A Therapeutic Vaccine Using Activated Tumor Cells by Salmonella Infection and Interleukin-2 Induces Antitumor Immunity In B-Cell Lymphoma

Abstract 2841

Therapeutic vaccination holds great potential as complementary treatment for non-Hodgkin's lymphoma (NHL). Interleukin-2 (IL2) has a wide range of immunologic effects and the ability to induce regression of metastatic human tumors. We have previously reported in a murine lymphoma model that vaccination with irradiated tumor cells combined with a depot formulation of IL2 elicits strong anti-tumor specific immunity and extended survival. B NHL cells are antigen presenting cells, but the lack of expression of co-stimulatory molecules leads to anergy. We found a significant up-regulation of the expression of some of these molecules (CD80, CD86, CD40 and MHC class II) in lymphoma cells infected by Salmonella Typhimurium (SL) and analyzed whether this approach could improve their antigen-presenting function.

Using a murine A20 NHL model we studied the in vivo antitumor effect of the administration of a vaccine composed of irradiated and activated tumor cells by SL infection and IL2 in alum. Five groups of mice received at days 3 and 7 after tumor cell inoculation by subcutaneous injections one of the following: activated A20 cells with IL2 in alum (A20-SL-IL2); activated A20 cells (A20-SL); A20 cells with IL2 in alum (A20-IL2), A20 cells (A20) and phosphate-buffered saline as control. Mice were followed for survival and immune response was evaluated.

Vaccinated mice with A20-IL2 and A20-SL showed a greater survival than control groups. Moreover, mice that received A20-SL-IL2 showed an even longer survival compared with all other groups (p=0,035). These results suggest a synergic effect of activated A20 cells by SL infection and IL2 in alum. Prolonged survival was related with a marked increase on the number of intratumoral CD4+ T cells (p=0.0001), CD8+ T cells (p=0.0001), NK cells (p=0.001), NKT cells (p=0.001), neutrophils (p=0.0001) and the production of IFN-γ by CD4+ T cells (p=0.009). Additionally, intratumoral CD4+, CD8+ and NK cells showed a significantly higher percentage of activation antigen (CD69) expression. Further, strong tumor antigen-specific cellular responses were detected at systemic level. Proliferation assays showed enhanced proliferation upon stimulation with irradiated A20 cells in splenocytes from A20-SL-IL2 and A20-IL2 vaccinated mice (p=0.0001). Both, A20 activated cells by SL infection and IL2 were required for induction of an effective immune response that impacted on cancer progression. Interesting, all mice receiving any form of IL2 showed higher numbers of intratumoral regulatory T cells (Treg) which might have a role in tumor progression in these animals. Nevertheless, the overall effect was a better antitumor immune response and less disseminated disease, suggesting that therapeutic vaccination overcomes this potential detrimental effect.

Overall, the results presented here indicate that vaccination with activated A20 cells combined with a depot formulation of IL2 elicits strong anti-tumor specific immunity and extended survival. This approach promises to be an interesting strategy, with therapeutic value, to promote systemic immunity against human NHL.