Khalid Shah, MS, PhD, director of the Center for Stem Cell Therapies and Imaging, Harvard Medical School, and vice chair of research, Brigham and Women’s Hospital, talks to contributing editor Tanuja Koppal, PhD, about recent innovations in cell engineering and editing, which has in turn led to advances in cell therapy. Dr. Shah talks about the work that he is doing in this area, while highlighting some practical considerations when it comes to translational research and technology investments.
Q: How do you define cell therapy, and what are some of the advances in cell engineering that have made cell therapy promising?
A: Cell therapy involves taking a normal cell, modifying or engineering it, and putting it into a patient to treat the disease. The type of cell therapy depends on where the cell comes from. In some cases, the patient’s own cells can be extracted, modified, and delivered back into the body to generate the desired effect, which is referred to as autologous cell therapy. However, in some cases the time from disease diagnosis to starting the treatment is very short, and cell therapy, which often takes three to six months to put in place, is not an option. In such cases, cells available off the shelf from a donor that have been previously engineered are used; this is referred to as allogeneic cell therapy. Cell therapy needs to be defined in the context of the disease. For diseases that are not life-threatening, autologous cell therapy should be preferred; whereas in diseases like cancer, where time is of the essence, allogeneic approaches need to be considered for finding the right treatment option.
Cells that are commonly used for cell therapy include stem cells, lymphocytes, dendritic cells, and pancreatic islet cells, and they have been used to treat cancer and autoimmune diseases, to repair joints or a weakened immune system, and for CNS (central nervous system) disorders. Chimeric antigen receptor (CAR) T cell therapy uses a patient’s own (autologous) immune cells (T cells) that are engineered to express a receptor that recognizes and binds to an antigen on the malignant cell. Once activated, these T cells can then destroy the malignant cell. Recently, there has been a shift from CAR T cells to natural killer (NK) cell therapy, as NK cells can be transferred from one healthy individual to a patient (allogeneic) without the risk of an immune reaction, as there is no haploidization in these cells. Another alternative is to use induced pluripotent stem cells (iPSC) from the patient to derive the T cells or NK cells and minimize the risk for immune rejection.
Q: Can you highlight some of the practical considerations for cell selection, growth, gene editing, and delivery of vectors that readers will find useful?
A: Some of the key questions that need to be answered for selecting the right cell therapy begin with identifying the disease that is being treated and finding out what’s being done currently to treat this disease. Any new therapy that is introduced will have to be tailored to the current standard of care. Once those questions are answered, a correct model that mimics the disease has to be established in order to test the new therapy in a specific setting. It is essential to understand the underlying biology behind the disease in order to develop mechanism-based cell therapies for that disease type. For example, very often tumor cells are heterogenous and therefore resistant to one type of therapeutic that is released from an engineered cell. This demands changing the therapeutic or developing cells that have multiple targets on the surface of the tumor cell or tumorassociated endothelial cell.
Once the biology is well understood and the disease model is established, the ultimate source of the cell has to be determined. Will it come from the patient (autologous) or will it come from a healthy donor (allogeneic)? How are the cells going to be grown, engineered, and delivered into the patient? Engineering the cells is a complex process, and there will be many questions related to whether we are going to transfect the cells with lentivirus or AAV (adeno-associated virus) vectors? How are we going to get the gene or the CAR T to a specific locus within the cell? For clustered regularly interspaced short palindromic (CRISPR)-based editing, questions on how to design the guide RNA (gRNA) or deliver the CRISPR-associated (Cas) protein, will need to be answered.
Q: How have you approached these questions in your lab in terms of developing new cell therapies?
A: In our experience, we have found that iPSC and mesenchymal cells are much easier to modify and edit than T cells and NK cells. We typically start out by testing the cell therapy in mouse models. We use dual imaging to image different cell populations, such as the tumor cell and stem cell, or CAR T cell homing, which uses fluorescence and bioluminescence markers. Incorporation of these imaging markers in vivo using genetic engineering leads to real-time information and leaves very little room for doubt when interpreting results. I recommend that real-time in vivo imaging markers be used from the very beginning to figure out what is happening inside the cell in real time. Are the cells still alive? Is the drug reaching its target? How are the cells responding to the therapy? These are all questions that need to be addressed, even before developing a therapeutic. Manufacturing and good manufacturing practice considerations need to be addressed further downstream.
We are focusing on three main things. First, we are developing cell-based therapies that are targeted toward certain receptors on the surface or within the cell. The fundamental questions related to how our cell surface receptor targeted therapeutic cells kill the tumor cell in a mechanism-based way or how the tumor cells develop resistance to the cell therapy always need to be answered. As the expression of a variety of cell surface receptors in different tumor types varies, we focus on developing cell-based therapies for a specific type of tumor by first understanding its mechanism of action; and once we have validated it extensively in a particular tumor type, then we can potentially use it for other tumor types, if applicable. Developing and exploring stem cell, T cell, or NK cell therapy without prior knowledge of the disease or the mechanism by which cell-based therapies work in such disease models is not going to go a long way.
Second, we are engineering cells to express ligands, antagonists, and antibodies or release oncolytic viruses by understanding which receptor(s) they are targeting. In general, we tend to utilize therapeutics that have the ability to target both cell proliferation and cell death pathways in tumor cells and tumor-associated cells in the microenvironment, which is also quite unique. We are creating molecules that can target cell surface receptors that are specifically expressed on tumor cells. Third, even if we have the right therapy, but it is not tested in the right disease model that can mimic what’s happening to the patient in the clinic, it won’t work. Hence, we are developing mouse tumor models that are key to this translation and are also utilizing imaging techniques that can be used as markers during this process.
Khalid Shah, MS, PhD, is the director of the Center for Stem Cell Therapeutics and Imaging at Harvard Medical School and the Center of Excellence in Biomedicine at Brigham and Women’s Hospital (BWH). He is also the vice chair of research for the Department of Neurosurgery at BWH and a principal faculty at Harvard Stem Cell Institute in Boston. Dr. Shah and his team have pioneered major developments in the cell therapy field, successfully developing experimental models to understand basic cancer biology and therapeutic cells for cancer. Recently, Dr. Shah’s laboratory has reverse engineered cancer cells using CRISPR/Cas9 technology and utilized them as therapeutics to treat cancer. He has founded two biotech companies, AMASA Therapeutics and ALIM Therapeutics, whose main objective is the clinical translation of therapeutic stem cells in cancer patients.