Rejection of metastatic 4T1 breast cancer by attenuation of Treg cells in combination with immune stimulation

Dendritic cells engineered to secrete anti-GITR antibodies are effective adjuvants to dendritic cell-based immunotherapy

A number of monoclonal antibodies (mAbs) have been studied for their ability to enhance immune responses. Although these antibodies are effective in pre-clinical and clinical studies, they are costly and have occasionally been associated with adverse effects such as autoimmunity and cytokine storm. Numerous studies have shown that treatment of mice with an agonistic mAb, clone DTA-1, targeting murine glucocorticoid-induced tumor necrosis factor receptor (GITR) results in enhanced immune responses in tumor-bearing animals. Herein, we evaluate the novel approach of transfecting dendritic cell (DC) with mRNA encoding the heavy and light chain of the anti-GITR mAb. We show the induction of significantly enhanced tumor immunity by vaccinating with a combination of anti-GITR-secreting DC and tumor antigen-presenting DC. This enhancement is comparable to that seen with systemically delivered mAb along with the antigen-presenting DC. Importantly, when anti-GITR was delivered using RNA-transfected DC, we observed no evidence of autoimmune hypopigmentation in any tumor-free mice. We also show enhanced induction of cytotoxic T-lymphocyte responses, which is only observed when the antigen-presenting and antibody-secreting DC are co-injected at the same site. To illustrate the broad utility of this strategy, we show that DC transfected with mRNA encoding GITR-ligand/Fc fusion protein is also an effective tumor vaccine adjuvant.

Therapeutic immunity by adoptive tumor-primed CD4(+) T-cell transfer in combination with in vivo GITR ligation

Tumor-primed CD4(+) T cells from splenocytes of tumor-rejection mice in combination with in vivo glucocorticoid-induced tumor necrosis factor receptor (GITR) ligation (the combination therapy) elicited effective host CD8(+) T cell-dependent therapeutic immunity against a murine breast tumor. GITR ligation in vitro enhanced tumor-primed CD4(+) T-cell activity and partially abrogated regulatory T cells (Treg) suppressor function. Dendritic cells (DCs) from tumor-draining lymph nodes (TDLNs) of tumor-bearing mice treated by the combination therapy stimulated Ag-specific T cells and produced interleukin (IL)-12 ex vivo. Whereas tumor-primed CD4(+) T cells or in vivo GITR ligation alone induced a tumor-specific interferon (IFN)-gamma-producing cellular response, the combination therapy enhanced and sustained it. Furthermore, the combination therapy in vivo attenuated Treg's ability to suppress IL-12 production by DCs and IFN-gamma production by effectors ex vivo. Importantly, tumor-primed CD4(+) CD25(-) T cells from splenocytes of untreated tumor-bearing mice in combination with in vivo GITR ligation also elicited an effective therapeutic effect in this model. These data suggest that the combination therapy may improve DC function, accentuate tumor-specific T-cell responses, and attenuate Treg suppressor function, thereby eliciting effective therapeutic immunity.