Glioblastoma is the most common and aggressive type of primary brain tumor. Despite therapeutic advances over the past decade, the diagnosis of glioblastoma is associated with a median overall survival time of 15-18 months and a 5-year survival rate of less than 5%. Even if treatment with the current standard of care for glioma patients, which consists of surgery, temozolomide, and radiotherapy, is initially successful, nearly all malignant gliomas eventually recur. At the moment of recurrence, no treatment successfully cures the disease. 

Naturally occurring or genetically modified viruses that selectively kill cancer cells are called oncolytic viruses. 

In our laboratory, we have developed a platform of oncolytic viruses termed Delta-24. A new generation of this cancer-selective oncolytic adenovirus model, Delta-24-RGD, has arrived in the clinical arena and has been tested in patients with recurrent glioblastoma showing encouraging safety and efficacy results. Thus, 20% of patients treated with Delta-24-RGD as a single treatment survived more than 3 years after a single dose of this biological agent. Unfortunately, rapid clearance of the virus by the immune system prevents a response in a higher percentage of patients. In addition to other pre-clinical and clinical evidence, data from our clinical trial demonstrate that to improve the percentage of patients that respond to the therapy, we need to decrease the immune response against the virus, which in turn will increase the immune response against the tumor. 

Therefore, this proposal aims to improve the response to virotherapy by attenuating the immune response against oncolytic adenovirus, with the goal of boosting the anti-tumor efficacy of this strategy. To this end, we propose two different strategies that can eventually be combined in a clinical trial. The first approach consists of making the virus less detectable by the immune system via substituting the most immunogenic viral protein with another viral protein for which the patients have not developed a pre-existing immune response. This new virus will persist longer in the tumor environment and thus maintain the window of opportunity to develop an anti-tumor immune response for a more prolonged time. 

Our second approach involves the generation of tolerogenicity for the virus. To achieve this objective, we will target dendritic cells, which are in charge of the antigen presentation to the immune effector cells, using nano molecules to deliver viral antigens. 

This strategy will diminish the response of the immune system against viral antigens, allowing the immune defenses to be focused on the tumor. If this highly innovative project is successful, we have the resources and infrastructure already in place to further translate these two strategies, as single approaches or in combination, to treat malignant brain tumors in the clinical scenario. 

Relapsed or drug-resistant leukemia and/or lymphoma are very difficult to cure using the traditional work horses of cancer therapy, surgery, radiation and chemotherapy. New classes of therapies need to be developed. In my laboratory we are using the patient’s immune system to directly attack the disease. This therapy harnesses the power of T cells, a type of immune cell, and uses gene therapy to redirect the function of the T cell so that it can target a patient’s leukemia and/or lymphoma. These are exciting times for immune-based therapy and we expect that the experiments funded by ACGT will provide critical insights into designing new ways of using T-cells to treat patients.

ACGT funds were used to genetically modify T cells to redirect their specificity to desired tumor-associated antigens (TAA).  This was accomplished by the development of a chimeric antigen receptor (CAR) that redirects specificity to TAA displayed on the cell surface independent of the major histocompatibility complex (MHC).  Over the course of our funding we developed a 1st generation CAR that relies solely on CD3-ζ endodomain to activate T cells for CAR-dependent lysis (major finding #1).  This resulted in our first gene therapy trial infusing CD19-specific CAR+ T cells after lymphodepleting chemotherapy (major finding #2).  This trial showed that the design of the CAR was insufficient to fully-activate T cells for a fully competent signal and that the presence of bacterial and viral transgenes in the expression vector led to deleterious immune-mediated clearance.  Therefore, a 2nd generation CAR was designed that could not only lyse CD19+ tumor targets, but could activate the T cells for sustained proliferation by signaling through CD28 as well as CD3-ζ (major finding #3).  We developed a new non-viral gene transfer strategy based on the Sleeping Beauty (SB) system (major finding #4) to improve the efficiency of CAR integration and together with the development of CD19+ artificial antigen presenting cells (aAPC, major finding #5), we developed an approach to generate T cells without the need to express immunogenic transgenes.  A next-generation clinical trial for first-in-human application of the SB system and CD19+ aAPC has been favorably reviewed by NIH-OBA (major finding #6) and is currently being reviewed by the FDA (major finding #7).  This upcoming trial will infuse autologous 2nd generation CD19-specific T cells in patients who are undergoing autologous hematopoietic stem-cell transplantation.  In addition to developing the scientific rational for targeted therapy using CAR+ T cells we also developed the infrastructure to translate basic immunology into applied practice by establishing a laboratory within a laboratory that operates in compliance with current good laboratory practices. This group works seamlessly with the manufacturing team to generate clinical-grade T cells in compliance with current good manufacturing practice. Furthermore, we established a clinical trials team to be able to conduct gene therapy trials, including a regulatory affairs group to handle the administrative burden of reporting to institutional and federal regulatory oversight bodies.  And, we put in place a group to undertake correlative studies to help understand the biologic impact of adoptive transfer of T cells.  In aggregate, with the help of ACGT funding we were able to develop a program to genetically modify T cells with desired specificity for CD19+ tumors and initiate a series of gene therapy trials to test the safety and feasibility of infusing CAR+ T cells.