Immune checkpoint blockade (ICB) has revolutionized cancer treatment, yet quality of life and continuation of therapy can be constrained by immune-related adverse events (irAEs). Limited understanding of irAE mechanisms hampers development of approaches to mitigate their damage. To address this, we examined whether mice gained sensitivity to anti-CTLA-4 (αCTLA-4)–mediated toxicity upon disruption of gut homeostatic immunity. We found αCTLA-4 drove increased inflammation and colonic tissue damage in mice with genetic predisposition to intestinal inflammation, acute gastrointestinal infection, transplantation with a dysbiotic fecal microbiome, or dextran sodium sulfate administration. We identified an immune signature of αCTLA-4–mediated irAEs, including colonic neutrophil accumulation and systemic interleukin-6 (IL-6) release. IL-6 blockade combined with antibiotic treatment reduced intestinal damage and improved αCTLA-4 therapeutic efficacy in inflammation-prone mice. Intestinal immune signatures were validated in biopsies from patients with ICB colitis. Our work provides new preclinical models of αCTLA-4 intestinal irAEs, mechanistic insights into irAE development, and potential approaches to enhance ICB efficacy while mitigating irAEs.

Conventional dendritic cells (cDCs) are a critical immune population, composed of multiple subsets, and responsible for controlling adaptive immunity and tolerance. Although migratory type 1 cDCs (CD103⁺ cDC1s in mice) are necessary to mount CD8⁺ T cell-mediated anti-tumor immunity, whether and how tumors modulate CD103⁺ cDC1 function remain understudied. Signal Transducer and Activator of Transcription 3 (STAT3) mediates the intracellular signaling of tumor-associated immunosuppressive cytokines, such as interleukin (IL)-10; thus, we hypothesized that STAT3 restrained anti-tumor immune responses elicited by CD103⁺ cDC1s. Herein, we show that in vitro-derived STAT3-deficient (Stat3^∆/∆) CD103⁺ cDC1s are refractory to the inhibitory effects of IL-10 on Toll-like receptor 3 (TLR3) agonist-induced maturation responses. In a tumor vaccination approach, we found Stat3^∆/∆ CD103⁺ cDC1s restrained mammary gland tumor growth and increased mouse survival more effectively than STAT3-sufficient CD103⁺ cDC1s. In addition, vaccination with Stat3^∆/∆ CD103⁺ cDC1s elicited increased amounts of tumor antigen-specific CD8⁺ T cells and IFN-γ⁺ CD4⁺ T cells in tumors and tumor-draining lymph nodes versus phosphate-buffered saline (PBS)-treated animals. Furthermore, IL-10 receptor-deficient CD103⁺ cDC1s controlled tumor growth to a similar degree as Stat3^∆/∆ CD103⁺ cDC1s. Taken together, our data reveal an inhibitory role for STAT3 in CD103⁺ cDC1 maturation and regulation of anti-tumor immunity. Our results also suggest IL-10 is a key factor eliciting immunosuppressive STAT3 signaling in CD103⁺ cDC1s in breast cancer. Thus, inhibition of STAT3 in cDC1s may provide an important strategy to improve their efficacy in tumor vaccination approaches and cDC1-mediated control of anti-tumor immunity.

Significance: Inflammation degrades hematopoietic stem and progenitor (HSPC) function, leading to myeloid-skewing and bone marrow failure. We show that the transcriptional regulator STAT3 has an intrinsic protective role in the hematopoietic system, which is necessary to preserve HSPCs and lineage-balanced hematopoiesis. We find that concomitant removal ofUbe2n, encoding the proinflammatory signal transducer Ubc13, mitigates hematopoietic failure, myeloid overproduction, and a majority of transcriptional deregulation withinStat3-null HSPCs. These data imply an epistatic relationship betweenStat3andUbe2n, and suggest that STAT3 protects the hematopoietic system from the effects of excessive proinflammatory signaling by restraining Ubc13.

JAA-F11 is a highly specific mouse monoclonal to the Thomsen-Friedenreich Antigen (TF-Ag) which is an alpha-O-linked disaccharide antigen on the surface of ~80% of human carcinomas, including breast, lung, colon, bladder, ovarian, and prostate cancers, and is cryptic on normal cells. JAA-F11 has potential, when humanized, for cancer immunotherapy for multiple cancer types. Humanization of JAA-F11, was performed utilizing complementarity determining regions grafting on a homology framework. The objective herein is to test the specificity, affinity and biology efficacy of the humanized JAA-F11 (hJAA-F11). Using a 609 target glycan array, 2 hJAA-F11 constructs were shown to have excellent chemical specificity, binding only to TF-Ag alpha-linked structures and not to TF-Ag beta-linked structures. The relative affinity of these hJAA-F11 constructs for TF-Ag was improved over the mouse antibody, while T20 scoring predicted low clinical immunogenicity. The hJAA-F11 constructs produced antibody-dependent cellular cytotoxicity in breast and lung tumor lines shown to express TF-Ag by flow cytometry. Internalization of hJAA-F11 into cancer cells was also shown using a surface binding ELISA and confirmed by immunofluorescence microscopy. Both the naked hJAA-F11 and a maytansine-conjugated antibody (hJAA-F11-DM1) suppressed in vivo tumor progression in a human breast cancer xenograft model in SCID mice. Together, our results support the conclusion that the humanized antibody to the TF-Ag has potential as an adjunct therapy, either directly or as part of an antibody drug conjugate, to treat breast cancer, including triple negative breast cancer which currently has no targeted therapy, as well as lung cancer.

Type I conventional dendritic cells (cDC1s) are an essential Ag-presenting population required for generating adaptive immunity against intracellular pathogens and tumors. While the transcriptional control of cDC1 development is well understood, the mechanisms by which extracellular stimuli regulate cDC1 function remain unclear. We previously demonstrated that the cytokine-responsive transcriptional regulator STAT3 inhibits polyinosinic:polycytidylic acid [poly(I:C)]-induced cDC1 maturation and cDC1-mediated antitumor immunity in murine breast cancer, indicating an intrinsic, suppressive role for STAT3 in cDC1s. To probe transcriptional mechanisms regulating cDC1 function, we generated novel RNA sequencing datasets representing poly(I:C)-, IL-10–, and STAT3-mediated gene expression responses in murine cDC1s. Bioinformatics analyses indicated that poly(I:C) stimulates multiple inflammatory pathways independent of STAT3, while IL-10–activated STAT3 uniquely inhibits the poly(I:C)-induced type I IFN (IFN-I) transcriptional response. We validated this mechanism using purified cDC1s deficient for STAT3 or IFN signaling. Our data reveal IL-10–activated STAT3 suppresses production of IFN-β and IFN-γ, accrual of tyrosine phosphorylated STAT1, and IFN-stimulated gene expression in cDC1s after poly(I:C) exposure. Moreover, we found that maturation of cDC1s in response to poly(I:C) is dependent on the IFN-I receptor, but not the type II IFN receptor, or IFN-λ. Taken together, we elucidate an essential role for STAT3 in restraining autocrine IFN-I signaling in cDC1s elicited by poly(I:C) stimulation, and we provide novel RNA sequencing datasets that will aid in further delineating inflammatory and anti-inflammatory mechanisms in cDC1s.