Expression of Human CD18 in Murine Granulocytes and Improved Efficiency for Infection of Deficient Human Lymphoblasts

Abstract

The CD18 gene encodes the β₂-subunit of leukocyte integrins, and mutations in this gene cause extreme host susceptibility to bacterial and fungal infection. Because expression of CD18 is restricted to bone marrow-derived cells, this disorder is considered an excellent candidate for somatic gene therapy utilizing ex vivo infection of bone marrow stem cells. We have constructed a retroviral vector expressing CD18 with the Moloney murine leukemia virus (Mo-MLV) long terminal repeat (LTR) as the promoter, and high-titer ecotropic and amphotropic producer cell lines were isolated using the GP+E-86 and GP+envAM12 safe packaging cell lines. Infection of CD18-deficient lymphoblasts resulted both in expression of immunodetectable CD18 at 35–40% of normal levels on 55–60% of cells and in functional restoration of CD18-dependent aggregation. All of 16 mice transplanted with syngeneic bone marrow infected with the CD18 retrovirus expressed human CD18 on 17–36% of granulocytes at 2 weeks after transplantation, and expression was appropriately up-regulated in response to stimulation with zymosan-activated serum. This recombinant retrovirus should prove useful for further studies of somatic gene therapy for CD18 deficiency. CD18 deficiency is a rare but lethal human genetic disorder, which is an attractive candidate for somatic gene therapy. A high-titer retrovirus enabled an efficient correction of the adhesion defect in human deficient lymphoblasts, and the virus was used to infect murine bone marrow cells. Wilson et al. have further substantiated the potential for treatment of CD18 deficiency by somatic gene therapy.