Clonal distribution of BLV positive cells in sheep infected by leukemogenic versus attenuated viruses. Autoradiogram of run-off products (see method). The degree of clonal expansion of infected cells over time was measured by semiquantitative quadruplicate IPCR for each animal. (A) Animals #4546 and #4544 were inoculated with the leukemogenic molecular clones pBLVTax106+293 and pBLVA60V, respectively. (B) Animals #4543 and #4539 were inoculated with the attenuated molecular clones pBLVCRE3X and pBLVCRX3, respectively.