CRISPR gene editing has evolved over the past decade from an experimental tool to a therapeutic platform with clinical trials in multiple areas: hematology, oncology, and rare, infectious, and metabolic diseases. In 2025, over 65 clinical trials evaluated CRISPR technologies or base editors to treat human diseases. One of these led to the development of CasgevyTM—approved for the treatment of sickle cell anemia and beta-thalassemia—which involves ex vivo genetic modification of the patient’s own CD34+ hematopoietic stem cells using CRISPR-Cas9.[1] An in vivo gene therapy technique for hypercholesterolemia has also shown positive findings.[2]
The encouraging results of related research were recently published in the journal Nature, in an article entitled “RNA-triggered cell killing with CRISPR-Cas12a2”.[3] The report describes a radical innovation consisting of the programmed elimination of eukaryotic cells by RNA-activated Cas12a2, an enzyme of the CRISPR-Cas system. This opens a new treatment paradigm complementary to classical gene editing.
A new breakthrough in gene therapy
Cas12a2 is a type V CRISPR nuclease that is activated only upon recognizing a complementary target RNA transcript, triggering indiscriminate degradation of the host cell’s double-stranded DNA (dsDNA).
As the study authors explain, “Triggering Cas12a2 elicits rampant double-stranded DNA breaks […], leading to cell death.”
This mechanism enables the selective elimination of cells with a specific gene expression profile, bypassing the need for genome editing.
Elimination of yeast and human cells
Selectively eliminating cells, tissues, and organisms based on their genetic or physiological identity has been a central pillar of the life sciences. While molecular and cellular interventions are often highly effective in eliminating harmful cells using specific proteins, these methods cannot be applied to certain genetic or transcriptional states, or to undruggable scenarios, such as mutations in non-coding sequences or complex etiologies.
One of the biochemical properties of the Cas12a2 nuclease employed in this study is that it is triggered by the recognition of targeted DNA or RNA; consequently, it can be used to selectively eliminate cells based on their expression state through the presence of transcriptional RNA. Nucleases previously used in CRISPR technology, such as Cas9, produce a milder effect without causing cell death, instead inducing breaks at specific sites in the DNA for subsequent editing, or target gene elimination (knockout). However, Cas12a2 can induce cell death as a result of targeted cleavage at multiple sites in the genome, for example, by targeting highly repetitive elements of dsDNA. The massive destruction of DNA, without subsequent repair, inevitably leads to induced apoptosis of the cells in which it occurs.
As a proof of concept, the authors tested the idea in a simple eukaryotic cell model, the yeast S. cerevisiae. To that end, they transformed a plasmid carrying a ribonucleoprotein (RNP) complex expressing Cas12a2 fused to nuclear localization signals (NLSs) and a designed guide RNA targeting the transcript of a non-essential yeast gene, ADE2.
The assay resulted in no editing (repair) of the target gene by preventing the formation of HR-type DNA breaks (breaks that leave homologous ends) at the specific target site, which are then repaired in the presence of an exogenous DNA template. The presence of Cas12a2 prevents repair and drives collateral RNA cleavage activity in the yeast cells, despite the opportunity for localized DNA repair provided by the specific donor DNA template. This preliminary study demonstrated the capacity of the system to eliminate S. cerevisiae yeast cells.
Next, they tested Cas12a2 activity in human cells from the experimental HeLa-GFP culture (GFP is a marker that causes a fluorescent reaction when active and can be observed under a fluorescence microscope).
The result was similar to that of the action on yeast cells. Electroporation (a method used to deliver the RNP system with Cas12a2 and the guide RNA) into HeLa-GFP cells depleted the human cell population by targeting the GFP transcript through RNA-specific recognition, resulting in an 86% reduction in viable cells. This elimination was shown to be effective even with poor expression of the target RNA.
Following this experimental assay in human cell cultures, the next step was to test on endogenous transcripts in four human cell lines derived from cancers (melanoma, lung, and head and neck cancer) with transcript levels ranging from undetectable to highly expressed, and differing between cell lines.
Cas12a2 decreased cellular expression across all cell types, even when targeting poorly expressed transcripts. The large number of DNA breaks in the cells led to cell cycle arrest and cell death.
In summary, these results demonstrate that Cas12a2 can be programmed to induce specific cell depletion even for poorly expressed transcripts in multiple cell types and with different delivery modalities.
It is also important to note that the number of DNA break foci in treated cells as a result of the action of RNA-triggered Cas12a2 is comparable to the levels observed in cells treated with anti-cancer drugs widely used in chemotherapy. The major difference, however, is that these drugs cause indiscriminate DNA damage in both healthy and cancer cells, whereas Cas12a2 only induces DNA damage above background levels when cells express the target transcript.
Promising aspects of the new technique
Similarly, given the ability of Cas12a2 to eliminate human cells on the basis of a selected target transcript, the authors tested the potential of this technique in other scenarios, such as eliminating cells chronically infected with human papillomavirus (HPV) while sparing uninfected ones, and selectively eliminating cancer cells with established somatic point mutations, such as those harboring mutations in the KRAS oncogene. Again, the results demonstrated the validity of the technique. Cas12a2 generates extensive chromosomal dsDNA breaks followed by cell cycle arrest and, primarily, apoptotic cell death of unwanted cells, without affecting healthy cells.
This capacity of the proposed system for massive, selective elimination of specific cell populations (such as tumor cells) suggests that its future application could signify a huge breakthrough in the fight against cancer, providing a safer and more effective alternative to the options currently available.
The authors likewise hope to extend the application of the new technique to other eukaryotes, including additional animals and fungi, as well as protists and plants. The potential also extends to other applications, such as gene drives to link cell killing to gamete formation or sex selection, which is of particular interest against insects or other infectious organisms, with applications in medicine, agriculture, and livestock.
State of current research in therapeutic applications of gene therapies
According to a report by Genotipia, research into CRISPR gene-editing-based therapies in 2025 was based on:
- Ex vivo editing of hematopoietic cells (Casgevy, BEAM‑101).
- In vivo editing using AAV or nanoparticles (BEAM‑301, VERVE‑102).
- Modified cell therapies (autologous and allogeneic CAR‑T).
- Base editing and Cas13 for eye, metabolic, and immune diseases.
- Elimination of pathogens (EBT‑101 for HIV, CRISPR‑Cas3 in bacteriophages).
Advantages of Cas12a2 editing compared to currently available techniques
Compared with these therapies, the proposed Cas12a2 approach would offer the following improvements:
In hematology, compared to current editing techniques to correct certain genes such as HBB or G6PC1, the new proposal would allow the elimination of pathological clones (e.g. resistant sickle cells).
In oncology, current procedures using edited CAR-T cells, PD-1/CISH editing, etc., would be improved with the capacity of the new system to directly eliminate tumor cells based on their mutated RNA.
In the case of infectious diseases, the elimination of HIV or HBV viral DNA (responsible for AIDS and hepatitis B, respectively), the proposed technique would allow the selective and highly efficient eradication of cells infected by active RNA viruses.
For rare diseases, current methods rely on correcting the affected gene sequences, while the Cas12a2-based technique would allow the direct elimination of cells with aberrant or toxic gene expression.
Finally, in the case of base editing techniques, which allow specific DNA nucleotides to be modified without inducing double-strand breaks, the application of Cas12a2 would enable the selection of only correctly edited cells, drastically reducing the risk of occurrence of the aforementioned “off-target effects”.
Bioethical assessment
First, in terms of its therapeutic potential, the superior efficacy and safety expected of this technique would allow its use in patients refractory to currently available pharmacological treatments. Its use would allow the selective elimination of cells infected by persistent viruses.
Second, with respect to its safety, it would represent a breakthrough in terms of the ability to select specific target cell lineages, thereby avoiding unintended effects on healthy cells.
Finally, it could potentially remove the need for permanent genome editing, in contrast to other techniques based on such approaches.
Nevertheless, the proposed strategy is not without risks. Among the most important are the following:
- a) Unwanted activation
Although the article discussed herein states that no off-target effects were detected, activation depends on RNA expression, which can vary due to stress, inflammation, somatic mutations, or other epigenetic alterations.
- b) Collateral tissue damage
Massive cell death can trigger systemic inflammation or toxicity.
- c) In vivo inoculation
As with other CRISPR therapies, delivery via LNPs (lipid nanoparticles) or viral vectors can result in immunogenicity.
- d) Long-term effects
The consequences of activating Cas12a2 in complex tissues or whole organisms are unknown.
- e) Justice and access
The associated costs, technical complexity, and infrastructure requirements of these techniques pose barriers to broad patient access, as is the case with other gene therapies already available today (Casgevy costs $2.2 million in the US and £1.65 million in the UK). Similar to other complex therapies, prices are expected to drop as research progresses and treatments are simplified.
- f) Autonomy and informed consent.
Cas12a2 introduces new elements that must be explained to the patient, such as the fact that it does not modify genes but rather kills cells; that its activation depends on the expression of RNA, not of DNA; the irreversibility of the process once activated; and the possibility of including accidental or incomplete activation scenarios.
- g) Considerations on non-therapeutic uses.
Risks arising from the possible unauthorized use of this technique, such as military applications or manipulation of human cell populations without ethical oversight, must be taken into account. In this scenario, international regulation that can anticipate these risks is necessary.
Conclusion
Cas12a2 represents a new category of CRISPR tool, not aimed at editing but at selectively eliminating cells according to their RNA. Its proven applications— such as the elimination of infected cells, enrichment of edited cells, or the destruction of tumor cells with specific mutations—complement and expand the current landscape of CRISPR clinical trials.
Its therapeutic potential is huge, but so too are the ethical challenges in terms of its safety, specificity, governance, and equity in access. The responsible integration of Cas12a2 into precision medicine will require robust regulatory frameworks and continuous assessment of risks and benefits.
Julio Tudela
Bioethics Observatory – Institute of Life Sciences
Catholic University of Valencia
Nicolás Jouve
Professor Emeritus of Genetics at the University of Alcalá
Member of the Bioethics Observatory of the Catholic University of Valencia
References
[1] Lesmana, H., Kim, S.Y., Corado, A.M., Poskanzer, S.A.; ACMG Therapeutics Committee8∗documents@acmg.net. Casgevy (exagamglogene autotemcel) and Lyfgenia (lovotibeglogene autotemcel) for individuals 12 years and older with sickle cell disease (SCD) and recurrent vaso-occlusive crises (VOC): A therapeutics bulletin of the American College of Medical Genetics and Genomics (ACMG). Genet Med Open.10;2 (2024) 101875.
[2] Naddaf, M. First trial of ‘base editing’ in humans lowers cholesterol – but raises safety concerns. Nature. 2023 Nov 13. doi: 10.1038/d41586-023-03543-z.
[3] Scholz, P., Thompson, J., Crosby, KT et al. RNA-induced cell elimination with CRISPR-Cas12a2. Nature (2026). https://doi.org/10.1038/s41586-026-10466-y
