IL-9 as a naturally orthogonal cytokine with optimal JAK/STAT signaling for engineered T cell therapy

Cytokines and their receptors enable precise tuning of T cell function. Leveraging this biology holds tremendous promise for optimizing antitumor immunity. Arming T cells with a synthetically orthogonal interleukin (IL)-9 receptor (o9R), for instance, permits facile engraftment and potent anti-tumor functions. Exploiting the paucity of wild-type IL-9R expression and the safety of high doses of IL-9, here, we showed that, compared with o9R, T cells engineered with wild-type IL-9R exhibited superior tissue infiltration, stemness, and anti-tumor activity. These qualities were consistent with a stronger Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signal, which included canonically IL-12-driven STAT4 in addition to STAT1/3/5. IL-9R T cells were exquisitely sensitive to perturbations of proximal signaling, including structure-guided attenuation, amplification, and rebalancing of JAK/STAT signals. Biased IL-9R mutants showed that STAT1 acts as a rheostat between stem-like and effector states. In summary, we identify IL-9/IL-9R as a naturally orthogonal cytokine-receptor pair with an optimal JAK/STAT signaling profile for engineered T cell therapy.