CTLA4 and cancer: Despite the lack of changes in the proliferation rate of MDA-MB-231 cancer cells in the presence of anti-CD3-stimulated PBMC alone following 24-h co-culture, we found that inhibition of CTLA-4 on the surface of mononuclear cells allowed for significant reduction of proliferating cancer cells, even when compared to MDA-MB-231 affected by lymphocytes alone.