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Mycobacterium vaccae (SRL172): a potential immunological adjuvant evaluated in rat prostate cancer
D Hrouda1, B E Souberbielle, J Kayaga
1Department of Urology, St George's Hospital, London, UK.
Objective:
To evaluate the potential of heat-killed Mycobacterium vaccae (SRL172) as a nonspecific immunostimulant and as an adjuvant to whole tumour cell vaccination in the rat model of prostate cancer.
Materials And Methods:
SRL172 was used as a vaccine in the prevention and treatment of subcutaneous tumours in rats. Prevention experiments were conducted using subcutaneous MAT-LyLu tumours in Copenhagen rats, comparing vaccination with SRL172 alone, SRL172 plus autologous cells, and bacille Calmette-Guèrin (BCG) plus autologous cells before tumour implantation. Treatment experiments were conducted using subcutaneous MAT-LyLu tumours in the Copenhagen 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-LyLu tumours. In the Lobund-Wistar rat vaccination with autologous whole tumour cells and SRL172 significantly delayed the growth of established tumours.
Conclusion:
Mycobacterium vaccae deserves further evaluation as an adjuvant to whole tumour cell vaccination in a phase I clinical trial in patients with prostate cancer.