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

Abstract

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.

Lentivector cryptic splicing mediates increase in CD34+ clones expressing truncated HMGA2 in human X-linked severe combined immunodeficiency

“…In a study with a transgenic mouse model that expressed 3′UTR truncated HMGA2 , a growth advantage was seen for HMGA2 expressing bone-marrow cells after serial transplantation, but no malignancy was observed 39 . In a recent rhesus macaque model 40 transplanted with CD34+ cells transduced with a lentivector to constitutively over-express 3′ UTR truncated HMGA2 under control of the MSCV promoter, these cells demonstrated increased self-renewal potential that was self-limiting and did not result in any hematological malignancies even after three generations of transplantation 40 .…”

Chromatin modifier Hmga2 promotes adult hematopoietic stem cell function and blood regeneration in stress conditions

“…NF-kB TF has been implicated in the activation of Igf2bp2/Imp2 transcription in mouse embryonic fibroblast cells in cooperation with Hmga2 (Cleynen et al, 2007 ), suggesting a link between these genes and transcriptional regulation in HSCs mediated by TNF-α. The overexpression of Hmga2 in WT adult HSCs is not sufficient for the development of malignancy in mice and non-human primates (Kumar et al, 2019 ; Bonner et al, 2021 ; Sun et al, 2022 ) and also presumably in humans after gene therapies (Cavazzana-Calvo et al, 2010 ). Since TNF-α levels are constitutively elevated in aged humans and patients with MDS (Sawanobori et al, 2003 ; Vasto et al, 2007 ), the TNF-α-CK2-Hmga2 axis may increase the expression level of HMGA2 and contribute to the progression of MDS HSCs that harbor driver mutations.…”