A GM-CSF and IL-4 Fusion Cytokine Triggers Conversion of B-Cells to Tumoricidal Effectors

Abstract 1048

We have previously demonstrated that coupling of GMCSF at the N-terminus of common γ-chain interleukins IL2, IL15 and IL21 leads to meaningful gain-of function activity in interleukin-responsive lymphomyeloid cells. Considering the physiological and immunological importance of IL4 that is a member of γ-chain interleukins, we tested the bioactivity of a novel fusion cytokine consisting of a fusion between GM-CSF and IL-4 (GIFT4). We observed that GIFT4 leads to a pan-STAT hyper-phosphorylation response in resting splenic B-cells distinct from IL4 only and that treated B-cells up-regulated expression of MHCI/II, CD80 and CD86, secreted IL-12, IL-1a, IL-6, and substantial amounts of CCL3 and GM-CSF, akin to recently described innate response activator (IRA) B-cells (Science 335, 597, 2012). In vivo delivery of recombinant GIFT4 protein to normal mice leads to homeostatic expansion of splenic B cells and plasma cells as well as humoral hyper-responsiveness to antigenic challenge. We further showed that B16F0 melanoma cells engineered to secrete GIFT4 are immune-rejected in a B-cell dependent manner. The clinical effect was abolished when B16F0-GIFT4 cells were implanted in B-cell deficient μMT, CD4^−/−, CD8^−/− or FcγR^−/− mice consistent with a pivotal for B cells, their T-cell helper function and antibody-dependent cell-mediated cytotoxicity for the observed melanoma-specific therapeutic effect. Thus, GIFT4 defines a novel engineered cytokine that mediates endogenous expansion of B-cells with potent immune helper and antigen-specific effector function. We propose that GIFT4 protein could serve as a novel immunotherapeutic agent and defines a previously unrecognized potential of B-cells as tumoricidal effectors.