SHP-2 Regulates Myeloid Cell Differentiation, Anti-Tumor Responses and Innate Immune Memory

PD-1 is a T cell checkpoint inhibitor and the most extensively exploited therapeutic target of cancer immunotherapy. PD-1-mediated T cell inactivation is attributed to the function of SHP-2 phosphatase, which is activated by recruitment to PD-1 cytoplasmic tail. However, T cell-specific SHP-2 deletion did not improve anti-tumor immunity or altered responses to anti-PD-1 immunotherapy. Previously, we determined that PD-1 is also expressed in common myeloid progenitors and granulocyte/macrophage progenitors, which accumulate during cancer-driven emergency myelopoiesis and give rise to immunosuppressive myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAMs). In tumor-bearing mice with myeloid-specific PD-1 ablation, accumulation of MDSCs was prevented, while output of differentiated effector myeloid cells with monocytic lineage dominance was increased. However, the molecular mechanism remains elusive. It is also unknown whether a canonical PD-1:SHP-2 axis is operative in myeloid cells. Temporal activation of SHP-2 is critical for myeloid cell fate. Gain of function SHP-2 mutations, resulting in constitutive phosphatase activation, prevent myeloid differentiation and lead to the accumulation of immature myelocytes and development of leukemia. HOXA proteins, members of the HOX family of transcription factors involved in normal hematopoiesis, are targets of SHP-2, which dephosphorylates HOXA and prevents derepressing of HOXA target genes and myeloid cell differentiation. In addition, SHP-2 regulates the function of IFN regulatory factor (IRF)-8, a transcription factor that has a decisive role in myeloid progenitor differentiation toward monocytes and DCs. IRF8 phosphorylation is mandatory for its nuclear translocation and initiation of gene transcription. The cytoplasmic-nuclear shuttling of IRF8 is regulated by SHP-2, which dephosphorylates IRF8 and prevents its nuclear localization and transcriptional activation. We generated mice with conditional targeting of the Ptpn11 gene (encoding for Shp-2) in T cells (Shp2^f/fLckCre) or myeloid cells (Shp2^f/fLysMCre), and found that Shp2^f/fLysMCre but not Shp2^f/fLckCre mice had diminished tumor growth. As determined by RNA-sequencing, this was paralleled by the presence of inflammatory neutrophils and tumor-associated macrophages (TAMs) with molecular signatures of enhanced differentiation, phagocytosis and antigen-processing and presentation. SHP-2 deficient TAMs also had increased monocyte and dendritic cells (DCs) specification transcription factors, chemokine and cytokine production, and expression of immunostimulatory molecules that promote T cell recruitment and activation. Moreover, monocytes from tumor-bearing Shp2^f/fLysMCre mice suppressed tumor growth after transfer to naïve recipients indicating development of innate immune memory, named trained immunity. In bone marrow myelocytes, SHP-2 deletion enhanced GM-CSF-mediated phosphorylation of the transcription factors HOXA10 and IRF8 that promote myeloid differentiation and monocytic/moDC lineage commitment, respectively. In contrast, in WT bone marrow myelocytes GM-CSF induced PD-1 expression, phosphorylation and interaction with SHP-2, the Src family kinase Lyn, and GM-CSF receptor beta chain, indicating that the PD-1:SHP-2 axis targets a key pathway of myelocyte differentiation. Our results reveal a previously unidentified mechanistic role of SHP-2 and the PD-1:SHP-2 axis in regulating myeloid cell differentiation in the context of cancer and provide evidence that SHP-2 poses a signaling restrain to myeloid differentiation and monocyte lineage commitment resulting in a myeloid landscape that suppresses anti-tumor immunity. This process is hijacked by the PD-1/PD-L1 pathway.

Vlachos:Takeda Pharmaceutical: Current Employment; Singular Genomics: Research Funding; NextRNA: Consultancy; National Institute of Health: Research Funding; Mosaic: Consultancy; Guidepoint Global: Consultancy; Department of Defense: Research Funding; Botanisol Analytics: Research Funding.