CD4 and thymoma: NCE was not able to enhance Cd4 promoter function in the DP thymoma cell lines AKR1G1 or VL3-3M2 (Figure 2C), while the proximal enhancer (PE) functioned significantly better in these cell lines than in RLM11, consistent with previous observations that the proximal enhancer ability decreases with increasing maturation (21, 27).