Purpose: Tumor cells are known to secrete cytokines that modify their microenvironment in order to favor their survival and continuous proliferation. In this work, we evaluated if TGF-β secreted in vitro by cervical cancer cells could interfere with the proliferation and survival of lymphocytes.
Methods: Lymphocytes were obtained from peripheral blood of healthy human volunteers, and isolated by density gradient centrifugation and cultured in 96-well plates. Lymphocyte proliferation was induced with phytohemaglutinin and co-cultured with conditioned media (CM) from cervical cancer cell lines, and the inhibition of proliferation was evaluated after 72 h by the incorporated radioactivity and a CFSE-labeling assay. TGF-β quantification on these CM was evaluated by ELISA. Non-apoptotic cellular death was evaluated through disruption of cell membrane integrity by measuring the liberation of lactate dehydrogenase. The apoptosis process was evaluated by annexin-V and active caspase-3. The presence of CD4+ or CD8+ lymphocytes was evaluated by flow cytometry using specific antibodies.
Results: It was found that the conditioned media from these cells significantly inhibited the proliferation of lymphocytes and induced them to go into apoptosis. Antibodies against TGF-β almost completely blocked this activity, suggesting that this cytokine is responsible for the inhibitory activity. When the induced apoptosis on subpopulations of lymphocytes was evaluated, it was detected that the CD4+ cells were specifically targeted.
Conclusions: Cervical cancer cells secrete TGF-β that inhibits lymphocyte proliferation and induces apoptosis in CD4+, but not in CD8+ lymphocytes.