The present invention relates to a method, in particular an in vitro method, for identifying specific immune cells, in particular naïve CD8+ T-cells, comprising analyzing the methylation status of at least one CpG position in the mammalian gene region for endosialin (CD248), wherein a demethylation or lack of methylation of said gene region is indicative for a naïve CD8+ T-cell, when compared to a non-naïve CD8+ T-cell or any other (blood) cell type. The analyses according to the invention can identify naïve CD8+ T-cells on an epigenetic level and distinguish them from all other cells in complex samples, such as, for example, other blood or immune cells. The present invention furthermore provides an improved method for quantifying naïve CD8+ T-cells, in particular in com naïve CD8+ T-cells complex samples. The method can be performed with or without a step of purifying and/or enriching cells, preferably in whole blood and/or non-trypsinized tissue.