An IL-2 proaerolysin fusion toxin that selectively eliminates regulatory t cells to enhance antitumor immune response

Background Recent success with immune-checkpoint inhibitors in some tumor types has highlighted the power of the immune system to control and eradicate human cancer cells. However, these therapies have demonstrated a limited activity in prostate cancer, which has a more immunosuppressive microenvironment that can be because of the presence of a variety of inhibitory cell types, such as myeloid-derived suppressor cells, mesenchymal stem cells, and regulatory T cells (Tregs). One strategy to improve the efficacy of immune-based therapies for prostate cancer is to selectively eliminate these immunosuppressive cells within the tumor microenvironment. Methods We developed and characterized a chimeric protein consisting of the cytokine IL-2 fused to binding mutant of the highly toxic bacterial toxin proaerolysin (ie IL2-R336A). Results The IL2-R336A fusion protein selectively kills immunosuppressive Tregs that express the IL-2 receptor while having little to no effect on cells negative for this target. IL2-R336A depleted Tregs in both tumor bearing and nontumor bearing mice. Tumor bearing mice vaccinated with a GMCSF-expressing CT-26 GVAX vaccine had reduced tumor growth when given IL2-R336A before vaccination. IL2-R336A also enhanced immune response to a model hemagglutinin antigen (HA) in HA-tolerized mice. Conclusion These results suggest that this IL2-R336A toxin may be a useful in improving the therapeutic efficacy of antitumor vaccines by enhancing the immune response against target tumor antigens.