A. Bissonnette

Fusions of Dendritic Cells with Breast Carcinoma Stimulate the Expansion of Regulatory T Cells while Concomitant Exposure to IL-12, CpG Oligodeoxynucleotides, and Anti-CD3/CD28 Promotes the Expansion of Activated Tumor Reactive Cells

Vaccination of patients with dendritic cell (DC)/breast carcinoma fusions stimulated antitumor immune responses in a majority of patients with metastatic disease but only a subset demonstrate evidence of tumor regression. To define the factors that limit vaccine efficacy, we examined the biological characteristics of DC/breast carcinoma fusions as APCs and the nature of the vaccine-mediated T cell response. We demonstrate that fusion of DCs with breast carcinoma cells up-regulates expression of costimulatory and maturation markers and results in high levels of expression of IL-12 consistent with their role as activated APCs. Fusion cells also express the chemokine receptor CCR7, consistent with their ability to migrate to the draining lymph node. However, DC/breast cancer fusions stimulate a mixed T cell response characterized by the expansion of both activated and regulatory T cell populations, the latter of which is characterized by expression of CTLA-4, FOXP3, IL-10, and the suppression of T cell responses. Our results demonstrate that IL-12, IL-18, and TLR 9 agonist CpG oligodeoxynucleotides reduce the level of fusion-mediated regulatory T cell expansion. Our results also demonstrate that sequential stimulation with DC/breast carcinoma fusions and anti-CD3/CD28 results in the marked expansion of activated tumor-specific T cells. These findings suggest that DC/breast carcinoma fusions are effective APCs, but stimulate inhibitory T cells that limit vaccine efficacy. In contrast, exposure to TLR agonists, stimulatory cytokines, and anti-CD3/CD28 enhances vaccine efficacy by limiting the regulatory T cell response and promoting expansion of activated effector cells.

Immunomodulatory effects of vitamin D: implications for GVHD

GVHD remains a major source of morbidity and mortality after allogeneic BMT. GVHD is mediated by alloreactive T cells derived from the hematopoietic graft that target host tissues. Pre-clinical models have shown that presentation of alloantigens by host DCs results in the activation of donor-derived T cells that mediate GVHD. Strategies that interfere with the Ag-presenting capacity of DCs after allogeneic transplantation may decrease the risk of developing GVHD. Vitamin D is a hormone essential for calcium metabolism that shows immunomodulatory properties. We showed that correction of vitamin D deficiency appeared to mitigate manifestations of GVHD. In pre-clinical studies, we have shown that vitamin D inhibits DC maturation, polarizes T-cell populations toward the expression of Th2 as compared with Th1 cytokines, and blunts allogeneic T-cell proliferation in response to DC stimulation. Exposure to vitamin D resulted in increased expression of IDO, an enzyme responsible for tryptophan metabolism that is upregulated in tolerizing DCs. These data suggest that exposure to vitamin D results in immature DC populations that bias toward tolerizing rather than stimulatory T-cell populations. Vitamin D may therefore have a role in the prevention of GVHD.