Cancer immunotherapy is revolutionizing the treatment of many cancers. This revolution is being led by drugs that enhance the immune system’s T cell’s ability to kill cancer cells. This includes drugs such as Keytruda, an antibody that blocks a molecule called PD1 on T cells, and Kymriah, a living drug which is a product of using gene therapy to engineer a patient’s own T cells to better attack their cancer cells. Despite the amazing successes in some patients, unfortunately, not all patients respond to current immunotherapies.
One of the cell types that appears to be responsible for the failure is a cell type called a macrophage. Macrophages are part of the immune system and have a function in protecting us from infections. However, tumors can reprogram macrophages to suppress other cells of the immune system, which benefits the tumor by preventing killer immune cells from entering the tumor and killing the cancer cells. Considerable evidence indicates that eliminating the macrophages of a tumor could improve patient outcomes and response to treatments, but traditional pharmacological approaches for doing this have not shown clinical benefit.
To overcome the limitations of traditional drugs, we will harness the power of gene therapy and develop a new type of living drug in which we would gene engineer a patient’s own T cells to kill the immune suppressing macrophages in their tumors. This would eliminate a major barrier to immunotherapy treatment and help the patient’s immune system to eliminate cancer cells. This novel strategy will draw on the considerable advances in the gene therapy field that led to the development of Kymriah, and other drugs based on the use of chimeric antigen receptor (CAR).
We will develop a CAR that specifically kills macrophages in a tumor, while sparing macrophages in healthy tissue. We will test our strategy in preclinical animal models of lung and breast cancer to determine if our tumor macrophage killing CAR can lead to the elimination of aggressive tumors. We will also evaluate further refinements to the therapy to make these CAR even more potent at helping the immune system permanently eliminate different cancer. This project will lead to the development of a new gene and cell immunotherapy with the potential to treat a wide variety of cancers and help a patient’s own immune system end their cancer.
This Alliance for Cancer Gene Therapy Research Fellow is funded in part by Swim Across America.
We propose to test if protein transduction technology can improve the efficacy of adenoviral gene-therapy vectors for the treatment of cancer. In cell culture experiments, cancer cells can easily be eliminated with cancer targeted adenoviral gene-therapy vectors. However, in mice and humans, inefficient gene transfer remains a hurdle that has been extremely difficult to overcome. A p53-expressing adenoviral vector is in clinical use in China and has been placed on the fast track for FDA approval.
Published data indicate an extremely favorable safety profile, but overall, the therapeutic effect has been limited. Clearly, gene-transfer efficacy of adenoviral vectors has to be improved for more efficient therapy. The basic domain of HIV-1 Tat (a section of a protein made by the HIV virus, also called the protein transduction domain) can enter intact cells and has been used to deliver a wide variety of proteins to many cell types. Tat-fusion proteins, produced in bacteria, purified and then applied to cells, have been studied widely to manipulate cancer biology.
This approach is effective in cell culture experiments, but so far there is only limited evidence for efficacy in mouse tumor models. Very few studies have investigated the potential of the delivery of Tat-fusion proteins with gene therapy vectors. We hypothesize that Tat-fusion peptides expressed at high levels with an adenovirus will result in more effective treatment of solid tumors.
Furthermore, we hypothesize that smaller unfolded peptides fused to Tat will lead to more efficient distribution within tumors, compared to complexly folded large proteins. The delivery of peptides fused to a protein transduction domain with adenoviral vectors is a new approach that could find broad application.
The prevailing view suggests that lung tumors may not be good targets for vaccine therapy. The reason for this belief is the fact that in lung tumor patients we do not find any indication of immune activation including a complete absence of killer cells (cytotoxic T cells) that could recognize and kill the tumors. Lung tumors are therefore classified as non-immunogenic. We suggest that this circumstance is ideal for immunotherapy of non-small cell lung carcinoma by vaccination.
We have been developing vaccines that can generate killer cells against lung tumors (non-small cell lung carcinoma) by genetic engineering lung tumor cell lines adapted to grow in cell culture. We predict that a vaccine that can generate killer cells in lung tumor patients will be effective and that the patient tumor will be defenseless against killer cell attack because the tumor cells have never before been exposed to killer cells and have not evolved protective mechanisms.
In a phase I study we found that a lung tumor vaccine, designated B7-vaccine, was able to generate killer cells and seemed to provide clinical benefit to patients. In the study proposed here we have developed a novel vaccine approach for lung tumors based on a genetically modified, secreted form of heat shock protein gp96. The vaccine is comprised of lung tumor cells that secrete hsp-gp96 and thereby provide a very strong stimulus for the immune system to generate killer cells against lung tumors.
Our initial in vitro data and data in experimental mice indicate that the gp96-vaccine is over one million-fold more efficient in the generation of killer cells than normal proteins in the absence of gp96. These properties of tumor secreted gp96 make it an ideal vaccine. In addition, these properties allow us to study how gp96 induces immunity and how it may be able to restore immunity that is suppressed in the presence of existing tumors.
In this application we plan to pursue the clinical testing of the gp96-vaccine and to conduct further research into the underlying immune response. Understanding the underlying mechanisms will allow us to develop further reagents to improve vaccine efficiency.
Lung cancer remains one of the greatest public health threats, despite advancement in the understanding of molecular genetics. We have been accumulating preliminary data and developing reagents for this project for the past two years, and we are encouraged by the early results of using PUMA, a protein, as a novel target to selectively encourage apoptosis, cell death, in lung cancer cells. With this funding, we will be able to expand the research into animal model trials, and it is our hope that these efforts will allow us to examine the feasibility of moving PUMA gene therapy towards clinical trials.