23 April 2019

A gene therapy developed for babies with X-linked severe combined immunodeficiency (SCID‑X1) has substantially improved the immune function of all patients who received treatment, doctors reported last week.

Eight infants now have fully functioning immune systems and are living normal lives, US researchers reported in the New England Journal of Medicine.

The treatment involved inserting a correct copy of the IL2RG gene into the genome of the patients’ blood stem cells, using a modified lentiviral vector. The cells were frozen and tested before being returned to the patients.

Before undergoing the autologous stem cell transplant, the babies received two days of low-dose busulfan to make space for the treated cells.

The researchers report that in seven cases, normal numbers of multiple types of immune cell were re-established within four months of the therapy. One patient needed a second dose of blood stem cells.

All patients are off protective precautions such as isolation and prophylactic anti-microbial agents. In addition, three of the patients had normal responses to childhood vaccinations, an indicator of robust B cell function.

The doctor who led the project, Dr Brian Sorrentino, St. Jude Children's Research Hospital, Tennessee, USA, died after compiling the latest findings and submitting them for publication late last year.

His colleague Dr Ewelina Mamcarz said: “These patients are toddlers now, who are responding to vaccinations and have immune systems to make all immune cells they need for protection from infections as they explore the world and live normal lives. This is a first for patients with SCID-X1.”

The lentiviral vector used has ‘insulators’ to prevent activation of neighbouring genes and reduce the risk of triggering leukaemia – a problem which occurred in previous versions of the therapy.

The doctors said they expected most patients to experience “a complete durable immune response without side effects.”

Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said: “These exciting new results suggest that gene therapy may be an effective treatment option for infants with this extremely serious condition, particularly those who lack an optimal donor for stem cell transplant.

“This advance offers them the hope of developing a wholly functional immune system and the chance to live a full, healthy life.”

Source: Mamcarz, E., Zhou, S., Lockey, T., Abdelsamed, H., Cross, S.J., Kang, G., Ma, Z., Condori, J., Dowdy, J., Triplett, B., Li, C., Maron, G., Aldave Becerra, J.C., Church, J.A., Dokmeci, E., Love, J.T., da Matta Ain, A.C., van der Watt, H., Tang, X., Janssen, W., Ryu, B.Y., De Ravin, S.S., Weiss, M.J., Youngblood, B., Long‑Boyle, J.R., Gottschalk, S., Meagher, M.M., Malech, H.L., Puck, J.M., Cowan, M.J., & Sorrentino, B.P. (2019) “ Lentiviral Gene Therapy Combined with Low-Dose Busulfan in Infants with SCID-X1”, New England Journal of Medicine, available at doi: 10.1056/NEJMoa1815408


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