The interchain disulfide linkage of T-cell antigen receptor-alpha and -beta chains is a prerequisite for T-cell activation

CD3ζ-chain expression of human T lymphocytes is regulated by TNF via Src-like adaptor protein-dependent proteasomal degradation

Decreased expression of the TCR ζ-chain has been reported in several autoimmune, inflammatory, and malignant diseases, suggesting that ζ-chain downregulation is common at sites of chronic inflammation. Although ζ-chain is critically important in T lymphocyte activation, the mechanism of the decreased ζ-chain expression is less clear. Src-like adaptor protein (SLAP) is a master regulator of T cell activation; previous data have reported that SLAP regulates immunoreceptor signaling. We have examined the mechanism and the functional consequences of CD3 ζ-chain downregulation. TNF treatment of human T lymphocytes (15-40 ng/ml) selectively downregulates CD3 ζ-chain expression in a dose-dependent manner (p < 0.05) and decreases activation-induced IL-2 expression (p < 0.01). Although blocking of the lysosomal compartment fails to restore TNF-induced CD3 ζ-chain downregulation, inhibition of the proteasome prevented the effect of TNF. Both SLAP expression and the colocalization of SLAP with CD3 ζ-chain was enhanced by TNF treatment (p < 0.05 and p < 0.01, respectively), whereas TNF-induced ζ-chain downregulation was inhibited by gene silencing of SLAP with small interfering RNA. SLAP levels of the CD4(+) T lymphocytes isolated from patients with rheumatoid arthritis were more than 2-fold higher than that of the healthy donors' (p < 0.05); moreover, TNF treatment did not alter the SLAP expression of the CD4(+) cells of anti-TNF therapy-treated patients. Our present data suggest that TNF modulates T cell activation during inflammatory processes by regulating the amount of CD3 ζ-chain expression via a SLAP-dependent mechanism. These data provide evidence for SLAP-dependent regulation of CD3 ζ-chain in the fine control of TCR signaling.

Enhanced antitumor activity of T cells engineered to express T-cell receptors with a second disulfide bond

Adoptive transfer of genetically T-cell receptor (TCR)-modified lymphocytes has been recently reported to cause objective cancer regression. However, a major limitation to this approach is the mispairing of the introduced chains with the endogenous TCR subunits, which leads to reduced TCR surface expression and, subsequently, to their lower biological activity. We here show that it is possible to improve TCR gene transfer by adding a single cysteine on each receptor chain to promote the formation of an additional interchain disulfide bond. We show that cysteine-modified receptors were more highly expressed on the surface of human lymphocytes compared with their wild-type counterparts and able to mediate higher levels of cytokine secretion and specific lysis when cocultured with specific tumor cell lines. Furthermore, cysteine-modified receptors retained their enhanced function in CD4(+) lymphocytes. We also show that this approach can be employed to enhance the function of humanized and native murine receptors in human cells. Preferential pairing of cysteine-modified receptor chains accounts for these observations, which could have significant implications for the improvement of TCR gene therapy.

Novel cationic lipophilic peptides for oligodeoxynucleotide delivery

In search of new oligodeoxynucleotide (ODN) delivery agents, we evaluated novel peptides derived from core peptide H-GLRILLLKV-OH (CP). CP is a fragment designed from the T-cell antigen receptor (TCR) alpha-chain transmembrane sequence. CP was able to enter cells including T-cells and inhibited interleukin-2 (IL-2) production. To examine the effect of increased lipophilicity on cellular uptake and activity of CP, a lipoamino acid (2-aminododecanoic acid) was incorporated into peptide CP resulting in 2-aminodecanoyl-CP (LP). The toxicity of CP and LP was assessed by measuring the haemolytic activity. Neither compound caused any haemolysis of red blood cells. We have also compared the biological activities of the CP and LP. Using a T-cell antigen presentation assay, the more lipophilic LP caused greater inhibition of IL-2 production than the parent CP in the antigen stimulated T-cells. The LP also showed increased permeability than CP in the Caco-2 cell assay. We utilised the enhanced cell permeability property of LP in oligodeoxynucleotide ODN1 delivery. Isothermal titration calorimetry (ITC) suggested that CP and LP complex with ODN1 in a 12:1 (CP:ODN1) and 15:1 (LP:ODN1) ratio. These complexes were then transfected into human retinal pigment epithelial cells. The level of transfection was measured by the decreased production of the protein human vascular endothelial growth factor (hVEGF). The results revealed greater transfection efficiency for both CP and LP (47%, 55% more inhibition) compared to commercially available transfection agent cytofectin GSV. These results suggested that the CP and particularly its lipophilic analogue LP have the potential to be used as oligodeoxynucleotide delivery systems.

Dendritic cells, engineered to secrete a T-cell receptor mimic peptide, induce antigen-specific immunosuppression in vivo

A T-cell receptor mimic peptide (TCRpep) consisting of an 8-amino-acid peptide, homologous to the transmembrane region of the T-cell receptor (TCR) alpha chain, blocks T-cell activation after systemic application. When dendritic cells (DCs) were transduced to secrete the TCRpep and injected into mice, evidence of immunosuppression was observed. In a CD8-driven allergy model, the injection of DCs transduced with the TCRpep reduced inflammation markedly and in a CD4+ T cell-dependent model of multiple sclerosis (experimental autoimmune encephalitis, EAE), injection of TCRpep-secreting DCs abrogated EAE symptoms and prolonged survival. These effects were antigen specific, because transduced DCs that did not express the respective antigen failed to convey protection in the allergy model as well as in the EAE model. Thus these data show that DCs expressing the TCRpep are able to suppress T-cell activation and might be a useful tool for inducing antigen-specific immune suppression in vivo.