Active immunization of humans with dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells specialized to initiate T-cell immunity. The development of methods to generate large numbers of DCs has facilitated their application for immunotherapy. Recent studies have demonstrated the safety and immunogenicity of DCs in humans and have begun to outline the durability, kinetics, and nature of the elicited T-cell responses. However, DC-based immunotherapy remains a challenge and several parameters need to be examined to optimize immune responses, in order to maximize clinical efficacy against cancer and infectious diseases.

Intra-articular clonidine vs. morphine for post-operative analgesia following arthroscopic knee surgery (a comparative evaluation)

In a prospective, double-blind, randomised study, 30 ASA I patients were allocated to three groups in an attempt to find out the best post-operative analgesic following arthroscopic knee surgery under epidural anaesthesia. Group I patients received 5 mg of preservative-free morphine in 20 ml of normal saline, group II patients received 150 µg of clonidine in 20 ml of normal saline and group III patients received 20 ml of normal saline only. The post-operative pain was evaluated by a visual analogue scale and the need for rescue analgesic was assessed post-operatively for 12 h. We conclude that intra-articular administration of 150 µg of clonidine gives a longer lasting pain relief post-operatively (4-12 h) as compared to 5 mg of preservative-free morphine (3 h). No side effects were noted with either of the drugs.

Mature dendritic cells boost functionally superior CD8(+) T-cell in humans without foreign helper epitopes

We have recently shown that a single injection of mature, antigen-pulsed, human dendritic cells (DCs) rapidly elicits CD4(+) and CD8(+) T-cell immunity in vivo. The DCs were pulsed with 2 foreign proteins, keyhole limpet hemocyanin (KLH) and tetanus toxoid (TT), as well as an HLA A2.1-restricted influenza matrix peptide (MP). Responses to all 3 antigens peaked at 30-90 days after immunization and declined thereafter. To determine if the foreign helper proteins (TT and KLH) were essential for CD8(+) T-cell responses to the viral peptide, we reinjected 3 of the HLA-2.1 subjects with mature DCs pulsed with MP alone. All 3 volunteers showed a rapid boost in MP-specific immunity, and freshly sampled blood from 1 contained cytolytic T cells. In all 3 subjects, CD8(+) T-cell responses to booster DCs were faster and of greater magnitude than the responses to the first DC injection. Importantly, the T cells that proliferated after booster DC treatment secreted interferon-gamma upon challenge with much lower doses of viral peptide than those elicited after the first injection, indicating a higher functional avidity for the ligand. These data begin to outline the kinetics of T-cell immunity in response to DCs and demonstrate that booster injections of mature DCs enhance both qualitative and quantitative aspects of CD8(+) T-cell function in humans.

Identification of subdominant cytotoxic T lymphocyte epitopes encoded by autologous HIV type 1 sequences, using dendritic cell stimulation and computer-driven algorithm

Conventional analysis of the cytotoxic T lymphocyte (CTL) response to HIV-1 may underestimate the true breadth of CTL epitopes recognized. This underestimation could be due to several reasons, including (1) the use of laboratory-adapted stains of HIV or consensus sequences, which would lead to the identification of only highly conserved epitopes, (2) the use of EBV-transformed B cells (B-LCLs) and vaccinia virus constructs in standard assays that may obscure low level CTL responses due to high EBV or vaccinia reactivity, and (3) relatively insensitive assays wherein PBMCs instead of professional APCs are used to stimulate CTL responses. To address these problems, we first identified an immunodominant HLA-B7-restricted CTL epitope, by standard cloning methods, in a long-term nonprogressor (LTNP). To determine whether the patient had CTLs specific for autologous viral sequences other than the dominant epitope, proviral DNA was cloned and sequenced. A matrix-based epitope algorithm (EpiMatrix) was used to identify the top 2% of peptides from the viral sequences with the highest likelihood of binding to HLA-B7. These 55 peptides were synthesized and tested for HLA-B7 binding in a T2/B7 cell line; 10 peptides were able to stabilize HLA-B7 on the cell surface. By using peptide-pulsed autologous dendritic cells as a more sensitive method of CTL stimulation, we found three additional subdominant CTL epitopes.

Vaccinia virus inhibits the maturation of human dendritic cells: a novel mechanism of immune evasion

Vaccinia virus employs multiple mechanisms to evade the immune system, yet is highly immunogenic. We studied the interaction between vaccinia and human dendritic cells (DCs), potent APCs. DCs develop from precursor cells in two stages: an immature stage in which Ag uptake and processing occur, and a mature stage in which there is up-regulation of costimulatory and HLA molecules and efficient T cell activation. Vaccinia virus undergoes an abortive replication in both stages of DCs and induces apoptotic cell death. Furthermore, maturation of immature DCs and consequently T cell activation are inhibited. Obstruction of DC maturation may constitute a novel mechanism by which vaccinia attempts to evade the immune response.

Communicating bronchopulmonary pancreatic foregut malformation

Bronchopulmonary foregut malformations include intralobar and extralobar pulmonary sequestrations, bronchogenic cysts, and communicating bronchopulmonary foregut malformations (CBPFM). These malformations, formes frustes, originate as developmental abnormalities of ventral foregut budding of the tracheobronchial tree or the gastrointestinal tract. The communication's patency with the parent viscus determines if a contained malformation occurs, or if an abnormal communication persists as a CBPFM. This case demonstrates a unique example of a CBPFM in which the main pancreatic duct communicated with pulmonary parenchyma through a retroperitoneal fistula.

Presentation of epstein-barr virus latency antigens to CD8(+), interferon-gamma-secreting, T lymphocytes

Epstein-Barr virus (EBV) infects more than 95 % of the human population and causes an asymptomatic life-long infection in the majority of EBV carriers. Cell-mediated immunity provides resistance to EBV, as demonstrated by the occurrence of EBV-induced post-transplant lymphoproliferative disease in immunosuppressed patients. Here we looked for IFN-gamma-producing T lymphocytes in the blood of healthy donors with a rapid enzyme-linked immunospot (ELISPOT) assay, comparing as antigen presenting cells monocytes and dendritic cells (DC) infected with recombinant vaccinia virus (rVV). We found a strong CD8(+) ELISPOT response to one or more of the EBNA 3A, 3B and 3C antigens in the PBMC from 14 / 18 donors. The sensitivity of the overnight ELISPOT assay was increased using DC as antigen-presenting cells, including 3 / 3 individuals who lacked ELISPOT in PBMC. In addition, DC could markedly expand EBV-specific spots after a 7-day culture. In a smaller number of donors, we documented recognition of the subdominant LMP 1, LMP 2 and EBNA 1 antigens that are expressed in a variety of EBV-associated malignancies. Therefore our data provide more evidence for the efficacy of DC in eliciting rapid responses to EBV latency antigens in circulating CD8(+) T cells.

Dendritic cells are resistant to apoptosis through the Fas (CD95/APO-1) pathway

Immunoregulation of lymphocytes and macrophages in the peripheral immune system is achieved in part by activation-induced cell death. Members of the TNF receptor family including Fas (CD95) are involved in the regulation of activation-induced cell death. To determine whether activation-induced cell death plays a role in regulation of dendritic cells (DCs), we examined interactions between Ag-presenting murine DCs and Ag-specific Th1 CD4+ T cells. Whereas mature bone marrow- or spleen-derived DCs expressed high levels of Fas, these DCs were relatively insensitive to Fas-mediated killing by the agonist mAb, Jo-2, as well as authentic Fas ligand expressed on the CD4+ T cell line, A.E7. The insensitivity to Fas-mediated apoptosis was not affected by priming with IFN-gamma and/or TNF-alpha or by blocking the DC survival signals TNF-related activation-induced cytokine and CD40L. However, apoptosis could be induced with C2-ceramide, suggesting that signals proximal to the generation of ceramide might mediate resistance to Fas. Analysis of protein expression of several anti-apoptotic mediators revealed that expression of the intracellular inhibitor of apoptosis Fas-associated death domain-like IL-1-converting enzyme-inhibitory protein was significantly higher in Fas-resistant DCs than in Fas-sensitive macrophages, suggesting a possible role for Fas-associated death domain-like IL-1-converting enzyme-inhibitory protein in DC resistance to Fas-mediated apoptosis. Our results demonstrate that murine DCs differ significantly from other APC populations in susceptibility to Fas-mediated apoptosis during cognate presentation of Ag. Because DCs are most notable for initiation of an immune response, resistance to apoptosis may contribute to this function.

Induction of Epstein-Barr virus-specific cytotoxic T-lymphocyte responses using dendritic cells pulsed with EBNA-3A peptides or UV-inactivated, recombinant EBNA-3A vaccinia virus

Cell-mediated immunity, especially the cytotoxic T lymphocyte (CTL), provides resistance to Epstein-Barr virus (EBV), as is demonstrated by the occurrence of posttransplant lymphoproliferative disease in immunosuppressed patients. We set out to use dendritic cells (DCs) to elicit anti-EBV-specific CTLs in culture. In unselected, HLA-B8(+) donors, monocyte-derived mature DCs were pulsed with the HLA-B8-restricted EBNA-3A peptide, FLRGRAYGL, and added to autologous T cells for 7 days at a DC:T ratio of 1:5 to 1:60. The cultured cells specifically lysed EBNA-3A peptide-pulsed, HLA-B8(+), B-lymphoblastoid cell lines in a 5-hour (51)Cr-release assay. The generation of CTLs did not require the addition of interleukin-2. In comparison, monocytes were weak antigen-presenting cells. DCs were then infected with recombinant vaccinia-EBNA-3A. Vaccinia infection significantly decreased the viability of immature DCs after 3 days of culture (to 25% to 45%) but had a smaller effect on mature DC recovery (40% to 70%). To decrease these cytopathic effects and to expand the potential use of vaccinia vectors for DC therapy in immunocompromised patients, we successfully used psoralen and UV-inactivated virus. Mature DCs pulsed with either live or inactivated vaccinia EBNA-3A virus could elicit strong EBNA-3A-specific CTLs. Therefore, mature DCs are powerful stimulators of EBV-specific CTLs and their major histocompatibility complex class I products can even be charged with UV-inactivated recombinant vaccinia.

Changes in frequency of HIV-1-specific cytotoxic T cell precursors and circulating effectors after combination antiretroviral therapy in children

Combination antiretroviral therapy has had a major role in reducing human immunodeficiency virus type 1 (HIV-1) plasma viral loads in HIV-1-infected adults but a variable effect in infants, in whom complete viral suppression appears to be less readily achieved. In adults, after the reduction in plasma viremia, there is a decrease in the numbers of circulating cytotoxic T cell (CTL) effectors and precursors in the majority of patients. This longitudinal study assessed the effect of combination drug therapy on the frequency of HIV-1-specific CTL responses in 8 HIV-1-infected children. Following treatment, the frequency of HIV-1-specific CTL responses initially increased, especially in children with incomplete viral suppression but with increasing CD4+ cell counts. In children with complete viral suppression, the frequency of HIV-1-specific CTL responses decreased, suggesting that viral replication is required to maintain CTL responses in the systemic circulation.

Rapid generation of broad T-cell immunity in humans after a single injection of mature dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells that initiate protective T-cell immunity in mice. To study the immunogenicity of DCs in humans, we injected 9 healthy subjects subcutaneously with a control injection of autologous monocyte-derived, mature DCs, followed 4-6 weeks later by DCs pulsed with keyhole limpet hemocyanin (KLH), HLA-A*0201-positive restricted influenza matrix peptide (MP), and tetanus toxoid (TT). Four more subjects received these antigens without DCs. Injection of unpulsed DCs, or antigens alone, failed to immunize. Priming of CD4(+) T cells to KLH was observed in all 9 subjects injected with KLH-pulsed DCs, and boosting of TT-specific T-cell immunity was seen in 5 of 6 subjects injected with TT-pulsed DCs. Injection of antigen-pulsed DCs led to a severalfold increase in freshly isolated MP-specific, IFN-gamma-secreting CD8(+) T cells in all 6 HLA-A*0201-positive subjects, as early as 7 days after injection. When T cells were boosted in culture, there was an increase in MHC tetramer-binding cells and cytotoxic T cells after DC vaccination. These data provide the first controlled evidence of the immunogenicity of DCs in humans, and demonstrate that a single injection of mature DCs rapidly expands T-cell immunity.

A recombinant vaccinia virus based ELISPOT assay detects high frequencies of Pol-specific CD8 T cells in HIV-1-positive individuals

OBJECTIVES

HIV-1-specific CD8 T cells are considered to be critical in anti-HIV responses. It is important to quantify these cells and to determine their antigenic targets. Here quantification of interferon (IFN)-gamma secreting, virus-specific cells was achieved with an enzyme linked immuno spot (ELISPOT) assay.

METHODS

Peripheral blood mononuclear cells (PBMC) were infected with recombinant vaccinia vectors expressing HIV-1 genes (gag, pol, env or nef) and added to wells precoated with anti-IFN-gamma monoclonal antibodies. Spot forming cells (SFC), i.e. antigen-specific T cells were detected 24 h later by the addition of biotinylated anti-IFN-gamma monoclonal antibodies, followed by avidin-bound biotinylated horseradish peroxidase.

RESULTS

In a cohort of 19 patients, of whom 15 were on highly active antiretroviral therapy, 18 had primed T cells directed against one or more HIV-1 antigens (P < 0.0001). Pol-specific T cells routinely dominated the CD8 response with frequencies up to 2000 SFC per 10(6) PBMC. In HLA A*0201-positive patients, the vaccinia vectors detected much higher frequencies of SFC than haplotype-restricted peptides. Elimination of CD8 T cells resulted in > 90% loss of antigen-specific SFC when vaccinia virus was used as a vector. The number of CD8 SFC exceeded the number of memory cells detected in limiting dilution assays by > 1 log10, whereas a correlation was found between the frequency of effector cells detected by both ELISPOT and MHC class I peptide tetramer assays.

CONCLUSIONS

Vaccinia virus vectors used in ELISPOT assays are useful for determining the frequency and specificity of CD8 T cells for individual HIV-1 gene products. The dominance of cytolytic T lymphocytes (CTL) recognizing pol proteins suggests that this antigen should be considered in vaccine strategies.

Dendritic cells generated from blood monocytes of HIV-1 patients are not infected and act as competent antigen presenting cells eliciting potent T-cell responses

The CTL response to HIV-I can be vigorous, but antigen presenting cell requirements have not been studied in detail. To approach this question, we have examined the dendritic cell populations that can be obtained from the blood of HIV-1 infected individuals. We studied 13 asymptomatic patients, who spanned a wide range of plasma viremia and CD4 counts. We show here that sizeable numbers of mature dendritic cells can be generated from nonproliferating progenitors in the blood of HIV + patients using a recently developed approach. The procedure involves two steps. The first step or 'priming' phase is a 7 day culture of T-cell depleted mononuclear cells in medium supplemented with GM-CSF and IL-4. The second step or 'differentiation' phase requires the exposure to monocyte conditioned medium. The yields of DCs from HIV + individuals were comparable to normal blood donors, 0.4 - 3 x 10(6) mature dendritic cells from 50 ml of blood. Strong APC function was evident for both the proliferation of allogeneic T-cells in the MLR, and the generation by syngeneic T-cells of class I restricted, CTL responses to influenza virus. A panel of dendritic cell restricted markers are expressed, including CD83, p55, and perinuclear CD68. By semi-quantitative PCR analysis, the cytokine derived cells did not express HIV-1 DNA. We suggest that these blood derived dendritic cells will be effective for studies of immune responses to HIV-1 antigens and may be considered as adjuvants for active immunotherapy.

Comparison of ondansetron with ondansetron and dexamethasone in prevention of PONV in diagnostic laparoscopy

PURPOSE

To compare the efficacy of ondansetron-dexamethasone combination with ondansetron alone for prevention of postoperative nausea and vomiting (PONV).

METHODS

This double blind, randomized study was carried out in 51 female patients, aged 20-40 yr, ASA-1 physical status undergoing gynecological diagnostic laparoscopy. Group 1 (n = 26) received 4 mg ondansetron i.v. and group 2 (n = 25) received a combination of 4 mg ondansetron and 8 mg dexamethasone i.v. soon after induction of anesthesia. Postoperatively patients were assessed hourly for four hours and then at 24 hr for nausea, vomiting, pain and post anesthetic discharge score. Vomiting occurring up to two hours was considered early vomiting and from 2-24 hr as delayed vomiting.

RESULTS

The postoperative nausea score was lower in patients receiving a combination of ondansetron and dexamethasone (3.76) than ondansetron alone (4.38) at 0 hr (P < 0.01), 2 hr (P < 0.05) and 24 hr (P < 0.01). In group 1, 38.5% of patients had a nausea score of > or = 5 (major nausea) compared with only 12% of patients in group 2 (P < 0.025). The overall incidence of vomiting was greater in group 1 (35%) than in group 2 (8%) (P < 0.05). The combination group showed better control of delayed vomiting compared with the ondansetron group (4% vs 35%) (P < 0.01).

CONCLUSION

The combination of ondansetron and dexamethasone provides adequate control of PONV, with delayed PONV being better controlled than early PONV.

Efficient presentation of phagocytosed cellular fragments on the major histocompatibility complex class II products of dendritic cells

Cells from the bone marrow can present peptides that are derived from tumors, transplants, and self-tissues. Here we describe how dendritic cells (DCs) process phagocytosed cell fragments onto major histocompatibility complex (MHC) class II products with unusual efficacy. This was monitored with the Y-Ae monoclonal antibody that is specific for complexes of I-Ab MHC class II presenting a peptide derived from I-Ealpha. When immature DCs from I-Ab mice were cultured for 5-20 h with activated I-E+ B blasts, either necrotic or apoptotic, the DCs produced the epitope recognized by the Y-Ae monoclonal antibody and stimulated T cells reactive with the same MHC-peptide complex. Antigen transfer was also observed with human cells, where human histocompatibility leukocyte antigen (HLA)-DRalpha includes the same peptide sequence as mouse I-Ealpha. Antigen transfer was preceded by uptake of B cell fragments into MHC class II-rich compartments. Quantitation of the amount of I-E protein in the B cell fragments revealed that phagocytosed I-E was 1-10 thousand times more efficient in generating MHC-peptide complexes than preprocessed I-E peptide. When we injected different I-E- bearing cells into C57BL/6 mice to look for a similar phenomenon in vivo, we found that short-lived migrating DCs could be processed by most of the recipient DCs in the lymph node. The consequence of antigen transfer from migratory DCs to lymph node DCs is not yet known, but we suggest that in the steady state, i.e., in the absence of stimuli for DC maturation, this transfer leads to peripheral tolerance of the T cell repertoire to self.

Neutralizing monoclonal antibodies block human immunodeficiency virus type 1 infection of dendritic cells and transmission to T cells

Prevention of the initial infection of mucosal dendritic cells (DC) and interruption of the subsequent transmission of HIV-1 from DC to T cells are likely to be important attributes of an effective human immunodeficiency virus type 1 (HIV-1) vaccine. While anti-HIV-1 neutralizing antibodies have been difficult to elicit by immunization, there are several human monoclonal antibodies (MAbs) that effectively neutralize virus infection of activated T cells. We investigated the ability of three well-characterized neutralizing MAbs (IgG1b12, 2F5, and 2G12) to block HIV-1 infection of human DC. DC were generated from CD14(+) blood cells or obtained from cadaveric human skin. The MAbs prevented viral entry into purified DC and the ensuing productive infection in DC/T-cell cultures. When DC were first pulsed with HIV-1, MAbs blocked the subsequent transmission to unstimulated CD3(+) T cells. Thus, neutralizing antibodies can block HIV-1 infection of DC and the cell-to-cell transmission of virus from infected DC to T cells. These data suggest that neutralizing antibodies could interrupt the initial events associated with mucosal transmission and regional spread of HIV-1.

Tumor-specific killer cells in paraneoplastic cerebellar degeneration

Models for immune-mediated tumor regression in mice have defined an essential role for cytotoxic T lymphocytes (CTLs); however, naturally occurring tumor immunity in humans is poorly understood. Patients with paraneoplastic cerebellar degeneration (PCD) provide an opportunity to explore the mechanisms underlying tumor immunity to breast and ovarian cancer. Although tumor immunity and autoimmune neuronal degeneration in PCD correlates with a specific antibody response to the tumor and brain antigen cdr2, this humoral response has not been shown to be pathogenic. Here we present evidence for a specific cellular immune response in PCD patients. We have detected expanded populations of MHC class I-restricted cdr2-specific CTLs in the blood of 3/3 HLA-A2.1+ PCD patients, providing the first description, to our knowledge, of tumor-specific CTLs using primary human cells in a simple recall assay. Cross-presentation of apoptotic cells by dendritic cells also led to a potent CTL response. These results indicate a model whereby immature dendritic cells that engulf apoptotic tumor cells can mature and migrate to draining lymph organs where they could induce a CTL response to tissue-restricted antigens. In PCD, peripheral activation of cdr2-specific CTLs is likely to contribute to the subsequent development of the autoimmune neuronal degeneration.

Immature dendritic cells phagocytose apoptotic cells via alphavbeta5 and CD36, and cross-present antigens to cytotoxic T lymphocytes

Dendritic cells, but not macrophages, efficiently phagocytose apoptotic cells and cross-present viral, tumor, and self-antigens to CD8(+) T cells. This in vitro pathway corresponds to the in vivo phenomena of cross-priming and cross-tolerance. Here, we demonstrate that phagocytosis of apoptotic cells is restricted to the immature stage of dendritic cell (DC) development, and that this process is accompanied by the expression of a unique profile of receptors, in particular the alphavbeta5 integrin and CD36. Upon maturation, these receptors and, in turn, the phagocytic capacity of DCs, are downmodulated. Macrophages engulf apoptotic cells more efficiently than DCs, and although they express many receptors that mediate this uptake, they lack the alphavbeta5 integrin. Furthermore, in contrast to DCs, macrophages fail to cross-present antigenic material contained within the engulfed apoptotic cells. Thus, DCs use unique pathways for the phagocytosis, processing, and presentation of antigen derived from apoptotic cells on class I major histocompatibility complex. We suggest that the alphavbeta5 integrin plays a critical role in the trafficking of exogenous antigen by immature DCs in this cross-priming pathway.

Utility of transesophageal echocardiography during port-access minimally invasive cardiac surgery

In this study, we sought to determine the use of transesophageal echocardiography (TEE) as the primary imaging technique to assist in the placement of endovascular catheters during minimally invasive, port-access cardiac surgery. The recent development of endovascular catheters that are placed via the femoral artery and vein has enabled patients to be placed on cardiopulmonary bypass without the need for direct visualization of the heart or great vessels via sternotomy. This has allowed cardiac surgery to be performed through smaller thoracotomy incisions. Placement of these catheters has previously been performed with fluoroscopic guidance, which has major imaging limitations. Thirty-six patients underwent port-access cardiac surgery at our institution during the study period. All patients underwent intraoperative TEE. We used TEE to visualize the coronary sinus os, right atrium and superior vena cava, and thoracic aorta to assist with placement of the coronary sinus catheter, venous cannula, and endoaortic clamp. Twenty patients underwent mitral valve surgery, 14 patients coronary artery bypass grafting, 1 patient aortic valve replacement, and 1 patient repair of an atrial septal defect by the port-access approach. TEE was able to adequately visualize the cardiac structures and assist in the placement of the endovascular catheters in all patients. Fluoroscopy was only helpful as an aid to TEE for placement of the coronary sinus catheter. TEE is an excellent imaging modality for the proper placement of these new endovascular catheters, obviating the need for fluoroscopy, except to be on standby and for placement of the coronary sinus catheter.

Comparison of psychomotor functions and sedation following premedication with oral diazepam and clonidine in children

In a prospective, double-blind, controlled, randomized study, the psychomotor functions and sedation were assessed after premedication with diazepam and clonidine in children. Forty children in the age-group of 5-8 years, undergoing elective surgery under general anesthesia were studied. Twenty children (group 1) received oral clonidine 4 microg/kg, and 20 children (group 2) received oral diazepam 0.2 mg/kg, 120 minutes before induction of anesthesia. Sedation and psychomotor functions were assessed in both groups, before and after 60-90 minutes of administration of premedication. The results of the study showed that mean sedation score in group 1 was 8 +/- 1.07, and 9 +/- 0.64 in group 2. On intergroup comparison the sedation was found to be comparatively better in group 2 than group 1 (p < 0.05). The performance of psychomotor functions decreased after premedication in both the groups as compared to that before premedication (p < 0.05). The psychomotor functions were depressed more in diazepam group than in the clonidine group (p < 0.05). Thus, it is concluded that clonidine produces good sedation and causes less effect on psychomotor functions and therefore can be used for premedication in children.

Dendritic cells acquire antigen from apoptotic cells and induce class I-restricted CTLs

CD8+ cytotoxic T lymphocytes (CTLs) mediate resistance to infectious agents and tumours. Classically, CTLs recognize antigens that are localized in the cytoplasm of target cells, processed and presented as peptide complexes with class I molecules of the major histocompatibility complex (MHC). However, there is evidence for an exogenous pathway whereby antigens that are not expected to gain access to the cytoplasm are presented on MHC class I molecules. The most dramatic example is the in vivo phenomenon of cross-priming: antigens from donor cells are acquired by bone-marrow-derived host antigen-presenting cells (APCs) and presented on MHC class I molecules. Two unanswered questions concern the identity of this bone-marrow-derived cell and how such antigens are acquired. Here we show that human dendritic cells, but not macrophages, efficiently present antigen derived from apoptotic cells, stimulating class I-restricted CD8+ CTLs. Our findings suggest a mechanism by which potent APCs acquire antigens from tumours, transplants, infected cells, or even self-tissue, for stimulation or tolerization of CTLs.

Oculocardiac reflex during retinal surgery using peribulbar block and nitrous narcotic anesthesia

BACKGROUND AND OBJECTIVES

This study was designed to examine the effects of local and general anesthesia on the oculocardiac reflex (OCR) in adults during retinal detachment surgery, with an aim of determining the safest type of anesthesia and on which extraocular muscle traction causes a higher incidence of OCR.

PATIENTS AND METHODS

The study was performed on 30 American Society of Anesthesiologists-I patients (age range 40-60 years) who were undergoing retinal detachment surgery. Fifteen patients underwent surgery with general anesthesia and 15 were given a local peribulbar block. A fixed traction of 400 g was applied to all the extraocular muscles, and the heart rate, rhythm, and electrocardiogram of each patient was monitored.

RESULTS

The overall incidence of OCR was higher with general anesthesia (63.3%) than with local anesthesia (14.4%). There was a significant decrease in heart rate for the rectus muscles (P < .0005) as well as the oblique muscles (P < .005) during traction with general anesthesia. All four rectus muscles were equally sensitive in eliciting the reflex. The incidence of dysrhythmias was 20% with general anesthesia and 6.67% with local anesthesia.

CONCLUSION

This study showed that local anesthesia produces less bradycardia and ectopic arrhythmias and, therefore, may be safer and better than general anesthesia for surgeries in which traction of extraocular muscles is required.

The distinctive features of influenza virus infection of dendritic cells

CD8+ cytolytic T lymphocytes (CTLs) are considered to be critical mediators for resistance to influenza virus infection. We have previously demonstrated that dendritic cells are potent antigen presenting cells in the development of anti-influenza CTLs. Here we identify distinctive features of the interaction of influenza virus with dendritic cells. Exposure of dendritic cells to influenza virus at MOIs of 2-4:1 leads to > 90% infection, as manifested by the expression of the viral proteins HA and NS1. The infection is non-toxic as viral protein expression is sustained for > 2 days with retention of viability, but little infectious virus is produced. Substantial induction of the anti-viral cytokine IFN-alpha also occurs. Influenza infection of macrophages also results in viral protein expression in a majority of cells, and synthesis of IFN-alpha. In contrast to dendritic cells, macrophages display evidence of apoptosis within 10-12 hours, and the majority of cells die within 24-36 hours. During this interval macrophages synthesize > 10-fold higher levels of virus than dendritic cells. Infected dendritic cells but not macrophages, can induce substantial CTL responses from purified blood CD8+ T cells in the absence of exogenous cytokines such as IL-2. Low levels of infection (MOIs of 0.02) are sufficient to generate potent CTL responses. Influenza virus expressing non-cleaved HA does not elicit CTLs indicating that virus must access the cytoplasm of dendritic cells to utilize traditional class I processing pathways. These observations indicate that DCs are distinct in their handling of influenza virus and for the induction of anti-viral immunity.

Intraepidermal lymphocytes in psoriatic lesions are activated GMP-17(TIA-1)+CD8+CD3+ CTLs as determined by phenotypic analysis

The onset and persistence of psoriatic lesions are linked to the presence of an inflammatory infiltrate of CD3+ lymphocytes that includes CD4+ and CD8+ subsets. Since a primary susceptibility factor for psoriasis is the Class I HLA-Cw6 molecule, we set out to learn more about the features of the epidermal CD8+ lymphocytes. The markers tested were GMP-17, a cytotoxic granule protein found in activated cytotoxic lymphocytes (CTLs), and the alpha chain of the IL-2 receptor (CD25), a plasma membrane molecule found on activated T cells. Lymphocytes in lesional skin expressed the GMP-17 protein, whereas lymphocytes in non-lesional skin, resolving lesional skin and normal skin had little or no GMP-17. By flow cytometry analysis, lesional epidermal GMP-17+ cells were CD8+CD3+, with a subpopulation expressing the activation marker CD25+. Due to the abundance of activated GMP-17+CD8+CD3+ lymphocytes (the phenotype of activated cytotoxic cells) in psoriatic lesions compared to non-lesional and normal skin, we hypothesize that they are contributing directly to the psoriatic phenotype.

A monocyte conditioned medium is more effective than defined cytokines in mediating the terminal maturation of human dendritic cells

Mature human dendritic cells can be generated in substantial numbers from nonproliferating progenitors in human blood using a two-step protocol. T cell-depleted mononuclear cells are first cultured with granulocyte-macrophage colony-stimulating factor and interleukin-4 (IL-4) and then exposed to monocyte conditioned medium (MCM). The dendritic cells generated using this approach are rendered terminally mature and are the most potent antigen presenting cells identified to date in humans. We sought to characterize factors in MCM that induce the terminal differentiation of dendritic cells. MCM contained substantial, although varying, quantities of several factors including tumor necrosis factor-alpha, IL-1beta, IL-6, and interferon-alpha. However, none of the four factors, individually or in various combinations, could fully substitute for the MCM to generate irreversibly differentiated dendritic cells. The yields, percentage of cells expressing the mature phase marker CD83, and mixed leukocyte reaction-stimulatory function were lower when defined cytokines were used in the place of MCM. Therefore, the full maturation of dendritic cells, because it entails changes in many known cell and molecular properties, requires a number of different cytokines that are released in tandem from appropriately stimulated monocytes. We propose that MCM-matured dendritic cells will be the most effective adjuvants for immunotherapy in vivo.

Generation of monocyte-derived dendritic cells from precursors in rhesus macaque blood

While the dendritic cells (DCs) of mouse and man have been extensively studied, until recently those of non-human primates remained poorly characterized. We present a method for generating large numbers of DCs from precursors in rhesus macaque blood, based on techniques developed for human blood. For 7 days, a T cell-depleted population of mononuclear cells was cultured in 1% human plasma with GM-CSF and IL-4, both to initiate DC differentiation and to inhibit macrophage development. On day 7, 50% of the culture medium was replaced with a monocyte-conditioned medium (MCM), which is required for the final maturation of the DCs into potent stimulators of the allogeneic MLR. Between 0.5 and 1.0 x 10(6) DCs can be generated from 20 ml of rhesus macaque blood. We compared these cytokine-generated DCs to the adherent macrophages present in the same cultures. Cytokine-generated DCs were considerably more potent at stimulating allogeneic T cells than adherent macrophages. Furthermore, the DCs had a distinct morphology and phenotype, with long processes, high levels of p55, and a characteristic perinuclear collection of intracellular CD68. In contrast, adherent macrophages expressed very low levels of p55, and high diffuse levels of CD68. Macaque DCs generated by this method may be useful in vaccine development and for studies of SIV pathogenesis.

Comparative study of oral clonidine and diazepam as premedicants in children

In a prospective, double-blind, controlled study the efficacy of clonidine was assessed in children, with respect to sedation, intubation response, and recovery. Fifty children, aged 4-12 years, undergoing general anesthesia were studied. Twenty-five children (group I) received oral diazepam) 0.2 mg/kg and another 25 children (group II) received oral clonidine 3 micrograms/kg, 90-120 minutes before induction of anesthesia. The level of sedation, hemodynamic changes to laryngoscopy and intubation, the recovery from anesthesia were noted and compared between the groups. Clonidine 3 micrograms/kg produced sedation comparable to diazepam 0.2 mg/kg (p > 0.1). There was significant (p > 0.01) attenuation of hemodynamic intubation response with clonidine. The recovery with clonidine was not delayed (p < 0.01). Clinically significant hypotension and bradycardia were not observed in any of the patients. We conclude that clonidine 3 micrograms/kg produces sedation comparable to diazepam 0.2 mg/kg and also attenuates the intubation response without increasing the incidence of complications.

Dendritic cells as immunogens for human CTL responses

The cellular requirements for generating potent human CD8+ CTLs to influenza A virus in vitro have been defined. Furthermore, we have developed improved methods for generating large numbers of DCs from non-proliferating progenitors. These developments have enabled the design of new strategies to elicit CTLs in vivo. For example, together with IL-12, antigen-pulsed DCs may be a useful approach for boosting CTL responses against infectious agents and malignancies. Our results also reopen the potential use of inactivated virus preparations as immunogens for CTL responses.

Efficient interaction of HIV-1 with purified dendritic cells via multiple chemokine coreceptors

HIV-1 actively replicates in dendritic cell (DC)-T cell cocultures, but it has been difficult to demonstrate substantial infection of purified mature DCs. We now find that HIV-1 begins reverse transcription much more efficiently in DCs than T cells, even though T cells have higher levels of CD4 and gp120 binding. DCs isolated from skin or from blood precursors behave similarly. Several M-tropic strains and the T-tropic strain IIIB enter DCs efficiently, as assessed by the progressive formation of the early products of reverse transcription after a 90-min virus pulse at 37 degrees C. However, few late gag-containing sequences are detected, so that active viral replication does not occur. The formation of these early transcripts seems to follow entry of HIV-1, rather than binding of virions that contain viral DNA. Early transcripts are scarce if DCs are exposed to virus on ice for 4 h, or for 90 min at 37 degrees C, conditions which allow virus binding. Also the early transcripts once formed are insensitive to trypsin. The entry of a M-tropic isolates is blocked by the chemokine RANTES, and the entry of IIIB by SDF-1. RANTES interacts with CCR5 and SDF-1 with CXCR4 receptors. Entry of M-tropic but not T-tropic virus is ablated in DCs from individuals who lack a functional CCR5 receptor. DCs express more CCR5 and CXCR4 mRNA than T cells. Therefore, while HIV-1 does not replicate efficiently in mature DCs, viral entry can be active and can be blocked by chemokines that act on known receptors for M- and T-tropic virus.

Improved methods for the generation of dendritic cells from nonproliferating progenitors in human blood

We have investigated an improved method for generating sizable numbers of mature dendritic cells from nonproliferating progenitors in human blood. The procedure uses 1% human plasma in the place of 10% fetal calf serum and involves two steps. The first step or 'priming' phase is a 6-7 day culture of T cell depleted mononuclear cells in medium supplemented with GM-CSF and IL-4. The second step or 'differentiation' phase requires the exposure to macrophage conditioned medium. This medium cannot be replaced by several known cytokines such as TNF-alpha, IL-1, IL-6, IL-12 and IL-15, and cannot be inhibited with neutralizing antibodies to IL-1, TNF-alpha, IL-6 or IL-12 alone, or in combination. Using this two-step approach, we obtain substantial yields. About 1-3 x 10(6) mature dendritic cells are generated from 40 ml of blood vs. < 0.1 x 10(6) from noncytokine treated blood. The dendritic cells derive from progenitors found primarily in a radioresistant population of CD14+ and adherent blood mononuclear cells and have all the features of mature cells. They include a stellate cell shape, nonadherence to plastic, and very strong T cell stimulatory activity. Strong APC function was evident for both the proliferation of allogeneic T cells in the MLR, and the generation by syngeneic T cells of class I restricted, CTL responses to influenza virus. A panel of dendritic cell restricted markers is also expressed, including CD83, p55, and perinuclear CD68. All of these dendritic cell properties are retained for at least 3 days when the cytokines are removed, suggesting that these populations are stable and terminally differentiated. We suggest that these cells will be effective in vivo as adjuvants for active immunotherapy.

Allelic variants of human TCR BV17S1 defined by restriction fragment length polymorphism, single strand conformation polymorphism, and amplification refractory mutation system analyses

Several human TCR BV gene subfamilies, including BV3, BV14, and BV17S1, are single member genes but are overutilized among activated CD4+ synovial T cells in the rheumatoid arthritis (RA). To define the role of these TCR BV genes in the pathogenesis of disease, it is critical to characterize the genomic organization and the allelic variations of these genes. In this study we describe allelic variations of BV17S1 defined by restriction fragment length polymorphism (RFLP), single strand conformation polymorphism (SSCP), and amplification refractory mutation system (ARMS) analyses. A single nucleotide replacement (C/T) results in an amino acid substitution (F/L) in the leader and distinguishes BV17S1*1 from BV17S1*2. This nucleotide substitution was found to create a BsmAI restriction enzyme recognition site in BV17S1*2. Therefore genotypic analyses can be performed either by the SSCP or RFLP method. The analyses of 75 unrelated individuals show that the frequency for allele BV17S1*1 is 52.7% and for allele BV17S1*2 is 47.3%. Both alleles are functionally expressed and are distributed within CD4+/CD8+ T cell subsets. Another point mutation in the CDR2 region of BV17S1, which results in the amino acid replacement of Gln by His, originally identified form a cDNA clone, has now been confirmed as an allele by ARMS analysis using genomic DNA preparations and designated to as BV17S1*3. Screening of this CDR2 related variant among normal populations indicates that this is a rare allele (1 of 75). Although this variant may be of functional significance, the genotypic analysis and functional studies are difficult due to the low frequency of BV17S1*3. In an attempt to define a correlation between BV17S1 allelic usage and susceptibility to RA, the germline distribution of BV17S1 alleles *1 and *2 has been examined in a small number of RA patients and no skewed usage has been identified.

IL-12 in conjunction with dendritic cells enhances antiviral CD8+ CTL responses in vitro

CD8+ cytolytic T lymphocytes (CTLs) are important mediators for resistance to infections and malignant diseases. IL-12 enhances proliferative and cytolytic responses by killer cells, but its function in the generation of human antiviral CD8+ T cell responses has not been defined. We therefore evaluated the role of IL-12 in the generation of CTLs to influenza-infected dendritic cells. IL-12 was not detectable in supernatants of infected-dendritic cells, or during CTL generation. Furthermore, anti-IL-12 antibody did not block CTL generation. However, exogenous IL-12 (30-300 pg/ml) enhanced CD8+ T cell proliferative and cytolytic responses. The effect was greatest in individuals with weak reactivity to influenza virus or at antigen-presenting cell (APC):T cell ratios of 1:100 or less. IL-12 augmented interferon-gamma production during CTL generation. The CTL enhancing effects of the cytokine, however, could not be blocked by neutralizing anti-interferon-gamma antibody. Together with IL-12, antigen-pulsed dendritic cells may be a useful approach for boosting CTL responses against infectious agents and malignancies.

Inactivated influenza virus, when presented on dendritic cells, elicits human CD8+ cytolytic T cell responses

Inactivated or subunit virus preparations have been excellent vaccines for inducing antibody responses. Generation of cytolytic T cell responses, however, is thought to require replicating virus, primarily to provide sufficiently large amounts of cytoplasmic proteins for processing and presentation on major histocompatibility complex class I molecules by antigen-presenting cells. Potent human CD8+ cytolytic T cell responses to live replicating influenza A virus are generated when dendritic cells are used as the antigen-presenting cells. Here, we demonstrate that dendritic cells pulsed with poorly replicating, heat- or ultraviolet-inactivated influenza virus, induce equally strong CD8+ cytolytic T lymphocyte responses. The cytotoxic T lymphocytes are generated in the apparent absence of CD4+ helper cells or exogenous cytokines. Active viral protein synthesis is not required to charge class I molecules on dendritic cells. When pulsed with inactivated virus, < 1% of dendritic cells express nonstructural protein 1, which is only synthesized in the infectious cycle. To be optimally effective, however, the inactivated virus must retain its fusogenic activity, and presumably access the cytoplasm of dendritic cells. The data indicate, therefore, that dendritic cells require only small amounts of viral protein to charge class I molecules, most likely via traditional class I processing pathways. These results reopen the potential use of inactivated virus preparations as immunogens for cytotoxic T lymphocyte responses.

Retroviral gene transfer into retinal pigment epithelial cells followed by transplantation into rat retina

In this preliminary report, we describe a technique for gene transfer into the retina using a retrovirus vector. We transferred the bacterial LacZ gene and the neomycin-resistance gene into pigmented wild-type rat retinal pigment epithelial (RPE) cells in culture. The RPE culture was exposed to retrovirus, and infected cells were selected with a neomycin analog (G418). The LacZ gene product was detected by X-Gal histochemistry in 95-100% of drug-resistant cells. These genetically labeled cells were transplanted into the subretinal space of two 15- to 25-day-old albino RCS rats, which have an inherited retinal degeneration syndrome. The retinas were fixed and stained with X-Gal at 3 and 6 weeks after transplantation. At both time points, pigmented, LacZ-containing cells were seen in the subretinal space. Further, there were several rows of photoreceptor nuclei in the transplant area of the approximately 2-month-old rats, while in the control contralateral eye the photoreceptor nuclei were virtually absent, as for untreated animals, suggesting that the transplanted LacZ-marked, wild-type RPE cells may have helped preserve photoreceptors. The technique for gene transfer into RPEs followed by transplantation thus provides a means for gene therapy in organisms with a genetic defect in RPE cells.

Maternal care receptivity and its relation to perinatal and neonatal mortality. A rural study

A longitudinal study was conducted on 212 pregnant women from May 1987 to April 1988. Maternal Care Receptivity (MCR) "an innovative approach" was adopted for the assessment of maternal care services provided to pregnant mothers at their door steps. During follow-up, scores were allotted to each of the services rendered and antenatal status of pregnant women. Depending on the score--MCR was classified as high (11 to 8), moderate (7 to 4) or poor (3 to 0). Perinatal and neonatal deaths were recorded and an inverse relationship between MCR and perinatal and mortalities was observed (z = 5.46, p < 0.0001). Significantly, no perinatal or neonatal deaths occurred in women with high MCR. One of the most important cause of high PNMR and neonatal mortality rate in developing countries is poor MCR, i.e., under utilization of even the existing maternal health services. The main reasons for this under utilization appear to be poverty, illiteracy, ignorance and lack of faith in modern medicine.

Influenza virus-infected dendritic cells stimulate strong proliferative and cytolytic responses from human CD8+ T cells

Antigen-specific, CD8+, cytolytic T lymphocytes (CTLs) could potentially provide resistance to several infectious and malignant diseases. However, the cellular requirements for the generation of specific CTLs in human lymphocyte cultures are not well defined, and repetitive stimulation with antigen is often required. We find that strong CD8+ CTL responses to influenza virus can be generated from freshly isolated blood T cells, as long as dendritic cells are used as antigen presenting cells (APCs). Small numbers of dendritic cells (APC:T cell ratio of 1:50-1:100) induce these CTL responses from most donors in 7 d of culture, but monocytes are weak or inactive. Whereas both dendritic cells and monocytes are infected with influenza virus, the former serve as effective APCs for the induction of CD8+ T cells while the latter act as targets for the CTLs that are induced. The strong CD8+ response to influenza virus-infected dendritic cells is accompanied by extensive proliferation of the CD8+ T cells, but the response can develop in the apparent absence of CD4+ helpers or exogenous lymphokines. CD4+ influenza virus-specific CTLs can also be induced by dendritic cells, but the cultures initially must be depleted of CD8+ cells. These findings should make it possible to use dendritic cells to generate human, antigen-specific, CD8+ CTLs to other targets. The results illustrate the principle that efficient T cell-mediated responses develop in two stages: an afferent limb in which dendritic cells are specialized APCs and an efferent limb in which the primed T cells carry out an immune response to many types of presenting cells.

Human blood contains two subsets of dendritic cells, one immunologically mature and the other immature

Two subsets of dendritic cells, differing in T-cell stimulatory function, have been purified directly from human blood. Both subsets are positive for major histocompatibility complex (MHC) class II expression and negative for lineage-specific antigens (e.g. CD3, CD14, CD16, CD19 negative), but are separated by exploiting differences in expression of the beta 2-integrin, CD11c. The CD11c-negative subset is functionally immature, requiring monocyte-derived cytokines to develop into typical dendritic cells. The CD11c-positive subset has potent T-cell stimulating activity and expresses the activation antigen CD45RO, unlike its immature counterpart. However, these mature cells only develop typical dendritic morphology and high levels of MHC proteins and adhesins after a period of culture independent of exogenous cytokines. Although the freshly isolated mature dendritic cells resemble monocytes in cytospin preparations, the former lack CD14 and have a much stronger primary T-cell stimulatory capacity. We hypothesize that the CD11c-negative immature cells are marrow-derived precursors to tissue dendritic cells, such as epidermal Langerhans' cells, while the CD11c-positive cells are derived from tissues where they have been activated by antigen, and are en route to the spleen or lymph nodes to stimulate T-cell responses there.

Human T-cell responses to Mycoplasma arthritidis-derived superantigen

When injected into mice, Mycoplasma arthritidis causes a chronic arthritis that resembles rheumatoid arthritis, histologically. The organism produces a superantigen termed Mycoplasma arthritidis mitogen or MAM, that in humans preferentially expands T cells whose antigen receptors express V beta 17. T cells with this phenotype appear to be increased in rheumatoid synovial effusions. We describe a novel approach to isolating and characterizing human MAM-reactive T-cell lines and determining their T-cell receptor (TCR) V beta usage. Lines were prepared from T cells that clustered with dendritic cells during a 2-day exposure to MAM. Cluster and noncluster fractions of T cells were then expanded by using feeder cells and a polyclonal mitogen. Most of the MAM reactivity was found in dendritic T-cell clusters, as were most of the T cells expressing TCR V beta 17. After expansion, 76% of the cluster-derived T-cell lines were MAM reactive, while no reactivity was seen in cell lines derived from the noncluster fraction. Of the MAM-reactive lines, 49% expressed V beta 17 on some or all of the cells. Cell lines from both cluster and noncluster fractions were analyzed for TCR V beta mRNA expression by PCR amplification. Other V beta genes (5.1, 7, 8, 12, and 20) were found to be expressed by lines that were MAM reactive, although these were not a major component of the cluster-derived T cells. Some non-cluster-derived lines expressed V beta s 17, 12, and 7, but these proved to be nonreactive to MAM. Therefore, dendritic cells can be used to immunoselect and characterize T cells that express superantigen-reactive TCRs.

Presentation of mycobacterial antigens by human dendritic cells: lack of transfer from infected macrophages

When exposed to a challenge of 10 Mycobacterium bovis BCG cells per antigen-presenting cell, most human monocytes engulf several organisms. In contrast, blood dendritic cells which are potent antigen-presenting cells for several antigens are not detectably phagocytic for mycobacteria. We investigated the possibility that infected macrophages might regurgitate antigens for presentation by populations of human blood dendritic cells. Macrophages were infected with M. bovis BCG, mixed with uninfected dendritic cells, and added to immune T cells, either bulk T cells or cloned populations from BCG vaccinees or patients recovering from tuberculosis. The macrophages were from donors who were mismatched to the T cells so that transfer of antigen to major histocompatibility complex-matched dendritic cells could be evaluated. As we describe, there was no evidence for the transfer of mycobacterial antigens from macrophages to dendritic cells in a form that was stimulatory for the T cells.

Dendritic cells freshly isolated from human blood express CD4 and mature into typical immunostimulatory dendritic cells after culture in monocyte-conditioned medium

A procedure has been developed to isolate dendritic cells to a high degree of purity from fresh blood. Prior enrichment methods have relied upon an initial 1-2-d culture period. Purified fresh isolates lack the characteristic morphology, phenotype, and immunostimulatory function of dendritic cells. The purified cells have the appearance of medium sized lymphocytes and express substantial levels of CD4, but lack the T cell molecules CD3, CD8, and T cell receptor. When placed in culture, the cells mature in a manner resembling the previously described, cytokine-dependent maturation of epidermal dendritic cells (Langerhans cells). The cells enlarge and exhibit many cell processes, express much higher levels of major histocompatibility complex class II and a panel of accessory molecules for T cell activation, and become potent stimulators of the mixed leukocyte reaction. Among the many changes during this maturation process are a fall in CD4 and the appearance of high levels of B7/BB1, the costimulator for enhanced interleukin 2 production in T cells. These changes are not associated with cell proliferation, but are dependent upon the addition of monocyte-conditioned medium. We suggest that the freshly isolated CD4-positive blood dendritic cells are recent migrants from the bone marrow, and that subsequent maturation of the lineage occurs in tissues in situ upon appropriate exposure to cytokines.

Interaction of Mycoplasma arthritidis superantigen with human T cells

To define the interaction site of T cell antigen receptors (TCRs) with the superantigen of Mycoplasma arthritidis (MAM), we characterized the TCRs of human MAM-reactive T cell lines and T cell clones. Most MAM-reactive T cells express the V beta 17 gene segment; however, other V beta may also be used and not all V beta 17+ TCRs are MAM-reactive. Alignment of MAM-reactive and MAM-nonreactive V beta sequences suggests that MAM does not interact with a single site encoded by a V beta segment but that several sites may be involved or that other TCR elements contribute to formation of the MAM recognition site.