Short course single agent therapy with an LFA-3-IgG1 fusion protein prolongs primate cardiac allograft survival

In vitro Evidence That Combination Therapy With CD16-Bearing NK-92 Cells and FDA-Approved Alefacept Can Selectively Target the Latent HIV Reservoir in CD4+ CD2hi Memory T Cells

Elimination of the latent HIV reservoir remains the biggest hurdle to achieve HIV cure. In order to specifically eliminate HIV infected cells they must be distinguishable from uninfected cells. CD2 was recently identified as a potential marker enriched in the HIV-1 reservoir on CD4+ T cells, the largest, longest-lived and best-characterized constituent of the HIV reservoir. We previously proposed to repurpose FDA-approved alefacept, a humanized α-CD2 fusion protein, to reduce the HIV reservoir in CD2hi CD4+ memory T cells. Here, we show the first evidence that alefacept can specifically target and reduce CD2hi HIV infected cells in vitro. We explore a variety of natural killer (NK) cells as mediators of antibody-dependent cell-mediated cytotoxicity (ADCC) including primary NK cells, expanded NK cells as well as the CD16 transduced NK-92 cell line which is currently under study in clinical trials as a treatment for cancer. We demonstrate that CD16.NK-92 has a natural preference to kill CD2hi CD45RA- memory T cells, specifically CD45RA- CD27+ central memory/transitional memory (TCM/TM) subset in both healthy and HIV+ patient samples as well as to reduce HIV DNA from HIV+ samples from donors well controlled on antiretroviral therapy. Lastly, alefacept can combine with CD16.NK-92 to decrease HIV DNA in some patient samples and thus may yield value as part of a strategy toward sustained HIV remission.

Can We Repurpose FDA-Approved Alefacept to Diminish the HIV Reservoir?

Current anti-retroviral treatment (ART) for HIV is effective in maintaining HIV at undetectable levels. However, cessation of ART results in immediate and brisk rebound of viremia to high levels. This rebound is driven by an HIV reservoir mainly enriched in memory CD4+ T cells. In order to provide any form of functional HIV Cure, elimination of this viral reservoir has become the focus of current HIV cure strategies. Alefacept was initially developed for the treatment of chronic plaque psoriasis. Alefacept is a chimeric fusion protein consisting of the CD2-binding portion of human leukocyte function antigen-3 (LFA3) linked to the Fc region of human IgG1 (LFA3-Fc). Alefacept was designed to inhibit memory T cell activation that contributes to the chronic autoimmune disease psoriasis by blocking the CD2 coreceptor. However, it was found to deplete memory T cells that express high levels of CD2 via NK cell-mediated antibody dependent cell cytotoxicity (ADCC) in vivo. Phase II and phase III clinical trials of alefacept with psoriasis patients demonstrated promising results and an excellent safety profile. Subsequently, alefacept has been successfully repurposed for other memory T cell-mediated autoimmune diseases including skin diseases other than psoriasis, organ transplantation and type I diabetes (T1D). Herein, we review our specific strategy to repurpose the FDA approved biologic alefacept to decrease and hopefully someday eliminate the HIV reservoir, for which CD2hi memory CD4+ T cells are a significant contributor.

Use of Alefacept for Preconditioning in Multiply Transfused Pediatric Patients with Nonmalignant Diseases

Transfusion-related alloimmunization is a potent barrier to the engraftment of allogeneic hematopoietic stem cells in patients with nonmalignant diseases (NMDs). Memory T cells, which drive alloimmunization, are relatively resistant to commonly used conditioning agents. Alefacept, a recombinant leukocyte function antigen-3/IgG1 fusion protein, targets CD2 and selectively depletes memory versus naive T cells. Three multiply transfused pediatric patients with NMD received a short course of high-dose i.v. alefacept (.25 mg/kg/dose on days -40 and -9 and .5 mg/kg/dose on days -33, -26, -19, and -12) before undergoing unrelated allogeneic transplant in the setting of reduced-intensity pretransplant conditioning and calcineurin inhibitor-based post-transplant graft-versus-host disease (GVHD) prophylaxis. Alefacept infusions were well tolerated in all patients. Peripheral blood flow cytometry was performed at baseline and during and after alefacept treatment. As expected, after the 5 weekly alefacept doses, each patient demonstrated selective loss of CD2(hi)/CCR7(-)/CD45RA(-) effector memory (Tem) and CD2(hi)/CCR7(+)/CD45RA(-) central memory (Tcm) CD4(+) and CD8(+) T cells with relative preservation of the CD2(lo) Tem and Tcm subpopulations. In addition, depletion of CD2(+) natural killer (NK) cells also occurred. Neutrophil recovery was rapid, and all 3 patients had 100% sorted (CD3/CD33) peripheral blood donor chimerism by day +100. Immune reconstitution (by absolute neutrophil, monocyte, and lymphocyte counts) was comparable with a cohort of historical control patients. All 3 patients developed GVHD but are all now off immune suppression and >2 years post-transplant with stable full-donor engraftment. These results suggest that alefacept at higher dosing can deplete both memory T cells and NK cells and that incorporating CD2-targeted depletion into a reduced-intensity transplant regimen is feasible and safe in heavily transfused patients.

Primate models in organ transplantation

Large animal models have long served as the proving grounds for advances in transplantation, bridging the gap between inbred mouse experimentation and human clinical trials. Although a variety of species have been and continue to be used, the emergence of highly targeted biologic- and antibody-based therapies has required models to have a high degree of homology with humans. Thus, the nonhuman primate has become the model of choice in many settings. This article will provide an overview of nonhuman primate models of transplantation. Issues of primate genetics and care will be introduced, and a brief overview of technical aspects for various transplant models will be discussed. Finally, several prominent immunosuppressive and tolerance strategies used in primates will be reviewed.

Alefacept combined with tacrolimus, mycophenolate mofetil and steroids in de novo kidney transplantation: a randomized controlled trial

Memory T cells play a central role in mediating allograft rejection and are a rational target for immunosuppressive therapy. Alefacept is a recombinant LFA3/IgG1 fusion protein that reduces the number of memory T cells in both psoriatic lesions and the peripheral circulation of psoriasis patients. This study evaluated the efficacy and safety of alefacept compared with placebo when combined with tacrolimus, mycophenolate mofetil and corticosteroids in de novo renal transplant recipients. Between December 2007 and March 2009 patients were randomized in a double-blind fashion to receive alefacept (n = 105) or placebo (n = 107) for 3 months and were then followed for a further 3 months. The primary efficacy endpoint was the incidence of biopsy-confirmed acute T cell mediated rejection (Banff grade ≥ 1) through Month 6. Memory T cell counts were significantly reduced in the alefacept group from Week 3 to study end compared with placebo. However, there was no significant difference between the alefacept and placebo groups for the primary efficacy endpoint (alefacept, 11.0% vs. placebo, 7.0%, p = 0.3). Patient and graft survival as well as renal function was similar between treatment groups. Safety and tolerability were generally similar between the treatment arms. Malignancy was higher in the alefacept treatment arm.

Lymphodepletional strategies in transplantation

Because lymphocytes were shown to mediate transplant rejection, their depletion has been studied as a mechanism of preventing rejection and perhaps inducing immunologic tolerance. Agents that profoundly deplete lymphocytes have included monoclonal antibodies, cytotoxic drugs, and radiation. We have studied several such agents but focused on antibodies that deplete not only peripheral blood lymphocytes, but also lymph node lymphocytes. Depletion of lymph node T lymphocytes appears to permit peripheral tolerance at least for T cells in animal models. Nevertheless, B-cell responses may be resistant to such approaches, and T memory cells are likewise relatively resistant to depleting antibodies. We review the experimental and clinical approaches to depletion strategies and outline some of the pitfalls of depletion, such as limitations of currently available agents, duration of tolerance, infection, and malignancy. It is notable that most tolerogenic strategies that have been attempted experimentally and clinically include depleting agents even when they are not named as the underlying strategy. Thus, there is an implicitly acknowledged role for reducing the precursor frequency of donor antigen-specific lymphocytes when approaching the daunting goal of transplant tolerance.

Co-stimulation blockade as a new strategy in kidney transplantation: benefits and limits

New immunosuppressive drugs have greatly decreased the frequency of graft failure due to acute rejection but have had little impact on long-term graft survival. This is due, at least in part, to the broad non-immune effects of the current immunosuppressive drugs, which are involved in the death of patients and in chronic allograft dysfunction, particularly due to their nephrotoxicity. Recent progress in the development of biologicals, i.e. antibodies and fusion proteins, allows precise targeting of the immune system, preventing the non-immune side effects encountered with current protocols. In particular, targeting of the two most important co-stimulation pathways critical for T-cell activation, i.e. B7/CD28 and CD40/CD40L, has provided excellent results in many experimental models of organ transplantation. This has led to the clinical development of belatacept, a cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA4-Ig) fusion protein, which has proved to be efficient in preventing acute rejection in kidney transplant recipients. Its use is associated with improved renal function and a better metabolic profile than calcineurin inhibitors. However, because belatacept does not selectively target alloreactive T lymphocytes and must be combined with classical immunosuppressive drugs, infectious and neoplastic complications may occur, particularly post-transplantation lymphoproliferative disorders. We also address the current development of molecules targeting other co-stimulatory pathways (CD40/CD40L, leukocyte function-associated antigen [LFA]-1/intercellular adhesion molecule [ICAM], CD2/LFA-3). Many unresolved issues regarding the use of co-stimulation blocking agents are also discussed, e.g. their long half-life, which can be problematic in cases of serious adverse events, their long-term safety and efficacy, and the lack of monitoring tools to allow modulation of their use over time.

The immunosuppressive pipeline: meeting unmet needs in liver transplantation

Liver transplantation is now recognized as the treatment of choice for end-stage liver failure. Its success can be attributed largely to the generation of selective immunosuppressive agents, which have resulted in a dramatic reduction in the incidence of acute rejection and improvements in the short- and long-term outcomes of patients. However, the unresolved limitation of current immunosuppressive agents is long-term toxicity, which results in increases in the incidence and severity of cardiovascular, neurological, and renal diseases. Our recent understanding of the pathways of cell activation has resulted in the development of a new generation of immunosuppressive agents that may address the challenges facing transplantation today and allow the minimization or substitution of existing agents. Furthermore, advances in our understanding of the mechanisms of tolerance and the identification of biomarker signatures hold the promise that in some patients transplantation may be able to be performed without the need for long-term immunosuppression (tolerance).

Alefacept in the treatment of psoriasis

Alefacept is the first biologic agent approved by the US Food and Drug Administration for the treatment of psoriasis. To date, more than 1000 patients with moderate to severe psoriasis have been enrolled in phase III clinical trials of alefacept. More than 30% of patients treated with 2 courses of alefacept reached a Physician's Global Assessment of clear to almost clear, and approximately 40% and 70% of patients achieved a Psoriasis Area Severity Index score of 75 and 50 after the same regimen. Alefacept is well tolerated, and there have been no reports of significant systemic toxicity or serious treatment-related adverse events.

What's next in the pipeline

The first decade of the new millennium has been disappointing for transplant therapeutics: no new immunosuppression agents have been approved. Several high profile drugs and biologics failed the rigors of clinical trials or had disappointing preclinical results (FTY720, FK778, anti-CDI54, anti-IL15, anti-CD28, R3421). Several challenges face the industry and clinical investigators in bringing novel drugs to the clinic including the difficulty in targeting new endpoints for toxicities or chronic allograft disease since acute rejection has been reduced to below 15% as well as the Food and Drug Administration insistence of excluding the use of immunosuppression regimens embraced by the transplant community in control arms of clinical trials. Currently six new agents, 3 small molecules (ISA247, a semisynthetic analogue of cyclosporine; AEB071, a protein kinase C isoforms inhibitor; CP 690,550, a selective Janus kinase inhibitor) are in phase II trials and 3 biologics (belatacept, a second generation CTLA4Ig; efalizumab, a humanized antiCD11a [LFA1] monoclonal antibody; and alefacept, a LFA3-IgG1 fusion receptor protein) are in phase II/III clinical trials. The preclinical pipeline is not only full but promises to address previously neglected targets and fulfill unmet medical needs in transplant therapeutics.

Structure-activity studies of peptides from the "hot-spot" region of human CD2 protein: development of peptides for immunomodulation

CD2 is a cell surface protein belonging to the immunoglobulin superfamily (IgSF) that plays a key role in mediating adhesion between human T-lymphocytes and target cells. The interaction between cell-adhesion molecules CD2 and CD58 is critical for immune response. Modulation or inhibition of these interactions has been shown to be therapeutically useful. Synthetic 12-mer linear and cyclic peptides and cyclic hexapeptides from the beta-turn and beta-strand region (hot spot) of human CD2 protein were designed to modulate CD2-CD58 interaction. The 12-amino acid synthetic cyclic peptides effectively blocked the interaction between CD2 and CD58 proteins as demonstrated by E-rosetting and heterotypic adhesion assays. NMR and molecular modeling studies indicated that these cyclic peptides exhibit beta-turn structure in solution and closely mimic the beta-turn structure of the surface epitopes of CD2 protein. The designed cyclic peptides with beta-turn structure have the ability to modulate CD2-CD58 interaction.

Rapid response to alefacept given to patients with steroid resistant or steroid dependent acute graft-versus-host disease: a preliminary report

We evaluated the effect of alefacept (Amevive), a novel dimeric fusion protein, in steroid resistant/dependent acute graft-versus-host-disease (aGVHD). Seven patients were treated in eight aGVHD episodes. GVHD grade at treatment initiation and at peak ranged 2-4 (median 2.5) and 2-4 (median 4), respectively. System involvement at GVHD peak included skin (n=7), gastrointestinal tract (n=5) and liver (n=3). All patients responded. However, one patient with skin GVHD and two with gastrointestinal GVHD featuring an early initial response (IR) exacerbated and CR was not achieved. Skin GVHD responded rapidly with a median of 1 day to IR and 7 days to CR. Intestinal response was slower with median 7.5 days to IR. Of the four patients that achieved IR, CR was achieved in only one (40 days to CR). None of the patients had significant hepatic GVHD before treatment so no hepatic effect of alefacept could be determined. No immediate alefacept-related side effects were observed. Late side effects included infections (aspergillus sinusitis, pneumonia, bacteremia, pharyngeal thrush), pancytopenia and hemorrhagic cystitis. Three patients had CMV reactivation while on alefacept. We conclude that alefacept may have a beneficial effect in controlling aGVHD. Further investigations in larger cohorts of patients and controlled studies are warranted.

Changes in Soluble Adhesion Molecules in Gingival Crevicular Fluid Following Periodontal Surgery

BACKGROUND

Inflammation of periodontal tissues during postoperative wound healing is mediated by cell surface adhesion molecules. Soluble forms of these antigens have also been identified and shown to be important in immunoregulatory processes, but have previously not been investigated during periodontal repair and regeneration. The present study has examined the presence and possible changes in soluble intercellular adhesion molecule-1 (sICAM-1; CD54) and lymphocyte function-associated antigen-3 (sLFA-3; CD58) in gingival crevical fluid (GCF) following periodontal surgery.

METHODS

GCF samples were collected from four groups: 1) a guided tissue regeneration (GTR) test; 2) a GTR control, at least one complete tooth unit away from the periodontal defect; 3) a conventional flap (CF) surgery; and 4) a crown lengthening (CL). Sandwich enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of sICAM-1 and sLFA-3 in the GCF samples.

RESULTS

A marked increase in GCF volumes was found in all sites after surgery, although a persistent increase was associated only with the period of membrane retention at the GTR test sites. In addition, sICAM-1 and sLFA-3 were found in the GCF of healthy as well as diseased sites prior to treatment and the total amounts of both increased transiently following surgical intervention, especially sLFA-3. However, the concentrations of these GCF components, particularly sICAM-1, tended to decrease.

CONCLUSIONS

The temporal decrease in the concentration of sICAM-1 and sLFA-3 in GCF may serve to enhance inflammatory reactions at surgically-treated periodontal sites, thereby limiting repair and regeneration in the periodontium. These soluble adhesion molecules may thereby be of potential therapeutic value and might also be useful markers for monitoring periodontal wound healing.

Alefacept for the treatment of psoriasis: A review of the current literature and practical suggestions for everyday clinical use

Alefacept is the first biologic therapy approved by the United States Food and Drug Administration for the management of patients with moderate-to-severe chronic plaque psoriasis. Alefacept is a fully human fusion protein with a dual mechanism of action inhibiting T-cell activation as well as selectively reducing memory T cells. More than 2000 psoriasis patients have been treated with alefacept in clinical trials. These studies reveal an excellent clinical response, with 33% of patients achieving a Psoriasis Area Severity Index (PASI) score of 75 and 57% of patients achieving a PASI 50 after one course of alefacept. Patients achieving both PASI 75 and PASI 50 have significant improvements in their quality of life. The best responders can have long remissions, and there is a tendency toward continued improvement with subsequent courses of alefacept. The safety profile over the short and intermediate term is excellent. Preliminary data regarding alternate dosing regimens, transitioning patients from conventional systemics to alefacept, and combining alefacept with ultraviolet light therapy will be highlighted. We also will discuss our practical approach to patient selection, CD4 monitoring, management of infections while on alefacept, as well as decisions regarding retreatment and combination therapy.

A novel, rapid and sensitive heterotypic cell adhesion assay for CD2-CD58 interaction, and its application for testing inhibitory peptides

The immunoglobulin CD2 is a cell adhesion molecule that mediates T-cell activation by binding to its receptor CD58 on antigen-presenting cells (APCs). Modulation or inhibition of this interaction has been shown to be therapeutically useful. E-rosetting assay is usually applied in the study of the modulation of CD2-CD58 interaction. In this study, we demonstrated a novel, rapid and sensitive heterotypic cell adhesion assay for CD2-CD58 interaction. The CD2 expression on the surface of Jurkat cells and the CD58 expression on the Caco-2 cells were confirmed by flow cytometry and ELISA studies, respectively. Then Jurkat cells were fluorescent-labeled with 2 microM of BCECF-AM for 45 min at 37 degrees C before adding to confluent Caco-2 monolayers cultured in 96-well culture dishes. After 30 min, non-adherent Jurkat cells were removed by washing with PBS, while the monolayer-associated Jurkat cells were lysed with 0.5 ml of 2% Triton X-100 in 0.1 M NaOH. Fluorescence (FL) was quantitated using a microplate fluorescence analyzer with BCECF's excitation maximum of 485 nm and emission maximum of 535 nm. This method was successfully applied for testing inhibitory peptides to CD2-CD58 interaction.

Alefacept: a review of the literature and practical guidelines for management

Alefacept is the first biologic agent approved for the treatment of chronic, moderate to severe plaque-type psoriasis. It is a fully human fusion toxin, which binds to CD2, blocks costimulatory signaling, and selectively induces apoptosis of activated memory T cells involved in the pathogenesis of psoriasis. Alefacept has a slow onset of action, peaking approximately 18 weeks after the first injection of a 12-week course. However, it has several important advantages over the existing conventional immunosuppressive therapies for psoriasis: it is associated with long remissions without the need for maintenance therapy; its efficacy improves with subsequent courses; and it has a high safety profile. This review summarizes the mechanism of action of alefacept and the results of the clinical trials, with special emphasis on efficacy, pharmacodynamic effects on circulating lymphocytes, and safety and tolerability. Current guidelines based on the best available data to date are also presented.

T lymphocyte-endothelial cell interactions

Human vascular endothelial cells (EC) basally display class I and II MHC-peptide complexes on their surface and come in regular contact with circulating T cells. We propose that EC present microbial antigens to memory T cells as a mechanism of immune surveillance. Activated T cells, in turn, provide both soluble and contact-dependent signals to modulate normal EC functions, including formation and remodeling of blood vessels, regulation of blood flow, regulation of blood fluidity, maintenance of permselectivity, recruitment of inflammatory leukocytes, and antigen presentation leading to activation of T cells. T cell interactions with vascular EC are thus bidirectional and link the immune and circulatory systems.

Psoriasis: immunopathogenesis and evolving immunomodulators and systemic therapies; U.S. experiences

BACKGROUND

Psoriasis is a chronic inflammatory skin disorder that is presently without a permanent cure. Up to 40% of patients with psoriasis also develop psoriatic arthritis. The mainstay armamentarium to treat psoriasis systemically includes methotrexate, cyclosporin and oral retinoids, all with significant potential for toxicity and the need for close laboratory supervision. The although the exact mechanism of psoriasis is still unclear, the involvement of T-cell-mediated cytokine expression in the aetiology of psoriasis is becoming clearer. The goal of modern treatment is to target such immune responses that lead to the formation of psoriatic plaques and psoriatic arthritis using selective immunomodulating pharmacotherapy. The advantages of these biological agents are less toxic systemic side-effect profiles that will improve the quality of life in psoriatic patients.

OBJECTIVES

This review article describes current and emerging selective immunotherapies and systemic therapies for the treatment of psoriasis, and will briefly discuss disease immunopathogenesis.

METHODS

Literature review.

RESULTS AND CONCLUSIONS

Given the role of the inflammatory immune responses in the pathogenesis of psoriasis, the goal of modern medicine and pharmacotherapy lies in the design and use of specific targets in cell-mediated immune reactions and the modulation of the expression of various inflammatory cytokines. The clinical evidence of efficacy of some of these new biological immunomodulatory agents from several U.S.-based research studies and clinical experiences is convincing.

Design, structure and biological activity of β-turn peptides of CD2 protein for inhibition of T-cell adhesion

The interaction between cell-adhesion molecules CD2 and CD58 is critical for an immune response. Modulation or inhibition of these interactions has been shown to be therapeutically useful. Synthetic 12-mer linear and cyclic peptides, and cyclic hexapeptides based on rat CD2 protein, were designed to modulate CD2-CD58 interaction. The synthetic peptides effectively blocked the interaction between CD2-CD58 proteins as demonstrated by antibody binding, E-rosetting and heterotypic adhesion assays. NMR and molecular modeling studies indicated that the synthetic cyclic peptides exhibit beta-turn structure in solution and closely mimic the beta-turn structure of the surface epitopes of the CD2 protein. Docking studies of CD2 peptides and CD58 protein revealed the possible binding sites of the cyclic peptides on CD58 protein. The designed cyclic peptides with beta-turn structure have the ability to modulate the CD2-CD58 interaction.

Clinical trials of transplant tolerance: slow but steady progress

The search for tolerance therapies that would thwart the alloimmune response following organ transplantation while preserving a patient's protective immune response has been a formidable goal for clinical immunologists. Over the past few decades, a more detailed understanding of the molecular events associated with T-cell recognition and activation has demonstrated the feasibility of various tolerance approaches, such as costimulation blockade, in numerous animal models of both autoimmunity and transplantation. Yet, only a few promising new therapies have reached the early stages of human clinical development. In contrast, the use of T-cell depleting induction therapy has become widespread, and new trials have been designed with immunosuppressive drug withdrawal in mind. Furthermore, nonmyeloablative mixed chimeric approaches have allowed complete immunosuppressive withdrawal in some limited cases. In the course of these investigations, however, what has become increasingly clear is that the distinctions between immunosuppression and tolerance have been blurred as the success and durability of the therapies rely as much on the state of the organ and organism as they do the mechanism of action of the drug. In this review, we provide a summary of the progress and lessons in promoting clinical transplant tolerance and an overview of promising agents.

Immunotherapy for autoimmune and inflammatory renal diseases

Immune-mediated renal disease (IMRD) accounts for 20 - 30% of the cases of end stage renal failure. It frequently occurs in the context of multi-system autoimmune disorders, including systemic lupus erythematosus (SLE) and primary systemic vasculitis. Current therapies are partially effective and comprise the combination of steroids with an immunosuppressive, such as cyclophosphamide. Their toxicity contributes to the morbidity and mortality of these disorders, and long-term treatment is necessary to prevent relapse. There is a clear need for better-targeted, more effective and less toxic therapy. Advances in our understanding of the immunopathogenesis of inflammatory autoimmune renal disease have identified potential targets for newer agents and have improved the monitoring of therapeutic responses. Recent experience with newer therapies in IMRD is reviewed. This has typically involved small, non-randomised, open-label trials and has addressed reversible features of disease activity. Larger, randomised comparisons to standard therapy are needed along with assessment of long-term efficacy and safety.

Treatment targeted to cell surface epitopes

Expression of a variety of surface epitopes is a characteristic feature of immune cells. Receptors and adhesion molecules are the most predominant ones. It is also characteristic that epitope expression is modulated during cellular activation. In inflammatory skin diseases these structures can be used to define not only the type of cell but also their activity status. The availability of monoclonal antibodies and fusion proteins enabled to target cellular surface epitopes in order to modulate the cellular function as a principle of treatment. In psoriasis receptor-targeted therapy has been developed and tested in a considerable number of clinical trials. However, these approaches revealed that not all the strategies are equally effective. In this review the development of receptor-targeted treatment for skin disorders, mainly psoriasis, is described. Clinical as well as experimental data obtained with the various compounds employed are discussed with regard to clinical efficacy, safety and tolerability.

Alefacept treatment in psoriatic arthritis: reduction of the effector T cell population in peripheral blood and synovial tissue is associated with improvement of clinical signs of arthritis

OBJECTIVE

To investigate whether alefacept (a fully human lymphocyte function-associated antigen 3 [LFA-3]/IgG1 fusion protein that blocks the LFA-3/CD2 interaction) is able to reduce the signs and symptoms of joint inflammation in patients with active psoriatic arthritis (PsA).

METHODS

Eleven patients with active PsA were treated with alefacept for 12 weeks in an open-label and explorative study. Clinical joint assessment and laboratory assessments were performed at baseline and after 4, 9, 12, and 16 weeks of treatment. Serial synovial tissue (ST) biopsy specimens from an inflamed index joint (knee, ankle, wrist, or metacarpophalangeal joint) were obtained by arthroscopy at baseline and after 4 and 12 weeks of treatment.

RESULTS

At the completion of treatment, 6 of 11 patients (55%) fulfilled the Disease Activity Score (DAS) response criteria. Nine patients (82%) fulfilled the DAS response criteria at any point during the study. There was a statistically significant reduction in CD4+ lymphocytes (P < 0.05), CD8+ lymphocytes (P = 0.05), and CD68+ macrophages (P < 0.02) in the ST after 12 weeks of treatment compared with baseline. The ST and peripheral blood of those patients fulfilling the DAS response criteria contained more CD45RO+ cells at baseline and displayed a significant reduction in these cells compared with nonresponding patients.

CONCLUSION

The changes in ST, together with the improvement in clinical joint scores, after treatment with alefacept support the hypothesis that T cell activation plays an important role in this chronic inflammatory disease. Furthermore, since alefacept, a T cell-specific agent, led to decreased macrophage infiltration, the data indicate that T cells are highly involved in synovial inflammation in PsA.

Contemporary immunosuppression in renal transplantation

Over the past 3 decades, renal allograft survival has improved significantly as a result of the development of powerful immunosuppressive agents. Nevertheless, the overall half-life of renal allografts has increased marginally during that time period, owing to drug-related nephrotoxicity and chronic rejection. New immunosuppressive agents are being evaluated because of the need for a reduction in the dose of nephrotoxic calcineurin inhibitors and corticosteroids. Additional agents have demonstrated the ability to retard the onset of chronic rejection in preclinical transplant models. In concert with these efforts, approaches are in development to alleviate the ever increasing shortage of donor organs, including the as yet unrealized goals of successful and practical xenotransplantation and the bioartificial kidney. Further identification and development of novel agents that target the specific components of the allograft response will provide the key to the achievement of donor-specific tolerance, the "Holy Grail" of solid organ transplantation.

Mechanisms of tolerance induction: blockade of co-stimulation

Induction of tolerance to transplantation antigens is believed to be a promising way to achieve long-term allograft survival without a deleterious immunosuppressive regimen. T-cell activation, which is an essential feature of graft rejection, requires a first signal provided by T-cell receptor (TCR) ligation and a second signal provided by engagement of co-stimulatory molecules with their respective ligands on antigen-presenting cells. The coordinated triggering of these two independent signalling systems ensures the full T-cell activation, including proliferation and acquisition of effector function. TCR occupancy in the absence of co-stimulatory signals leads to a sustained loss of antigen responsiveness called clonal anergy, which could be of major importance in transplantation. In vivo, co-stimulation blockade was indeed shown to allow for long-term allograft survival in several transplantation models. However, the current continuous identification of new co-stimulatory molecules suggests that a functional redundancy of the system exists and that tolerance to transplantation antigens might be achieved more easily through the combined blockade of two or several co-stimulatory signals. In this review, we analyse the biological effects of the disruption of some co-stimulation pathways in vitro and in vivo and discuss their potential interest for tolerance induction.

Treatment of chronic plaque psoriasis by selective targeting of memory effector T lymphocytes

BACKGROUND

Psoriatic plaques are characterized by infiltration with CD4+ CD45RO+ and CD8+ CD45RO+ memory effector T lymphocytes. The recombinant protein alefacept binds to CD2 on memory effector T lymphocytes, inhibiting their activation.

METHODS

In a multicenter, randomized, placebo-controlled, double-blind study, we evaluated alefacept as a treatment for psoriasis. Two hundred twenty-nine patients with chronic psoriasis received intravenous alefacept (0.025, 0.075, or 0.150 mg per kilogram of body weight) or placebo weekly for 12 weeks, with follow-up for 12 additional weeks. Before treatment, the median scores on the psoriasis area-and-severity index were between 14 and 20 in all groups (0 denotes no psoriasis and 72 the most severe disease possible).

RESULTS

Alefacept was well tolerated and nonimmunogenic. The mean reduction in the score on the psoriasis area-and-severity index two weeks after treatment was greater in the alefacept groups (38, 53, and 53 percent in the groups receiving 0.025, 0.075, and 0.150 mg per kilogram, respectively) than in the placebo group (21 percent, P<0.001). Twelve weeks after treatment, 28 patients who had received alefacept alone were clear or almost clear of psoriasis. Three patients in the placebo group were clear or almost clear; all three had received additional systemic therapy for psoriasis. Alefacept reduced peripheral-blood memory effector T-lymphocyte (CD45RO+) counts, and the reduction in the number of memory-effector T lymphocytes was correlated with the improvement in psoriasis.

CONCLUSIONS

Treatment with alefacept for 12 weeks is associated with improvement in chronic plaque psoriasis; some patients have a sustained clinical response after the cessation of treatment. Alefacept selectively targets CD45RO+ memory effector T lymphocytes, suggesting that they have a role in the pathogenesis of psoriasis.

LFA-3 (CD58) mediates T-lymphocyte adhesion in chronic inflammatory infiltrates

Previous studies have suggested that LFA-3 has an important role in a number of chronic inflammatory pathologies, although an active role for LFA-3 within in vivo inflammatory reactions has not previously been directly observed in humans. To assess the importance of LFA-3 in this process, this study used an adaptation of the Stamper-Woodruff lymphocyte adhesion assay to measure the binding of exogenous activated lymphocytes to the T-cell-dominated chronic inflammatory infiltrate of oral lichen planus. Antibody blockade experiments showed that anti-LFA-3 monoclonal antibody reduced lymphocyte adhesion by approximately 29%, while anti-ICAM-1 produced a reduction of 26%. These results thus suggest that both LFA-3 and ICAM-1 are likely to mediate cell-cell interactions within lesional tissues in vivo. Moreover, these findings are also the first to directly demonstrate that LFA-3-mediated adhesion, like that of ICAM-1, is functionally important in the molecular pathology of inflammatory mucosal disease.

Gene therapy in transplantation

Facilitation of solid organ and cell transplantation depends on metabolic and immunologic factors that can be manipulated ex vivo and in vivo using gene transfer technology. Vectors have been developed which can optimally transfer relevant genes to various tissues and organs. Interventions aimed at promoting tissue preservation before transplantation, prevention of oxidative stress and immunological rejection have recently become attractive options using viral and nonviral gene delivery vehicles. Further understanding of the mechanisms involved in tolerance induction as well as the facilitation of xenogeneic engraftment have made possible a variety of avenues that can be exploited using gene transfer technology.

Functional glycan-free adhesion domain of human cell surface receptor CD58: design, production and NMR studies

A general strategy is presented here for producing glycan-free forms of glycoproteins without loss of function by employing apolar-to-polar mutations of surface residues in functionally irrelevant epitopes. The success of this structure-based approach was demonstrated through the expression in Escherichia coli of a soluble 11 kDa adhesion domain extracted from the heavily glycosylated 55 kDa human CD58 ectodomain. The solution structure was subsequently determined and binding to its counter-receptor CD2 studied by NMR. This mutant adhesion domain is functional as determined by several experimental methods, and the size of its binding site has been probed by chemical shift perturbations in NMR titration experiments. The new structural information supports a 'hand-shake' model of CD2-CD58 interaction involving the GFCC'C" faces of both CD2 and CD58 adhesion domains. The region responsible for binding specificity is most likely localized on the C, C' and C" strands and the C-C' and C'-C" loops on CD58.

Role of endothelial cells in allograft rejection

The immunological properties of endothelial cells suggest they perform a pivotal role in acute and chronic rejection following solid organ transplantation. Their constitutive expression of MHC class II molecules (which initiate allograft rejection by activating CD4 T cells) and accessory molecules allows them to present foreign antigen by both the direct and indirect route to the recipient's immune system. The costimulatory molecules used by endothelial cells appear to differ from those used by traditional antigen-presenting cells such as B cells and dendritic cells. Release of non-HLA antigens from damaged endothelial cells results in a chronic antibody response--possibly contributing to graft vasculopathy and chronic rejection. Further understanding of the factors that regulate MHC class II and accessory molecule expression on endothelial cells could lead to novel strategies of therapeutic intervention.

Potent Apoptotic Signaling and Subsequent Unresponsiveness Induced by a Single CD2 mAb (BTI-322) in Activated Human Peripheral T Cells

Manipulation of CD2 molecules with CD2 mAb pairs has been shown to deliver apoptotic signals to activated mature T cells. We show that BTI-322, a CD2 mAb directed at a peculiar epitope of CD2, can trigger on its own the apoptotic death of IL-2-activated peripheral T cells and of OKT3-stimulated T cells, contrasting in this respect with a series of other mouse or rat CD2 mAb. F(ab′)2 fragments were as potent as the whole Ab. BTI-322-induced apoptosis proceeded in a few hours and was independent of the Fas/Fas ligand system. Less than 5 ng/ml of BTI-322, added at the begining of culture, were able to eliminate within 4 days most CD3+ cells from OKT3- and IL-2-stimulated lymphocytes, the only cells remaining being CD16+CD2− NK cells. T cell proliferative responses induced by a mitogenic CD2 mAb pair or by PHA-P (which mainly binds to CD2) were not inhibited by BTI-322. In this case, the apoptotic effect was successfully counteracted by simultaneous enhancement of T cell divisions. Thus, the killing effect of BTI-322 was most effective when T cells were exclusively stimulated through the CD3/TCR complex. Apoptosis of the responding T cells may explain why T cells recovered from a primary MLC performed in the presence of BTI-322 responded to third party cells but not to the primary stimulatory cells. These data constitute the rational basis for the use of BTI-322 for inducing tolerance in human allotransplantation.

Prevention of transplant rejection: current treatment guidelines and future developments

In the past 2 decades, progressive improvements in the results of organ transplantation as a therapeutic strategy for patients with end-stage organ disease have been achieved due to greater insight into the immunobiology of graft rejection and better measures for surgical and medical management. It is now known that T cells play a central role in the specific immune response of acute allograft rejection. Strategies to prevent T cell activation or effector function are thus all potentially useful for immunosuppression. Standard immunosuppressive therapy in renal transplantation consists of baseline therapy to prevent rejection and short courses of high-dose corticosteroids or monoclonal or polyclonal antibodies as treatment of ongoing rejection episodes. Triple-drug therapy with the combination of cyclosporin, corticosteroids and azathioprine is now the most frequently used immunosuppressive drug regimen in cadaveric kidney recipients. The continuing search for more selective and specific agents has become, in the past decade, one of the priorities for transplant medicine. Some of these compounds are now entering routine clinical practice: among them are tacrolimus (which has a mechanism of action similar to that of cyclosporin), mycophenolate mofetil and mizoribine (which selectively inhibit the enzyme inosine monophosphate dehydrogenase, the rate-limiting enzyme for de novo purine synthesis during cell division), and sirolimus (rapamycin) [which acts on and inhibits kinase homologues required for cell-cycle progression in response to growth factors, like interleukin-2 (IL-2)]. Other new pharmacological strategies and innovative approaches to organ transplantation are also under development. Application of this technology will offer enormous potential not only for the investigation of mechanisms and mediators of graft rejection but also for therapeutic intervention.

Blockade of CD2-LFA-3 interactions protects human skin allografts in immunodeficient mouse/human chimeras

A human skin allograft injury model in immunodeficient mice, engrafted with human peripheral blood mononuclear cells from a different donor, has been used to test whether reagents that block human T cell CD2 interactions with its principal ligand, LFA-3 (CD58), can inhibit immune reactions in vivo. In this model, human skin grafts show a reproducible pattern of progressive human T-cell infiltration and human graft microvascular injury that resembles human first-set skin graft rejection. Murine Mab to human LFA-3 or human LFA-3-IgG1 fusion protein, but not isotype-matched control antibodies, each markedly protected skin grafts from leukocyte infiltration and injury. These data provide the first evidence that LFA-3 functions in vivo and establish the ability of this new model to test human-specific immune modulators.

Immunoadhesins as research tools and therapeutic agents

An immunoadhesin is a fusion protein that combines the target-binding region of a receptor, an adhesion molecule, a ligand, or an enzyme, with the Fc region of an Ig. Immunoadhesins provide a unique tool for identifying unknown binding targets and for elucidating molecular interactions that control biological function. Recent studies suggest that immunoadhesins also may be useful therapeutically, as inhibitors of autoimmune and inflammatory diseases.