Increased Lactate in AML Blasts Upregulates TOX Expression, Leading to Exhaustion of CD8 Cytolytic T Cells

Recently, the role of lactate as merely an end product of cancer cell metabolism has been reassessed. Lactate has been implicated in more biological processes than previously understood and drives tumor progression. Here, we demonstrated that the bone marrow lactate concentrations in acute myeloid leukemia (AML) patients were substantially higher than those in their healthy control counterparts. Moreover, AML blasts from bone marrow expressed significantly higher lactate dehydrogenase-A (LDHA) levels. Further studies revealed that LDHA expression was regulated through the HIF1α pathway. Elevated lactate levels were indicative of alterations in CD8 T cell cytolytic phenotype and activity. An in vitro study showed that the lactate treatment group had significantly higher percentages of CD8 TEM and CD8 TEMRA cells as well as higher PD-1 expression in these cells than the control group. Lactate induced the loss of the effector function of CD8 T cells by altering lytic granule exocytosis. T cell dysfunction is characterized by an increase in terminally differentiated phenotypes, sustained expression of PD-1, and accelerated decline of cytolytic competence. Moreover, the TOX gene was found to be correlated with lactate production and implicated in CD8 T cell dysfunction. AML patients in complete remission after chemotherapy had markedly lower lactate concentrations, reduced CD8 TEM and CD8 TEMRA cells and PD-1 expression, and increased perforin and granzyme B. However, no difference was found in the relapsed patients. The study presented here has established lactate as a predictive biomarker for patient response to antitumor therapies and demonstrated that targeting this gene in AML patients could be a meaningful precision therapeutic strategy.