Type I IFN, Ly6C+ cells, and Phagocytes Support Suppression of Peritoneal Carcinomatosis Elicited by a TLR and CLR Agonist Combination

Abstract

Metastatic cancer involving spread to the peritoneal cavity is referred to as peritoneal carcinomatosis and has a very poor prognosis. Our previous study demonstrated a toll-like receptor (TLR) and Ctype lectin receptor (CLR) agonist pairing of monophosphoryl lipid A (MPL) and trehalose-6,6'dicorynomycolate (TDCM) effectively inhibits tumor growth and ascites development following TA3-Ha and EL4 challenge through a mechanism dependent upon B-1a cell-produced natural IgM and complement. In the current study, we investigated additional players in the MPL/TDCM-elicited response. MPL/TDCM treatment rapidly increased type I IFN levels in the peritoneal cavity along with myeloid cell numbers, including macrophages and Ly6C hi monocytes. Type I IFN receptor (IFNAR1 -/-) mice produced tumor-reactive IgM following MPL/TDCM treatment, but failed to recruit Ly6C + monocytes and were not afforded protection during tumor challenges. Clodronate liposome depletion of phagocytic cells, as well as targeted depletion of Ly6C + cells, also ablated MPL/TDCM-induced protection. Cytotoxic mediators known to be produced by these cells were required for effects. TNF was required for effective TA3-Ha killing and nitric oxide was required for EL4 killing. Collectively, these data reveal a model whereby MPL/TDCM-elicited anti-tumor effects strongly depend on innate cell responses, with B-1a cell-produced tumor-reactive IgM and complement pairing with myeloid cell-produced cytotoxic mediators to effectively eradicate tumors in the peritoneal cavity.

Type 1 interferon supports B cell responses to polysaccharide antigens but is not required for MPL/TDCM adjuvant effects on innate B cells

“…Finally, with regard to innate B1 cell production of Abs, IFNAR is required for B1 cell lymph node trafficking and IgM production in response to influenza virus infection due to its role in regulating CD11b conformational changes (24). However, it is not required for monophosphoryl lipid A-induced tumor reactive natural IgM production by B1a cells (7), despite its dependence on the TLR4-TRIF activation pathway (25). Given the significantly reduced activation and expansion of IFNAR −/− TNP-specific B cells 5 days post TNP-Ficoll immunization, along with early effects of IFNAR deficiency on both IgM and IgG production, IFNAR signaling appears to be important for supporting early B cell activation events required for optimal responses to TI-2 Ags.…”

“…First, we demonstrate type I IFN signaling on B cells supports optimal Ab responses to TI-2 Ags, including pneumococcal polysaccharides, via support of early B cell activation and expansion. Second, we demonstrate an MPL-based adjuvant that significantly augments primary and secondary responses to TI-2 Ags ( 6), induces type I IFN production in vivo (7), and requires TRIF signaling for optimal adjuvant effects (6), does not require type I IFN for its effects and moreover, restores defective TI-2 Ab responses caused by IFNAR deficiency. Finally, we demonstrate MPL/TDCM elicits its adjuvant effects by largely promoting Ab production by innate-like B cells (ie., B-1b and CD23 -B cells).…”

“…Wild-type (WT), mumt (Ighm tm1Cgn ), CD19 Cre (B6.129P2(C)-Cd19 tm1(cre)Cgn /J) and B1-8hi IgH knock-in (V H B1-8 Tg) mice were on a C57BL/6 background (Jackson Laboratories). Ifnar1-deficient (IFNAR −/− ) and floxed IFNAR fl/fl (Ifnar1 tm1Uka ) mice were as previously described (7). Studies used age- and sex-matched mice housed in an SPF facility and were approved by Wake Forest School of Medicine’s Animal Use Committee.…”

“…We previously reported MPL/TDCM induced type I IFN production in vivo (7), likely through the effects of MPL on TLR4-TRIF activation of type I IFN production (8). Importantly, a previous study demonstrated the TLR3 agonist, poly(I:C), increased Ab responses to NP-Ficoll via a mechanism dependent upon IFNAR signaling and follicular B cells (9).…”

A TLR4–TRIF-dependent signaling pathway is required for protective natural tumor-reactive IgM production by B1 cells

“…Protection is elicited through a mechanism dependent upon B-1a cellproduced natural IgM reactive against TACAs and complement. Phagocytes also play a supportive role in the therapeutic effects of MPL/TDCM treatment through production of cytotoxic intermediates and likely engaging in mechanisms of complement-dependent cellular cytotoxicity [25]. MPL signals through the TLR4/MD2 complex [26] whereas TDCM relies on the CLRs, Mincle and MCL, which require the Fc receptor common γ chain (FcRγ) for signaling [27].…”