Intravital imaging of splenic classical monocytes modifying the hepatic CX3CR1+ cells motility to exacerbate liver fibrosis via spleen-liver axis.

CX3CR1+ cells play a crucial role in liver fibrosis progression. However, changes in the migratory behavior and spatial distribution of spleen-derived and hepatic CX3CR1+ cells in the fibrotic liver as well as their influence on the liver fibrosis remain unclear. METHODS: The CX3CR1GFP/+ transgenic mice and CX3CR1-KikGR transgenic mice were used to establish the CCl4-induced liver fibrosis model. Splenectomy, adoptive transfusion of splenocytes, in vivo photoconversion of splenic CX3CR1+ cells and intravital imaging were performed to study the spatial distribution, migration and movement behavior, and regulatory function of CX3CR1+ cells in liver fibrosis. RESULTS: Intravital imaging revealed that the CX3CR1GFP cells accumulated into the fibrotic liver and tended to accumulate towards the central vein (CV) in the hepatic lobules. Two subtypes of hepatic CX3CR1+ cells existed in the fibrotic liver. The first subtype was the interacting CX3CR1GFP cells, most of which were observed to distribute in the liver parenchyma and had a higher process velocity; the second subtype was mobile CX3CR1GFP cells, most of which were present in the hepatic vessels with a faster moving speed. Splenectomy ameliorated liver fibrosis and decreased the number of CX3CR1+ cells in the fibrotic liver. Moreover, splenectomy rearranged CX3CR1GFP cells to the boundary of the hepatic lobule, reduced the process velocity of interacting CX3CR1GFP cells and decreased the number and mobility of mobile CX3CR1GFP cells in the fibrotic liver. Transfusion of spleen-derived classical monocytes increased the process velocity and mobility of hepatic endogenous CX3CR1GFP cells and facilitated liver fibrosis progression via the production of proinflammatory and profibrotic cytokines. The photoconverted splenic CX3CR1+ KikRed+ cells were observed to leave the spleen, accumulate into the fibrotic liver and contact with hepatic CX3CR1+ KikGreen+ cells during hepatic fibrosis. CONCLUSION: The splenic CX3CR1+ monocytes with classical phenotype migrated from the spleen to the fibrotic liver, modifying the migratory behavior of hepatic endogenous CX3CR1GFP cells and exacerbating liver fibrosis via the secretion of cytokines. This study reveals that splenic CX3CR1+ classical monocytes are a key driver of liver fibrosis via the spleen-liver axis and may be potential candidate targets for the treatment of chronic liver fibrosis.

Intravital molecular imaging reveals that ROS-caspase-3-GSDME-induced cell punching enhances humoral immunotherapy targeting intracellular tumor antigens.

Tumor antigens (TAs)-induced humoral immune responses or TAs-specific antibodies have great application prospects for tumor therapy. However, more than half of TAs are intracellular antigens (intra-Ags) that are hardly recognized by antibodies. It is worthy to develop immunotherapeutic strategies for targeting intra-Ags. Methods: We used the far-red fluorescent protein tfRFP as an intracellular antigen to immunize mice and generated a liver metastasis model by injecting tfRFP-expressing B16 melanoma cells (tfRFP-B16) via the spleen. Intravital molecular imaging and atomic force microscopy were performed to visualize the formation of tfRFP antigen-antibody complexes (also known as immune complexes) and punched holes in cell membranes. Results: The results showed that the tfRFP-elicited immune responses inhibited the metastasis of tfRFP-expressing melanoma cells in the liver. In the circulating tfRFP-B16 tumor cells, elevated reactive oxygen species (ROS) induced slight caspase-3 activation, a probable key factor in the cleavage of gasdermin E (GSDME) proteins and punching of holes in the tumor cell membrane. Increased tumor cell membrane permeability led to the release of intra-Ag tfRFP and binding with anti-tfRFP antibodies. The formation of tfRFP antigen-antibody complexes on the membranes of tfRFP-B16 cells activated complement components to form membrane attack complexes to further destroy the cell membrane. Neutrophils were rapidly recruited, and F4/80+ macrophages phagocytized the dying tumor cells. Conclusion: The process of circulating tumor cell elimination in the tfRFP-immunized mice was triggered through the ROS-caspase-3-GSDME pathway to form intra-Ag-antibody immune complexes, which were involved in the activation of the complement system, as well as the recruitment of neutrophils and F4/80+ macrophages. An intra-Ag-elicited humoral immune response is a potent strategy for eliminating liver metastasis, which is unaffected by the liver immune tolerogenic status.

Intravital molecular imaging reveals the restrained capacity of CTLs in the killing of tumor cells in the liver.

Cytotoxic T lymphocytes (CTLs) and their gene-engineered cells display great application prospects in tumor immunotherapy. The timing of CTL-induced molecular events in tumor cells is unclear, and we also unknow whether the killing efficiency of CTLs is restrained in the liver, an immunotolerant organ with a high tumor incidence. Methods: We used intravital imaging to dynamically monitor the fluorescence resonance energy transfer (FRET) signals of caspase-3 and calcium sensor in tumor cells after transferring CTLs into tumor-bearing mice. Results: Our data show that several CTLs attacked on one tumor cell, and on average each CTL killed 1.24 ± 0.11 tumor cells per day in the liver, which was much less efficient than that in the spleen (3.18 ± 0.26 tumor cells/CTL/day). The killing efficiency of CTLs is restrained in the liver and can be reversed by blocking immunosuppressive cytokine. Tumor cells exposed to CTLs appeared to have prolonged calcium influx, which occurred dozens of minutes before caspase-3 activity. Conclusion: The quantitative characterization of these molecular and cellular events provides accurate information to evaluate the efficiency of cellular immunotherapy against tumors and understand the impact of an organ's immune status.

Immune modulation of liver sinusoidal endothelial cells by melittin nanoparticles suppresses liver metastasis.

Liver sinusoidal endothelial cells (LSECs) are responsible for the immunologic tolerance of liver which is a common site for visceral metastases, suggesting its potential role as an target for cancer immunotherapy. However, targeted modulation of LSECs is still not achieved thus far. Here, we report LSECs are specifically targeted and modulated by melittin nanoparticles (α-melittin-NPs). Intravital imaging shows that LSECs fluoresce within 20 s after intravenous injection of α-melittin-NPs. α-melittin-NPs trigger the activation of LSECs and lead to dramatic changes of cytokine/chemokine milieu in the liver, which switches the hepatic immunologic environment to the activated state. As a result, α-melittin-NPs resist the formation of metastatic lesions with high efficiency. More strikingly, the survival rate reaches 80% in the spontaneous liver metastatic tumor model. Our research provides support for the use of α-melittin-NPs to break LSEC-mediated immunologic tolerance, which opens an avenue to control liver metastasis through the immunomodulation of LSECs.

Self-Assembled "Off/On" Nanopomegranate for In Vivo Photoacoustic and Fluorescence Imaging: Strategic Arrangement of Kupffer Cells in Mouse Hepatic Lobules.

Kupffer cells (KCs), potent scavenger cells located in hepatic sinusoids, constantly phagocytize and degrade foreign materials to maintain metabolism and clearance. Understanding the strategic KC arrangement which links to their spatial location and function in hepatic lobules, the basic functional unit in the liver, is highly valuable for characterizing liver function. However, selectively labeling KCs and characterizing their function in vivo remains challenging. Herein, a fast self-assembled pomegranate structure-like nanoparticle with "nanopomegranate seeds" of dye aggregates has been developed, which has dual-modality "off/on" capability. This nanopomegranate shows good photostability, a high extinction coefficient, a high KC labeling efficiency (98.8%), and better visualization of KC morphology than commercial FluoSpheres. In vivo photoacoustic (PA) and fluorescence imaging consistently visualize that KCs are strategically distributed along the central vein (CV)-portal triad (PT) axis in each liver lobule: more and larger KCs exist in areas closer to the PTs. The high-resolution PA quantitative data further revealed that the density of KCs was linearly dependent on the r n/ rmax ratio (their relative location along the CV-PT axis) ( R2 = 0.7513), and the KC density at the outermost layer is almost 246-fold that at the innermost layer (each layer is 8 µm). Notably, the phagocytic ability of KCs located in layers with r n/ rmax ratios of 0.167-0.3 varies in a zigzag pattern, as evidenced by their different PA intensities. Additionally, the fluorescence imaging quantitation suggests similar fluorescence activation of nanopomegranate in KCs. Nanopomegranates combined with dual-modality imaging reveal the strategic arrangement of KCs in vivo, greatly extending our understanding of liver physiology.

Molecular-Targeted Immunotherapeutic Strategy for Melanoma via Dual-Targeting Nanoparticles Delivering Small Interfering RNA to Tumor-Associated Macrophages.

Tumor-associated macrophages (TAMs) are a promising therapeutic target for cancer immunotherapy. Targeted delivery of therapeutic drugs to the tumor-promoting M2-like TAMs is challenging. Here, we developed M2-like TAM dual-targeting nanoparticles (M2NPs), whose structure and function were controlled by α-peptide (a scavenger receptor B type 1 (SR-B1) targeting peptide) linked with M2pep (an M2 macrophage binding peptide). By loading anti-colony stimulating factor-1 receptor (anti-CSF-1R) small interfering RNA (siRNA) on the M2NPs, we developed a molecular-targeted immunotherapeutic approach to specifically block the survival signal of M2-like TAMs and deplete them from melanoma tumors. We confirmed the validity of SR-B1 for M2-like TAM targeting and demonstrated the synergistic effect of the two targeting units (α-peptide and M2pep) in the fusion peptide (α-M2pep). After being administered to tumor-bearing mice, M2NPs had higher affinity to M2-like TAMs than to tissue-resident macrophages in liver, spleen, and lung. Compared with control treatment groups, M2NP-based siRNA delivery resulted in a dramatic elimination of M2-like TAMs (52%), decreased tumor size (87%), and prolonged survival. Additionally, this molecular-targeted strategy inhibited immunosuppressive IL-10 and TGF-ß production and increased immunostimulatory cytokines (IL-12 and IFN-γ) expression and CD8+ T cell infiltration (2.9-fold) in the tumor microenvironment. Moreover, the siRNA-carrying M2NPs down-regulated expression of the exhaustion markers (PD-1 and Tim-3) on the infiltrating CD8+ T cells and stimulated their IFN-γ secretion (6.2-fold), indicating the restoration of T cell immune function. Thus, the dual-targeting property of M2NPs combined with RNA interference provides a potential strategy of molecular-targeted cancer immunotherapy for clinical application.