Because of the ability to bridge innate and adaptive defenses, there is great interest in utilizing TLR agonists in boosting anti-tumor immunity. In our preliminary studies to investigate the implications of TLR expression in breast cancer, we asked whether murine mammary carcinomas expressed TLR. Indeed, each of the four murine mammary carcinomas expressed TLR2, 3 and 4. More strikingly, four out of four mammary carcinomas responded to TLR agonists with a dose dependent increase in chemokine expression, and three out of four of the tumors exhibited decreased growth rate in vivo, but not in vitro, following TLR agonist treatment. Thus, these data show that mammary carcinomas express TLR and are capable of responding to TLR agonists in a manner that may be useful in the development of immunotherapeutic strategies for fighting cancer. The hypothesis of this study is that TLR agonist treated breast cancer cells elicit a beneficial immune response dependent upon factors downstream of MyD88 dependent signaling. To address this hypothesis, there are three specific aims: 1) determine whether MyD88 dependent signaling is necessary for decreased growth of TLR agonist treated tumors, 2) determine whether MyD88 independent signaling is necessary for decreased growth of TLR agonist treated tumors and, 3) determine whether growth inhibition of TLR agonist treated tumors is due to a tumor-specific T cell mediated immune response.
Specific aim 1 and 2 will be accomplished by delivering the 4T1 tumor with and without MyD88 or TICAM-2 (for MyD88 independent) signaling capabilities to mice. For this purpose, RNA interference will be used. 4T1 cell lines with reduced MyD88 or TICAM-2 expression, as well as controls, will be assessed for TLR dependent inhibition of growth. The third specific aim will determine whether TLR agonist treated 4T1 exhibit decreased growth in vivo due to a tumor-specific T cell mediated immune response. For this purpose, the TLR agonist treated and untreated 4T1 will be monitored in CD4 or CD8 depleted mice. Analysis of vaccine draining lymph nodes for the frequency of tumor-specific T cells, as well as assaying tumor reactivity using T cell proliferation and cytokine release assays, will also be performed. The results from this project may open the door to new therapies for the treatment of patients with cancer. For instance, because TLR agonists function as adjuvants, many natural and synthetic TLR agonists are currently being evaluated for their ability to enhance antigen-specific immune responses in humans. If we find that ligation of TLR, naturally expressed by murine mammary carcinoma cells, increases anti-tumor immunity, then many of the TLR agonists now being clinically evaluated as adjuvants may find an application in the treatment of patients with cancer.
Because toll-like receptor agonists enhance immune responses, many natural and synthetic toll-like receptor agonists are currently being evaluated for their ability to enhance antigen-specific immune responses against infectious diseases in humans. If we find that treating tumor cells with toll-like receptor agonists increases anti-tumor immunity, toll-like receptor agonists already being clinically evaluated may find an application in the treatment of patients with cancer. The results from this project therefore may open the door to new therapies for the treatment of patients with cancer.
