Editor's note: In this installment of Expert Opinion, Benjamin Demoulin, PhD, Director of Cell Therapy Innovation at Cellistic, answers questions about using iPSCs in NK cell therapy development

NKs are increasingly being explored as cell therapy treatments because of their promising safety and efficacy profile. However, autologous NK treatments also have some limitations. How do you see this, and do you feel like allogeneic NK therapies are able to overcome these issues?

NK cells were first tested against cancer in the 1980’s in the form of lymphokine-activated killer cells1. Since that time, ongoing research into NK biology has improved and NK cells are generally regarded as non-toxic and safe to use in stand-alone therapies. Although the feasibility and safety of NK cell therapy has been established, there are some limitations, among which are ‘self’ recognition by inhibitory killer immunoglobulin-like (KIR) receptors on infused NK cells, blocking activation and reduction of overall anti-cancer activity, or persistence upon injections. Arming your NKs with CARs helps overcome this activation limit. CAR-NKs have been used to target a wide range of hematological malignancies and solid tumors in pre-clinical studies2, and can be generated as an “off-the-shelf”, allogeneic therapy.

An additional concern is the extensive treatment regimen patients receive prior to NK cell collection and therapy, which can impair cell expansion and function after infusion. This is a common issue with autologous cell therapies: because cell therapy is used as a final treatment option, patients receive multiple lines of chemotherapy before the hospital collects their cells for autologous therapy production. These cells are basically poisoned by the chemotherapy, causing cell exhaustion, inactivity and possible cell death. With allogeneic cell therapy, you use healthy donor cells as starting material, eliminating this risk. Of course, there is immunological consideration to avoid cell rejection. Through genome editing or creating HLA homozygous donor banks, you can help ensure that doesn’t happen.

Within the NK trend, so to speak, allogeneic cell therapies seem to be on the rise, but there are some challenges to overcome. In your opinion, what is needed for allogeneic NK cell therapy to become a reality? 

This is very true. I fully believe in the allogeneic approach being the future of cell therapies in general, and more specifically, for NK cell therapy. NKs are considered safer than CAR-T, because they do not trigger GvHD. However, there are some other challenges to address. Right now, there is a lack of proven efficacy data that allogeneic NKs are equivalent to the status quo (autologous NK therapy). There is also a lack of longer-term efficacy data for allogeneic therapies in general. Filling those data gaps is only a matter of time, given the vast amount of research that is currently being done and is really exciting.

Another challenge to make allogeneic NK cell therapy a success is scalability. It is key to start thinking about scaling up very early in the cell therapy development process, for example when choosing your starting material. Donor cells can either be mature cells, or cells in a multipotent or pluripotent state. With the risk of sounding biased, for me, the latter is the obvious choice. At Cellistic, we work exclusively with human induced pluripotent stem cells (iPSC), because of their ability to solve the scalability issue. For NK cell therapy, therapeutic doses are calculated around 5x106 per kg of body weight. This requires a vast amount of dosing material and a robust and expandable starting material. When handled with the required expertise, iPSCs have the advantage of proliferating indefinitely. Then, when the differentiation process starts, the cells expand even further while differentiating to the target mature cells. These differentiation expansion multiples can reach between 1000 to 2,500-fold expansions for NK and up to 100,000 fold-expansions for T cells, numbers that could never be achieved when using primary cells. Adding the expansion that can be achieved at the iPSC stage, in theory, adds up to an infinite supply of mature cells. 

That’s huge! Apart from scalability, are there any other benefits to using iPSCs as starting material for allogeneic NK cell therapies?

Honestly, there are many reasons for choosing human iPSCs as your starting material for allogeneic cell therapy. Apart from the scalability advantage, which for me would already be enough reason, let me zoom in on another key benefit, concerning gene editing. When using iPSCs, gene edits only need to be done once in the process, at the iPSC stage. After performing your gene edits, you select the perfect clone that bears the exact gene edits required, without any off-target integrations or karyotype instabilities, and use it for amplification. This is a huge advantage compared to current strategies that are generally using expensive GMP viral vectors, which integrate randomly in the genome of only a part of the target cells. After expansion, the iPSC population uniformly contains these exact same gene edits, providing a continuous supply of genetically identical cells as starting material and offering opportunities for product standardization and process robustness. 

What is your advice for therapeutic developers working on NK cell therapy? 

In short: come and meet us! There are so many exciting new things to explore and develop together.
-Laughing- I know that’s too easy, coming from me. But in all honesty: I’ve truly been amazed by the work that the scientific team is doing and the developments they are reporting. We’re currently developing know-how in iPSC-based NK cell differentiation and the team has solved several technical issues, with some solutions that I believe are new to the field. Working with Cellistic actually means using that know-how to speed up your cell therapy development. You bring the required gene edits, and we bring the rest: iPSC development, differentiation, fine-tuning and GMP production. 

More generally speaking, my best advice is to put the best team together to make your therapeutic development a success. Whether it is an in-house team, or you decide to work with a partner, make sure you have the resources required for each step of your development process. 




[1] West EJ, Scott KJ, Jennings VA, Melcher AA. Immune activation by combination human lymphokine-activated killer and dendritic cell therapy. Br J Cancer 2011;105(6):787–95 doi 10.1038/bjc.2011.290
[2] Liu, S., Galat, V., Galat4, Y. et al. NK cell-based cancer immunotherapy: from basic biology to clinical development. J Hematol Oncol 14, 7 (2021). https://doi.org/10.1186/s13045-020-01014-w