3' UTR-truncated HMGA2 overexpression induces non-malignant in vivo expansion of hematopoietic stem cells in non-human primates.

Vector-mediated mutagenesis remains a major safety concern for many gene therapy clinical protocols. Indeed, lentiviral-based gene therapy treatments of hematologic disease can result in oligoclonal blood reconstitution in the transduced cell graft. Specifically, clonal expansion of hematopoietic stem cells (HSCs) highly expressing HMGA2, a chromatin architectural factor found in many human cancers, is reported in patients undergoing gene therapy for hematologic diseases, raising concerns about the safety of these integrations. Here, we show for the first time in vivo multilineage and multiclonal expansion of non-human primate HSCs expressing a 3' UTR-truncated version of HMGA2 without evidence of any hematologic malignancy >7 years post-transplantation, which is significantly longer than most non-human gene therapy pre-clinical studies. This expansion is accompanied by an increase in HSC survival, cell cycle activation of downstream progenitors, and changes in gene expression led by the upregulation of IGF2BP2, a mRNA binding regulator of survival and proliferation. Thus, we conclude that prolonged ectopic expression of HMGA2 in hematopoietic progenitors is not sufficient to drive hematologic malignancy and is not an acute safety concern in lentiviral-based gene therapy clinical protocols.

Cytoplasmic binding partners of the platelet integrin alphaIIb beta3.

Platelets function physiologically in mediating hemostasis, but are also associated with many pathological conditions, such as thrombosis, which can lead to myocardial infarction and/or stroke. Therefore, the study of platelet regulation and signaling has been of great interest and is necessary for generating effective anti-platelet therapeutics. One platelet signaling molecule of particular interest is the integrin alphaIIb beta3, which binds Fg and mediates platelet cross-linking. The integrin itself as well as cytoplasmic proteins that interact with alphaIIb beta3 have become potential targets for anti-platelet therapies. One such protein that has been shown to directly regulate alphaIIb beta3 function is calcium- and integrin-binding protein 1 (CIB1). CIB1 has been implicated in alphaIIb beta3 activation and outside-in signaling through the integrin. By increasing our understanding of CIB1 and other proteins that like it, associate with integrin alphaIIb beta3, and the signaling events that result from those interactions, we may bring ourselves closer to more effective therapies. In the present work, we explore known cytoplasmic binding partners of the integrin alphaIIb beta3 and their effect on alphaIIb beta3, focusing on CIB1.

Quantitative shearing linear amplification polymerase chain reaction: an improved method for quantifying lentiviral vector insertion sites in transplanted hematopoietic cell systems.

In gene therapy trials targeting blood disorders, it is important to detect dominance of transduced hematopoietic stem cell (HSC) clones arising from vector insertion site (VIS) effects. Current methods for VIS analysis often do not have defined levels of quantitative accuracy and therefore can fail to detect early clonal dominance. We have developed a rapid and inexpensive method for measuring clone size based on random shearing of genomic DNA, minimal exponential PCR amplification, and shear site counts as a quantitative endpoint. This quantitative shearing linear amplification PCR (qsLAM PCR) assay utilizes an internal control sample containing 19 lentiviral insertion sites per cell that is mixed with polyclonal samples derived from transduced human CD34+ cells. Samples were analyzed from transplanted pigtail macaques and from a participant in our X-linked severe combined immunodeficiency (XSCID) lentiviral vector trial and yielded controlled and quantitative results in all cases. One case of early clonal dominance was detected in a monkey transplanted with limiting numbers of transduced HSCs, while the clinical samples from the XSCID trial participant showed highly diverse clonal representation. These studies demonstrate that qsLAM PCR is a facile and quantitative assay for measuring clonal repertoires in subjects enrolled in human gene therapy trials using lentiviral-transduced HSCs.