The glycosylphosphatidylinositol-anchored lymphocyte antigen CDw52 is associated with the epididymal maturation of human spermatozoa

(Patho)Physiology of Glycosylphosphatidylinositol-Anchored Proteins I: Localization at Plasma Membranes and Extracellular Compartments

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) are anchored at the outer leaflet of plasma membranes (PMs) of all eukaryotic organisms studied so far by covalent linkage to a highly conserved glycolipid rather than a transmembrane domain. Since their first description, experimental data have been accumulating for the capability of GPI-APs to be released from PMs into the surrounding milieu. It became evident that this release results in distinct arrangements of GPI-APs which are compatible with the aqueous milieu upon loss of their GPI anchor by (proteolytic or lipolytic) cleavage or in the course of shielding of the full-length GPI anchor by incorporation into extracellular vesicles, lipoprotein-like particles and (lyso)phospholipid- and cholesterol-harboring micelle-like complexes or by association with GPI-binding proteins or/and other full-length GPI-APs. In mammalian organisms, the (patho)physiological roles of the released GPI-APs in the extracellular environment, such as blood and tissue cells, depend on the molecular mechanisms of their release as well as the cell types and tissues involved, and are controlled by their removal from circulation. This is accomplished by endocytic uptake by liver cells and/or degradation by GPI-specific phospholipase D in order to bypass potential unwanted effects of the released GPI-APs or their transfer from the releasing donor to acceptor cells (which will be reviewed in a forthcoming manuscript).

The sequential natalizumab – alemtuzumab therapy in patients with relapsing forms of multiple sclerosis (SUPPRESS) trial – Part I: Rationale and objectives

Background

Natalizumab is a recombinant humanized monoclonal antibody (mAb) against α4-integrin that is approved for relapsing forms of multiple sclerosis (MS). Natalizumab is associated with an increased risk of developing progressive multifocal leukoencephalopathy (PML), and with disease reactivation after cessation of treatment that is likely mediated by an accumulation of pro-inflammatory lymphocytes in the blood during therapy. Alemtuzumab is a mAb against CD52 that reduces the number of peripheral lymphocytes.

Rationale

To determine if treatment with alemtuzumab after natalizumab reduces disease activity in patients with relapsing forms of MS. This review article will outline the rationale and objectives of the sequential natalizumab – alemtuzumab therapy in patients with relapsing forms of multiple sclerosis (SUPPRESS; ClinicalTrials.gov ID: NCT03135249) trial in greater detail than would be feasible in a manuscript that summarizes the study results.

Methods

The SUPPRESS trial is single arm, open-label, multicenter, efficacy pilot study that aims to establish a disease-free state over a 24-months period in patients who received the natalizumab- alemtuzumab sequential therapy. Participants will be recruited from four different sites. The primary endpoint is the annualized relapse rate (ARR) from the time of cessation of natalizumab treatment. Key secondary endpoint is freedom of relapse at 12-months, the number of new/enlarging T2 lesions on magnetic resonance imaging (MRI), and the number of gadolinium (Gd)-enhancing lesions on MRI. An exploratory endpoint is the Expanded Disability Status Scale (EDSS), retinal nerve fiber layer (RNFL) thickness assessment by optic coherence tomography (OCT) and assessment of quality of life (QoL) measures by a pre-defined, self-administered testing battery. To evaluate immunological effects, blood leukocytes will be collected and immunophenotyped by multi-parameter flow cytometry.

Conclusion

The SUPPRESS trial will provide clinical, imaging, and biological data to determine whether sequential natalizumab to alemtuzumab combination therapy establish a disease-free state in patients with relapsing forms of MS.

The immune-related gene CD52 is a favorable biomarker for breast cancer prognosis

Background

An increasing number of studies have demonstrated a role for the tumor microenvironment in tumorigenesis, disease progression, and therapeutic response. This present study aimed to screen the significant immune-related genes and their possible role in the prognosis of breast cancer (BRCA).

Methods

The transcriptome data and clinical data of breast cancer were collected from The Cancer Genome Atlas (TCGA), and the immune scores and stromal scores were calculated by ESTIMATE algorithm. The differentially expressed genes were screened base on immune and stromal scores (high score vs. low score), than the intersected genes were used for subsequent functional enrichment analysis and protein-protein interaction (PPI) analysis. Furthermore, the key gene was identified by the intersection of the hub genes of PPI network and the prognostic genes of breast cancer. Finally, we explored the infiltration of immune cells of BRCA base on the CIBERSORT algorithm, and analysis the relationship between key gene and immune cells.

Results

High levels of CD52 expression were detected in the early stages of breast cancer and were associated with favorable prognosis. Overexpression of CD52 led to higher infiltrations of M1 macrophages, monocytes, T follicular helper cells, and resting memory CD4 T cells. Downregulation of CD52 resulted in high infiltrations of M2 macrophages. Therefore, high expression of CD52 may negatively regulate the infiltration of M2 macrophages but accelerate the infiltration of anti-cancer immune cells, and thus, high expression of CD52 may have a protective effect in breast cancer patients.

Conclusions

CD52 can increase the infiltration of anti-cancer immune cells but inhibit the infiltration of M2 macrophages, thereby improving the prognosis of breast cancer patients.

Adolescent male fertility following reduced-intensity conditioning regimen for hematopoietic stem cell transplantation in non-malignant disorders

INTRODUCTION

The effects of RIC for HSCT on male fertility remain unknown. We investigated spermatogenesis and gonadal hormonal status among adolescent male patients who received RIC HSCT for non-malignant diseases.

PATIENTS AND METHODS

Patients with non-malignant disease who had undergone a RIC HSCT were recruited and evaluated for spermatogenesis via semen analysis and gonadal hormonal function via serum hormone levels. Those who had received prior chemotherapy or radiation were excluded from the study. We reviewed the charts to record demographic factors, conditioning regimen and complications during and after transplant.

RESULTS

Five patients were enrolled. The median age at the time of transplant was 15 years (range, 11-19 years), and the median time between bone marrow transplant and semen analysis was 5 years (range, 3-11 years). Median age of patients was 20 years (range, 18-25 years) at the time of the study. Serum FSH and LH levels were elevated in four patients, and inhibin B levels were low for age in three patients. Semen analysis showed two patients had azoospermia, and the remaining three patients showed severe oligozoospermia. Normal morphology and motility were seen in only one patient.

CONCLUSION

This case series suggests that RIC transplants may be associated with impaired spermatogenesis and sequential follow-up is necessary given the potential for either permanent impairment or delayed recovery. Further larger studies are needed to confirm these findings.

Review of the Clinical Pharmacokinetics and Pharmacodynamics of Alemtuzumab and Its Use in Kidney Transplantation

Alemtuzumab is a humanized monoclonal antibody against CD52 and causes depletion of T and B lymphocytes, monocytes, and NK cells. Alemtuzumab is registered for the treatment of multiple sclerosis (MS) and is also used in chronic lymphocytic leukemia (CLL). Alemtuzumab is used off-label in kidney transplantation as induction and anti-rejection therapy. The objective of this review is to present a review of the pharmacokinetics, pharmacodynamics, and use of alemtuzumab in kidney transplantation. A systematic literature search was conducted using Ovid Medline, Embase, and Cochrane Central Register of controlled trials. No pharmacokinetic or dose-finding studies of alemtuzumab have been performed in kidney transplantation. Although such studies were conducted in patients with CLL and MS, these findings cannot be directly extrapolated to transplant recipients, because CLL patients have a much higher load of CD52-positive cells and, therefore, target-mediated clearance will differ between these two indications. Alemtuzumab used as induction therapy in kidney transplantation results in a lower incidence of acute rejection compared to basiliximab therapy and comparable results as compared with rabbit anti-thymocyte globulin (rATG). Alemtuzumab used as anti-rejection therapy results in a comparable graft survival rate compared with rATG, although infusion-related side effects appear to be less. There is a need for pharmacokinetic and dose-finding studies of alemtuzumab in kidney transplant recipients to establish the optimal balance between efficacy and toxicity. Furthermore, randomized controlled trials with sufficient follow-up are necessary to provide further evidence for the treatment of severe kidney transplant rejection.

Alemtuzumab for Multiple Sclerosis

Alemtuzumab is a humanised anti-CD52 monoclonal antibody approved for use in active, relapsing multiple sclerosis (MS). Administration results in a rapid depletion of circulating lymphocytes with a subsequent beneficial immune reconstitution. Early open-label experience and recent clinical trials have demonstrated a dramatic effect on relapse rates as well as a positive effect on radiological disease outcomes and disability measures. Despite a mechanism of action that results in profound lymphopaenia, opportunistic infections are rarely seen and no excess association with malignancy has been identified. However, acquired autoimmune disease (AID) is a common adverse event following treatment, necessitating rigorous monitoring in order to facilitate prompt detection and management. Despite this issue, a unique dosing schedule and durability of effect make alemtuzumab a welcome addition to currently available treatment options for MS.

Alemtuzumab in the treatment of multiple sclerosis: key clinical trial results and considerations for use

Alemtuzumab is a humanized monoclonal antibody therapy that has recently been approved in over 30 countries for patients with active relapsing-remitting multiple sclerosis. It acts by targeting CD52, an antigen primarily expressed on T and B lymphocytes, resulting in their depletion and subsequent repopulation. The alemtuzumab clinical development program used an active comparator, subcutaneous interferon beta-1a, to show that alemtuzumab is a highly efficacious disease-modifying therapy, with benefits on relapses, disability outcomes, and freedom from clinical disease and magnetic resonance imaging activity. The safety profile was consistent across studies and no new safety signals have emerged during follow-up in the extension study. Infusion-associated reactions are common with alemtuzumab, but rarely serious. Infection incidence was elevated with alemtuzumab in clinical studies; most infections were mild or moderate in severity. Autoimmune adverse events occurred in approximately a third of patients, manifesting mainly as thyroid disorders, and less frequently as immune thrombocytopenia or nephropathy. A comprehensive monitoring program lasting at least 4 years after the last alemtuzumab dose allows early detection and effective management of autoimmune adverse events. Further experience with alemtuzumab in the clinic will provide needed long-term data.

Intractable and highly active relapsing multiple sclerosis - role of alemtuzumab

Alemtuzumab is a humanized recombinant monoclonal antibody that was recently approved by the US Food and Drug Administration and the European Medicines Agency for the management of relapsing forms of multiple sclerosis (MS). It has been utilized for the management of chronic lymphocytic leukemia, bone marrow and renal transplantation, or graft versus host disease. Because of its immunomodulatory properties, it was brought into clinical development in MS. One Phase II (CAMMS223) and two Phase III clinical trials (CARE-MSI and -II) have evaluated the safety and efficacy of alemtuzumab in patients with relapsing-remitting MS. Even though its efficacy profile and long-lasting effect have attracted much interest among physicians and patients, it has significant potential adverse effects that may limit its use to patients with active disease. Here, we review the history of drug development of alemtuzumab. Furthermore, we outline the postulated mechanisms of action, clinical evidence, and safety of alemtuzumab for its use as a disease-modifying agent in active and highly active MS.

Successful fertility restoration after allogeneic hematopoietic stem cell transplantation

OBJECTIVE

Myeloablative conditioning regimens given prior to hematopoietic stem cell transplantation (HSCT) frequently cause permanent sterility in men. In patients with sickle cell disease (SCD) we use a nonmyeloablative regimen with sirolimus, alemtuzumab, and low-dose total-body irradiation (300 centigrays) with gonadal shielding preceding allogeneic HSCT. We report here the restoration of azoospermia in a patient with SCD after allogeneic HSCT. We discuss the impact of our patient's underlying chronic medical conditions and the therapies he had received (frequent blood transfusions, iron chelating drugs, ribavirin, hydroxyurea, opioids), as well as the impact of the nonmyeloablative conditioning regimen on male gonadal function, and we review the literature on this topic.

METHODS

We determined the patient's reproductive hormonal values and his semen parameters before, during, and after HSCT and infertility treatment. In addition, we routinely measured his serum laboratory parameters pertinent to SCD and infertility, such as iron and ferritin levels. A karyotype analysis was performed to assess the potential presence of Klinefelter syndrome. Finally, imaging studies of the patient's brain and testes were done to rule out further underlying pathology.

RESULTS

A 42-year-old man with SCD, transfusional iron overload, and hepatitis C underwent a nonmyeloablative allogeneic HSCT. One year later he desired to father a child but was found to be azoospermic in the context of hypogonadotropic hypogonadism. Restoration of fertility was attempted with human chorionic gonadotropin (2,000 IU) plus human menopausal gonadotropin (75 IU follicle-stimulating hormone) injected subcutaneously 3 times weekly. Within 6 months of treatment, the patient's serum calculated free testosterone value normalized, and his sperm count and sperm motility improved. After 10 months, he successfully initiated a pregnancy through intercourse. The pregnancy was uncomplicated, and a healthy daughter was delivered naturally at term.

CONCLUSION

Despite exposure to several gonadotoxins, transfusional iron overload and nonmyeloablative conditioning with radiation causing severe testicular atrophy suggesting extensive damage to seminiferous tubules and possibly Leydig cells, gonadotropins were efficacious in restoring our patient's reproductive capability.

The effects of CAMPATH-1H on cell viability do not correlate to the CD52 density on the cell surface

Graft versus host disease (GvHD) is one of the main complications after hematological stem cell transplantation (HSCT). CAMPATH-1H is used in the pre-transplant conditioning regimen to effectively reduce GvHD by targeting CD52 antigens on T cells resulting in their depletion. Information regarding CD52 expression and the effects of CAMPATH-1H on immune cells is scant and limited to peripheral blood (PB) T and B cells. To date, the effects of CAMPATH-1H on cord blood (CB) cells has not been studied. Here we aimed to analyze CD52 expression and the effects of CAMPATH-1H on fresh or frozen, resting or activated, PB mononuclear cells (PBMC) and CB mononuclear cells (CBMC). In resting state, CD52 expression was higher in CB than PB T cell subsets (653.66±26.68 vs 453.32±19.2) and B cells (622.2±20.65 vs 612.0±9.101) except for natural killer (NK) cells where CD52 levels were higher in PB (421.0±9.857) than CB (334.3±9.559). In contrast, CD52 levels were comparable across all cell types after activation. CAMPATH-1H depleted resting cells more effectively than activated cells with approximately 80–95% of apoptosis observed with low levels of necrosis. There was no direct correlation between cell surface CD52 density and depleting effects of CAMPATH-1H. In addition, no difference in cell viability was noted when different concentrations of CAMPATH-1H were used. CD52 was not expressed on HSC but began to be expressed as the cells differentiate, implying that CAMPATH-1H could potentially affect HSC differentiation and proliferation. Our study provides insightful information, which contributes to the better understanding in the use of CAMPATH-1H as part of the conditioning regime in HSCT.

Drug safety evaluation of alemtuzumab for multiple sclerosis

INTRODUCTION

Alemtuzumab is a humanised anti-CD52 mAb which has recently been licensed for the treatment of relapsing multiple sclerosis in Europe.

AREAS COVERED

The efficacy and safety of alemtuzumab from open label, Phase II and Phase III trials is reported.

EXPERT OPINION

Alemtuzumab causes rapid and profound complement mediated lysis of circulating lymphocytes and allows beneficial modulation of the immune system during a subsequent reconstitution phase. Clinical trials have demonstrated superior efficacy against an active comparator, with reduction in annualised relapse rates and sustained accumulation of disability at 3 years and sustained efficacy at 5 years. The main adverse effects are mild to moderate infusion reactions, an increased incidence of mild to moderate infections and autoimmune adverse events. Thyroid disorders are the most common form of autoimmune adverse events, occurring in approximately one third of patients. Overt Graves' hyperthyroidism represents approximately half of these cases. Careful patient selection and structured monitoring programs allow for effective patient management resulting in a favourable risk benefit profile.

Human peripheral blood mononuclear cells exhibit heterogeneous CD52 expression levels and show differential sensitivity to alemtuzumab mediated cytolysis

Alemtuzumab is a monoclonal antibody that targets cell surface CD52 and is effective in depleting lymphocytes by cytolytic effects in vivo. Although the cytolytic effects of alemtuzumab are dependent on the density of CD52 antigen on cells, there is scant information regarding the expression levels of CD52 on different cell types. In this study, CD52 expression was assessed on phenotypically distinct subsets of lymphoid and myeloid cells in peripheral blood mononuclear cells (PBMCs) from normal donors. Results demonstrate that subsets of PBMCs express differing levels of CD52. Quantitative analysis showed that memory B cells and myeloid dendritic cells (mDCs) display the highest number while natural killer (NK) cells, plasmacytoid dendritic cells (pDCs) and basophils have the lowest number of CD52 molecules per cell amongst lymphoid and myeloid cell populations respectively. Results of complement dependent cytolysis (CDC) studies indicated that alemtuzumab mediated profound cytolytic effects on B and T cells with minimal effect on NK cells, basophils and pDCs, correlating with the density of CD52 on these cells. Interestingly, despite high CD52 levels, mDCs and monocytes were less susceptible to alemtuzumab-mediated CDC indicating that antigen density alone does not define susceptibility. Additional studies indicated that higher expression levels of complement inhibitory proteins (CIPs) on these cells partially contributes to their resistance to alemtuzumab mediated CDC. These results indicate that alemtuzumab is most effective in depleting cells of the adaptive immune system while leaving innate immune cells relatively intact.

The N-linked carbohydrate moiety of male reproductive tract CD52 (mrt-CD52) interferes with the complement system via binding to C1q

Antisperm antibody detected in infertile female patients' sera has been shown to correlate with reduced fertility. The antibody showed strong complement-dependent cytotoxicity as determined by the sperm immobilization test (SIT). CD52 is a human glycosylphosphatidylinositol (GPI)-anchored antigen present in lymphocytes and male reproductive tracts (mrt), including mature sperm and seminal plasma. Recently, purified mrt-CD52 from human seminal plasma has been reported to interfere with the classical complement pathway, but not lectin binding or alternative pathways of the complement system. The purpose of this study is to determine which stage of the classical pathway mrt-CD52 regulates. mrt-CD52 was purified from human seminal plasma or intact sperm membrane. Immunoprecipitation assay was performed with the reaction of mrt-CD52, human complement and mAb H6-3C4. Immunoprecipitate was formed by the carbohydrate moiety of mrt-CD52, but not by the GPI-anchor peptide. The C1q molecule (29 kDa) was detected in the immunoprecipitates by Western blotting analysis probed with anti C1q antibody, indicating that the carbohydrate moiety of mrt-CD52 binds to C1q. Also, the complement-dependent SIT revealed that purified CD52 inhibited sperm immobilization activity by antisperm antibody. These results suggest that mrt-CD52 protects sperm function from complement attack if antisperm antibody is generated in the female reproductive tracts.

Alemtuzumab induction of intracellular signaling and apoptosis in malignant B lymphocytes

The molecular changes induced by alemtuzumab following binding of CD52 on B tumor cells were investigated. Alemtuzumab alone had no detectable impact on cell signaling but cross-linking of alemtuzumab on the surface of B tumor lines with anti-human Fc antibodies induced a transient Ca(2+) flux followed by phosphorylation of several kinases involved in stress and survival pathways, and expression of associated proteins including TNF-α. Cross-linking of alemtuzumab also induced capping and caspase-dependent apoptosis of the tumor lines. When using primary cells from B-CLL patients, alemtuzumab alone was capable of inducing protein phosphorylation and apoptosis through the cross-linking of alemtuzumab by FcγRIIb receptors on B-CLL cells. Apoptosis was prevented by blocking of FcγRIIb receptors with anti-CD32 antibody. Overall, our results indicate that cross-linking of alemtuzumab on B tumor cells can occur naturally through Fc receptor interaction and leads to the activation of specific cellular pathways and induction of apoptosis.

[Alemtuzumab: a further option for treatment of multiple sclerosis]

Alemtuzumab is a humanized monoclonal therapeutic antibody that targets the CD52 antigen which s expressed on most cells of the lymphoid lineage, exclusive of precursors. Alemtuzumab rapidly depletes CD52(+) cells from the peripheral blood. This depletion is long-lasting, and cells repopulate in a specific pattern with B cells and regulatory T cells peaking first. Alemtuzumab was examined for clinical utility in two open-labelled intervention trials in multiple sclerosis (MS). Because of very promising results its clinical efficacy was further explored in a clinical phase-II trial using s.c. interferon beta-1a as the active comparator. Severe or opportunistic infections were surprisingly rare given the long-term lymphopenia. However, up to 30% of patients developed some antibody-mediated autoimmunity. The thyroid gland was the most frequently affected organ. Immune-mediated thrombocytopenic purpura and Goodpasture's syndrome were additionally observed. This review summarizes the pre-clinical and clinical development of alemtuzumab and discusses potential modes of action as well as the pathogenetic link to the treatment emergent autoimmune phenomena.

Identification of bovine CD52-like molecule by monoclonal antibody IVA-543: distribution of CD52-like molecule in the bull genital tract

The bovine maturation-associated sperm membrane antigen CD52-like molecule has been analysed using a mouse anti-sperm monoclonal antibody developed against bull spermatozoa. The antigen recognised by monoclonal antibody IVA-543 was detected on blood mononuclear cells (including lymphocytes and monocytes) and on a minor population of polymorphonuclear leukocytes. The bovine CD52-like molecule is secreted by the epididymal epithelium and then it is inserted into the sperm membrane during the epididymal transport in the distal part of epididymis. The CD52-like molecule was absent from spermatozoa derived from testes, and the highest proportion of IVA-543-reactive sperm was observed in the cauda epididymis (91.6%). This study has shown that the new molecule identified on bovine cells has properties analogous to those previously described for CD52 molecules in man, mouse, rat, monkey, and dog.

Effect of anti-mouse CD52 monoclonal antibody on mouse intestinal intraepithelial lymphocytes

BACKGROUND

CD52 monoclonal antibody (mAb) has been used therapeutically in lymphocytic leukemia, autoimmune disease, and organ transplantation. But the effect of CD52 mAb on intestinal intraepithelial lymphocytes (IELs) was unknown. The aim of this study was to assess the influence of anti-mouse CD52 mAb on IELs.

METHODS

Twenty male C57BL/6 mice were randomly assigned to a treatment or a control group. The treatment group received anti-mouse CD52 mAb (20 mug, subcutaneously), whereas the control group received the same volume of phosphate-buffered solution. On the seventh day after treatment, mice were killed, and ileum and colon were obtained for histopathology and immunohistochemistry examination, IELs were isolated for flow cytometric analysis and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis. Furthermore, the intestinal permeability was measured by lactulose-mannitol test.

RESULTS

The number and viability of IELs were decreased significantly in treatment compared with the control group. There were significant differences between the two groups considering IELs phenotypes. In addition, the proportion of apoptotic IELs in CD52 mAb treatment group was significantly higher than the control group (19.59%+/-3.13% and 2.02%+/-0.33%, respectively; P<0.05). Furthermore, lactulose-mannitol test showed a marked increase intestinal permeability after CD52 treatment (90.38%+/-5.96% and 46.02%+/-6.40%, respectively; P<0.05).

CONCLUSION

Anti-mouse CD52 mAb could induce more IELs to apoptosis and result in reducing the number of IELs, which may disrupt intestinal barrier function.

Molecular biology of sperm maturation in the human epididymis

Male infertility is a frequent cause of childlessness, and, indeed, a comparison of the contributions to conception failure made by male and female factors shows them to be equally frequent. In practice, male infertility appears to be resistant to most treatments. However, the major reason for this may be that often attempts are carried out without knowing the cause of the problem. Unlike in women, obstructions and hormonal disorders are rare in male infertility. Rather, it would appear that sperm disorders are the most common cause, reflecting a variety of pathogenetic mechanisms. Defects in sperm morphology, defective sperm movement, deficient development or functional failure of the acrosome, and the excessive generation of reactive oxygen species are changes that are often seen in infertile semen, but little is known about their aetiology. In 5–10% of men being treated for infertilty, an autoimmune reaction against spermatozoa is observed. Although the correlation between the presence of systemic antisperm antibodies and fertility potential is poor, the appearance of sperm-bound antibodies of immunoglobulin class IgA in semen seems to be closely associated with infertility. Studies in laboratory animals and humans have shown that complementary adhesion molecules are located on the surface of oocytes and spermatozoa. These molecules interact and lead to gamete fusion. Abnormalities in these molecules on the sperm surface might be expected to contribute to male infertility. However, their clinical significance has not yet been documented, and the molecular basis of human gamete interaction is far from being understood. Therefore, the key to understanding male infertility may lie in basic research which directly targets the fundamental cellular and molecular biology of the human spermatozoon.

Cellular expression, trafficking, and function of two isoforms of human ULBP5/RAET1G

Background

The activating immunoreceptor NKG2D is expressed on Natural Killer (NK) cells and subsets of T cells. NKG2D contributes to anti-tumour and anti-viral immune responses in vitro and in vivo. The ligands for NKG2D in humans are diverse proteins of the MIC and ULBP/RAET families that are upregulated on the surface of virally infected cells and tumours. Two splicing variants of ULBP5/RAET1G have been cloned previously, but not extensively characterised.

Methodology/Principal Findings

We pursue a number of approaches to characterise the expression, trafficking, and function of the two isoforms of ULBP5/RAET1G. We show that both transcripts are frequently expressed in cell lines derived from epithelial cancers, and in primary breast cancers. The full-length transcript, RAET1G1, is predicted to encode a molecule with transmembrane and cytoplasmic domains that are unique amongst NKG2D ligands. Using specific anti-RAET1G1 antiserum to stain tissue microarrays we show that RAET1G1 expression is highly restricted in normal tissues. RAET1G1 was expressed at a low level in normal gastrointestinal epithelial cells in a similar pattern to MICA. Both RAET1G1 and MICA showed increased expression in the gut of patients with celiac disease. In contrast to healthy tissues the RAET1G1 antiserum stained a wide variety or different primary tumour sections. Both endogenously expressed and transfected RAET1G1 was mainly found inside the cell, with a minority of the protein reaching the cell surface. Conversely the truncated splicing variant of RAET1G2 was shown to encode a soluble molecule that could be secreted from cells. Secreted RAET1G2 was shown to downregulate NKG2D receptor expression on NK cells and hence may represent a novel tumour immune evasion strategy.

Conclusions/Significance

We demonstrate that the expression patterns of ULBP5RAET1G are very similar to the well-characterised NKG2D ligand, MICA. However the two isoforms of ULBP5/RAET1G have very different cellular localisations that are likely to reflect unique functionality.

CD52 is synthesized in cumulus cells and secreted into the cumulus matrix during ovulation

PROBLEM

Early studies have shown that an antibody to male reproductive tissue CD52 is a pathogenic factor of infertility. The molecule contains a unique carbohydrate antigen that induces antibodies interfering with sperm function. However, the characteristic properties of CD52 in female reproductive tissues are not known. We examined the expression and localization of CD52 in mature expanded cumulus masses.

METHOD OF STUDY

Mouse cumulus oocyte complexes were collected from [C57B1/6; DBA/2] F1 female mice having a superovulation treatment. Human cumulus cells were obtained from infertile patients taking in vitro fertilization-embryo transfer treatment under informed consent. CD52 messenger RNA (mRNA) and protein were detected using RT-PCR, quantitative PCR, western blotting and immunohistochemical methods.

RESULTS

CD52 mRNA was found both in the human and mouse cumulus cells. Mouse CD52 mRNA was detected in cumulus cells but not oocytes and significantly increased after ovulation. The expression of the molecule was also confirmed at the protein level. Immunostaining with anti CD52 peptide antibody revealed that CD52 is present in cumulus cells and the extracellular matrix.

CONCLUSION

We first showed the expression of CD52 in human cumulus cells. CD52 has some functional roles around fertilization in females as well as in males.

The GPI-anchored CD52 antigen of the sperm surface interacts with semenogelin and participates in clot formation and liquefaction of human semen

CD52 is a human glycosylphosphatidylinositol (GPI)-anchored antigen exclusively expressed in leukocytes and epididymal cells. It is also present in sperm, being inserted in their plasma membrane as they pass through the epididymis. In a previous paper we identified a new CD52 form without GPI anchor by fast performance liquid chromatography (FPLC) fractionation of semen components. The form has a lower negative charge than the GPI-anchored form and occurs as the only CD52 form in prostasome-free seminal plasma. It was also found associated with the ejaculated sperm, but in contrast to the GPI-anchored one, it is lost during the capacitation process. In this paper we indicate that (1) the GPI-anchored CD52 of the sperm surface serves as receptor for semenogelin I during clot formation, (2) liquefaction involves cleavage of the GPI anchor from certain CD52 molecules, releasing sperm from the clot and the soluble antigen bound to semenogelin fragments into the seminal plasma and (3) the clot is a sponge-like structure housing sperm. Soluble CD52 was immunopurified from the soluble CD52-containing FPLC fraction using CAMPATH-1G and was found to be complexed with a semenogelin-derived peptide of the carboxyl terminal portion of semenogelin I, having the sequence SQTEKLVAGKQI and starting from amino acid 376. Immunoprecipitation and immunoblot analyses using CAMPATH-1G and anti-semenogelin as immunoprecipitating antibodies and anti-gp20 and anti-semenogelin as immunoblot detectors of the corresponding antigens, confirmed that the soluble CD52 formed a complex with semenogelin. The semenogelin-CD52 soluble form was found to be a direct consequence of the liquefaction process since only the GPI-anchored CD52 was recovered in uniquefied semen after recovering sperm and seminal plasma by urea solubilization of the clot.

Alemtuzumab (Campath-1H) in the treatment of chronic lymphocytic leukemia

Alemtuzumab (Campath-1H) is a humanized IgG1 monoclonal antibody that targets the human CD52 antigen. CD52 is expressed by a variety of lymphoid neoplasms and most human mononuclear cell subsets. In 2001, alemtuzumab was approved for marketing in the United States and Europe for use in patients with fludarabine-refractory chronic lymphocytic leukemia (CLL). In heavily pretreated patients with CLL, the overall response rate (ORR) is approximately 35%, and in previously untreated patients the ORR is greater than 80%, with a recent randomized study suggesting it is superior to alkylator-based therapy. Importantly, alemtuzumab is effective in patients with high-risk del(17p13.1) and del(11q22.3) CLL. Alemtuzumab combination studies with fludarabine and/or monoclonal antibodies such as rituximab have demonstrated promising results. Alemtuzumab is also being studied in CLL patients as consolidation therapy for treatment of minimal residual disease, in preparation for stem cell transplantation and to prevent acute and chronic graft versus host disease. Alemtuzumab is frequently associated with acute 'first-dose' reactions when administered intravenously, but is much better tolerated when administered subcutaneously without loss of therapeutic efficacy. Additional potential adverse events associated with alemtuzumab administration include myelosuppression as well as profound cellular immune dysfunction with the associated risk of viral reactivation and other opportunistic infections. Additional studies detailing the mechanism of action of alemtuzumab as well as new strategies for prevention of opportunistic infections will aid in the future therapeutic development of this agent.

The sperm agglutination antigen-1 (SAGA-1) glycoforms of CD52 are O-glycosylated

CD52 is composed of a 12 amino acid peptide with N-linked glycans bound to the single potential glycosylation site at position 3, and a glycosylphosphatidylinositol-anchor attached at the C-terminus. Some glycoforms of this molecule expressed in the male reproductive tract are recognized by complement-dependent sperm-immobilizing antibodies in infertile patients making this antigen an important target for immunocontraception and fertility studies. Although the amount of posttranslational modification is already remarkable for such a small polypeptide, O-glycosylation of CD52 has additionally been implicated by several studies, but never rigorously characterized. In this report, we show clear evidence for the presence of O-glycans in CD52 preparations immunopurified using the murine S19 monoclonal antibody generated against sperm agglutination antigen-1 (SAGA-1), a male reproductive tract specific form of CD52. The O-glycans have been characterized by MALDI-TOF and tandem mass spectrometry after reductive elimination and permethylation. The data indicate that the major SAGA-1 O-glycans are core 1 and 2 mucin-type structures, with and without sialic acid (NeuAc(0-2)Hex(1-3)HexNAc(1-2)HexNAcitol). Minor fucosy- lated O-glycans are also present including some struc- tures with putative Le(y) epitopes (NeuAc(0-1)Fuc(1-3)Hex(1-2) HexNAc(0-1)HexNAcitol). Analysis of O-glycopeptides by tandem mass spectrometry provided an additional level of support for the O-glycosylation of SAGA-1. Elucidation of the O-glycosylation of SAGA-1 adds to the complexity of this molecule and may help to explain its biological activity.

Biochemical property and immunogenicity of mouse male reproductive tract CD52 (mrt-CD52)

Male reproductive tract CD52 (mrt-CD52) is known to be a pathogenic antigen for immunological infertility. Although human CD52 has been extensively investigated, the properties of mouse CD52 are not well elucidated. This study was conducted, therefore, to examine the tissue distribution, molecular composition and immunogenicity of mouse mrt-CD52. Immunohistological studies with an antibody to a synthetic peptide showed that mouse CD52 was localized mainly in the cauda epididymis and vas deferens, but not in the testis, liver, kidney or spleen. The molecule was composed of Asn (N)-linked and The/Ser (O)-linked carbohydrates as well as a glycosylphosphatidyl (GPI) anchor portion. Purified mrt-CD52 preparations produced antibodies by subcutaneous and intranasal immunization in both male and female mice. These antisera showed sperm-immobilizing activities with complement to mouse sperm. The research indicated mouse CD52 had similar biochemical and immunological properties to human CD52. This animal experiment is a good model for investigating human mrt-CD52 antibody detected in infertile patients.

Alemtuzumab induces caspase-independent cell death in human chronic lymphocytic leukemia cells through a lipid raft-dependent mechanism

Alemtuzumab is a humanized IgG1 kappa antibody directed against CD52, a glycosyl-phosphatidylinositol linked cell-membrane protein of unknown function. Herein, we demonstrate that alemtuzumab promotes rapid death of chronic lymphocytic leukemia (CLL) cells in vitro, in a complement and accessory cell free system. Using minimal detergent solubilization of CLL membranes, we found that CD52 colocalizes with ganglioside GM-1, a marker of membrane rafts. Fluorescence microscopy revealed that upon crosslinking CD52 with alemtuzumab+anti-Fc IgG, large patches, and in many cases caps, enriched in CD52 and GM-1 formed upon the CLL cell plasma membrane. Depletion of membrane cholesterol or inhibition of actin polymerization significantly diminished the formation of alemtuzumab-induced caps and reduced alemtuzumab-mediated CLL cell death. We compared alemtuzumab-induced direct cytotoxicity, effector cell-mediated toxicity and complement-mediated cytotoxicity of CLL cells to normal T cells. The direct cytotoxicity and observed capping was significantly greater for CLL cells as compared to normal T cells. Cell-mediated and complement-mediated cytotoxicity did not significantly differ between the two cell types. In summary, our data support the hypothesis that alemtuzumab can initiate CLL cell death by crosslinking CD52-enriched lipid rafts. Furthermore, the differential direct cytotoxic effect suggests that CD52 directed antibodies could possibly be engineered to more specifically target CLL cells.

Alemtuzumab

Alemtuzumab is a humanized monoclonal antibody against CD52, a small glycosylphosphatidylinositol-anchored glycoprotein that is highly expressed on normal T- and B-lymphocytes, and on a large proportion of malignant lymphoid cells, but not on hematopoietic progenitor cells. Over the past several years, a number of clinical trials have demonstrated the clinical activity of alemtuzumab in treating patients with chronic lymphocytic leukemia, T-cell malignancies such as T-prolymphocytic leukemia and cutaneous T-cell lymphoma, as well as in the prevention and therapy of graft-versus-host disease in the setting of allogeneic stem cell transplantation. Its application in a number of autoimmune disorders is currently under investigation. The most significant side effect of alemtuzumab is predisposition to infections related to the associated profound lymphopenia. Despite this, and with appropriate and more effective antibiotic prophylaxis, it is likely that we will witness an expansion of the role of alemtuzumab in the future.

Different glycoforms of the human GPI-anchored antigen CD52 associate differently with lipid microdomains in leukocytes and sperm membranes

CD52 is a human GPI-anchored antigen, expressed exclusively in the immune system and part of the reproductive system (epididymal cells). Sperm cells acquire the antigen from the epididymal secretions when transiting in the epididymal corpus and cauda. The peptide backbone of CD52, consisting of only 12 aminoacids, is generally considered no more than a scaffold for post-translational modifications, such as GPI-anchor and especially N-glycosylation which occur at the third asparagine. The latter modification is highly heterogeneous, especially in the reproductive system, giving rise to many different glycoforms, some of which are tissue specific. A peculiar O-glycan-containing glycoform is also found in reproductive and immune systems. We determined to locate CD52 in microdomains of leukocytes and sperm membranes using two antibodies: (1) CAMPATH-1G, the epitope of which includes the last three aminoacids and part of the GPI-anchor of glycoforms present in leukocytes and sperm cells; (2) anti-gp20, the epitope of which belongs to the unique O-glycan-bearing glycoform also present in both cell types. Using a Brij 98 solubilization protocol and sucrose gradient partition we demonstrated that the CD52 glycoforms recognized by both antibodies are markers of typical raft microdomains in leukocytes, whereas in capacitated sperm the O-glycoform is included in GM3-rich microdomains different from the cholesterol and GM1-rich lipid rafts with which CAMPATH antigen is stably associated. The importance of the association between GM3 and O-glycans for formation of specialized microdomains was confirmed by heterologous CD52 insertion experiments. When prostasomes from human seminal fluid were incubated with rat sperm from different epididymal regions, the CD52 glycoform recognized by anti-gp20 decorated rat epididymal corpus and cauda sperm, associated with the same low-cholesterol GM3-rich sperm membrane fractions as in human sperm. The glycoforms recognized by CAMPATH-1G were not found in rat sperm. The relationship between this differential insertion and differences in glycosylation of rat and human CD52 is discussed.

Antigenic epitope for sperm-immobilizing antibody detected in infertile women

CD52 is a glycosylphosphatidylinositol (GPI) anchor protein occurring in lymphocytes, the epididymis, seminal plasma and on ejaculated sperm surface. The molecular structure of male reproductive tract CD52 (mrtCD52) is quite different from that of lymphocyte CD52 except for a peptide sequence comprising 12 amino acids. The carbohydrate molecule may thus provide antigenic epitopes to females. The repeated N-acetyllactosamine units of the N-linked carbohydrate present in the mrtCD52 were identified as a pathogenic antigen for infertility using a monoclonal antibody (MAb H6-3C4) generated from an infertile patient's peripheral blood lymphocyte. We suggested also the possible presence of O-linked carbohydrate in human mrtCD52, although it is not known whether this carbohydrate is immunogenic or not. This article gives an overview of the structure and function of mrtCD52 as well as the fertilization-blocking mechanism of the antibody against this molecule.

Epitope analysis of immunoglobulins against gp20, a GPI-anchored protein of the human sperm surface homologous to leukocyte antigen CD52

Gp20 is a sialylglycoprotein of the human sperm surface related to maturation and capacitation and is homologous to CD52, a glycosyl- phosphatidyl-inositol (GPI)-anchored protein highly expressed in lymphocytes, monocytes, eosinophils, and epididymal cells, described by the monoclonal antibody family CAMPATH. The CAMPATH antigen is characterized by a very short peptide (12 amino acids) and an N-linked oligosaccharide chain bound to the asparagine located in the third position and a GPI anchor bound to the C-terminal serine. The CAMPATH epitope includes three amino acids at the C-terminus and part of the GPI anchor. It has been suggested that anti-gp20 interacts with the same peptide recognized by CAMPATH antibodies but with a different epitope, since it describes the corresponding antigen in a different way. For example, it localizes the corresponding antigen in the equatorial region of the sperm head when sperm are capacitated, whereas CAMPATH antibodies bind all over the sperm surface. Our results indicate that the anti-gp20 epitope does not include the peptide backbone, the GPI anchor, or the N-glycans but consists of O-linked oligosaccharide chains bound to a unique CD52 glycoform present both in sperm and leukocytes. This is suggested by results obtained using many different approaches, such as immunoblot analysis of gp20 after removal of N- and O-glycans and after jacalin (Artocarpus integrifolia agglutinin)-affinity chromatography.

Alemtuzumab (CAMPATH 1H) induction therapy in cadaveric kidney transplantation--efficacy and safety at five years

Alemtuzumab is a powerful lymphocyte depleting antibody currently being evaluated in solid organ transplantation. This paper describes 5-year results of a single center study of alemtuzumab as induction in renal transplantation. Thirty-three renal transplant recipients received 20 mg alemtuzumab on day 0 and 1, followed by half-dose cyclosporin monotherapy (trough concentration 75-125 ng/mL) from day 3. They were compared in a retrospective contemporaneous-controlled manner with 66 kidney transplant recipients transplanted in the same period and center who received conventional immunosuppression with cyclosporin, azathioprine and prednisolone. In the alemtuzumab group 12% of recipients died compared to 17% in the control group (p = 0.48); likewise graft loss was similar in both groups (21% vs. 26%, respectively, p = 0.58). Incidence of acute rejection was also comparable at 5 years (31.5% vs. 33.6%), although the pattern of rejection was different with 14% patients in the alemtuzumab group experiencing rejection over 1 year post-transplant compared to none in the control group. There was no significant difference between groups in terms of infection or serious adverse events. While acknowledging the limitations of a relatively small single-center study, results suggest that alemtuzumab induction allowed satisfactory long-term patient and graft survival equivalent to that seen with standard triple immunosuppression, while avoiding steroid therapy.

Advances in the use of monoclonal antibodies in the therapy of chronic lymphocytic leukemia

Monoclonal antibody (moAb)-based therapies are evolving as an integrated component in the treatment of chronic lymphocytic leukemia (CLL). Advantages such as different mechanisms of action (compared with those of chemotherapy), no or minimal stem cell toxicity, as well as the absence of hair loss and delayed nausea may result in a rapidly increasing usage of these agents in different phases of the disease. The combination of moAbs with chemotheraputic agents has shown promising results in early studies as well as their role in the eradication of minimal residual disease (MRD). The availability of an increasing number of new moAbs together with a better understanding of their effector function will hopefully lead to improved therapeutic outcomes for patients with CLL and related disorders.

Possible presence of O-linked carbohydrate in the human male reproductive tract CD52

Male reproductive tract CD52 (mrtCD52) is an antigen recognized by a complement-dependent sperm-immobilizing monoclonal antibody (SI-Abs) derived in an infertile patient. The molecule has been shown to contain a unique N-linked carbohydrate that does not cross-react with other tissues. In this study, we have investigated whether O-linked carbohydrate as well as N-linked carbohydrate is present in mrtCD52 using specific lectins and anti-CD52 core peptide antiserum. The lectin PNA, which recognizes O-linked carbohydrate [Galbeta1-3GalNAc], reacted with mrtCD52 and showed a similar polymorphic reaction pattern to that of the anti-peptide antiserum in western blotting analysis on two-dimensional SDS-PAGE. The PNA-reactive spots disappeared after removal of O-linked carbohydrate, but not after removal of N-linked carbohydrate. These results suggest that O-linked carbohydrate is present in mrtCD52. The moiety may possibly contribute to a specific antigenic epitope of mrtCD52.

Expression of gp20, a human sperm antigen of epididymal origin, is reduced in spermatozoa from subfertile men

gp20, a sialylglycoprotein of human sperm homologous to CD52, is present everywhere on the surface of the freshly ejaculated sperm but is prevalently localized in the equatorial region of the head of capacitated sperm. In the present study, we confirmed this feature on large scale and correlated equatorial exposure of the antigen to the presence of serum albumin (SA) in the capacitation medium. Furthermore, we analyzed the relationship between the presence of the antigen and its equatorial exposure after capacitation and fertility, by comparing immunostaining for gp20 in the motile fraction of spermatozoa from fertile and subfertile men. A significantly higher percentage of nonimmunostained spermatozoa before capacitation (38.5% +/- 23 vs. 12% +/- 7, P < 0.0001) and a lower increase in the percentage of sperm with equatorial localization after capacitation (19.3% +/- 25 vs. 34.6% +/- 22, P = 0.039) were observed in subfertile men (n = 60) compared to fertile men (n = 15). In the whole study group, a positive correlation was also found between the percentage of spermatozoa exhibiting equatorial localization in capacitated samples and normal head forms (R = 0.50; P < 0.0001).

Analysis of CREM-dependent gene expression during mouse spermatogenesis

The transcription factors CREM, CREB, and ATF-1 constitute a subfamily of beta-Zip transcription factors. Several different kinase cascades regulate the activity of these proteins. The activator splice-isoform CREMtau is specifically and highly expressed in post-meiotic germ cells during mouse spermatogenesis. Male mice lacking CREMtau expression are sterile because of stage-specific arrest of sperm maturation as the spermatids undergo apoptosis. In order to characterize the genes that are controlled by CREM during post-meiotic differentiation of round spermatids, we compared the expression levels of mRNA prepared from testes of wild-type and CREM-deficient mice by suppression subtractive hybridization (SSH) and affymetrix oligonucleotide arrays. A set of 956 unique sequences found in the CREM SSH library was further characterized by generating stage-specific expression profiles during spermatogenesis by hybridization with cDNA from pre-pubertal mice at defined stages of spermatogenesis using nylon DNA arrays. The resulting expression profiles were arranged in a linear order according to similarity in their profile shapes to find co-regulation of functionally related genes. Our data shows that a large number of genes are transcriptionally activated in round spermatids when CREM activity is maximal, including functional groups like transcription factors, proteins involved in signal transduction, and metabolic enzymes, therefore providing novel information of post-meiotic expression of many known as well as novel genes that are either directly or indirectly influenced by CREM expression.

All-trans-retinoic acid induces CD52 expression in acute promyelocytic leukemia

It is well known that all-trans-retinoic acid (ATRA) can induce myeloid cell differentiation in acute promyelocytic leukemia (APL) cells. In this study, we found that ATRA treatment of the APL cell line NB4 induced the expression of CD52, both at transcriptional and translational levels. CD52 is a 21- to 28-kDa nonmodulating cell surface glycosylphosphatidylinositol-linked glycoprotein expressed on lymphocytes and monocytes, but not in human myeloid cells. The ATRA-dependent induction of CD52 expression was not observed in non-promyelocytic leukemia cell lines such as K562, U937, and HL-60, suggesting that induction of CD52 by ATRA may be specific to leukemic cells that express promyelocytic leukemia-retinoic acid receptor alpha (PML-RARalpha) or are at the promyelocytic stage of myeloid development. Antibodies against CD52 are used therapeutically against lymphocytes in certain leukemias and in patients undergoing transplantation. An ATRA-induced high level of CD52 expression might potentially serve as a novel therapeutic target in treatment of APL.

A male genital tract-specific carbohydrate epitope on human CD52: implications for immunocontraception

The identification of unique sperm surface epitopes that are not expressed or exposed in the female reproductive tract is a key element in the development of antibody-based contraceptives. Western blotting and immunohistochemistry were performed to define the tissue distribution of the S19 epitope, which has been proposed as a target for immunocontraception. S19 is an IgG1 murine monoclonal antibody (mAb) directed to an N-linked carbohydrate epitope on a 15-25 kDa glycoprotein, sperm agglutination antigen-1 (SAGA-1), containing a peptide core identical to that of the lymphocytic surface protein CD52. In this study, the S19 epitope was shown to be absent from human lymphocytes, demonstrating a distinction between this epitope and the CAMPATH epitope that is recognized by an antibody against the terminal tripeptide and GPI-anchor of CD52. Further tissue specificity analysis identified the S19 epitope in the epithelium of the human epididymis and vas deferens, as well as on both epididymal and ejaculated spermatozoa. In contrast, the S19 epitope was absent in the five human female reproductive tract and 18 other somatic tissues tested. These results support the use of the S19 epitope as a contraceptive immunogen and the suitability of the S19 mAb as an intravaginal contraceptive. To test the agglutinating activity of the S19 mAb in a formulation designed for vaginal use, S19 mAb were bound to the surface of Novasomes, a multilamellar liposome delivery vehicle. S19-Novasome formulations agglutinated human spermatozoa and were as effective as unbound S19 mAb, demonstrating the feasibility of spermistatic contraceptives targeted to the male reproductive tract specific carbohydrate epitope.

Analysis of a human sperm CD52 glycoform in primates: identification of an animal model for immunocontraceptive vaccine development

Sperm agglutination antigen-1 (SAGA-1) is a human male reproductive tract glycoform of CD52. Unique modification of CD52 N-linked oligosaccharide chains in the epididymis and vas deferens results in the appearance of a carbohydrate epitope that is localized over the entire surface of human spermatozoa. SAGA-1 was characterized by the sperm-inhibitory murine monoclonal antibody (mAb) S19, and it is the target antigen of a human mAb (H6-3C4) associated with antibody-mediated infertility. Collectively, sperm surface localization, antibody inhibition of sperm function, and potential reproductive-tissue specificity identify SAGA-1 as an attractive candidate contraceptive immunogen. To establish an animal model for the study of SAGA-1 in immunologic infertility and immunocontraceptive development, we investigated the appearance of the S19 carbohydrate epitope in nonhuman primates. The S19 mAb demonstrated little to no immunoreactivity by Western blot analysis with protein extracts of spermatozoa from the baboon, marmoset, bonnet, cynomolgus, and pigtailed macaques. Immunohistochemical analysis identified CD52 in the bonnet monkey epididymis; however, the N-linked carbohydrate moiety recognized by the S19 mAb, and unique to SAGA-1, was absent. In contrast, the S19 carbohydrate epitope was identified in chimpanzee sperm extracts by Western blot analysis and in chimpanzee epididymal tissue sections by immunohistochemical analysis, indicating that it is conserved in this close relative of the human. Chimpanzee testis, seminal vesicle, and prostate do not express the S19 epitope. Although anti-CD52 immunoreactivity was identified in the spleen, the carbohydrate moiety recognized by the S19 mAb was absent, corroborating data in the human that demonstrated tissue-specific glycosylation of sperm CD52. Immunofluorescent analysis indicated that the chimpanzee homologue of sperm CD52 was present over the entire spermatozoon. In addition, the S19 mAb agglutinated chimpanzee spermatozoa in a manner similar to the effect observed on human spermatozoa. These data indicate that the distinctive carbohydrate moiety of human sperm CD52 is present in the chimpanzee, and they identify the chimpanzee as the most appropriate primate model to study the potential of this unique CD52 glycoform as a contraceptive immunogen.

Alemtuzumab: a novel monoclonal antibody

Antibody-based treatment is a novel, effective management strategy for a variety of diseases. Alemtuzumab (CAMPATH) is an example of a monoclonal antibody (mAb) that was initially developed in the laboratory and has completed its journey by being approved for therapeutic use in humans. The main clinical applications of alemtuzumab include treatment of lymphoid malignancies, particularly chronic lymphocytic leukaemia (CLL) and T-cell prolymphocytic leukaemia (T-PLL) and prevention of graft versus host disease (GVHD) and graft rejection in bone marrow and solid organ transplant recipients. Alemtuzumab administration is accompanied by a characteristic first-dose reaction due to cytokine release that consists of fever, rigors, rash and, at times, dyspnea and hypotension. The most significant toxic effect is profound, prolonged lymphopenia and the subsequent increased risk of opportunistic infections; antibiotic prophylaxis is recommended for patients undergoing alemtuzumab treatment. Alemtuzumab has demonstrated clinical activity as a single agent and has an acceptable toxicity profile. It has significant therapeutic potential, especially against lymphoid malignancies.

Surface of human sperm bears three differently charged CD52 forms, two of which remain stably bound to sperm after capacitation

gp20 is a sialoglycoprotein of the human sperm surface with a core peptide homologous to the leukocyte antigen CD52, a GPI-anchored glycosylated protein which is described by the monoclonal antibody CAMPATH-1. Comparative analyses, by means of CAMPATH and anti-gp20, indicated that they describe it in morphologically and functionally different ways, suggesting that the respective epitopes are different but also casting doubt on the immunological identity of the antigen. In the present study, we used immunodepletion to demonstrate that CAMPATH and anti-gp20 interact with the same antigen, but that anti-gp20 has a much higher avidity for the antigen than CAMPATH. Anion exchange fractionation analysis of the antigen revealed three differently charged gp20-CD52 forms, the least charged of which, was largely without a GPI-anchor. All three forms were associated with freshly ejaculated sperm, whereas capacitated sperm only contained the two GPI-anchored, more charged forms, which were also the ones found in the prostasome fraction of seminal plasma and in leukocytes. The two charged, GPI-anchored forms were described as homogeneous by anti-gp20, since they ran as a singlet; the third form ran as a doublet. When tested for insertion into Jurkat T cells, the medium charged form inserted the most readily and the less charged one could not be inserted at all.

The effect of treatment with Campath-1H in patients with autoimmune cytopenias

We describe 21 patients with severe and life-threatening autoimmune cytopenias resistant to standard immunosuppression who were treated with the monoclonal antibody Campath-1H. Four patients had autoimmune neutropenia, four had autoimmune haemolytic anaemia, four had pure red cell aplasia, one had immune thrombocytopenia purpura (ITP), three had autoimmune haemolytic anaemia and ITP (Evan's syndrome), three had autoimmune pancytopenia (ITP, autoimmune neutropenia and autoimmune haemolytic anaemia), one had ITP (associated with acquired Glanzmann's disease) and autoimmune neutropenia, and one had ITP and red cell aplasia. Campath-1H was administered at a dose of 10 mg/d as an intravenous infusion for 10 d. Responses were seen in 15 patients, which were sustained in six. Relapse occurred in eight patients after Campath-1H treatment. Patients entering the study later, received cyclosporine after Campath-1H in an attempt to reduce the incidence of relapse. Three patients received a second course of Campath-1H; all responded but later relapsed. Fourteen patients are alive at a median of 12 months (range 4-61) after Campath-1H. Campath-1H represents an alternative therapeutic option for severe, refractory autoimmune cytopenias.

Changes of the major sperm maturation-associated epididymal protein HE5 (CD52) on human ejaculated spermatozoa during incubation

HE5 (CD52) is a glycoprotein which is secreted by the epididymis and which becomes inserted onto maturing spermatozoa. We have previously shown that, in cynomolgus monkey spermatozoa, changes occur upon maturation rendering cryptic the epitope to the monoclonal antibody CAMPATH-1G; the recognition site is then re-exposed during incubation under capacitation conditions. The present study investigated human ejaculated spermatozoa during incubation under similar conditions, using monoclonal antibodies that recognize different epitopes of the HE5 molecule comprising parts of the N-glycan (2E5) or peptide segments, including (CAMPATH-1G) or excluding (097) the glycosylphosphatidylinositol (GPI) anchor, to reveal modifications of sperm surface HE5. Flow cytometric analysis showed equally high percentages (approximately 90%) of viable spermatozoa cross-reacting with the antibodies before and after 6 h incubation. However, during incubation, the staining intensity increased 57% with CAMPATH-1G, 31% with 097, but remained unchanged with 2E5. The lymphocyte CD52 antibody CF1D12 stained only approximately 10% of spermatozoa either before or after incubation. Western blotting of sperm protein extracts using lectins indicated an increase in the exposure of sialic acid residues of HE5 after incubation. These results suggest that during incubation in capacitating conditions, there is an opening up of the HE5 glycoprotein molecule, increasing accessibility of some sialic acid residues and of the core peptide, particularly the GPI anchor.