Combining Cryo-Thermal Therapy with Anti-IL-6 Treatment Promoted the Maturation of MDSCs to Induce Long-Term Survival in a Mouse Model of Breast Cancer

Immunosuppression plays a significant role in tumor recurrence and metastasis, ultimately causing poor survival outcomes. Overcoming immunosuppression and stimulating durable antitumor immunity are essential for tumor treatment. In our previous study, a novel cryo-thermal therapy involving liquid nitrogen freezing and radiofrequency heating could reduce the proportion of Myeloid-derived suppressor cells (MDSCs), but the remaining MDSCs produced IL-6 by the NF-κB pathway, resulting in an impaired therapeutic effect. Therefore, here we combined cryo-thermal therapy with anti-IL-6 treatment to target the MDSC-dominant immunosuppressive environment, thereby optimizing the efficacy of cryo-thermal therapy. We found that combinational treatment significantly increased the long-term survival rate of breast cancer-bearing mice. Mechanistic investigation revealed that combination therapy was capable of reducing the proportion of MDSCs in the spleen and blood while promoting their maturation, which resulted in increased Th1-dominant CD4(+) T-cell differentiation and enhancement of CD8(+) T-mediated tumor killing. In addition, CD4(+) Th1 cells promoted mature MDSCs to produce IL-7 through IFN-γ, indirectly contributing to the maintenance of Th1-dominant antitumor immunity in a positive feedback loop. Our work suggests an attractive immunotherapeutic strategy targeting the MDSC-dominant immunosuppressive environment, which would offer exciting opportunities for highly immunosuppressive and unresectable tumors in the clinic.