Developing an ‘Off-the-Shelf’ Engineered γδ T Cell Therapy for Multiple Myeloma

Abstract

Multiple myeloma is a plasma cell malignancy with limited treatment options and a poor prognosis in those with relapsed/refractory disease. In recent years, adoptive transfer of genetically engineered T cells, such as chimeric antigen receptor (CAR)-T cell therapy has realized remarkable clinical responses in hematologic malignancies. The conventional CAR-T cell platform confers tumour antigen specificity of conventional T cells, known as αβ T cells, and these treatments have shown impressive response rates in individuals with relapsed/refractory myeloma. CAR-T cell therapy employs a patients’ own T cells (aka autologous therapy), which significantly reduces accessibility to patients as manufacturing is incredibly costly and lengthy. These challenges may be addressed by off-the-shelf T cell therapies that can be administered to patients on-demand at time of need. A non-conventional T cell population, known as γδ T cells, represent an attractive platform for an off-the-shelf T cell therapy as they can be safely transferred to unrelated hosts without the risk of developing graft-versus-host disease. The natural propensity of γδ T cells to kill myeloma cells can be markedly enhanced by genetic engineering to express synthetic receptors directed at common myeloma targets, such as B cell maturation antigen (BCMA). I have developed an in vitro model, allowing for the assessment of recursive stimulation of engineered γδ Τ cells in response to myeloma targets, to better understand the fundamental biology and long-term functionality of our cell product. In chapter I, I found that engineered γδ T cells can robustly expand upon primary stimulation to myeloma targets, however this response is ablated upon subsequent exposure. Upon further investigation, this work found that γδ Τ cells lose their ability to produce cytokine and to bind strongly to tumour targets following stimulation, which does not seem to be a result of impaired synthetic receptor signaling. In chapter II, I explored the effect of IL-15 supplementation during recursive stimulation and found that IL-15 was able to recover impaired expansion and proliferation of γδ T cells upon restimulation with myeloma targets. In chapter III, I investigated the use of PI3K and mTOR inhibitors during γδ T cell manufacturing to enrich T cells with more memory-like features. While these inhibitors were able to skew the cells towards higher memory, we did not observe improved functionality in the context of recursive stimulation. The work presented herein describes fundamental properties of γδ T cells in the context of anti-tumour immunity and presents potential methods by which to enhance their functionality and long-term persistence.