Activated T cells rely on aerobic glycolysis and glutaminolysis in order to proliferate and differentiate into effector cells. Therefore, ntervention in these metabolic pathways inhibits proliferation. The aim of the present study was to evaluate the effects of Krebs' cycle inhibition at the level of malate dehydrogenase-2 (MDH2) in human activated T cells using the MDH2 inhibitor LW6. Activated T cells from healthy volunteers were cultured in the presence or absence of LW6 and cytotoxicity, cell proliferation and the expression levels of hypoxia-inducible factor (HIF)-1α, c-Myc, p53, cleaved caspase-3 and certain enzymes involved in glucose metabolism and glutaminolysis were evaluated. The results revealed that LW6 was not toxic and decreased apoptosis and the levels of the pro-apoptotic tumor suppressor p53. In addition, LW6 inhibited T-cell proliferation and decreased the levels of c-Myc, HIF-1α, glucose transporter-1, hexokinase-II, lactate dehydrogenase-A and phosphorylated pyruvate dehydrogenase. By contrast, LW6 increased the levels of pyruvate dehydrogenase. These alterations may lead to decreased production of pyruvate, which preferentially enters into the Krebs' cycle. Furthermore, LW6 decreased the levels of glutaminase-2, while increasing those of glutaminase-1, which may preserve glutaminolysis, and possibly pyruvate-malate cycling, potentially protecting the cells from energy collapse. In summary, the inhibition of MDH2 in activated T cells abrogates proliferation without adversely affecting cell survival. Adaptations of cellular glucose and glutamine metabolism may prevent energy collapse.