Extracellular pH affects the proliferation of cultured human T cells and their expression of the interleukin-2 receptor

Ex vivo expansion of T cells is an important aspect of many cellular immuno therapy protocols, and the effects of the culture environment on the cells must be understood to produce large numbers of functional cells. Extracellu lar pH is a Fundamental parameter that has many different effects on cultur ed cells. In this study, peripheral blood mononuclear cells were stimulated with phytohemagglutinin and cultured at pH values of 7.0, 7.2, or 7.4. The effects of pH on the cells were studied during the 2 to 3 weeks of prolife ration resulting from phytohemagglutinin stimulation, in order to examine t he culture kinetics over realistic lime scales for ex vivo expansion. The p roliferation capacity of the T cells increased more than three-fold for the pH 7.0 and 7.2 cultures compared with the pH 7.4 cultures. The culture pH also affected the kinetics of the interleukin-2 receptor down-regulation pr ocess. The faster receptor down-regulation in both the pH 7.2 and 7.4 cultu res resulted in a more than twofold greater fraction of interleukin-2 recep tor(+) cells in the pH 7.0 cultures. Although the fraction of apoptotic cel ls (using the Annexin V flow-cytometric method) remained less than 10%, we observed 27% more apoptosis in the pH 7.4 cultures than in the 7.2 cultures and 49% more apoptosis in the pH 7.4 cultures than in the 7.0 cultures. Th ese effects on interleukin-2 receptor expression and cellular apoptosis may partially explain the observed effects of pH on T-cell proliferation.