Systemic CTLA-4 blockade ameliorates glioma-induced changes to the CD4+ T cell compartment without affecting regulatory T-cell function.

PURPOSE: Patients with malignant glioma suffer global compromise of their cellular immunity, characterized by dramatic reductions in CD4(+) T cell numbers and function. We have previously shown that increased regulatory T cell (T(reg)) fractions in these patients explain T-cell functional deficits. Our murine glioma model recapitulates these findings. Here, we investigate the effects of systemic CTLA-4 blockade in this model. EXPERIMENTAL DESIGN: A monoclonal antibody (9H10) to CTLA-4 was employed against well-established glioma. Survival and risks for experimental allergic encephalomyelitis were assessed, as were CD4(+) T cell numbers and function in the peripheral blood, spleen, and cervical lymph nodes. The specific capacities for anti-CTLA-4 to modify the functions of regulatory versus CD4(+)CD25(-) responder T cells were evaluated. RESULTS: CTLA-4 blockade confers long-term survival in 80% of treated mice, without eliciting experimental allergic encephalomyelitis. Changes to the CD4 compartment were reversed, as anti-CTLA-4 reestablishes normal CD4 counts and abrogates increases in CD4(+)CD25(+)Foxp3(+)GITR(+) regulatory T cell fraction observed in tumor-bearing mice. CD4(+) T-cell proliferative capacity is restored and the cervical lymph node antitumor response is enhanced. Treatment benefits are bestowed exclusively on the CD4(+)CD25(-) T cell population and not T(regs), as CD4(+)CD25(-) T cells from treated mice show improved proliferative responses and resistance to T(reg)-mediated suppression, whereas T(regs) from the same mice remain anergic and exhibit no restriction of their suppressive capacity. CONCLUSIONS: CTLA-4 blockade is a rational means of reversing glioma-induced changes to the CD4 compartment and enhancing antitumor immunity. These benefits were attained through the conferment of resistance to T(reg)-mediated suppression, and not through direct effects on T(regs).

Systemic anti-CD25 monoclonal antibody administration safely enhances immunity in murine glioma without eliminating regulatory T cells.

PURPOSE: Elevated proportions of regulatory T cells (T(reg)) are present in patients with a variety of cancers, including malignant glioma, yet recapitulative murine models are wanting. We therefore examined T(regs) in mice bearing malignant glioma and evaluated anti-CD25 as an immunotherapeutic adjunct. EXPERIMENTAL DESIGN: CD4+CD25+Foxp3+GITR+ T(regs) were quantified in the peripheral blood, spleens, cervical lymph nodes, and bone marrow of mice bearing malignant glioma. The capacities for systemic anti-CD25 therapy to deplete T(regs), enhance lymphocyte function, and generate antiglioma CTL responses were assessed. Lastly, survival and experimental allergic encephalitis risks were evaluated when anti-CD25 was combined with a dendritic cell-based immunization targeting shared tumor and central nervous system antigens. RESULTS: Similar to patients with malignant glioma, glioma-bearing mice show a CD4 lymphopenia. Additionally, CD4+CD25+Foxp3+GITR+ T(regs) represent an increased fraction of the remaining peripheral blood CD4+ T cells, despite themselves being reduced in number. Similar trends are observed in cervical lymph node and spleen, but not in bone marrow. Systemic anti-CD25 administration hinders detection of CD25+ cells but fails to completely eliminate T(regs), reducing their number only moderately, yet eliminating their suppressive function. This elimination of T(reg) function permits enhanced lymphocyte proliferative and IFN-gamma responses and up to 80% specific lysis of glioma cell targets in vitro. When combined with dendritic cell immunization, anti-CD25 elicits tumor rejection in 100% of challenged mice without precipitating experimental allergic encephalitis. CONCLUSIONS: Systemic anti-CD25 administration does not entirely eliminate T(regs) but does prevent T(reg) function. This leads to safe enhancement of tumor immunity in a murine glioma model that recapitulates the tumor-induced changes to the CD4 and T(reg) compartments seen in patients with malignant glioma.