For cell-based therapies to progress successfully from preclinical testing into clinical care, immuno-oncology researchers need to design tumor biology-driven cell therapies and test them on relevant preclinical models that realistically depict human tumors and their microenvironment.
Gene-editing and engineering technologies have evolved significantly over the last decade. In the present day, autologous cells from a patient can be isolated, gene edit/engineered and utilized to treat the patient from whom the cells were derived originally. Recently, reverse engineered patients' cancer cells have been shown to kill their own type, thus offering another autologous approach.
Allogeneic cell-based therapies offer an off-the-shelf approach and utilize cells from healthy donors for use in cancer patients. These include stem cells and different induced pluripotent stem cell (iPSC) derived cell types, which have been shown to home to multiple targets after simultaneously being equipped with antitumor agents and kill switches.
One pioneer in cell-based therapies for solid tumors, particularly primary and metastatic tumors in the brain, Khalid Shah, MS, PhD, Director, Center for Stem Cell Therapeutics and Imaging, BWH-Harvard Medical School, has created a research program on the vision of "creating an 'off-the-shelf' therapeutic offerings for cancer that would positively impact the quality of life of individuals affected across the globe."
Types of cell-based therapies tools for cancer
Manufacturing methods separate available cell-based therapies into two categories: allogeneic and autologous.
Allogeneic therapies, created from unrelated donor tissue samples (e.g., bone marrow, adipose fat) can be produced in large batches using Good Manufacturing Practices (GMP), which offer researchers multiple advantages (Bartel, n.d.):
- Readily available (off-the-shelf)
- Used to treat a large number of patients
- Quality controlled product
Examples of allogeneic therapies include the following:
- Engineered stem cells
- Mesenchymal stem cells (MSCs), which are derived from adult stem cells, umbilical cord, or adipose fat.
- iPSCs derived natural killer (NK) cells.
Given that glioblastoma is an unmet need and the majority of the patients have only 2-3 weeks between diagnosis and surgery, Shah said one has to be realistic in their choice of cell-based therapies, which is why he leans toward allogeneic cells. Having worked with many engineered stem cell types, Shah's lab has settled on mesenchymal and is looking at possible combinations with chimeric antigen receptor (CAR) T cells and reverse engineered cancer cells.
Autologous therapies are custom produced for an individual patient, in which tissue/cells are removed and returned to the same individual (Stuckey & Shah, 2014; Bartel, n.d.). This biologic product is often produced on-site where the patient is receiving care and requires enhanced measures to ensure the sample is returned to the correct patient (Bartel, n.d.).
Examples of autologous therapies include the following:
- Engineered cancer cells
- CAR T cell therapy
CAR T cells are still challenging in solid tumors, according to Shah, requiring researchers to consider tumor microenvironment, PD-L1/PD-1 expression, and treatment resistance. "The more we understand the biology of the tumor and the interaction of different cell types within the tumor microenvironment, the more we can overcome these challenges," said Shah.
Challenges in immunotherapeutic development
Cell-based immunotherapies offer enormous potential to transform the standard of care in cancer. Many cell therapies, however, do not progress into clinical care. Researchers may observe variable response rates (Sambi, 2019). Promising results in simple preclinical models may not be generated in more complex models (Hegde, 2020).
To overcome the most common challenges in developing cell-based therapies, Shah outlines three basic principles:
- Understand the mechanism behind the function of therapeutic gene-edited/engineered therapeutic cells.
- Develop and characterize preclinical tumor models that mimic the clinical setting of tumor growth, resection, resistance, and recurrence.
- Understand the current treatment regimen for each cancer type.
Understanding tumor biology
"The molecular mechanisms of tumors should drive cell-based therapies," said Shah. Profiling tumors reveals new targets for engineered stem cells. Shah has designed stem cell therapies for a range of antitumor agents with many targets, including the following:
- Proapoptotic proteins: Stem cells engineered to express therapeutic proteins (tumor necrosis factor-related apoptosis-inducing ligand [TRAIL]) that bind to death receptors (death receptors [DR4/5]) on tumor cells (Kavari & Shah, 2019), and a variant of this therapeutic protein, epidermal growth factor receptor (EGFR) targeted nanobody (ENb), fused to TRAIL (ENb-TRAIL), which simultaneously binds to EGFR and DR4/5, to induce apoptosis in TRAIL-resistant tumor cells (van de Water, 2012; Zhu, 2017). These cells also included an activatable safety kill switch.
- Oncolytic viruses: MSCs armed with oncolytic herpes simplex virus (oHSV) and PD-L1 blockade that increase IFNγ-producing CD8+ tumor-infiltrating T lymphocytes (Du, 2017).
- Immune therapy: Engineered MSCs, encapsulated in synthetic extracellular matrix, which secrete IFNβ, to boost the immune response from CD4/CD8 T cells, when placed in a tumor resection cavity (Choi S. H., 2017).
By targeting multiple receptors, scientists can work to overcome common obstacles such as limited efficacy from poor pharmacokinetics, therapy resistance, and the heterogeneity of tumor cells, while also helping to improve precision and efficacy (Stuckey & Shah, 2014; Kavari & Shah, 2019).
The multiple target approach
Shah's lab is building multiple bifunctional stem cell-releasing therapeutics, which target multiple receptors either on the tumor cells or in the tumor microenvironment. These include targeting DR4/5 and EGFR or CD36 receptors simultaneously.
CAR T cells can cross the blood-brain barrier and penetrate dense glioblastoma tumor tissue, but with isolated success in regressing advanced disease in clinical studies (Hughes-Parry, 2019). To address both tumor-specific EGFRvIII-positive and EGFRvIII-negative tumor cells, researchers added a second target for wild-type EGFR. To avoid harming healthy cells expressing EGFR, they added a bi-specific T cell engager or "BiTE" to create a dual-binding CAR (Choi B. D., 2019).
Better models needed to move discoveries out of the laboratory
To align the preclinical testing of gene-edited and engineered cell therapies with the complex tumor microenvironment, scientists must adopt physiologically relevant models that mimic the clinical settings.
"At present, we don't have enough preclinical tumor models that authentically replicate clinical settings," said Shah.
Traditional models do not replicate how cancer cells adapt and evolve. The tumor microenvironment is fluid, evolving — responding to therapeutic interventions and developing resistance.
For many years Shah's lab focused on treating solid primary and metastatic brain tumors. Upon resection, tumor tissue was used in patient-derived xenograft (PDX) models to study treatments for glioblastoma. In Shah's PDX models, resected tumors grew faster than the unresected ones. "When you resect the tumor, you refresh the tumor, you basically bring growth factors back in, and they grow much faster," said Shah.
Shah's laboratory has also developed different brain metastatic (i.e., breast, melanoma, and lung) models and showed that arterial injection of cell-based therapies to be the ideal platform to test these therapeutics in clinical settings.
Anticipating clinical realities
It is essential to understand the current treatment regimen for each cancer type to translate novel therapies into clinical settings. In the case of primary brain tumors, Shah has had to anticipate the impact of temozolomide on stem cells or CAR T cells. The compressed time frame between diagnosis and surgery strongly influenced Dr. Shah's decision to use allogeneic stem cells. His laboratory has extensively shown that resection removes myeloid derived suppressor cells from the core of the tumor, potentially leaving the brain derived macrophages at the edges of the tumor.
It is crucial to stratify patients to anticipate resistance and the full range of responses to immunotherapy, including toxic cytokine storm syndromes. "Every individual's immune system is going to react differently to cell-based therapies," said Shah. "Some individuals will respond well, and others will not."
Shah anticipates the field will evolve over the next five years to include immune profiling, capable of examining the impact of the microbiome on treatment response. "We will probably confirm that most of our immune system is influenced by the gut," he said.
It is this broader perspective, said Shah, that will help investigators move cell-based therapies from the bench to the bedside: "Investigators must step out of their comfort zone to anticipate the downstream challenges faced by patients, clinicians, and manufacturing."
About Khalid Shah, MS, PhD
Dr. Khalid Shah is the Vice Chair of Research for the Department of Neurosurgery at Brigham and Women's Hospital (BWH), Boston, MA, and Directs two Centers: 1) Center for Stem Cell Therapeutics and Imaging and 2) Center of Excellence in Biomedicine. He is also the Associate Professor at Harvard Medical School 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 engineering targeted stem cells and immune cells for cancer. These studies have been published in a number of high impact journals like Nature Neuroscience, PNAS, Nature Reviews Cancer, JNCI, Stem Cells, and Lancet Oncology. Even gaining attention in the public domain, Dr. Shah's stem cell work has been highlighted in the media worldwide, including features on BBC and CNN.
Recently, Dr. Shah's laboratory reverse engineered cancer cells using CRISPR/Cas9 technology and utilized them as therapeutics to treat cancer. This work was published in journal Science Translational Medicine and highlighted worldwide, including features by Scientific American, New York Times, and NPR.
Dr. Shah currently holds positions on numerous councils, advisory and editorial boards in the fields of cell therapy and oncology. To translate the exciting therapies developed in his laboratory into clinics, he has founded two biotech companies to bring engineered cell therapy into patient care.
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