Tumor rejection in Cblb -/- mice depends on IL-9 and Th9 cells

BACKGROUND

Casitas B lymphoma-b (Cbl-b) is a central negative regulator of cytotoxic T and natural killer (NK) cells and functions as an intracellular checkpoint in cancer. In particular, Th9 cells support mast cell activation, promote dendritic cell recruitment, enhance the cytolytic function of cytotoxic T lymphocytes and NK cells, and directly kill tumor cells, thereby contributing to tumor immunity. However, the role of Cbl-b in the differentiation and antitumor function of Th9 cells is not sufficiently resolved.

METHODS

Using Cblb ^-/- mice, we investigated the effect of knocking out Cblb on the differentiation process and function of different T helper cell subsets, focusing on regulatory T cell (Treg) and Th9 cells. We applied single-cell RNA (scRNA) sequencing of in vitro differentiated Th9 cells to understand how Cbl-b shapes the transcriptome and regulates the differentiation and function of Th9 cells. We transferred tumor-model antigen-specific Cblb ^-/- Th9 cells into melanoma-bearing mice and assessed tumor control in vivo. In addition, we blocked interleukin (IL)-9 in melanoma cell-exposed Cblb ^-/- mice to investigate the role of IL-9 in tumor immunity.

RESULTS

Here, we provide experimental evidence that Cbl-b acts as a rheostat favoring Tregs at the expense of Th9 cell differentiation. Cblb ^-/- Th9 cells exert superior antitumor activity leading to improved melanoma control in vivo. Accordingly, blocking IL-9 in melanoma cell-exposed Cblb ^-/- mice reversed their tumor rejection phenotype. Furthermore, scRNA sequencing of in vitro differentiated Th9 cells from naïve T cells isolated from wildtype and Cblb ^-/- animals revealed a transcriptomic basis for increased Th9 cell differentiation.

CONCLUSION

We established IL-9 and Th9 cells as key antitumor executers in Cblb ^-/- animals. This knowledge may be helpful for the future improvement of adoptive T cell therapies in cancer.

JAK/STAT disruption induces immuno-deficiency: Rationale for the development of JAK inhibitors as immunosuppressive drugs

Cytokines are mediating immune cells responses through the activation of the JAK/STAT signaling pathway. Being critical for immune cells, a defective JAK/STAT signaling leads to various immune disorders, such as immunodeficiency. In contrast, hyperactivation of JAK/STAT signaling is linked to autoimmunity and cancer. Targeting the JAK/STAT proteins by small protein inhibitors impedes immune cell function by uncoupling cells from cytokine effects and by interfering with functional immune cell hallmarks, such as cell migration. This review will explore immune syndromes driven by JAK/STAT deregulation and discuss the emerging role of JAK inhibitors as immunosuppressive drugs used in autoimmunity and transplantation medicine.

Get a grip on immune cells by inhibiting JAKs

JAK inhibitors are approved for myelofibrosis (MF) and polycythemia vera (PV), as they reverse inflammation-associated splenomegaly and symptoms. Notably, JAK inhibitors only marginally affect disease burden. The anti-inflammatory effects of JAK inhibitors affects DC, T and NK cells explaining their therapeutic potential for limitation of cancer-associated inflammation, Graft-versus-Host Disease (GvHD) and autoimmunity.

JAK Inhibition Impairs NK Cell Function in Myeloproliferative Neoplasms

Ruxolitinib is a small-molecule inhibitor of the JAK kinases, which has been approved for the treatment of myelofibrosis, a rare myeloproliferative neoplasm (MPN), but clinical trials are also being conducted in inflammatory-driven solid tumors. Increased infection rates have been reported in ruxolitinib-treated patients, and natural killer (NK) cells are immune effector cells known to eliminate both virus-infected and malignant cells. On this basis, we sought to compare the effects of JAK inhibition on human NK cells in a cohort of 28 MPN patients with or without ruxolitinib treatment and 24 healthy individuals. NK cell analyses included cell frequency, receptor expression, proliferation, immune synapse formation, and cytokine signaling. We found a reduction in NK cell numbers in ruxolitinib-treated patients that was linked to the appearance of clinically relevant infections. This reduction was likely due to impaired maturation of NK cells, as reflected by an increased ratio in immature to mature NK cells. Notably, the endogenous functional defect of NK cells in MPN was further aggravated by ruxolitinib treatment. In vitro data paralleled these in vivo results, showing a reduction in cytokine-induced NK cell activation. Further, reduced killing activity was associated with an impaired capacity to form lytic synapses with NK target cells. Taken together, our findings offer compelling evidence that ruxolitinib impairs NK cell function in MPN patients, offering an explanation for increased infection rates and possible long-term side effects associated with ruxolitinib treatment.