In vitro priming of cytotoxic T lymphocytes against poorly immunogenic epitopes by engineered antigen‐presenting cells

Abstract

Cytotoxic T lymphocytes (CTL) recognize antigenic peptides presented by major histocompatibility complex class I (MHC-I) molecules on the surface of target cells. Optimal induction of CD8+ CTL depends on the amount of relevant peptide/MHC-I complexes and the presence of co-stimulatory molecules on antigen-presenting cells (APC). The antigen-processing defective mutant cell line RMA-S, when cultured at low temperature, expresses high amounts of MHC-I molecules that do not contain endogenously derived peptides. These "empty" MHC-I molecules can be stabilized by addition of MHC-binding peptides. RMA-S cultured at low temperatures with selected peptides have been used for in vitro CTL induction with conflicting results. RMA-S cells do not express detectable amounts of B7 co-stimulatory molecule. This could explain their unpredictable efficiency as APC. We have evaluated whether RMA-S cells, stably transfected with cDNA encoding for the human B7.1 molecule could provide effective co-stimulation for CD8+ T lymphocytes. RMA-S/B7 cells, loaded with different synthetic peptides, demonstrated a high and sometimes unique efficiency for in vitro primary CTL induction, even when "sub-optimal" antigen peptides were used. Most importantly, RMA-S/B7 cells pulsed with naturally processed peptides extracted from the poorly immunogenic B16 melanoma cells were able to prime CD8+ cells against B16 melanoma. We conclude that the use of RMA-S/B7 cells as APC represents an ideal strategy for in vitro CTL immunization without prior in vivo priming. This system may also help to address the issue of the different contributions of co-stimulation and relative occupancy of MHC-I by single peptide epitopes in CTL priming.

Overexpression of interleukin‐15 in vivo enhances antitumor activity against mhc class I‐negative and ‐positive malignant melanoma through augmented NK activity and cytotoxic T‐cell response

“…B16 is a spontaneous and weakly immunogenic melanoma, which nevertheless contains Ags able to activate a specific CTL response. 23 In our study, we showed that IL-15 Tg mice developed a significant level of Ag-specific CTLs after inoculation with MHC class I-positive melanoma cells, which contribute to retardation of the tumor growth. The tumor growth of MHC class I-negative melanoma cells was also retarded in IL-15 Tg mice, and the antitumor activity against MHC class I-negative melanoma cells was found to depend exclusively on the presence of NK cells.…”

“…22 MHC class I-expressing melanoma cells contain Ags able to activate cytotoxic CD8 ϩ T cells, although they are weakly immunogenic. [23][24][25] On the other hand, MHC class I-deficient melanoma is not destroyed by cytotoxic CD8 ϩ T cells but is susceptible to NK cells, 26 most of which express MHC class I-specific inhibitory receptors. 27,28 We report here that the tumor growth of both MHC class I-expressing and -deficient B16 melanoma cells is severely retarded in IL-15 Tg mice.…”

Inhibitory effect of the polyinosinic‐polycytidylic acid/cationic liposome on the progression of murine B16F10 melanoma

“…Interestingly, however, the low immunogenicity of B16 melanoma does not necessarily result in the failure to induce an effective anti-tumor immune response. Indeed, APC pulsed with B16-derived peptide epitopes are capable of eliciting specific CTL reactions directed against B16 melanoma both in vitro [24] and in vivo [25]. Furthermore, the transfection of B16 with the K b molecule converts it into a strongly immunogenic tumor in vivo [26] and renders it susceptible to rejection by immunocompetent mice [27].…”

Characterization of Lung γδ T Cells Following Intranasal Infection withMycobacterium bovisBacillus Calmette-Guérin

“…IL-12 production, indirectly induced by ␥␦ T cells, may participate in the induction of CD8 T cells. Additionally, up-regulation of costimulatory molecules, such as CD80 and CD86 (36), on macrophages and/or dendritic cells by ␥␦ T cells would be another mechanism of supporting CD8 T cell induction (37).…”