Tumor-immunotherapeutic Efficacy of Serratia marcescens Polyribosomes1

The ability of polyribosomes, obtained from several bacterial species, to suppress the development of cutaneous SaD2 fibrosarcomas in DBA/2 mice was evaluated. Suppression of tumor appearance depended upon the tumor load at the time of treatment, dose of polyribosomes, and species source of polyribosomes, with Serratia marcescens being superior to Escherichia coli, Streptococcus pneumoniae, Mycobacterium bow's (Pasteur), Mycobacterium smegmatis, and Propionibacterium acnes (formerly Corynebacterium parvum). A single injection of 5 or 50 fig of Serratia polyribosomes at the tumor site 72 hr after the intradermal administration of 1.5 x 103 SaD2 cells resulted in 66 to 95% survival. All untreated animals expired within 50 days. Tumor suppression occurred at both flank and footpad sites. Presensitization with polyribosomes and incorporation of polyribosomes into adjuvant were not required for the tumor-suppressive effect. Treatment of Serratia polyribosomes with RNase or pronase reduced the number of survivors. Endotoxin was not detectable with the Limulus amebocyte lysate assay.