TCR stimulation without co-stimulatory signals induces expression of "tolerogenic" genes in memory CD4 T cells but does not compromise cell proliferation

Memory T cells resist co-stimulatory blockade and present a unique therapeutic challenge in transplantation and autoimmune diseases. Herein, we determined whether memory T cells express less "tolerogenic" genes than naïve T cells to reinforce a proliferative response under the deprivation of co-stimulatory signals. The expression of ~40 tolerogenic genes in memory and naïve CD4⁺ T cells was thus assessed during an in vitro TCR stimulation without co-stimulation. Briefly, upon TCR stimulation with an anti-CD3 mAb alone, memory CD4⁺ T cells exhibited more proliferation than naïve CD4⁺ T cells. To our surprise, at 24h upon anti-CD3 mAb stimulation, memory CD4⁺ T cells expressed more than a 5-fold higher level of the transcription factor Egr2 and a 20-fold higher level of the transmembrane E3 ubiquitin ligase GRAIL than those in naïve T cells. Hence, the high-level expression of tolerogenic genes, Egr2 and GRAIL, in memory CD4⁺ T cells does not prevent cell proliferation. Importantly, anti-CD3 mAb-stimulated memory CD4⁺ T cells expressed high protein/gene levels of phosphorylated STAT5, Nedd4, Bcl-2, and Bcl-XL. Therefore, co-stimulation-independent proliferation of memory CD4⁺ T cells may be due to elevated expression of molecules that support cell proliferation and survival, but not lack of tolerogenic molecules.