We demonstrated that a recombinant banana lectin (rBanLec), which structural characteristics and physiological impacts highly resemble those reported for its natural counterparts, binds murine peritoneal macrophages and specifically modulates their functional characteristics. By using rBanLec in concentrations ranging from 1 μg to 10 μg to stimulate resident (RMs) and thioglycollate-elicited (TGMs) peritoneal macrophages from BALB/c and C57BL/6 mice, we have shown that effects of rBanLec stimulation depend on its concentration but also on the functional status of macrophages and their genetic background. rBanLec, in a positive dose-dependent manner, promotes the proliferation of TGMs from both BALB/c and C57BL/6 mice, while its mitogenic influence on RMs is significantly lower (BALB/c mice) or not detectable (C57BL/6 mice). In all peritoneal macrophages, irrespective of their type and genetic background, rBanLec, in a positive dose dependent manner, enhances the secretion of IL-10. rBanLec stimulation of RMs from both BALB/c and C57BL/6 resulted in a positive dose-dependent promotion of proinflammatory phenotype (enhancement of NO production and IL-12 and TNFα secretion, reduction of arginase activity). Positive dose-dependent skewing toward proinflammatory phenotype was also observed in TGMs from C57BL/6 mice. However, the enhancement of rBanLec stimulation promotes skewing of TGMs from BALB/c mice towards anti-inflammatory profile (reduction of NO production and IL-12 secretion, enhancement of arginase activity and TGFβ and IL-4 secretion). Moreover, we established that rBanLec binds oligosaccharide structures of TLR2 and CD14 and that blocking of signaling via these receptors significantly impairs the production of TNFα and NO in BALB/c macrophages. Since the outcome of rBanLec stimulation depends on rBanLec concentration as well as on the functional characteristics of its target cells and their genetic background, further studies are needed to investigate its effects under physiological and specific pathological conditions.

Therapeutic innate immune stimulation within the tumor microenvironment can potentiate endogenous antitumor T cell immunity. Strategies for controlled activation of cGAS/STING signaling are currently under intense investigation. DNase 3’-repair exonuclease 1 (TREX1) is essential for cellular DNA disposal, which prevents autoimmunity ensuing from cGAS/STING activation by endogenous DNA. TREX1-deficient tumor cells elicit enhanced protective immunity in syngeneic models. Here, we showed that induced inactivation of the Trex1 gene in host (non-cancer) cells yields improved type I IFN- and T cell-dependent control of established TREX1-competent tumors. Host TREX1 deficiency was well tolerated and triggered selective immune cell infiltration into tumors but not into other tissues. Induced systemic loss of TREX1 in tumor-bearing mice resulted in enhanced intra-tumoral T cell proliferation and massive increase in numbers of effector and effector-like ‘exhausted’ cells, enabling complete rejection in combination with checkpoint inhibition. To conclude, systemic TREX1 inhibition is a promising approach to boost anti-tumor immunity and to overcome immune evasion mediated by cancer cell-intrinsic cGAS/STING inactivation.

Background: The global burden of inflammatory bowel diseases (IBDs), including ulcerative colitis and Crohn’s disease, is constantly rising. As IBDs significantly reduce patients’ quality of life, prevention and efficient treatment of IBDs are of paramount importance. Although the molecular mechanisms underlying IBD pathogenesis are still not completely understood, numerous studies indicate the essential role of oxidative stress in the progression of the diseases. Objective: The aim of this study was to investigate whether prophylactic administration of recombinant banana lectin (rBanLec) could positively affect antioxidative mechanisms in the colon and thus prevent or alleviate the severity of experimental colitis induced in C57BL/6 mice. Methods: The prophylactic potential of rBanLec, a mannose-binding lectin with immunomodulatory properties, was investigated in a model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in C57BL/6 mice. Mice received rBanLec at various doses (0.1, 1 and 10 μg/mL) before the induction of colitis. The severity of the disease was assessed by weight loss and reduction in colon length, and correlated with histopathological findings, cytokine milieu, and oxidative stress markers in the colon. Results: The obtained results revealed that pretreatment with a low dose of rBanLec (0.1 μg/mL) significantly reduced the severity of TNBS-induced colitis, as indicated by reduced weight loss, less severe histopathological damage, and a favorable anti-inflammatory cytokine milieu (increased IL-10 and TGFβ). In addition, rBanLec pretreatment improved the activity of antioxidant enzymes (SOD, CAT, and GST) and reduced markers of oxidative stress such as nitric oxide levels at the peak of the disease. In contrast, higher doses of rBanLec exacerbated inflammatory responses. Conclusions: Our findings indicate that at low doses rBanLec can alleviate the severity of colitis by modulating oxidative stress and promoting anti-inflammatory cytokine responses, positioning rBanLec as a potential candidate for treating IBDs.

Therapeutic innate immune-stimulation within the tumor microenvironment can potentiate endogenous antitumor T-cell immunity. Strategies for controlled activation of cGAS/STING signaling are currently under intense investigation. DNase 3′-repair exonuclease 1 (TREX1) is essential for cellular DNA disposal, which prevents autoimmunity ensuing from cGAS/STING activation by endogenous DNA. TREX1-deficient tumor cells elicit enhanced protective immunity in syngeneic models. In this study, we showed that induced inactivation of the Trex1 gene in host (noncancer) cells yields improved type I IFN- and T-cell–dependent control of established TREX1-competent tumors. Host TREX1 deficiency was well tolerated and triggered selective immune cell infiltration into tumors but not into other tissues. Induced systemic loss of TREX1 in tumor-bearing mice resulted in enhanced intratumoral T-cell proliferation and massive increase in numbers of effector and effector-like “exhausted” cells, enabling complete rejection in combination with checkpoint inhibition. To conclude, systemic TREX1 inhibition is a promising approach to boost antitumor immunity and to overcome immune evasion mediated by cancer cell–intrinsic cGAS/STING inactivation.Significance:Selective inflammation of tumor tissue and efficient tumor immune control by systemically induced loss of TREX1 support the potential efficacy and therapeutic window for treating cancer with TREX1 inhibitors.

Figure S2 shows gating of immune cell populations in tumor tissue as well as quantification of immune cells in tumor, tumor-draining lymph node and spleen.

Figure S6 shows the inflammatory switch of the intra-tumoral myeloid compartment in TREX1 iKO hosts.