Elevated cfDNA after exercise is derived primarily from mature polymorphonuclear neutrophils, with a minor contribution of cardiomyocytes

Strenuous physical exercise causes a massive elevation in the concentration of circulating cell-free DNA (cfDNA), which correlates with effort intensity and duration. The cellular sources and physiological drivers of this phenomenon are unknown. Using methylation patterns of cfDNA and associated histones, we show that cfDNA in exercise originates mostly in extramedullary polymorphonuclear neutrophils. Strikingly, cardiomyocyte cfDNA concentration increases after a marathon, consistent with elevated troponin levels and indicating low-level, delayed cardiac cell death. Physical impact, low oxygen levels, and elevated core body temperature contribute to neutrophil cfDNA release, while muscle contraction, increased heart rate, β-adrenergic signaling, or steroid treatment fail to cause elevation of cfDNA. Physical training reduces neutrophil cfDNA release after a standard exercise, revealing an inverse relationship between exercise-induced cfDNA release and training level. We speculate that the release of cfDNA from neutrophils in exercise relates to the activation of neutrophils in the context of exercise-induced muscle damage.

From gatekeepers to providers: regulation of immune functions by cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are major protumorigenic components of the tumor microenvironment in solid cancers. CAFs are heterogeneous, consisting of multiple subsets that display diverse functions. Recently, CAFs have emerged as major promoters of immune evasion. CAFs favor T cell exclusion and exhaustion, promote recruitment of myeloid-derived suppressor cells, and induce protumoral phenotypic shifts in macrophages and neutrophils. With the growing appreciation of CAF heterogeneity came the understanding that different CAF subpopulations may be driving distinct immune-regulatory effects, interacting with different cell types, and perhaps even driving opposing effects on malignancy. In this review we discuss the current understanding of CAF-immune interactions, their effect on tumor progression and therapeutic response, and the possibility of exploiting CAF-immune interactions as potential targets for cancer therapy.

The Bilateral Interplay between Cancer Immunotherapies and Neutrophils’ Phenotypes and Sub-Populations

Immunotherapy has become a leading modality for the treatment of cancer, but despite its increasing success, a substantial number of patients do not benefit from it. Cancer-related neutrophils have become, in recent years, a subject of growing interest. Distinct sub-populations of neutrophils have been identified at advanced stages of cancer. In this study, we aimed to evaluate the role of neutrophils in mediating the efficacy of immune checkpoint inhibitors (ICI) treatments (α-PD-1/PD-L1), by assessing lung tumor models in mice. We found that G-CSF overexpression by the tumor significantly potentiates the efficacy of ICI, whereas neutrophils’ depletion abrogated their responses. Adoptive transfer of circulating normal-density neutrophils (NDN) resulted in significantly reduced tumor growth, whereas low-density neutrophils (LDN) had no effect. We next investigated the effect of ICI on neutrophils’ functions. Following α-PD-L1 treatment, NDN displayed increased ROS production and increased cytotoxicity toward tumor cells but decreased degranulation. Together, our results suggest that neutrophils are important mediators of the ICI treatments and that mainly NDN are modulated following α-PD-L1 treatment. This research provides a better understanding of the function of neutrophils following immunotherapies and their impact on the efficacy of immunotherapy, supporting better understanding and future improvement of currently available treatments.

Tumor-Derived Factors Differentially Affect the Recruitment and Plasticity of Neutrophils

Neutrophils play a key role in cancer biology. In contrast to circulating normal-density neutrophils (NDN), the amount of low-density neutrophils (LDN) significantly increases with tumor progression. The correlation between these neutrophil subpopulations and intratumoral neutrophils (TANs) is still under debate. Using 4T1 (breast) and AB12 (mesothelioma) tumor models, we aimed to elucidate the source of TANs and to assess the mechanisms driving neutrophils' plasticity in cancer. Both NDN and LDN were found to migrate in response to CXCL1 and CXCL2 exposure, and co-infiltrate the tumor site ex vivo and in vivo, although LDN migration into the tumor was higher than NDN. Tumor-derived factors and chemokines, particularly CXCL1, were found to drive neutrophil phenotypical plasticity, inducing NDN to transition towards a low-density state (LD-NDN). LD-NDN appeared to differ from NDN by displaying a phenotypical profile similar to LDN in terms of nuclear morphology, surface receptor markers, decreased phagocytic abilities, and increased ROS production. Interestingly, all three subpopulations displayed comparable cytotoxic abilities towards tumor cells. Our data suggest that TANs originate from both LDN and NDN, and that a portion of LDN derives from NDN undergoing phenotypical changes. NDN plasticity resulted in a change in surface marker expression and functional activity, gaining characteristics of LDN.

Fusobacterium nucleatum CbpF Mediates Inhibition of T Cell Function Through CEACAM1 Activation

F. nucleatum is an anaerobic bacterium that is associated with several tumor entities and promotes tumorigenesis. Recent evidence suggests that F. nucleatum binds the inhibitory receptor carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1) via the trimeric autotransporter adhesin CbpF. However, whether this binding is functional or whether other fusobacterial trimeric autotransporter adhesins are involved in CEACAM1 activation is unknown. In this study, using F. nucleatum mutants lacking the type 5c trimeric autotransporter adhesins fvcA (CbpF), fvcB, fvcC, and fvcD, we show that F. nucleatum CbpF binds and activates CEACAM1 and also binds carcinoembryonic antigen (CEA), a tumor-associated protein. We further find that CEACAM antibodies directed against the CEACAM N-terminal domain block the CbpF-CEACAM1 interaction. In functional assays, we demonstrate CbpF-dependent inhibition of CD4⁺ T cell response. Thus, we characterize an immune evasion mechanism in which F. nucleatum uses its surface protein CbpF to inhibit T cell function by activating CEACAM1.

Tumor-Associated Neutrophils Drive B-cell Recruitment and Their Differentiation to Plasma Cells

A major mechanism through which neutrophils have been suggested to modulate tumor progression involves the interaction and subsequent modulation of other infiltrating immune cells. B cells have been found to infiltrate various cancer types and play a role in tumor immunity, offering new immunotherapy opportunities. Nevertheless, the specific impact of tumor-associated neutrophils (TAN) on B cells has largely been overlooked. In the current study, we aimed to characterize the role of TANs in the recruitment and modulation of B cells in the tumor microenvironment (TME). We showed that TANs actively participate in the recruitment of B cells to the TME and identified TNFα as the major cytokine mediating B-cell chemotaxis by TANs. The recruitment of CD45⁺B220⁺CD138^- splenic B cells by TANs in vitro resulted in B-cell phenotypic modulation, with 68.6% ± 2.1% of the total migrated B cells displaying a CD45^-B220⁺CD138⁺ phenotype, which is typical for plasma cells. This phenotype mirrored the large proportion (54.0% ± 6.1%) of CD45^-B220⁺CD138⁺ intratumoral B cells (i.e., plasma cells) in Lewis lung carcinoma tumors. We next confirmed that the differentiation of CD45⁺B220⁺CD138^- B cells to functionally active CD45^-B220⁺CD138⁺ plasma cells required contact with TANs, was independent of T cells, and resulted in IgG production. We further identified membranal B-cell activating factor (BAFF) on TANs as a potential contact mechanism mediating B-cell differentiation, as blocking BAFF-receptor (BAFF-R) significantly reduced IgG production by 20%. Our study, therefore, demonstrates that TANs drive the recruitment and modulation of B cells into plasma cells in the TME, hence opening new avenues in the targeting of the immune system in cancer.

Blocking Migration of Polymorphonuclear Myeloid-Derived Suppressor Cells Inhibits Mouse Melanoma Progression

Simple Summary

Myeloid-derived suppressor cells (MDSC) represent a heterogeneous myeloid cell population that is expanded in tumor bearing hosts and substantially contributes to immunosuppression, representing thereby a valuable therapeutic target. Our study analyzes polymorphonuclear (PMN) and monocytic (M) MDSC subsets regarding their immunosuppressive capacity and recruitment mechanisms in murine melanoma. The immunosuppressive activity of both subsets was comparable. We identified the C-X-C Motif Chemokine Receptor (CXCR) 2/chemokine C-X-C motif ligand (CXCL) 1 axis as an important mediator of PMN-MDSC recruitment. Inhibition of CXCR2 resulted in a decreased infiltration of tumors with PMN-MDSC and increased survival of melanoma bearing mice. Furthermore, adjuvant treatment of mice with resected tumors reduced the infiltration of pre-metastatic sites with PMN-MDSC and the occurrence of distant metastasis. The decrease in PMN-MDSC infiltration was accompanied by an increase in natural killer (NK) cell frequency, suggesting an important role of PMN-MDSC in suppressing the NK cell-mediated anti-tumor response.

Abstract

Background: Despite recent improvement in the treatment of malignant melanoma by immune-checkpoint inhibitors, the disease can progress due to an immunosuppressive tumor microenvironment (TME) mainly represented by myeloid-derived suppressor cells (MDSC). However, the relative contribution of the polymorphonuclear (PMN) and monocytic (M) MDSC subsets to melanoma progression is not clear. Here, we compared both subsets regarding their immunosuppressive capacity and recruitment mechanisms. Furthermore, we inhibited PMN-MDSC migration in vivo to determine its effect on tumor progression. Methods: Using the RET transgenic melanoma mouse model, we investigated the immunosuppressive function of MDSC subsets and chemokine receptor expression on these cells. The effect of CXCR2 inhibition on PMN-MDSC migration and tumor progression was studied in RET transgenic mice and in C57BL/6 mice after surgical resection of primary melanomas. Results: Immunosuppressive capacity of intratumoral M- and PMN-MDSC was comparable in melanoma bearing mice. Anti-CXCR2 therapy prolonged survival of these mice and decreased the occurrence of distant metastasis. Furthermore, this therapy reduced the infiltration of melanoma lesions and pre-metastatic sites with PMN-MDSC that was associated with the accumulation of natural killer (NK) cells. Conclusions: We provide evidence for the tumor⁻promoting properties of PMN-MDSC as well as for the anti-tumor effects upon their targeting in melanoma bearing mice.