Personalised gene therapy is no longer science fiction – it’s reality

Long evenings in the lab and at the computer, plans that don’t work out, and paperwork that buries scientists under piles of forms. And yet they so often say: I love this job.“When you plan a project or an experiment and draw on the full spectrum of knowledge in your field, and you still have that naïve idea that everything will work. That’s my favourite phase,” says molecular biologist RNDr (Doctor of Natural Sciences, Czech postgraduate degree) Karolina Škvárová Kramarzová, PhD, from the Department of Paediatric Haematology and Oncology, the CLIP Laboratory Centre, the Second Faculty of Medicine, and Motol and Homolka University Hospitals.

What are the responsibilities of a principal investigator at the Second Faculty of Medicine?

My main focus is scientific work: I provide the conceptual leadership for projects and manage my research team. Working with people is something I find deeply fulfilling, especially supervising students. I enjoy watching them learn to think about experiments and gradually grow – both professionally and personally. I also teach a little, but science remains the most important part of my work, from designing projects to writing and publishing papers. When you plan something new and draw on the full spectrum of knowledge in your field, and you still have that idealised vision that everything will work – that is the phase I like the most.

Then, of course, comes the part where you have to work out why some experiments aren’t working, why the results don’t make sense, why the hypothesis didn’t hold. That is the more frustrating phase. But overall, I find the nature of scientific work truly beautiful. What I would most like to eliminate, however, is the administrative burden associated with research grants.

How much time do you still spend in the laboratory?

That time is decreasing significantly; I mainly get to the lab to help the team during busy periods. As I progress in my academic career, I have more responsibilities towards the Faculty and the scientific community, and less time for hands‑on laboratory work. But I have enjoyed this work from the very beginning, including the manual aspects, which I like to return to because they give me a welcome break from grant‑related worries and similar obligations.

 

 

How diverse is your team? Does it include natural scientists, doctors, and biologists?

We have both medical doctors and colleagues from biology – different fields and different areas of expertise. That’s exactly how I like it. For example, I contribute experience in molecular biology to the project, while my colleagues bring expertise in medicine or biochemistry. And it works well; everyone brings something new. But our team has one important thing in common: it is a group of very inspiring people with a good sense of humour. When you’re a doctoral student at the beginning of your career, you don’t yet realise how much time you’ll end up spending at work. We don’t want to overburden anyone, but that’s simply the nature of experimental research – it can’t really be done from eight to four. Sometimes you’re in the lab from eight until ten because the experiment runs longer, and you have to be flexible. Science in general requires drive and motivation, especially at moments when experiments aren’t working. That’s when the people around you matter the most.

 

 

What specifically does your team focus on within CLIP?

We study the role of genes and their mutations – more precisely, the errors in genes that underlie the onset and progression of rare diseases. At the same time, we test strategies for correcting these mutations. Gene editing is what connects both areas. We are not defined by a single topic. I could say that the core of my work lies in the development of gene therapy, which is the focus of my current research grant, but a large part of our activity is dedicated to studying the function of genes and genetic mutations. A good example of this is our collaboration with the team of Prof Eva Froňková, which, among other things, works with patients who have unclear diagnoses and where a genetic cause is suspected. In such patients, DNA testing is carried out to identify mutations responsible for the disease.

Diagnosing these cases is extremely challenging; identifying a potentially causal mutation or defect requires highly specialised expertise. Moreover, pinpointing candidate mutations is often not sufficient – it is frequently necessary to demonstrate experimentally that the mutation is indeed the cause of the patient’s condition. And this is precisely where our team plays a key role.

 

 

Can you give a specific example?

We had a patient with severe anaemia who did not respond to standard treatment. Based on DNA testing, our colleagues identified a potentially causal mutation in a gene that encodes one of the folate transporters. This transporter is located on the surface of cells and carries folate (vitamin B9) inside, which is essential for the synthesis of nucleic acids, especially in rapidly dividing cells such as blood‑forming cells. In this patient, we were not only able to confirm the genetic cause of his condition, but he is now also receiving targeted treatment in the form of high‑dose vitamin B9, effectively bypassing the reduced activity of the transporter.

What methods do you use for such analyses?

Each case is handled by a multidisciplinary team, ranging from clinicians to those of us in translational research. This allows us to formulate a hypothesis about how a mutation may affect a patient – from specific cellular processes all the way to manifestations at the tissue or organ level. Based on this, we prepare a comprehensive experimental plan to demonstrate whether the mutation is truly causal. We use a wide range of molecular and cell‑biology methods. Even so, it can happen that we initially head in the wrong direction. On one occasion, we modelled a mutation and tested our hypothesis, but for a long time nothing was working. Meanwhile, the patient’s condition changed and new symptoms emerged that no longer fit the original hypothesis. Our colleagues therefore reanalysed his DNA, and in the end we discovered that a different mutation was responsible.

Like a real-life Dr. House?

A very frustrated Dr. House. We spent three years on the case.

 

 

Can such data be used for other patients?

In studies where the cause cannot be identified, the contribution is more along the lines of “this is not the right direction”. But in successful projects, some may argue that it is a lot of work for just one or a few patients. However, the value is significant. If you discover a new genetic disease, it is entered into databases such as OMIM (Online Mendelian Inheritance in Man) or ClinVar. These databases record that mutations in a given gene may be responsible for a specific condition. If, anywhere in the world, a patient with similar symptoms later appears and is referred to the appropriate specialist, that specialist will certainly consult these resources.

If the patient has the same mutation, the diagnosis is essentially made. If the mutation occurs in a different part of the gene, it is then necessary to determine whether it affects the protein’s structure or function — but this process is already easier, as the area of interest has been narrowed down. So every such publication, even if it is based on a single patient, contributes to our ability to decipher the genetic basis of diseases on a global scale.

 

 

In this context, people often speak of a genomic era in medicine, in which the causes of disease are revealed at the level of individual genes. Is this era still ongoing? 

I would say that it is, at least in part, because we still do not know the function or significance of many regions of our DNA. But we can also view the present as the beginning of a new era – the era of gene editing. Not only are we now able to identify the causes of genetic diseases, but we also know how to correct them. And it’s not only about repairing mutations; we can introduce a wide range of changes into the DNA of cells to achieve a therapeutic effect – for example, switching a gene off. This truly is the future of medicine, without a doubt. Gene editing can be applied to genetically determined diseases, but also, for instance, to oncological conditions or infectious diseases. Suddenly we have a tool that can change the genetic code of our cells and move personalised medicine to the next level. It is no longer science fiction – it is reality.

 

 

Could you mention some important milestones in gene editing?

From a clinical standpoint, one of the greatest milestones is undoubtedly the approval of the first gene‑editing‑based treatment in 2023. This is the medicine Casgevy, which uses the CRISPR‑Cas method (more on the method in the box below, editor’s note) to edit human haematopoietic cells for the treatment of sickle‑cell disease and β‑thalassaemia – conditions that affect millions of people worldwide. These diseases are caused by errors in the gene encoding a component of haemoglobin. However, this therapy does not repair the mutation in the strict sense of the word. Instead, the need for precise correction is elegantly bypassed: the therapeutic effect is achieved by switching off a specific regulatory gene, which is technically more straightforward.

Something entirely different, however, is last year’s study based on the case of an infant with carbamoyl phosphate synthetase 1 (CPS1) deficiency, in whom a precise repair of the causal mutation was carried out directly in vivo. This represents another major milestone – and not only for our field. Nature even listed the boy among the ten most influential people who shaped science in 2025.

 

 

This case is often described as an example of personalised medicine. But developing a treatment for a single patient must be extremely expensive, right? Of course, as a parent, I would want my child to have such a chance at treatment.

The study demonstrated a remarkable scientific success, but it also highlighted the limitations that currently prevent similar therapies from reaching more patients. One of the biggest obstacles is the financial aspect. Even though the treatment for this boy was developed, tested and approved in the unbelievably short timeframe of six months, the financial demands of developing such therapies are extremely high – largely because they are created entirely for a single individual. The treatment for “baby KJ” will, in all likelihood, never be used again, and that presents a significant challenge.

 

 

Companies that invest huge sums in drug development need to recoup their costs.

Exactly – and that is not realistic within the current system for developing and approving medicines, which is primarily designed for drugs intended for large patient populations. One possible solution would be to divide the entire process into individual steps, or modules, most of which could be identical for patients with different mutations or even different diseases – and these could therefore be approved and prepared in advance. Personalisation would then apply only to a single, specific part of the editing tool that targets the patient’s precise mutation. This should dramatically reduce both the development time and the cost of treatment.

 

 

Going back to the very beginning, discussions about gene editing often mention boundaries that must not be crossed — that scientists are “playing God”. Have you ever encountered such reactions?

We are embarking on something that was long considered taboo – we interfere with DNA and change it. That is now a reality. But I don’t think we are playing God. I have respect for the technology itself and for ensuring that it is used appropriately. There are many other methods, technologies and physical phenomena that benefit humanity but can also be misused. It is up to us how we choose to use them. Take ionising radiation, for example: it helps patients with cancer, but in the case of a nuclear bomb it becomes a catastrophe for humanity. Is that a reason not to irradiate patients? I don’t think so. Gene editing must be approached with respect and responsibility – but without unnecessary demonisation.

 

 

It begs the question: where is your no‑go line?

Editing human embryos, definitely. First and foremost because I am aware of the technical limitations of current editing technologies. And although these tools are developing rapidly and improving at an extraordinary pace, they will probably always retain a certain – albeit minimal – error rate.

Is gene editing different in adults compared to embryos?

Yes, fundamentally. When editing somatic cells – whether in a child or an adult — you are not affecting the genomes of future generations. However, when you modify germ cells or the embryo itself, the changes are passed on to the patient’s descendants, their children, and so on. And that is a “no‑go zone” for me, both from a technical and ethical standpoint. For example, the negative impact of certain changes in DNA may only become apparent later in the patient’s life – but by then it is too late, because the modification has already been transmitted to the next generation. And that is a responsibility that, in my view, humanity should not take on.

Nevertheless, there are studies that show progress in this direction. What is your view on them?

From a technical standpoint, they are fascinating in their own way. For example, the study demonstrating the ability to eliminate a specific chromosome using CRISPR‑Cas as a potential future treatment for patients with Down syndrome is technically remarkable. However, for the reasons mentioned above, I do not yet see any real clinical application for such approaches.

 

 

The most famous case is that of the so‑called “CRISPR babies”. Could you explain a little more about it?

In 2018, the Chinese scientist He Jiankui edited human embryos using the CRISPR‑Cas method, resulting in the birth of at least three children who became known as the “CRISPR babies”. His aim was to switch off the CCR5 gene, which enables the HIV virus to enter cells. He claimed he wanted to create individuals resistant to HIV. However, the entire experiment was indefensible from both a medical and an ethical standpoint.

How did the scientific community react?

Very negatively. It was widely seen as crossing a boundary that should not have been crossed – and certainly not with the technologies available at the time. It later became clear that, due to the imprecision of CRISPR‑Cas, the CCR5 gene had not been completely switched off on some alleles. There were also extensive discussions about the potential consequences of lacking the CCR5 gene on other functions of the human body. At this point, we do not know what will happen to these children; we will simply have to wait and see. He Jiankui ultimately spent three years in prison for the experiment, but as far as I am aware, he has since returned to scientific work.

So there is consensus among experts, but what about lay people – or when you teach students about the method? How do they react?

I haven’t yet encountered anyone who reacted in a strongly negative way. I sometimes ask my students whether they would allow the DNA of their embryos to be edited if it could eliminate a genetic disease in their future children. Most are against it, but I do see some hands raised in favour.

 

 

CRISPR‑Cas9 is no longer the only method available today. Are there others, perhaps even more advanced ones?

There are now many methods available. From a clinical perspective, prime editing and base editing are becoming particularly prominent, as they are more precise and safer than the classical CRISPR‑Cas approach. This generation of editing tools is therefore sometimes referred to as CRISPR 2.0.

How do you use these methods in your research?

Our research also focuses on bone marrow failure syndromes, specifically the congenital forms. In these patients, we know the exact mutations that cause the disease. At present, the only definitive treatment for their haematological complications is a bone marrow transplant. However, this is highly demanding and depends on the availability of a suitable donor. Gene therapy could offer an alternative if we were able to correct the mutation in the patient’s own haematopoietic cells. Prime and base editing appear ideal for this, as they are more precise and can circumvent the problems some of these patients have with DNA repair.

Our aim, therefore, is to develop these new editing tools for specific mutations that cause bone marrow failure syndromes, and to test how effectively, accurately and safely they can repair them. Experience with the classical CRISPR‑Cas9 method has shown that only extensive practical use will reveal the limitations and characteristics that need to be refined for clinical application.

How do you see the future of the field?

Our field is marked by rapid and substantial technological progress in genome‑editing tools, and this development is set to continue. New and improved approaches are emerging all the time, and we have certainly not yet reached the limits of what is possible. From a clinical perspective, I believe that the treatment of certain genetically determined diseases using gene editing will become standard practice in the relatively near future – although the economic and regulatory barriers will need to be addressed first. As for whether we will be therapeutically editing embryos within the next decade, I do not think so. That said, our field has repeatedly shown that its progress can far exceed expectations. In any case, I will be following these advances with great interest.