Differential capacity of chaperone-rich lysates in cross-presenting human endogenous and exogenous melanoma differentiation antigens.

The goal of immune-based tumor therapies is the activation of immune cells reactive against a broad spectrum of tumor-expressed antigens. Vaccines based on chaperone proteins appear promising as these proteins naturally exist as complexes with various protein fragments including those derived from tumor-associated antigens. Multi-chaperone systems are expected to have highest polyvalency as different chaperones can carry distinct sets of antigenic fragments. A free-solution isoelectric focusing (FS-IEF) technique was established to generate chaperone-rich cell lysates (CRCL). Results from murine systems support the contention that CRCL induce superior anti-tumor responses than single chaperone vaccines. We established an in vitro model for human melanoma to evaluate the capacity of CRCL to transfer endogenously expressed tumor antigens to the cross-presentation pathway of dendritic cells (DC) for antigen-specific T cell stimulation. CRCL prepared from human melanoma lines contained the four major chaperone proteins Hsp/Hsc70, Hsp90, Grp94/gp96 and calreticulin. The chaperones within the melanoma cell-derived CRCL were functionally active in that they enhanced cross-presentation of exogenous peptides mixed into the CRCL preparation. Superior activity was observed for Hsp70-rich CRCL obtained from heat-stressed melanoma cells. Despite the presence of active chaperones, melanoma cell-derived CRCL failed to transfer endogenously expressed melanoma-associated antigens to DC for cross-presentation and cytotoxic T cell (CTL) recognition, even after increasing intracellular protein levels of tumor antigen or chaperones. These findings reveal limitations of the CRCL approach regarding cross-presentation of endogenously expressed melanoma-associated antigens. Yet, CRCL may be utilized as vehicles to enhance the delivery of exogenous antigens for DC-mediated cross-presentation and T cell stimulation.

Ifosfamide impairs the allostimulatory capacity of human dendritic cells by intracellular glutathione depletion.

Ifosfamide, a clinically potent chemotherapeutic agent, causes the depletion of intracellular glutathione (GSH) levels in various cell types. GSH is the major intracellular reductant against oxidative stress. 4-Hydroxyifosfamide (4-OH-IF), the activated form of ifosfamide, depletes GSH levels in T cells and natural killer (NK) cells; this is accompanied by a decrease in T-cell and NK-cell function. Here we demonstrate for the first time that human monocyte-derived dendritic cells (DCs) express higher constitutive levels of GSH and are less sensitive to 4-OH-IF-induced GSH depletion than T cells and NK cells. Treatment of DCs with 4-OH-IF significantly reduced their ability to stimulate allogeneic T-cell proliferation and interferon-gamma (IFN-gamma) production. Ifosfamide also decreased DC interleukin-12p70 (IL-12p70) production after stimulation with lipopolysaccharide (LPS) and IFN-gamma. The decrease in allostimulatory capacity and in IFN-gamma and IL-12 production correlated with a decrease in intracellular GSH in the DCs. The responses could be restored by reconstituting DC GSH levels with glutathione monoethyl ester (GSH-OEt). 4-OH-IF had no inhibitory effect on the ability of DCs to present exogenously added tyrosinase peptide to tyrosinase-specific cytotoxic T lymphocytes (CTLs). These studies suggest that in cancer patients treated with ifosfamide, protection strategies based on glutathione reconstitution may enhance DC function.

Tumor-derived heat shock protein 70 peptide complexes are cross-presented by human dendritic cells.

Our study demonstrates that tumor-derived heat shock protein (HSP)70 chaperones a tyrosinase peptide and mediates its transfer to human immature dendritic cells (DCs) by receptor-dependent uptake. Human tumor-derived HSP70 peptide complexes (HSP70-PC) thus have the immunogenic potential to instruct DCs to cross-present endogenously expressed, nonmutated, and tumor antigenic peptides that are shared among tumors of the melanocytic lineage for T cell recognition. T cell stimulation by HSP70-instructed DCs is dependent on the Ag bound to HSP70 in that only DCs incubated with HSP70-PC purified from tyrosinase-positive (HSP70-PC/tyr(+)) but not from tyrosinase-negative (HSP70-PC/tyr(-)) melanoma cells resulted in the specific activation of the HLA-A*0201-restricted tyrosinase peptide-specific cytotoxic T cell clone. HSP70-PC-mediated T cell stimulation is very efficient, delivering the tyrosinase peptide at concentrations as low as 30 ng/ml of HSP70-PC for T cell recognition. Receptor-dependent binding of HSP70-PC and active cell metabolism are prerequisites for MHC class I-restricted cross-presentation and T cell stimulation. T cell stimulation does not require external DC maturation signals (e.g., exogenously added TNF-alpha), suggesting that signaling DC maturation is an intrinsic property of the HSP70-PC itself and related to receptor-mediated binding. The cross-presentation of a shared human tumor Ag together with the exquisite efficacy are important new aspects for HSP70-based immunotherapy in clinical anti-cancer vaccination strategies, and suggest a potential extension of HSP70-based vaccination protocols from a patient-individual treatment modality to its use in an allogeneic setting.