Differential effects of low-dose fludarabine or 5-fluorouracil on the tumor growth and myeloid derived immunosuppression status of tumor-bearing mice

Tumor cell derived osteopontin and prostaglandin E2 synergistically promote the expansion of myeloid derived suppressor cells during the tumor immune escape phase

The immune escape stage in cancer immunoediting is a pivotal feature, transitioning immune-controlled tumor dormancy to progression, and augmenting invasion and metastasis. Tumors employ diverse mechanisms for immune escape, with generating immunosuppressive cells from skewed hematopoiesis being a crucial mechanism. This led us to suggest that tumor cells with immune escape properties produce factors that induce dysregulations in hematopoiesis. In support of this suggestion, this study found that mice bearing advanced-stage tumors exhibited dysregulated hematopoiesis characterized by the development of splenomegaly, anemia, extramedullary hematopoiesis, production of immunosuppressive mediators, and expanded medullary myelopoiesis. Further ex vivo studies exhibited that conditioned medium derived from EL4lu2 cells could mediate the expansion of myeloid derived suppressor cells (MDSCs) in bone marrow cell cultures. The protein array profiling results revealed the presence of elevated levels of osteopontin (OPN), prostaglandin E2 (PGE2) and interleukin 17 (IL-17) in the culture medium derived from EL4luc2 cells. Accordingly, substantial levels of these factors were also detected in the sera of mice bearing EL4luc2 tumors. Among these factors, only PGE2 alone could increase the number of MDSCs in the BM cell cultures. This effect of PGE2 was significantly potentiated by the presence of OPN but not IL-17. Finally, in vitro treatment of EL4luc2 cells with pioglitazone, a modulator of OPN and cyclooxygenase 2 (COX-2) resulted in a significant reduction in cell proliferation in EL4luc2 cells. Our findings highlight the significant role played by tumor cell-derived OPN and PGE2 in fostering the expansion of medullary MDSCs and in promoting tumor cell proliferation. Furthermore, these intertwined cancer processes could be key targets for pioglitazone intervention.

Myeloid-derived suppressor cells (MDSCs): what do we currently know about the effect they have against anti-PD-1/PD-L1 therapies?

Recent advances in cancer treatment such as PD-1/PD-L1 checkpoint inhibitors have prompted multiple research studies to determine all of the factors that influence response or failure to these new treatments. One of those identified factors is myeloid-derived suppressor cells (MDSCs). These cells were identified and described for the first time in 2007 in laboratory mice and cancer patients. Previous studies showed that a greater number of MDSCs was directly related to a greater tumour volume. There are two clearly identified subpopulations: Mononuclear-type myeloid-derived suppressor cells (M-MDSCs) and polymorphonuclear (PMN-MDSCs). These cell population subtypes play a very important role, depending on the type of cancer, since they have the particularity of expressing PD-L1, which interacts with PD-1, inhibiting the expansion of cytotoxic T lymphocytes, promoting resistance to these treatments.

5-FU mediated depletion of myeloid suppressor cells enhances T-cell infiltration and anti-tumor response in immunotherapy-resistant lung tumor

Tumor microenvironment (TME) is a heterogeneous system consisting of both cellular and acellular components. The growth and progression of tumors rely greatly on the nature of TME, marking it as an important target in cancer immunotherapy. Lewis Lung Carcinoma (LLC) is an established murine lung cancer model representing immunologically 'cold' tumors characterized by very few infiltrated cytotoxic T-cells, high levels of Myeloid-Derived Suppressor Cells (MDSCs) and Tumor-Associated Macrophages (TAMs). Here, we report various strategies we applied to reverse the non-immunogenic character of this cold tumor by imparting: a) immunogenic cell death using Hypericin nanoparticle-based photodynamic therapy (PDT), b) repolarising TAM using a TLR7/8 agonist, resiquimod, c) immune checkpoint inhibition using anti-PD-L1 and d) depleting MDSCs using low-dose 5-fluorouracil (5-FU) chemotherapy. Interestingly, the nano-PDT, resiquimod or anti-PD-L1 treatment had no major impact on tumor growth, whereas low-dose 5-FU-mediated depletion of MDSCs showed significant anti-tumor effect, primarily caused by the increased infiltration of CD8⁺ cytotoxic T-cells (∼96%). Though we have tested combining PDT with resiquimod or 5-FU for any synergistic effect, low-dose 5-FU alone showed better response than combinations. In effect, we show that depletion of MDSCs using low-dose 5-FU was one of the best methods to augment infiltration of CD8⁺ cytotoxic T-cells into a cold tumor, which is resistant to conventional therapies including immune checkpoint inhibitors.

Decoding the Myeloid-Derived Suppressor Cells in Lymphoid Malignancies

Myeloid-derived suppressor cells (MDSCs) are immature myeloid precursors which emerged as a potent regulator of the immune system, exerting suppressive properties in diverse disease settings. In regards to cancer, MDSCs have an established role in solid tumors; however, their contribution to immune regulation during hematologic malignancies and particularly in lymphomas remains ill-defined. Herein focused on lymphoma, we discuss the literature on MDSC cells in all histologic types, and we also refer to lessons learned by animal models of lymphoma. Furthermore, we elaborate on future directions and unmet needs and challenges in the MDSC field related to lymphoma malignancies which may shed light on the complex nature of the immune system in malignancies.

Doxil chemotherapy plus liposomal P5 immunotherapy decreased myeloid-derived suppressor cells in murine model of breast cancer

Myeloid-derived suppressor cells (MDSCs) play a pivotal role in cancer. To overcome the problem of the MDSCs in the tumor microenvironment in this study, a combination of immunotherapy and chemotherapy was used. For this purpose, a liposomal formulation of P5 peptide and PEGylated liposomal doxorubicin (Doxil®) was utilized to treat mice bearing HER2⁺ tumor model. The results revealed that Doxil® administration before immunotherapy had not only reduced the population and functions of the MDSCs in the spleen (P < 0.001) and the tumor microenvironment (P < 0.05) but had also supported further immunotherapy including enhanced CD4⁺ (P < 0.01) and CD8⁺ lymphocyte (P < 0.001) population and IFN-γ production (P < 0.001). This effect was also more pronounced with a liposomal P5 and Doxil® compared with free peptide and doxorubicin. In conclusion, the results demonstrated that Doxil® plus liposomal P5 could have a decreasing effect on MDSCs and tumor growth, and it could be beneficial in breast cancer treatment.

Protective effects of IFN-γ on the kidney of type- 2 diabetic KKAy mice

BACKGROUND

Development of novel therapeutic strategies that specifically target diabetic kidney disease (DKD) is urgently needed.

METHODS

Male KKAy mice were divided randomly into three equal groups - KK, KI, and KF; Male C57BL/6 mice were the control group. All KKAy mice were fed a high-fat diet. From the 16th week, the KI group was given IFN-γ, and the KF group was assigned to be treated with fludarabine. C57BL/6 mice were always fed a normal mouse diet. Every 4 weeks, body weight, random blood sugar, urine albumin and urea of all mice were measured. At the 20th week, all mice were killed, renal tissue was obtained to observe the pathological manifestations and extract proteins, and transforming growth factor- beta1 (TGF-β1), collagen IV and Janus kinase 2/signal transducers and activators of transcription 1 (JAK2/STAT1) pathway proteins were measured by western blot.

RESULTS

The present study showed that all KKAy mice appeared obese and hyperglycaemic from 12 weeks old and exhibited an increased urine albumin-to-creatinine ratio (ACR) from 16 weeks old. At the 20th week, compared to the KK group, the KI group showed lower ACR, more overexpression of P-STAT1 and less expression of TGF-β1 and collagen IV proteins in renal tissue. The KI group mice showed less accumulation of glomerular mesangial matrix than those in the KK group.

CONCLUSIONS

Our results indicate that IFN-γ might activate STAT1 to suppress the overexpression of TGF-β1 and collagen IV proteins and attenuate the excessive accumulation of mesangial matrix under DKD conditions in KKAy mice.