The development of an immune competent mouse model for the study of immunosuppressive mechanisms is important for improving the efficacy of
brain tumor immunotherapy. In the present study we investigated regulatory T cells (Tregs),
TGF-beta1 and other putative immunosuppressive
cytokines using GL261 mouse
glioma in C57BL mice. We explored whether
tumor growth factor-beta1 (TGF-beta1) is expressed and secreted by
glioma cells constitutively or in response to a T-cell mediated immunity (simulated by
conditioned media from T cells (TCM) activated by anti-CD3 antibody). We also investigated TGF-beta1's role in Treg mediated immunosuppression by quantifying TGF-beta1secretion from T regulatory cells (Tregs) co-incubated with GL261 cells as compared to Tregs alone. Finally, we studied other newly identified
cytokines that were secreted preferentially by
glioma cells in response to CD3 activated TCM versus
cytokines secreted by
glioma cells in absence of T-cell activation (naïve TCM). TGF-beta1expression was studied using RT-PCR and secretion was quantified using ELISA. A 308
protein cytokine array was used to identify and quantify
cytokine expression. TGF-beta1expression and secretion from
glioma cells was found to be up-regulated by
conditioned media from CD3-activated T cells, suggesting that this immunosuppressive
cytokine is not secreted constitutively but in response to immunity.
TGF-beta1 was not found to be differentially secreted by Tregs co-incubated with
glioma cells as compared to Tregs alone. This data suggest that TGF-beta1immunosupppression may not be a Treg dependent mechanism in this
glioma model. Finally, the
cytokine array elucidated several other
cytokines which were up-regulated or down-regulated by CD3-activated TCM. These results have several implications for enhancing
immunotherapy treatment, including the potential benefit of TGF-beta1inhibition in conjunction with
immunotherapy, as well as the illumination of several other potential
cytokine targets to be explored as shown by the
cytokine array.