Philip, BM; (2015) RQR8: A universal safety switch for cellular therapies. Doctoral thesis , UCL (University College London).

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Abstract

Cancer immunotherapy represents a rapidly developing field with potential to address shortcomings from current therapies. A compact marker-suicide gene reliant upon off-the-shelf reagents would offer considerable utility for these adoptive cellular therapies. Marker genes enable measurement of transduction efficiency and allow purification of transduced cells while suicide genes facilitate deletion of T-cells in case of toxicity. Previous marker genes include Neomycin resistance, truncated nerve growth factor receptor and CD34. However limitations of current marker genes include immunogenicity, unexpected biological activity and long coding regions respectively. Similarly, several suicide genes have been described with Herpes Simplex Virus Thymidine Kinase and inducible Caspase 9 in clinical use. Here, limitations include either immunogenicity or limited availability of the inducing drug. We sought to generate a compact marker-suicide gene that enables clinical grade sorting and effective deletion using CD34 cliniMACS and rituximab respectively. By using minimal epitopes required for binding, we hoped to reduce the size of the construct. We first sought to locate the epitope from CD34 which binds QBEnd10, the monoclonal antibody used in Miltenyi cliniMACS CD34 selection system. By epitope mapping, we identified a 16 amino acid linear fragment of CD34, which demonstrates approximately equivalent binding of QBEnd10 as the native antigen. Next, we sought to incorporate rituximab binding epitopes to engender rituximab mediated deletion. Following optimisation we established a 136 amino acid construct, designated RQR8, composed of two rituximab binding epitopes flanking the QBEnd10 epitope on a CD8 stalk which enables selection with the cliniMACS CD34 system and deletion through both CDC and ADCC with rituximab. Further, we demonstrate functional co-expression of RQR8 alongside chimeric antigen receptors and transgenic T-cell receptors. Finally, we validate functional efficacy of RQR8 deletion in vivo through a murine haploidentical transfer model. We predict that RQR8 will make T-cell gene therapy both safer and cheaper.

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