Klaus Okkenhaug

Neutrophils are essential frontline immune cells in the defence against bacterial pathogens such as Staphylococcus aureus , but their killing machinery also causes host tissue damage. How neutrophils regulate these processes remains incompletely understood. Here, we profiled the proteome and phosphoproteome of human neutrophils across a two-hour exposure to S. aureus , alongside five simultaneous functional readouts, before investigating how an initial encounter modulates the response to a second. The phosphoproteomic response resolved into qualitatively distinct early and late windows: the early landscape drives particle uptake, while by the late window this machinery is deactivated, with a broadly supressed kinome, and cells geared towards inflammatory output. Correlating protein phosphorylation and functional kinetics — an approach we term KINETIC — implicates putative mediators of key neutrophil antimicrobial functions. A genome-wide CRISPR knockout screen in neutrophil-like PLB-985 cells, sorted on phagocytic load, recovered canonical engulfment machinery among the strongest facilitators of phagocytosis, additionally identifying the lysosomal Ragulator-mTORC1 nutrient sensing pathway and HOPS complex corresponding to the KINETIC-identified pathways. Conversely, the NRF2 repressor KEAP1 was the strongest phagocytic brake, positioning oxidative burden as a regulator of phagocytic appetite. Neutrophils in the late window exhibited impaired phagocytosis and phagosomal acidification on S.aureus re-challenge. Underlying these functional deficits, cells in the late window were refractory across multiomic layers: a second S. aureus meal altered no phosphoprotein, protein, or transcript, whereas the chemoattractants PAF and fMLP evoked a largely consistent phosphoproteomic programme, delineating the phenotype as receptor-specific rather than a global loss of signalling capacity. Consistent with de-repressing the antioxidant response via genetic loss of KEAP1 increasing phagocytosis, reducing ROS production via inhibition of the NADPH oxidase resulted in a partial rescue of phagocytosis of the re-exposed S.aureus . Together, these findings describe a ROS-gated phagocytic rheostat, enabling neutrophils to meter their phagocytic appetite according to their exposure history, likely limiting uptake of pathogens they lack the capacity to effectively digest. Inappropriate activation of this rheostat under conditions of physiological stress or severe illness may underpin the defects in phagocytosis identified in such patients.

Steroid hormones are well-known regulators of mast cell function, but whether mast cells themselves produce steroids de novo and influences their effector function has remained unknown. Here, we show that mast cells constitutively express the steroidogenic enzyme cytochrome P450 family 11 subfamily A member 1 (Cyp11a1) and produce pregnenolone. Cyp11a1 expression was detected across tissue-resident mast cells from multiple organs, was conserved in human mast cells, and was enhanced by interleukin-3 signaling and after activation. We identified Cyp11a1 as a Gata2-dependent, superenhancer-associated mast cell gene, placing steroidogenesis within the core mast cell transcriptional program. Loss of Cyp11a1 altered transcriptomic and proteomic programs in mast cells, with effects on pathways linked to cell growth, immune signaling, and effector function. Functionally, Cyp11a1-deficient mast cells showed increased degranulation in response to both immunoglobulin E (IgE)–dependent and IgE-independent stimulation. In vivo, loss of Cyp11a1 reduced mast cell abundance in several tissues but exacerbated passive cutaneous anaphylaxis. These findings identify cell-intrinsic steroidogenesis as a regulatory pathway that restrains mast cell activation and anaphylactic responses.

Intraepithelial lymphocytes (IEL) are conserved across vertebrates and commonly enriched in γδ T cells. Several such γδ IELs depend upon homeostatic interactions of their T cell receptors (TCRs) with butyrophilin-like (BTNL) proteins expressed by healthy enterocytes and colonocytes. What limits such interactions from inducing full-blown T cell activation which would disrupt barrier integrity is unknown. Here, using primary IEL, we describe an atypical TCR signalling pathway (“signal 1”) downstream of BTNL engagement, that fails to activate either global protein synthesis or cell proliferation. This attenuation could be overcome by provision of a co-stimulator (“signal 2”) or inflammatory cytokines (“signal 3”). It could also be relieved cell-intrinsically by blocking a lipid phosphatase. These findings can, at least in part, explain how extrinsic and intrinsic regulators permit IEL to be constitutively active in healthy tissues and additionally make full-blown responses to adaptive TCR ligands during tissue perturbation.

Reactive oxygen species (ROS) promote genomic instability and fuel oncogenic signaling in cancer, but antioxidant therapies have so far failed to improve, or worsen, cancer outcomes. Emerging data suggest that T cells depend on ROS for signal transduction. In this study, we show that tumors exploit this dependency, releasing antioxidant enzymes into the tumor environment to suppress T cell–mediated antitumor immunity. The interstitial fluid of tumors possesses potent antioxidant activity, associated with enrichment of the antioxidant enzyme peroxiredoxin 1 (PRDX1). Extracellular PRDX1 deprives T cells of ROS, preventing oxidative inactivation of phosphatases required for T cell receptor–driven kinase signaling and effector function. Prdx1 is up-regulated upon cancer immunoediting, and loss of PRDX1 within tumors enhances antitumor immunity and immunotherapy responses. These findings define a redox-dependent mechanism of tumor immunosuppression that is potentially amenable to therapeutic intervention.

Amoeboid cell migration is key to efficient T cell immunity. Spatial polarization of organelles within cells, including endo-lysosomes, is a prerequisite of migration. However, how ultrastructural polarization is linked to the signaling requirements governing T cell migration remains unknown. Here we show that signaling molecules generated by endo-lysosome-localized kinases regulate velocity of amoeboid migration. Specifically, imaging of T cells identifies accumulation of endo-lysosomes decorated with the lipid kinases VPS34–PIKfyve at the uropod of polarized cells. Activity of VPS34 and PIKfyve regulates speed, but not directedness, of migrating T cells. Mechanistically, PI(3,5)P ₂ generated by the sequential action of VPS34 and PIKfyve, mediates Ca ²⁺ efflux from lysosomes via the mucolipin TRP cation channel 1 (TRPML1), thus controlling activity of myosin IIA and hence the generation of propulsive force through retrograde actin flow. The VPS34–PIKfyve kinases also regulate velocity of myeloid cells, as well as of the amoeba Dictyostelium discoideum – establishing the axis as an evolutionarily conserved speed control system of amoeboid cell migration.

Adoptive T cell therapies are limited by poor persistence of transferred cells. Attempts to enhance persistence have focused on genetic induction of constitutively hyperactivated but potentially oncogenic T cell states. Physiological T cell responses are maintained by quiescent stem-like/memory cells dependent upon the transcription factor BACH2. Here we show that quantitative control of BACH2 dosage regulates differentiation along the continuum of stem and effector CD8⁺ T cell states, enabling engineering of synthetic states with persistent antitumor activity. While conventional high-level overexpression of BACH2 enforces quiescence and hinders tumor control, low-dose BACH2 expression promotes persistence without compromising effector function, enhancing anticancer efficacy. Mechanistically, low-dose BACH2 partially attenuates Jun occupancy at highly AP-1-dependent genes, restraining terminal differentiation while preserving effector programs. Similarly, dose optimization enables effective deployment of quiescence factor FOXO1. Thus, quantitative control of gene payloads yields qualitative effects on outcome with implications for quiescence factor deployment in cell therapy.

Breast cancer, particularly triple-negative breast cancer (TNBC), evades the body’s immune defences, in part by cultivating an immunosuppressive tumour microenvironment. Here, we show that suppressing local steroidogenesis can augment anti-tumour immunity against TNBC. Through targeted metabolomics of steroids coupled with immunohistochemistry, we profiled the existence of immunosuppressive steroids in TNBC patient tumours and discerned the steroidogenic activity in immune-infiltrating regions. In mouse, genetic inhibition of immune cell steroidogenesis restricted TNBC tumour progression with a significant reduction in immunosuppressive components such as tumour associated macrophages. Steroidogenesis inhibition appears to bolster anti-tumour immune responses in dendritic and T cells by impeding glucocorticoid signalling. Undertaking metabolic modelling of the single-cell transcriptomics and targeted tumour-steroidomics, we pinpointed the predominant steroidogenic cells. Inhibiting steroidogenesis pharmacologically using a identified drug, posaconazole, curtailed tumour expansion in a humanised TNBC mouse model. This investigation paves the way for targeting steroidogenesis and its signalling pathways in breast cancer affected by immune-steroid maladaptation.

Metastasis is the spread of cancer cells from primary tumours to distant organs and is the cause of 90% of cancer deaths globally^1,2. Metastasizing cancer cells are uniquely vulnerable to immune attack, as they are initially deprived of the immunosuppressive microenvironment found within established tumours³. There is interest in therapeutically exploiting this immune vulnerability to prevent recurrence in patients with early cancer at risk of metastasis. Here we show that inhibitors of cyclooxygenase 1 (COX-1), including aspirin, enhance immunity to cancer metastasis by releasing T cells from suppression by platelet-derived thromboxane A₂ (TXA₂). TXA₂ acts on T cells to trigger an immunosuppressive pathway that is dependent on the guanine exchange factor ARHGEF1, suppressing T cell receptor-driven kinase signalling, proliferation and effector functions. T cell-specific conditional deletion of Arhgef1 in mice increases T cell activation at the metastatic site, provoking immune-mediated rejection of lung and liver metastases. Consequently, restricting the availability of TXA₂ using aspirin, selective COX-1 inhibitors or platelet-specific deletion of COX-1 reduces the rate of metastasis in a manner that is dependent on T cell-intrinsic expression of ARHGEF1 and signalling by TXA₂ in vivo. These findings reveal a novel immunosuppressive pathway that limits T cell immunity to cancer metastasis, providing mechanistic insights into the anti-metastatic activity of aspirin and paving the way for more effective anti-metastatic immunotherapies.

Summary: Steroid hormones regulate cell physiology and immune function, with dysregulated steroidogenesis promoting cancer progression by supporting tumour growth and suppressing anti-tumour immunity. Targeting CYP11A1, the first and rate-limiting enzyme in steroid biosynthesis, has shown promise in cancer therapy, but safe and effective inhibitors remain an unmet need. Undertaking in silico structure-based drug repurposing approach, we found Posaconazole as an inhibitor of CYP11A1. The docking pose analysis showed that Posaconazole can form multiple hydrogen bonds and hydrophobic interactions with the key residues at the binding site and the cofactor, stabilising the protein-ligand complex. We validated its inhibition efficiency in cell-based assays. In a mouse model of lung metastasis, we demonstrated that Posaconazole restricts metastatic cancer growth by stimulating anti-tumour immunity. These findings highlight Posaconazole’s potential as a research tool to study steroidogenesis and as a candidate for further preclinical and clinical evaluation in pathological conditions associated with local steroid production, such as steroidogenic tumours.

The gut microbiome modulates immunotherapy treatment responses, and this may explain why immune checkpoint inhibitors, such as anti-PD-1, are only effective in some patients. Previous studies correlated lipopolysaccharide (LPS)-producing gut microbes with poorer prognosis; however, LPS from diverse bacterial species can range from immunostimulatory to inhibitory. Here, by functionally analysing faecal metagenomes from 112 patients with melanoma, we found that a subset of LPS-producing bacteria encoding immunostimulatory hexa-acylated LPS was enriched in microbiomes of clinical responders. In an implanted tumour mouse model of anti-PD-1 treatment, microbiota-derived hexa-acylated LPS was required for effective anti-tumour immune responses, and LPS-binding antibiotics and a small-molecule TLR4 antagonist abolished anti-PD-1 efficacy. Conversely, oral administration of hexa-acylated LPS to mice significantly augmented anti-PD-1-mediated anti-tumour immunity. Penta-acylated LPS did not improve anti-PD-1 efficacy in vivo and inhibited hexa-acylated LPS-induced immune activation in vitro. Microbiome hexa-acylated LPS therefore represents an accessible predictor and potential enhancer of immunotherapy responses.