6. Reliable biomarkers for CD4+CD25+ regulatory T cells? CD25 GITR CTLA-4 CD4+CD25+ Regulatory T cell NO marker after T cell activation. Only in the naïve T cell repertoire. Need better marker. Galectin-1 CD103 Ly6 4-1BB Unidentified X,Y,Z ?? Neuropilin-1 OX-40 Piccirillo et al. Trends in Immunology July 2004