Lentiviral Vector-Mediated Gene Transfer Restores CD18 Expression in Long-Term Repopulating Hematopoietic Stem and Progenitor Cells Isolated from a Patient with Leukocyte Adhesion Deficiency Type 1

Leukocyte adhesion deficiency type 1 (LAD-1) is an inherited primary immunodeficiency caused by loss-of-function mutation within the ITGB2 gene, which encodes the beta2 integrin subunit CD18. Individuals with LAD-1 experience significant loss of neutrophil-mediated innate cellular immune function, resulting in delayed wound healing, severe periodontitis, and life-long bouts of bacterial infection. LAD-1 is a prime candidate for lentiviral vector-mediated genetic intervention as i) it is an intractable, potentially life-threatening disease with limited treatment options, ii) it is amenable to current ex vivo gene therapy procedures, and iii) partial phenotypic correction would present a high likelihood of significant clinical benefit. Allogeneic stem cell transplant can be curative, but suffers from matched donor availability and the potential for graft-versus-host disease. Autologous ex vivo gene therapy may provide a viable alternative to allogeneic transplant in LAD-1 patients. We have evaluated the ability of a CD18-expressing lentiviral vector (LV-hCD18) to mediate ex vivo transduction of LAD-1 patient-derived CD34+ hematopoietic stem and progenitor cells (HSPCs) and subsequent long-term LAD-1 HSPC engraftment in immunodeficient NOD-scid IL2Rg null (NSG) mice. An open reading frame encoding human CD18 was placed under the transcriptional control of the MND promoter (a modified retroviral promoter associated with high levels of stable transgene expression) and packaged in VSV-G-pseudotyped lentiviral particles. After 1 day of pre-stimulation, LAD-1 HSPCs were transduced with LV-hCD18 (MOI = 10) in the presence or absence of transduction-enhancing adjuvants, poloxamer 407 (P407) and prostaglandin E2 (PGE 2), for 24 hours. Sublethally irradiated NSG mice (7 mice/group) were transplanted with either mock-transduced LAD-1 HSPCs, LAD-1 HSPCs transduced in the absence of adjuvants, or LAD-1 HSPCs transduced in the presence of P407/PGE 2. Bone marrow was harvested at ~5.5 months post-transplant for flow cytometric analyses of engraftment efficiency, transgene marking, and human blood cell lineage reconstitution. Bone marrow from mice that received mock-transduced LAD-1 HSPCs showed an average total of 6.45 ± 2.54% (mean ± SEM) CD45+ human cells. Mice that received LAD-1 HSPCs transduced in the absence of adjuvants showed 7.99 ± 1.82% CD45+ human cells, whereas mice transplanted with LAD-1 HSPCs transduced in the presence of adjuvants showed 7.33 ± 1.90% CD45+ cells. A Kruskal-Wallis statistical test indicated no significant difference in the level of human cell engraftment among the recipient groups (P=0.72). Consistent with the LAD-1 phenotype, human myeloid cells from mice that received mock-transduced LAD-1 HSPCs displayed only background levels of CD18 marking (0.13 ± 0.06% CD45+CD13+CD18+ cells). Mice that received LAD-1 HSPCs transduced in the absence of adjuvants showed 4.05 ± 0.40% CD18+ human myeloid cells (range 2.19% to 5.50%), whereas mice that received LAD-1 HSPCs transduced in the presence of P407/PGE 2 showed 9.56 ± 0.96% CD18+ human myeloid cells (range 4.63% to 13.10%), thus representing a >2-fold increase in in vivo, vector-mediated transgene marking levels when adjuvant was used. Moreover, vector-mediated expression of CD18 rescued endogenous expression of a major CD18 heterodimerization partner in neutrophils, CD11b. In mock-transduced LAD-1 HSPC recipients, CD13+ human myeloid cells were devoid of cell surface CD11b expression (0.01 ± 0.01% CD45+CD13+CD11b+ cells). In contrast, CD13+ human myeloid cells in mice that received LAD-1 HSPCs transduced in the absence of adjuvant showed detectable levels of CD11b expression (2.62 ± 0.19% of CD18-expressing human myeloid cells), and CD11b levels were increased to 6.90 ± 0.98% in LAD-1 HSPCs transduced in the presence of P407/PGE 2. Multilineage engraftment, as evidenced by the presence of CD3+ T cells and CD20+ B cells, was noted within all groups; however, human myeloid cells represented the most prominent human blood cell compartment observed. Colony-forming-unit assays of transduced cells and non-transduced control cells pre-transplant showed similar clonogenic output and colony diversity. In sum, successful transduction, engraftment, transgene marking, CD11b rescue, and multilineage reconstitution supports further development of lentiviral vector-mediated gene therapy for LAD-1. Disclosures No relevant conflicts of interest to declare.