During tumor development, immune cells can fight tumor spread by proliferating, migrating and adapting to the surrounding environment. Tumor cells can also disrupt the immune system's response by affecting the function of immune cells. But at present, researchers know little about the internal spatial structure of tumor tissue, and whether these spatial structures affect the anti-tumor function of immune cells is also unclear.
In order to obtain the spatial information of the interaction between tumor cells and immune cells in lung cancer tissues, the researchers used the KP lung cancer mouse model (Kras/Trp53 mutation) to simulate tumorigenesis through the airway, and then let these mice receive immunotherapy. Six to nine weeks after onset, tumor tissues were sectioned, followed by H&E staining, mRNA in situ hybridization, and cycle immunofluorescence (CyCIF) analysis. Among them, H&E images can provide position data of tumor nodules and normal tissue anatomy (including trachea and blood vessels). In the CyCIF analysis, the researchers segmented cells in tumor tissue into individual cells and quantified the staining intensity of individual cells, using the distance of individual cells relative to tumor nodules, tumor margins, and blood vessels, forming a cell network.
In order to enable immune cells to attack tumors more effectively, researchers injected two kinds of antigens into tumor cells, namely chicken ovalbumin SIINFEKL (SIIN) and synthetic peptide SIYRYYGL (SIY), and the tumor model after the injection of antigens was named LucOS, LucOS contains various types of lymphocytes (such as neutrophils, T cells and B cells).
Examining 2.6 million cells in normal lung tissue and LucOS, the researchers found that lymphocytes were predominantly clustered at the junction of normal and tumor tissue. These lymphocytes are mainly T cells and B cells. By analyzing their spatial structure, the researchers found a lymphatic network connected by direct cell-cell contact, in which T cells and B cells accounted for more than 50%, and the percentage of T cells and B cells was related to the size of the lymphatic network, the smaller lymphatic network contains more T cells, and the larger lymphatic network contains more B cells. After analyzing the size and composition of the lymphatic network, the researchers found that the core members of the lymphatic network are T cells, which expand their ranks by recruiting B cells. In addition, some CD103+ dendritic cells existed around the lymphatic network, which provided support for the formation of the lymphatic network. The reason why T cells can target tumors is inseparable from the chemokine receptor on its surface, CXCR3. CXCR3 can recognize and bind to chemokines such as CXCL9, CXCL10 and CXCL11 to enhance the immune response.
Researchers wondered what role the lymphatic network plays in fighting tumors. The researchers then examined the changes in T cells in tumor tissues of mice vaccinated with anti-tumor vaccines (therapeutic vaccines against SIIN and SIY antigens) and PD-1/CTLA-4 immune checkpoint inhibitors (ICBs). Results Three kinds of CD8+ T cells with different morphologies were observed, namely primitive CD8+ T cells expressing TCF1+PD-1+, CD8+ T cells with strong cytotoxicity and CD8+ T cells in fatigue state. Previous studies have shown that TCF1+PD-1+ naive CD8+ T cells can enhance the therapeutic effect of ICB in mice and humans. In this paper, the researchers also observed that after ICB treatment, more CD8+ T cells were generated in the lymphatic network and the antitumor effect was enhanced. The researchers believe that during ICB treatment, the lymphatic network retains the original characteristics of CD8+ T cells and helps TCF1+PD-1+ original CD8+ T cells differentiate into more lethal CD8+ T cells.
The researchers tested whether these phenomena were also present in human lung cancer tissue. Results The lymphatic network rich in TCF1+PD-1+ primitive CD8+ T cells was also found in early lung adenocarcinoma, and the lymphatic network can also provide a favorable spatial environment for CD8+ T cells to attack tumors. This study reveals the spatial arrangement of immune cells in tumors, in which T cells and B cells form a lymphatic network, which provides favorable conditions for T cells to attack tumors and enhances the immune response.