Disease Roundup: Sickle Cell Disease and CRISPR
This roundup was originally published on 30th December 2021. It was updated on 24th November 2021 to reflect further developments in the CRISPR medicine field for sickle cell disease.
Sickle cell disease (SCD) is a group of diseases that are characterised by defective adult haemoglobin, and it belongs to a larger family of autosomal-recessive blood disorders known as the haemoglobinopathies (See Fact Box).
A number of treatments exist to manage the symptoms and complications of SCD but none of these are curative. Hydroxyurea was the first medication to obtain FDA approval for SCD (1997). It is an anti-cancer agent that promotes the production of foetal haemoglobin by a poorly understood mechanism and is widely used today despite side effects. Recently-approved treatments include Endari (2017), which increases L-glutamine levels in the blood triggering a cascade of events that reduces oxidative stress in sickled cells, allowing them to retain some function, Oxbryta (2019), which prevents defective haemoglobin from aggregating, thus ameriolating the symptoms of SCD, and Adakveo (2019), a monoclonal antibody that blocks P-selectin, thus lessening the inflammation associated with SCD.
Gene editing provides new hopes for SCD patients
Fortuantely for the millions of SCD sufferers worldwide, decades of research to unravel the genetic pathways involved in regulating haemoglobin production has opened doors for diverse gene-editing approaches that aim to cure the disease.
There are currently seven clinical-stage candidates in development, five of which aim to restore foetal haemoglobin (HbF) expression through gene editing of patient-derived cells, while the other two aim to tackle the root of disease by direcly repairing the underlying disease mutation.
FACT BOX: Sickle Cell Disease (SCD) and Foetal Haemoglobin
SCD results from a single-point mutation in the haemoglobin subunit beta (HBB) gene and is associated with a range of symptoms and life-life complications. Vaso-occlusive crises (VOEs or VOCs) are the most commonly encountered complication in severe SCD, and these occur when small blood vessels get blocked because of sickled red blood cells which tend to be stiffer than healthy cells, and because the defective form of haemoglobin seen in SCD (haemoglobin S) renders the red blood cell membranes sticky.
Daily treatment for SCD patients is limited to symptom control, dietary intervention and pain management. While a bone marrow transplant from a healthy matched donor has traditionally been the only (albeit slight) hope of a cure for the haemoglobinopathies, gene-editing technology unleashes the possibility to cure a patient using their own cells. Central to many of the current approaches is foetal haemoglobin (HbF).
HbF is highly expressed and critical during foetal development, but then rapidly suppressed early in life. Extensive research on the molecular mechanisms of the haemoglobinopathies revealed that the B-cell lymphoma/leukaemia 11A gene, BCL11A, is a negative regulator of HbF expression, and that its disruption could restore HbF expression and reverse SCD in mice by compensating for the lack of functional adult haemoglobin. Since the discovery of this so-called haemoglobin switch, reactivation of HbF expression has emerged as a dominating therapeutic strategy for SCD (as well as beta-thalassemia).
1. CTX001: Vertex Pharmaceuticals, US and CRISPR Therapeutics, U.S.
CTX001 is co-developed by Vertex Pharmaceuticals and CRISPR Therapeutics as a one-time curative treatment for severe sickle cell disease (SCD) and the related disease blood transfusion-dependent beta-thalassemia (TDT). Specifically, CRISPR-Cas9 is used to delete the BCL11A in a patient’s own haematopoietic stem cells (HSPCs) ex vivo, and the engineered cells are then transplanted back into the patient where they express HbF to restore healthy red blood cell levels.
The ongoing Phase 1/2 CLIMB-111 (TDT) and CLIMB-121 (SCD) trials for CTX001 were the first CRISPR gene-edited therapy trials to be sponsored by US-based companies, and the most recent clinical data released in June 2021 is promising. At the time this data was released, seven patients with severe SCD who were treated with CTX001 in the CLIMB-121 trial, and whose follow-up period was long enough to warrant initial safety and efficacy assessments, showed a similar pattern of response, with rapid and sustained increases in total haemoglobin and HbF. These patients were also free of vaso-occlusive crises (VOCs), a major complication of severe SCD (see Fact Box).
As of June 2021, two patients with SCD in the CLIMB-121 trial had follow-up of greater than one year, demonstrating a stable and durable response to treatment. Bone marrow allelic editing data collected from four SCD patients with at least six months of follow-up, of which two had 12 months of follow-up, also demonstrated a durable effect. The safety data from all seven patients were generally consistent with an autologous stem cell transplant and myeloablative conditioning. No serious adverse events were considered related to CTX001, and the majority of non-serious adverse events were considered mild to moderate. Enrollment and dosing are ongoing.
2. BIVV003: Sanofi, France
BIVV003 is an ex vivo-engineered autologous HSPC therapy that is designed to express HbF through BCL11A disruption. In contrast to CTX001, BIVV003 is edited using a zinc finger nuclease (ZFN) mRNA that targets the BCL11A locus. BIVV003 is developed using Californian Sangamo Therapeutics proprietary ZFN technology.
The candidate is being developed as a one-time intravenous treatment for severe SCD, and is currently undergoing evaluation in the Phase 1/2 PRECIZN-1 study for severe SCD, which is sponsored by Sanofi. The study will evaluate its safety, tolerability, and efficacy of autologous HSPC transplantation using BIVV003 in approximately 8 adult patients. Patient participation in this trial is approximately 136 weeks, and enrolled subjects will be asked to participate in a separate long-term follow-up study to monitor the safety and efficacy of BIVV003 treatment for a total of 15 years post-transplant.
At last year’s American Society of Hematology Annual Meeting, Sangamo presented results from ex vivo studies of BIVV003 that showed efficiency BCL11A disruption in both alleles, increased HbF expression and reduced sickling in red blood cells isolated from non-treated SCD patients.
In March 2021, Sangamo Therapeutics announced that the European Medicines Agency’s Committee for Orphan Medicinal Products (COMP) released details supporting the Orphan Designation of BIVV003. This decision was partially based on early clinical data from three patients that had 52 weeks, 13 weeks, and 29 days of follow-up, respectively. In the same company press release, it was also revealed that Sangamo and Sanofi expect to submit updated data from the PRECIZN-1 trial for presentation at a medical meeting later this year.
3. OTQ923 and HIX763: Novartis, Switzerland
Switzerland-based Novartis Pharmaceuticals initiated a first-in-patient, Phase 1/2, proof-of-concept study last year to follow patients for two years after transplantation of one of two ex vivo CRISPR-edited autologous HSPC experimental therapies for SCD.
The experimental therapies are OTQ923 and HIX763, both of which are designed to reduce the biologic activity of the B-cell lymphoma/leukaemia 11A protein (BCL11A), increasing fetal haemoglobin (HbF) and reducing complications of SCD.
The study, which is open-label and non-randomised, will be split into 3 distinct sections that will individually assess the candidate therapies in adults and children. The first part of the study will include treatment of adults with OTQ923, the second part will include treatment of adults with HIX763, and the third part will include treatment of children 2-17 years old with either OTQ923 or HIX763.
OTQ923 and HIX763 are CRISPR-edited HSPCs that are developed using CRISPR-Cas9 RNA guides identified through a collaboration between Novartis and Intellia Therapeutics. The trial is currently in the recruitment stage for a total of 30 participants and the expected completion date is in November 2023.
4. EDIT-301: Editas Medicine, U.S.
EDIT-301 is being developed by Editas Medicine as an autologous CRISPR-edited cell therapy for the treatment of severe SCD. The new candidate will be assessed in the RUBY Phase 1/2 trial in 40 adult participants between the ages of 18 and 50 years.
EDIT-301 is the first experimental medicine developed using CRISPR-Cas12a gene-editing technology, and it is specifically edited using a CRISPR-Cas12a ribonucleoprotein to enhance the HBG1/2 promoter region in the beta-globin locus of patient-derived HPSCs. Naturally-occurring HbF-inducing mutations at the HBG1/2 region support the clinical relevance of using gene editing to enhance the HBG1/2 promoter, and this strategy has been shown to increase the red blood cell levels of HbF.
Editas presented data at the 25th European Hematology Association meeting last summer demonstrating that red blood cells derived from EDIT-301 HSPCs exhibit a sustained in vivo increase in HbF in animal models. In August 2020, Editas obtained Rare Pediatric Disease Designation for EDIT-301 as a potentially best-in-class treatment for SCD in children from birth to 18 years. The company obtained FDA clearance to initiate the RUBY trial in January 2021. At the European Hematology Association Congress in June 2021, the company released pre-clinical data on EDIT-301 supporting the inititiation of the RUBY trial for severe SCD.
The single-arm, open-label, multicenter RUBY trial is actively recruiting, and the overall goal is to evaluate the efficacy, safety and tolerability of EDIT-301 in adults with severe SCD.
5. CRISPR_SCD001, University of California, U.S.
Mark Walters, MD at University of California, San Francisco Benioff Children's Hospital Oakland, in collaboration with University of California, Los Angeles and University of California, Berkeley is sponsoring a Phase 1/2 clinical trial for severe SCD in 9 participants between the ages of 12 and 35 years old.
During the study, the participants will receive a single intravenous transfusion of CRISPR_SCD001, which is an experimental therapy based on red blood cells that are CRISPR-edited to directly correct the mutation in the beta-globin gene responsible for SCD. Before transfusion, each partipicant will undergo a myeloablative conditioning procedure with the chemotherapeutic busulfan. Myeloablative conditioning destroys the cells in the bone marrow to prevent rejection of the transfused CRISPR_SCD001 therapy.
The estimated study start date i.e. the date on which the first participant is expected to be enrolled, is 1st December 2021 and the study completion date i.e. the date whereby data is available on the last study participant is set to May 28th, 2026.
6. GPH101: Graphite Bio, U.S.
Graphite Bio, a spinout of Stanford University obtained FDA clearance in December 2020 for its lead CRISPR therapy candidate GPH101 to advance to clinical trials for severe SCD.
Similarly to CRISPR_SCD001, GPH101 is also designed to correct the HBB point mutation, and is anticipated to provide a permanent cure by targeting the root cause of disease and restoring completely normally-functioning red blood cells. The therapy is engineered using patient-derived HSPCs that are edited using Cas9-sgRNA gene-editing machinery and a DNA repair template, in a mechanism that essentially cuts the mutation out of the genome and replaces it with the correct sequence. Cas9-sgRNA is delivered through ribonucleoprotein protein (RNP) complexes while corrected DNA template delivery is achieved through an adeno-associated virus 6 (AAV6) vector.
In a presentation at the 39th Annual J.P. Morgan Healthcare Conference in January of this year, Graphite Bio demonstrated curative gene correction with its CRISPR approach at GMP (good manufacturing practice) clinical scale. A research report co-authored by Matthew Porteus MD PhD, of The California Institute for Regenerative Medicine and Stanford University, who has overseen the pre-clinical manufacturing and FDA-required safety studies for GPH101, demonstrated that AAV-mediated CRISPR-Cas9 correction of the HBB mutation improved SCD symptoms in a humanised mouse model for the disease.
GPH101 will be assessed in CEDAR, a Phase 1/2 multi-center, open-label study to evaluate the safety, efficacy and pharmacodynamics of the new therapeutic candidate in adult and adolescents with severe SCD. Last week, Graphite Bio reported that it had enroled the first patient in the CEDAR trial, which it plans to dose in the first half of 2022, with initial proof-of-concept data expected by the end of next year.
7. BEAM-101, Beam Therapeutics, U.S.
BEAM-101 is the first base-edited therapy candidate for a haemoglobinopathy, and is developed as a patient-specific, autologous HSPC therapy designed as a one-time treatment for SCD and TBT. Earlier this month, Beam Therapeutics announced that the U.S. FDA had cleared BEAM-101 for clinical evaluation as a treatment for SCD.
BEAM-101 cells are engineered ex vivo with an ABE that incorporates A → G base edits in the HBG1 and HBG2 gene promoters, which regulate the expression of HbF. These edits mimic the naturally-occurring HbF-inducing mutations observed in individuals that continue to produce foetal haemoglobin beyond infancy, leading to reactivation of HbF expression to compensate for the lack of adult haemoglobin in SCD. The BEAM-101 base-editing reagents are delivered to patient-derived haemopoetitic stem cells via electroporation. Results from animal studies reveal high levels of base editing and robust HbF induction after long-term in vivo engraftment with BEAM-101 cells.
According to a company press release, BEAM-101 is envisioned to be a one-time treatment for patients with SCD, and plans are underway to initiate the BEACON-101 trial, which will be a Phase 1/2 clinical trial to assess the safety and efficacy of BEAM-101 for the treatment of SCD.
We strive to keep you updated with clinical and pre-clinical news from the CRISPR Medicine field. For a complete overview of current gene editing clinical trials, check out CRISPR Medicine News' Clinical Trials Database.
Articleex-vivoRibonecleoprotein (RNP)Adeno-associated virus (AAV)Beta-ThalassemiaSickle Cell Disease, SCDBlood diseaseRare DiseaseCalifornia Institute for Regenerative Medicine (CIRM)University of CaliforniaBase editorsCRISPR-CasCas12aCas9ZFN - Zinc finger nucleasesBeam Therapeutics Inc.CRISPR Therapeutics AGEditas Medicine, Inc.Graphite Bio, Inc.Intellia Therapeutics, Inc.Novartis AGSangamo Therapeutics Inc.Sanofi S.AVertex Pharmaceuticals, Inc.TrialsClinical