Ex vivo activation of the GCN2 pathway metabolically reprograms T cells leading to enhanced adoptive cell therapy
The manipulation of T cell metabolism to enhance anti-tumor activity is an area of active investigation. Here, we report that activating the amino acid starvation response in effector CD8+ T cells ex vivo using the General Control Non-depressible 2 (GCN2) agonist halofuginone (halo) enhances oxidative metabolism and effector function. Further characterization revealed that halo-treated CD8+ T cells increased expression of the large neutral amino acid (LNAA) transporter CD98 as well as the co-stimulatory marker 4-1BB. Mechanistically, we identified autophagy coupled with the CD98-mTOR axis as key downstream mediators of the phenotype induced by halo treatment. The adoptive transfer of halo-treated CD8+ T cells into mice bearing well-established tumors led to robust tumor control and curative responses. Halo-treated T cells also synergized in vivo with a 4-1BB agonistic antibody to control tumor growth in a mouse model resistant to immunotherapy.  Importantly, treatment of human CD8+ T cells with halo resulted in similar metabolic and functional reprogramming. These findings demonstrate that activating the amino acid starvation response with the GCN2 agonist halofuginone can enhance T cell metabolism, effector function and anti-tumor activity, with the potential to augment existing clinical immunotherapeutic approaches. Overall design: 12 CD8+ T-cell Samples profiled by RIBO-Seq: 3 Halofuginone (HALO)-treated samples, Ribosome-Protected RNA Fragments (RPF) profiled; 3 Control samples, RPF-profiled; 3 Halo-treated samples, total RNA profiled; 3 control samples, total RNA profiled.