Mycobacterium vaccae (SRL172): a potential immunological adjuvant evaluated in rat prostate cancer

Objective To evaluate the potential of heat-killed Mycobacterium vaccae (SR L172) as a nonspecific immunostimulant and as an adjuvant to whole tumour c ell vaccination in the rat model of prostate cancer. Materials and methods SRL172 was used as a vaccine in the prevention and tr eatment of subcutaneous tumours in rats. Prevention experiments were conduc ted using subcutaneous MAT-LyLu tumours in Copenhagen rats, comparing vacci nation with SRL172 alone, SRL172 plus autologous cells, and bacille Calmett e-Guerin (BCG) plus autologous cells before tumour implantation. Treatment experiments were conducted using subcutaneous MAT-LyLu tumours in the Copen hagen rat and subcutaneous PAIII tumours in the Lobund-Wistar rat, Tumours were induced by subcutaneous injection with tumour cells. Animals were then vaccinated with autologous cells, autologous cells plus SRL172, or SRL172 alone, Results SRL172 was effective as an adjuvant to autologous whole tumour cell vaccination in the prevention of MAT-LyLu tumours and the survival benefit was equivalent to that provided when the adjuvant was live-attenuated BCG. SRL172 alone did not reduce tumour take or tumour growth in this model and neither strategy was effective in delaying the growth of established MAT-L yLu tumours, In the Lobund-Wistar rat vaccination with autologous whole tum our cells and SRL172 significantly delayed the growth of established tumour s, Conclusion Mycobacterium vaccae deserves further evaluation as an adjuvant to whole tumour cell vaccination in a phase I clinical trial in patients wi th prostate cancer.