Memory CD8+ T cells induce precocious effector differentiation of naive T cells through quorum sensing-like behavior

Some unicellular organisms exhibit collective decision-making through intercellular communication once a quorum of members sense an environmental stress. Whether T cells at different states of differentiation may also synchronize their behavior on a population basis through direct interactions remains unclear. We report that memory CD8+ T cells (TMem) directly interact with naive T cells (TN) during priming, affecting the phenotypic, functional, transcriptional and metabolic differentiation of TN-derived progeny. This previously unrecognized, contact and concentration-dependent interaction between naive (TN) and memory CD8+ T cells (TMem) directly enhanced TN effector differentiation through non-apoptotic Fas signaling resulting in downstream Akt pathway activation. TN primed with TMem exhibited significantly impaired persistence and antitumor activity compared with TN primed alone. Disruption of FasL-Fas signaling in TN cells limited differentiation and enhanced anti-tumor immunity while provision of exogenous FasL in the absence of TMem impaired anti-tumor immunity by augmenting TN differentiation. These findings reveal that the full therapeutic potential of TN-derived cells for adoptive immunotherapy requires physical separation from TMem prior to priming or antagonism of Fas-signaling. FACS-sorted in vitro differentiated TMem samples were without stimulation (0 hours) (n=3), and FACS-sorted in vitro differentiated TMem samples were stimulated using CD3-specific and CD28-specific antibodies and IL-2 for 18 (n=3) and 96 (n=3) hours. FACS-sorted naive Pmel-1 CD8+ T cell samples were without stimulation (0 hours) (n=3), and FACS-sorted TN-derived Pmel-1 CD8+ T cell samples were stimulated using CD3-specific and CD28-specific antibodies and IL-2 for 18 (n=3) and 96 (n=3) hours. FACS-sorted TN-derived Pmel-1 CD8+ T cell samples were stimulated in the presence of TMem using CD3-specific and CD28-specific antibodies and IL-2 for 18 (n=3) and 96 (n=3) hours. FACS-sorted in vitro differentiated TMem samples were stimulated in the presence of TN using CD3-specific and CD28-specific antibodies and IL-2 for 18 (n=3) and 96 (n=3) hours. All samples were done in triplicate as biological repeats.