Publisher Summary This chapter attempts to identify the principles and issues elucidated in animal models that may provide insights for the development of effective approaches to modulate T cell functions to promote the eradication of human tumors. The importance of T cells in surveillance against the outgrowth of tumor cells is probably best demonstrated with virally transformed tumors, such as EBV-induced B cell lymphomas, which occur with markedly increased frequency in transplant patients specifically depleted of T cells, and with UV-induced squamous cell cancers that occur with high frequency in renal transplant patients. Second, the reasons for the growth of presumably immunogenic tumors in immunocompetent hosts have become more apparent with an improved understanding of the function of T cell subsets and the requirements for the induction and expression of T cell responses. The earlier perceptions that cytotoxic T cells recognize foreign proteins integrally inserted in the cell membrane had focused efforts for more than a decade on the use of the powerful new monoclonal antibody technology combined with biochemical purification techniques to isolate tumor antigens expressed on the cell membrane. However, analyses of the requirements for recognition of virally infected cells by CD8 + cytotoxic T cells demonstrated that Class I-restricted T c do not recognize integral membrane proteins but rather recognize intracellular proteins that are synthesized in the cytoplasm. Tumors containing unique or mutated and potentially immunogenic cellular proteins may selectively or predominantly elicit only CD4 + or CD8 + T cell responses because the antigen is adequately presented in the context of only one MHC molecule, and in this setting only T cells from the subset restricted to that MHC molecule appear effective in tumor therapy.

Adoptive T cell therapy of tumors: mechanisms operative in the recognition and elimination of tumor cells.

Article de synthese sur: - l'effet de la fixation specifique de l'antigene aux immunoglobulines de membrane, aux recepteurs Fc, et autres molecules de la surface cellulaire sur la presentation de l'antigene; - le mecanisme de la fixation et de la degradation de l'antigene

Receptor-mediated antigen uptake and its effect on antigen presentation to class II-restricted T lymphocytes.

Adsorptive-mediated transcytosis (AMT) provides a means for brain delivery of medicines across the blood-brain barrier (BBB). The BBB is readily equipped for the AMT process: it provides both the potential for binding and uptake of cationic molecules to the luminal surface of endothelial cells, and then for exocytosis at the abluminal surface. The transcytotic pathways present at the BBB and its morphological and enzymatic properties provide the means for movement of the molecules through the endothelial cytoplasm. AMT-based drug delivery to the brain was performed using cationic proteins and cell-penetrating peptides (CPPs). Protein cationization using either synthetic or natural polyamines is discussed and some examples of diamine/polyamine modified proteins that cross BBB are described. Two main families of CPPs belonging to the Tat-derived peptides and Syn-B vectors have been extensively used in CPP vector-mediated strategies allowing delivery of a large variety of small molecules as well as proteins across cell membranes in vitro and the BBB in vivo. CPP strategy suffers from several limitations such as toxicity and immunogenicity—like the cationization strategy—as well as the instability of peptide vectors in biological media. The review concludes by stressing the need to improve the understanding of AMT mechanisms at BBB and the effectiveness of cationized proteins and CPP-vectorized proteins as neurotherapeutics.

https://link.springer.com/content/pdf/10.1208%2Fs12248-008-9055-2.pdf

CNS Delivery Via Adsorptive Transcytosis

Delivery of peptides and proteins through the blood-brain barrier.

Active targeting of brain tumors using nanocarriers.

We have shown that a cationized form of bovine serum albumin (BSA) produced by substituting anionic side chain carboxylic groups with aminoethylamide groups possesses unique immunologic properties. The two forms of antigen, native (nBSA) and cationized (cBSA), cross-react at the level of the B cell, as evidenced by the ability of antibody raised against one form to react with the other and by inhibition assays using ELISA. T cell cross-reactivity was also observed in proliferation assays, but the amount of cBSA required for stimulation was 500 times less than the amount of native protein needed. In vivo, cBSA produced responses which, at their optimal levels, were at least double the response to nBSA and which showed a different kinetic pattern, peaking later and lasting longer than the response to the native molecule. Moreover, antibodies were produced in response to administration of cBSA but not nBSA when given i.v. in saline, without an adjuvant. Although a mechanism for these phenomena is not yet clear, we speculate that the cBSA may have a greater affinity for antigen-presenting cells or for the T cell receptor, or that the altered structure may enhance recognition of the molecule by APC and/or helper T cells.

Cationization of protein antigens. I. Alteration of immunogenic properties.

Cationization of BSA generates a molecule that mounts antibody responses of increased magnitude and duration and induces T cell proliferation at concentrations 500 times less than native BSA (nBSA). To explain the alteration in immunogenic properties of this Ag, the uptake of nBSA and cationized BSA (cBSA) by splenic APC has been investigated. T cell proliferation assays were conducted with nBSA and cBSA preparations with varying degrees of substitution. An inverse correlation between the degree of cationization and the amounts of Ag needed for optimal T cell reactivity was observed. To determine whether affinity for APC resulted in an increased uptake of cBSA, splenic APC were incubated with nBSA or cBSA for varying amounts of time. Comparisons were made at each time point between untreated Ag-pulsed APC (Ag uptake) and paraformaldehyde-fixed Ag-pulsed APC (processed Ag). Proliferation of T cells primed with nBSA or cBSA increased in proportion to the amount of time of APC exposure to high concentrations of nBSA, first appearing after a 2-h pulse and peaking at 8 h. Conversely, untreated APC needed only a 30-min cBSA exposure to induce either nBSA- or cBSA-primed T cell proliferation, indicating a rapid uptake of cBSA. Comparisons with proliferation induced by paraformaldehyde-fixed cBSA APC indicate that nBSA T cells recognize a lag phase-processed form of cBSA, whereas a majority of cBSA T cells recognize either a rapidly processed form of cBSA, or a membrane-processed cBSA molecule without a classical lag phase processing event. When monensin was used as an inhibitor of fluid phase pinocytosis in splenic APC, the presentation of nBSA was inhibited by 85%, but the presentation of cBSA was inhibited by only 20%. These results imply that nBSA enters the cell by fluid phase pinocytosis, whereas cBSA enters by a nonspecific adsorptive mechanism. The different modes of cellular entry for the two molecules, nBSA and cBSA, resulting in a rapid uptake of cBSA, may have important ramifications on T cell activation and immunoregulation.

R J Apple

Papers

Cationization of protein antigens. I. Alteration of immunogenic properties.

Cationization of protein antigens. IV. Increased antigen uptake by antigen-presenting cells.