Surgery using Gene Scissors: Targeted Gene Modification with CRISPR

“Like a toothache throughout the entire body” – this is how patients with sickle cell disease describe the frequent pain episodes, also known as vaso-occlusive crises [1]. During these episodes, sickle-shaped red blood cells obstruct small blood vessels and impair the oxygen supply to tissues [2]. Like β-thalassemia, sickle cell disease is a severe inherited blood disorder that affects hemoglobin production. As hemoglobin is responsible for transporting oxygen throughout the body, these diseases can lead to blood vessel blockages, painful crises, and chronic organ damage [3]. For a long time, allogeneic stem cell transplantation was the only potentially curative treatment option. However, many patients lack a suitable donor, and the procedure carries significant risks, including graft rejection and graft-versus-host disease (GvHD) [3].

In February 2024, treatment options for patients with sickle cell disease and transfusion-dependent β-thalassemia expanded significantly with the EU approval of exagamglogene autotemcel (exa-cel; Casgevy®), the first approved CRISPR/Cas-based therapy. The treatment involves genetically modifying the patients’ own blood stem cells ex vivo before reinfusing them. This one-time treatment marked a major milestone for CRISPR-based therapies [1]. The therapy is now also being used in Germany: In May 2026, a patient with β-thalassemia became the first in Germany to receive Casgevy® as part of routine clinical care at Charité University Hospital Berlin. According to Charité, he has not required blood transfusions since the treatment [4].

1) The Molecular Scissors: Targeted Gene Editing with CRISPR

2) Advancing Research with CRISPR Tools from BPS Bioscience

3) Switching Off a Gene: CRISPR Knockouts

4) Targeted Gene Modifications: CRISPR Knock-ins

5) Activating a Gene: CRISPR Activation (CRISPRa)

The Molecular Scissors: Targeted Gene Editing with CRISPR

But how does this gene therapy work? The goal of CRISPR therapy is to stimulate blood stem cells to produce more fetal hemoglobin (HbF). The gene BCL11A plays a key role by suppressing HbF production. By selectively inactivating BCL11A, HbF levels can be increased, helping to reduce the disease-causing effects of abnormal hemoglobin in sickle cell disease and β-thalassemia [5]. And the tool for this targeted intervention? The CRISPR molecular scissors.

CRISPR is based on a natural antiviral defense mechanism in bacteria. Following a viral attack, bacteria store small fragments of viral DNA as a kind of molecular memory. These fragments are used to generate guide RNAs, which direct the Cas9 endonuclease (CRISPR-associated protein 9) to matching viral DNA sequences during a subsequent infection. Cas9 then cuts the DNA at the targeted site, rendering the virus harmless [6; 7].

For targeted gene editing in mammalian cells, a gene-specific guide RNA (gRNA) directs Cas9 to the desired DNA site, where the nuclease creates a double-strand break. Different genetic modifications can arise during the subsequent repair process. In a knockout, small insertions or deletions (indels) often lead to gene inactivation. In a knock-in, a DNA template is additionally provided for homology-directed repair (HDR), enabling the targeted introduction of mutations or other DNA sequences (Fig. 1) [6; 7].

Figure 1: The mechanism of the CRISPR-Cas9 system. A guide RNA (gRNA) directs the Cas9 protein to a complementary DNA sequence, where Cas9 creates a double-strand break. The cell then repairs the break either through non-homologous end joining (NHEJ), which can introduce small insertions or deletions (indels) that inactivate the target gene, or through homology-directed repair (HDR). In the latter case, a suitable DNA template can be used to introduce a specific mutation or a new DNA sequence into the genome [7].

Advancing Research with CRISPR Tools from BPS Bioscience

The approval of CRISPR-based therapies for sickle cell disease and β-thalassemia highlights the enormous potential of this technology. CRISPR-Cas9 supports a wide range of applications, from investigating gene function and creating disease models to developing novel therapeutic approaches [8]. For these research projects, our partner BPS Bioscience offers a broad portfolio of CRISPR tools, including cell lines, Cas proteins, and viral vectors. These tools enable targeted gene knockouts and knock-ins, as well as gene activation.

Switching Off a Gene: CRISPR Knockouts

CRISPR-Cas9 is particularly well suited for targeted gene inactivation. Depending on the experimental design, researchers can generate heterogeneous cell pools or stable clonal cell lines. While cell pools offer a quick and cost-effective starting point, stable cell lines provide a well-defined basis for long-term studies and reproducible experiments.

For custom CRISPR knockout assays, BPS Bioscience offers ready-to-use Cas9-expressing cell lines and cell pools. Gene-specific gRNAs can be introduced, for example, by electroporation or lentiviral transduction. Recombinant Cas proteins are also available for in vitro cleavage assays, allowing researchers to compare the cutting efficiency of different gRNAs. In addition, BPS Bioscience offers integrating and non-integrating gRNA/Cas9 lentiviruses for direct transduction, as well as AAVs carrying the more compact Cas9 from Staphylococcus aureus (SaCas9) [6; 7].