Chimeric antigen receptor (CAR) T cells benefit patients with treatment resistant B-cell leukemia, B-cell lymphoma and multiple myeloma, raising hopes that CAR T cells could be used to treat “solid” cancers, including breast cancer, lung cancer, pancreatic cancer, brain cancer, and sarcomas. Studies show that CAR T cells can work against solid cancers in mouse models, but they also reveal challenges that must be overcome for treating human patients. 

One major challenge relates to the fact that the protein targets that CAR T cells recognize in leukemia/lymphoma/myeloma are not expressed on vital normal tissues, whereas CAR T-cell targets for solid cancers are generally expressed on vital tissues as well, albeit at lower levels. Therefore, CAR T cells targeting solid cancers pose greater risk to harming normal tissue.

A related challenge relates to greater suppression and evasion of immune responses by solid cancers, which requires more potent CAR T cells. These competing issues (“increased risk for toxicity combined with a need for greater potency”) have led to limited progress for solid tumors.

The Mackall lab recently developed a new CAR T-cell platform that both increases potency AND increases safety. 

SNIP-CARs allow “remote control” of CAR T cells using a drug administered as a pill. SNIP-CARs contain a molecule (called a protease) that continuously “snips” the CAR molecule in half, preventing its function unless a drug is present to inhibit the “snipping protease.” Drugs that inhibit the protease are FDA-approved and well-tolerated. SNIP-CARs are “OFF” at baseline but are able to be activated (they still require the tumor target to be activated) in the presence of the drug.

In mouse models where standard CAR T cells killed the animals due to toxicity, stopping the drug after the animals became ill allowed complete recovery. Surprisingly, in settings where toxicity was not an issue, SNIP-CARs plus daily dosing of the drug resulted in greater tumor control than seen with standard CAR T cells. This is due to the variations in drug levels by drug metabolism, which provided the CAR T cells with periods of activation followed by periods of “rest.” Finally, in situations where tumor and normal vital tissue shared the target and standard CAR T cells killed the animals, a lower dose of the drug allowed the SNIP-CAR T cells to attack the tumor but ignore the normal tissue. 

This proposal generates the necessary processes, procedures and materials needed to test SNIP-CARs in patients with solid cancers whose solid cancers are not effectively treated with standard therapies. The proposal will amplify ACGT investment by leveraging substantial infrastructure in place at Stanford University to greatly accelerate clinical testing of a cutting-edge cancer gene therapy platform for patients with critical unmet need.

Glioblastoma (GBM) is a highly malignant brain cancer that cannot be cured with surgery, radiation and chemotherapy. Survival of patients afflicted with this cancer is less than 15 months. Several clinical trials have failed to improve this survival. Even immunotherapy that has seen success for several cancers has not been effective in GBM.

Oncolytic viruses are laboratory engineered versions of viruses designed to specifically attack tumor cells, like GBM. This causes GBM cell death but also sets up a “vaccine-like” response, allowing for the immune system to further attack and hopefully destroy the GBM.

Dr. Chiocca has been involved in clinical trials of oncolytic viruses for GBM and has completed a 51-patient clinical trial in GBM using an oncolytic virus based on herpes simplex virus 1 (HSV). Using experience and knowledge from this trial, he proposes to bring a “next-generation” oncolytic HSV to the clinic. This “next generation” oncolytic virus was designed to increase the ability of the virus to grow in and destroy GBM cells while also remaining safe in normal tissues. To get this new oncolytic virus to the clinic to treat human patients, Dr. Chiocca needs to perform studies requested by the FDA to show that the clinical lots can be grown and have met predefined quality metrics, and that this new oncolytic HSV possesses a safety profile in mice that allows dosing in human patients. These studies, which will be funded through a grant from ACGT, will allow Dr. Chiocca to file an Investigational New Drug application to the FDA that will permit him to start this new clinical trial.

Glioblastoma is the most common and aggressive type of primary brain tumor. Despite therapeutic advances over the past decade, the diagnosis of glioblastoma is associated with a median overall survival time of 15-18 months and a 5-year survival rate of less than 5%. Even if treatment with the current standard of care for glioma patients, which consists of surgery, temozolomide, and radiotherapy, is initially successful, nearly all malignant gliomas eventually recur. At the moment of recurrence, no treatment successfully cures the disease. 

Naturally occurring or genetically modified viruses that selectively kill cancer cells are called oncolytic viruses. 

In our laboratory, we have developed a platform of oncolytic viruses termed Delta-24. A new generation of this cancer-selective oncolytic adenovirus model, Delta-24-RGD, has arrived in the clinical arena and has been tested in patients with recurrent glioblastoma showing encouraging safety and efficacy results. Thus, 20% of patients treated with Delta-24-RGD as a single treatment survived more than 3 years after a single dose of this biological agent. Unfortunately, rapid clearance of the virus by the immune system prevents a response in a higher percentage of patients. In addition to other pre-clinical and clinical evidence, data from our clinical trial demonstrate that to improve the percentage of patients that respond to the therapy, we need to decrease the immune response against the virus, which in turn will increase the immune response against the tumor. 

Therefore, this proposal aims to improve the response to virotherapy by attenuating the immune response against oncolytic adenovirus, with the goal of boosting the anti-tumor efficacy of this strategy. To this end, we propose two different strategies that can eventually be combined in a clinical trial. The first approach consists of making the virus less detectable by the immune system via substituting the most immunogenic viral protein with another viral protein for which the patients have not developed a pre-existing immune response. This new virus will persist longer in the tumor environment and thus maintain the window of opportunity to develop an anti-tumor immune response for a more prolonged time. 

Our second approach involves the generation of tolerogenicity for the virus. To achieve this objective, we will target dendritic cells, which are in charge of the antigen presentation to the immune effector cells, using nano molecules to deliver viral antigens. 

This strategy will diminish the response of the immune system against viral antigens, allowing the immune defenses to be focused on the tumor. If this highly innovative project is successful, we have the resources and infrastructure already in place to further translate these two strategies, as single approaches or in combination, to treat malignant brain tumors in the clinical scenario. 

Children with diffuse midline gliomas (DMGs) – a type of brain cancer – continue to have a dismal prognosis, and most children die within one year of diagnosis. Recent studies have shown that the majority of these tumors carry a specific mutation referred to as H3.3K27M. Researchers have shown that this specific mutation is present in almost all DMG tumor cells but not in normal cells within the body, making this an attractive target for immunotherapy approaches that activate an immune response against the cancer cells. Immunotherapy has shown phenomenal improvements in the outcome of adults and children with specific types of cancers, such as melanoma and leukemia. However, we are just starting to implement such novel and promising approaches for DMGs in the clinic.

With this proposal, we will test the benefit of a specific immunotherapy approach referred to as adoptive T-cell transfer, which gives the patient a large number of killer T cells. More specifically, we will test an approach known as engineered T-cell receptor (TCR) therapy, in which killer T cells are engineered to be specific to a piece of protein on the surface of tumor cells.

We have been able to show in the laboratory that we can make T cells specifically recognizing DMG cells with the H3.3K27M – and that these specific T cells can kill tumor cells. Based on these exciting data, we propose to test this new therapy approach in the clinic. Participants who are newly diagnosed with an H3.3K27M DMG are eligible for this clinical trial. They will undergo collection of their own T cells, and these T cells will subsequently be engineered in the laboratory to recognize the specific H3.3K27M mutation. These modified T cells will then be given back to the participants once they have completed standard-of-care radiation therapy and a conditioning short chemotherapy course. We hypothesize that these modified T cells will now be able to kill the cancer cells carrying the specific H3.3K27M mutation.

Within this project, we will assess if such a therapy approach is feasible and safe. Precisely, we will test how many of these specifically modified T cells are able to be given back to participants without causing too many side effects. Further, we will perform specific tests from blood samples from trial participants to assess how long these modified T cells survive. To better understand responses, we will use advanced molecular technologies to assess the blood of participants. This information will help us to improve our ability to assign patients to the right therapies and make even more effective tumor-targeting T cells in the future.

This project has the potential to significantly impact the treatment approach for a disease for which we have not achieved any improvement for the last several decades and is the first of its kind for this devastating disease.