Antithymocyte globulins in renal transplantation-from lymphocyte depletion to lymphocyte activation: The doubled-edged sword.

Compelling data suggest that lymphocyte depletion following T cell depleting therapy may induce prolonged CD4 T cell lymphopenia and trigger lymphocyte activation in some patients. These profound and non-reversible immune changes in T cell pool subsets are the consequence of both impaired thymic renewal and peripheral homeostatic proliferation. Chronic viral challenges by CMV play a major role in these immune alterations. Even when the consequences of CD4 T cell lymphopenia have been now well described, recent studies shed new light on the clinical consequences of immune activation. In this review, we will first focus on the mechanisms involved in T cell pool reconstitution after T cell depletion and further consider the clinical consequences of ATG-induced T cell activation and senescence in renal transplant recipients.

Quantitative phosphoproteomic analysis reveals a role for serine and threonine kinases in the cytoskeletal reorganization in early T cell receptor activation in human primary T cells.

Protein phosphorylation-dephosphorylation events play a primary role in regulation of almost all aspects of cell function including signal transduction, cell cycle, or apoptosis. Thus far, T cell phosphoproteomics have focused on analysis of phosphotyrosine residues, and little is known about the role of serine/threonine phosphorylation in early activation of the T cell receptor (TCR). Therefore, we performed a quantitative mass spectrometry-based analysis of the global phosphoproteome of human primary T cells in response to 5 min of TCR activation with anti-CD3 antibody. Combining immunoprecipitation with an antiphosphotyrosine antibody, titanium dioxide phosphopeptide enrichment, isobaric tag for the relative and absolute quantitation methodology, and strong cation exchange separation, we were able to identify 2814 phosphopeptides. These unique sites were employed to investigate the site-specific phosphorylation dynamics. Five hundred and seventeen phosphorylation sites showed TCR-responsive changes. We found that upon 5 min of stimulation of the TCR, specific serine and threonine kinase motifs are overrepresented in the set of responsive phosphorylation sites. These phosphorylation events targeted proteins with many different activities and are present in different subcellular locations. Many of these proteins are involved in intracellular signaling cascades related mainly to cytoskeletal reorganization and regulation of small GTPase-mediated signal transduction, probably involved in the formation of the immune synapse.

Targeting B cells and antibody in transplantation.

There has been increasing interest in the role played by B cells, plasma cells and their associated antibody in the immune response to an allograft, driven by the need to undertake antibody-incompatible transplantation and evidence suggesting that B cells play a role in acute cellular rejection and in acute and chronic antibody-mediated rejection. A number of immunosuppressive agents have emerged which target B cells, plasma cells and/or antibody, for example, the B cell-depleting CD20 antibody rituximab. This review describes recent developments in the use of such agents, our understanding of the role of B cells in alloimmunity and the application of this knowledge toward novel therapies in transplantation. It also considers the evidence to date suggesting that B cells may act as regulators of an alloimmune response. Thus, future attempts to target B cells will need to address the problem of how to inhibit effector B cells, while enhancing those with regulatory capacity.

Thymoglobulin induction protects liver allografts from ischemia/reperfusion injury.

BACKGROUND: Interventions that minimize hepatic ischemia/reperfusion injury (IRI) can expand the donor organ pool. Thymoglobulin (TG) induction therapy has been shown to ameliorate delayed graft function and possibly decrease IRI in cadaver renal transplants recipients. This controlled randomized trial was designated to assess the ability of TG to protect against IRI in liver transplant recipients. PATIENTS AND METHODS: Twenty-two cadaveric liver transplant recipients were randomized to receive either TG (1.5 mg/kg/dose) during the anhepatic period and QOD x2 doses or no TG. No differences in recipients' demographics were present and donor characteristics were similar in terms of age, cause of death, and cold ischemia time. Maintenance immunosupression consisted of Tacrolimus (or Cyclosporine) and steroids for both groups. Donor biopsies were obtained during organ procurement, cold storage and 1 h after re-vascularization. Post-operative liver function tests were monitored. Early graft function, length of stay, patient and graft survival rates, incidence of primary non-function and rate of rejection were assessed. RESULTS: Patient and graft survival at 3 months was 100%. There was no incidence of primary graft non-function and no need for re-transplantation. The incidence of acute rejection was similar between the two groups. Patients in the TG group had significant decreases in alanine aminotransferase test at day 1 compared to the control group (p = 0.02). There were also near significant decreases of total bilirubin at day 5 and shorter length of hospitalization. Liver biopsy (at procurement, when cold, and post-reperfusion) of TG group demonstrated a trend for increased central ballooning. CONCLUSION: The TG allowed for more compromised liver grafts to be transplanted with less clinical evidence of IRI and improved function. Further studies on the degree of apoptosis in the liver biopsy post-reperfusion are underway.

Humoral mechanisms in T cell vaccination: induction and functional characterization of anti-lymphocytic autoantibodies.

T cell vaccination, the application of syngeneic attenuated T cells, has been shown to prevent effectively and treat experimental autoimmune diseases, but its mechanisms of action are poorly understood. Here we present data on the induction of a humoral anti-T cell response by T cell vaccination, capable of strongly inhibiting T cell proliferation and of ameliorating experimental autoimmune disease. T cell vaccination in the Lewis rat induced autoantibodies reactive with several syngeneic T cell proteins. These autoantibodies were not detectable in normal Lewis sera as assessed by immunoblotting and flow cytometry with intact syngeneic T cells. The autoantibody reactivity was not restricted to one idiotype, was detected as early as 1 week after vaccination and was dominated by IgG, suggesting the boosting of a naturally preformed humoral network by T cell vaccination. Recovery from passively or actively induced experimental autoimmune encephalomyelitis (EAE) in the Lewis rat, too, could be shown to be associated with the development of anti-T cell autoantibodies. In vitro, both the post-EAE and the post-vaccination sera had a strong suppressive effect on the proliferation of syngeneic T cell clones. This inhibition was shown to be mediated by antibodies and to be partly complement-dependent. In vivo, both kinds of sera were able to ameliorate EAE. This protective effect of the post-vaccination sera was not idiotype-specific, since sera obtained after T cell vaccination with an unrelated T cell clone were similarly effective in suppressing EAE. These results suggest that anti-lymphocytic antibodies might play an immunoregulatory role that can be positively manipulated by T cell vaccination.

Human pregnancy serum suppresses the proliferative response of lymphocytes to autologous PHA-activated T lymphoblasts.

PROBLEM: We have previously demonstrated that human serum can suppress the proliferative response in autologous mixed lymphocyte reaction (AMLR) in which phytohemagglutinin (PHA)-activated T lymphoblasts act as stimulators (T-TPHA AMLR). The aim of the present work was to determine whether pregnancy serum (PS) possesses an inhibitory capacity similar or different in magnitude. METHODS: Sixteen PS were added to T-TPHA AMLR cultures and the proliferative response was compared with that in the presence of human serum. The effect of PS on the IL-2 dependent proliferation of PHA-activated T Lymphoblasts was examined as well. RESULTS: PS induced a significantly more pronounced suppression of T-TPHA AMLR than human serum (P < 0.05). One PS tested was not inhibitory but rather stimulatory. This PS was obtained from a woman who subsequently had IUGR. The inhibition is related to the existence of a serum inhibitory factor and not to the lack of a serum supporting factor. PS inhibited not only T-TPHA AMLR of the same woman but also T-TPHA AMLR of other individuals as well, implying that the inhibitor is a non-MHC restricted factor. IL-2 dependent cell proliferation was not inhibited by PS, implying that the inhibitor detected in T-TPHA AMLR is not a general cell proliferation inhibitor. CONCLUSIONS: These results suggest that a non-MHC restricted inhibitory factor present in PS may play an important biological role in regulating local immune responses in the fetal-placental unit mediated by autoreactive T cells restricted to autologous activated T lymphocytes.

Adoptively transferred ex vivo activated memory T cells with cyclophosphamide: effective tumor-specific chemoimmunotherapy of advanced metastatic murine melanoma and carcinoma.

Autolymphocyte therapy (ALT) is adoptive cellular therapy of neoplastic disease based upon ex vivo activation of autologous peripheral blood mononuclear cells by either the supernatant derived from a previously prepared one-way mixed lymphocyte culture (MLC) or using low doses of the mitogenic monoclonal antibody anti-CD3 and a mixture of previously prepared autologous cytokines (T3CS). We have previously demonstrated that nonspecific ex vivo activation of splenocytes from murine tumor-bearing hosts (TBH) using an MLC supernatant or T3CS without the use of tumor antigen results in the expansion of the CD44+ (memory) T-cell subset. These memory T cells or autolymphocytes (ALT cells) mediate in vivo specificity when infused into murine TBH. To determine if cyclophosphamide (CY) could enhance the effectiveness of these ALT cells, C57BL/6J TBH with B16 melanoma or Lewis lung (3LL) carcinoma were treated with adoptive chemoimmunotherapy (ACIT) consisting of ALT cells and varying doses of CY. ALT cells were derived from the splenocytes of C57BL/6J TBH with B16 melanoma or 3LL carcinoma and activated ex vivo with T3CS. 3LL or B16 TBH received ALT cells derived from 3LL TBH splenocytes, B16 TBH splenocytes, CY alone, or ACIT with ALT cells and CY. Significantly greater antitumor activity as demonstrated by a decreased number of lung metastases (Day 21) and cure of primary and metastatic disease (Day 100) was seen in B16 or 3LL TBH that received ACIT using CY with B16-derived and 3LL-derived ALT cells, respectively, rather than ALT cells alone, CY alone, or ACIT with CY and reciprocal tumor-derived ALT cells. TBH cured by ACIT using CY and ALT cells derived from syngeneic TBH with the identical tumor displayed tumor-specific immunity as they were able to reject a lethal challenge of their previous B16 or 3LL tumor but not reciprocal tumors. TBH cured by ACIT using CY and ALT cells derived from splenocytes of syngeneic TBH with reciprocal tumors were able to reject lethal challenges of both tumors. These data demonstrate that effective ACIT using CY combined with ex vivo T3CS-activated CD44+ memory T cells from TBH conveys long-term tumor-specific immunity.

Pretransplant and posttransplant antibodies in human corneal transplantation.

The purpose of this study was to measure the association between antibody formation and endothelial corneal allograft reactions in 533 consecutive corneal graft recipients. The median follow-up time of these recipients was 732 days. Pretransplant panel-reactive antibodies were not found to be associated with endothelial corneal allograft reactions. Out of 533 recipients, 239 developed posttransplant antibodies during the course of this study. The formation of posttransplant antibodies was frequent in recipients with pretransplant antibodies and in HLA-A,-B-incompatible recipients. Posttransplant antibodies most often appeared within the first six months after transplantation whereas endothelial allograft reactions most often occurred later. Out of 65 recipients who developed PPRA and underwent an allograft reaction, 53 had a PPRA peak prior to, or at about the time of, the allograft reaction. Corneal allograft reaction events diagnosed during the second and third year after surgery were correlated with PPRA formation during the first year after grafting. The 36-month reaction-free survival rate of transplants was estimated at 72% in recipients with PPRA compared with 86% in recipients without PPRA (log rank P value = 0.002). Furthermore, posttransplant antibody formation altered the outcome of corneal allografts in both HLA-A and -B-compatible and -incompatible recipients. These findings suggest that posttransplant antibody development represents a high risk of endothelial corneal allograft reactions.

Determinación de anticuerpos y aloanticuerpos linfocitoxicos en pacientes candidatos a trasplante renal

Las pruebas cruzadas para detectar la presencia de anticuerpos linfocitotóxicos en el suero de candidatos a trasplante renal, son decisivas en el estudio pretrasplante. En el presente estudio se reportan los hallazgos en 97 pacientes con insificiencia renal crónica, candidatos a trasplantes y 127 posibles donantes vivos relacionados. Las pruebas incluyerón detección de anticuerpos antilifocitos T y B separadamente a 4,20 y 37 grados contra linfocitos del posible donante y contra las células autólogas. Se incluye además el tratamiento con ditiotreitol (DTT) para diferenciar entre los isotopos IgM e IgG. Los resultados muestran que 40.2 por ciento de los pacientes y 16.5 por ciento (p<=0.04) de los donantes clínicamente sanos tiene anticuerpos que pueden reaccionar con células alogénicas. Los aloanticuerpos se dectectaron en 38 por ciento de los pacientes. La mayoria de los anticuerpos estaban dirigidos contra los linfocitos B (71.7 por ciento) y correspondieron al isotipo IgM (66.7 por ciento), aunque tambien se detectaron tanto auto como aloanticuerpos IgG.No se detectó un efecto significativo de las trasfuciones o embarazos previos en el desarrollo de anticuerpos ni de aloanticuerpos. De otro lado se observó una frecuencia significativamente mayor (p=0.0009) de donantes intrafamiliares con autoanticuerpos positivos, en pacientes tambien positivos para autoanticuerpos que de receptores negativos para autoanticuerpos positivos que fueron trasplantados con riñones provenientes de sus donantes intrafamiliares o de cadáver, tienen sus injertos funcionantes hasta un año después. Los pacientes sin autoanticuerpos presentaron una menor sobrevida de sus injertos especialmente en el caso de los injertos de cadáver, de los cuales soló sobrevivió la tercera parte después de un año. Los resultados hacen énfasis en la necesidad de realizar las pruebas cruzadas previas al trasplante en condiciones que permitan obtener la mayor información posible sobre los anticuerpos linfocitotóxicos presentes en el suero de los pacientes candidatos a trasplante renal.

Treatment of adults with severe aplastic anemia: primary therapy with antithymocyte globulin (ATG) and rescue of ATG failures with bone marrow transplantation.

PURPOSE: To evaluate a policy of immunosuppression with antithymocyte globulin (ATG) as primary therapy for adults with severe aplastic anemia (SAA) regardless of the availability of an HLA-identical bone marrow donor. PATIENTS AND METHODS: Thirty-one consecutive adults with SAA who satisfied the age criteria for allogeneic bone marrow transplantation (BMT) (age less than 51 years) were treated with ATG 20 mg/kg/day for 10 days along with high-dose corticosteroids. Patients with an HLA-identical donor received a transplant if they did not respond to ATG or if they developed life-threatening complications during or soon after ATG administration. Eight patients with no response to ATG were also treated with oral cyclosporine 12.5 mg/kg/day. RESULTS: Eleven patients had a complete and five a partial response to ATG; two patients improved with cyclosporine treatment, resulting in an overall response rate of 58% to immunosuppression. Nine of 14 patients with donors received a BMT: seven because they did not respond to ATG and two because of serious infections. Seven grafts were obtained from related and two from unrelated donors. There was no significant difference in survival between those with and without a related HLA-identical donor (log-rank p value = 0.969). At a median follow-up of 58 months, 26 of 31 are alive with an actuarial survival of 80% at 5 years. Two patients died of infection, two died from complications of BMT, and one remains transfusion-dependent. One patient died of refractory leukemia at 30 months; one patient relapsed with hypoplasia 95 months after initial therapy with ATG. He showed a complete response to treatment with cyclosporine. No other late hematologic events have occurred. CONCLUSIONS: This treatment approach resulted in the restoration of hematopoiesis and independence from transfusion in 80% of patients with SAA entered into the study. The efficacy of allogeneic BMT in salvaging cases in which ATG failed does not appear to be compromised. Follow-up for the development of clonal hematologic disorders remains an important part of this treatment policy.

The quality of initial function following renal transplantation determined by creatinine elimination kinetics. Comparison of Minnesota antilymphocyte globulin and cyclosporine induction immunosuppression.

To compare the effect of type of induction immunosuppression on the quality of initial renal allograft function, we identified 35 cadaver donor kidney pairs in which one recipient of a kidney from a given pair received induction immunosuppression with Minnesota antilymphocyte globulin (MALG group) while the recipient of the contra-lateral kidney received cyclosporine from day zero (CsA group). In the absence of an existing quantitative measure to assess and compare the status of those grafts that function primarily, we defined the half-life of creatinine elimination (t1/2SCr) as such an outcome measure based on a review of creatinine elimination kinetics. All organs were procured with in-situ perfusion and en-bloc removal. Total cold storage times, rewarm times, and perioperative management were comparable for the two groups. In the MALG group, the mean t1/2SCr) was not different from that in the CsA group (1.38 +/- 0.96 days vs 1.35 +/- 1.2 days P = NS). Multiple regression analysis performed on the differences in recipient age, number of DR-B locus matches, total cold ischemia time, rewarm time, and central venous pressure at reperfusion of a given donor pair demonstrated no significant impact of any of these differences on the difference in t1/2SCr for the same pair set in this sample. The nadir of serum creatinine achieved in the first five days posttransplant was somewhat higher in the CsA group (234 +/- 131 mumol/L) as compared with the MALG group (200 +/- 132 mumol/L) but the difference was not significant. A similar nonsignificant trend was observed in the comparison of mean serum creatinine values at 30 days posttransplant (MALG group: 158 +/- 62 mumol/L vs. CsA group: 200 +/- 141 mumol/L). Only one of seventy recipients (CsA group) was dialyzed within the first 5 days posttransplant for an overall incidence of ATN of less than 2%. Fourteen of 35 (40%) recipients in both groups received treatment for acute rejection. The mean time to first treatment for acute rejection episode was shorter in the CsA group than the MALG group (10 +/- 8 days vs 23 +/- 24 days, P = 0.055). Graft survival at one year was not different for the two groups (92% vs. 87% for the MALG and CsA groups respectively, P = NS).(ABSTRACT TRUNCATED AT 400 WORDS)

Murine antiidiotypic monoclonal antibodies that bear the internal image of HLA-DR allospecificities.

Hybridization of murine myeloma cells P3-X63-Ag8.653 with splenocytes from a BALB/c mouse immunized with the syngeneic anti HLA-DR1,4,w6,w8,w9 MAb AC1.59 resulted in the development of 108 hybridomas secreting antiidiotypic antibodies. 100 of them inhibited the binding of MAb AC1.59 to target cells. Detailed analysis of the antiidiotypic MAb F5-444, F5-830, F5-963, F5-1126, F5-1336, and F5-1419 showed that all of them recognize idiotopes within or spatially close to the antigen combining site of MAb AC1.59. In cross-blocking experiments, the six antiidiotypic MAbs cross-blocked each other. It is likely that the six MAbs recognize spatially close, but not identical idiotopes because they elicited antiantiidiotypic antibodies of different or similar, but not identical specificity and differ in their ability to elicit anti-HLA class II antibodies. The latter, which were found only in sera from BALB/c mice immunized with antiidiotypic MAb F5-444 and F5-830, mimic the specificity of MAb AC1.59 and express the idiotope defined by the immunizing antiidiotypic MAb. These results indicate that the MAb F5-444 and F5-830 are antiidiotypes beta and the remaining four are antiidiotypes gamma.

Inhibitory effect of anti-class II antibody on the spontaneous activation of B cells in patients with systemic lupus erythematosus. Analysis with IL-1 production and IL-1 receptor expression.

The mechanism of the spontaneous activation of B cells in patients with SLE was analyzed from the standpoint of the production of IL-1 from B cells and the expression of IL-1R on B cells. SLE B cells spontaneously produced IL-1-like factors which stimulated murine thymocyte proliferative responses. Their m.w. was about 17,000 and their isoelectric point was 4.8. The IL-1-like activity produced by B cells was absorbed with rabbit anti-IL-1 alpha antibody, but not with anti-IL-1 beta antibody. The differentiation of SLE B cells was enhanced by rIL-1 alpha, beta or IL-1-like factors produced by SLE B cells in a concentration-dependent manner. SLE B cells expressed large number of IL-1R detected by FITC-conjugated IL-1 alpha. By a Percoll gradient density centrifugation, IL-1-producing cells and B cells responsive to IL-1 were enriched in a higher density fraction, but were reduced in a lower density fraction. IL-1R-positive B cells were enriched in the lower density fraction, but were depleted in the higher density fraction. However, the expression of IL-1R on the lower density B cells was reduced by 2-day culture. The expression of IL-1R on the higher density B cells was increased during a 2-day culture. Anti-class II antibody inhibited the production of IL-1R on the higher density B cells. These results suggest that the cellular interaction among B precursor cells mediated by class II Ag induces the production of IL-1 and the expression of its receptors on their surface and the interaction between IL-1 and its receptors stimulates B precursor cells to spontaneously differentiate into Ig-producing cells as an autocrine mechanism in patients with SLE.

Anti-Qa-2-induced T cell activation. The parameters of activation, the definition of mitogenic and nonmitogenic antibodies, and the differential effects on CD4+ vs CD8+ T cells.

The MHC Ag Qa-2 is a glycolipid anchored class I molecule expressed at high levels on all peripheral T lymphocytes. In this study we found that anti-Qa-2 antibodies could stimulate the proliferation of murine T cells in vitro. Anti-Qa-2-induced proliferation required secondary cross-linking with anti-Ig antibody and the presence of PMA. Only Qa-2+ strains could be induced to proliferate by anti-Qa-2 antibody, but under the conditions employed, anti-CD3 could induce proliferation in Qa-2+ and Qa-2-strains. Interestingly, only anti-Qa-2 reagents directed against the alpha 3 domain of the Qa-2 class I molecule were effective in inducing proliferation. Furthermore, unlike purified CD4+ cells, purified CD8+ cells were unable to be stimulated by the anti-Qa-2 antibodies. These results lead to the inclusion of Qa-2 in a group of physiologically relevant, glycolipid-anchored, cell-surface molecules, mobilization of which can generate signals that initiate the proliferation of T cells. Such molecules may play a secondary role in cellular activation after the primary engagement of the TCR.

Common epitope in human immunodeficiency virus (HIV) I-GP41 and HLA class II elicits immunosuppressive autoantibodies capable of contributing to immune dysfunction in HIV I-infected individuals.

We previously reported the identification of highly conserved homologous regions located in the carboxy terminus of the HIV I gp41-envelope (aa 837-844), and the amino-terminal of the beta chain of all human HLA class II antigens (aa 19-25). Murine monoclonal antibodies, raised against synthetic peptides from these homologous regions, bound not only to the isolated peptides, but also to the native gp160 and class II molecules. In this study one-third of sera from HIV I-infected individuals, at different disease stages, were found to react with both the gp41 and class II-derived peptides. These sera also reacted with "native" HLA class II molecules. The potential affects of such autoantibodies on normal immune functions were examined. It was found that in the presence of class II-cross-reactive (but not control) sera, the proliferative responses of normal CD4+ T cells to tetanus toxoid and allogeneic stimuli were markedly decreased. In addition, these sera could eliminate class II-bearing cells by antibody dependent cellular cytotoxicity. Similar affects were seen with affinity-purified IgG antibodies from patients' sera. Thus, the "molecular mimicry" between HIV I and HLA class II antigens, may lead to the generation of autoantibodies in HIV I-infected individuals that may contribute to the early functional impairment of CD4+ T cell observed in many HIV I-infected individuals.

Comparison of rat and rat-mouse chimeric anti-murine CD4 antibodies in vitro. Chimeric antibodies lyse low-density CD4+ cells.

GK1.5, a rat anti-mouse CD4 mAb, is effective in the treatment of several autoimmune syndromes, induces tolerance to co-administered Ag, and prolongs allograft survival. We have constructed a family of molecules with GK1.5 V regions and mouse gamma 1, gamma 2a, gamma 2b, or gamma 3 constant regions to investigate the mechanisms underlying the effectiveness of GK1.5. The rat-mouse chimeric antibodies are specific for murine CD4 and have identical binding curves as rat GK1.5 on CD4+ T cells. The chimeric GK1.5 gamma 2a, GK1.5 gamma 2b, and GK1.5 gamma 3 antibodies are more efficient than rat GK1.5 at C-mediated cytotoxicity. This is attributed to the enhanced capacity of the chimeric antibodies, compared to rat GK1.5, to lyse CD4+ cells with a low cell surface Ag density. This observation may have important implications for therapy.

The improved lytic function and in vivo efficacy of monovalent monoclonal CD3 antibodies.

A series of hybrid-hybridomas were derived by the cell fusion of a CD3 antibody-secreting hybridoma with other Ig-producing cell lines. The Ig molecules secreted by these hybrid-hybridomas were fractionated by ion-exchange chromatography, and fractions containing monovalent CD3 antibodies were tested for complement-mediated lysis of T cells. Two monovalent CD3 antibodies with mixed heavy chain isotypes were very poor in lysis but, in contrast, a monovalent antibody possessing two identical rat gamma 2b heavy chains but two non-identical light chains was found to be more lytic with human complement than the parental bivalent CD3 antibody. The difference in lysis was not readily explicable in terms of a difference in complement activation at the level of C1q binding or cell-associated C3. A highly purified batch of this lytic monovalent CD3 antibody was prepared in a form suitable for in vivo therapy. In a preliminary clinical study in one patient with a T lymphoma in leukemic phase this monovalent CD3 antibody was found to be very effective in depleting CD3+ tumor cells in the peripheral blood and bone marrow. The cells in the peripheral blood were completely cleared and there was no evidence for antigenic modulation. In addition the antibody was able to reverse cell-mediated kidney rejection in three kidney graft patients. These results suggest that monovalent antibody may be effective in vivo as well as in vitro and that a fuller clinical evaluation is justified.

In vitro fixation of C3d and C5b-9 on platelets by human platelet reactive antibodies.

Most platelet-reactive autoantibodies and alloantibodies are not able to fix complement in vitro. However, exceptions have been found. These antibodies are usually characterized by the conventional platelet complement fixation test. A recently developed competitive enzyme immunoassay for quantitation of platelet-associated immunoglobulins and a modification thereof allowed the quantitative study of fixation of C3d and the membrane attack complex (C5b-9) on platelets by HLA antibodies, human platelet autoantibodies, and drug-dependent antibodies (ddab). The highest amounts of both complement products were fixed through ddabs, whereas autoantibodies only showed moderate complement fixation. This enzyme immunoassay is a valuable tool for the characterization of the complement-fixing properties of platelet-reactive antibodies.

Resting human peripheral blood lymphocytes can be activated to cytolytic function by antibodies to CD3 in the absence of exogenous interleukin-2.

We investigated the ability of anti-CD3 antibodies to activate resting human peripheral blood lymphocytes (PBL) to a cytolytic function. We found that two anti-CD3 antibodies, but not an anti-CD4, anti-CD8, or anti-CD2 antibody, could activate resting unseparated PBL to become killer cells in the absence of exogenous interleukin-2 (IL-2), although exogenous recombinant IL-2 (rIL-2) synergized with anti-CD3. We also found that these anti-CD3 antibodies were active in the absence of rIL-2 only when linked to a solid surface such as a Sepharose bead or a plastic tissue culture plate. Cytolytic activity was measured in several ways: (i) by the ability of activated PBL to lyse the NK-sensitive line K562, and (ii) by the ability of these cells to lyse a CD10+ (CALLA+), NK-resistant target in the presence of either concanavalin A (lectin-dependent lysis) or an anti-CD10-anti-CD3 heterodimer. At least two different types of cytolytic cells were activated by anti-CD3 antibodies, an NK-like cell, which was CD2+CD3-CD4-CD8-CD16+-NKH1a+, and a CTL-like cell, which was CD2+CD3+CD4-CD8+CD16-NKH1a-. The former cell lysed the K562 line and the latter cell lysed Namalwa in the presence of the anti-CD10-anti-CD3 heterodimer or concanavalin A. The NK-like cell was probably activated by endogenous IL-2 produced by the anti-CD3-activated CD3+ cells and both the NK and CTL-like cells required the presence of adherent cells for maximal activity. The dose response and the kinetics of anti-CD3 activation of PBL to cytolytic activity were also studied. The use of the anti-CD3-activated cytolytic cells as effectors in anti-CD3 heterodimer-mediated lysis of tumor cells may be a novel approach to the therapy of cancer, and a comparison with the well-studied rIL-2/lymphokine-activated killer (LAK) system is discussed.