Concomitant deletion of Ptpn6 and Ptpn11 in T cells fails to improve anticancer responses

Anticancer T cells acquire a dysfunctional state characterized by poor effector function and expression of inhibitory receptors, such as PD-1. Blockade of PD-1 leads to T cell reinvigoration and is increasingly applied as an effective anticancer treatment. Recent work challenged the commonly held view that the phosphatase PTPN11 (known as SHP-2) is essential for PD-1 signaling in T cells, suggesting functional redundancy with the homologous phosphatase PTPN6 (SHP-1). Therefore, we investigated the effect of concomitant Ptpn6 and Ptpn11 deletion in T cells on their ability to mount antitumour responses. In vivo data show that neither sustained nor acute Ptpn6/11 deletion improves T cell-mediated tumor control. Sustained loss of Ptpn6/11 also impairs the therapeutic effects of anti-PD1 treatment. In vitro results show that Ptpn6/11-deleted CD8+ T cells exhibit impaired expansion due to a survival defect and proteomics analyses reveal substantial alterations, including in apoptosis-related pathways. These data indicate that concomitant ablation of Ptpn6/11 in polyclonal T cells fails to improve their anticancer properties, implying that caution shall be taken when considering their inhibition for immunotherapeutic approaches.

Abstract P051: Function of shp-1 and shp-2 phosphatases in T cell-mediated anti-tumor response

After exposure to chronic inflammatory stimuli, the immune system can switch from a functional state where it acts to reestablish homeostasis to a dysfunctional state. In the context of cancer, T cells that become exposed to continuous stimulation eventually reach a state of exhaustion, characterized by poor effector function and expression of inhibitory receptors, such as PD-1. Although PD-1 signaling inhibition leads to T cell reinvigoration and has been applied as an effective treatment versus a wide range of tumors, the signaling pathway downstream of this receptor is still poorly understood. Recent work from others and us challenged the notion that the phosphatase shp-2 is essential for activation of the molecular cascade downstream PD-1 receptor engagement. The shp-2 homologue (shp-1) has also been associated with PD-1 signaling in T cells and functional redundancy between these phosphatases might occur downstream of this receptor. Therefore, we investigated the effect of shp-1 and the combination of both (shp-1/2) downstream of PD-1 by knocking out these phosphatases in T cells in a mouse model. In vivo results after tumor engraftment suggest that shp-1 as well as shp-1/2 deletion in T cells are not sufficient to ameliorate tumor control. Furthermore, ablation of shp-1 and shp-1/2 impair the beneficial effects of the anti-PD1 treatment. In fact, deletion of both phosphatases leads to decrease CD8+ T cell presence in the tumor microenvironment and in vitro results show that these cells have impaired survival. This data implies that elimination or inhibition of shp-1/2 is not a suitable strategy for effective immunotherapeutic approaches as well as highlights the importance of further elucidating the mechanisms behind this important inhibitory pathway.

Citation Format: Pedro Ventura, Milica Gakovic, Berenice Fischer, Sarah Thomson, Hanif J Khameneh, Alessandro Zenobi, Giorgia Rota, Eric Vivier, Walter Birchmeier, Doreen Cantrell, Greta Guarda. Function of shp-1 and shp-2 phosphatases in T cell-mediated anti-tumor response [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P051.

Tuning MPL signaling to influence hematopoietic stem cell differentiation and inhibit essential thrombocythemia progenitors

Thrombopoietin (TPO) and the TPO-receptor (TPO-R, or c-MPL) are essential for hematopoietic stem cell (HSC) maintenance and megakaryocyte differentiation. Agents that can modulate TPO-R signaling are highly desirable for both basic research and clinical utility. We developed a series of surrogate protein ligands for TPO-R, in the form of diabodies (DBs), that homodimerize TPO-R on the cell surface in geometries that are dictated by the DB receptor binding epitope, in effect "tuning" downstream signaling responses. These surrogate ligands exhibit diverse pharmacological properties, inducing graded signaling outputs, from full to partial TPO agonism, thus decoupling the dual functions of TPO/TPO-R. Using single-cell RNA sequencing and HSC self-renewal assays we find that partial agonistic diabodies preserved the stem-like properties of cultured HSCs, but also blocked oncogenic colony formation in essential thrombocythemia (ET) through inverse agonism. Our data suggest that dampening downstream TPO signaling is a powerful approach not only for HSC preservation in culture, but also for inhibiting oncogenic signaling through the TPO-R.

Decoupling the Functional Pleiotropy of Stem Cell Factor by Tuning c-Kit Signaling

Most secreted growth factors and cytokines are functionally pleiotropic because their receptors are expressed on diverse cell types. While important for normal mammalian physiology, pleiotropy limits the efficacy of cytokines and growth factors as therapeutics. Stem cell factor (SCF) is a growth factor that acts through the c-Kit receptor tyrosine kinase to elicit hematopoietic progenitor expansion but can be toxic when administered in vivo because it concurrently activates mast cells. We engineered a mechanism-based SCF partial agonist that impaired c-Kit dimerization, truncating downstream signaling amplitude. This SCF variant elicited biased activation of hematopoietic progenitors over mast cells in vitro and in vivo. Mouse models of SCF-mediated anaphylaxis, radioprotection, and hematopoietic expansion revealed that this SCF partial agonist retained therapeutic efficacy while exhibiting virtually no anaphylactic off-target effects. The approach of biasing cell activation by tuning signaling thresholds and outputs has applications to many dimeric receptor-ligand systems.

Synthekines are surrogate cytokine and growth factor agonists that compel signaling through non-natural receptor dimers

Cytokine and growth-factor ligands typically signal through homo- or hetero-dimeric cell surface receptors via Janus Kinase (JAK/TYK), or Receptor Tyrosine Kinase (RTK)-mediated trans-phosphorylation. However, the number of receptor dimer pairings occurring in nature is limited to those driven by natural ligands encoded within our genome. We have engineered synthethic cytokines (synthekines) that drive formation of cytokine receptor dimer pairings that are not formed by endogenous cytokines and that are not found in nature, and which activate distinct signaling programs. We show that a wide range of non-natural cytokine receptor hetero-dimers are competent to elicit a signaling output. We engineered synthekine ligands that assembled IL-2Rβ/IL-4Rα or IL-4Rα/IFNAR2 receptor heterodimers, that do not occur naturally, triggering signaling and functional responses distinct from those activated by the endogenous cytokines IL-2, IL-4, and IFN. Furthermore, hybrid synthekine ligands that dimerized a JAK/STAT cytokine receptor with a receptor tyrosine kinase (RTK) also elicited a signaling response. Synthekines represent a new family of synthetic ligands with pre-defined receptors, but 'orphan' functions, that enable the full combinatorial scope of dimeric signaling receptors encoded within the human genome to be exploited for basic research and drug discovery.

Pleiotropic effects of Sox2 during the development of the zebrafish epithalamus

The zebrafish epithalamus is part of the diencephalon and encompasses three major components: the pineal, the parapineal and the habenular nuclei. Using sox2 knockdown, we show here that this key transcriptional regulator has pleiotropic effects during the development of these structures. Sox2 negatively regulates pineal neurogenesis. Also, Sox2 is identified as the unknown factor responsible for pineal photoreceptor prepatterning and performs this function independently of the BMP signaling. The correct levels of sox2 are critical for the functionally important asymmetrical positioning of the parapineal organ and for the migration of parapineal cells as a coherent structure. Deviations from this strict control result in defects associated with abnormal habenular laterality, which we have documented and quantified in sox2 morphants.

Two rare disease-associated Tyk2 variants are catalytically impaired but signaling competent

Tyk2 belongs to the Janus protein tyrosine kinase family and is involved in signaling of immunoregulatory cytokines (type I and III IFNs, IL-6, IL-10, and IL-12 families) via its interaction with shared receptor subunits. Depending on the receptor complex, Tyk2 is coactivated with either Jak1 or Jak2, but a detailed molecular characterization of the interplay between the two enzymes is missing. In human populations, the Tyk2 gene presents high levels of genetic diversity with >100 nonsynonymous variants being detected. In this study, we characterized two rare Tyk2 variants, I684S and P1104A, which have been associated with susceptibility to autoimmune disease. Specifically, we measured their in vitro catalytic activity and their ability to mediate Stat activation in fibroblasts and genotyped B cell lines. Both variants were found to be catalytically impaired but rescued signaling in response to IFN-α/β, IL-6, and IL-10. These data, coupled with functional study of an engineered Jak1 P1084A, support a model of nonhierarchical activation of Janus kinases in which one catalytically competent Jak is sufficient for signaling provided that its partner behaves as proper scaffold, even if inactive. Through the analysis of IFN-α and IFN-γ signaling in cells with different Jak1 P1084A levels, we also illustrate a context in which a hypomorphic Jak can hamper signaling in a cytokine-specific manner. Given the multitude of Tyk2-activating cytokines, the cell context-dependent requirement for Tyk2 and the catalytic defect of the two disease-associated variants studied in this paper, we predict that these alleles are functionally significant in complex immune disorders.

The role of RPGR in cilia formation and actin stability

Mutations in the retinitis pigmentosa GTPase regulator (RPGR) protein cause one of the most common and severe forms of inherited retinal dystrophy. In spite of numerous studies, the precise function of RPGR remains unclear, as is the mechanism by which RPGR mutations cause retinal degeneration. We have analysed the function of RPGR by RNA interference-mediated translational suppression [knockdown (KD)] using a model cellular system for studying the formation, maintenance and function of primary cilia (human telomerase-immortalized retinal pigmented epithelium 1 cells). We observed that RPGR-deficient cells exhibited reduced numbers of cilia, slower cell cycle progression and impaired attachment to fibronectin, but showed no migration defects in a wound-healing assay. RPGR KD cells showed stronger actin filaments, associated with basal dysregulation of the Akt, Erk1/2, focal adhesion kinase and Src signalling pathways, as well as a 20% reduction in β1-integrin receptors at the cell surface and impaired fibronectin-induced signalling. Stronger actin filaments and impairment of the above signalling pathways suggest a common underlying mechanism for all of the cellular phenotypes observed in RPGR KD cells. Our data underline a novel function for RPGR in cilia formation and in the regulation of actin stress filaments, suggesting that, in the retina, it may regulate nascent photoreceptor disc formation by regulating actin-mediated membrane extension.

The Stat3-activating Tyk2 V678F mutant does not up-regulate signaling through the type I interferon receptor but confers ligand hypersensitivity to a homodimeric receptor

Tyk2 is a Jak family member involved in cytokine signaling through heterodimeric-type receptors. Here, we analyzed the impact of the Val(678)-to-Phe substitution on Tyk2 functioning. This mutation is homologous to the Jak2 Val(617)-to-Phe mutation, implicated in myeloproliferative disorders. We studied ligand-independent and ligand-dependent Jak/Stat signaling in cells expressing Tyk2 V678F. Moreover, the effect of Tyk2 V678F was monitored in the context of the native heterodimeric interferon alpha receptor and in the context of a homodimeric receptor chimera, EpoR/R1, containing the ectodomain of the erythropoietin receptor. We show that Tyk2 V678F has increased catalytic potential in vivo and in vitro and more so when it is anchored to the homodimeric receptor. Tyk2 V678F leads to constitutive Stat3 phosphorylation but has no notable effect on the canonical interferon alpha-induced signaling. However, if anchored to the homodimeric EpoR/R1, the mutant confers to the cell increased sensitivity to erythropoietin. Thus, despite the catalytic gain of function of Tyk2 V678F, the effect on ligand-induced signaling is manifest only when two mutant enzymes are juxtaposed via the homodimeric receptor.