Idiotype vaccination following ABMT can stimulate specific anti-idiotype immune responses in patients with B-cell lymphoma.

Vaccination with the idiotype (Id) protein derived from B-cell malignancies can produce Id-specific immune responses that correlate with improved remission duration and survival rates in patients with follicular non-Hodgkin's lymphoma (NHL). A state of minimal or no residual disease correlates strongly with the laboratory detection of a cellular or humoral immune response. High-dose cytotoxic therapy (HDCT) with autologous stem cell support (autologous bone marrow transplantation [ABMT]) can provide profound cytoreduction of B-cell NHL, but the potential immune suppression associated with myeloablative therapy may compromise a patient's ability to mount a specific immune response. To determine whether patients with NHL could mount detectable immuneresponses following ABMT, Id vaccines were administered at 2 to 12 months following myeloablative therapy to a series of patients with relapsed or resistant B-cell NHL. Two different vaccination strategies produced robust immune responses against KLH in all patients, supporting the capacity of the reconstituted immune system following HDCT to react against a strong antigen. Combining the results from both vaccination strategies, 10 of 12 patients mounted Id-specific humoral or cellular responses. Vaccinations were consistently well tolerated. Of the 12 patients, 7 have experienced prolonged remissions with a follow-up from HDCT ranging from 3 to more than 11 years. Our experience serves to document the ability of the recovering immune system to react against both self and xenotypic antigens and supports the feasibility and safety of antigen-specific vaccination following myeloablative therapy in patients with B-cell NHL.

Idiotype vaccination using dendritic cells after autologous peripheral blood progenitor cell transplantation for multiple myeloma.

The idiotype (Id) determinants on the multiple myeloma immunoglobulin can serve as tumor-specific antigens. An anti-Id immune response may stem the growth of the malignant clone. We report on 26 patients treated at our institution with high-dose chemotherapy and peripheral blood progenitor cell transplantation (PBPCT) and vaccinated with the Id protein. The patients received chemotherapy and PBPCT to establish a minimal residual disease state. After high-dose therapy, the patients received a series of monthly immunizations consisting of 2 intravenous infusions of dendritic cells (DCs) pulsed with either Id protein or Id coupled with keyhole limpet hemocyanin (KLH) as an immunogenic carrier protein, followed by subcutaneous boosts of Id-KLH conjugates. DCs were obtained in all patients from a leukapheresis product 3 to 9 months after PBPCT. Patients were observed for toxicity, immune responses, and tumor status. The DC infusions and the administration of Id-KLH boosts were well tolerated, with patients experiencing only minor and transient side effects. Of the patients, 24 of 26 generated a KLH-specific cellular proliferative immune response. Only 4 patients developed an Id-specific proliferative immune response. Three of these immune responders were in complete remission at the time of vaccination. A total of 17 patients are alive at a median follow-up of 30 months after transplantation. Id vaccination with autologous DCs is feasible for myeloma patients after transplantation. Id-specific cellular responses can be induced in patients who are in complete remission. Further studies are needed to increase the rate of anti-Id immune responses in patients who do not achieve complete remission.

Idiotype vaccination using dendritic cells after autologous peripheral blood stem cell transplantation for multiple myeloma--a feasibility study.

The idiotype (Id) determinant on the multiple myeloma (MM) protein can be regarded as a tumor-specific marker. Immunotherapy directed at the MM Id may stem the progression of this disease. We report here on the first 12 MM patients treated at our institution with high-dose therapy and peripheral blood stem cell transplantation (PBSCT) followed by Id immunizations. MM patients received PBSCT to eradicate the majority of the disease. PBSCT produced a complete response in 2 patients, a partial response in 9 patients and stable disease in 1 patient. Three to 7 months after high-dose therapy, patients received a series of monthly immunizations that consisted of two intravenous infusions of Id-pulsed autologous dendritic cells (DC) followed by five subcutaneous boosts of Id/keyhole limpet hemocyanin (KLH) administered with adjuvant. Between 1 and 11 x 10(6) DC were obtained by leukapheresis in all patients even after PBSCT. The administration of Id-pulsed DC and Id/KLH vaccines were well tolerated with patients experiencing only minor and transient side effects. Two of 12 patients developed an Id-specific, cellular proliferative immune response and one of three patients studied developed a transient but Id-specific cytotoxic T-cell (CTL) response. Eleven of the 12 patients generated strong KLH-specific cellular proliferative immune responses showing the patients' immunocompetence at the time of vaccination. The two patients who developed a cellular Id-specific immune response remain in complete remission. Of the 12 treated patients, 9 are currently alive after autologous transplantation with a minimum follow-up of 16 months, 2 patients died because of recurrent MM and 1 patient succumbed to acute leukemia. These studies show that patients make strong anti-KLH responses despite recent high-dose therapy and that DC-based Id vaccination is feasible after PBSCT and can induce Id-specific T-cell responses. Further vaccine development is necessary to increase the proportion of patients that make Id-specific immune responses. The clinical benefits of Id vaccination in MM remain to be determined.

Isolation and utilization of human dendritic cells from peripheral blood to assay an in vitro primary immune response to varicella-zoster virus peptides.

A human dendritic cell-based assay used to monitor a T cell proliferation response to viral peptides in vitro is described. Dendritic cells and autologous CD4+ T cells were isolated from peripheral blood by a series of density-gradient centrifugations or magnetic bead separations (or both). Peptides corresponding to residues of the immediate early protein, IE62, of varicella-zoster virus (VZV) were used as stimulating antigens, and persons with no history of varicella and no humoral or cellular immunity to VZV served as naive donors for the assays. Three VZV-susceptible donors were tested, and all demonstrated an in vitro response to multiple VZV peptides. This assay has potential as a screen to establish the immunogenicity of viral antigens in vitro using T cells from naive donors.

CTL response to Mycobacterium tuberculosis: identification of an immunogenic epitope in the 19-kDa lipoprotein.

The successful resolution of infection with Mycobacterium tuberculosis (M.tb) is believed to involve the induction of CTLs that are capable of killing cells harboring this pathogen, although little information is known about the MHC restriction or fine specificity of such CTLs. In this study, we used knowledge of the HLA-A*0201-binding motif and an immunofluorescence-based peptide-binding assay to screen for potential HLA-A*0201-binding epitopes contained in the 19-kDa lipoprotein of M.tb (M.tb19). CD8+ T cells derived from HLA-A*0201+ patients with active tuberculosis (TB) as well as tuberculin skin test-positive individuals who had no history of TB were used as effector cells to determine whether these epitopes are recognized by in vivo-primed CTLs. An in vitro vaccination system using HLA-A*0201+ dendritic cells (DCs) as APCs was used to determine whether these epitopes can sensitize naive CD8+ T cells in vitro, leading to the generation of Ag-specific CTLs. The results show that an HLA-A*0201-binding peptide comprised of residues 88 to 97 of M.tb19 (P88-97) is recognized by circulating CD8+ CTLs from both healthy tuberculin skin test-positive individuals and patients with active TB but not by tuberculin skin test-negative subjects. Moreover, dendritic cells pulsed with this peptide induced class I MHC-restricted CTLs from the T cells of healthy unsensitized persons. Finally, CTL lines that were specific for P88-97 were shown to lyse autologous monocytes that had been infected acutely with the H37Ra strain of M.tb. These results demonstrate that M.tb19 elicits HLA class I-restricted CTLs in vitro and in vivo that recognize endogenously processed Ag. Epitopes of the type identified here may prove useful in the design of an M.tb vaccine.

Evidence that T cell activation is required for HIV-1 entry in CD4+ lymphocytes.

The relationship of T cell activation to HIV entry and generation of viral DNA intermediates was studied in freshly isolated CD4+ T lymphocytes. Unstimulated cells exposed to infectious virus for up to 48 h did not synthesize any detectable unintegrated HIV DNA duplex forms or integrated genomic provirus. However, activation of these cells with either PHA or OKT3 (anti-CD3) mAb before viral exposure resulted in the generation of unintegrated HIV DNA after 6 h and integrated copies after 24 h. Cell-to-cell fusion studies showed significantly attenuated fusion between freshly isolated resting T cells and T cells constitutively expressing high levels of HIV envelope glycoprotein (HXB/gpt) compared with T cells first stimulated with either PHA or OKT3 mAb. The baseline fusion observed with resting T cells is believed to be a consequence of allogeneic stimulation by the HXB/gpt cell line. These results provide evidence that HIV entry and HIV envelope-dependent cell-to-cell fusion require T cell activation.

Activation of HLA-restricted EBV-specific cytotoxic T cells does not require CD4+ (helper) T cells or exogenous cytokines.

MHC-restricted, viral Ag-specific "memory" CTL are thought to play a decisive role in the defense against pathogenic viruses. However, the requirements for activating such CTL remain controversial. In particular, the role of CD4+ helper cells and their soluble products (e.g., IL-2) are uncertain. To approach these questions as they relate to EBV-specific CTL, highly purified CD8+ T cells from healthy EBV-seropositive individuals were cultured with autologous irradiated EBV-transformed B lymphoblastoid cell lines (LCL), in the presence or absence of autologous CD4+ cells or 1 to 10 U/ml purified rIL-2. The results indicate that the induction of CTL requires neither Th cells nor exogenous IL-2. The CTL generated from isolated CD8+ cells were HLA class I restricted as demonstrated by their ability to lyse targets sharing at least one HLA-A or -B Ag with the stimulating autologous LCL. Furthermore, a mAb (W6/32) to a common determinant on HLA class I Ag blocked both the generation and effector phases of killing, whereas an HLA class II directed mAb had no effect. Addition of an IL-2R-specific antibody (anti-Tac) to the culture medium blocked induction of CTL, suggesting that endogenously produced IL-2 plays an obligatory role in this system. Paraformaldehyde fixation of LCL abrogated their ability to function as stimulator cells; however, addition of 2 U/ml exogenous IL-2 to fixed LCL cultured with CD8+ cells allowed for the induction of highly specific CTL. These results indicate that EBV-specific memory CTL can be activated in the absence of CD4+ helper cells or their soluble products, but nonetheless require Ag and IL-2.

Recombinant interleukin 2 enhanced natural killer cell-mediated cytotoxicity in human lymphocyte subpopulations expressing the Leu 7 and Leu 11 antigens.

Highly purified recombinant human interleukin 2 (rIL 2) markedly augments the natural killer (NK) cell-mediated cytotoxicity of peripheral blood lymphocytes. In this study, we examined the cellular and metabolic basis of rIL 2-mediated activation of human lymphocyte subpopulations expressing the NK cell-associated surface antigens Leu 7 and Leu 11. All rIL 2-responsive cytotoxic NK cells were found within the subset of lymphocytes expressing the Leu 11 marker, an antigen associated with the Fc-IgG receptor on human NK cells. Cells lacking the Leu 11 antigen, including cells expressing another NK cell-associated marker, Leu 7, did not express NK cell-mediated cytotoxicity either before or after rIL 2 treatment. By contrast, rIL 2 augmented the NK activity of both Leu7-,11+ and Leu 7+,11+ subpopulations. Activation of Leu 11+ NK cells resulted from a direct effect of rIL 2 on these cells and neither required nor was amplified by the presence of T lymphocytes. Enhanced NK cell-mediated cytotoxicity occurred within 4 hr after exposure to rIL 2, and was blocked by the protein synthesis inhibitor cyclohexamide, but not by the DNA synthesis inhibitor mitomycin C or 1500 rad of x-irradiation. Neither Tac antigen, a high-affinity receptor for IL 2, nor other activation markers, such as transferrin receptor or HLA-DR antigen, were detectable on a significant proportion of Leu 11+ cells, either before or after incubation with rIL 2 for 48 hr. In addition, saturating concentrations of antibodies to each of these markers had no effect on the enhancement of NK activity by rIL 2. Finally, preliminary experiments with neutralizing antibodies to gamma- and alpha-interferons also failed to prevent rIL 2 enhancement of NK cell-mediated cytotoxicity, suggesting that rIL 2 does not mediate its effect via release of these cytokines.

Human recombinant interleukin-2 partly reconstitutes deficient in-vitro immune responses of lymphocytes from patients with AIDS.

The lymphokine interleukin-2 is required for the development of various cell-mediated immune functions that are known to be deficient in patients with acquired immunodeficiency syndrome (AIDS). The effects of pure human recombinant interleukin-2 (rIL-2), produced by Escherichia coli containing the cloned human gene, on in-vitro immune responses were studied in 16 patients with AIDS and 10 age-matched healthy heterosexual men. Exposure of lymphocytes from most AIDS patients to 1-100 U/ml rIL-2, increased mitogen and alloantigen induced proliferation and augmented natural killer (NK) cell function in a dose-dependent manner. NK activity was the function most consistently improved, with deficient patient responses uniformly restored to normal after incubation of effector cells with rIL-2. Patient responsiveness to rIL-2 did not appear to depend upon the primary manifestation of disease (opportunistic infection, Kaposi's sarcoma, or both) or other clinical variables. rIL-2 also augmented the responses of lymphocytes from health subjects, but to a lesser degree. Pure rIL-2 seems capable of at least partly reconstituting some in-vitro immunological defects characteristic of AIDS. The availability of highly purified rIL-2 makes in-vivo testing feasible.

Activation of antigen-specific suppressor T cells in the presence of cyclosporin requires interactions between T cells of inducer and suppressor lineage.

To probe the mechanism of suppressor T cell generation in man, we have carried out mixed leukocyte reactions (MLR) in the presence of cyclosporin (CsA), a fungal metabolite which prevents the generation of cytotoxic lymphocytes while permitting activation of suppressor cells. After a 12-d MLR in the presence of 1 microgram/ml CsA, T cells were fractionated into subsets with monoclonal antibodies, and each subset was tested for the ability to inhibit a second fresh MLR that is devoid of CsA. The results show that Leu 2+ T cells derived from the first culture suppress the second MLR in an HLA-DR antigen-specific manner and in the absence of detectable lysis of stimulator cells. However, Leu 2+ cells do not develop into suppressor cells unless acted upon by alloantigen-primed Leu 3+ inducer cells. Furthermore, only those Leu 3+ cells that also express the Leu 8 marker (Leu 3+, 8+) are capable of inducing suppressor cells. Thus, antigen-specific feedback inhibition of an immune response in man results from an ordered series of interactions between T cells of distinct phenotype.

Human T lymphocyte proliferation induced by a pan-T monoclonal antibody (anti-Leu 4): heterogeneity of response is a function of monocytes.

Anti-Leu-4 is a murine monoclonal antibody that defines a molecule of 20,000 to 25,000 daltons present on all mature T lymphocytes in man. When cultured in the presence of 10 to 1000 ng/ml anti-Leu-4, the T cells of most individuals proliferate with peak responses on the third day of culture. T cells of both helper and suppressor lineages proliferate, but only in the presence of monocytes. Approximately 40% of individuals tested responded weakly or not at all to anti-Leu-4, despite normal responses to other stimuli. The variation in responsiveness between individuals could not be explained by differences in Leu-4 antigen density on the surface of T cells, differences in the rate of Leu-4 antigen modulation, or structural differences in the Leu-4 molecule as defined by the method of two-dimensional polyacrylamide gel electrophoresis. In the presence of monocytes from high responders, the T cells from low responders proliferated vigorously to anti-Leu-4, whereas monocytes from low responders failed to support proliferation by high responder T cells. On the other hand, low responder monocytes did not prevent T cells from proliferating in the presence of high responder monocytes. These results suggest that the failure of some individuals to respond to anti-Leu-4 is due to the absence or dysfunction of an essential monocyte population.

Blocking of human T lymphocyte functions by anti-Leu-2 and anti-Leu-3 antibodies: differential inhibition of proliferation and suppression.

We have shown previously that monoclonal antibodies to the Leu-2 and Leu-3 T cell antigens block the response of their respective subsets in allogeneic MLR. The present study was an effort to explore the mechanism of inhibition and to determine if anti-Leu-2 and anti-Leu-3 antibodies affect the responses to stimuli in addition to alloantigens. Our results indicate that antibodies to Leu-2 and Leu-3 have profound inhibitory effects on proliferation by their respective T cell subsets responding to a variety of stimuli, including specific soluble antigens and alloantigen. This effect was characterized by the following features: a) For optimal inhibition of proliferation, antibody must be present at the onset of antigenic stimulation. b) Inhibition is augmented by increasing the concentration of antibody or decreasing the concentration of antigen. c) Fab fragments of both anti-Leu-2a and anti-Leu-3a antibodies also block proliferation. In addition to their effects on T cell proliferation, anti-Leu-3 antibody blocked T cell-dependent lg synthesis induced in MLR, and anti-Leu-2 antibody prevented the induction, in vitro, of Leu-2+3- suppressor cells of lg synthesis. Taken together, these results suggest that antibodies to antigenic determinants on the Leu-2 and Leu-3 molecules competitively block segments of these structures that bind to alloantigen or nominal antigen. On the other hand, anti-Leu-2a antibody failed to block suppression of the MLR by in vivo activated, antigen-specific Leu-2+3- suppressor cells, which suggests that the Leu-2a epitope does not transmit antigen-specific signals from these differentiated suppressor T cells.

Use of the fluorescence-activated cell sorter to quantitate and enrich for subpopulations of human skin cells.

A variety of immunologic staining techniques were compared in a quantitative study of antigen expression by human epidermal cells. Virtually all nucleated epidermal cells express beta 2-microglobulin, which is associated with HLA-A, -B, and -C antigens, whereas only about 4% expressed T6, an antigen expressed by Langerhans cells but not other cells in the skin. With the fluorescence-activated cell sorter (FACS), epidermal cell suspensions were selectively enriched 10- to 15-fold for T6-positive Langerhans cells. An average of 6.5% of cells were specifically stained by anti-HLA-DR antibody. When dispersed cells stained with anti-DR plus peroxidase were examined with the technique of immunoelectron microscopy, only mononuclear leukocytes (probably Langerhans cells) were stained. After separating HLA-DR positive skin cells with the FACS, the DR-positive population but not the DR-negative population stimulated proliferation of allogeneic responder lymphocytes, indicating that sorted cells are metabolically active. We conclude that HLA-DR antigen is not expressed by keratinocytes in normal human skin cell suspensions and that the FACS can be used to selectively enrich or deplete skin cell suspensions of antigenically distinct subpopulations such as Langerhans cells.

Cultured human epidermal cells do not synthesize HLA-DR.

All nucleated cells express HLA-A, B, and C antigens. However, only a few cells, including epidermal cells, demonstrate HLA-DR antigens which are potent transplantation immunogens in man. The current study was undertaken to determine if epidermal cell continue to synthesize and/or express HLA-DR antigens after prolonged in vitro culture. Epidermal cells cultured for 7 days or more no longer stimulated allogeneic lymphocytes in the epidermal cell-lymphocyte reaction. Indirect immunofluorescence light microscopy of cultured cells using mouse monoclonal antibody to HLA-DR antigen confirmed that these cells do not express HLA-DR antigens whereas they retain beta 2-microglobulin. Detergent extracts of 12-day cultured epidermal cells biosynthetically labeled with 35 S-methionine were immunoprecipitated with monoclonal anti-DR antibody and analyzed by the method of two-dimensional polyacrylamide gel electrophoresis. No radiolabeled proteins were found on these gels in the regions where HLA-DR molecules are known to migrate. These data indicate that HLA-DR antigen is absent from cultured epidermal cells. Finally, we describe a technique for growing epidermal cells on a gelatin membrane which allows subsequent removal of intact cell monolayers from the culture dish. Such monolayers may be useful for purposes of transplantation.

Activation of human T lymphocyte subsets: helper and suppressor/cytotoxic T cells recognize and respond to distinct histocompatibility antigens.

This study was directed at determining the major histocompatibility complex (MHC) antigens recognized by helper (Leu-3) and suppressor-cytotoxic (Leu-2) T lymphocyte subsets in man. These 2 subsets were isolated from peripheral blood with monoclonal antibodies and challenged in vitro with various stimuli. Only Leu-3 cells proliferated in response to autologous nonrosetting cells and soluble antigens, suggesting that helper but not suppressor-cytotoxic T cells recognize autologous HLA-DR antigen. Furthermore, only Leu-3 T cells responded to allogeneic DR antigen; this was shown in reactions between 2 siblings who were HLA-identical except for a single disparity at HLA-DR caused by a crossover event. Leu-3 cells activated in primary allogeneic mixed leukocyte reactions (MLR) responded equally in secondary allogeneic MLR to the priming cells and to cells that were identical at HLA-DR but discordant at HLA-A, B, and C to the priming cell. The antigens responsible for stimulating Leu-2 cells in allogeneic MLR were not identified, although the results are compatible with a role for HLA-A and B antigens and exclude a dominant role for HLA-DR. These data indicate that the helper and suppressor-cytotoxic T cell subsets in man respond differentially to MHC antigens in a manner analogous to the murine Lyt-2- 3- and Lyt-2+ 3+ populations.

Induction of immunoglobulin-secreting cells in the allogeneic mixed leukocyte reaction: regulation by helper and suppressor lymphocyte subsets in man.

The existence of functionally distinct T lymphocyte subsets in man, initially demonstrated with heteroantisera, has been confirmed with monoclonal reagents. Two major subsets have been defined: Leu-2 cells, which effect cell mediated lymphocytotoxicity (CML), and Leu-3 cells, which amplify CML and other T cell functions. This study is an effort to determine the effects of these subsets on the immunoglobulin secretion induced in the human mixed leukocyte reaction (MLR). T cells were separated from non-T cells by rosetting with sheep erythrocytes and were fractionated into Leu-2 and Leu-3 subsets by solid phase immunoabsorption with monoclonal antibodies. T cell subsets were cultured with autologous non-T cells and irradiated allogeneic stimulator non-T cells. Secretion of IgM and IgG was measured by a reverse hemolytic plaque assay. MLR-induced antibody secretion was specifically dependent on the Leu-3 T lymphocyte subset. The Leu-2 subset was incapable of generating large numbers of IgM- or IgG-secreting cells, and, in fact, suppressed the Leu-3-induced response. Exposure of Leu-3 cells to a dose of irradiation sufficient to prevent their proliferation in MLR did not reduce induced immunoglobulin secretion. Leu-2-mediated suppression, however, was sensitive to low dose irradiation. Thus Ig secretion in human MLR is regulated by a balance of helper activity from the Leu-3 subset and suppressor activity from the Leu-2 subset.

Antibodies to membrane structures that distinguish suppressor/cytotoxic and helper T lymphocyte subpopulations block the mixed leukocyte reaction in man.

Two major subsets of human T lymphocytes that are functionally analogous to the mouse Lyt-2+ and Lyt-2- subsets have been defined by their expression of two thymus-dependent membrane antigens, Leu-2 and Leu-3. Leu-2+,3- cells have suppressor/cytotoxic functions and Leu-2-,3+ cells have helper functions. These studies were designed to determine the effects of adding IgG1 monoclonal anti-Leu-2 and anti-Leu-3 antibodies to the mixed leukocyte reaction (MLR). At high concentrations, each antibody partially inhibited the proliferative response of unseparated T cells and abolished the response of the isolated subset having the appropriate phenotype. An IgG1 monoclonal antibody to HLA-A2 and an IgG2a antibody to Leu-1, a pan-T antigen, failed to inhibited the MLR. These results suggest that the Leu-2 and Leu-3 antigens may have a direct role in the mechanism whereby T cells recognize and respond to alloantigen.

Studies of a human T lymphocyte antigen recognized by a monoclonal antibody.

A monoclonal antibody (designated L17F12) detects an antigen present on 95-100% of human peripheral T lymphocytes, the majority of thymocytes, and acute lymphocytic leukemia T cells but not B cells, B-cell lines, or monocytes. Examination of frozen tissue sections by the immunoperoxidase method revealed that the cells expressing this antigen were found predominantly in the medulla of thymus and in T-cell zones of lymph node and spleen. The antigen recognized by L17F12 was associated with a cell-surface glycoprotein of 67,000 daltons. L17F12 was used to isolate this molecule from human thymocytes, normal peripheral T cells, leukemic T cells, and T-cell lines. Expression of this antigen on normal T cells was not diminished by prolonged exposure in vitro to various T-cell stimuli. In the absence of complement, L17F12 bound to T cells without altering proliferative functions, thus enabling rapid purification of functionally intact T cells. In the presence of complement, L17F12 was cytolytic for T cells, providing the basis for depletion of T cells from heterogeneous populations. These data suggest that the monoclonal antibody L17F12 recognizes a specific T-cell differentiation protein. This antibody will be useful in studies of the human immune system.

Inhibition of cell mediated immune responses by 8-methoxypsoralen and long-wave ultraviolet light: a possible explanation for the clinical effects of photoactivated psoralen.

Human thymus-derived lymphocytes proliferate when cultured with lymphocyes or epidermal cells from unrelated individuals because such cells express HLA-D antigens, which are recognized as foreign by thymus-derived lymphocytes. The current study demonstrates that these responses are inhibited if either the stimulator cells or responder cells are pretreated with the combination of 8-methoxypsoralen and long-wave ultraviolet light. Additional studies revealed that photoactivated 8-methoxypsoralen has a lethal effect on lymphocytes and monocytes but not on the majority of epidermal cells. These obervations suggest that the dramatic beneficial effect of PUVA on patients with psoriasis and other skin disorders may be due to a toxic effect on immunocompetent cells in the epidermis, which results in inhibition of cell mediated immune responses.

Ia antigen on peripheral blood mononuclear leukocytes in man. II. Functional studies of HLA-DR-positive T cells activated in mixed lymphocyte reactions.

Blast transformation of T cells in response to allogeneic lymphocytes is followed by expression of HLA-DR antigen on up to 60% of the T cells. Murine monoclonal antibody to HLA-DR antigen was used to separate alloactivated T cells into those T cells that express high quantities of DR antigen (DR+) and those that express little or no DR antigen (DR-), and each population was tested in a variety of assays. DR+, but not DR-, T cells stimulated fresh allogeneic and autologous T cells to proliferate and supported proliferation by fresh autologous T cells to soluble antigens. Alloactivated T cells were suppressive of fresh mixed lymphocyte reactions (MLR) and suppression by irradiated DR+ T cells was specific for the DR antigens of the initial stimulator cell. Suppression of the MLR by DR+ T cells was not a result of altered kinetics or cell-mediated cytotoxicity. DR+ T cells released soluble factors that suppressed fresh allogeneic responses. These data indicate that alloactivated DR+ T cells may provide antigen-specific feedback inhibition of the MLR.