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My paper of the Month - Lentiviral gene therapy for X-linked chronic granulomatous disease.

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Each month one member of the EBMT Scientific Council will select and comment a recent paper in the field of stem cell transplantation and cellular therapy that was published in high ranked journals.

For this month Newsletter, Arjan Lankester, Chair of the Inborn Errors Working Party, comments on the publication entitled “Lentiviral gene therapy for X-linked chronic granulomatous disease." published in Nature Medicine.

Lentiviral gene therapy for X-linked chronic granulomatous disease.

Authors: Donald B Kohn, Claire Booth, Elizabeth M Kang, Sung-Yun Pai, Kit L Shaw, Giorgia Santilli, Myriam Armant, Karen F Buckland, Uimook Choi, Suk See De Ravin, Morna J Dorsey, Caroline Y Kuo, Diego Leon-Rico, Christine Rivat, Natalia Izotova, Kimberly Gilmour, Katie Snell, Jinhua Xu-Bayford Dip, Jinan Darwish, Emma C Morris, Dayna Terrazas, Leo D Wang, Christopher A Bauser, Tobias Paprotka, Douglas B Kuhns, John Gregg, Hayley E Raymond, John K Everett, Geraldine Honnet, Luca Biasco, Peter E Newburger, Frederic D Bushman, Manuel Grez, H Bobby Gaspar, David A Williams, Harry L Malech, Anne Galy, Adrian J Thrasher and the Net4CGD consortium

Nature Medicine Vol 26 February 2020, 200-206

Chronic granulomatous disease (CGD), one of the more than 400 currently identified monogenic primary immune disorders1, is an inherited disorder of phagocytic cells caused by defects in one of six different genes affecting the NADPH-oxidase system in these cells. The X-linked form, representing about two thirds of the cases, is caused by mutations in the CYBB gene encoding for the gp91phox subunit. In this paper, Kohn and colleagues report the first and promising multicenter results of a lentiviral-based gene therapy approach in nine severely affected pediatric and young adult X-CGD patients. With the aim to increase safety and efficacy a self-inactivating lentiviral vector incorporating codon-optimized CYBB was used, and a chimeric internal promotor was included to preferentially drive expression in phagocytes. Gene therapy products were generated making use of CD34-selected cells from G-CSF and plerixafor-mobilized leukapheresis products. The drug product was infused after busulfan-based myeloablative conditioning. Engraftment occurred in all patients with at least 15% oxidase (DHR)-positive neutrophils within the first month. Two patients died at 1 and 3 months after engraftment from acute sterile pneumonitis and intracranial bleed, respectively, probably linked to pre-existing comorbidity. Six of the surviving seven patients had stable engraftment, i.e vector copy numbers (0.4-1.8 copies per neutrophil) and oxidase positive cells (16-46%), at 12 months. One patient, after initial robust engraftment accompanied by an immune reconstitution inflammatory syndrome,  gradually lost the corrected cells within 18 months and remained well on antibiotic prophylaxis. Longitudinal vector integration site analysis revealed multiple unique integration sites without evidence for clonal expansion. No evidence for gene silencing was found. All patients with stable engraftment were without new infections and antibiotic prophylaxis, and without signs or recurrence of colitis at last follow-up. Together, the data demonstrate feasibility, safety and efficacy of this lentiviral-based gene therapy in a cohort of severely affected X-CGD patients.

CGD patients are usually characterized by severe and recurrent fungal or bacterial infections, and may also present with inflammatory bowel disease2. Allogeneic stem cell transplantation (SCT) has been demonstrated in many studies to be a, and so far the only, curative option for CGD patients. Successful outcome has been achieved even in the setting of active infections and colitis 3-5. Still, and despite ongoing improvements in transplant outcomes, graft-versus-host disease remains a significant limitation of SCT particularly in case of alternative donor transplantation. Hematopoietic stem/progenitor cell gene therapy, when safe and equally effective, may overcome this limitation and has the potential to become an alternative for SCT. The data in this study clearly demonstrate feasibility and safety of this novel lentiviral-based gene therapy approach. In previous studies with gammaretroviral vectors serious genotoxic side effects were observed resulting in malignant transformation of gene modified cells. Moreover, efficacy of the treatment was hampered by methylation-based transgene silencing. With a follow-up of at least 12 months none of these treatment related side effects were observed in seven surviving patients in whom six had stable engraftment of corrected cells. The reason for loss of the initially engrafted gene-corrected cells in one patient remained unresolved although the quality of the collected and corrected stem/progenitor cells from an inflammatory environment and the use of myelosuppressive medication were suggested as possible explanations. The authors report in the discussion that four additional patients have been treated, including three children. A similar decline in gene corrected cells following initial engraftment was observed in these three pediatric patients, so far for unknown reasons. Insight in the mechanisms responsible for this impaired persistence of corrected stem/progenitor cells is pivotal for further development and implementation of gene therapy in X-CGD and other candidate diseases.  

Similar as in SCT, in the setting of gene therapy myeloablative conditioning is required for sustainable engraftment of genetically-modified hematopoietic stem/progenitor cells and thereby long lasting curative effect. As a consequence, chemotherapy related acute and long term toxicities will be largely comparable with those in SCT, although the lack of immune suppressive components in the gene therapy conditioning will limit the risk for early infectious complications.

With current gene therapy approaches only partial correction of the progenitor cells and thus their offspring can be achieved. In diseases like severe combined immunodeficiency this is not a problem since the corrected cells will have a growth advantage. In X-CGD and related diseases, gene therapy will result in a condition comparable with mixed chimerism after SCT or with a carrier status. Whether this impacts on clinical outcome will differ per disease. In X-linked CGD, carriers are often asymptomatic, however symptomatic carriers have been reported6. Whether a similar phenomenon  may occur following gene therapy is currently unknown. In the study by Kohn and colleagues, the clinical outcome in the stably engrafted patients seems so far very good, still longer follow-up of patients will be required to provide the definite answer.

Given the promising results in this study the question can be raised which X-CGD patients may benefit most from gene therapy as alternative for SCT. Patients with sigificant co-morbidity and older patients in which SCT, especially with an alternative donor, is considered too riskful can be considered obvious candidates. However, when stable engraftment of gene corrected cells and clinical efficacy is demonstrated in a larger group of patients, gene therapy may also become an alternative for those patients that are currently considered candidates for SCT. 

1. Human Inborn Errors of Immunity: 2019 Update of the IUIS Phenotypical Classification. Bousfiha A, Jeddane L, Picard C, Al-Herz W, Ailal F, Chatila T, Cunningham-Rundles C, Etzioni A, Franco JL, Holland SM, Klein C, Morio T, Ochs HD, Oksenhendler E, Puck J, Torgerson TR, Casanova JL, Sullivan KE, Tangye SG. J Clin Immunol 2020 
2. Holland SM Chronic granulomatous disease. Hematol. Oncol. Clin. N. Am. 2013, 27: 89-99
3. Güngör T, Teira P, Slatter M, Stussi G, Stepensky P, Moshous D, Vermont C, Ahmad I, Shaw PJ, Telles da Cunha JM, Schlegel PG, Hough R, Fasth A, Kentouche K, Gruhn B, Fernandes JF, Lachance S, Bredius R, Resnick IB, Belohradsky BH, Gennery A, Fischer A, Gaspar HB, Schanz U, Seger R, Rentsch K, Veys P, Haddad E, Albert MH, Hassan M; Inborn Errors Working Party of the European Society for Blood and Marrow Transplantation. Reduced-intensity conditioning and HLA-matched haemopoietic stem-cell transplantation in patients with chronic granulomatous disease: a prospective multicentre study. Lancet, 2014, 383: 436-4
4. Allogeneic Reduced-Intensity Hematopoietic Stem Cell Transplantation for Chronic Granulomatous Disease: a Single-Center Prospective Trial. Parta M, Kelly C, Kwatemaa N, Theobald N, Hilligoss D, Qin J, Kuhns DB, Zerbe C, Holland SM, Malech H, Kang EM. J Clin Immunol 2017, 37: 548-558
5. Chronic Granulomatous Disease-Associated IBD Resolves and Does Not Adversely Impact Survival Following Allogeneic HCT. Marsh RA, Leiding JW, Logan BR, Griffith LM, Arnold DE, Haddad E, Falcone EL, Yin Z, Patel K, Arbuckle E, Bleesing JJ, Sullivan KE, Heimall J, Burroughs LM, Skoda-Smith S, Chandrakasan S, Yu LC, Oshrine BR, Cuvelier GDE, Thakar MS, Chen K, Teira P, Shenoy S, Phelan R, Forbes LR, Chellapandian D, Dávila Saldaña BJ, Shah AJ, Weinacht KG, Joshi A, Boulad F, Quigg TC, Dvorak CC, Grossman D, Torgerson T, Graham P, Prasad V, Knutsen A, Chong H, Miller H, de la Morena MT, DeSantes K, Cowan MJ, Notarangelo LD, Kohn DB, Stenger E, Pai SY, Routes JM, Puck JM, Kapoor N, Pulsipher MA, Malech HL, Parikh S, Kang EM; submitted on behalf of the Primary Immune Deficiency Treatment Consortium. J Clin Immunol 2019, 39: 653-667.
6. X-linked carriers of chronic granulomatous disease: Illness, lyonization, and stability. Marciano BE, Zerbe CS, Falcone EL, Ding L, DeRavin SS, Daub J, Kreuzburg S, Yockey L, Hunsberger S, Foruraghi L, Barnhart LA, Matharu K, Anderson V, Darnell DN, Frein C, Fink DL, Lau KP, Long Priel DA, Gallin JI, Malech HL, Uzel G, Freeman AF, Kuhns DB, Rosenzweig SD, Holland SM. J Allergy Clin Immunol, 2018, 141: 365-371