Preclinical development of a tandem CART / HSC transplantation platform for hematologic malignancies

PROJECT SUMMARY Chimeric antigen receptor (CAR) T cell therapy has revolutionized the treatment of hematologic cancers. However, to date, there are only 7 FDA-approved CAR-T therapies, with indications limited to advanced B cell and plasma cell-based malignancies, rendering a large proportion of patients with hematologic malignancies ineligible for CAR-T. Ship of Theseus (SoT) is collaborating with the University of Pennsylvania Center for Cellular Immunotherapies (CCI) to develop a CAR-T regimen applicable to virtually all hematologic malignancies. CCI has developed a CAR-T cell therapy directed against the pan-leukocyte marker CD45 (CAR45) to be used in conjunction with CRISPR base-editing of the CD45 epitope in healthy donor hematopoietic stem cells (HSCs) and downstream lineages, introducing a CD45-function-preserving mutation which evades CAR-T cell recognition in the engineered HSC graft. The main technical limitation of this approach is the number of CD34+ hematopoietic stem and progenitor cells (HSPCs) that can be obtained from the patient, as (i) considerable losses occur during the ex vivo manufacturing process, and (ii) ex vivo expansion is associated with loss of “stemness”. SoT has developed an exogenously delivered protein derived from transcription factor HOXB4 (HOXB4m), which causes HSCs to rapidly replicate without loss of pluripotency. The combination of SoT’s HSC expansion with CCI’s base editing strategy is a rational and mutually-reinforcing application of two novel technologies that is expected to reduce the length of post-transplant neutropenia and improve patient outcomes following CAR-T. The overarching goal of this application is to demonstrate that HOXB4m treatment can enhance the efficacy of the CD45-epitope edited HSC platform, without impairing its safety profile. We will first demonstrate the efficacy and safety of HOXB4m treatment to preserve stemness and improve engraftment of CAR45-resistant donor HSCs (Aim 1). We will then demonstrate the in vivo efficacy of CAR45 to treat an AML xenograft after engraftment of HOXB4m-treated, CAR45-resistant donor HSCs (Aim 2). This Phase I STTR project will provide support for the feasibility of our comprehensive approach to CAR-T cell therapy for hematologic malignancies, setting up a Phase II project in which we will complete rigorous in vivo testing in additional models of hematological malignancy.