Salmonella Enterica serovar Typhimurium As a Therapy for B-Cell Lymphoma

Abstract 4968

Patients with non-Hodgkin's lymphoma (NHL) respond well to treatment, but relapses are frequent after a period of months or years. This highlights the need for new therapeutic modalities for these patients.

Since nineteenth century there are many reports that tumors may undergo spontaneous regression after a bacterial infection. There is great interest in developing anti-tumoral therapies based on living microorganisms because they show some selective replication or preferential accumulation in tumor microenvironment. Salmonella is a facultative anaerobic bacteria, which has the ability to colonize and replicate under both anoxia and oxygenated areas of tumors. Several therapies had evaluated the administration of Salmonella alone or used as a vector for relevant molecules in different solid cancer models. To date, many clinical trials have been conducted using live attenuated Salmonella and have demonstrated the safety of it use. Although many groups have studied the anticancer therapeutic effect of Salmonella, the mechanism responsible for its efficacy is unknown. However, it is known that anti-tumor properties of the bacteria mainly depend on activation of innate and adaptive immune responses.

We previously developed a reproducible syngenic model of B-cell lymphoma in Balb/c mouse based upon the A20 NHL cell line. Using this model, we studied the in vivo antitumor effect of the administration of intratumoral attenuated Salmonella Typhimurium (LVR01). Mice were injected with A20 cells and, after tumor became palpable, were divided in groups and treated intratumorally with one of the following: 3 inoculations of 1×10⁶Salmonella LVR01, 1 inoculation of 1×10⁶Salmonella LVR01 and plus 2 of PBS or 3 inoculations of PBS as a control group. Mice were followed for survival and immune response was evaluated.

Mice treated with 3 inoculations of Salmonella LVR01 showed a greater survival than others groups (p=0,0001). Prolonged survival was associated with a marked increase on the number of intratumoral CD8+ T cells (p=0.001) and neutrophils (p=0.012). Additionally, intratumoral CD8+ and NK cells showed a significantly higher percentage of activation antigen (CD69) expression. Further, we found a significant increase in the expression of IFN-g mRNA in tumor tissue of mice inoculated with 3 doses of Salmonella (p=0.03). At systemic level, we measured cytokine concentration in the supernatant of splenocytes stimulated with tumor cells and we found that only mice receiving 3 inoculation with Salmonella showed an tumor antigen specific response as evidenced by increased production of IFN-□ (p=0,004) and IL-12p70 (p=0,025).

Overall, the results presented here indicate that inoculation with 3 doses of Salmonella induces in vivo recruitment of both innate and adaptative immune cells to the tumor site and elicit an anti-tumor immunity at systemic level that results in an extended survival. This approach promises to be an interesting strategy, with therapeutic value, to promote systemic immunity against human NHL.