B7-H3-Engager T cells for the immunotherapy of osteosarcoma
The long-term goal of this project is to develop an effective immunotherapy for patients with osteosarcoma (OS) using a novel genetic modification strategy to generate tumor-specific T cells. While patients with localized OS have a 5-year disease-free survival rate of approximately 60%, the prognosis for patients with metastatic disease is significantly worse, despite aggressive multimodality treatment. Given these results, novel therapies are needed to treat OS, especially for patients with metastatic disease. Immunotherapies have potential to meet these needs, as they are both tumor-specific and cause only minimal collateral damage. We use T cells for our immunotherapy of OS efforts because this approach allows selection and further manipulation of the most potent antitumor effector cells. Immunotherapy with antigen-specific T cells, such as chimeric antigen receptor (CAR) T cells, has shown promise as cancer therapy in preclinical and early clinical trials. Despite early successes, a major constraint to current T-cell therapies is limited amplification of the T-cell response after infusion into patients. Here we propose a highly innovative strategy to enhance the anti-OS T-cell response: by genetically modifying T cells to secrete a novel bispecific T-cell engager protein. The antigenic target for our approach is B7-H3, a protein expressed on several pediatric sarcomas, including OS, Ewing’s Sarcoma, and rhabdomyosarcoma. The bispecific engager consists of two single chain variable fragments (scFvs) that are specific for CD3 and B7-H3. Upon binding B7-H3, the engager renders both modified T cells, and unmodified, ‘bystander’ T cells tumor specific, resulting in a vast amplification of the T-cell mediated antitumor response. Thus, we now hypothesize that B7-H3-specific Engager (B7-H3-ENG) T cells – unlike B7-H3-specific CAR (B7-H3-CAR) T cells, will recruit other T cells locally, amplifying antitumor effects. The objective of this proposal is to preclinically evaluate B7-H3-ENG T cells by testing this hypothesis in two interrelated research aims. Aim 1: to compare the effector function of B7-H3-ENG and B7-H3-CAR T cells in vitro. We will compare the ability of B7-H3-ENG and B7-H3-CAR T cells to i) produce cytokines, ii) proliferate, iii) activate ‘bystander’ T cells and iv) kill B7-H3 positive (B7-H3+) OS cells. Aim 2: to compare the antitumor activity of B7-H3-ENG and B7-H3-CAR T cells in vivo. We will determine the ability of B7-H3-ENG and B7-H3-CAR T cells to i) proliferate ii) redirect bystander T cells, and iii) demonstrate antitumor activity in a xenograft model of metastatic OS (LM7), which has been successfully established in our laboratory. Data generated by this study should demonstrate feasibility and potential antitumor activity of Engager T-cell therapy for OS and potentially other B7-H3+ sarcomas, and provide justification for developing Phase I clinical studies, for which we would seek separate funding.