Growing evidence supports the importance of gut microbiota in the control of tumor growth and response to therapy. Here, we select prebiotics that can enrich bacterial taxa that promote anti-tumor ...immunity. Addition of the prebiotics inulin or mucin to the diet of C57BL/6 mice induces anti-tumor immune responses and inhibition of BRAF mutant melanoma growth in a subcutaneously implanted syngeneic mouse model. Mucin fails to inhibit tumor growth in germ-free mice, indicating that the gut microbiota is required for the activation of the anti-tumor immune response. Inulin and mucin drive distinct changes in the microbiota, as inulin, but not mucin, limits tumor growth in syngeneic mouse models of colon cancer and NRAS mutant melanoma and enhances the efficacy of a MEK inhibitor against melanoma while delaying the emergence of drug resistance. We highlight the importance of gut microbiota in anti-tumor immunity and the potential therapeutic role for prebiotics in this process.
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•Mucin and inulin, prebiotics, inhibit melanoma growth in syngeneic mouse models•Changes in gut microbiota taxa by these prebiotics induce anti-tumor immunity•Inulin attenuates melanoma resistance to MEKi in a mouse melanoma model•Inulin and mucin elicit distinct microbiota changes and an additive effect in select models
Li et al. show that the gut microbiota effect on anti-tumor immunity is affected by inulin or mucin, prebiotics that inhibit melanoma and colon cancer growth in syngeneic models and attenuate melanoma resistance to MEKi. These studies highlight a potential therapeutic role for prebiotics in shaping the microbiota composition to promote anti-tumor immunity.
Immune checkpoint inhibition targeting T cells has shown tremendous promise in the treatment of many cancer types and are now standard therapies for patients. While standard therapies have focused on ...PD-1 and CTLA-4 blockade, additional immune checkpoints have shown promise in promoting anti-tumor immunity. PSGL-1, primarily known for its role in cellular migration, has also been shown to function as a negative regulator of CD4
T cells in numerous disease settings including cancer. PSGL-1 is highly expressed on T cells and can engage numerous ligands that impact signaling pathways, which may modulate CD4
T cell differentiation and function. PSGL-1 engagement in the tumor microenvironment may promote CD4
T cell exhaustion pathways that favor tumor growth. Here we highlight that blocking the PSGL-1 pathway on CD4
T cells may represent a new cancer therapy approach to eradicate tumors.
Chronic infections and cancers evade the host immune system through mechanisms that induce T cell exhaustion. The heterogeneity within the exhausted CD8
T cell pool has revealed the importance of ...stem-like progenitor (Tpex) and terminal (Tex) exhausted T cells, although the mechanisms underlying their development are not fully known. Here we report High Mobility Group Box 2 (HMGB2) protein expression is upregulated and sustained in exhausted CD8
T cells, and HMGB2 expression is critical for their differentiation. Through epigenetic and transcriptional programming, we identify HMGB2 as a cell-intrinsic regulator of the differentiation and maintenance of Tpex cells during chronic viral infection and in tumors. Despite Hmgb2
CD8
T cells expressing TCF-1 and TOX, these master regulators were unable to sustain Tpex differentiation and long-term survival during persistent antigen. Furthermore, HMGB2 also had a cell-intrinsic function in the differentiation and function of memory CD8
T cells after acute viral infection. Our findings show that HMGB2 is a key regulator of CD8
T cells and may be an important molecular target for future T cell-based immunotherapies.
Effective T cell differentiation during acute virus infections leads to the generation of effector T cells that mediate viral clearance, as well as memory T cells that confer protection against ...subsequent reinfection. While inhibitory immune checkpoints have been shown to promote T cell dysfunction during chronic virus infections and in tumors, their roles in fine tuning the differentiation and responses of effector and memory T cells are only just beginning to be appreciated. We previously identified PSGL-1 as a fundamental regulator of T cell exhaustion that sustains expression of several inhibitory receptors, including PD-1. We now show that PSGL-1 can restrict the magnitude of effector T cell responses and memory T cell development to acute LCMV virus infection by limiting survival, sustaining PD-1 expression, and reducing effector responses. After infection, PSGL-1-deficient effector T cells accumulated to a greater extent than wild type T cells, and preferentially generated memory precursor cells that displayed enhanced accumulation and functional capacity in response to TCR stimulation as persisting memory cells. Although, PSGL-1-deficient memory cells did not exhibit inherent greater sensitivity to cell death, they failed to respond to a homologous virus challenge after adoptive transfer into naïve hosts indicating an impaired capacity to generate memory effector T cell responses in the context of viral infection. These studies underscore the function of PSGL-1 as a key negative regulator of effector and memory T cell differentiation and suggest that PSGL-1 may limit excessive stimulation of memory T cells during acute viral infection.
Hyperthermia uses exogenous heat induction as a cancer therapy. This work addresses the acute and long-term effects of hyperthermia in the highly metastatic melanoma cell line B16-F10.
Melanoma cells ...were submitted to one heat treatment, 45°C for 30 min, and thereafter were kept at 37°C for an additional period of 14 days. Cultures maintained at 37°C were used as control. Cultures were assessed for the heat shock reaction.
Immediately after the heat shock, cells began a process of fast degradation, and, in the first 24 h, cultures showed decreased viability, alterations in cell morphology and F-actin cytoskeleton organization, significant reduction in the number of adherent cells, most of them in a process of late apoptosis, and an altered gene expression profile. A follow-up of two weeks after heat exposure showed that viability and number of adherent cells remained very low, with a high percentage of early apoptotic cells. Still, heat-treated cultures maintained a low but relatively constant population of cells in S and G(2)/M phases for a long period after heat exposure, evidencing the presence of metabolically active cells.
The melanoma cell line B16-F10 is susceptible to one hyperthermia treatment at 45°C, with significant induced acute and long-term effects. However, a low but apparently stable percentage of metabolically active cells survived long after heat exposure.
Chronic viral infections where the antigen persists long-term, induces an exhaustion phenotype in responding T cells. It is now evident that immune checkpoints on T cells including PD-1, CTLA-4, and ...PSGL-1 (
) are linked with the differentiation of exhausted cells. Chronic T cell receptor signaling induces transcriptional signatures that result in the development of various exhausted T cell subsets, including the stem-like T cell precursor exhausted (Tpex) cells, which can be reinvigorated by immune checkpoint inhibitors (ICIs). While PSGL-1 has been shown to inhibit T cell responses in various disease models, the cell-intrinsic function of PSGL-1 in the differentiation, maintenance, and reinvigoration of exhausted T cells is unknown. We found
T cells had increased expansion in melanoma tumors and in early stages of chronic viral infection. Despite their increase, both WT and
T cells eventually became phenotypically and functionally exhausted. Even though virus-specific
CD4
and CD8
T cells were increased at the peak of T cell expansion, they decreased to lower levels than WT T cells at later stages of chronic infection. We found that
CD8
Tpex (SLAMF6
TIM3
, PD-1
TIM3
, TOX
, TCF-1
) cell frequencies and numbers were decreased compared to WT T cells. Importantly, even though virus-specific
CD4
and CD8
T cells were lower, they were reinvigorated more effectively than WT T cells after anti-PD-L1 treatment. We found increased
expression in Hepatitis C-specific CD8
T cells in patients with chronic infection, whereas these levels were decreased in patients that resolved the infection. Together, our findings showed multiple PSGL-1 regulatory functions in exhausted T cells. We found that PSGL-1 is a cell-intrinsic inhibitor that limits T cells in tumors and in persistently infected hosts. Additionally, while PSGL-1 is linked with T cell exhaustion, its expression was required for their long-term maintenance and optimal differentiation into Tpex cells. Finally, PSGL-1 restrained the reinvigoration potential of exhausted CD4
and CD8
T cells during ICI therapy. Our findings highlight that targeting PSGL-1 may have therapeutic potential alone or in combination with other ICIs to reinvigorate exhausted T cells in patients with chronic infections or cancer.
Inflammatory bowel disease (IBD) is prevalent, but the mechanisms underlying disease development remain elusive. We identify a role for the E3 ubiquitin ligase RNF5 in IBD. Intestinal epithelial ...cells (IECs) express a high level of RNF5, while the colon of Rnf5−/− mice exhibits activated dendritic cells and intrinsic inflammation. Rnf5−/− mice exhibit severe acute colitis following dextran sodium sulfate (DSS) treatment. S100A8 is identified as an RNF5 substrate, resulting in S100A8 ubiquitination and proteasomal-dependent degradation that is attenuated upon inflammatory stimuli. Loss of RNF5 from IECs leads to enhanced S100A8 secretion, which induces mucosal CD4+ T cells, resulting in Th1 pro-inflammatory responses. Administration of S100A8-neutralizing antibodies to DSS-treated Rnf5−/− mice attenuates acute colitis development and increases survival. An inverse correlation between RNF5 and S100A8 protein expression in IECs of IBD patients coincides with disease severity. Collectively, RNF5-mediated regulation of S100A8 stability in IECs is required for the maintenance of intestinal homeostasis.
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•Severe intestinal inflammation resembling acute colitis in DSS-treated Rnf5−/− mice•RNF5 regulates S100A8 stability and pro-inflammatory responses•Neutralizing S100A8 antibodies attenuate acute colitis in DSS-treated Rnf5−/− mice•Inverse expression of RNF5 and S100A8 in IBD patients coincides with disease severity
Fujita et al. show that RNF5 regulation of S100A8 stability in intestinal epithelial cells defines the degree of pro-inflammatory response, culminating in severe intestinal inflammation following DSS treatment to Rnf5−/− mice. Neutralizing S100A8 antibodies attenuates acute colitis phenotypes, and inverse RNF5/S100A8 expression coincides with clinical severity in IBD patients.
Understanding the mechanisms underlying anti-tumor immunity is pivotal for improving immune-based cancer therapies. Here, we report that growth of BRAF-mutant melanoma cells is inhibited, up to ...complete rejection, in Siah2
mice. Growth-inhibited tumors exhibit increased numbers of intra-tumoral activated T cells and decreased expression of Ccl17, Ccl22, and Foxp3. Marked reduction in Treg proliferation and tumor infiltration coincide with G1 arrest in tumor infiltrated Siah2
Tregs in vivo or following T cell stimulation in culture, attributed to elevated expression of the cyclin-dependent kinase inhibitor p27, a Siah2 substrate. Growth of anti-PD-1 therapy resistant melanoma is effectively inhibited in Siah2
mice subjected to PD-1 blockade, indicating synergy between PD-1 blockade and Siah2 loss. Low SIAH2 and FOXP3 expression is identified in immune responsive human melanoma tumors. Overall, Siah2 regulation of Treg recruitment and cell cycle progression effectively controls melanoma development and Siah2 loss in the host sensitizes melanoma to anti-PD-1 therapy.
PSGL-1 (P-selectin glycoprotein-1) is a T cell-intrinsic checkpoint regulator of exhaustion with an unknown mechanism of action. Here, we show that PSGL-1 acts upstream of PD-1 and requires ...co-ligation with the T cell receptor (TCR) to attenuate activation of mouse and human CD8+ T cells and drive terminal T cell exhaustion. PSGL-1 directly restrains TCR signaling via Zap70 and maintains expression of the Zap70 inhibitor Sts-1. PSGL-1 deficiency empowers CD8+ T cells to respond to low-affinity TCR ligands and inhibit growth of PD-1-blockade-resistant melanoma by enabling tumor-infiltrating T cells to sustain an elevated metabolic gene signature supportive of increased glycolysis and glucose uptake to promote effector function. This outcome is coupled to an increased abundance of CD8+ T cell stem cell-like progenitors that maintain effector functions. Additionally, pharmacologic blockade of PSGL-1 curtails T cell exhaustion, indicating that PSGL-1 represents an immunotherapeutic target for PD-1-blockade-resistant tumors.
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•PSGL-1 restrains TCR signaling and glycolytic potential of CD8+ T cells•PSGL-1 deficiency limits CD8+ T cell exhaustion and supports precursor populations•Co-ligation of PSGL-1 and the TCR promotes T cell exhaustion in CD8+ T cells•PSGL-1 therapeutic blockade promotes T cell responses and melanoma tumor control
In this study, Hope et al. reveal intrinsic mechanisms through which the cell surface molecule PSGL-1 (P-selectin glycoprotein-1) modulates T cell responses and drives differentiation to terminal exhaustion in chronic virus infection and melanoma. Their study highlights the targetability of PSGL-1 as an emerging immune checkpoint blockade strategy.
Abstract
Effective T cell responses depend on adhesion mechanisms that guide T cells to sites of infection and inflammation. P-selectin glycoprotein ligand-1 (PSGL-1) has been shown to impact T cell ...migration; however, its role in the differentiation of responding T cells has not been investigated. Since PSGL-1 is highly expressed on naïve, effector, and memory T cells with varying degrees of glycosylation that impact ligand binding, we hypothesized that PSGL-1 may regulate T cell fates. Using mice deficient in PSGL-1 and we found that PSGL-1 limited the magnitude of the ensuing T cell response. PSGL-1-deficient mice had an increased accumulation of anti-viral CD4+ and CD8+ T cells after acute LCMV infection. Virus-specific PSGL-1-deficient T cells had enhanced survival and were not hyper proliferative. Furthermore, PSGL-1-deficient T cells had superior effector function, downregulation of PD-1 and other inhibitory receptors and changes in their transcriptional signature. After viral clearance, more CD4+ and CD8+ PSGL-1-deficient T cells survived to form memory cells. Interestingly, memory T cells from PSGL-1-deficient mice sustained PD-1 downregulation implying that PSGL-1 may regulate inhibitory receptors in memory T cells. Our findings highlight a previously unrecognized role for PSGL-1 in negatively regulating T cell differentiation during acute viral infection.
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