Gene Therapy and Immunotherapy

FAS LIGAND GENE-BASED IMMUNOTHERAPY FOR CANINE OSTEOSARCOMA STUDY IS NOW OPEN FOR PATIENT ENROLLMENT THROUGH COLORADO STATE UNIVERSITY. FOR INFORMATION, CLICK HERE

In the area of cancer immunotherapy, we have developed a number of models that allow us to test the feasibility of using the immune system to fight cancer. We recently showed that gene therapy could be used safely and had potential to increase disease-free survival or remission times in naturally occurring melanoma of pet dogs. (see, Bianco et al, Cancer Gene Ther. 2003) (see Figure 1). This is the first step to develop new treatments that will help not only dogs, but also people with malignant melanoma. However, even these treatments seem to produce uneven results, helping some patients but not others. Therefore, in collaboration with Dr. Don Bellgrau of the Department of Immunology and the Cancer Center at the University of Colorado Health Sciences Center, we decided to investigate what is unique about the T lymphocytes that are able to respond to and kill tumors. Using laboratory models of lung cancer and melanoma, we have shown that we can generate protective immune responses that prevent or delay tumor growth. (see, Modiano et al, Clin Immunol. 2004) We are currently working to characterize the unique biochemical features of these cells, so we can then improve our ability to design therapies that target and activate these tumor specific cells. In particular, our results show that ectopic expression of FasL leads to inflammation and tumor cell apoptosis that generates protective antitumor T cell responses (see Figure 2). Ongoing experiments are aimed at optimizing strategies to translate this therapy to cancer-bearing patients.

We also have studied mechanisms that influence the immune response to tumors. A major obstacle of cancer immunotherapy is the fact that tumor cells are recognized as “self” by cells of the immune system. Various mechanisms contribute to maintain tolerance to self. In the periphery, cells receive MHC signals that support survival and can promote activation. Hence, this potentially dangerous situation is overcome by an active process of negative regulation that is enforced by MHC tuning, as well as by transcription factors such as LKLF, Tob, and NFATc2. (see, Baksh et al, Mol Cell. 2002) In collaboration with Don Bellgrau’s group, we are working to define the antitumor activity of T cells in an MHC-barren environment. The survival and activation requirements in this environment are different for CD4 and CD8 cells (see Figure 3). Our goal is to use this model to determine if biochemical pathways that mediate tolerance can be manipulated to improve immunotherapeutic outcomes.

Finally, we are interested in exploring how use of tobacco products influences the origin and progression of lymphoma and leukemia, as well as how it impacts responses to immunotherapy. Recent work from our lab using human and mouse models showed that nicotine enforces negative regulation of T cell proliferation by activating NFATc2. (see, Frazer-Abel et al, J Pharmacol Exp Ther. 2004) (see section 1 on Immune Cell Activation). Further exploration of this phenomenon using siRNA to eliminate expression of selected cholinergic receptors in T cells suggests that tonic signaling through nicotinic receptors contributes to T cell survival, and that these receptors are also necessary for calcium flux generated by ligation of the TCR. Nicotinic receptors appear to be similarly involved in survival of myeloid cells. As tobacco use is a major risk factor for development of acute myeloid leukemia, we are studying the possible role of anti-apoptotic effects of nicotine and nicotine receptors in the pathogenesis of this disease. In collaboration with Don Bellgrau, we also are studying the influence of tobacco use on outcomes of cancer immunotherapy in laboratory models of lung cancer.

Figure 1. Effect of FasL gene therapy in a dog with oral melanoma. (Left) Dog #2 from a clinical trial at presentation after the tumor was surgically de-bulked, and a mass measuring 19 mm x 14 mm x 1 mm was left for administration of gene therapy. (Right) The same dog 7 days after FasL gene therapy, when the tumor measured 14 mm x 8 mm x 1 mm. The dog was subsequently treated with surgery (hemi-mandibulectomy) and radiation therapy. He eventually died from causes unrelated to his tumor. From Bianco et al, Cancer Gene Therapy 10:726, 2003.

Figure 2. Antitumor Effects of FasL Gene Transfer. Ectopic expression of FasL can induce antitumor immunity against both Fas-sensitive and Fas-resistant tumors. In Fas sensitive tumors, the interaction between Fas and FasL leads to apoptosis, which in turn can provide priming antigens for an immune response. In both cases, ectopic expression of FasL promotes inflammation via interaction with Fas on host leukocytes (neutrophils and macrophages). The inflammatory response kills the tumor cells, making tumor antigens available to prime the immune system. [From Modiano et al, Cancer Therapy, 2004].

Figure 3. Survival of naïve CD4 and CD8 T cells adoptively transferred into an MHC-Barren environment. Naïve T cells from a B6 donor were transferred to a B6, MHC class I and MHC class II double deficient recipient. After 15 days, spleen cells were examined for survival of CD4 and CD8 T cells.