Instead, we find that cytokine stimulation induces VCAM-1 expression by glioma cells, an observation of potential significance for understanding cytokine influences on glioma progression and dissemination. These experiments were prompted by efforts to use cytokinestimulation paradigms to increase IL13Ra2 expression on glioma cells and thereby increase the efficacy of IL13Ra2 targeted therapies for brain tumors. Based on the many studies which reported induction of IL13Ra2 on a variety of cell types following cytokine stimulation, we envisioned that this strategy for IL13Ra2 induction may be conserved for glioblastoma as well. Indeed, following cytokine stimulation, we did observe induction of a cell surface antigen on both primary glioblastoma cell lines and the monocyctic cell line THP-1, which was strongly detected by the commercially available putative IL13Ra2-targeted monoclonal antibody B-D13-PE. However, during the course of these studies, we encountered a series of discrepancies in the behavior of the B-D13-PE antibody that led us to question its binding specificity, and whether the induced antigen following cytokine stimulation was really IL13Ra2. In particular, following cytokine stimulation, B-D13-PE immunoreactivity did not correlate with either the immunoreactivity of the highlycharacterized IL13Ra2-specific goat polyclonal antibody AF146 or IL13Ra2 mRNA levels. Further, the cytokine induced B-D13-PE antigen did not bind IL-13 or elicit lysis by IL13Ra2-redirected CAR T cells, and B-D13-PE binding on cytokine stimulated cells could not be blocked by soluble IL13Ra2-Fc. Therefore, our data indicate that neither TNF/IL-4, TNF/IL-13, nor TNF alone induce cell surface IL13Ra2 upregulation on glioma cells, and therefore that these cytokine treatments are not a viable strategy for expanding the targetability of IL13Ra2 by immunotherapy. Instead, our data definitively demonstrate that the cytokine induced antigen recognized by B-D13-PE is VCAM-1, as demonstrated by B-D13 immunoprecipitation/mass spectrometry, as well as soluble receptor competition studies. Many studies have reported induction of IL13Ra2 on a variety of cell types following cytokine stimulation, and induction of IL13Ra2 has been reported to be involved in TGF-b1 production. However, all of these studies used the B-D13 antibody to evaluate protein induction, and thus may have inadvertently mis-identified the induction of IL13Ra2 protein following cytokine stimulation. It should be noted, however, that qPCR and knockdown studies do support IL13Ra2 induction in some cell types. In fact, consistent with previous reports, we find that THP-1 cells show induction of IL13Ra2 mRNA 13 to 15-fold after overnight treatment with TNF and IL-13 or IL-4, although the level of IL13Ra2 expression was more than 13.6-fold lower than that expressed by the U251T glioma cell line and not at sufficient levels to be detected by flow cytometry using the IL13.