LEOPARD syndrome (LS) is an autosomal dominant "RASopathy" that manifests with congenital heart disease. Nearly all cases of LS are caused by catalytically inactivating mutations in the protein tyrosine phosphatase (PTP), non-receptor type 11 (PTPN11) gene that encodes the SH2 domain-containing PTP-2 (SHP2). RASopathies typically affect components of the RAS/MAPK pathway, yet it remains unclear how PTPN11 mutations alter cellular signaling to produce LS phenotypes. We therefore generated knockin mice harboring the Ptpn11 mutation Y279C, one of the most common LS alleles. Ptpn11 Y279C/+ (LS/+) mice recapitulated the human disorder, with short stature, craniofacial dysmorphia, and morphologic, histologic, echocardiographic, and molecular evidence of hypertrophic cardiomyopathy (HCM). Heart and/or cardiomyocyte lysates from LS/+ mice showed enhanced binding of Shp2 to Irs1, decreased Shp2 catalytic activity, and abrogated agonist-evoked Erk/Mapk signaling. LS/+ mice also exhibited increased basal and agonist-induced Akt and mTor activity. The cardiac defects in LS/+ mice were completely reversed by treatment with rapamycin, an inhibitor of mTOR. Our results demonstrate that LS mutations have dominant-negative effects in vivo, identify enhanced mTOR activity as critical for causing LS-associated HCM, and suggest that TOR inhibitors be considered for treatment of HCM in LS patients.

The prospects for using autologous induced pluripotent stem cells (iPSCs) in cell replacement therapy have been tempered by evidence that undifferentiated, syngeneic mouse iPSCs are immunogenic upon transplantation. However, the immunogenicity of more therapeutically relevant differentiated cells remains unexplored. Here, we differentiated mouse iPSCs into embryoid bodies (EBs) or representative cell types spanning the three embryonic germ layers and assessed their immunogenicity in vitro and after their transplantation into syngeneic recipients. We found no evidence of increased T cell proliferation in vitro, rejection of syngeneic iPSC-derived EBs/tissue-specific cells (TSCs) after transplantation, or an antigen-specific secondary immune response. Thus, differentiated cells derived from syngeneic iPSCs do not appear to be rejected after transplantation. We also found little evidence of an immune response to undifferentiated, syngeneic iPSCs. Our data support the idea that differentiated cells generated from autologous iPSCs could be applied for cell replacement therapy without eliciting immune rejection.

Chimeric antigen receptor modified T cell (CAR-T) technology, a promising immunotherapeutic tool, has not been applied specifically to treat liver metastases (LM). While CAR-T delivery to LM can be optimized by regional intrahepatic infusion, we propose that liver CD11b+Gr-1+ myeloid-derived suppressor cells (L-MDSC) will inhibit the efficacy of CAR-T in the intrahepatic space. We studied anti-CEA CAR-T in a murine model of CEA+ LM and identified mechanisms through which L-MDSC expand and inhibit CAR-T function. We established CEA+ LM in mice and studied purified L-MDSC and responses to treatment with intrahepatic anti-CEA CAR-T infusions. L-MDSC expanded three-fold in response to LM and their expansion was dependent on GM-CSF, which was produced by tumor cells. L-MDSC utilized PD-L1 to suppress anti-tumor responses through engagement of PD-1 on CAR-T. GM-CSF, in cooperation with STAT3, promoted L-MDSC PD-L1 expression. CAR-T efficacy was rescued when mice received CAR-T in combination with MDSC depletion, GM-CSF neutralization to prevent MDSC expansion, or PD-L1 blockade. As L-MDSC suppressed anti-CEA CAR-T, infusion of anti-CEA CAR-T in tandem with agents targeting L-MDSC is a rational strategy for future clinical trials.

Metastatic spread of colorectal cancer (CRC) to the peritoneal cavity is common and difficult to treat, with many patients dying from malignant bowel obstruction. Chimeric antigen receptor T cell (CAR-T) immunotherapy has shown great promise, and we previously reported murine and phase I clinical studies on regional intrahepatic CAR-T infusion for CRC liver metastases. We are now studying intraperitoneal (IP) delivery of CAR-Ts for peritoneal carcinomatosis. Regional IP infusion of CAR-T resulted in superior protection against CEA+ peritoneal tumors, when compared to systemically infused CAR-Ts. IP CAR-Ts also provided prolonged protection against IP tumor re-challenges and demonstrated an increase in effector memory phenotype over time. IP CAR-Ts provided protection against tumor growth at distant subcutaneous (SC) sites in association with increases in serum IFNγ levels. Given the challenges posed by immunoinhibitory pathways in solid tumors, we combined IP CAR-T treatment with suppressor cell targeting. High frequencies of myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) were found within the IP tumors, with MDSC expressing high levels of immunosuppressive PD-L1. Combinatorial IP CAR-T treatment with depleting antibodies against MDSC and Treg further improved efficacy against peritoneal metastases. Our data support further development of combinatorial IP CAR-T immunotherapy for peritoneal malignancies.

Ligands of the endothelial-enriched tunica interna endothelial cell kinase 2 (Tie2) are markedly imbalanced in severe infections associated with vascular leakage, yet regulation of the receptor itself has been understudied in this context. Here, we show that TIE2 gene expression may constitute a novel vascular barrier control mechanism in diverse infections. Tie2 expression declined rapidly in wide-ranging models of leak-associated infections, including anthrax, influenza, malaria, and sepsis. Forced Tie2 suppression sufficed to attenuate barrier function and sensitize endothelium to permeability mediators. Rapid reduction of pulmonary Tie2 in otherwise healthy animals attenuated downstream kinase signaling to the barrier effector vascular endothelial (VE)-cadherin and induced vascular leakage. Compared with wild-type littermates, mice possessing one allele of Tie2 suffered more severe vascular leakage and higher mortality in two different sepsis models. Common genetic variants that influence TIE2 expression were then sought in the HapMap3 cohort. Remarkably, each of the three strongest predicted cis-acting SNPs in HapMap3 was also associated with the risk of acute respiratory distress syndrome (ARDS) in an intensive care unit cohort of 1,614 subjects. The haplotype associated with the highest TIE2 expression conferred a 28% reduction in the risk of ARDS independent of other major clinical variables, including disease severity. In contrast, the most common haplotype was associated with both the lowest TIE2 expression and 31% higher ARDS risk. Together, the results implicate common genetic variation at the TIE2 locus as a determinant of vascular leak-related clinical outcomes from common infections, suggesting new tools to identify individuals at unusual risk for deleterious complications of infection.Tie2 | endothelium | infection | angiopoietin | permeability

Assumptions that liver immune cells and immunosuppressive pathways are similar to their counterparts in other spaces have led to gaps in our understanding of intrahepatic neoplasm aggressiveness. Myeloid-derived suppressor cells (MDSCs) are potent inhibitors of antitumor immunity and pose a major obstacle to solid tumor treatment. Liver MDSCs (L-MDSCs) associated with liver metastases (LM) are particularly problematic by contributing to intrahepatic immunosuppression that promotes tumor progression. L-MDSCs have been reported to expand in response to granulocyte-macrophages colony-stimulating factor (GM-CSF) and suppress antitumor immunity in LM. To extend these findings, we examined mechanisms of intrahepatic immunosuppression exploited by L-MDSCs. We found that the majority of L-MDSCs co-expressed GM-CSF receptor (GM-CSF-R), indoleamine 2,3-dioxygenase (IDO) and programmed death ligand 1 (PD-L1), while demonstrating high levels of signal transducer and activator of transcription factor 3 (STAT3) activation. GM-CSF-secreting tumor cells induced STAT3 phosphorylation in L-MDSCs in addition to expression of IDO and PD-L1. GM-CSF or GM-CSF-R blockade markedly reduced L-MDSC IDO and PD-L1 expression, implicating tumor-derived GM-CSF in supporting L-MDSC-immunoinhibitory molecule expression. Small-molecule inhibitors of Janus-activated kinase 2 (JAK2) and STAT3 also dramatically diminished IDO and PD-L1 expression in L-MDSCs. We determined that STAT3 exerts transcriptional control over L-MDSC IDO and PD-L1 expression by binding to the IDO1 and PD-L1 promoters. Our data suggest that the GM-CSF/JAK2/STAT3 axis in L-MDSCs drives immunosuppression in a model of LM and blockade of this pathway may enable rescue of intrahepatic antitumor immunity.

Immunosuppressive myeloid-derived suppressor cells (MDSC) subvert antitumor immunity and limit the efficacy of chimeric antigen receptor T cells (CAR-T). Previously, we reported that the GM-CSF/JAK2/STAT3 axis drives liver-associated MDSC (L-MDSC) proliferation and blockade of this axis rescued antitumor immunity. We extended these findings in our murine liver metastasis (LM) model, by treating tumor-bearing mice with STAT3 inhibitors (STATTIC or BBI608) to further our understanding of how STAT3 drives L-MDSC suppressive function. STAT3 inhibition caused significant reduction of tumor burden as well as L-MDSC frequencies due to decrease in pSTAT3 levels. L-MDSC isolated from STATTIC or BBI608-treated mice had significantly reduced suppressive function. STAT3 inhibition of L-MDSC was associated with enhanced antitumor activity of CAR-T. Further investigation demonstrated activation of apoptotic signaling pathways in L-MDSC following STAT3 inhibition as evidenced by an upregulation of the pro-apoptotic proteins Bax, cleaved caspase-3, and downregulation of the anti-apoptotic protein Bcl-2. Accordingly, there was also a decrease of pro-survival markers, pErk and pAkt, and an increase in pro-death marker, Fas, with activation of downstream JNK and p38 MAPK. These findings represent a previously unrecognized link between STAT3 inhibition and Fas-induced apoptosis of MDSCs. Our findings suggest that inhibiting STAT3 has potential clinical application for enhancing the efficacy of CAR-T cells in LM through modulation of L-MDSC.

ObjectiveProgrammed cell death protein 1 (PD-1) checkpoint inhibition and adoptive cellular therapy have had limited success in patients with microsatellite stable colorectal cancer liver metastases (CRLM). We sought to evaluate the effect of interleukin 10 (IL-10) blockade on endogenous T cell and chimeric antigen receptor T (CAR-T) cell antitumour function in CRLM slice cultures.DesignWe created organotypic slice cultures from human CRLM (n=38 patients’ tumours) and tested the antitumour effects of a neutralising antibody against IL-10 (αIL-10) both alone as treatment and in combination with exogenously administered carcinoembryonic antigen (CEA)-specific CAR-T cells. We evaluated slice cultures with single and multiplex immunohistochemistry, in situ hybridisation, single-cell RNA sequencing, reverse-phase protein arrays and time-lapse fluorescent microscopy.ResultsαIL-10 generated a 1.8-fold increase in T cell-mediated carcinoma cell death in human CRLM slice cultures. αIL-10 significantly increased proportions of CD8+ T cells without exhaustion transcription changes, and increased human leukocyte antigen - DR isotype (HLA-DR) expression of macrophages. The antitumour effects of αIL-10 were reversed by major histocompatibility complex class I or II (MHC-I or MHC-II) blockade, confirming the essential role of antigen presenting cells. Interrupting IL-10 signalling also rescued murine CAR-T cell proliferation and cytotoxicity from myeloid cell-mediated immunosuppression. In human CRLM slices, αIL-10 increased CEA-specific CAR-T cell activation and CAR-T cell-mediated cytotoxicity, with nearly 70% carcinoma cell apoptosis across multiple human tumours. Pretreatment with an IL-10 receptor blocking antibody also potentiated CAR-T function.ConclusionNeutralising the effects of IL-10 in human CRLM has therapeutic potential as a stand-alone treatment and to augment the function of adoptively transferred CAR-T cells.