Designing novel T-cell therapies for acute myeloid leukaemia utilising native and chimeric receptors

Abstract

Acute myeloid leukaemia (AML) carries a dismal prognosis in the event of relapse following conventional chemotherapy and allogeneic haematopoietic stem cell transplant (HSCT), with no definite therapeutic options. Adoptive T-cell therapies in the form of CD19-specific chimeric antigen receptors T-cells have produced remarkable outcomes in relapsed and refractory B-cell malignancies. However, replicating this success in myeloid malignancies is not straightforward, chiefly due to heterogeneity of overexpressed antigens in AML, and significant overlap of potential target antigens on normal myeloid and haematopoietic progenitors, which could in turn lead to intolerable myelosuppression. This thesis describes pre-clinical development of a suite of adoptive T-cell therapeutic products which is envisaged to be applied clinically with a combinatorial approach.

Preferentially expressed antigen in melanoma (PRAME) is a cancer-testis antigen overexpressed in a large proportion of AML and therapy with ex vivo expanded PRAME-specific T-cells can be useful in maintaining remission. A straightforward method of expanding these cells from healthy donors was developed, phenotype and function of the products tested.

CAR T-cells against the myeloid antigens CD13, CD33, CD34 were developed based on single chain variable fragments (scFv) from monoclonal antibodies (mAbs) and optimised by exploration of effect of spacer domains on the phenotype and function of products. CAR T-cells against CD123 were developed using its natural ligand interleukin (IL)-3 with the effect of point mutations in the IL-3 sequence explored. The use of the synthetic Notch (synNotch) system was then explored as a way to manage myelotoxicity by developing T-cells engineered to be activated only in the presence of a combination of lineage specific and leukaemia associated antigens.

While many refinements will be required, adoptive T-cell therapies may find utility as bridging, definitive or adjunct therapy in AML. The work described in this thesis is the first step in designing T-cells that realise this utility.