Targeted beta-globin gene conversion in human hematopoietic CD34(+ )and Lin(-)CD38(-)cells

Chimeric oligonucleotides have been used successfully to correct point and frameshift mutations in several cell types, as well as in animal and plant models. However, their application to primitive human blood cells has been limited. In this investigation, chimeric oligonucleotides designed to direct a site-specific nucleotide exchange in the human beta-globin gene (an A to T substitution within codon 6) were introduced into normal human CD34(+) and Lin(-)CD38(-) cells via microinjection. This A to T nucleotide exchange introduces the single site mutation responsible for sickle cell anemia. In 23% of experimental samples, gene conversion was detected in the progeny of microinjected CD34(+) and Lin(-)CD38(-) cells that were cultured for at least 4 weeks. In addition, gene conversion was detected in the erythroid progeny of Lin(-)CD38(-) cells at the mRNA level. Conversion rates as high as 10-15% in 11% (five of 44) of experimental samples were confirmed by allele-specific PCR and sequence analysis of genomic DNA from the progeny of microinjected Lin(-)CD38(-) cells. Given that as few as 10% normal hematopoietic cells are sufficient to keep patients free of sickle cell disease, the level of conversion we have achieved in some samples may well be of therapeutic benefit in patients with sickle cell disease.