In vitro and animal model studies by scientists at University College London (UCL) have demonstrated the feasibility of a gene therapy approach to correct the deficiency of a regulatory protein, CTLA4, in immune T cells, resulting in a rare inborn error of immunity. The study, published in Science Translational Medicinecould lead to a new treatment for CTLA4 deficiency that affects regulatory and effector T cells, leading to autoimmunity and often a severe clinical phenotype.
CTLA4 insufficiency occurs in individuals with only one working copy of CTLA4 who produce too little protein to properly regulate the immune system. The condition also lowers immunological memory, so that patients suffer from repeated infections with the same pathogens and can lead to a type of blood cancer (lymphomas).
In this study, the researchers targeted the defective gene in primary T cells collected from patients with CTLA-4 deficiency. Using homology-directed repair (HDR) CRISPR/Cas9 gene editing, they inserted the normal complementary DNA sequence of CTLA-4 into the first intron (non-coding region) of the CTLA-4 genomic locus. This restored CTLA-4 levels in patient-derived cells to those seen in healthy T cells and rescued normal cell function in vitro.
“Genes that play critical roles in controlling immune responses are not turned on all the time and are very tightly regulated,” said Emma Morris, PhD, professor of clinical gene and cell therapy, director of the Division of Infection and Immunity from UCL, and co-senior author of this study. “The technique we have used allows us to leave intact the natural (endogenous) mechanisms that control gene expression, while correcting the error in the gene itself.”
The team also performed experiments in mouse models of the disease that do not express CTLA-4 in any cells. The researchers grafted T cells with normal CTL4 expression into these mice and showed that it prevented the abnormal expansion of T cell populations (lymphoproliferation) in vivo.
“It’s really exciting to think about bringing this treatment to patients. If we can improve their symptoms and reduce their risk of lymphoproliferative disease, that will be a big step forward,” said Claire Booth, PhD, professor of gene therapy at UCL and co-senior author of the study. “This article is important because we are using the latest gene editing techniques to precisely correct these T cells, which is a new approach in inborn errors of immunity.”
Currently, CTLA-4 deficiency is treated by bone marrow transplantation that replaces the stem cells responsible for producing T cells. However, transplantation is accompanied by risks of rejection, prolonged immunosuppressive therapy, infections, and long hospital visits.
“Correcting the patient’s T cells can improve many of the symptoms of the disease, while also being much less toxic than a bone marrow transplant,” Booth said. “Collecting and correcting the T cells is easier. With this approach, the amount of time patients would need in the hospital would be much less.”
The study was led by Thomas Fox, PhD, a Wellcome Trust Clinical Doctoral Fellow at UCL, and based on the work of co-author Pietro Genovese, PhD, a researcher at the Dana-Farber Cancer Institute.
The researchers say the gene-editing therapy they’ve developed in this proof-of-principle study could be adapted to address other conditions. “It allows us to correct genes that are dysregulated or overactive, but it also allows us to understand much more about gene expression and regulation,” Morris said.