Beyond the antigen receptor: editing the genome of T-cells for cancer adoptive cellular therapies

Abstract

Recent early stage clinical trials evaluating the adoptive transfer of patient CD8(+) T-cells re-directed with antigen receptors recognizing tumors have shown very encouraging results. These reports provide strong support for further development of the therapeutic concept as a curative cancer treatment. In this respect combining the adoptive transfer of tumor-specific T-cells with therapies that increase their anti-tumor capacity is viewed as a promising strategy to improve treatment outcome. The ex vivo genetic engineering step that underlies T-cell re-direction offers a unique angle to combine antigen receptor delivery with the targeting of cell-intrinsic pathways that restrict T-cell effector functions. Recent progress in genome editing technologies such as protein- and RNA-guided endonucleases raise the possibility of disrupting gene expression in T-cells in order to enhance effector functions or to bypass tumor immune suppression. This approach would avoid the systemic administration of compounds that disrupt immune homeostasis, potentially avoiding autoimmune adverse effects, and could improve the efficacy of T-cell based adoptive therapies.

Keywords: T-cells; cancer; cell therapies; genome editing; immune checkpoints.

Figures

Figure 1

(A) Schematic diagram of the ZFN, TALEN, and CRISPR/Cas9 genome editing tools. (B) Inhibition of T-cell activation by immune checkpoint receptors and downstream signaling proteins. Several co-inhibitory receptors (PD-1, BTLA, and LAIR-1) inhibit T-cell signaling by recruiting the SHP-1 and/or SHP-2 tyrosine phosphatases at proximity of the TCR signaling complex via ITIMs and ITSMs. This results in the dephosphorylation of proximal kinases downstream of TCR triggering. In addition PD-1 ligation was shown to induce increased expression of the Cbl-b E3 ubiquitin ligase, which targets signaling molecules for degradation. Activation of the CD200R leads to the recruitment of DOK2 and RasGAP to its intra-cellular domain, resulting in the inhibition of downstream MAP kinases. The adenosine receptor 2A and PGE2 receptors EP2 and EP4 modulate T-cell activation through mobilization of the cAMP-PKAI-CSK pathway. CSK phosphorylates the inhibitory C-terminal tyrosine residue of Src kinases and negatively regulates TCR signaling. A2AR, adenosine A2a receptor; APC, antigen-presenting cell; BTLA-4, B- and T-lymphocyte attenuator; Cbl-b, casitas B-cell lymphoma; CTL, cytotoxic T-lymphocyte; DOK-1/2, docking protein 1/2; EP2/4, prostaglandin E receptor 2/4; Erk, extra-cellular signal regulated kinases; ITIM, immunoreceptor tyrosine-based inhibition motif; ITSM, immunoreceptor tyrosine-based switch motif; GPCR, G-protein coupled receptor; LAG-3, lymphocyte-activation gene 3; LAIR-1, leukocyte-associated immunoglobulin-like receptor 1; Lck, lymphocyte-specific protein tyrosine kinase; MHC1, major histocompatibility complex class 1; PD-1, programed death receptor 1; PD1-L1, programed death receptor 1-ligand 1; SHP-1, Src homology 2 domain containing protein tyrosine phosphatase; TCR, T-cell receptor; TIGIT, T-cell immunoreceptor with Ig and ITIM domains; TIM-3, T-cell immunoglobulin domain and mucin domain 3.