title: Factors affecting the efficiency of CD8+ T cell cross-priming with exogenous antigens.
abstract: Processing of exogenous protein Ags by APC leads predominantly to presentation of peptides on class II MHC and, thus, stimulation of CD4+ T cell responses. However, "cross-priming" can also occur, whereby peptides derived from exogenous Ags become displayed on class I MHC molecules and stimulate CD8+ T cell responses. We compared the efficiency of cross-priming with exogenous proteins to use of peptide Ags in human whole blood using a flow cytometry assay to detect T cell intracellular cytokine production. CD8+ T cell responses to whole CMV proteins were poorly detected (compared with peptide responses) in most CMV-seropositive donors. Such responses could be increased by using higher doses of Ag than were required to achieve maximal CD4+ T cell responses. A minority of donors displayed significantly more efficient CD8+ T cell responses to whole protein, even at low Ag doses. These responses were MHC class I-restricted and dependent upon proteosomal processing, indicating that they were indeed due to cross-priming. The ability to efficiently cross-prime was not a function of the number of dendritic cells in the donor's blood. Neither supplementation of freshly isolated dendritic cells nor use of cultured, Ag-pulsed dendritic cells could significantly boost CD8 responses to whole-protein Ags in poorly cross-priming donors. Interestingly, freshly isolated monocytes performed almost as well as dendritic cells in inducing CD8 responses via cross-priming. In conclusion, the efficiency of cross-priming appears to be poor in most donors and is dependent upon properties of the individual's APC and/or T cell repertoire. It remains unknown whether cross-priming ability translates into any clinical advantage in ability to induce CD8+ T cell responses to foreign Ags.
authors.affiliation: BD Immunocytometry Systems, San Jose, CA 95131, USA. holden_maecker@bdis.com
authors.forename: H T
authors.initials: HT
authors.lastname: Maecker
authors.forename: S A
authors.initials: SA
authors.lastname: Ghanekar
authors.forename: M A
authors.initials: MA
authors.lastname: Suni
authors.forename: X S
authors.initials: XS
authors.lastname: He
authors.forename: L J
authors.initials: LJ
authors.lastname: Picker
authors.forename: V C
authors.initials: VC
authors.lastname: Maino
mesh_terms: D000914:Antibodies, Viral / Q000097:blood; D000938:Antigen-Presenting Cells / Q000166:cytology / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology* / Q000494:pharmacology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000821:virology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism / Q000821:virology; D002452:Cell Count; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis; D003587:Cytomegalovirus / Q000276:immunology*; D003713:Dendritic Cells / Q000166:cytology / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology; D006801:Humans; D007700:Kinetics; D008213:Lymphocyte Activation / Q000276:immunology*; D009895:Opsonin Proteins / Q000097:blood; D010750:Phosphoproteins / Q000276:immunology* / Q000494:pharmacology; D017186:Titrimetry; D014763:Viral Matrix Proteins / Q000276:immunology* / Q000494:pharmacology
chemical_list: D000914:Antibodies, Viral; D000956:Antigens, Viral; D016207:Cytokines; D018984:Epitopes, T-Lymphocyte; D015395:Histocompatibility Antigens Class I; D009895:Opsonin Proteins; D010750:Phosphoproteins; D014763:Viral Matrix Proteins; C065418:cytomegalovirus matrix protein 65kDa