Anti–BCR-ABL AS-ODNs inhibit BCR-ABL mRNA expression. CML DR⁺ cells were incubated in serum-free medium with or without addition of breakpoint-specific and control ODNs. PCR amplification of BCR-ABL mRNA extracted from 25,000 DR⁺cells was performed as described in the text, amplified samples were size separated by gel-electrophoresis, ethidium bromide stained, and photographed. β-Actin controls were run for each sample. In the representative experiment shown here, the b₃a₂breakpoint was present in the cells studied. Cells were incubated either without any ODNs (CONTROL), or with b₃a₂antisense ODNs (B3A2AS), b₃a₂ missense ODNs (B3A2MS), or b₂a₂ antisense ODNs (B2A2 AS).