Metabolic Screening of Cytotoxic T-cell Effector Function Reveals the Role of CRAC Channels in Regulating Lethal Hit Delivery.

Cytotoxic T lymphocytes (CTL) mediate cytotoxicity toward tumor cells by multistep cell-cell interactions. However, the tumor microenvironment can metabolically perturb local CTL effector function. CTL activity is typically studied in two-dimensional (2D) liquid coculture, which is limited in recapitulating the mechanisms and efficacy of the multistep CTL effector response. We here developed a microscopy-based, automated three-dimensional (3D) interface coculture model suitable for medium-throughput screening to delineate the steps and CTL effector mechanisms affected by microenvironmental perturbation. CTL effector function was compromised by deregulated redox homeostasis, deficient mitochondrial respiration, as well as dysfunctional Ca release-activated Ca (CRAC) channels. Perturbation of CRAC channel function dampened calcium influx into CTLs, delayed CTL degranulation, and lowered the frequency of sublethal hits (i.e., additive cytotoxicity) delivered to the target cell. Thus, CRAC channel activity controls both individual contact efficacy and CTL cooperativity required for serial killing of target cells. The multistep analysis of CTL effector responses in 3D coculture will facilitate the identification of immune-suppressive mechanisms and guide the rational design of targeted intervention strategies to restore CTL effector function.