Antibody OKT3 Research Articles

The effects of intraoperative administration of OKT3 during renal transplantation.

The use of the monoclonal antibody OKT3 for induction immunosuppression in renal transplantation is increasing--however, the safety of intraoperative administration continues to be questioned because of first-dose effects. The current study was designed to examine the effects of intraoperative administration of OKT3 on the cardiovascular and pulmonary systems in 161 consecutive renal transplant recipients. Patients receiving OKT3 intraoperatively during renal transplant (99 cadaver recipients) were compared with 62 patients not administered the drug (31 cadaver, 25 living-related-donor, 6 living-nonrelated donor). Intraoperative airway pressure (highest, average), O2 saturation (SaO2), temperature, blood pressure changes, cardiac rhythm, and bronchospasm were compared in these two groups. Significant physiologic changes noted in the group receiving OKT3 included increased temperature (both intraoperative and postoperative), decreased SaO2 (postoperative), and increased FiO2 (postoperative). Despite these differences, no clinically significant changes were noted in the group receiving OKT3. OKT3 induction given at the time of surgery was associated with a significantly increased one- and three-year graft function. This study demonstrates that first-dose administration of OKT3 intraoperatively during renal transplantation is safe and effective.

OKT3 induction in pediatric renal transplantation.

Twenty cadaveric renal transplant patients (mean age 12.5 +/- 4.8 years) received 14 days (mean 13.0 +/- 2.8 days) of OKT3 (mean dose 0.16 +/- 0.09 mg/kg) along with prednisone 0.5 mg/kg per day, azathioprine 2 mg/kg per day and cyclosporine 5 mg/kg per day which was increased to obtain therapeutic levels before the discontinuation of OKT3. Actuarial patient and graft survival were 100% and 50%, respectively, at both 1 and 5 years. Four children lost their grafts within the first 48 h. One loss was technical in origin, the remaining 3 had pathological evidence of vascular thrombosis. Of the remaining 16 children, 12 (75%) experienced rejection episodes within the first 2 months post transplant (mean 27 +/- 15 days). Successful reversal of early rejection episodes was achieved in 11 of 12 patients. Clinically significant cytomegalovirus infection occurred in 4 patients and resulted in graft loss in 2 patients. Circulating OKT3 levels ranging from 1,000 to 32,000 ng/ml were seen in all patients within the first 48 h. There was a rapid and total depletion of circulating CD3-positive lymphocytes in all patients. Anti-isotypic and anti-idiotypic OKT3 antibodies were assessed by enzyme-linked immunosorbent assay (ELISA), and blocking anti-idiotypic antibodies were detected by immunofluorescence inhibition assay. Positive OKT3 antibody titers were detected in 11 children by ELISA and 10 children by immunofluorescence inhibition assay.(ABSTRACT TRUNCATED AT 250 WORDS)

RAPID DETECTION OF ANTI-OKT3 ANTIBODIES WITH THE TRANSTAT ASSAY1

The ability to successfully reuse OKT3, a mouse monoclonal antibody, is dependent upon the host's response to the antibody during and following the first treatment course. Antiidiotypic and/or antiisotypic antibodies may develop after exposure to OKT3. Antiidiotypic antibodies will bind OKT3, rendering it ineffective, while antiisotypic antibodies do not influence the efficacy of OKT3. A new membrane-based immunoassay, Transtat OKT3 (Sangstat Medical Corp, Menlo Park, CA) detects anti-OKT3 antibodies in less than 15 min. It allows simultaneous detection of antiidiotype and antiisotype antibodies. A total of 180 serum samples were initially analyzed by ELISA; results were negative, low-titer (1:100), or high-titer (> or = 1:1000). Retrospectively, these same samples were analyzed by Transtat for both anti-OKT3 (idiotype) and IgG2a (isotype). A total of 109 samples of 180 (60.6%) tested negative by ELISA and Transtat, while 71 (39.4%) tested positive. Of the negative samples by ELISA, 98 of 109 (89.9%) also tested anti-OKT3-negative by Transtat. Of the 109 specimens that were anti-OKT3 negative by Transtat, 98 (89.9%) tested negative by ELISA. There were 22 discrepant samples between the two methods; all were low-titer-positive (ELISA and Transtat). The 71 positive ELISA samples consisted of 53 low-titer (1:100) and 18 high-titer (> or = 1:1000), while the 71 anti-OKT3 positive Transtat samples consisted of 44 low-titer (1:10) and 27 high-titer (1:50). Sixty of 71 (84.5%) ELISA-positive samples were also positive by Transtat. Similarly, 60 of 71 (84.5%) Transtat-positive samples were also positive by ELISA. Of 71 patient samples positive for anti-OKT3 antibodies, 63 had an antiisotypic component present by Transtat. In conclusion, the Transtat OKT3 assay for measuring OKT3 and IgG2a antibodies offers a rapid and accurate assay for OKT3 monitoring.

Kaposi's Sarcoma in Kidney Transplant Recipients

To the Editor.— Kaposi's sarcoma (KS) is a vascular tumor whose exact origin is not yet fully understood. Its increasing incidence in patients who are immunosuppressed and in patients with the acquired immunodeficiency syndrome has increased our awareness of this disease. We describe our population of kidney transplant patients in whom KS developed. Patients and Methods.— A population of 820 kidney transplant patients who underwent follow-up of at least 6 months' duration was entered into the study. Immunosuppressive therapy consisted of methylprednisolone and azathioprine (conventional therapy) for 316 patients who underwent transplantation before 1983. Since February 1983, another 504 patients were treated with cyclosporine alone or in combination with methylprednisolone (double therapy) or with methylprednisolone and azathioprine (triple therapy). Rejection episodes were treated with intravenous methylprednisolone pulses (500 to 1000 to 500 mg each) for 3 consecutive days. In cases of steroid-resistant rejections, antithymocyte globulin or monoclonal OKT3 antibodies were

OKT3 antibody formation after OKT3 induction therapy: [formula omitted], PK Hennessy, RJ Tesi, The Ohio State University Department of Surgery, Columbus, OH

OKT3 antibody formation after OKT3 induction therapy: [formula omitted], PK Hennessy, RJ Tesi, The Ohio State University Department of Surgery, Columbus, OH

Migration of Langerhans Cells into the Epidermis of Human Skin Grafted onto Nude Mice

In a previous study, it was demonstrated that human Langerhans cells (LC) are preserved in human skin grafted onto a nude mouse. Moreover, although it was observed that mouse LC of the host invade skin grafts from allogeneic mouse or rat, they do not penetrate in human skin grafts. In most of the human skin equivalent systems produced in vitro, LC appear to be lost. The present study was designed to investigate whether the mouse LC will repopulate a human skin equivalent. For this purpose, two different systems of skin equivalent have been grafted into the nude mouse. They were composed of human keratinocytes deposited on dead human dermis, or on lattice composed of human fibroblasts embedded in type I collagen. At different times after grafting, the presence of LC in the transplants was assayed either by indirect immunofluorescence or by electron microscopy. Indirect immunofluorescence was performed on frozen sections or on epidermal sheets with anti-Ia, anti-HLA-DR, or OKT6 antibodies. It was observed that, at 2 months after grafting, Ia(+) HLA-DR(-) OKT6(-) cells are present in grafted human epidermis. Moreover, LC with typical Birbeck granules are also detected by electron microscopy. It could be concluded, from this study, that mouse LC can repopulate human epidermis devoid of human LC.

The ELAM-1 ligand sialosyl-Le(X) is present on Langerhans cells isolated from stratified epithelium.

In this study we show the expression of the newly identified carbohydrate ligand, sialosyl-Le(X) on Langerhans cells. The receptor for sialosyl-Le(X) is the endothelial leukocyte adhesion molecule-1 (ELAM-1) present on activated endothelial cells. Using flow cytometry, Langerhans cells were selected due to positivity for an antibody against CD1a and low orthogonal light scatter. The CD1a antigen stained by the OKT6 antibody is considered a maturational marker of Langerhans cells in agreement with the specific labeling of dendritic cells in the epithelium only. Double immunostaining (OKT6/anti-sialosyl-Le(X)) using flow cytometry and immunohistochemistry demonstrated that almost all OKT6-positive cells in normal stratified epithelium expressed sialosyl-Le(X). Conversely, by immunohistochemistry of oral epithelium with acute inflammation, additional dendritic cells negative for OKT6 were found to express sialosyl-Le(X). In addition, sialosyl-Le(X)-positive but not OKT6-positive dendritic cells were found in the submucosa. These findings indicate that the carbohydrate antigen sialosyl-Le(X) is expressed earlier than the CD1a antigen in the maturation of the Langerhans cell lineage. Future studies should aim at investigating the importance of adhesion between sialosyl Le(X) and ELAM-1 in epithelial recruitment of Langerhans cells.

Quantitation and phenotyping of T cell clones by flow cytometry

In order to efficiently analyze large numbers of T cell clones, a method for analysis of small cell cultures by flow cytometry was developed. The aim was to assess cloning efficiency, growth rate and phenotype of T cell clones. The reliability of the flow cytometer for quantitation of cell populations was documented by repeated analysis of manually counted cell samples. In the concentration range from 3000 to 195,000 cells/ml, the correlation coeffient between counts obtained by the flow cytometer and manual cell counts was 0.999 and within-assay coefficients of variation were below 4%. Cell cultures containing less than 200 cells were reliably quantified. The technique was applied for analysis of T cell clonings with different mitogens and in the presence of varying amounts of serum. To reduce time and labour, the cultures were analyzed only 10 days after cloning, when the clones contained less than 100,000 cells. The sensitivity of the flow cytometer in the detection of immunolabeled cells made further expansion of cell cultures unnecessary, thus greatly reducing manual labour and experiment turnover time. The commonly used mitogens phytohemagglutinin (PHA) and the antibody OKT3 resulted in comparable cloning efficiencies and clone sizes. Human serum was essential for high cloning efficiency as well as for continued growth, and could not be substituted with an increased amount of fetal calf serum. When cloning with interleukin-2 at 20,000 U/ml, two growing cell types were identified. The majority of the clones contained CD3 +, CD4 +, or CD8 + T cells. Ten out of 60 cultures however, contained cells with the sol CD3 −16 56 + NK cell phenotype, indicating that the culture conditions stimulated proliferation of two different cell types. The described method can be applied for rational analysis of large numbers of minute cell cultures, in for example evaluation of different cloning conditions and estimation of precursor cell frequencies in limiting dilution analysis. The simultaneous phenotyping allows precursor cell analysis under conditions that stimulate growth of more than one cell type.

The preferential expansion of functional CD4+ lymphocyte populations in vitro.

We describe a simple and inexpensive chemical procedure for the selective expansion of human CD4+ lymphocytes. The method employs L-leucine methyl ester (LME) to deplete monocytes and large granular lymphocytes, as well as to inhibit growth of CD8+ lymphocytes. LME treatment eliminates granular cells, but most CD8+ lymphocytes, B-lymphocytes, and CD4+ lymphocytes remain. Peripheral blood mononuclear cells (PBMCs) from normal and HIV-positive individuals are treated with LME for 1 h at ambient temperature and cultured in the presence of IL-2 to expand the cell number. Stimulation with the T-cell mitogens concanavalin A, phytohemagglutinin, or OKT3 antibody augments lymphocyte expansion and within 1-3 weeks the culture is greatly enriched (90-100%) in CD4+ lymphocytes. LME-treated lymphocytes expand up to 10-fold during culture in the presence of IL-2 alone and up to 400-fold following treatment with T-cell mitogens. The immune function of LME-treated and expanded peripheral blood lymphocytes was examined using the response to the recall antigens tetanus toxoid and Candida albicans. Fresh PBMCs exposed to these recall antigens proliferated readily. Similarly, LME-treated lymphocytes following expansion responded to these recall antigens with good fidelity to the original PBMC response patterns in four of six donors. The expanded and LME-treated lymphocytes also exhibited good mitogen responses in three of three donors. The LME procedure allows for the simple and inexpensive generation of expanded, immunologically functional, CD4+ lymphocytes.

Humanized OKT3 antibodies: successful transfer of immune modulating properties and idiotype expression.

Antibodies that possess the Ag-binding regions of OKT3 within the context of a human framework (Hu-OKT3 Ab) offer distinct advantages for optimizing anti-CD3 mAb therapy. First, manipulation of Ab genes to produce humanized Ab that retain Ag-binding activity may circumvent antigenicity problems. Second, Ab gene engineering provides a means for modifying functional properties, including T cell activation and immune suppression. The purpose of this study was to determine the functional properties of Hu-OKT3 Ab and to compare the functional properties and idiotypes of Hu-OKT3 Ab to those of murine OKT3. Three Hu-OKT3 IgG4 Ab, a chimeric OKT3 antibody (cOKT3-1) (grafted sequences comprising all OKT3 VH and VL regions) and two complementarity determining region (CDR)-grafted antibodies, gOKT3-5 and gOKT3-6 (grafted sequences comprising only OKT3 VH and VL CDR and some framework amino acids, were analyzed. Initial studies demonstrated that the cOKT3 and gOKT3-5 Ab bound selectively to T cells and competitively inhibited OKT3-FITC binding with avidities similar to that of murine OKT3. Binding avidity of the gOKT3-6 Ab was markedly less than that of the other two Hu-OKT3 Ab. Serologic analysis suggested that cOKT3 and gOKT3-5 Ab possess idiotypes (combining sites) similar to murine OKT3. T cell activation potency of all three Hu-OKT3 Ab was assessed by proliferation, induction of activation marker expression (IL-2R and Leu 23), and lymphokine production (TNF-alpha and IFN-gamma). The cOKT3 and gOKT3-5 Ab demonstrated T cell activation potencies similar to murine OKT3 as assessed by each parameter. CD3 coating and modulation by these two Ab was effective but somewhat less potent than that observed with OKT3. Finally, cOKT3 and gOKT3-5 Ab both inhibited CTL activity comparably to murine OKT3. In conclusion, these studies indicate that gOKT3-5 and cOKT3 Ab possess immune modulating properties similar to murine OKT3 and thus offer attractive alternatives to murine OKT3 for in vivo therapy.

Role of cross-linking in stepwise activation of T cells.

Activation of T cells is a complex process which we have hypothesized involves a series of functional intermediates possessing some, but not all, of the characteristics of fully functional effector cells. We have identified two such functional intermediates, the poised T cell (poTc) and the pre-effector T cell (peTc). poTc do not proliferate or mediate cytolytic activity but are responsive to help in the form of interleukin 2 (IL-2); peTc are proliferating cells which are not cytolytic. Here the role of T-cell receptor/CD3 complex cross-linking in generating these functional intermediates is examined and it is shown that cells can be driven to different stages of functional maturation depending upon the sequence of antibody binding to CD3 and cross-linking. Highly purified T cells can be activated to poTc stage if they are first labelled with the anti-CD3 monoclonal antibody OKT3 and then cross-linked with goat anti-mouse IgG-coated beads. If the OKT3 antibody is first bound to the IgG-coated beads and then added to highly purified T cells, peTc are generated. In both cases the intermediates can be driven to become fully functional effector cells by the addition of IL-2. Finally, by removing the OKT3-bound beads during the activation process, were are able to show that poTc and peTc are sequential intermediates along the same pathway of activation.

Monoclonal antibodies to common epitopes of the human [formula omitted] T-cell receptor preferentially activate CD45RA + T-cells

The murine monoclonal antibody BMA 031 (IgG2b) is directed to a monomorphic epitope on the human α β T-cell receptor. In contrast to anti-CD3 antibodies of the IgG2b isotype, BMA 031 is able to induce a proliferative response in T-cells from IgG2b low responders. This response occurs independently of cross-linking conditions indicating that the mode of activation differs from stimulation by the anti-CD3 antibody OKT3 (IgG2a) which strictly depends on cross-linking conditions. To further characterize the stimulatory potential of the two antibodies we studied the lymphocyte subsets responsive to stimulation by BMA 031 and OKT3. In CD45RA + cells both antibodies exhibited similar effects. They induced weak expression of the 55-kDa chain of the interleukin-2 receptor (CD25), virtually no interleukin-2 secretion, but nevertheless strong proliferation. In CD45R0 + cells OKT3 and BMA 031 showed markedly different effects. OKT3 stimulated strong CD25 expression, strong interleukin-2 production, and marked proliferation. In contrast, CD45R0 + cells stimulated by BMA 031 showed only weak CD25 expression but neither interleukin-2 production nor proliferation. These data suggest that CD45RA + and CD45R0 + cells differ in their capability to produce interleukin-2 upon stimulation via the CD3/T-cell receptor complex and also in the requirement for interleukin-2 to mount a proliferative response. The differential effect of OKT3 and BMA 031 in CD45R0 + cells probably results from the failure of BMA 031 to trigger interleukin-2 production which may be a consequence of its inability to induce CD3/T-cell receptor cross-linking in IgG2b low responders. BMA 031 is therefore a useful tool for the selective activation of CD45RA + cells in these individuals.

The experience of administration of 15-deoxyspergualin on rejection in kidney transplant recipients

We report here the favorable results of clinical application of 15-deoxyspergualin (DSG) as a rescue therapy for rejection episodes in kidney transplant recipients. DSG was discovered in Japan and was proved to be a novel immunosuppressant in various animal transplantation models. The immunosuppressive mechanism of DSG is unclear yet, but its point of action is supposed to be in the early immuno response to allogeneic stimulation without the regulation of cytokine production. We performed the administration of DSG in fifteen patients, who had rejection episodes, with a dosage of 3 mg/kg/day or 5 mg/kg/day for five days by drip infusion. In the group of recipients who had rejection episodes within six months after kidney transplantation, DSG proved effective on six out of seven acute rejection episodes and induced favorable remission. And in the group of recipients who had rejection episodes after six months since kidney transplantation, DSG proved effective on all of ten rejection episodes. There was not a difference of effectiveness in respect to the dosage of DSG. The side effect of DSG treatment was mainly leukopenia but in most cases these leukopenia was remitted just under careful observation. Some patients complained the sense of abdominal discomfort. But so far, we did not encounter serious or critical side effects and complications during all the time of progression. Another benefit was that DSG was able to reverse the rejection episode even in the patient who had already treated with anti lymphocyte globulin and/or anti CD3 monoclonal antibody OKT3. We concluded that the administration of DSG as a rescue therapy was not accompanied by the serious side effects and was most effective against acute rejection after kidney transplantation.

Analysis of Infectious Complications Occurring After Solid-Organ Transplantation

To improve our understanding of posttransplant infections, we analyzed bacterial, viral, fungal, parasitic, and other infections in 604 consecutive recipients of kidney (n = 518), kidney-pancreas (n = 82), kidney-liver (n = 3), or kidney-islet (n = 1) allografts (355 cadaveric, 14 living-unrelated, 235 living-related donors) who also received cyclosporine, azathioprine, and prednisone immunosuppression. Recipients of cadaveric grafts received additional induction immunosuppression (antilymphocyte globulin or murine monoclonal antibody OKT3). Rejection episodes were treated with high-dose steroids, and either antilymphocyte globulin or OKT3 was administered when clinically indicated. Perioperative antibiotics and posttransplant prophylactic acyclovir sodium or ganciclovir sodium, trimethoprim-sulfamethoxazole, and clotrimazole or nystatin (Mycostatin) were administered to all recipients. Two hundred thirteen patients (35.3%) were found to have had no identifiable infections, while 391 (64.7%) had either isolated bacterial (97 [16.1%]), viral (53 [8.8%]), or fungal (34 [5.6%]) infections or combination (concurrent or sequential) infections with bacterial plus viral (46 [7.6%]), bacterial plus fungal (66 [10.9%]), viral plus fungal (20 [3.3%]), bacterial plus viral plus fungal (64 [10.6%]), or bacterial plus viral plus fungal plus parasitic (11 [1.8%]) pathogens in the posttransplantation period. Renal allograft survival (percentage, actuarial method) was diminished in patients with infections at both 1 year (91% vs 83%) and 3 years (81% vs 76%) after transplantation, as was actuarial patient survival (1 year, 97% vs 92%; 3 years, 93% vs 88%). We conclude that infection remains a major cause of both patient demise and allograft loss following successful solid-organ transplantation.

OKT3 treatment of steroid-resistant rejection in pediatric liver transplant recipients.

Of a total of 187 consecutive liver grafts in 149 pediatric recipients, 59 episodes of steroid-resistant, biopsy-proven rejection (32% of grafts) were treated with OKT3 monoclonal antibody. After 59 OKT3-treated episodes, liver function at the end of treatment was normal in 40%, improved in 35%, and unchanged in 24%. Of 21 partial responses, 12 episodes eventually resolved to yield an overall complete response rate of 59%. CD3-positive T-cells greater than 5% occurred during 61% of OKT3-treated rejection episodes and was associated with impaired efficacy of OKT3 (30% complete response rate). Six grafts were re-treated with OKT3 for rejection and in all CD3-positive T-cells could not be maintained less than 5%. Of the six grafts requiring repeat OKT3, five failed-retreatment and required retransplantation. OKT3 antibodies of low titer were found prior to a second use of OKT3 in 65% of episodes. Patients treated with OKT3 after failing more than two preceding steroid courses had a significantly increased chance of graft loss (57%; p = 0.01). We conclude that this group of pediatric patients appeared less responsive to OKT3 compared to other series combining pediatric and adult recipients, possibly due to a more vigorous immune response in the child.

Activation via the CD3 and CD16 pathway mediates interleukin-2- dependent autocrine proliferation of granular lymphocytes in patients with granular lymphocyte proliferative disorders

Granular lymphocytes (GLs) in patients with GL-proliferative disorders (GLPDs) are known to express the interleukin-2 receptor (IL-2R) beta chain (p70–75) constitutively and to proliferate in response to stimulation with IL-2 via the beta chain. In this report, we found that the anti-CD3 monoclonal antibody (MoAb) OKT3 could induce the proliferation of GLs from patients with T-cell lineage GLPDs (T-cell receptor-alpha beta+/CD3+16+), but not that of natural killer (NK) cell lineage GLs (T-cell receptor-alpha beta-/CD3–16+). In contrast, the anti-CD16 MoAb 3G8 that reacts with NK-lineage GLs could induce the proliferation of these GLs but not that of GLs with a T-cell phenotype. Furthermore, the anti-CD16 MoAbs CLB FcR gran1 (VD2) and OK-NK, which react with both T- and NK-lineage GLs, induced the proliferation of GLs with both T- and and NK-cell phenotypes. The proliferative response induced via the CD3 or IgG Fc receptor III (Fc gamma RIII: CD16) pathway was shown to be associated with the IL-2-dependent autocrine pathway by various findings, including the induction of endogenous IL-2 production, the coexpression of the IL-2R alpha chain (p55) and the IL- 2R beta chain, and the inhibition of GL proliferation by anti-IL-2 or anti-IL-2R MoAb. These results suggest that GL proliferation is mediated at least partly through the IL-2-dependent autocrine pathway, and that the TCR/CD3 complex in T-cell phenotype GLs and the Fc gamma RIII in both T- and NK-cell phenotype GLs play a role in their activation in GLPDs.

Activation via the CD3 and CD16 Pathway Mediates Interleukin-2-Dependent Autocrine Proliferation of Granular Lymphocytes in Patients With Granular Lymphocyte Proliferative Disorders

Granular lymphocytes (GLs) in patients with GL-proliferative disorders (GLPDs) are known to express the interleukin-2 receptor (IL-2R) beta chain (p70-75) constitutively and to proliferate in response to stimulation with IL-2 via the beta chain. In this report, we found that the anti-CD3 monoclonal antibody (MoAb) OKT3 could induce the proliferation of GLs from patients with T-cell lineage GLPDs (T-cell receptor-alpha beta+/CD3+16+), but not that of natural killer (NK) cell lineage GLs (T-cell receptor-alpha beta-/CD3-16+). In contrast, the anti-CD16 MoAb 3G8 that reacts with NK-lineage GLs could induce the proliferation of these GLs but not that of GLs with a T-cell phenotype. Furthermore, the anti-CD16 MoAbs CLB FcR gran1 (VD2) and OK-NK, which react with both T- and NK-lineage GLs, induced the proliferation of GLs with both T- and and NK-cell phenotypes. The proliferative response induced via the CD3 or IgG Fc receptor III (Fc gamma RIII: CD16) pathway was shown to be associated with the IL-2-dependent autocrine pathway by various findings, including the induction of endogenous IL-2 production, the coexpression of the IL-2R alpha chain (p55) and the IL-2R beta chain, and the inhibition of GL proliferation by anti-IL-2 or anti-IL-2R MoAb. These results suggest that GL proliferation is mediated at least partly through the IL-2-dependent autocrine pathway, and that the TCR/CD3 complex in T-cell phenotype GLs and the Fc gamma RIII in both T- and NK-cell phenotype GLs play a role in their activation in GLPDs.

Analysis and isolation of human transferrin receptor using the OKT-9 monoclonal antibody covalently crosslinked to magnetic beads

A method is described for the use of magnetic beads as a solid phase for the immunoprecipitation of labeled proteins. The anti-human transferrin receptor monoclonal antibody OKT-9 has been coupled to sheep anti-mouse IgG1-coated magnetic beads using the crosslinking agent dimethyl pimelimidate. The transferrin receptor is readily detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography following immunoprecipitation from 35S-labeled cell lysates. When compared with precipitations using OKT-9 coupled to protein G Sepharose the magnetic beads result in fewer nonspecific bands. The protocol described is generally applicable to the identification of labeled proteins. In addition, because magnetic beads are amenable to covalent crosslinking procedures they can be used for the purification of proteins from complex mixtures. Covalently crosslinked OKT-9 sheep anti-mouse IgG1-coated magnetic beads have been used to affinity purify unlabeled transferrin receptor from cell lysates giving comparable purity and yield to transferrin Sepharose isolated transferrin receptor. The major advantages offered by magnetic beads compared to conventional affinity matrices are low nonspecific binding and the rapidity with which the purification can be performed.

In vitro and in vivo activated T cells display increased sensitivity to PGE 2

In this study we report that in vitro activation of T cells increased the cyclic AMP response to subsequent prostaglandin E 2 (PGE 2) stimulation severalfold per cell. This sensitization of T cells to PGE 2-induced cyclic AMP generation was observed when the T cells had been stimulated in vitro for 5 days with either the CD3 monoclonal antibody OKT3, phytohemagglutinin, or the combination phytohemagglutinin plus the phorbol ester PMA. Enhanced cyclic AMP generation following mitogenic activation was seen in response to both PGE 2 and forskolin, a direct activator of the adenylate cyclase, indicating that the amount of adenylate cyclase had increased during the in vitro activation course. In order to investigate whether various T cell subsets in general and in vivo activated T cells in particular would differ in their susceptibility to PGE 2, we isolated CD4 +, CD8 +, CD4 −CD8 −, CD4 +CD45RO + (“memory”), and CD4 +CD45RA + (“virgin”) T cells and studied PGE 2-mediated inhibition of CD3-induced proliferation, as well as cyclic AMP generation in response to PGE 2, respectively. We found that CD8 + T cells are more susceptible to PGE 2 inhibition and produce more cyclic AMP than CD4 + T cells. Double-negative T cells (enriched for γδ T cell receptor positive cells) were found to be sensitive to PGE 2 as well. Within the CD4 + T cell population, CD45RO + (“memory”) T cells were significantly more sensitive to PGE 2-mediated suppression than CD45RA + (“virgin”) T cells. CD45RO + cells required a 10-fold lower dose of PGE 2 for half-maximum suppression of proliferation. However, no difference in cyclic AMP production could be demonstrated between these two subsets. We propose that substantial heterogeneity exists among peripheral blood T lymphocyte subsets regarding their sensitivity to the immunosuppressive action of PGE 2 and that the sensitivity of individual cells changes in the course of an immune response.

Laboratory Monitoring of Therapy with OKT3 and Other MurineMonoclonal Antibodies

The first monoclonal antibody (MAb) approved by the Food and Drug Administration (FDA) for therapeutic use, OKT3, is now a standard treatment for organ allograft rejection. This article reviews the interpretation of laboratory tests used to manage patients treated with MAb. Emphasis is placed on OKT3, with which the experience is also the greatest, although comparisons with other MAbs in clinical trials is also discussed.