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

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.     

Interaction of papain-digested HLA class I molecules with human alloreactive cytotoxic T lymphocytes (CTL)

Acute immunological rejection events of transplanted allogeneie organs are strongly dependent on T cell reactivity against foreign MHC products. The recognition requirements of alloreactive cytotoxic T cells arc of particular interest for finding approaches to modulating allorcactivity. The role of the allogeneic MHC molecule itself and/or an associated peptide in the interaction with the T cell receptor is still, however, unclear. Our studies have focused on the interactions of papain-digested HLA class I molecules with alloreactivc CD8⁺ CTL. These polypeptidcs, consisting of the polymorphic α1 and α2 and the monomorphic α3 domains, were used in both soluble and immobilized form to study their functional effects on anti-HLA-A2 reactive CTL. Purified polypeptides were of molecular mass 32–34 kD. HLA-A2 polypcptides (0–55 μg/ml) in soluble form induced half-maximal reduction of CTL cytotoxicity. These concentrations were quantitatively comparable to the effective doses of intact HLA class I molecules, which contain the hydrophobic transmembrane domain and the intracytoplasmic tail. In addition, specific activation requirements of these CTL were investigated in a serine esterasc release assay. Maximal degranulation was observed after 2 h of antigen contact. Purified HLA class I molecules allospccifically activated the anti-HLA-A2 CTL to degranulate serine esterase, when immobilized on plastic microtitre plates. Thus, polypeptidcs containing the polymorphic αl and α2 domains of human class I molecules potentially modulate the cytotoxic T cell response. This might have implications for the reduction or prevention of allograft rejection in recipients of foreign organs.     

HBsAg体外冲击的慢性乙肝患者树突状细胞的生物学特性及其对HBV特异性CTL的诱导作用

目的 :研究HBsAg冲击的慢性乙肝患者单核细胞来源的树突状细胞 (DCs)的功能状况及体外对HBV特异性CTL的诱导作用 ,初步探讨诱导特异性抗HBV细胞免疫的途径。方法 :分离慢性乙肝患者外周血单核细胞 ,以GM CSF +IL 4 +TNF α培养诱导DCs,加入HBsAg冲击以诱导HBV特异性DCs。采用FCM测定细胞表面免疫分子CD1a、CD83、CD86、CD80、CD4 0以及HLA DR的表达水平 ,ELISA法检测培养上清中细胞因子IL 6、IL 12的分泌含量 ,MTT法测定DC刺激同种异体淋巴细胞增殖的能力 ,LDH法检测DC诱导的患者外周血T细胞对HepG2 2 2 15 (转染HBVDNA)、HepG2肝癌细胞株及K5 6 2白血病细胞株的细胞毒作用。结果 :HBsAg冲击的DC其表达CD1a、CD83、CD86、CD80、CD4 0、HLA DR表面分子明显高于对照组 (P <0 0 1,P <0 0 5 ) ,分泌IL 12的水平也高于对照组 (P <0 0 1) ,而分泌IL 6的水平则较对照组显著降低(P <0 0 1) ;HBsAg冲击的DC刺激同种异体淋巴细胞增殖的能力明显增强 (P <0 0 5 ) ,并可有效地诱导自体CTL对转HBV基因的HepG2 2 2 15细胞高效特异性杀伤作用 (P <0 0 1)。结论 :慢性乙型肝炎患者单核细胞来源的DCs经HBsAg抗原冲击后 ,生物学活性增强 ,并且能有效地诱导对HBV特异性反应的CTL。     

Peptide specific expansion of CD8(+) T cells by recombinant plate bound MHC/peptide complexes

Development of methods for efficient in vitro stimulation and expansion of peptide specific CD8⁺ T cells is compelling not only with respect to adoptive T cell therapy but also regarding analysis of T cell responses and search for new immunogenic peptides. In the present study, a new approach to in vitro T cell stimulation was investigated. By use of an antigenic peptide derived from the cytomegalovirus (CMVp) we tested the stimulatory efficacy of recombinant plate bound MHC molecules (PB-MHC), being immobilized in culture plates. A single stimulation of non-adherent peripheral blood mononuclear cells (NA-PBMCs) with PB-MHC/CMVp resulted in significant expansion of CMVp specific CD8⁺ T cells, which was comparable to that achieved by CMVp pulsed mature dendritic cells (DCs). By repeated exposure of NA-PBMCs to PB-MHC/CMVp more than 60% CMVp specific CD8⁺ T cells, representing a 240-fold expansion, were reached after only two stimulations. Although stimulation with PB-MHC/CMVp clearly demonstrated efficient peptide specific expansion of CD8⁺ T cells, there was a tendency to proliferative exhaustion of the cells after 3-4 stimulations. Thus, it will be of interest to examine the effect of new stimulatory cocktails, e.g. cytokines and co-stimulatory molecules, by use of the present rapid and easy-to-use method of expanding peptide specific T cells.     

MAdCAM-1 costimulates T cell proliferation exclusively through integrin α4β7, whereas VCAM-1 and CS-1 peptide use α4β1: evidence for “remote” costimulation and induction of hyperresponsiveness to B7 molecules

We have analyzed the effects of the α⁴ integrin ligands mucosal addressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1), and the fibronectin CS-1 splice variant on T cell activation. Immobilized MAdCAM-1 and VCAM-1 IgG-Fc chimeras and a fibronectin CS-1 peptide efficiently costimulate T cell proliferation when antigen presentation is mimicked by anti-CD3 antibody. VCAM-1-Fc and fibronectin CS-1, which are adhesive ligands for both the α⁴ β₁ and α⁴ β₇ integrins, medicate T cell costimulation exclusively through integrin α⁴ β₁, but not through α⁴ β₇. The inability of VCAM-1-Fc to costimulate via α⁴ β₇ suggests that cell adhesion per se is insufficient, and that exquisite recognition and activation events must be triggered. MAdCAM-1-Fc mediates costimulation exclusively via α⁴ β₇, and can both synergize with and induce hyperresponsiveness to the classical costimulator B7-2. MAdCAM-1-Fc and VCAM-1-Fc, but not B7-2, effectively costimulate when immobilized on sites spatially distant from the anti-CD3 antibody (“remote” costimulation). In vitro, the relative potencies of the CAM were VCAM-1-Fc > ICAM-1-Fc > MAdCAM-1-Fc > B7-Fc, except at high concentrations where ICAM-1 was the most potent. Features of costimulatory CAM revealed by this study have important implications for the design of immunotherapeutic vaccine strategies to combat cancer and infection.     

Presentation of a horse cytochrome c peptide by multiple H-2b class I major histocompatibility complex (MHC) molecules to C57BL/6- and bm1-derived cytotoxic T lymphocytes: Presence of a single MHC anchor residue may confer efficient peptide-specific CTL recognition

In this study the immunogenic tryptic fragment from a horse cytochrome c (cyt c) digest recognized by cytotoxic T lymphocytes (CTL), induced by in vitro peptide stimulation from C57BL/6 (B6) and mutant B6.C-H-2^bm1 (bm1) mice is identified. An identical sequence, p40—53, is recognized by CTL from both B6 and bm1 mice. In addition, both B6 and bm1 cloned CTL lines display unusual major histocompatibility complex (MHC) class I-restricted recognition of this peptide in that they respond to it in the context of H-2K^b, H-2D^b, and H-2K^bm1 class I molecules, although the sequence lacks the usual structural K^b and D^b peptide-binding motifs. Truncated analogues which resemble the lengths of naturally processed MHC class I-presented peptides, confer reactivity for B6 and bm1 CTL against EL4 (H-2^b) targets as well as the L cell transfectants, L + K^b, L + D^b, and L + K^bm1. The antigenic peptide with the greatest potency is p41—49, which appears to be generated by angiotensin converting enzyme cleavage of the full-length p40—53 tryptic peptide. The minimum antigenic peptide recognized by both B6 and bm1 CTL, and which targets lysis on each of the transfectants, is the hexamer p43—48 peptide from horse cyt c. Residues Pro⁴⁴ and Thr⁴⁷, which occupy polymorphic positions with respect to other species-variant cyt c molecules, influence recognition of these peptides differently for the B6 and bm1 CTL. The ability of H-2K^b, H-2D^b, and mutant H-2K^bm1 class I molecules to present the same peptide to a single cloned CTL is discussed in the context of current knowledge of peptide anchor residues and side chain-specific binding pockets in the MHC class I peptide-binding site.     

In vitro cell-mediated immune responses to Plasmodium falciparum schizont antigens in adults from a malaria endemic area: CD8+ T lymphocytes inhibit the response of low responder individuals

Plasmodium falciparum schizont extract and purified protein derivative were used to stimulate peripheral blood mononuclear cells obtained from healthy aparasitemic Gabonese individuals with lifelong exposure to malaria infection and non-Gabonese control subjects who have had had no clinical malaria. In vitro lymphoproliferation was measured by uptake of tritiated thymidine, while production of interleukin-2, interferon-gamma, and soluble CD8+ were measured by immunoenzymatic assays. Enumeration of interferon-gamma-producing cells was done using a modified immunoenzyme spot assay. Twenty-eight percent of Gabonese subjects were determined to be low responders in the lymphoproliferative assay, with a tritiated thymidine uptake of less than 6000 c.p.m. The proportions of T cell subsets and the kinetics of the proliferative response were similar in the low and the high responders. Removal of CD8+ T cells from mononuclear cells of low responders or culture of purified CD4+ T cells from the same individuals resulted in a 7-fold increase in the proliferative response to the schizont antigen but not to purified protein derivative (PPD). A similar increase in the proliferative response was seen in the low but not the high responder mononuclear cell cultures stimulated with the schizont antigen in the presence of exogenous interleukin 2 (IL-2) or in the presence of anti-HLA-DQ antibody. Low responder mononuclear cell cultures stimulated with schizont antigen but not PPD produced 3-fold less IL-2, 14-fold less interferon-gamma (IFN-gamma), and 3-fold more soluble CD8 than high responder mononuclear cell cultures. Removal of CD8+ T cells from low responder mononuclear cells resulted in a 2-fold increase in IL-2 production and a 4-fold increase in IFN-gamma production in response to schizont antigen. High responder mononuclear cells stimulated with schizont antigen contained four times as much IFN-gamma-producing cells as low responder cultures, with each IFN-gamma-producing cell producing three times the amount of IFN-gamma as that produced by an IFN-gamma-producing cell in low responder cultures. Removal of CD8+ T cells from low responder mononuclear cells led to a significant increase in the amount of IFN-gamma produced at the single cell level in response to schizont antigen stimulation. In such cultures, the amount of IFN-gamma produced by a single cell was similar between high and low responders. We conclude that in certain individuals, T cell responses to schizont antigen are actively down-regulated by activated schizont-specific CD8+ suppressor T cells.(ABSTRACT TRUNCATED AT 400 WORDS)