α fetoprotein (AFP)-derived peptide epitopes can be recognized by human T cells in the context of MHC class I. We determined the identity of AFP-derived peptides, presented in the context of HLA-A*0201, that could be recognized by the human (h) T cell repertoire. We screened 74 peptides and identified 3 new AFP epitopes, hAFP137–145, hAFP158–166, and hAFP325–334, in addition to the previously reported hAFP542–550. Each possesses two anchor residues and stabilized HLA-A*0201 on T2 cells in a concentration-dependent class I binding assay. The peptides were stable for 2–4 h in an off-kinetics assay. Each peptide induced peptide-specific T cells in vitro from several normal HLA-A*0201 donors. Importantly, these hAFP peptide-specific T cells also were capable of recognizing HLA-A*0201+/AFP+ tumor cells in both cytotoxicity assays and IFN-γ enzyme-linked immunospot assays. The immunogenicity of each peptide was tested in vivo with HLA-A*0201/Kb-transgenic mice. After immunization with each peptide emulsified in CFA, draining lymph node cells produced IFN-γ on recognition of cells stably transfected with hAFP. Furthermore, AFP peptide-specific T cells could be identified in the spleens of mice immunized with dendritic cells transduced with an AFP-expressing adenovirus (AdVhAFP). Three of four AFP peptides could be identified by mass spectrometric analysis of surface peptides from an HLA-A*0201 human hepatocellular carcinoma (HCC) cell line. Thus, compelling immunological and physiochemical evidence is presented that at least four hAFP-derived epitopes are naturally processed and presented in the context of class I, are immunogenic, and represent potential targets for hepatocellular carcinoma immunotherapy.

Radiation is generally considered to be an immunosuppressive agent that acts by killing radiosensitive lymphocytes. In this study, we demonstrate the noncytotoxic effects of ionizing radiation on MHC class I Ag presentation by bone marrow-derived dendritic cells (DCs) that have divergent consequences depending upon whether peptides are endogenously processed and loaded onto MHC class I molecules or are added exogenously. The endogenous pathway was examined using C57BL/6 murine DCs transduced with adenovirus to express the human melanoma/melanocyte Ag recognized by T cells (AdVMART1). Prior irradiation abrogated the ability of AdVMART1-transduced DCs to induce MART-1-specific T cell responses following their injection into mice. The ability of these same DCs to generate protective immunity against B16 melanoma, which expresses murine MART-1, was also abrogated by radiation. Failure of AdVMART1-transduced DCs to generate antitumor immunity following irradiation was not due to cytotoxicity or to radiation-induced block in DC maturation or loss in expression of MHC class I or costimulatory molecules. Expression of some of these molecules was affected, but because irradiation actually enhanced the ability of DCs to generate lymphocyte responses to the peptide MART-127–35 that is immunodominant in the context of HLA-A2.1, they were unlikely to be critical. The increase in lymphocyte reactivity generated by irradiated DCs pulsed with MART-127–35 also protected mice against growth of B16-A2/Kb tumors in HLA-A2.1/Kb transgenic mice. Taken together, these results suggest that radiation modulates MHC class I-mediated antitumor immunity by functionally affecting DC Ag presentation pathways.

Dendrimers have been proposed as therapeutic gene delivery platforms. Their superior transfection efficiency is attributed to their ability to buffer the acidification of the endosome and attach to the nucleic acids. For effective transfection the strategy is to synthesize novel dendrimers that optimize both of these traits, but the prediction of the buffering behavior in the endosome remains elusive. It is suggested that buffering dendrimers induce an osmotic pressure sufficient to rupture the endosome and release nucleic acids, which forms to sequestrate most internalized exogenous materials. Presented here are the results of a computational study modeling osmotically-driven endosome burst, or the “proton sponge effect.” The approach builds on previous cellular simulation efforts by linking the previous model with a sponge protonation model then observing the impact on endosomal swelling and acidification. Calibrated and validated using reported experimental data, the simulations offer insights into defining the properties of suitable dendrimers for enhancing gene delivery as a function of polymer structure.

A novel dual-mode contrast agent was formulated through the addition of an optical near infrared (NIR) probe to a perfluorocarbon (PFC)-based 19F magnetic resonance imaging (MRI) agent, which labels inflammatory cells in situ. A single PFC-NIR imaging agent enables both a qualitative, rapid optical monitoring of an inflammatory state and a quantitative, detailed and tissue-depth independent magnetic resonance imaging (MRI). The feasibility of in vivo optical imaging of the inflammatory response was demonstrated in a subcutaneous murine breast carcinoma model. Ex vivo optical imaging was used to quantify the PFC-NIR signal in the tumor and organs, and results correlated well with quantitative 19F NMR analyses of intact tissues. 19F MRI was employed to construct a three-dimensional image of the cellular microenvironment at the tumor site. Flow cytometry of isolated tumor cells was used to identify the cellular localization of the PFC-NIR probe within the tumor microenvironment. Contrast is achieved through the labeling of host cells involved in the immune response, but not tumor cells. The major cellular reservoir of the imaging agent were tumor-infiltrating CD11b+ F4/80low Gr-1low cells, a cell subset sharing immunophenotypic features with myeloid-derived suppressor cells (MDSCs). These cells are recruited to sites of inflammation and are implicated in immune evasion and tumor progression. This PFC-NIR contrast agent coupled to non-invasive, quantitative imaging techniques could serve as a valuable tool for evaluating novel anticancer agents.

The performance of an in situ-forming injectable membrane designed to retain antibody molecules in vivo is described. The system entails an aqueous mixture of peptide amphiphiles (referred to as"EAK16-II" and "EAKH6") and intermediate proteins (anti-H6 antibody and protein A/G) through which therapeutic IgG molecules are colocalized and oriented. Scanning electron micrographs show IgG molecules localized on the EAK16-II/EAKH6 membrane. IgG were captured via specific interactions and remained biologically active in vitro. Upon administration into mice subcutaneously, the amphiphilic peptides coassembled into stable His-tags displaying materials locally. The system was shown to retain in vivo a fluorescent dye-labeled IgG in two epithelial tumor lines. IgG coadministered with the system were found to remain in 4T1 mouse mammary tumors for up to 120 h, while free antibody was cleared within the first 24 h. Decreased clearance was also found in B16 melanoma established in mouse footpads. These studies demonstrated that the immobilizing mechanism was effective in enhancing the retention of IgG locally in vivo. The injectable system may be used to enhance the delivery of immune modulatory antibodies in tumors.

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Small-interfering RNA (siRNA) is both a powerful tool in research and a promising therapeutic platform to modulate expression of disease-related genes. Malignant tumors are attractive disease targets for nucleic acid-based therapies. siRNA directed against oncogenes, and genes driving metastases or angiogenesis have been evaluated in animal models and in some cases, in humans. The outcomes of these studies indicate that drug delivery is a significant limiting factor. This review provides perspectives on in vivo validated nanoparticle-based siRNA delivery systems. Results of recent advances in liposomes and polymeric and inorganic formulations illustrate the need for mutually optimized attributes for performance in systemic circulation, tumor interstitial space, plasma membrane, and endosomes. Physiochemical properties conducive to efficient siRNA delivery are summarized and directions for future research are discussed.

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