Transplantation of antisense oligonucleotide (odn) purged autografts in chronic myeloid leukaemia (cml)

In CML, some patients may become Ph negative following intensive therapy, and stem cells harvested at this time may be used for autografting. However, many patients do not become completely Ph negative. ODN directed against BCR-ABL will specifically decrease BCRABL mRNA, provided cells are first permeabilised with Streptolysin-O (SL-O). We used 18-mer chimaeric methylphosphonate: phosphodiester linked (4-9-4) ODN complementary to 9 bases either side of the BCR-ABL junction to purge harvests ex vivo in 3 CML patients who remained completely Ph +ve after 2 courses of intensive therapy. After CD34 selection and SL-O permeabilisation, harvests were purged with 20 Molar ODN. After purging, all individual CFU-GM colonies grown from the 2 b3a2 breakpoint cases remained positive for BCR-ABL mRNA. In contrast, all 18 colonies grown from the b2a2 breakpoint case were BCR-ABL mRNA negative. Patients were conditioned with Busulphan 16mg/kg. Initial post-transplant course was uneventful, though the time to 0.5 x lO'/Litre neutrophils was slow at 25-35 days. Both chronic phase patients remain well and off treatment without haematological evidence of CML at +183 and +69 days. The b2a2 accelerated phase patient died of myeloid blast transformation at day +91. Whilst SL-O facilitated ODN-purged autografting appears feasible, longer follow-up is required to establish its clinical benefit in CML.