Repurposed.

That single word carries more weight in oncology than most people realize. For over half a century, I have watched the field chase shiny new molecules - and occasionally stumble upon something remarkable hiding in plain sight inside the medicine cabinet. Ponatinib, a drug that has spent the better part of a decade doing perfectly respectable work against leukemia, has just been caught moonlighting in the immunotherapy department. And honestly? Its side hustle might outshine the day job.

A team led by Hiroyoshi Nishikawa and colleagues at Nagoya University published new findings in Nature Communications showing that ponatinib - sold as Iclusig and originally designed to wallop the BCR-ABL protein in chronic myeloid leukemia - quietly inhibits two signaling pathways in T cells that nobody was paying much attention to in this context: LCK and PI3K. The payoff? It coaxes CD8+ T cells into becoming stem cell memory T cells, or TSCM cells, which are essentially the special forces of your adaptive immune system (Okuhiro et al., 2026).

What on Earth Is a TSCM Cell, and Why Should You Care?

Think of your immune system's CD8+ T cells as an army. Most soldiers fight, get tired, and retire. But TSCM cells are the drill sergeants who never really age out - they self-renew, maintain long-term memory of the enemy, and can spin up fresh battalions of killer T cells whenever a tumor tries to make a comeback. They represent roughly 2-4% of circulating CD8+ T cells, and they are marked by the transcription factor TCF1, which has become something of a celebrity in tumor immunology circles (Siddiqui et al., 2019).

The trouble is, generating enough TSCM cells for clinical use has been like trying to bottle lightning. Various groups have fiddled with cytokines, metabolic tweaks, and signaling inhibitors, but a reliable, clinically practical method has remained elusive. Enter ponatinib, stage left, completely uninvited.

The Mechanism: Turning Down the Volume on T Cell Overdrive

Here is where the molecular choreography gets elegant. LCK is the very first kinase that fires when a T cell receptor recognizes its target - it is, in a sense, the ignition switch for T cell activation. PI3K, meanwhile, sits downstream and drives T cells toward an effector fate: fight now, ask questions later. By tamping down both pathways simultaneously, ponatinib enhances the transcriptional activity of TCF7 and FOXO1 - two factors that steer T cells toward that coveted stem-like memory state instead of burning out in a blaze of cytotoxic glory.

One particularly satisfying detail: the inhibition has to be stable and sustained. Intermittent dosing does not cut it. The T cells apparently need a consistent, gentle hand on the brake rather than someone frantically pumping the pedal. Those of us who remember the early interferon days, when everyone assumed more signal meant better outcomes, can appreciate the irony. Sometimes less really is more.

From Bench to (Potentially) Bedside

In mouse tumor models, ponatinib showed antitumor efficacy on its own and performed even better when combined with PD-1 checkpoint blockade. This dovetails nicely with earlier work showing ponatinib remodels the tumor microenvironment by suppressing PD-L1 expression, boosting CD8+ T cell infiltration, and clearing out tumor-associated macrophages - those traitorous immune cells that tumors recruit as bodyguards (Barnwal et al., 2023).

Perhaps most exciting for the CAR-T field: ponatinib treatment increased the proportion of TSCM cells among chimeric antigen receptor T cells while reducing exhaustion markers. CAR-T exhaustion has been the Achilles' heel of solid tumor therapy for years, and any drug that can keep these engineered warriors fresher for longer deserves serious attention.

The Bigger Picture

Drug repurposing has a distinguished, if underappreciated, history. Thalidomide's resurrection for multiple myeloma. Aspirin's anti-cancer properties. Now ponatinib joins this quietly revolutionary tradition. A separate study even identified ponatinib as having the highest binding energy to PD-L1 among all screened FDA-approved drugs - stronger than purpose-built antibodies in some preclinical models (Gou et al., 2023).

We are still in the early chapters of this story. Mouse models are not patients, and ponatinib carries its own baggage - cardiovascular toxicity has been a persistent concern in its leukemia indication. But the principle established here is sound and, I would argue, beautiful: a drug designed to shut down a rogue kinase in cancer cells turns out to simultaneously train the immune system's best soldiers. After fifty years of watching the field, I can tell you that the most consequential discoveries rarely arrive with fanfare. They arrive sideways, dressed as something else entirely.

References:

Okuhiro Y, Ito S, Watanabe K, et al. Ponatinib inhibits LCK and PI3K signaling and promotes CD8+ T stem cell memory cell development. Nature Communications. 2026. DOI: 10.1038/s41467-026-71375-2. PMID: 41946709.
Barnwal A, Tamang R, Das S, Bhattacharyya J. Ponatinib delays the growth of solid tumours by remodelling immunosuppressive tumour microenvironment through the inhibition of induced PD-L1 expression. British Journal of Cancer. 2023;129(10):1549-1564. DOI: 10.1038/s41416-023-02316-9. PMID: 37400678.
Gou Q, Dong C, Jin J, et al. Repurposing Ponatinib as a PD-L1 Inhibitor Revealed by Drug Repurposing Screening and Validation by In Vitro and In Vivo Experiments. ACS Pharmacology & Translational Science. 2023;6(2):281-289. DOI: 10.1021/acsptsci.2c00214. PMCID: PMC9926522.
Siddiqui I, Schaeuble K, Chennber V, et al. Intratumoral Tcf1+PD-1+CD8+ T Cells with Stem-like Properties Promote Tumor Control in Response to Vaccination and Checkpoint Blockade Immunotherapy. Immunity. 2019;50(1):195-211. DOI: 10.1016/j.immuni.2018.12.021. PMID: 30635237.
Chen Y, et al. Stem-like CD8+ T cells in cancer. Frontiers in Immunology. 2024;15:1426418. DOI: 10.3389/fimmu.2024.1426418.

Disclaimer: The image accompanying this article is for illustrative purposes only and does not depict actual experimental results, data, or biological mechanisms.