NKT Cell Immunotherapy for Metastatic Breast Cancer

Breast cancer is the most common type of cancer in Canadian women and the second leading cause of cancer deaths. Despite advances in screening and treatments, a significant number of patients experience local recurrence or spread of their cancer to other organs, and 15-20% will not survive past the first five years. This highlights the continued need for new therapeutic strategies to combat this disease. One approach is to enhance tumour control by manipulating the function of the immune system (immunotherapy) to target cancer cells better. Dr. Johnston’s laboratory has been examining the anti-tumour properties of a rare population of white blood cells called natural killer T (NKT) cells. Activation of NKT cells can induce potent anti-tumor responses that control tumour growth and prevent metastasis (the spread of cancer cells). Dr. Johnston’s group has found that NKT cell activation following surgical removal of established breast tumours can enhance the control of breast cancer metastasis and increase survival in experimental models. Dr. Johnston’s group will work to optimize the beneficial effects of NKT cell based immunotherapies and determine whether NKT cell activation can be combined with other drug therapies to improve outcomes. This work will increase our understanding of the immune system and help establish the parameters for future clinical trials with breast cancer patients. Aim 1: Optimizing DC-based NKT cell activation for the clearance of breast cancer metastases.In experiments with the 4T1 model, adoptive transfer of DCs loaded with the glycolipid alpha-GalCer induced more efficient NKT cell activation and better survival than treatment with free glycolipids. Since alpha-GalCer-loaded DCs spare NKT cells from anergy (unresponsiveness to restimulation) they could be used to deliver multiple NKT cell stimulations. Therefore, we will optimize DC-based NKT cell immunotherapy by determining the optimal timing for delivery of sequential DC transfers. We will also establish whether specific DC subsets (CD8+ and CXCL16+ DCs) induce better survival outcomes.Aim 2: Impact of NKT cell immunotherapy on immunosuppression and tumour immunity.NKT cell activation can stimulate the development and expansion of tumour-specific T cells to generate long term immunity. Long term survivors will be tested for tumour-specific immunity via the ability to reject secondary tumour challenges. The generation of tumour-specific effector T cells will also be examined ex vivo by measuring IFN-gamma recall responses to tumour antigens and lysis of 4T1 and EO771 target cells. NKT cells may also influence the activity of suppressive immune cells induced by the tumour environment. In our previous studies, alpha-GalCer-loaded DC therapy prevented accumulation of myeloid derived suppressor cells (MDSCs), but it was not clear whether this was due to a direct effect on MDSCs or elimination of tumour cells. The effects of NKT cell activation on MDSC and regulatory T cell (Treg) number and activity will be assessed by flow cytometry and in vitro suppression assays in mice with and without tumour resection.Aim 3: NKT cell immunotherapy in combination with immune-stimulating chemotherapy.Low dose chemotherapy with cyclophosphamide (CPA), doxorubicin (DOX), and paclitaxel (PTX) can control tumours by inhibiting suppressive immune cells and stimulating tumour immunity. Combining low dose chemotherapy with further immune stimulation enhances tumour control, but the role of NKT cells and NKT cell based immunotherapy has not been explored. Therefore, we will test whether post-surgical treatment with CPA, DOX, or PTX will enhance the anti-metastatic activity of alpha-GalCer-loaded DCs. We hypothesize that combined post-surgical chemotherapy with NKT cell based immunotherapy will improve survival, enhance tumour immunity, and reduce immune suppression, compared to individual therapies.