Virus Specific T-Lymphocytes Genetically Modified to Target the CD19 Antigen Eradicates Systemic Lymphoma In Mice

Abstract 2092

Human T-cells can be genetically modified to target tumor antigens through tumor antigen-specific artificial T-cell receptors termed chimeric antigen receptors (CARs). To provide a therapeutic option for patients with relapsed leukemia following allogeneic stem cell transplant (allo-SCT) we have developed a novel immunotherapy utilizing donor derived virus specific cytotoxic T-lymphocytes genetically modified to target the CD19 antigen expressed on most B-cell acute lymphoblastic leukemias (B-ALL). We have previously demonstrated that donor T-cells modified to express a CAR specific to the B-cell antigen CD19, termed 19–28z, traffic to systemic sites of tumor and successfully eradicate human CD19⁺ tumors in a SCID-Beige mouse model. This therapy is currently under clinical investigation using autologous T-cells for adults with chronic lymphocytic leukemia (CLL) and B-ALL (BB-IND 13266). However, in the setting of allo-SCT, a lymphocyte infusion of genetically modified donor T-cells has the potential to cause graft versus host disease (GVHD). In our center's experience with infusions of donor derived EBV-CTLs and EBV-CTLs derived from third party donors for treatment of EBV associated lymphoma we have noted no alloreactivity or development of GVHD in the recipient. Furthermore, we and others have shown EBV-CTLs have long term persistence following adoptive transfer which may enhance the anti-tumor efficacy of genetically modified T-lymphocytes. To this end we postulate the therapeutic use of infusions of donor derived EBV-CTLs genetically modified to target the CD19 antigen in patients with relapsed leukemia post allo-SCT.

To investigate the ability of EBV-CTLs to be genetically modified to express our anti-CD19 CAR (19-28z) via gammaretroviral vector gene transfer we tested 3 established EBV-CTL donor cell lines. We compared EBV-CTL activation using autologous EBV B-cell lymphoblastoid cell lines (EBV-BLCL), beads coated with agonistic CD3 + CD28 monoclonal antibodies (Invitrogen Carlsbad, CA), or a combination of BLCL + beads. Transduction efficiency ranged from 25–75% and was consistently higher in the EBV-CTL groups activated using EBV-BLCL alone. In standard ⁵¹Cr release cytotoxicity assay 19–28z⁺ EBV-CTLs exhibited specific cytotoxicity against the CD19⁺ human tumor cell lines BA-25 (B-ALL), Raji (Burkitt 's lymphoma) and the mouse thymoma cell line EL4 modified to express the human CD19 antigen (EL4-hCD19⁺). In contrast the untransduced EBV-CTLs failed to lyse these targets. However, both 19–28z⁺ EBV-CTLs and the untransduced EBV-CTLs retained the ability to specifically lyse autologous BLCL but not autologous PHA-blasts showing retained EBV specificity. Finally we tested the ability of 19–28z⁺ EBV-CTLs to eradicate established systemic Raji tumor in our SCID-Beige model of disease. Mice were injected with 5×10⁵ Raji-eGFP-fire fly luciferase (Raji-eGFP-FFLuc) tumor cells via tail vein injection six days prior to T-lymphocyte injection. Established tumor was confirmed using bioluminescence imaging (BLI) prior to T-lymphocyte infusion. Mice were treated via tail vein injection with 7.5 × 10⁶ 19–28z⁺ EBV-CTL (n = 5) or control EBV-CTLs (n= 4). Control mice all died of systemic disease (<35 days) following T-lymphocyte infusion while treated mice all showed long term survival (>100 days). These results validate the therapeutic potential of tumor targeted genetically modified EBV-specific T-lymphocytes which may provide a therapeutic option for patients with relapsed CD19+ B-ALL following allo-SCT.