Expression of human CD18 in murine granulocytes and improved efficiency for infection of deficient human lymphoblasts

Visualization of integrin molecules by fluorescence imaging and techniques

Integrin molecules are transmembrane αβ heterodimers involved in cell adhesion, trafficking, and signaling. Upon activation, integrins undergo dynamic conformational changes that regulate their affinity to ligands. The physiological functions and activation mechanisms of integrins have been heavily discussed in previous studies and reviews, but the fluorescence imaging techniques -which are powerful tools for biological studies- have not. Here we review the fluorescence labeling methods, imaging techniques, as well as Förster resonance energy transfer assays used to study integrin expression, localization, activation, and functions.

Lentiviral Vector-Mediated Correction of a Mouse Model of Leukocyte Adhesion Deficiency Type I

Leukocyte adhesion deficiency type I (LAD-I) is a primary immunodeficiency caused by mutations in the ITGB2 gene and is characterized by recurrent and life-threatening bacterial infections. These mutations lead to defective or absent expression of β₂ integrins on the leukocyte surface, compromising adhesion and extravasation at sites of infection. Three different lentiviral vectors (LVs) conferring ubiquitous or preferential expression of CD18 in myeloid cells were constructed and tested in human and mouse LAD-I cells. All three hCD18-LVs restored CD18 and CD11a membrane expression in LAD-I patient-derived lymphoblastoid cells. Corrected cells recovered the ability to aggregate and bind to sICAM-1 after stimulation. All vectors induced stable hCD18 expression in hematopoietic cells from mice with a hypomorphic Itgb2 mutation (CD18^HYP), both in vitro and in vivo after transplantation of corrected cells into primary and secondary CD18^HYP recipients. hCD18⁺ hematopoietic cells from transplanted CD18^HYP mice also showed restoration of mCD11a surface co-expression. The analysis of in vivo neutrophil migration in CD18^HYP mice subjected to two different inflammation models demonstrated that the LV-mediated gene therapy completely restored neutrophil extravasation in response to inflammatory stimuli. Finally, these vectors were able to correct the phenotype of human myeloid cells derived from CD34⁺ progenitors defective in ITGB2 expression. These results support for the first time the use of hCD18-LVs for the treatment of LAD-I patients in clinical trials.

The potential for therapy of immune disorders with gene therapy

Several hurdles remain before gene therapy will be a part of mainstream medical therapy; however, the preliminary report of success in HSC correction in patients with XSCID provides hope that gene therapy will become a reality.

Transduction of human hematopoietic cells and cell lines using a retroviral vector containing a modified murine CD4 reporter gene

To investigate conditions for improving transduction efficiencies of human hematopoietic stem or progenitor cells using retroviral vectors, we constructed a retroviral vector containing a modified murine CD4 cDNA reporter gene with a truncated cytoplasmic domain to prevent signaling. The advantages of using this truncated murine CD4 reporter gene include: (i) CD4 is well characterized with well-known cell signaling pathways, (ii) truncation of the cytoplasmic domain of CD4 has been demonstrated to abrogate signaling, (iii) the truncated murine CD4 is easily detectable on the cell surface with no cross-reaction to human CD4, (iv) a variety of monoclonal antibodies directed against the murine CD4 molecule are available commercially, and (v) expression of a truncated CD4 molecule in a transgenic mouse in vivo does not interfere with hematopoiesis. We cloned the truncated murine CD4 reporter gene into the retroviral vector LXSN, packaged this vector using PG13 retrovirus packaging cells, and transduced hematopoietic cell lines representing erythroid, myeloid, megakaryocyte, and lymphoid lineages using vector-containing medium harvested from the murine CD4 producer line. After seven daily exposures to vector-containing medium, all cell lines expressed murine CD4 on the cell surface, and 5-7% of human CD34+ cells expressed murine CD4 on the cell surface after 3 days of exposure to murine CD4 vector-containing medium. Colony-forming cell assays assessing progenitor cells demonstrated the presence of transduced cells in the CD34+ population. These results demonstrate the utility of using a modified murine CD4 gene in a retroviral vector to allow optimization of in vitro transduction conditions of human hematopoietic cells and to facilitate identification of the lineages that have been transduced using different growth factors, prior to clinical trials using retroviral vectors.