ENTPD1 and neoplasm: However, CD39 expression was then quantified separately within each CD8+ T cell residency group, finding that CD39 was expressed by the majority of DP tumor-resident CD8+ T cells (DN mean = 9.352%, SP mean = 10.78%, DP mean = 50.62%), with the CD39+ proportion being significantly higher in DP compared to DN (p = 0.0305, Figure 1C).