Acute myelogenous leukemia blasts as accessory cells during in vitro T lymphocyte activation

The ability of acute myelogenous leukemia (AML) blasts to mediate costimulatory signals during T lymphocyte activation was investigated in an experimental model where monoclonal T cell populations were stimulated with standardized activation signals (anti-CD3, anti-CD2, and anti-CD28 monoclonal antibodies and phytohemagglutinin). Proliferative T cell responses were detected for all AML patients (n = 16) when irradiated leukemia blasts were used as accessory cells during activation. T cell cytokine release was also observed for all patients when nonirradiated AML accessory cells were used, and for most patients a broad cytokine response (interleukin (IL) 2, IL4, IL10, IL13, and interferon-gamma) was detected. However, both T cell proliferation and cytokine release showed a wide variation among AML patients, and T cell responsiveness was in addition dependent both on the nature of the activation signal and on differences between individual T cell clones. The accessory cell function of AML blasts showed no correlation with the release of any single immunomodulatory soluble mediator (IL1beta, IL6, TNF-alpha, soluble IL2 receptors) or the expression of any particular adhesion/costimulatory membrane molecule (CD54, CD58, CD80, and CD86) by the blasts. However, blocking studies with anti-CD58 and anti-CD80/86 monoclonal antibodies demonstrated that both pathways can be involved when AML blasts are used as accessory cells, but the relative importance and the final effects of signaling through these pathways differ between AML populations. Although there is a wide interpatient variation, we conclude that for a majority of patients the native AML blasts can mediate adequate costimulatory signals needed for accessory cell-dependent T cell activation.