall survival rates of 50% in stage IV metastatic melanoma patients
• Discussed the development of scale up and scale out technologies while conducting a large, multi-center phase III clinical trial
John Yu, Immunocellular Therapeutics Inc• Presented the company’s focus on targeting brain cancer stem cell-associated antigens, shared with the neural crest, by utilizing peptide-pulsed DC vaccines
• This program reached phase 2 clinical development following optimization of the vaccine formulation
Claudia Palena, NIH• Discussed in context of the target Brachyury, a Phase I clinical trial of a yeast recombinant vector encoding this protein, sponsored by Globimmune, in patients with carcinoma
• This vaccine platform, consisting of heat-killed recombinant Saccharomyces cerevisiae has been developed through a collaborative effort between the National Cancer Institute and GlobeImmune