Immunoregulatory cell therapy with lentiviral-mediated FOXP3 converted CD4+ T cells into Treg cells: towards the proof-of-concept application in IPEX syndrome

Background & Aim FOXP3 is an essential transcription factor for the regulatory T cell (Treg) function and therefore is a key regulator for the tolerance maintenance. Treg cell therapy, either with freshly isolated or expanded in vitro, has been proven to be safe but still challenging because of difficulties in isolating sufficient number of pure Treg cells, stability of the expanded preparations and Treg plasticity in vivo under pro-inflammatory conditions. The key role of FOXP3 and Treg cells in immune function is exemplified by immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX), a monogenic primary immune regulatory disease caused by mutations in FOXP3, that lead to impaired Treg cell function and early onset autoimmune manifestations. Our recent international retrospective study demonstrated suboptimal disease-free survival from current therapeutic options such as immunosuppression and allogeneic hematopoietic stem cell transplantation. Therefore, there is a great unmet medical need in patients with IPEX syndrome. Methods, Results & Conclusion We investigated lentiviral FOXP3 gene transfer (LV-FOXP3) in CD4+ T cells as an innovative approach to generate in large number stable Treg cells that could provide therapeutic benefit to IPEX patients lacking functional Treg. We have shown that LV-FOXP3 can converts IPEX patients-derived CD4+ effector T cells into Treg-like cells (CD4LV-FOXP3 T cells). To better investigate the safety and efficacy of this approach and to make it suitable for large scale GMP generation of CD4LV-FOXP3 T cells, we optimized the original lentiviral vector and we assessed the phenotype and function of CD4LV-FOXP3 T cells both in vitro using transcriptome analysis and in vivo in different humanized mice models. CD4LV-FOXP3 T cells express key molecules in common with freshly isolated Treg cells. CD4LV-FOXP3 T cells can significantly extend the survival of xeno GVHD model mice, both in autologous and allogenic conditions and they can suppress xeno GVHD reaction caused by secondary infusion of responder cells. These data indicated CD4LV-FOXP3 T cells have a sustained suppressive function in the various autologous in vivo mice models. In conclusion, we completed the preclinical requirement for the use of the CD4LV-FOXP3 cell product in IPEX syndrome. The Proof-of-concept trial in a severe monogenic pediatric disease will open to future clinical applications of CD4LV-FOXP3 cell therapy in other autoimmune and immunodysregulatory disorders of different origin.