Helper T cells down-regulate CD4 expression upon chronic stimulation giving rise to double-negative T cells

Double-negative T (DNT) cells are αβTCR+CD3+CD4−CD8−NK1.1− cells that constitute a small but significant proportion of the αβTCR+ T cells. Their developmental pathway and pathological significance remain unclear. In the present study, we utilized chronic in vitro stimulation of CD4+ T cells to mimic immune hyper-activation of autoimmune lymphoproliferative syndrome and systemic lupus erythematosus, conditions characterized by DNT cells accumulation. After approximately 4–5 rounds of stimulation, the CD3+CD4− population became apparent. These cells did not express CD8, NK1.1, γδTCR, or B220, exhibited a highly proliferative effector phenotype, and were dependent on T cell receptor (TCR) stimulation for survival. Moreover, CD3+CD4− cells expressed MHC class II-restricted αβTCR, indicative of their origin from a CD4+ T cell population. The results presented herein illustrate a novel method of DNT cell generation in vitro and suggest that immune hyper-activation could also be implicated in the genesis of the disease-associated DNT cells in vivo.