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Gene editing may enhance CAR T-cell therapy for hematologic malignancies
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Researchers at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine in St. Louis have used gene editing technology known as CRISPR to engineer human T cells to attack certain cancers.
Results from studies conducted in mice have laid the groundwork for a trial in humans.
“Cancerous T cells and healthy T cells have the same CD7 protein on their surfaces,” John F. DiPersio, MD, PhD — deputy director of and Virginia E. and Sam J. Golman professor of medicine in oncology at Siteman Cancer Center at Washington University in St. Louis — said in a press release. “But if we program T cells to target CD7, they would attack the cancerous cells and each other, thus undermining this approach. To prevent this T-cell fratricide, we used CRISPR/Cas9 gene editing to remove CD7 from healthy T cells so they no longer carry the target.”
HemOnc Today spoke with DiPersio about this approach, the timeline for when trials may be conducted in humans, and when this approach — if proven effective and safe — could be adopted in clinical practice.
Question: How did this technology come about?
Answer: The technology was born from a number of different brainstorming sessions. We have talked about targeting leukemia as a focus in my lab. There is a lot of focus, interest and success in targeting B-cell leukemias and lymphomas because of the target CD19 — which is selectively expressed on B cells — and the fact that people can live without B cells. T cells — which are the effector platform of chimeric antigen receptor (CAR) T cells — do not express this B-cell antigen, so it is a ‘perfect storm’ for targeting B-cell cancers. We are trying to figure out how to extend this technology beyond the B-cell malignancies and target other cancers. Nearly one-third of all leukemias and lymphomas are derived from T cells. These T-cell lymphomas are difficult to treat and no effective targeted therapies are available. One of the impediments is trying to figure out how to use a T cell to target a T-cell malignancy where all of the potential surface targets are also expressed on normal mature effector T cells. People have tried to do this but have failed because of fratricide, which is when the CAR T cells kill themselves because they target antigens that are expressed on both malignant T cells and the CAR T themselves. The second major problem is that, in order for one to successfully target B-cell leukemias and lymphomas, malignant B cells have to be separated from normal T cells. This is quite easy to do because they are phenotypically different and, thus, T cells can be pulled out without contamination with malignant B cells. As for T-cell malignancies, mature T cells and malignant T cells appear similar or identical; thus, there is no way to easily separate the two populations and genetically manipulate normal T cells without significant contamination with malignant cells. These are two huge impediments and suggested to us that both may be overcome by using a combination of gene editing and gene therapy. We knew that gene editing as a science was getting better and more efficient using various nuclease platforms. So, what if we gene edited a mature T cell so that the target we are going after on malignant T cells was present only on the malignant T cells and not on CAR T? This would allow us to effectively and selectively target the malignant T cells without risk of CAR T fratricide.
Q: How does this process work?
A: We first identify an overexpressed surface target — CD7 initially — on malignant T cells and then use CRISPR/Cas9 gene editing to delete target gene CD7 in normal T cells. We are then able to use these CD7 gene-edited T cells as a source for the insertion of a CD7 CAR using lentiviral gene transfer. These CAR T would be resistant to fratricide and target CD7 on malignant T cells. However, we still have the issue of contamination of the normal T cells with malignant T cells. If we also gene-edit or delete CD7 in any contaminating malignant T cells, then we would render these contaminating malignant T cells resistant to our CD7 CAR T therapy, thus undermining our general approach for curative therapy. To get around this second major obstacle, we thought that if we could gene-edit these T cells not only to delete the target gene we are going after — CD7 — but also one of the genes in T cells responsible for allogeneic or ‘non-self’ recognition (T-cell receptor/CD3), this would allow us to use ‘off-the-shelf’ third-party T cells from normal donors, thus eliminating any chance of malignant cell contamination and, when infused into an unrelated donor, any chance of graft-versus-host disease. We developed high-efficiency multiplex gene editing of T cells to delete target CD7, which is highly overexpressed in all T-cell malignancies and one of the subunits of the T-cell receptor, which is critical for assembly of entire T-cell receptor complex on the surface of the T cell. With these genetic modifications we now have ‘off-the-shelf’ T cells from a third party that can use these to treat any person at any time and can be made and stored ahead of time.
Q: Where will you and colleagues go from here in terms of scaling up manufacturing of gene-edited CAR T cells for clinical trials?
A: We are doing this now. For gene therapy-related studies, we are stuck in a quandary. There is no number of grants that one can get from NIH to support this transition from preclinical and discovery-based research to the clinic. We have made an important discovery and we have developed a way of overcoming major obstacles to treat T-cell cancers, but the truth is we cannot get enough NIH funds and grants to do anything more than to further advance the preclinical research. This cannot easily be transitioned into the clinic without institutional support, and institutions do not generally have the money to support the clinical development of genetically modified T cells. Philanthropic donors are needed for us to make the transition from the preclinical setting to the clinic. This is where we are right now. Finally, we hope that — if effective — this will be commercialized by a private biotech.
Q: What is the timeline for when trials with humans may take place?
A : I have been contacted by a number of patients already who are in desperate situations with relapsed T-cell acute lymphoblastic leukemia and want to come to Washington University to get treated. I have had to explain to them that we have only performed preclinical studies, but that we plan to scale up and actually make a product for patients to be treated. This whole process, even at lightning speed, will take probably 18 months to 3 years. – by Jennifer Southall
Reference:
Cooper ML, et al. Leukemia. 2018;doi:10.1038/s41375-018-0065-5.
For more information:
John F. DiPersio, MD, PhD, can be reached at jdipersi@wustl.edu.
Disclosure: DiPersio reports no relevant financial disclosures.