Successful Combination of Sequential Gene Therapy and Rescue Allo-HSCT in Two Children with X-CGD - Importance of Timing

Abstract

We report on a series of sequential events leading to long-term survival and cure of pediatric X-linked chronic granulomatous disease (X-CGD) patients after gamma-retroviral gene therapy (GT) and rescue HSCT. Due to therapyrefractory life-threatening infections requiring hematopoietic stem cell transplantation (HSCT) but absence of HLAidentical donors, we treated 2 boys with X-CGD by GT. Following GT both children completely resolved invasive Aspergillus nidulans infections. However, one child developed dual insertional activation of ecotropic viral integration site 1 (EVI1) and signal transducer and activator of transcription 3 (STAT3) genes, leading to myelodysplastic syndrome (MDS) with monosomy 7. Despite resistance to mismatched allo-HSCT with standard myeloablative conditioning, secondary intensified rescue allo-HSCT resulted in 100 % donor chimerism and disappearance of MDS. The other child did not develop MDS despite expansion of a clone with a single insertion in the myelodysplasia syndrome 1 (MDS1) gene and was cured by early standard allo-HSCT. The slowly developing dominance of clones harboring integrations in MDS1-EVI1 may guide clinical intervention strategies, i.e. early rescue allo-HSCT, prior to malignant transformation. GT was essential for both children to survive and to clear therapy-refractory infections, and future GT with safer lentiviral self-inactivated (SIN) vectors may offer a therapeutic alternative for X-CGD patients suffering from life-threatening infections and lacking HLA-identical HSC donors.

Update on the safety and efficacy of retroviral gene therapy for immunodeficiency due to adenosine deaminase deficiency

“…43 Unfortunately, in some cases, hematologic malignancies occurred, including 5 of 20 patients affected by X-linked SCID, 44 3 of 13 patients treated for chronic granulomatous disease, [45][46][47] and 7 of 10 patients with Wiskott-Aldrich syndrome. 48 In some patients, leukemia and myelodysplasia occurred within 3 years of GT.…”

Successful outcome following allogeneic hematopoietic stem cell transplantation in adults with primary immunodeficiency

“…For these patients, diagnosis can be delayed or difficult and the natural history of exceptionally rare underlying diseases is often unclear. In several PIDs, controversy surrounding optimum timing of Allo-HSCT remains, due to rarity of disease, lack of experience, emerging gene therapies, [14][15][16][17] and infrequent published outcome data due to the very low numbers in any 1 center.…”

Targeted Repair of CYBB in X-CGD iPSCs Requires Retention of Intronic Sequences for Expression and Functional Correction

“…More specifically for X-CGD, autologous HSC gene therapy using retrovirus vectors has demonstrated clinical benefit as salvage therapy for life-threatening infection, but long-term gene marking has been low and life-threatening myelodysplasia caused by insertional mutagenesis has been observed with vector derived from murine spleen focus-forming virus. 3,4 We previously demonstrated a "safe-harbor" gene therapy approach for correction of X-CGD patient induced pluripotent stem cells (iPSCs) using zinc-finger nucleases (ZFNs) to mediate targeted insertion of a codon-optimized CYBB minigene into the AAVS1 locus under the control of a constitutive CAG promoter. 5,6 This resulted in constitutive expression of gp91 phox , which restored ROS production upon in vitro differentiation of iPSCs into granulocytes.…”