IL-6Secreted By Tumor Associated Macrophages Promotes DLBCL Chemoresistance Via Expansion Of The CSCs Population

DLBCL (Diffuse Large B cell lymphoma) is one of the most common NHL Non-Hodgkin’s lymphomas (NHL) accounting for30-40%of lymphoma. Chemotherapy is the standard of care DLBCL, of which CHOP is the classic therapeuticregimen. Recent report indicate that patients, after therapy with CHOP, have1.2years’ progression free survival, a45%survival rate at five years and only27.6%survival rate at ten. Thus, although front line treatment can have immediate impact, relapse remains a critical issue in this disease.Tumor-associated macrophages (TAM) are a major component of leukocytic infiltrate of tumors and serve as a paradigm for cancer-related inflammation. It was reported that an increased infiltration of TAMs was strongly associated with decreased survival among patients with classic Hodgkin’s lymphoma, providing a new biomarker for risk stratification. Mechanistically, TAMs improve tumor progression by influencing several different biological programs within tumors. For example, TAMs secrete VEGF, PDGF, TGF-β which can impact tumor cells directly or can influence angiogenesis, while PDGF and EGF secreted by TAMs directly increase tumor and stromal cell proliferation and migration. In addition, matrix metalloproteinases and cathepsins are highly expressed in TAMs, impacting extracellular matrix remodeling as well as enhancing tumor growth and metastasis. However, to date, TAMs have not been strongly linked tumorchemoresistance.Increasing evidence suggests that CSCs promote tumor relapse due to their intrinsic resistance to chemo-and radio-therapies. CSCs were initially identified by their expression of various cell surface antigens, and subsequently via hallmark functional assays including sphere formation dye efflux, or aldehydedehydrogenase (ALDH) activity assays.Here, we report that Tumor-associated macrophages (TAMs) promote the progression of a number of tumors, as well aschemoresistance in DLBCL. TAMs promote a CSC-like phenotype in DLBCL cells characterized by increased ALDH1A1, Sox-2, Oct-4, Nanog and KLF-4gene expression. Importantly, DLBCL co-culture with monocyte lines enhanced bothchemoresistance and CSC-like phenotypes.To examine whether tumor-associated macrophage might be induced by the tumor cells themselves to contribute to drug resistance. We compared the mRNA secretomes of U937cells cultured in the presence or absence of DLBCL. IL-6was noted as one of the highest changed genes in TAMs. IL-6has been implicated in both metastasis and stem cell regulation, and thus served as one of the principle candidates from cross-talk between tumor and mococyte cells. Blocking IL-6function via either method was sufficient to inhibit tumor resistance. The experiments indicated that IL-6is both necessary and sufficient to confer the resistance phenotype.Next, to evaluate IL-6levels in DLBCL, we collected serum from136patients before or after chemotherapy. When patient serum was measured for IL-6, the base line serum IL-6correlated to the IPI score and gender. In addition, patients with high serum IL-6levels were found to have a significantly shorter event-free and five-year survivalrates relative to those with low serum IL-6levels. No significant difference in IL-6levels was associated with treatment, but there was a trend towards increased serum IL-6post-therapy (p=0.08). The result suggests that chemoresistance may be promoted as an undesired effect of chemotherapy itself.In in vivo studies, we used immunohistochemistry to examine TAMs infiltration levels by staining CD163in139samples. All samples detected had TAMs infiltration (7%-50.5%).The result turned out that there was a positive correlation between TAMs infiltration and disease progression. TAMs infiltration correlated with International Prognostic Index (IPI) score.All in all, Tumor-associated macrophages (TAMs) promote the progression of a number of tumors, as well as chemoresistance in DLBCL. Patients who exhibited high levels of serum IL-6were associated with poor overall prognosis. Supporting this notion, tumor infiltration by TAMs directly correlated with disease severity.