Translatome Shifting Enhances Efficacy of Cellular Immunotherapies

The immune system makes decisions in response to complex combinations of microbial or adjuvant inputs. However, the combinatorial effects of multi-input stimulations on the protein life cycle of immune cells remain largely unknown. Here, we systematically measured changes in global protein synthesis induced by an adjuvant triplet combination in primary innate immune dendritic cells using polysome profiling and proteomics. We uncover global shifts in mRNA translation upon cell stimulation with the adjuvant triplet but not with its composite singles and pairs. Triplet effects on proteome regulation identify a metabolic circuit centered on glutamate which impacts the translational output of dendritic cells. Moreover, using small molecule and genetic perturbations, we show that intercellular glutamate metabolism increases the activation of T cells by dendritic cells in response to adjuvant triplet stimulation. Strikingly, we find that adjuvant triplet effects also modify the level and epitranscriptomic state of the transfer RNA for glutamate (tRNA-Glu), leading to a translational bias for glutamate-rich proteins as validated using codon-tagged fluorescent reporters in innate immune cells. Genetic deletion of the enzyme complex installing the post-transcriptional thiol modification on tRNA-Glu impacted the translational response to adjuvant triplets and reversed the glutamate codon bias. Notably, we show that manipulating the level of tRNA-Glu in innate or adaptive immune cell-based therapies led to potent anti-tumor effects in mouse models of solid tumors. Thus, our work demonstrates that tailoring the translatome of immune cells by modifying tRNA levels and epitranscriptomes is a strategy to improve cellular immunotherapy outcomes.