Out-of-Sequence Signal 3 Paralyzes Primary CD4+ T Cell Dependent Immunity

Primary T cell activation involves the integration of three distinct signals delivered in sequence: 1) antigen recognition, 2) costimulation, and 3) cytokine-mediated differentiation and expansion. Strong immunostimulatory events such as immunotherapy or infection induce profound cytokine release causing bystander T cell activation, thereby increasing the potential for autoreactivity and need for control. We show that during strong stimulation, a profound suppression of primary CD4+ T cell-mediated immune responses ensued and was observed across preclinical models and patients undergoing high-dose interleukin-2 (IL-2) therapy. This suppression targeted naïve CD4+ but not CD8+ T cells and was mediated through transient suppressor of cytokine signaling-3 (SOCS3) inhibition of the STAT5b transcription factor signaling pathway. These events resulted in complete paralysis of primary CD4+ T cell activation affecting memory generation, induction of autoimmunity, as well as impaired viral clearance. These data highlight the critical regulation of naïve CD4+ T cells during inflammatory conditions. The molecular mechanisms of primary T cell activation and regulation in response to strong immunostimulation were investigated in mice treated with immunotherapy. For this, BALB/c mice (3 mice per group) were either treated with immunotherapy (anti-CD40 and IL-2) or with a control (rat IgG and PBS). Subsequently, peripheral blood mononuclear cells were FACS-sorted based on markers specific for CD4+ or CD8+ T cells and for naive (CD62L+/CD44low) or memory (CD44high) cell marker expression. There are a total of 8 samples, which represent pooled cells from the corresponding T cell subset from all mice in each treatment group. Total cellular RNA was isolated and then microarray gene expression profiling performed with Affymetrix GeneChip Mouse Gene 2.0 Sense Target (ST) Arrays.