Immunogenic cell death (ICD) causes release of tumour antigens and damage associated molecular patterns which recruit and activate antigen presenting cells (APCs) by binding to their pattern recognition receptors (PRRs). This leads to their production of the pro-inflammatory cytokines required for adaptive immune cell activation (e.g., Cytotoxic T Lymphocytes [CTLs]). The non-receptor tyrosine kinase Fes, which is abundantly expressed in innate immune cells, dampens innate immune responses by inhibiting PRR signaling. We hypothesize that this same Fes-dependent mechanism which serves to limit the consequences of overactive innate immunity, such as septic shock, causes Fes to inhibit successful anti-cancer immunotherapy by preventing efficient priming of cancer specific CTLs by APCs.
Immunoblot analysis assessed PRR signaling in wildtype (WT) or fes-/- bone marrow derived macrophages (BMDMs). C57BL/6 WT or fes-/- mice orthotopically engrafted with E0771 triple-negative breast cancer or B16-F10 melanoma cells were treated with vehicle or doxorubicin and assessed for tumour growth and survival. Tumours and spleens were harvested to analyze immune profiles by flow cytometry. In separate experiments, E0771 and B16-F10 tumor bearing WT and fes-/- mice were treated with doxorubicin and either IgG control or anti-PD-1 antibody.
Fes-/- BMDMs display stronger PRR signaling in vitro compared to WT following LPS stimulation. In vivo, we show increased tumour control and survival in Fes-/- mice compared to WT, which was further enhanced by stimulating ICD with doxorubicin. Fes-/- mice demonstrated increased CTL and NK cell activation and PD-1 positivity, which was enhanced by doxorubicin, indicating a novel role of Fes in regulating CTL and NK cell activation. Additionally, we found a shift from M2- to M1-polarized tumour associated macrophages in Fes-/- versus WT mice. Finally, when treated with anti-PD-1 antibody, Fes-/- mice demonstrated greater tumour control and survival than WT.
Consistent with improved overall- and disease-free survival observed in low Fes-expressing cancer patients, our results identify Fes as a potential novel therapeutic target to enhance anti-cancer immunotherapy.
The authors.
Canadian Cancer Society, Canadian Breast Cancer Foundation, Canadian Institutes of Health Research.
All authors have declared no conflicts of interest.