The role of interleukin-3 and stem cell factor in classical Hodgkin disease

The microenvironment in classical Hodgkin lymphoma: an actively shaped and essential tumor component

Classical Hodgkin lymphoma (cHL) is characterized by a minority of tumor cells derived from germinal center B-cells and a vast majority of non-malignant reactive cells. The tumor cells show a loss of B-cell phenotype including lack of the B-cell receptor, which makes the tumor cells vulnerable to apoptosis. To overcome this threat, tumor cells and their precursors depend on anti-apoptotic and growth stimulating factors that are obtained via triggering of multiple membrane receptors. In addition, tumor cells shape the environment by producing a wide variety of chemokines and cytokines. These factors alter the composition of the microenvironment and modulate the nature and effectiveness of the infiltrating cells. The attracted cells enhance the pro-survival and growth stimulating signals for the tumor cells. To escape from an effective anti-tumor response tumor cells avoid recognition by T and NK cells, by downregulation of HLA molecules and modulating NK and T-cell receptors. In addition, the tumor cells produce immune suppressive cytokines that inhibit cytotoxic responses. In this review the relevance of the microenvironment in the pathogenesis of cHL will be discussed.

The role of interleukin-3 in classical Hodgkin's disease

Classical Hodgkin's disease (HD) is a peculiar form of lymphoma characterized by a low frequency of tumor cells, the so-called Hodgkin (H) and Reed/Sternberg (RS) cells, embedded in a background of non-neoplastic (reactive) cells believed to be recruited and activated by H-RS cell-derived cytokines/chemokines. How these tumor cells can survive in such a seemingly hostile environment has confused researchers. We have previously identified interleukin (IL)-3 receptor (R) expression as a common feature of classical HD and unveiled the potential role of IL-3 as a growth and anti-apoptotic factor for H-RS cells. More then 90% of malignant cells of classical HD usually express the alpha chain of the IL-3R (IL-3R(alpha)), as evidenced by immunostaining of frozen sections and cell suspensions from neoplastic lymph nodes. Consistently, HD-derived cell lines (L428, KMH2, HDLM2 and L1236) express the alpha and beta chains that form IL-3R, both at the mRNA and protein level, with a molecular size of IL-3R(alpha) identical (70 kDa) to that expressed by human myeloid cells. Exogenous IL-3 promotes the growth of cultured H-RS cells, such an effect being potentiated by IL-9 and stem cell factor (SCF) co-stimulation, and is able to partially rescue tumor cells from apoptosis induced by serum deprivation. Finally, cultured H-RS cells are able to increase the production of IL-3 by pre-activated T cells, suggesting an involvement of IL-3/IL-3R interactions in the cellular growth of HD through paracrine mechanisms. This review will outline the biological activity of IL-3 and summarize the evidence indicating IL-3 as a growth and anti-apoptotic factor for H-RS cells in classical HD.

Interactions between tissue fibroblasts in lymph nodes and Hodgkin/Reed-Sternberg cells

Classic Hodgkin's Disease (cHD) is a lymphoid neoplasia characterized by a few malignant Hodgkin and Reed-Sternberg (H-RS) cells embedded in an abundant background of non-tumor cells. In this context, fibrosis is a common morphologic feature of HD lesions, being found more frequently in cHD subtypes. The clinical and histopathologic features of cHD are thought to be largely due to the effects of a wide variety of cytokines and chemokines primarily produced by H-RS cells, as well as by the surrounding reactive component. In the present review, first we propose three mechanisms putatively explaining fibroblast activation and fibrosis in HD: (1) unbalanced production of the pro-fibrogenic Th2 over Th1 cytokines; (2) production of TGF-beta, b-FGF and IL-13 by H-RS cells; (3) activation of fibroblasts by CD40L-expressing cells of the HD microenvironment. Second, we suggest some molecular pathways involving cytokines produced by HD-derived fibroblasts (SCF, IL-7, IL-6) supposedly responsible for H-RS proliferation and rescue from apoptosis. Finally, we describe the role of specific molecules produced by H-RS cells in the regulation of HD-derived fibroblast production of chemokines, in turn involved in T-lymphocytes and recruitment of eosinophils.

Lack of c-kit (CD117) expression in CD30+ lymphomas and lymphomatoid papulosis

c-Kit receptor (CD117) is expressed by erythroid, megakaryocytic, and myeloid precursors and mature mast cells and has been reported to be expressed in CD30+ lymphomas such as Hodgkin's disease and anaplastic large-cell lymphoma. Imatinib mesylate, a well-established inhibitor of bcr-abl tyrosine kinase, and currently used for the treatment of patients with chronic myeloid leukemia, also inhibits c-kit receptor kinase activity. In view of the possible use of imatinib as experimental therapy for patients with c-kit-positive tumors, we assessed c-kit expression in CD30+ cell lines and lymphomas. The cell lines were assessed using multiple methods (RT-PCR, flow cytometry, and Western blot). c-Kit expression was also immunohistochemically assessed in 168 CD30+ lymphomas including 87 classical Hodgkin's disease, 63 anaplastic large-cell lymphoma, and 15 cutaneous anaplastic large-cell lymphoma. We also studied 18 cases of lymphomatoid papulosis, a CD30+ lesion closely related to cutaneous anaplastic large-cell lymphoma. Neither c-kit mRNA nor protein was detected in any of the cell lines assessed. Furthermore, treatment with imatinib did not inhibit proliferation of cell lines in vitro. Using immunohistochemistry, only one of 183 (0.5%) lesions was positive for c-kit, the positive case being an ALK-negative anaplastic large-cell lymphoma. Our data demonstrate that expression of c-kit receptor is exceedingly rare among CD30+ lymphomas and lymphomatoid papulosis, suggesting that c-kit receptor is unlikely to be an appropriate target for therapeutic options such as imatinib in patients with these tumors.