Prophylactic and therapeutic effects of a humanized monoclonal antibody against the IL-2 receptor (DACLIZUMAB) on collagen-induced arthritis (CIA) in rhesus monkeys

CIA in the rhesus monkey is an autoimmune-based polyarthritis with inflammation and erosion of synovial joints that shares various features with human rheumatoid arthritis (RA). The close phylogenetic relationship between man and rhesus monkey makes the model very suitable for preclinical safety and efficacy testing of new therapeutics with exclusive reactivity in primates. In this study we have investigated the prophylactic and therapeutic effects of a humanized monoclonal antibody (Daclizumab) against the alpha-chain of the IL-2 receptor (CD25). When Daclizumab treatment was started well after immunization but before the expected onset of CIA a significant reduction of joint-inflammation and joint-erosion was observed. A therapeutic treatment, initiated as soon as the first clinical signs of CIA were observed, proved also effective since joint-degradation was abrogated. The results of this study indicate that Daclizumab has clinical potential for the treatment of RA during periods of active inflammation and suppression of the destruction of the joint tissues.

Is uterine papillary serous adenocarcinoma a manifestation of the hereditary breast-ovarian cancer syndrome?

BACKGROUND

Uterine papillary serous carcinoma (UPSC) shares common pathologic, genetic, and clinical features with other serous cancers of müllerian origin. The most common histologic type of ovarian tumor associated with BRCA mutations is papillary serous. Because of these histologic similarities, we postulated that, in some cases, UPSC may be a manifestation of a field defect in BRCA1 carriers, which also includes ovarian carcinoma, fallopian tube carcinoma, and primary peritoneal carcinoma.

METHODS

Fifty-six living patients with UPSC were contacted through their treating physicians and agreed to a family history interview and to provide a blood specimen for BRCA testing. The protein truncation test was used to detect mutations in exons 10 and 11 of BRCA1 and in exon 11 of BRCA2. The presence of four common mutations was assessed by PCR-based specific assays.

RESULTS

A high proportion of patients had a past history of breast cancer (11%) or a first-degree relative with breast cancer (29%). Four patients were from families with site-specific hereditary breast cancer. However, there was no clear example of the hereditary breast-ovarian cancer syndrome, and none of the 56 patients was found to carry a BRCA1 or BRCA2 mutation.

CONCLUSIONS

BRCA mutations do not appear to predispose to UPSC and this type of cancer does not appear to be a manifestation of the classical hereditary breast-ovarian cancer syndrome. The observed association between UPSC and breast cancer may be due to the presence of mutations in other cancer predisposing genes.

Successful in vivo blockade of CD25 (high-affinity interleukin 2 receptor) on T cells by administration of humanized anti-Tac antibody to patients with psoriasis

BACKGROUND

Daclizumab is a humanized antibody to the alpha-subunit (CD25) of the interleukin 2 (IL-2) receptor that blocks normal IL-2 binding to this receptor. Because IL-2 is a major stimulus for T-cell growth, blockade of the IL-2 receptor could be useful in treating T-cell-mediated (autoimmune) diseases.

OBJECTIVE

Our purpose was to determine whether adequate concentrations of antibody were achieved in circulating blood and in psoriatic skin lesions to saturate CD25 receptors. We also intended to measure clinical effect and safety of this agent when used alone (without other immunosuppressive drugs) in psoriasis.

METHODS

Nineteen patients with psoriasis in two centers received daclizumab at an initial dose of 2 mg/kg, then 1 mg/kg at weeks 2, 4, 8, and 12. To determine whether CD25 was blocked in vivo, flow cytometric studies measured (1) expression of CD25 on CD3(+) T cells derived from blood and (2) immuno-histochemistry measures of CD25(+) cells done on pretreatment and posttreatment biopsy specimens. Patients were followed up clinically with photographs and Psoriasis Area and Severity Index scores.

RESULTS

This study showed a consistent blockade of CD25 in peripheral blood and tissue during the first 4 weeks of therapy while the dosing was every 2 weeks. Variable desaturation of receptors began after 4 weeks, which correlated with a reversal in disease improvement. Patients with a pretreatment Psoriasis Area and Severity Index score of less than 36 showed a mean reduction in severity by 30% at 8 weeks (P =.02). During the 16 weeks of treatment, a 44.8% decrease in expression of the IL-2 receptor alpha-subunit was found. The absolute T-cell counts were calculated and showed no significant changes during the course of the study. No significant adverse events were produced by daclizumab during this study.

CONCLUSION

We therefore conclude that daclizumab is a well-tolerated agent that blocks CD25 expression in peripheral blood and skin. Furthermore, it may be useful in treating psoriasis in some patients.

Significance of the CAG repeat polymorphism of the androgen receptor gene in prostate cancer progression

PURPOSE

The CAG repeat polymorphism of the androgen receptor gene has been associated with an increased prostate cancer risk, and the repeat length correlated with cancer stage and grade at presentation. Men with an allele length of </= 18 CAG repeats have a 2-fold increase in risk for high-stage or high-grade prostate cancer, compared with patients with a longer CAG repeat. We examined the significance of the CAG repeat polymorphism of the androgen receptor gene for predicting prostate cancer progression among 318 patients treated by radical prostatectomy for clinically localized prostate cancer between 1987 and 1994.

MATERIALS AND METHODS

Leukocyte DNA was collected and genotyping of the CAG repeat polymorphism was performed using a PCR-based direct sequencing method. Risk ratios were calculated for developing biochemical recurrence for patients associated with an allele length of </= 18 CAG repeats, compared with patients with an allele length of >18 CAG repeats, controlling for grade, stage and serum PSA level at diagnosis using Cox proportional hazard modeling.

RESULTS

Overall, the CAG repeat allele was not predictive of recurrence; tumor grade, stage and PSA level at diagnosis were the only predictors of recurrence in a multivariate analysis. However, for patients at low risk for recurrence (Gleason score 2 to 6, stage pT2, and PSA </= 10 ng./ml.), the relative risk of recurrence associated with an allele of </= 18 CAG repeats was 8.07 (95% C.I., 2.02 to 32.2, p = 0.004), compared with patients with an allele length of >18 CAG repeats. In contrast, for patients at high risk of recurrence (Gleason score >/= 7, stage pT3/4, or PSA >10 ng./ml.), the relative risk associated with the </= 18 CAG repeat allele was 0.72 (95% C.I., 0.33 to 1.57, p = 0.41), compared with patients with the >18 CAG repeat allele.

CONCLUSIONS

The length of the CAG repeat polymorphism of the androgen receptor gene may be important for prostate cancer recurrence among patients who are otherwise at low risk for recurrence after radical prostatectomy. These findings have potential implications for patient selection for adjuvant treatment, and for the development of novel treatments.

A rapid fluorescent multiplexed-PCR analysis (FMPA) for founder mutations in the BRCA1 and BRCA2 genes

Mutations of the BRCA1 and BRCA2 genes account for approximately 80% of hereditary breast/ovarian cancer families, but the size of these two genes makes mutation analysis time-consuming and technically challenging. In some populations such as the Ashkenazi Jewish and the French-Canadian, a small number of recurrent founder mutations account for the majority of mutations in cancer families. We have therefore developed two rapid genetic screening tests, which allow us to detect three frequent frameshift mutations in the Ashkenazi Jewish population and five frameshift mutations in the French-Canadian population. These fluorescent non-radioactive methods permit the simultaneous detection of multiple mutations by generating multiplexed PCR-amplified gene fragments, and by discriminating these on the basis of their size in a denaturing polyacrylamide gel. Using these methods, we were able to correctly identify all mutants in a blinded analysis of 276 DNA samples, including 30 derived from paraffin-embedded tumor samples and 10 from buccal-cell brushes, with no false positive or false negative results. These techniques designed for the direct detection of recurrent mutations in the BRCA1 and BRCA2 genes, have the advantages of being efficient, sensitive, cost-effective, and are applicable to large scale screening for epidemiologic studies.

Treatment of uveitis with recombinant human interleukin-13

AIM

To evaluate the anti-inflammatory cytokine interleukin-13 (IL-13) for the treatment of uveitis.

METHODS

Uveitis was induced in monkeys by immunisation with human retinal S-antigen. Starting at the onset of disease, the animals were treated with IL-13 at 25 micrograms/kg, or vehicle control, injected subcutaneously once a day for 28 days. Intraocular inflammation was scored by indirect ophthalmoscopy for a period of 56 days. Circulating leucocyte levels were monitored.

RESULTS

Uveitis started unilaterally in all but one animal. IL-13 inhibited inflammation both in the eyes in which the disease was present when the treatment was initiated (p = 0.0001), and in the contralateral initially negative eyes (p = 0.0001). After cessation of therapy, there was a progressive increase of inflammation in the IL-13 treated group. However, the beneficial effect of IL-13 extended into the 4 week follow up period. IL-13 produced an increase in circulating polymorphonuclear neutrophils and a decrease in lymphocytes.

CONCLUSION

Administration of IL-13 appears to be a promising modality of treatment for severe uveitis.

Collagen-induced arthritis in rhesus monkeys: evaluation of markers for inflammation and joint degradation

The objective of this study was to analyse parameters in rhesus monkey collagen-induced arthritis (CIA) with which the inflammation and destruction of the joints can be described in quantitative terms. CIA was induced in genetically susceptible and resistant monkeys, which can be distinguished on the basis of the dominant resistance marker Mamu-A26. The disease course was monitored daily using a semiquantitative scoring system. Plasma samples were collected once or twice weekly and analysed for C-reactive protein (CRP). Urines were collected overnight once a week and analysed for excretion rates of the collagen cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP). The results show that periods of active CIA are characterized by substantial weight loss and increased plasma CRP levels, followed shortly thereafter by increased excretion rates of the collagen cross-links HP and LP. Remission of the disease can be recognized by a decline in plasma CRP levels and especially an increase in body weight. The highest CRP levels were found in the most severely arthritic monkeys, indicating a possible relationship of the absolute plasma CRP levels to the severity of inflammation. During periods of active arthritis, increased excretion rates of collagen cross-links HP and LP in the urine were found. In particular, the major collagen cross-link in articular cartilage, HP, showed a strong increase (9- to 15-fold). The excretion rates of LP, which is considered as a bone-specific degradation marker, only increased 4- to 6-fold, thus indicating predominant destruction of cartilage and less of bone. In conclusion, the severity of CIA can be monitored in a quantitative manner using plasma CRP levels, urinary excretion rates of HP and LP, and body weights, superimposed on semiquantitative clinical scores. The parameters also facilitate a more objective assessment of the effect of anti-arthritic drugs in the model than with the clinical scores alone.

Bispecific humanized anti-IL-2 receptor alpha beta antibodies inhibitory for both IL-2- and IL-15-mediated proliferation

Humanized anti-Tac (HAT) and Mik beta1 (HuMik beta 1) Abs directed at IL-2R alpha and IL-2R beta, respectively, inhibit IL-2 binding and biological activity and together act synergistically in vitro. The Abs have been used successfully in primate models of allograft rejection, graft-vs-host disease, and autoimmunity. We produced bifunctional humanized anti-IL-2R alpha beta Abs (BF-IgG) to combine the specificity of the two Abs into one entity by fusing HAT-producing NSO cells and HuMik beta 1-producing Sp2/0 cells. BF-IgG was purified using protein G-Sepharose affinity chromatography, followed by IL-2R alpha and IL-2R beta affinity chromatography and hydrophobic interaction chromatography. BF-IgG exhibited both anti-IL-2R alpha and anti-IL-2R beta specificities in binding assays. While the Ab binds the IL-2R with intermediate affinity (Kd = 2.82 nM), it does not inhibit IL-15 binding to its high affinity IL-15R. In Kit225/K6 (IL-2R alpha beta gamma+) cells, BF-IgG was 10-fold more potent than a HAT/HuMik beta 1 equimolar mixture in blocking IL-2-induced proliferation and, unexpectedly, was at least 65-fold more active than the mixture in blocking IL-15-induced proliferation. This dual inhibitory activity may be due to cross-linking of the IL-2R alpha and IL-2R beta, thus blocking IL-2 binding and possibly impeding the association of IL-2R beta with IL-15R. BF-IgG has potent immunosuppressant activities against both IL-2- and IL-15-mediated responses, and this antagonist could be more efficacious than HAT and/or HuMik beta 1 for the treatment of autoimmunity and the prevention of allograft rejection.

Bispecific humanized anti-IL-2 receptor alpha beta antibodies inhibitory for both IL-2- and IL-15-mediated proliferation

Humanized anti-Tac (HAT) and Mik beta1 (HuMik beta 1) Abs directed at IL-2R alpha and IL-2R beta, respectively, inhibit IL-2 binding and biological activity and together act synergistically in vitro. The Abs have been used successfully in primate models of allograft rejection, graft-vs-host disease, and autoimmunity. We produced bifunctional humanized anti-IL-2R alpha beta Abs (BF-IgG) to combine the specificity of the two Abs into one entity by fusing HAT-producing NSO cells and HuMik beta 1-producing Sp2/0 cells. BF-IgG was purified using protein G-Sepharose affinity chromatography, followed by IL-2R alpha and IL-2R beta affinity chromatography and hydrophobic interaction chromatography. BF-IgG exhibited both anti-IL-2R alpha and anti-IL-2R beta specificities in binding assays. While the Ab binds the IL-2R with intermediate affinity (Kd = 2.82 nM), it does not inhibit IL-15 binding to its high affinity IL-15R. In Kit225/K6 (IL-2R alpha beta gamma+) cells, BF-IgG was 10-fold more potent than a HAT/HuMik beta 1 equimolar mixture in blocking IL-2-induced proliferation and, unexpectedly, was at least 65-fold more active than the mixture in blocking IL-15-induced proliferation. This dual inhibitory activity may be due to cross-linking of the IL-2R alpha and IL-2R beta, thus blocking IL-2 binding and possibly impeding the association of IL-2R beta with IL-15R. BF-IgG has potent immunosuppressant activities against both IL-2- and IL-15-mediated responses, and this antagonist could be more efficacious than HAT and/or HuMik beta 1 for the treatment of autoimmunity and the prevention of allograft rejection.

A phase I trial of humanized anti-interleukin 2 receptor antibody in renal transplantation

The efficacy of murine monoclonal anti-interleukin 2 alpha chain receptor (Tac) antibodies is limited by a short half-life and the development of antibodies to the heterologous protein. The safety, pharmacokinetics-dynamics, and immunosuppressive effect of a humanized anti-Tac antibody (HAT) was evaluated in 12 renal transplant recipients. Ten patients received living related transplants (three HLA-identical matches and seven one-haplotype or zero-haplotype matches) and two patients received cadaver organs. The patients were divided into four HAT treatment arms: 0.5 mg/kg/week (n=4), 1 mg/kg/week (n=2), 0.5 mg/kg every other week (n=3), and 1 mg/kg every other week (n=3). The first dose of HAT was given within 12 hr before transplantation, and four additional doses were given after transplantation. Patients were also placed on cyclosporine, steroids, and azathioprine. Only one patient, a recipient of a cadaver kidney in the lowest HAT treatment arm, had a reversible rejection episode. The 10 recipients of living related transplants were compared with 17 historical controls treated with an identical immunosuppressive regimen except for HAT. Whereas none of the HAT-treated living related donor recipients had a rejection episode, 6 of 17 (41%) of the historical controls had a rejection episode in the first year after transplantation. There were no first-dose reactions after HAT therapy or other subsequent side effects. None of the patients experienced opportunistic infections or malignancies. One patient developed low-titer anti-HAT antibodies, although the patient maintained high serum HAT concentrations throughout the study. Immune monitoring showed that there were no changes in the percentage or absolute counts of CD3 cells or T-cell subsets after HAT therapy. However, there was a significant decrease in the number of circulating lymphocytes that expressed free Tac. The overall harmonic mean half-life of HAT was 273 hr. The results of this study indicate that HAT given at 1 mg/kg every other week for a total of five doses may provide therapeutic HAT concentration levels and result in good saturation of Tac receptors for at least 12 weeks after transplantation. In summary, HAT is safe and is well tolerated by patients. Its long half-life and lack of immunization could make it a very useful immunosuppressive drug.

Humanized antibodies against the alpha-chain of the IL-2 receptor and against the beta-chain shared by the IL-2 and IL-15 receptors in a monkey uveitis model of autoimmune diseases

We studied the efficacy and tolerance of humanized Ab interfering with the signal of the IL-2 and IL-15 receptors in a primate model of experimental autoimmune uveoretinitis. The inhibitory effects of humanized anti-Tac (HAT), an anti-IL-2R alpha-chain Ab, and HuMik beta1, an Ab directed at the beta-chain shared by the receptors of IL-2 and IL-15, were tested in culture on the proliferative response of monkey Con A-blast lymphocytes stimulated with IL-2 or IL-15. Uveitis was induced in cynomolgus monkeys by immunization with human recombinant retinal S-antigen. Treatment was initiated at the first sign of disease and consisted of HAT and HuMik beta1, alone or in combination, or vehicle control given by i.v. injection twice a week for 4 wk. Disease was evaluated by ocular funduscopy. The results in culture showed a significant dose-dependent inhibition of the IL-2-driven proliferation of lymphocytes by HAT. HuMik beta1 alone was ineffective against IL-2 stimulation, but had a marked potentiating effect in combination with HAT, independent of IL-15 signaling. IL-15-driven proliferation was inhibited by HuMik beta1, but not by HAT alone or in combination. In monkeys, experimental autoimmune uveoretinitis evolution was significantly inhibited by HAT treatment. HuMik beta1 alone had no effect on the disease. However, when used in combination, the two Ab markedly reduced the severity of ocular inflammation. The Ab were well tolerated. Only three monkeys, treated with HAT alone, made an Ab response against the injected Ab.

Humanized antibodies against the alpha-chain of the IL-2 receptor and against the beta-chain shared by the IL-2 and IL-15 receptors in a monkey uveitis model of autoimmune diseases

We studied the efficacy and tolerance of humanized Ab interfering with the signal of the IL-2 and IL-15 receptors in a primate model of experimental autoimmune uveoretinitis. The inhibitory effects of humanized anti-Tac (HAT), an anti-IL-2R alpha-chain Ab, and HuMik beta1, an Ab directed at the beta-chain shared by the receptors of IL-2 and IL-15, were tested in culture on the proliferative response of monkey Con A-blast lymphocytes stimulated with IL-2 or IL-15. Uveitis was induced in cynomolgus monkeys by immunization with human recombinant retinal S-antigen. Treatment was initiated at the first sign of disease and consisted of HAT and HuMik beta1, alone or in combination, or vehicle control given by i.v. injection twice a week for 4 wk. Disease was evaluated by ocular funduscopy. The results in culture showed a significant dose-dependent inhibition of the IL-2-driven proliferation of lymphocytes by HAT. HuMik beta1 alone was ineffective against IL-2 stimulation, but had a marked potentiating effect in combination with HAT, independent of IL-15 signaling. IL-15-driven proliferation was inhibited by HuMik beta1, but not by HAT alone or in combination. In monkeys, experimental autoimmune uveoretinitis evolution was significantly inhibited by HAT treatment. HuMik beta1 alone had no effect on the disease. However, when used in combination, the two Ab markedly reduced the severity of ocular inflammation. The Ab were well tolerated. Only three monkeys, treated with HAT alone, made an Ab response against the injected Ab.

Distinction between gamma c detection and function in YT lymphoid cells and in the granulocyte-macrophage colony-stimulating factor-responsive human myeloid cell line, Tf-1

Peripheral blood monocytes respond to interleukin-2 (lL-2) and express the gamma common (gamma c) subunit of the lL-2 receptor (lL-2R) complex. However, the role of lL-2 in myeloid development has recently become of interest for several reasons, including the effect gamma c mutations may or may not have on myeloid development in patients with XSCID. Many studies of lL-2 function in the myeloid cell lineage have been performed on a murine background. To study gamma c expression and function in human myeloid precursors, we introduced the human myelomonocytic cell line, Tf-1, with a retroviral vector containing the human lL-2R beta subunit to create functional human intermediate lL-2R consisting of beta gamma c dimers. We have characterized this transfected variant of Tf-1 (Tf-1 beta) with regard to its response to lL-2. Unlike the parental Tf-1 cell line that is deficient in both lL-2R alpha and lL-2R beta expression, the Tf-1 beta transfectant binds and responds to lL-2 through intermediate-affinity lL-2Rs. Scatchard analyses indicate the number of intermediate-affinity receptors on Tf-1 beta is similar to the number found on the well-characterized YT cell line. However, detection of gamma c on Tf-1 beta cells is dramatically less than on YT cells by Western blot analysis and is undetectable by flow cytometric studies and surface iodinations. The gamma c component on YT cells is readily detected by all three methods. We conclude from these studies that the intermediate-affinity lL-2Rs on the Tf-1 cell line behave differently than those on YT cells with respect to gamma c detection. Either the gamma c molecule itself is different, or the cellular environment in which it functions is altered. Elucidation of gamma c function on this cell line will allow for its use as a model in which other cytokines using gamma c (including lL-2, lL-4, and lL-15) can be studied on the same cellular background.

Preparation of a bispecific F(ab')2 targeted to the human IL-2 receptor

The heterodimer-forming leucine zippers Fos and Jun can efficiently mediate the formation of bispecific F(ab')2 when they are fused separately to two different Fab' fragments. This recombinant method can be used in conjunction with the humanization process to yield humanized bispecific F(ab')2. The potential immunogenicity of the leucine zippers can be eliminated by their removal using pepsin digestion. This method has been scaled up to produce hundreds of milligrams of a bispecific F(ab')2 that targets two subunits of the human IL-2 receptor.

IL-12 regulation of parasite antigen-driven IgE production in human helminth infections

Recombinant IL-12 inhibits IgE synthesis by IL-4-stimulated lymphocytes from healthy persons and influences the development of Th subset selection involved in Ig isotype selection. Whether endogenous IL-12 production modulates IgE synthesis in patients with elevated serum IgE is unknown. To examine this question we studied the effects of neutralizing anti-IL-12 or recombinant IL-12 on parasite Ag-driven polyclonal IgE production and corresponding IFN-gamma and IL-4 synthesis by PBMC from helminth-infected individuals. The addition of neutralizing anti-IL-12 Ab significantly inhibited parasite Ag-driven IgE production in 11 of 12 individuals (p &lt; 0.001). Recombinant IL-12 (1-10 U/ml) suppressed Ag-driven IgE production in a dose-dependent fashion up to 94% relative to untreated cultures. The effect of endogenous IL-12 on IgE production occurred, in part, by suppressing Ag-induced IL-4 and augmenting IFN-gamma production. IL-12 did not suppress IgE synthesis by purified B cells. An IFN-gamma-independent effect of IL-12 on Ag-driven IgE production was suggested by the ability of human rIL-12 to suppress IgE synthesis in the presence of neutralizing anti-IFN-gamma. This study demonstrates that IL-12 modulates helminth Ag-driven IgE production, in part, by regulating the relative quantities of IFN-gamma and IL-4 generated by Ag-specific lymphocytes.

IL-12 regulation of parasite antigen-driven IgE production in human helminth infections

Recombinant IL-12 inhibits IgE synthesis by IL-4-stimulated lymphocytes from healthy persons and influences the development of Th subset selection involved in Ig isotype selection. Whether endogenous IL-12 production modulates IgE synthesis in patients with elevated serum IgE is unknown. To examine this question we studied the effects of neutralizing anti-IL-12 or recombinant IL-12 on parasite Ag-driven polyclonal IgE production and corresponding IFN-gamma and IL-4 synthesis by PBMC from helminth-infected individuals. The addition of neutralizing anti-IL-12 Ab significantly inhibited parasite Ag-driven IgE production in 11 of 12 individuals (p < 0.001). Recombinant IL-12 (1-10 U/ml) suppressed Ag-driven IgE production in a dose-dependent fashion up to 94% relative to untreated cultures. The effect of endogenous IL-12 on IgE production occurred, in part, by suppressing Ag-induced IL-4 and augmenting IFN-gamma production. IL-12 did not suppress IgE synthesis by purified B cells. An IFN-gamma-independent effect of IL-12 on Ag-driven IgE production was suggested by the ability of human rIL-12 to suppress IgE synthesis in the presence of neutralizing anti-IFN-gamma. This study demonstrates that IL-12 modulates helminth Ag-driven IgE production, in part, by regulating the relative quantities of IFN-gamma and IL-4 generated by Ag-specific lymphocytes.

Activated T cells induce interleukin-12 production by monocytes via CD40-CD40 ligand interaction

Previous studies on the production of interleukin-12 (IL-12) have shown that it is released, together with other proinflammatory cytokines, shortly after exposure of phagocytic cells to a variety of pathogens. We here report that IL-12 is also released during the recall response to soluble antigen (Ag) devoid of intrinsic adjuvant activity. We show that activated T cells induce the production of IL-12 by monocytes via a mechanism involving the interaction of T cell-associated CD40 ligand with CD40 on monocytes. The data suggest that Ag presentation on monocytes favors the persistence of type 1 responses.

Human IL-12 p40 homodimer binds to the IL-12 receptor but does not mediate biologic activity

IL-12, a heterodimeric cytokine, consists of two disulfide-linked subunits, p40 and p35. We investigated the role of p40 in ligand binding and signal transduction by expressing this subunit alone in COS cells. Culture media of the transfected COS cells exhibited specific dose-dependent binding to KIT225/K6 cells, a human T cell line that expresses IL-12R. Analysis of the culture media by SDS-PAGE and Western blotting demonstrated the presence of 40-kDa monomers and 80-kDa disulfide-linked homodimers. The two p40 species were purified and identified by N-terminal sequencing and proteolytic peptide mapping. Characterization of the p40 proteins for binding and bioactivity showed that both the p40 monomer and dimer inhibited 125I-labeled IL-12 binding to IL-12R, but the 80-kDa species, having a 50% inhibitory concentration (IC50) of 20 to 70 ng/ml, was at least 20-fold more effective than the monomer. Although neither the monomer nor the dimer stimulated human PHA-blast proliferation, the 80-kDa dimer inhibited IL-12-induced proliferation in a dose-dependent manner with an IC50 of 65 ng/ml. The results suggest that the IL-12 p40 subunit contains the essential epitopes for receptor binding. However, a proper conformation required for high affinity binding is achieved only when p40 is associated with a p35 subunit or another p40 subunit. When p40 is associated with a p35 subunit, the heterodimer acts as an agonist mediating biologic activity. However, when p40 associates with another p40, the homodimer behaves as an antagonist in vitro.

Human IL-12 p40 homodimer binds to the IL-12 receptor but does not mediate biologic activity

IL-12, a heterodimeric cytokine, consists of two disulfide-linked subunits, p40 and p35. We investigated the role of p40 in ligand binding and signal transduction by expressing this subunit alone in COS cells. Culture media of the transfected COS cells exhibited specific dose-dependent binding to KIT225/K6 cells, a human T cell line that expresses IL-12R. Analysis of the culture media by SDS-PAGE and Western blotting demonstrated the presence of 40-kDa monomers and 80-kDa disulfide-linked homodimers. The two p40 species were purified and identified by N-terminal sequencing and proteolytic peptide mapping. Characterization of the p40 proteins for binding and bioactivity showed that both the p40 monomer and dimer inhibited 125I-labeled IL-12 binding to IL-12R, but the 80-kDa species, having a 50% inhibitory concentration (IC50) of 20 to 70 ng/ml, was at least 20-fold more effective than the monomer. Although neither the monomer nor the dimer stimulated human PHA-blast proliferation, the 80-kDa dimer inhibited IL-12-induced proliferation in a dose-dependent manner with an IC50 of 65 ng/ml. The results suggest that the IL-12 p40 subunit contains the essential epitopes for receptor binding. However, a proper conformation required for high affinity binding is achieved only when p40 is associated with a p35 subunit or another p40 subunit. When p40 is associated with a p35 subunit, the heterodimer acts as an agonist mediating biologic activity. However, when p40 associates with another p40, the homodimer behaves as an antagonist in vitro.

Humanized antibody directed to the IL-2 receptor beta-chain prolongs primate cardiac allograft survival

IL-2Rs are expressed by T cells activated in response to foreign histocompatibility Ags but not by normal cells. This difference in IL-2R expression is exploited by blockade of IL-2Rs to achieve immunosuppression. High affinity IL-2Rs involve three subunits, IL-2R alpha, IL-2R beta, and IL-2R gamma. Murine Mik beta 1, a mAb that blocks IL-2 binding to IL-2R beta, was developed as an immunosuppressive agent. There was modest prolongation of cynomolgus cardiac allograft survival in animals treated with murine Mik beta 1 (mean survival 11.8 +/- 1.6 days compared with 8.2 +/- 0.4 days in untreated animals; p = 0.06). However, murine Mik beta 1 is ineffective in recruiting primate effector cells and is neutralized by monkey Abs directed toward the infused Ab. To circumvent these limitations, a humanized form of Mik beta 1, which is a largely human IgG1k Ab, except that murine hypervariable regions are retained, was developed. In vivo plasma survival of humanized Mik beta 1 was threefold longer than simultaneously administered murine Mik beta 1 (terminal t1/2, 104 +/- 10 h vs 37 +/- 2 h). Furthermore, humanized Mik beta 1 manifests Ab-dependent cellular cytotoxicity, an activity that is absent with the parental murine Mik beta 1. Graft survival was significantly prolonged by humanized Mik beta 1 treatment with survivals of 22, 22, 24, 27, 44, and > 300 days (p vs control < 0.01; p vs murine Mik beta 1 < 0.01). Survival was not prolonged further (p > 0.3) by the addition of humanized anti-Tac, which blocks interaction of IL-2 with IL-2R alpha subunits. There was no toxicity attributable to the use of Mik beta 1 Abs. Thus, humanized Mik beta 1 prolonged cardiac allograft survival in primates without toxicity and may be effective as an adjunct to standard immunosuppressive therapy.

Humanized antibody directed to the IL-2 receptor beta-chain prolongs primate cardiac allograft survival

IL-2Rs are expressed by T cells activated in response to foreign histocompatibility Ags but not by normal cells. This difference in IL-2R expression is exploited by blockade of IL-2Rs to achieve immunosuppression. High affinity IL-2Rs involve three subunits, IL-2R alpha, IL-2R beta, and IL-2R gamma. Murine Mik beta 1, a mAb that blocks IL-2 binding to IL-2R beta, was developed as an immunosuppressive agent. There was modest prolongation of cynomolgus cardiac allograft survival in animals treated with murine Mik beta 1 (mean survival 11.8 +/- 1.6 days compared with 8.2 +/- 0.4 days in untreated animals; p = 0.06). However, murine Mik beta 1 is ineffective in recruiting primate effector cells and is neutralized by monkey Abs directed toward the infused Ab. To circumvent these limitations, a humanized form of Mik beta 1, which is a largely human IgG1k Ab, except that murine hypervariable regions are retained, was developed. In vivo plasma survival of humanized Mik beta 1 was threefold longer than simultaneously administered murine Mik beta 1 (terminal t1/2, 104 +/- 10 h vs 37 +/- 2 h). Furthermore, humanized Mik beta 1 manifests Ab-dependent cellular cytotoxicity, an activity that is absent with the parental murine Mik beta 1. Graft survival was significantly prolonged by humanized Mik beta 1 treatment with survivals of 22, 22, 24, 27, 44, and &gt; 300 days (p vs control &lt; 0.01; p vs murine Mik beta 1 &lt; 0.01). Survival was not prolonged further (p &gt; 0.3) by the addition of humanized anti-Tac, which blocks interaction of IL-2 with IL-2R alpha subunits. There was no toxicity attributable to the use of Mik beta 1 Abs. Thus, humanized Mik beta 1 prolonged cardiac allograft survival in primates without toxicity and may be effective as an adjunct to standard immunosuppressive therapy.

Evidence for an interleukin 4-inducible immunoglobulin E uptake and transport mechanism in the intestine

Immunoglobulin (Ig) E is the principal Ig involved in immediate hypersensitivities and chronic allergic diseases such as asthma. Helminths are the most potent infectious agents known for their capacity to stimulate IgE production during the course of infection. In rats, the nematode Trichinella spiralis typically elicits a strong parasite-specific IgE response during infection, and this IgE antibody has been shown to be protective against the parasite in passive transfer experiments. The study reported here analyzed the fate of 125I-labeled myeloma IgE (1R162) in normal and T. spiralis-infected rats after intravenous injection. T. spiralis infection induced a capacity for specific binding to the gut wall of 125I-IgE rather than 125I-IgG1, as well as the transport of IgE, but not IgG1, into the gut lumen. Peak intestinal uptake and transport of 125I-IgE occurred during the first and second weeks after injection but was not elevated in the fourth week, that is, after intestinal adult worms had been expelled. Neither 125I-IgE uptake in the gut wall nor transport to the lumen could be ascribed to tissue damage or vascular leakage. Luminal transport occurred in the small intestine and not the liver, which only transports low molecular weight degraded 125I-IgE. Calculations based on the amount of intact IgE in the lumen suggest that, in a 24-h period, up to 20% of injected 125I-IgE can be transported to the gut lumen during the peak transport period, between 6 and 14 d after infection. The intestinal IgE binding and transport response can be adoptively transferred with T. spiralis immune CD4+ OX22- (CD45RC-) lymphocytes, which are protective, but not the nonprotective sister population CD4+ OX22+ (CD45RC+) of lymphocytes isolated simultaneously from thoracic duct lymph of infected rats. The intravenous infusion of recombinant rat interleukin 4 also elicited significant intestinal uptake of 125I-IgE. We also present evidence for the presence of CD23 on rat intraepithelial lymphocytes. These data provide evidence for a novel, inducible, intestine-specific IgE uptake and transport mechanism.

Interleukin 12 is produced in vivo during endotoxemia and stimulates synthesis of gamma interferon

Gamma interferon (IFN-gamma) is produced in response to circulating lipopolysaccharide (LPS) and contributes to the lethality of endotoxic shock. To address the cellular source of IFN-gamma production in vivo, T cells and B cells were magnetically purified from C57BL/6 mouse spleens 5 h following endotoxin injection. IFN-gamma RNA was abundant in splenic CD4+ and CD8+ T cells and in a T- and B-cell-depleted population of splenocytes containing 34% NK1.1+ natural killer (NK) cells. Because interleukin 12 (IL-12) is a known inducer of IFN-gamma synthesis by cultured T cells and NK cells, we examined whether IL-12 might be involved in IFN-gamma release during endotoxemia. mRNA encoding the p40 subunit of IL-12 increased markedly in the spleens of C57BL/6 mice at 2 h after LPS injection, whereas p35 IL-12 mRNA was constitutively expressed at all times. Bioactive IL-12 (p70 heterodimer) was detected in mouse serum at 2 to 4 h after LPS injection. Similar results were obtained using a p40 subunit-specific enzyme-linked immunosorbent assay. Endotoxin-insensitive C3H/HeJ mice generated threefold less IL-12 p70 and IFN-gamma at these times than endotoxin-sensitive C3H/HeOuJ mice. Pretreatment of mice with polyclonal anti-mouse IL-12 antibody reduced IFN-gamma levels present at 6 h post-LPS nearly sixfold in three separate experiments. These studies support a role for IL-12 as a proximal stimulator of IFN-gamma release during endotoxemia.

Interleukin 12, interferon gamma, and tumor necrosis factor alpha are the key cytokines of the generalized Shwartzman reaction

The Shwartzman reaction is elicited by two injections of lipopolysaccharide (LPS) in mice. The priming LPS injection is given in the footpad, whereas the lethal LPS challenge is given intravenously 24 h later. The injection of interferon gamma (IFN-gamma) or interleukin 12 (IL-12) instead of the LPS priming injection induced the lethal reaction in mice further challenged with LPS. Antibodies against IFN-gamma when given together with the priming agent, prevented the lethal reaction in mice primed with either LPS, IL-12, or IFN-gamma. Antibodies against IL-12, when given together with the priming agent, prevented the lethal reaction in mice primed with either LPS or IL-12 but not with IFN-gamma. These results strongly suggest that LPS induces the release of IL-12, that IL-12 induces the production of IFN-gamma, and that IFN-gamma is the cytokine that primes macrophages and other cell types. Upon LPS challenge, the lethal Shwartzman reaction is induced by a massive production of inflammatory cytokines that act on the target sites already sensitized by IFN-gamma. If mixtures of TNF and IL-1 or mixtures of TNF and IFN-gamma are used to challenge mice previously primed with IFN-gamma or IL-12, mortality is induced. In the same conditions, the individual cytokines or a mixture of IL-1 and IFN-gamma do not replace the LPS challenge. When the mice are primed with LPS, the combination of TNF, IL-1, and IFN-gamma induced only a partial mortality incidence suggesting that the involvement of other LPS-induced factors.

IL-12 influences intrathymic T cell development

IL-12 has been implicated in the maturation and activation of peripheral T lymphocytes and NK cells. In the present study we have investigated the potential role of IL-12 in intrathymic T cell development. Treatment of mouse fetal thymic organ culture with IL-12 caused a significant reduction in size and cell number compared with the untreated controls. Flow cytometric analysis of the thymocytes recovered from these lobes showed differential effects on individual thymocyte subsets, most but not all of which were significantly decreased. In contrast, however, we observed an increase in both the percentage and cell number of alpha beta TCR+CD4-CD8+ thymocytes. This effect could be neutralized with an anti-IL-12 antibody, demonstrating the specificity of the influence of IL-12 in the fetal thymic organ culture system. IL-12 caused proliferation of isolated thymocyte subsets, particularly CD3+CD4-CD8+ cells in the presence of IL-2 and IL-4. Additionally, IL-12 induced significant proliferation of early CD3-CD4-CD8- triple negative CD44+CD25+ pro-T cells in combination with stem cell factor. We show that both the p35 and p40 chains of IL-12 are produced in the fetal and adult mouse thymus and that thymic stromal cells are a potential source of this cytokine.

IL-12 influences intrathymic T cell development

IL-12 has been implicated in the maturation and activation of peripheral T lymphocytes and NK cells. In the present study we have investigated the potential role of IL-12 in intrathymic T cell development. Treatment of mouse fetal thymic organ culture with IL-12 caused a significant reduction in size and cell number compared with the untreated controls. Flow cytometric analysis of the thymocytes recovered from these lobes showed differential effects on individual thymocyte subsets, most but not all of which were significantly decreased. In contrast, however, we observed an increase in both the percentage and cell number of alpha beta TCR+CD4-CD8+ thymocytes. This effect could be neutralized with an anti-IL-12 antibody, demonstrating the specificity of the influence of IL-12 in the fetal thymic organ culture system. IL-12 caused proliferation of isolated thymocyte subsets, particularly CD3+CD4-CD8+ cells in the presence of IL-2 and IL-4. Additionally, IL-12 induced significant proliferation of early CD3-CD4-CD8- triple negative CD44+CD25+ pro-T cells in combination with stem cell factor. We show that both the p35 and p40 chains of IL-12 are produced in the fetal and adult mouse thymus and that thymic stromal cells are a potential source of this cytokine.

Neutralization of IL-12 decreases resistance to Listeria in SCID and C.B-17 mice. Reversal by IFN-gamma

Interleukin-12 (IL-12) is necessary for the production of IFN-gamma by NK cells during the generation of innate immunity and by T cells for the development of the Th1 response during specific cell-mediated immunity. Here we demonstrate that the endogenous production of IL-12 is critical to the survival of both immunocompromised SCID mice and normal C.B-17 control mice during a primary infection with Listeria monocytogenes. When IL-12 is neutralized in vivo, both strains of mice die at a normally sublethal dose of Listeria. Anti-IL-12 antibody-treated mice showed a decrease in macrophage I-Ad expression and an increase Listeria burden in the spleen. Furthermore, as has been demonstrated in vitro, these effects of IL-12 in vivo were predominantly regulated through the production of IFN-gamma. Administration of IFN-gamma simultaneously with neutralizing antibodies to IL-12 restored macrophage I-Ad expression, limited the spread of the infection, and resulted in the survival of SCID mice. Thus, IL-12 is critical for resistance to infection with Listeria monocytogenes, and this resistance is mediated through stimulation by IL-12 of IFN-gamma production. Concomitant experiments confirmed that anti-TNF antibodies also resulted in uncontrolled infection and a decrease in macrophage I-Ad expression. However, administration of IFN-gamma restored the levels of I-Ad in macrophages but did not limit Listeria growth.

Neutralization of IL-12 decreases resistance to Listeria in SCID and C.B-17 mice. Reversal by IFN-gamma

Interleukin-12 (IL-12) is necessary for the production of IFN-gamma by NK cells during the generation of innate immunity and by T cells for the development of the Th1 response during specific cell-mediated immunity. Here we demonstrate that the endogenous production of IL-12 is critical to the survival of both immunocompromised SCID mice and normal C.B-17 control mice during a primary infection with Listeria monocytogenes. When IL-12 is neutralized in vivo, both strains of mice die at a normally sublethal dose of Listeria. Anti-IL-12 antibody-treated mice showed a decrease in macrophage I-Ad expression and an increase Listeria burden in the spleen. Furthermore, as has been demonstrated in vitro, these effects of IL-12 in vivo were predominantly regulated through the production of IFN-gamma. Administration of IFN-gamma simultaneously with neutralizing antibodies to IL-12 restored macrophage I-Ad expression, limited the spread of the infection, and resulted in the survival of SCID mice. Thus, IL-12 is critical for resistance to infection with Listeria monocytogenes, and this resistance is mediated through stimulation by IL-12 of IFN-gamma production. Concomitant experiments confirmed that anti-TNF antibodies also resulted in uncontrolled infection and a decrease in macrophage I-Ad expression. However, administration of IFN-gamma restored the levels of I-Ad in macrophages but did not limit Listeria growth.

Identification of sites on the human Fc epsilon RI alpha subunit which are involved in binding human and rat IgE

The high affinity IgE Fc receptor (Fc epsilon RI), found on mast cells and basophils, is a tetrameric receptor complex. The extracellular portion of the Fc epsilon RI alpha subunit consists of two immunoglobulin-like domains and binds IgE in the absence of the other subunits. To localize the high affinity IgE binding site within the Fc epsilon RI alpha subunit, we generated a series of chimeric receptor constructs where one of the two immunoglobulin-like domains was either deleted or substituted with those from the human Fc gamma RIIIA alpha or the rat Fc epsilon RI alpha subunit. The chimeric receptors were monitored for their capacity to bind human and rat IgE, and their reactivity with different antireceptor antibodies. Domain I substitutions maintained high affinity human IgE binding. Domain II substitutions resulted in a total loss of both human and rat IgE binding. Single-domain alpha subunits could not bind IgE, suggesting that both extracellular domains are required for proper protein folding or IgE binding. To further localize the IgE binding sites, homolog-scanning mutagenesis was performed. At least three independent regions of domain II encompassing residues 118-129, 136-150, and 148-162 were required for IgE binding. Our results suggest that domain II of the human Fc epsilon RI alpha confers most of the important contributions to the binding of the human IgE Fc molecule, whereas domain I of the rat Fc epsilon RI alpha makes important contributions to the binding of rat IgE.

Demonstration of the high-affinity IgE receptor on human Langerhans cells in normal and diseased skin

Epidermal dendritic cells of normal adult foreskin, and of lesional skin from patients with atopic eczema, stasis eczema and urticaria pigmentosa are shown to be highly reactive with two different monoclonal antibodies (29C6 and 6F7) specific for extracellular domains of the alpha-chain of the high-affinity IgE receptor. By their distribution pattern, the reactive cells are Langerhans cells. This is confirmed by immunoelectron microscopic demonstration of Birbeck granules in the labelled epidermal cells. Very weak staining is observed on the same cells with an antibody (Tü1) against the low-affinity IgE receptor. Pre-incubation of the sections with IgE partially blocks binding of 6F7 antibody. Langerhans cells, together with dermal mast cells, can therefore bind IgE with high efficiency, and may in this way participate in IgE-mediated cutaneous diseases.

Humanized Mik beta 1, a humanized antibody to the IL-2 receptor beta-chain that acts synergistically with humanized anti-TAC

Mik beta 1 is a mouse mAb directed at the beta-subunit of the human IL-2R (Tac) that inhibits IL-2 binding and inhibits IL-2 induction of large granular lymphocytes (LGL). Mik beta 1 alone does not inhibit IL-2-induced T-cell proliferation, but acts synergistically with anti-Tac to inhibit IL-2-induced proliferation of activated T cells. To evaluate these effects for possible therapy in humans, we constructed two humanized Mik beta 1 antibodies by combining the complementarity-determining regions of the murine antibody with human framework and constant regions. Compared with murine Mik beta 1, the two humanized Mik beta 1 antibodies, which differ in their degree of humanization, had similar affinities for IL-2R beta. The murine Mik beta 1 and one of the humanized Mik beta 1 antibodies were equivalent in competing for IL-2 binding to IL-2R beta and inhibiting IL-2 induction of LGL cytotoxicity. The activity of the second humanized antibody was significantly reduced. The three Mik beta 1 antibodies act synergistically to varying degrees with humanized anti-Tac to prevent IL-2-induced proliferation of activated T cells. This capacity to synergize paralleled their abilities to inhibit IL-2 binding. In addition, both humanized antibodies directed antibody-dependent cell-mediated cytotoxicity. We hope that humanized Mik beta 1 in combination with humanized anti-Tac will provide a new immunosuppressive therapy for the treatment of autoimmune diseases, graft-versus-host disease, and prevention of allograft rejection.

Humanized Mik beta 1, a humanized antibody to the IL-2 receptor beta-chain that acts synergistically with humanized anti-TAC

Mik beta 1 is a mouse mAb directed at the beta-subunit of the human IL-2R (Tac) that inhibits IL-2 binding and inhibits IL-2 induction of large granular lymphocytes (LGL). Mik beta 1 alone does not inhibit IL-2-induced T-cell proliferation, but acts synergistically with anti-Tac to inhibit IL-2-induced proliferation of activated T cells. To evaluate these effects for possible therapy in humans, we constructed two humanized Mik beta 1 antibodies by combining the complementarity-determining regions of the murine antibody with human framework and constant regions. Compared with murine Mik beta 1, the two humanized Mik beta 1 antibodies, which differ in their degree of humanization, had similar affinities for IL-2R beta. The murine Mik beta 1 and one of the humanized Mik beta 1 antibodies were equivalent in competing for IL-2 binding to IL-2R beta and inhibiting IL-2 induction of LGL cytotoxicity. The activity of the second humanized antibody was significantly reduced. The three Mik beta 1 antibodies act synergistically to varying degrees with humanized anti-Tac to prevent IL-2-induced proliferation of activated T cells. This capacity to synergize paralleled their abilities to inhibit IL-2 binding. In addition, both humanized antibodies directed antibody-dependent cell-mediated cytotoxicity. We hope that humanized Mik beta 1 in combination with humanized anti-Tac will provide a new immunosuppressive therapy for the treatment of autoimmune diseases, graft-versus-host disease, and prevention of allograft rejection.

Purification and characterization of human recombinant IgE-Fc fragments that bind to the human high affinity IgE receptor

The Fc-region of immunoglobulin E (IgE) comprising C epsilon 2, C epsilon 3, and C epsilon 4 domains is sufficient for binding to the alpha chain of the high affinity IgE-Fc receptor (Fc epsilon RI alpha). In order to identify the smallest Fc fragment capable of binding to the Fc epsilon RI alpha with high affinity, various regions of the IgE-Fc molecule were expressed in COS cells and investigated for their ability to bind Fc epsilon RI alpha. The smallest fragment that showed Fc epsilon RI alpha binding activity spans amino acids 329-547 and lacks the entire C epsilon 2 domain. Two active fragments, viz. Fc epsilon(315-547) (containing Cys328 which is responsible for interchain S-S bonding) and Fc epsilon(329-547), have been overexpressed in CHO cells and purified to homogeneity. The purified proteins bind to the Fc epsilon RI alpha with high affinity, similar to native IgE. SDS-polyacrylamide gel electrophoresis analyses indicate that Fc epsilon(315-547) is an S-S-linked dimer of apparent molecular mass of 68 kDa. Fc epsilon(329-547) appears on SDS-gel as three distinct bands at approximately 32 kDa, both under reducing and nonreducing conditions. However, size exclusion chromatography and analytical ultracentrifugation studies suggest that Fc epsilon(329-547) also remains associated as a dimer. The presence of N-linked glycosylation was detected in both proteins. The deglycosylated form of Fc epsilon(315-547) was isolated after Endo F/N-glycosidase F digestion and demonstrated to have binding activity comparable to that of the mock-digested protein. These results suggest that the presence of N-linked sugars is not necessary for Fc epsilon RI alpha binding. Both proteins blocked the release of histamine from RBL cells expressing human Fc epsilon RI alpha in a dose-dependent manner. The availability of these recombinant IgE-Fc proteins will be helpful in elucidating the key epitopes essential for the binding of IgE to its high affinity receptor.

Autoantibodies against the high-affinity IgE receptor as a cause of histamine release in chronic urticaria

BACKGROUND

Most urticarias are induced by vasoactive mediators such as histamine released from mast cells. Although mast cells are activated by allergens through cross-linking of cell-surface--bound IgE, this mechanism does not appear to explain most cases of chronic urticaria, which, when allergic, infectious, drug-induced, or physical causes cannot be identified, are classified as idiopathic.

METHODS

We recruited 26 patients with chronic idiopathic urticaria, in whom intradermal injection of autologous serum caused a wheal-and-flare response. Serum from four patients that induced marked histamine release from basophils from a donor with very low serum IgE levels was studied with respect to the IgE dependence of the histamine release, the activity of the IgG fractions, and the neutralizing effect of a recombinant preparation of the soluble extracellular domain of the alpha subunit of the high-affinity IgE receptor (sFc epsilon RI alpha).

RESULTS

The histamine-releasing activity of the serum was abolished by passive sensitization of basophils with myeloma IgE, enhanced after dissociation of IgE by treatment with lactic acid, and induced by IgG fractions from the serum of all four patients. Preincubation of the serum and isolated IgG with sFc epsilon RI alpha resulted in almost complete neutralization.

CONCLUSIONS

Histamine-releasing IgG autoantibodies against the alpha subunit of the high-affinity IgE receptor are present in the circulation of some patients with chronic urticaria. Autoantibody-induced cross-linking of IgE receptors may be an important mechanism in the pathogenesis of chronic urticaria and other diseases mediated by mast cells.

The anti-idiotypic response by cynomolgus monkeys to humanized anti-Tac is primarily directed to complementarity-determining regions H1, H2, and L3

The anti-ld response developed by cynomolgus monkeys to the humanized anti-Tac antibody was analyzed by using 12 humanized anti-Tac variants differing in V region structure. The majority of the monkey response was directed against idiotopes composed wholly or in part of complementarity-determining regions H1, H2, and L3. There was no detectable response directed solely to five single complementarity-determining regions examined or solely to the modified human V region framework.

The anti-idiotypic response by cynomolgus monkeys to humanized anti-Tac is primarily directed to complementarity-determining regions H1, H2, and L3

The anti-ld response developed by cynomolgus monkeys to the humanized anti-Tac antibody was analyzed by using 12 humanized anti-Tac variants differing in V region structure. The majority of the monkey response was directed against idiotopes composed wholly or in part of complementarity-determining regions H1, H2, and L3. There was no detectable response directed solely to five single complementarity-determining regions examined or solely to the modified human V region framework.

Conservation of signal transduction mechanisms via the human Fc epsilon RI alpha after transfection into a rat mast cell line, RBL 2H3

The high affinity receptor for IgE (Fc epsilon RI) is present on mast cells and basophils, and the aggregation of IgE-occupied receptors by Ag is responsible for the release of allergic mediators. The Fc epsilon RI is composed of at least three different subunits, alpha, beta, and gamma, with the alpha subunit binding IgE. The series of biochemical events linking receptor aggregation to the release of mediators has not been fully delineated. As a step towards understanding these processes, and for the development of functional cell lines, we have transfected the human Fc epsilon RI alpha subunit into the rat mast cell line RBL 2H3. These human Fc epsilon RI alpha-transfected cell lines have been characterized with respect to the association of the human alpha subunit with endogenous rat beta and gamma subunits and the ability of aggregated Fc epsilon RI alpha subunits to mediate a variety of biochemical events. The signal transduction events monitored include phosphoinositide hydrolysis, Ca2+ mobilization, tyrosine phosphorylation, histamine release, and arachidonic acid metabolism. In all cases, the events mediated by aggregating human Fc epsilon RI alpha subunits were indistinguishable from those produced via the rat Fc epsilon RI alpha. These results demonstrate that the human Fc epsilon RI alpha subunit can functionally substitute for the rat Fc epsilon RI alpha subunit during signal transduction. The availability of this cell line will provide a means of evaluating potential Fc epsilon RI antagonists.

Conservation of signal transduction mechanisms via the human Fc epsilon RI alpha after transfection into a rat mast cell line, RBL 2H3

The high affinity receptor for IgE (Fc epsilon RI) is present on mast cells and basophils, and the aggregation of IgE-occupied receptors by Ag is responsible for the release of allergic mediators. The Fc epsilon RI is composed of at least three different subunits, alpha, beta, and gamma, with the alpha subunit binding IgE. The series of biochemical events linking receptor aggregation to the release of mediators has not been fully delineated. As a step towards understanding these processes, and for the development of functional cell lines, we have transfected the human Fc epsilon RI alpha subunit into the rat mast cell line RBL 2H3. These human Fc epsilon RI alpha-transfected cell lines have been characterized with respect to the association of the human alpha subunit with endogenous rat beta and gamma subunits and the ability of aggregated Fc epsilon RI alpha subunits to mediate a variety of biochemical events. The signal transduction events monitored include phosphoinositide hydrolysis, Ca2+ mobilization, tyrosine phosphorylation, histamine release, and arachidonic acid metabolism. In all cases, the events mediated by aggregating human Fc epsilon RI alpha subunits were indistinguishable from those produced via the rat Fc epsilon RI alpha. These results demonstrate that the human Fc epsilon RI alpha subunit can functionally substitute for the rat Fc epsilon RI alpha subunit during signal transduction. The availability of this cell line will provide a means of evaluating potential Fc epsilon RI antagonists.

Human epidermal Langerhans cells express the high affinity receptor for immunoglobulin E (Fc epsilon RI)

It has been suggested that epidermal Langerhans cells (LC) bearing immunoglobulin E (IgE) may be involved in the genesis of atopic disease. The identity of the IgE receptor(s) on LC remained unclear, although it represents a crucial point in understanding cellular events linked to the binding of allergens to LC via IgE. In this report, we demonstrate that epidermal LC express the high affinity receptor for the Fc fragment of IgE (Fc epsilon RI) which has, so far, only been described on mast cells and basophils. Epidermal LC react with antibodies specific for the alpha subunit of the tetrameric (alpha, beta, 2 gamma) Fc epsilon RI. Specific transcripts for Fc epsilon RI alpha and Fc epsilon RI gamma were detected in LC and correspond to those of human basophils and of the human basophil cell line KU812. Furthermore, human basophils, KU812 cells, and LC express the putative beta subunit. Thus human LC express the complete structure of Fc epsilon RI. This finding opens new perspectives in the putative functional role of this structure on antigen-presenting cells.

Reduced immunogenicity and improved pharmacokinetics of humanized anti-Tac in cynomolgus monkeys

The anti-Tac mAb has been shown to bind to the p55 chain of the IL-2R, block IL-2 binding and inhibit T cell proliferation. A humanized form of anti-Tac (HAT) has been constructed that retains the binding properties of murine anti-Tac (MAT). These two mAb were evaluated in cynomolgus monkeys to compare relative immunogenicity and pharmacokinetic properties. Monkeys treated with HAT daily for 14 days exhibited anti-HAT antibody titers which were 5- to 10-fold lower than their MAT-treated counterparts and these antibodies developed later than in the MAT-treated monkeys. Two of four monkeys receiving a single injection of MAT developed anti-MAT antibodies, whereas none of four monkeys developed antibodies after a single treatment with HAT. In monkeys injected with either HAT or MAT daily for 14 days, the anti-antibody titers induced were inversely related to the amount of anti-Tac administered. Antibodies that developed against MAT were both anti-isotypic and anti-idiotypic, whereas those developed against HAT appeared to be predominantly anti-idiotypic. The pharmacokinetic properties, that is the half-life and area under the curve values, of HAT were also significantly different from those of MAT. The area under the curve values for HAT in naive monkeys were approximately twofold more than those for MAT, and the mean serum half-life of HAT was 214 h, approximately four- to fivefold more than MAT. These pharmacokinetic values were reduced in monkeys previously sensitized with HAT or MAT suggesting that the presence of anti-antibodies altered these parameters.

Reduced immunogenicity and improved pharmacokinetics of humanized anti-Tac in cynomolgus monkeys

The anti-Tac mAb has been shown to bind to the p55 chain of the IL-2R, block IL-2 binding and inhibit T cell proliferation. A humanized form of anti-Tac (HAT) has been constructed that retains the binding properties of murine anti-Tac (MAT). These two mAb were evaluated in cynomolgus monkeys to compare relative immunogenicity and pharmacokinetic properties. Monkeys treated with HAT daily for 14 days exhibited anti-HAT antibody titers which were 5- to 10-fold lower than their MAT-treated counterparts and these antibodies developed later than in the MAT-treated monkeys. Two of four monkeys receiving a single injection of MAT developed anti-MAT antibodies, whereas none of four monkeys developed antibodies after a single treatment with HAT. In monkeys injected with either HAT or MAT daily for 14 days, the anti-antibody titers induced were inversely related to the amount of anti-Tac administered. Antibodies that developed against MAT were both anti-isotypic and anti-idiotypic, whereas those developed against HAT appeared to be predominantly anti-idiotypic. The pharmacokinetic properties, that is the half-life and area under the curve values, of HAT were also significantly different from those of MAT. The area under the curve values for HAT in naive monkeys were approximately twofold more than those for MAT, and the mean serum half-life of HAT was 214 h, approximately four- to fivefold more than MAT. These pharmacokinetic values were reduced in monkeys previously sensitized with HAT or MAT suggesting that the presence of anti-antibodies altered these parameters.

High affinity human IgE receptor (Fc epsilon RI). Analysis of functional domains of the alpha-subunit with monoclonal antibodies

The binding of IgE to the high affinity Fc epsilon receptor (Fc epsilon RI) on mast cells and basophils is mediated by the alpha-subunit of the tetrameric receptor complex. Based on sequence homologies, the 50-kDa alpha-subunit is a member of the immunoglobulin superfamily of proteins and has two predicted disulfide-bonded loops. Monoclonal antibodies specific for the human alpha-subunit have been identified and separated into two major classes: inhibitory and noninhibitory antibodies. Inhibitory antibodies (i.e. 15A5) block 125I-IgE binding to a recombinant chimeric alpha-subunit (ch-alpha-protein) expressed on Chinese hamster ovary cells and immunoprecipitate 125I-labeled purified ch-alpha-protein. Noninhibitory antibodies (i.e. 22E7) immunoprecipitate both 125I-labeled ch-alpha-protein and the soluble complex of 125I-IgE cross-linked to ch-alpha-protein but do not block 125I-IgE binding to the ch-alpha-protein expressed on Chinese hamster ovary cells. Both classes of antibodies bind to natural Fc epsilon RI present on human basophils and induce histamine release from these cells. Inhibitory antibody 15A5 specifically binds to a peptide corresponding to amino acids 125-140 of the putative second domain of the alpha-subunit sequence. All the inhibitory antibodies compete with 125I-15A5 for binding to the ch-alpha-protein, indicating that these antibodies recognize inhibitory epitopes that are either identical or sterically overlapping. Noninhibitory antibodies (i.e. 22E7) do not block 125I-15A5 binding to the ch-alpha-protein. These data suggest that antibodies binding to the predicted second domain of the alpha-subunit can inhibit IgE binding to the alpha-subunit, while antibodies binding at a distance from this site do not inhibit IgE binding. These inhibitory antibodies may block IgE binding to the ch-alpha-protein by direct overlap, steric inhibition, or induced conformational changes of the receptor contact points for IgE.

Localization in human interleukin 2 of the binding site to the alpha chain (p55) of the interleukin 2 receptor

Human interleukin 2 (IL-2) analogs with defined amino acid substitutions were used to identify specific residues that interact with the 55-kDa subunit (p55) or alpha chain of the human IL-2 receptor. Analog proteins containing specific substitutions for Lys-35, Arg-38, Phe-42, or Lys-43 were inactive in competitive binding assays for p55. All of these analogs retained substantial competitive binding to the intermediate-affinity p70 subunit (beta chain) of the receptor complex. The analogs varied in ability to interact with the high-affinity p55/p70 receptor. Despite the lack of binding to p55, all analogs exhibited significant biological activity, as assayed on the murine CTLL cell line. The dissociation constants of Arg-38 and Phe-42 analogs for p70 were consistent with intermediate-affinity binding; the Kd values were not significantly affected by the presence of p55 in binding to the high-affinity IL-2 receptor complex. These results confirm the importance of the B alpha-helix in IL-2 as the locus for p55-receptor binding and support a revised model of IL-2-IL-2 receptor interaction.

Anti-Tac-H, a humanized antibody to the interleukin 2 receptor, prolongs primate cardiac allograft survival

High-affinity interleukin 2 receptors (IL-2Rs) are expressed by T cells activated in response to foreign histocompatibility antigens but not by normal resting T cells. To exploit this difference in IL-2R expression, anti-Tac-M, a murine monoclonal antibody specific for the IL-2R alpha chain, was used to inhibit organ allograft rejection. However, the use of murine anti-Tac as an immunosuppressive agent was limited by neutralization by human anti-murine antibodies and by weak recruitment of effector functions. To circumvent these difficulties, a humanized antibody to the IL-2R, anti-Tac-H, was prepared. This molecule is human with the exception of the hypervariable segments, which are retained from the mouse. In vivo survival of anti-Tac-H is 2.5-fold longer than simultaneously administered anti-Tac-M (terminal t1/2, 103 hr vs. 38 hr). In addition, anti-Tac-H is less immunogenic than anti-Tac-M when administered to cynomolgus monkeys undergoing heterotopic cardiac allografting. Specifically, all monkeys treated with anti-Tac-M developed measurable anti-anti-Tac-M levels by day 15 (mean onset, 11 days). In contrast, none of the animals receiving anti-Tac-H produced measurable antibodies to this monoclonal antibody before day 33. Finally, there was a prolongation of graft survival in the cynomolgus heterotopic cardiac allograft model in animals receiving anti-Tac. In animals that received anti-Tac-M, the allograft survival was prolonged compared to that of the control group (mean survival, 14 +/- 1.98 days compared to 9.2 +/- 0.48 days; P less than 0.025). Graft survival was further prolonged by anti-Tac-H with a mean survival of 20.0 +/- 0.55 days (compared to controls, P less than 0.001; compared to anti-Tac-M, P less than 0.02). There was no toxicity attributable to the administration of either form of anti-Tac. Thus, anti-Tac-H significantly prolonged allograft survival in primates, without toxic side effects, and may be of value as an adjunct to standard immunosuppressive therapy in humans.

The alpha subunit of the human IgE receptor (FcERI) is sufficient for high affinity IgE binding

The alpha subunit of the FcERI binds IgE with high affinity. Previous studies have demonstrated that alpha subunit expression requires the presence of beta and/or gamma subunits, and it is not known how these two subunits contribute to the ability of the alpha subunit to bind IgE. In this report, we describe the expression and characterization of a human chimeric alpha subunit. The data demonstrate that high affinity IgE binding does not require the presence of the beta and/or gamma subunits and that this activity is localized to the extracellular domain (residues 26-201) of the human alpha subunit. Permanent cell lines expressing the chimeric receptor were used to characterize the binding parameters of the alpha subunit. These cell lines provide a means of identifying therapeutic agents which may be effective in the treatment/management of allergic diseases.