“…Earlier work from this laboratory, utilizing the operationally simple and reproducible DA rat D-12 ascites tumor model, has shown that the weak spontaneous local resistance against this tumor can be markedly enhanced by attentuated or heat-killed facultative intracellular pathogens, such as BCG, CP, and/or LM, provided that these agents are inoculated into the same compartment several days before tumor-cell challenge (Keller, 1977. The tumor-protective effect induced by these microbial agents against this non-immunogenic tumor was readily and completely abolished by a variety of agents, e.g., silica particles, carrageenan andlor anti-IFNy, when administered locally several days before tumor-cell challenge (Keller, 1977. These and other findings (Keller et al, 1971) were taken as support for the concept that, in this particular experimental system, local natural mechanisms hold a key role in mediation of the anti-tumor resistance induced by the microbial pathogens.…”