The biotech AvroBio is taking the concept forward into clinical trials for acute myeloid leukemia. Cancer drugs come in many forms: small molecules, proteins such as cytokines and antibodies, bacteria, and viruses to name a few. Some cancer vaccines utilise irradiated and therefore non-proliferative cancer cell lines. However an emerging concept is the use of a patient’s live proliferating cancer cells as vectors to activate the immune system or delivery drugs to the tumour mass.
In a recent study of a mouse xenograft model of cancer the injection of live cancer cells expressing tumour necrosis factor alpha (TNF) reduced the tumour volume of primary tumours and metastases composed of the same cells as the TNF vector cells. This is thought to be due to the phenomenon of “tumour cell seeding” – circulating tumour cells returning to their site of origin. The clinical extension of this study would be to extract circulating tumour cells from a patient’s blood (not simple for solid tumours) or take a biopsy if possible from the primary tumour, transfect/ transduce with TNF and return the cells to the blood stream.
In a model of murine acute lymphoblastic leukaemia (ALL) it was found that administering mouse ALL cells transduced to express IL-12, an immune system activating cytokine, resulted in an immune response and clearing of the ALL. Importantly in mouse models of squamous cell carcinoma, osteosarcoma, prostate cancer and Lewis lung carcinoma administering cancer cells transduced with IL-12 also resulted in immune system activation and elimination of the tumours. The effectiveness of live cell vaccines may be related both to their ability to amplify the immune stimulatory signal through initial proliferation and their ability to physically target their tumour of origin.