Lack of EBNA-2 expression in cultured leukemic lymphoblasts. PCR amplification of EBNA-2a (lanes 1 through 6) and EBNA-2b (lanes 7 through 12) in 3 clones initiated from single leukemic cells (cases no. 1, 3, and 4) after 5 months of culture (lanes 2 through 4 and 8 through 10), in the EBNA-2a– (AD; lanes 6 and 11) and EBNA-2b– (C2BL16; lanes 5 and 12) positive cell lines, and in placenta DNA (negative control; lanes 1 and 7). The 116-bp (EBNA-2a) and 119-bp (EBNA-2b) PCR products could only be detected in the EBNA-2–positive lines. External lanes contain a molecular weight marker.