Jack A. Ragheb

Molecular regulation of interleukin-2 expression by CD28 co-stimulation and anergy

Summary: The consequences of T‐cell receptor engagement (signal I) are profoundly affected by the presence or absence of co‐stimulation (signal 2). T‐cell receptor (TCR) stimulation in the absence of CD 28‐mediated co‐stimulation not only results in little interleukin (IL)‐2 production, but induces a long lasting hyporesponsive state known as T‐cell clonal anergy The addition of CD 28 ligation to signal 1, on the other hand, results in the production of copious amounts of IL‐2. Our laboratory has utilized CD4+ Th1 clones in an effort to understand the molecular events resulting in enhanced IL‐2 production by co‐stimulation and the inhibition of IL‐ 2 production in anergy Our current studies have focused on defining the post‐transcriptional effects of CD28‐enhanced IL‐2 production The data suggest that a major component of CD28′s ability to regulate IL‐2 production occurs at the level of message stability and involves the 3′‐untranslated region of the message. In terms of anergy, our recent studies support the notion that it is not the result of TCR engagement in the absence of co‐stimulation. but rather signal 1 in the absence of IL‐2 receptor signaling and proliferation. Furthermore, T‐cell anergy appears to be an active negative state in which IL‐2 production is inhibited both at the level of signal transduction and by cis‐dominant repression at the level of the IL‐2 promoter.

A Double-masked, Randomized Study to Investigate the Safety and Efficacy of Daclizumab to Treat the Ocular Complications Related to Behcet's Disease

Purpose: To investigate the safety and efficacy of daclizumab (Zenapax, humanized anti-Tac, HAT) in controlling the ocular manifestations of Behçets disease. Design: Randomized, placebo-controlled, double-masked clinical trial. Participants: Seventeen participants with Behçets disease experiencing at least two prior ocular attacks and requiring treatment with immunosuppressive agents for the ocular complications of Behçets disease. Methods: Participants received either intravenous placebo or daclizumab (1 mg/kg) infusions every two weeks for six weeks, then every four weeks while continuing their standard immunosuppressive regimens. If clinically indicated, tapering of the standard immunosuppressive medications was allowed after six months of study enrollment. Complete ocular and physical examinations and an adverse event assessment were performed at baseline and prior to each study infusion. Main Outcome Measures: Primary safety endpoints were the development of a life-threatening complication or a severe opportunistic infection. Primary efficacy outcomes were the number of ocular attacks and an assessment of systemic immunosuppressive medications required during the study, including the ability to taper concomitant immunosuppressive therapy. Results: Nine participants randomized to daclizumab and eight to placebo were followed monthly. Follow-up ranged from one to 34 months, with a median follow-up of 15 months. Two participants randomized to daclizumab discontinued study therapy prior to the end of the study for personal reasons. No participant experienced a safety endpoint, and visual acuity remained stable in all participants during the course of the study. Ten participants (six daclizumab, four placebo) experienced ocular attacks requiring therapy. The median ocular attack rate during the study was greater in the daclizumab arm than the placebo arm (median 1.27 vs. 0.17 attacks/year, respectively). Participants in the placebo arm also experienced a greater reduction in the immunosuppressive medication score compared to participants receiving daclizumab (median –4.0 vs. –1.0, respectively). Conclusions: The observed results in the placebo group demonstrate that careful follow-up and treatment with standard combination immunosuppressive therapy can be effective for the management of the ocular complications of Behçets disease. In our small study, there was no suggestion that daclizumab was beneficial in comparison with placebo. However, the low observed attack rate limited our ability to make a definitive treatment group comparison.

IL-2 Receptor Blockade Inhibits Late, But Not Early, IFN-γ and CD40 Ligand Expression in Human T Cells: Disruption of Both IL-12-Dependent and -Independent Pathways of IFN-γ Production

mAbs directed against the α-chain (Tac/CD25) of the IL-2R are an emerging therapy in both transplantation and autoimmune disease. However, the mechanisms underlying their therapeutic efficacy have not been fully elucidated. Therefore, we examined the affect of IL-2R blockade on Th1 and Th2 cytokine production from human PBMC. Addition of a humanized anti-Tac Ab (HAT) to activated PBMC cultures inhibited IFN-γ production from CD4 and CD8 T cells by 80–90%. HAT partially inhibited production of TNF-α and completely inhibited production of IL-4, IL-5, and IL-10. Furthermore, IL-12, a central regulatory cytokine that induces IFN-γ, was undetectable in treated cultures. As T cell-dependent induction of IL-12 is regulated via CD40/CD40 ligand (CD40L) interactions, we examined the affect of HAT on CD40L expression. We found CD40L expression to be biphasic with an early (6 h) peak that is CD28/IL-2-independent, but a later peak (48 h) being CD28/IL-2-dependent and inhibited by HAT. Similarly, IFN-γ production at 6 h was CD28/IL-2-independent but CD28/IL-2-dependent and inhibited by HAT at 48 h. Nonetheless, addition of rCD40L or exogenous IL-12 to HAT-treated cultures could not restore IFN-γ production. The IFN-γ deficit in such cultures appears to be due to a direct inhibition by HAT of IL-12-independent IFN-γ production from T cells rather than altered expression of either the IL-12Rβ1 or IL-12Rβ2 chains. These data demonstrate that IL-2 plays a critical role in the regulation of Th1 and Th2 responses and impacts both IL-12-dependent and -independent IFN-γ production.

High-dose humanized anti-IL-2 receptor alpha antibody (daclizumab) for the treatment of active, non-infectious uveitis.

PURPOSE This study was designed to provide preliminary data regarding the safety and efficacy of high-dose humanized anti-IL-2 receptor (daclizumab) therapy for the treatment of active intermediate, posterior or panuveitis. METHODS Five patients were recruited into this non-randomized, prospective pilot study of high-dose intravenous induction daclizumab therapy given at doses of 8mg/kg at day 0 and 4mg/kg at day 14. Patients who did not meet a safety endpoint at the 3-week follow-up evaluation were given the option of continuing therapy with subcutaneous daclizumab at 2mg/kg every 4 weeks for 52 weeks. The primary outcome assessed was a two-step decrease in vitreous haze at day 21. Secondary outcomes evaluated included best-corrected visual acuity, retinal thickness as measured by optical coherence tomography, retinal vascular leakage assessed by fluorescein angiography, anterior chamber and vitreous cellular inflammation. RESULTS Four male patients and one female patient were enrolled. Diagnoses included birdshot retinochoroidopathy (two patients), Vogt-Koyanagi-Haradas disease, bilateral idiopathic panuveitis and bilateral idiopathic intermediate uveitis. By the 4th week, four of five patients demonstrated a two-step decrease in vitreous haze. The other participant did not meet this criterion until week 20, but all five patients maintained stability in vitreous haze grade throughout their follow-up periods. At enrollment, mean visual acuity (10 eyes in 5 patients) was 69.2 ETDRS letters and following treatment was 78.2 letters (p<0.12). Anterior chamber cell, vitreous cell, and vitreous haze also improved in the majority of eyes. Adverse events were generally mild except for one episode of left-lower lobe pneumonia requiring hospitalization and treatment. CONCLUSION This is the first demonstration that high-dose daclizumab can reduce inflammation in active uveitis. Daclizumab was well tolerated but there may be a potential increased risk of infection associated with immunosuppression. All five patients demonstrated a decrease in vitreous haze and measures of intraocular inflammation at final follow-up. The results of this small, non-randomized pilot study support the consideration of high-dose daclizumab therapy in cases of active posterior uveitis.

Human CD14hi monocytes and myeloid dendritic cells provide a cell contact–dependent costimulatory signal for early CD40 ligand expression

CD40L on CD4(+) T cells plays a vital role in the activation of antigen-presenting cells, thus catalyzing a positive feedback loop for T-cell activation. Despite the pivotal juxtaposition of CD40L between antigen-presenting cells and T-cell activation, only a T-cell receptor stimulus is thought to be required for early CD40L surface expression. We show, for the first time, that CD40L expression on peripheral blood CD4(+) T cells is highly dependent on a cell-cell interaction with CD14(hi)CD16(-) monocytes. Interactions with ICAM-1, LFA-3, and to a lesser extent CD80/CD86 contribute to this enhancement of CD40L expression but are not themselves sufficient. The contact-mediated increase in CD40L expression is dependent on new mRNA and protein synthesis. Circulating myeloid dendritic cells also possess this costimulatory activity. By contrast, CD14(lo)CD16(+) monocytes, plasmacytoid dendritic cells, B-cell lymphoma lines, and resting, activated, and Epstein-Barr virus-immortalized primary B cells all lack the capacity to up-regulate early CD40L. The latter indicates that a human B cell cannot activate its cognate T cell to deliver CD40L-mediated help. This finding has functional implications for the role of biphasic CD40L expression, suggesting that the early phase is associated with antigen-presenting cell activation, whereas the late phase is related to B-cell activation.

Targeted infection of HIV-1 Env expressing cells by HIV(CD4/CXCR4) vectors reveals a potential new rationale for HIV-1 mediated down-modulation of CD4

BackgroundEfficient targeted gene transfer and cell type specific transgene expression are important for the safe and effective expression of transgenes in vivo. Enveloped viral vectors allow insertion of exogenous membrane proteins into their envelopes, which could potentially aid in the targeted transduction of specific cell types. Our goal was to specifically target cells that express the T cell tropic HIV-1 envelope protein (Env) using the highly specific interaction of Env with its cellular receptor (CD4) inserted into the envelope of an HIV-1-based viral vector.ResultsTo generate HIV-1-based vectors carrying the CD4 molecule in their envelope, the CD4 ectodomain was fused to diverse membrane anchors and inserted together with the HIV-1 coreceptor CXCR4 into the envelopes of HIV-1 vector particles. Independent of the type of CD4 anchor, all chimeric CD4 proteins inserted into HIV-1 vector envelopes and the resultant HIV(CD4/CXCR4) particles were able to selectively confer neomycin resistance to cells expressing the fusogenic T cell tropic HIV-1 Env protein. Unexpectedly, in the absence of Env on the target cells, all vector particles carrying the CD4 ectodomain anchored in their envelope adhered to various cell types without infecting these cells. This cell adhesion was very avid. It was independent of the presence of Env on the target cell, the type of CD4 anchor or the presence of CXCR4 on the particle. In mixed cell populations with defined ratios of Env+/Env- cells, the targeted transduction of Env+ cells by HIV(CD4/CXCR4) particles was diminished in proportion to the number of Env- cells.ConclusionVector diversion caused by a strong, non-selective cell binding of CD4+-vector particles effectively prevents the targeted transduction of HIV-1 Env expressing cells in mixed cell populations. This Env-independent cell adhesion severely limits the effective use of targeted HIV(CD4/CXCR4) vectors designed to interfere with HIV-1 replication in vivo. Importantly, the existence of this newly described and remarkably strong CD4-dependent cell adhesion suggests that the multiple viral efforts to reduce CD4 cell surface expression may, in part, be to prevent cell adhesion to non-target cells and thereby to increase the infectivity of viral progeny. Preventing CD4 down-modulation by HIV-1 might be an effective component of a multi-faceted antiviral strategy.