Abstract PL03-01: CAR T cells for leukemia and more

Abstract

Abstract The pursuit of tumor-reactive T cells as a cancer therapy was provoked by the discovery of the graft-versus-leukemia effect in patients undergoing allogeneic hematopoietic stem cell transplantation. Adoptive T cells engineered to express high affinity T cell receptors (TCRs) and chimeric antigen receptors (CARs) has promise for a number of malignancies as an approach to overcome tolerance using autologous T cells (1-3). The adoptive transfer of Epstein-Barr virus (EBV)-specific T cells can prevent and treat post transplantation lymphomas, and the adoptive transfer of clonal populations of melanoma reactive CD4+ and CD8+ T cells has promise (4, 5). The majority of non-Hodgkin's lymphomas, acute lymphoblastic leukemias and chronic lymphocytic leukemias (CLL) express CD19, which is also expressed by normal B cells but not by hematopoietic stem cells or other tissues. Thus CD19 represents an attractive target for immunotherapy. Our preclinical studies show that combining robust T cell culture systems with lentiviral vector modified human T cells expressing CD19-specific chimeric antigen receptor (CART-19) has potent anti-leukemic efficacy in mice bearing established leukemic xenografts (6). 4-1BB-containing signaling endodomains enhance this activity. In an ongoing feasibility and safety clinical trial (ClinicalTrials.gov number NCT01029366), three patients with advanced relapsed and treatment refractory CLL have been treated (7, 8). CD3+CD45+ cells in leukapheresis products (range 2.3%-4.5%) were positively selected with anti-CD3/anti-CD28 magnetic beads prior to CART-19 lentiviral vector transduction and expansion. Patients were infused with a total of 0.3-5 x 109 total T cells, with 5%-27% of cells expressing CART-19. Two of three patients remain in complete remission beyond 8 months post infusion. The third patient had a very significant but partial response; he required corticosteroids 18 days after infusion, during an ongoing response, for symptoms presumably related to cytokine release. We observed significant in vivo expansion in all three patients accompanied by long-term persistence in blood and migration to bone marrow, and delayed onset tumor lysis syndrome accompanied by elevated levels for a broad range of cytokines. Clinical responses were documented by normalization of blood counts, resolution of adenopathy, and clearance of MRD when assessed by flow cytometry and deep sequencing for IgH rearrangements, cytogenetics, and FISH studies in the bone marrow in 2 of 3 patients. On target toxicities have been observed in all patients, including cytokine release but not cytokine storm, B cell depletion, plasma cell depletion and hypogammaglobulinemia requiring replacement serotherapy. Confirmation of these observations that T cells expand and traffic to tumor sites, stimulate synergistic antitumor immune activity, and persist long term in vivo potentially offers significant therapeutic and economic advantages over existing therapies and should be confirmed in larger numbers of patients, however, the therapeutic index with potent cell based CAR therapies will depend to a large extent on the specificity of the target. Trials testing CARs with specificity for mesothelin have begun (9), and an overview of this approach will be presented. In a complementary approach to CAR T cell therapy, the TCR repertoire can be altered by introduction of engineered TCRs. In conjunction with Adaptimmune Ltd, we are testing affinity enhanced MHC class I restricted TCRs with specificity for NY-ESO-1 and MAGE A3. In pre-clinical studies, T cells expressing a panel of these TCRs were evaluated for specificity and potency against normal and tumor cell lines and resulted in the identification of specific NY-ESO-1 and Mage-A3 TCRs which demonstrated enhanced tumor cell recognition in vitro and in vivo, in the absence of acquired cross reactivity. These TCRs are now being evaluated in ongoing clinical trials in metastatic melanoma and multiple myeloma (NCT01352286, and NCT01350401). In summary, engineered T cells represent a non-cross resistant form of therapy for the treatment of various cancers with the potential to provide major benefits over current treatments including reduction in cost and an improved safety profile.