Blocking USP30 Revives Exhausted Cancer-Fighting T Cells
Scientists found that inhibiting USP30, a mitochondrial enzyme, restores immune cell function and shrinks tumors in mice.
Summary
T cells that fight cancer often become 'exhausted' — losing their ability to kill tumors. Researchers at Ohio State University discovered that a protein called USP30, which blocks a cellular cleanup process called mitophagy, becomes overactive in exhausted T cells. When they deleted USP30 genetically or blocked it with a drug, T cells regained healthier mitochondria, produced more cancer-killing molecules like IFN-γ and TNF, and significantly slowed tumor growth in mouse models. The findings identify USP30 inhibition as a promising new strategy to enhance cancer immunotherapy, potentially complementing existing checkpoint blockade therapies.
Detailed Summary
T cell exhaustion is one of the central obstacles in cancer immunotherapy. Tumor-infiltrating CD8+ T cells, which normally act as the immune system's front-line killers, progressively lose their effectiveness in the immunosuppressive tumor microenvironment. A core driver of this dysfunction is mitochondrial deterioration — exhausted T cells accumulate damaged, fragmented mitochondria with reduced membrane potential, impaired oxidative phosphorylation, and excess reactive oxygen species. This study from The Ohio State University identifies a previously unappreciated molecular brake on mitochondrial quality control: the deubiquitinase USP30.
The researchers used multiple mouse tumor models — including B16-F10 melanoma and MC38 colon carcinoma — combined with in vitro chronic stimulation systems to model T cell exhaustion. They found that USP30 expression was significantly elevated in exhausted CD8+ T cells compared to functional effector T cells. Mechanistically, prolonged antigen stimulation through the T cell receptor (TCR) activates NFAT1 (nuclear factor of activated T cells 1), which directly binds to and transcriptionally upregulates the USP30 promoter. USP30 then antagonizes mitophagy by removing ubiquitin tags from damaged mitochondria that would otherwise be recognized for autophagic clearance, causing dysfunctional mitochondria to accumulate.
To test the functional consequences, the team generated T cell–specific USP30 knockout mice (USP30-KO) and adoptive transfer models. USP30-deficient CD8+ T cells showed markedly enhanced mitophagy flux (measured by mito-Keima reporter assays), improved mitochondrial membrane potential, reduced mitochondrial reactive oxygen species, and greater oxidative phosphorylation capacity. Phenotypically, these cells expressed lower levels of exhaustion markers including PD-1, TIM-3, and LAG-3, and produced significantly more effector cytokines — IFN-γ, TNF, and granzyme B — compared to wild-type exhausted T cells. In tumor-bearing mice, USP30-KO T cells showed enhanced tumor infiltration and substantially reduced tumor growth.
The pharmacological approach proved equally compelling. Treatment with MF-094, a selective small-molecule USP30 inhibitor, recapitulated the genetic findings. In both in vitro chronic stimulation models and in vivo tumor experiments, MF-094–treated T cells displayed improved mitochondrial health, reduced exhaustion marker expression, and enhanced effector function. Tumor growth was significantly suppressed in MF-094–treated animals, and the drug synergized with anti-PD-1 checkpoint blockade to achieve even greater tumor control than either treatment alone.
The study also analyzed human data, finding that USP30 expression inversely correlates with CD8+ T cell effector function in published tumor-infiltrating lymphocyte datasets, lending translational relevance. Limitations include that all in vivo experiments were conducted in immunocompetent mouse models; human clinical validation is needed. The study did not assess long-term toxicity of USP30 inhibition on normal tissues. Nevertheless, this work establishes USP30 as a druggable checkpoint of mitochondrial quality control in T cells and positions USP30 inhibitors as a novel class of immunotherapy adjuvants.
Key Findings
- USP30 expression was significantly upregulated in exhausted CD8+ T cells in both murine tumor models (B16-F10 melanoma, MC38 colon carcinoma) and chronic stimulation in vitro systems
- NFAT1 was identified as the direct transcriptional driver of USP30 upregulation downstream of prolonged TCR signaling, with NFAT1 binding confirmed at the USP30 promoter
- USP30-knockout T cells showed substantially enhanced mitophagy flux (mito-Keima assay), reduced mitochondrial ROS, and improved mitochondrial membrane potential versus wild-type exhausted T cells
- USP30-deficient CD8+ T cells produced significantly more IFN-γ, TNF, and granzyme B and expressed lower levels of exhaustion markers PD-1, TIM-3, and LAG-3 compared to controls
- Adoptive transfer of USP30-KO T cells into tumor-bearing mice led to markedly suppressed tumor growth relative to wild-type T cell transfer
- Pharmacological inhibition with MF-094 (selective USP30 inhibitor) recapitulated genetic deletion results and synergized with anti-PD-1 checkpoint blockade to achieve greater tumor suppression than either agent alone
- Human tumor-infiltrating lymphocyte dataset analysis showed USP30 expression inversely correlated with CD8+ T cell effector function, supporting translational relevance
Methodology
The study used murine in vivo tumor models (B16-F10 melanoma and MC38 colon carcinoma) in immunocompetent C57BL/6 mice, T cell–specific USP30 conditional knockout mice, and in vitro chronic TCR stimulation systems to model exhaustion. Mitophagy was quantified using the mito-Keima fluorescent reporter system; mitochondrial fitness was assessed via membrane potential dyes, ROS probes, and Seahorse metabolic assays. Pharmacological experiments used MF-094, a selective USP30 inhibitor, administered alone or in combination with anti-PD-1 antibody, with tumor growth and T cell phenotype as primary endpoints. Human translational analysis was performed using published tumor-infiltrating lymphocyte transcriptomic datasets.
Study Limitations
All in vivo efficacy experiments were performed in mouse tumor models; direct evidence of USP30 inhibition efficacy in human tumors or patients is lacking and will require clinical investigation. The study did not evaluate long-term safety or potential off-target effects of USP30 inhibition in non-immune tissues where USP30 also plays roles in mitochondrial homeostasis. No conflicts of interest were disclosed by the authors.
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