Shp1 Loss Enhances Macrophage Effector Function and Promotes Anti-Tumor Immunity

Abstract

Shp1, encoded by the gene Ptpn6 , is a protein tyrosine phosphatase that transduces inhibitory signals downstream of immunoreceptors in many immune cell types. Blocking Shp1 activity represents an exciting potential immunotherapeutic strategy for the treatment of cancer, as Shp1 inhibition would be predicted to unleash both innate and adaptive immunity against tumor cells. Antibodies blocking the interaction between CD47 on tumor cells and SIRPα on macrophages enhance macrophage phagocytosis, show efficacy in preclinical tumor models, and are being evaluated in the clinic. Here we found that Shp1 bound to phosphorylated peptide sequences derived from SIRPα and transduced the anti-phagocytic signal, as Shp1 loss in mouse bone marrow-derived macrophages increased phagocytosis of tumor cells in vitro . We also generated a novel mouse model to evaluate the impact of global, inducible Ptpn6 deletion on anti-tumor immunity. We found that inducible Shp1 loss drove an inflammatory disease in mice that was phenotypically similar to that seen when Ptpn6 is knocked out from birth. This indicates that acute perturbation of Shp1 in vivo could drive hyperactivation of immune cells, which could be therapeutically beneficial, though at the risk of potential toxicity. In this model, we found that Shp1 loss led to robust anti-tumor immunity against two immune-rich syngeneic tumor models that are moderately inflamed though not responsive to checkpoint inhibitors, MC38 and E0771. Shp1 loss did not promote anti-tumor activity in the non-inflamed B16F10 model. The observed activity in MC38 and E0771 tumors was likely due to effects of both innate and adaptive immune cells. Following Shp1 deletion, we observed increases in intratumoral myeloid cells in both models, which was more striking in E0771 tumors. E0771 tumors also contained an increased ratio of effector to regulatory T cells following Shp1 loss. This was not observed for MC38 tumors, though we did find increased levels of IFNγ, a cytokine produced by effector T cells, in these tumors. Overall, our preclinical data suggested that targeting Shp1 may be an attractive therapeutic strategy for boosting the immune response to cancer via a mechanism involving both innate and adaptive leukocytes.

Engineered CAR-Macrophages as Adoptive Immunotherapies for Solid Tumors

“…Similarly promising results were generated by Myers et al. upon targeting the tyrosine phosphatase Shp1, which signals downstream of SIRPα to propagate anti-phagocytic signals ( 62 ). Instead of irreversibly editing genes, numerous CRISPR-based technologies regulate gene transcription using a catalytically dead Cas9 (dCas9) and chromatin remodeling factors ( 63 ).…”

“…The authors in this study demonstrated that SIRPa-deficient macrophages gained potent anti-tumor properties and coordinated a robust immune response when delivered in combination with radiotherapy (61). Similarly promising results were generated by Myers et al upon targeting the tyrosine phosphatase Shp1, which signals downstream of SIRPa to propagate anti-phagocytic signals (62). Instead of irreversibly editing genes, numerous CRISPR-based technologies regulate gene transcription using a catalytically dead Cas9 (dCas9) and chromatin remodeling factors (63).…”

Two Duplicated Ptpn6 Homeologs Cooperatively and Negatively Regulate RLR-Mediated IFN Response in Hexaploid Gibel Carp

“…SHP1 is known to be a major regulator in this process (70,71). For example, the inducible deletion of Ptpn6 led to an increase in IFNg expression in the Ptpn6 fl/ fl ERT2-Cre mouse (72). Epstein-Barr virus (EBV) Tegument protein BGLF2 facilitates the recruitment of SHP1 to STAT1, which reduces STAT1 phosphorylation and thereby the induction of IFN and ISGs in HEK293 cells (73).…”

Putting the brakes on phagocytosis: “don't‐eat‐me” signaling in physiology and disease

“…Nonetheless, tyrosine phosphorylation of SIRPα at specific ITIMs permits the binding of SHP‐1 or SHP‐2 via their SH2 domains, which relieves repression on the catalytic phosphatase domain and allows for dephosphorylation of their respective substrates (Neel et al, 2003; Lorenz, 2009). It remains unclear whether these phosphatases compete for the same binding site(s), or bind distinct sites on SIRPα; however, current evidence supports the latter model (Takada et al, 1998; Myers et al, 2020). In addition to being a binding partner, SIRPα is also a substrate of these phosphatases (Timms et al, 1998).…”

“… Engagement of the CD47‐SIRP⍺ axis occurs in cis and in trans , which induces tyrosine phosphorylation of the ITIMs in the cytoplasmic tail of SIRP⍺. Phosphorylation at Y429 and Y453 of human SIRPα mediate binding of tyrosine phosphatase SHP‐1 (Myers et al, 2020). Dephosphorylation of non‐muscle myosin IIA is one proposed substrate of SHP‐1, resulting in disassembly of the actomyosin cytoskeleton.…”