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T lymphocytes in the normal human intestinal tract have been analysed in tissue sections by a double-marker immunofluorescence technique, combining antiserum to T lymphocyte antigen (HuTLA) with a monoclonal antibody detecting T cells of suppressor-cytotoxic phenotype (OKT8). The distribution of HLA-A -B, -C and Ia-like antigens in intestinal mucosa was also examined by a similar method. In small and large intestine 67 to 90% (mean 70%) of intraepithelial T lymphocytes were of suppressor-cytotoxic phenotype (OKT8+). In contrast, only 27 to 56% (mean 39%) of lamina propria T cells were OKT8+. Intestinal epithelial cells demonstrated strong membrane staining for HLA-A, -B, -C antigens. Ia-like antigens were detected on the epithelial cells of small intestinal villi, but not on colonic epithelial cells. Lamina propria macrophages expressed both HLA-A, -B, -C and Ia-like antigens, the latter having strong membrane and cytoplasmic fluorescence. The distribution of T cells with suppressor-cytotoxic or inducer phenotype in the intestinal epithelium and lamina propria may be related to the differential expression of Ia-like and HLA-A, -B, -C antigens in intestinal mucosa.

Mature T cells segregate phenotypically into one of two classes: those that express the surface glycoprotein CD4, and those that express the glycoprotein CD8. The CD4 molecule is expressed primarily on helper T cells whereas CD8 is found on cytotoxic and suppressor cells. A more stringent association exists, however, between these T-cell subsets and the major histocompatibility complex (MHC) gene products recognized by their T-cell receptors (TCRs). CD8+ lymphocytes interact with targets expressing class I MHC gene products, whereas CD4+ cells interact with class II MHC-bearing targets. To explain this association, it has been proposed that these 'accessory' molecules bind to monomorphic regions of the MHC proteins on the target cell, CD4 to class II and CD8 to class I products. This binding could hold the T cell and its target together, thus improving the probability of the formation of the trimolecular antigen: MHC: TCR complex. Because the TCR on CD4+ cells binds antigen in association with class II MHC, it has been difficult to design experiments to detect the association of CD4 with a class II molecule. To address this issue, we devised a xenogeneic system in which human CD4 complementary DNA was transfected into the murine CD4-, CD8- T-cell hybridoma 3DT-52.5.8, the TCR of which recognizes the murine class I molecule H-2Dd. The murine H-2Dd-bearing target cell line, P815, was cotransfected with human class II HLA-DR alpha, beta and invariant chain cDNAs. Co-culture of the parental T-cell and P815 lines, or of one parental and one transfected line resulted in a low baseline response. In contrast, a substantial increase in response was observed when CD4+ 3DT-52.5.8 cells were co-cultured with HLA-DR+ P815 cells. This result strongly indicates that CD4:HLA-DR binding occurs in this system and that this interaction augments T-cell activation.

Thymopoietin, a polypeptide hormone isolated from bovine thymus, induced in vitro the differentiation of prothymocytes to cells with the antigenic and functional characteristics of intrathymic thymocytes. These changes included the acquisition of the differentiation antigens TL and Thy-1 (theta) and the ability to respond to the mitogen Con-A. Thymopoietin appears to be highly speicfic in inducing the prothymocyte to be highly specific in inducing the prothymocyte to thymocyte differentiation and does not affect the pluripotential stem cell measured by the colony forming assay (CFU-S), the erythropoietin-sensitive cell or B-cells. Experiments are in progress to determine whether additional hormonal inductive signals are required to complete the differentiation of an immunologically competent T-cell.

Previous immunofluorescent studies have shown that differentiation antigens recognized by the monoclonal antibody (OKT6) are present on the external membranes of human epidermal Langerhans cells, cortical thymocytes and some cultured T cell lines. In the present investigation, the biochemical characteristics of the OKT6 recognized antigens derived from these three sources were compared. Following immunoprecipitation with OKT6, a single band with an approximate molecular weight of 52,000 daltons was identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (under both reducing and nonreducing conditions) in the detergent lysate of radioiodinated normal epidermal cells. A molecule with the same apparent molecular weight was immunoprecipitated from thymocytes and cultured MOLT-3 (T cell-acute lymphoblastic leukemia) cells. However, a low molecular weight protein of approximately 10,000 daltons was coprecipitated from these MOLT-3 cells. No electrophoretically identifiable antigens were precipitated from peripheral lymphocytes or monocytes with OKT6. These observations further distinguish Langerhans cells from classical monocytes, indicate that these cells express a membrane antigen otherwise characteristic of cortical thymocytes, and suggest the potential usefulness of the monoclonal antibody, OKT6, in further investigations of the functions and ontogeny of Langerhans cells.

Monoclonal antibodies that react with all T cells (OKT3), the inducer-helper T cell subset (OKT4), and the suppressor-cytotoxic T cell subset (OKT8) have been used to evaluate T cell and T cell subpopulations in synovial fluid (SF) from patients with rheumatoid arthritis (RA). We found that the immunoregulatory ratio of SF lymphocytes ranged from normal values to extremely low values indicating normal to excess numbers of OKT8+ cells. The rheumatoid synovium in patients with RA is characterized by the presence of lymphoid aggregates in which HLA-DR+ interdigitating cells form close contacts with a large number of OKT4+ T cells, while the OKT8+ T cells are sparse. It may be that the localizing mechanisms for OKT8+ suppressor cells in lymphoid aggregates are deficient in RA and the cells are thus permitted to pass into synovial exudates, resulting in an increase of OKT8+ cells in the SF.

We characterized T-lymphocyte subsets in peripheral blood of smokers (N = 60) and nonsmokers (N = 35). Total T-lymphocytes and T cell subsets were similar to nonsmokers in light and moderate smokers. In heavy smokers, total OKT3+ cells were increased, the percentage of OKT4+ cells was decreased, and percentage and total number of OKT8+ cells were increased. The ratio of OKT4+ to OKT8+ lymphocytes was decreased in heavy smokers. The percentage of OKT8+ cells and the OKT4+/OKT8+ ratio returned to normal in heavy smokers six weeks after they stopped smoking. These findings suggest that cigarette smoking causes reversible alterations in immunoregulatory T cells.

Thirty-two patients with acute leukemia, chronic granulocytic leukemia, or multiple myeloma received a T lymphocyte-depleted HLA-identical marrow. After being treated with pan-T monoclonal antibodies (MoAbs) and one round of baby rabbit complement, the mean percentage of T cell depletion was 94% +/- 4%. The number of residual viable T cell infused to the patient was 0.99 +/- 0.65 X 10(6) per kg body weight. The patients were conditioned with fractionated total body irradiation (TBI) (12 Gy) preceding high doses of cyclophosphamide (120 mg/kg). Methotrexate was used as an additional immunosuppressant in the first ten patients. For the following 22 patients no posttransplant immunoprophylaxis was administered. Eight patients died within three months due to complications related to transplantation. Engraftment was achieved in all evaluable patients, and no patient has a late graft failure. The proof of total chimerism was established in 24 patients. Twenty-four of 27 evaluable patients (88%) did not have an acute graft-v-host disease (GVHD) greater than grade 0 to 1. Two patients had a grade 2 (skin only), and one patient had a grade 4 acute GVHD (the latter had only 80% of T cell depletion). A medullary relapse occurred in 11 patients (nine of them had previously been defined as "high risk leukemia"). Our data suggest that it may not be necessary to deplete nearly all T cells to prevent acute GVHD in recipients of HLA-identical marrow.

Evidence is presented that the OKTA+ T cell subset in man, defined by a monoclonal hybridoma antibody, provides help for B lymphocyte differentiation in a PWM driven system. Both B cell proliferation and intracytoplasmic immunoglobulin synthesis are facilitated by OKT4+ and not by OKT4- T cells. Given earlier studies demonstrating that OKT4+ T cells were necessary for generation of T cytotoxic cells and the present study that OKT+ T cells are necessary for the differentiation of B cells, it would appear that the OKT+ population is the major human T helper (inducer) subset.

Induction of early lymphocyte differentiation was studied in vitro in fractionated bone marrow cells of newly hatched chickens, with alloantiserums to identify newly differentiated B cells (Bu-1+) and T cells (Th-1+). Thymus extract induced selective T cell differentiation; the activity of the extract corresponds to that of thymopoietin. Bursal extract induced both B cell and T cell differentiation, but at lower concentrations B cell differentiation was always greater. This activity is ascribed to a lymphocyte-differentiating hormone of the bursa of Fabricius, for which the name bursopoietin is suggested.

Thymopoietin is a polypeptide hormone of the thymus that consists of a 49 amino acid polypeptide chain of 5562 daltons. A peptide corresponding to positions 29-41 of bovine thymopoietin II was synthesized by the Merrifield solid-phase technique. This peptide was shown to have a purity (correct sequence) of 96% by amino acid and C terminal analyses and by a complete determination of the amino acid sequence by manual Edman degradations. It displayed a selectivity of action similar to that of thymopoietin itself, inducing the differentiation of T lymphocytes but not of complement receptor (CR+) B lymphocytes. Although a number of substances induce the differentiation of both T cells and CR+B cells under the conditions of assay in vitro, only thymopoietin and the synthetic peptide described in this report have been shown to induce the differentiation of T cells selectively. Our data establish that the key residues involved in the active site of thymopoietin are present within a synthetic polypeptide which constitutes a minor portion of the amino acid sequence of thymopoietin. Since this peptide had 3% activity by comparison with thymopoietin, the tertiary structure of thymopoietin may be required for optimal configuration of the active site to produce full biological activity.

The anti-T cell monoclonal antibody OKT3 was administered to renal allograft recipients. A dramatic depletion of peripheral T cells was immediately observed followed, after 2-5 days, by the reappearance of a limited but significant number of or OKT3-4+ or OKT3-8+T cells showing antigenic modulation of the OKT3-defined antigen. These cells recovered the OKT3 receptor after overnight in vitro incubation.

A polypeptide of 8500 molecular weight is described that induces the differentiation of T (thymus-derived) cell and B (bone-marrow-derived) cell immunocytes in vitro, apparently via beta-adrenergic receptors and adenylate cyclase activation. This polypeptide shows a high degree of evolutionary conservation, exhibiting close structural, functional, and immunological similarity when isolated from such diverse origins as cells of mammals and higher plants. This polypeptide was detected in animal cells, yeast, bacteria, and higher plants, and so may well be a universal constituent of living cells.

Three new techniques have been introduced for the phenotypic analysis of human thymocytes and T cells. Monoclonal antibodies of different subclasses (i.e. IgG1 and IgG2) were used in various combinations and labelled with subclass-specific second layers conjugated to different fluorochromes. Tissue sections were studied with combinations of monoclonal and conventional reagents, and anti-mouse Ig-coated macrobead columns were used to separate antibody-tagged cells. With the help of these simple techniques, four stage of thymocyte differentiation (prothymocyte, cortical, intermediate and medullary cell types) can be described in detail and the microanatomical relation of T cell subsets with other cell types studied.

In order to determine whether abnormalities of immunoregulatory T-cells occur in patients with lung cancer, we characterized peripheral T-lymphocytes in 26 patients with untreated lung cancer. The results in patients with primary squamous cancer (SC) (n = 10), primary adenocarcinoma (AC) (n = 7), and secondary lung metastases (M) (n = 9) were compared with each other and to subjects without cancer (n = 48), including nonsmokers (n = 29) and smokers (n = 19). We found that OKT3+ (mature, peripheral (T-lymphocytes, including both OkT4+ (inducer/helper) and OKT8+ (cytotoxic/suppressor) lymphocytes, were increased in light-to-moderate smokers, but that OKT4+ cells were decreased n heavy smokers (p less than 0.05). The ratio of OKT4+ to OKT8+ (4/8) lymphocytes, reflecting the balance of immunoregulatory cells, was normal in light-to-moderate smokers, but was decreased in heavy smokers (p less than 0.05). The profile of circulating T-cells in patients with SC was similar to the smokers. In contrast, in patients with AC, we found a decreased percentage of OKT8+ cells (p less than 0.05). The 4/8 ratio was elevated in patients with AC (p less than 0.05). In patients with M, there was a decreased percentage of OKT3+ cells reflected in both OKT4+ and OKT8+ subsets. The 4/8 ratio in patients with M was low. Thus, a number of abnormalities in circulating T-cells was found both in smokers and in patients with lung cancer. These results suggest that immunoregulatory abnormalities contribute to the pathogenesis of lung cancer.

The nature of Ia antigens which appear on human T cells after activation and the stimuli required for their expression was examined utilizing a monoclonal antibody reactive with the Ia antigen framework. T cells were purified using monoclonal antibodies directed either at the entire T-cell population (OKT3) or the T-cell inducer subset (OKT4). By indirect immunofluorescence, it was shown that the human T-cell population contains no detectable Ia+ cells in the resting state. In contrast, in excess of 60% of the T-cell population expresses Ia antigen after alloactivation in the mixed lymphocyte culture. Moreover, these Ia antigens are expressed within both the OKT4+ and OKT4- subsets. Similarly, phytohemagglutinin and concanavalin A induced approximately 20% of peripheral T cells to express Ia antigen and the expression of these antigens is not restricted to either OKT4 subset. In contrast, only the inducer T-cell population which proliferates maximally to soluble antigen expresses Ia antigens after activation by tetanus toxoid. Thus, the expression of human Ia antigens on unique T-cell subsets depends upon the activation stimuli utilized and ability of the individual subset to respond to a given stimulus. Additional studies indicated that Ia antigens appear on previously Ia- T cells after activation and do not result from clonal expansion of a small subset of Ia+ T cells.

Ten consecutive patients undergoing transplantation of bone marrow from histocompatible siblings for treatment of haematological malignancy took part in a pilot study to test the safety of in-vitro treatment of donor bone marrow with monoclonal antibody OKT3. Three male and seven female patients aged 7-34 years received concentrated bone marrow buffy-coat cells which had been incubated with OKT3 before infusion. In-vitro studies confirmed that almost all immunocompetent T lymphocytes in the bone-marrow samples were coated with OKT3 at the time of infusion. In vitro, neonatal rabbit complement inhibited the proliferation of bone-marrow T lymphocytes in samples preincubated with OKT3 to less than 4% of the mitogenic responses of the untreated bone marrow. In contrast, fresh autologous complement did not effectively lyse OKT3-treated bone-marrow cells. Infusion of OKT3-treated bone marrow was safely accomplished, and engraftment was achieved in all patients (mean 23 days). Nine of ten patients survived for more than 100 days after bone-marrow transplantation, but significant acute graft-versus-host disease (GvHD) requiring treatment with steroids developed in five of the ten. This finding suggests that further modifications for bone-marrow pretreatment will be needed to achieve effective prophylaxis against acute GvHD in histocompatible bone-marrow transplantation.

In this report, we explored the functional heterogeneity within the OKT4+ subset of human T cells. Evidence was obtained that although in vitro pokeweed mitogen-activated OKT4+ cells can function as radioresistant helper cells, these activated OKT4+ cells could also exert potent feedback suppression. Despite the induction of suppressor cells after pokeweed mitogen activation, the OKT4+ population maintains its original OKT3+, OKT4+, nd OKT8- surface phenotype. The suppressor cells contained within the activated OKT4+ population were found to be radiosensitive. Importantly, the suppression mediated by activated OKT4+ cells required the presence of radiosensitive cells contained within the resting OKT4+ population. Taken together, these results suggest that the OKT4+ subset of human T cells contains cells that can be activated to differentiate into suppressor cells independent of OKT8+ cells.

In the present report, we characterize a monoclonal antibody directed at a surface differentiation antigen on human T cells. The monoclonal antibody, OKT17, recognizes a cell surface antigen present on the majority of resting normal peripheral T cells. In contrast, OKT17 is unreactive with normal B cells, B cell lines, T cell lines, or SIg+ CLL. Interestingly, after activation, the antigen recognized by OKT17 is lost from a subset of OKT4+ cells. We took advantage of this finding to explore further the functional heterogeneity within activated OKT4+ cells. Evidence was obtained that the PWM-activated OKT4+ subset remaining after depletion of OKT17-reactive T cells (OKT4+ 17-) contains radiosensitive helperr cells but is devoid of suppressor cells. In contrast, the activated OKT4+ 17+ population contains potent radiosensitive suppressor cells as well as radioresistant helpe cells. Taken together, these studies suggest that the OKT17 monoclonal antibody can differentiate two functionally mature, activated OKT4+ human T cells: OKT4+ OKT17+ radiosensitive suppressor cells and OKT4+ 17- radiosensitive helper cells.

A series of mouse monoclonal antibodies reacting with human T cells of the helper/inducer subclass, OKT4, 4A, 4B, 4C, and 4D, have been reported. Using double-fluorescent staining and complement-mediated depletion, it was shown that the antigen(s) recognized by OKT4, 4A, 4B, 4C, and 4D antibodies are present on the same cell. Using FITC-labeled OKT4, 4A, 4B, 4C and 4D, a lack of competition between the antibodies for their epitopes was shown. Immunoprecipitation of the antigen recognized by each antibody yielded a molecule of approximately 60,000-62,000 Da. Sequential precipitation with several antibodies resulted in a minimum of additional precipitated antigen following removal of the first antigen. Capping of cell surface antigen with OKT4, followed by staining with OKT4, 4A, 4B, 4C, or 4D, indicated that the epitopes for all five antibodies co-cap. A sandwich ELISA assay using OKT4 and the other antibodies showed that molecules binding to OKT4A, 4B, 4C, and 4D also bound OKT4. It can therefore be concluded that monoclonal antibodies OKT4, 4A, 4B, 4C, and 4D recognize distinct epitopes present on a molecule of approximately 60-62,000 Da on human helper/inducer T cells.

Monoclonal antibodies specific for human T cell subsets have been tested for their immunosuppressive effect in a rhesus monkey skin graft model. Rhesus monkeys were injected i.v. daily with antibodies specific for helper T cells (OKT4 and 4A), for cytotoxic/suppressor T cells (OKT8A), or all peripheral T cells (OKT11A), and they received an allogeneic skin graft one or two days after the initial antibody treatment. The OKT4, 4A, and 11A antibodies prolonged skin graft survival, but OKT8A did not. All animals were carefully monitored regarding levels of T cell subsets and antibody formation to the injected monoclonal antibody. The relevant T cell subset was not eliminated from the circulation when OKT4 and OKT4A antibodies were given separately. The OKT4+ cells remained in the circulation coated with antibody. OKT4+ cells could no longer be demonstrated when both OKT4 and 4A were given simultaneously. However, this difference in effect on the OKT4+ cells did not influence skin graft survival time. All animals receiving monoclonal antibody treatment developed antimouse-Ig antibodies after 10 to 13 days of treatment, which presumably counteracted the effect of the antibodies. From these data it appears that the rhesus monkey is a useful animal model in which to investigate the potential of monoclonal antibodies against human lymphocyte subpopulations to modify and regulate the immune response in an orderly fashion.

Thymopentin, a synthetic pentapeptide fragment of thymopoietin (residues 32-36, Arg-Lys-Asp-Val-Tyr) is biologically active but susceptible to proteolytic digestion. Analogs were synthesized and studied for biological activity and susceptibility to peptidases. Amino acid changes were incorporated at positions known to not affect activity adversely and N-terminal acetylation and C-terminal amidation were used to increase resistance to proteolytic degradation by exopeptidases. Ac-Pro2-TP5-NH2 and Aib2-TP5-NH2 retained activity and were shown to exhibit a high degree of stability when incubated in human serum.

The development of monoclonal antibodies to human differentiation antigens and cytofluorographs have added a new dimension to immune monitoring. However, the technology is such that regionalization will most likely occur. We have demonstrated that human lymphocyte antigens OKT3, OKT4, OKT8 and OKT11 are stable in blood samples stored in ACD at room temperature for less than 72 h. This will allow samples to be analyzed in regional centers.

OKT3 monoclonal antibody to human T cells inhibits the target cell lysis mediated by allogeneic cytotoxic T cells and the generation of these effector cells in mixed lymphocyte culture. This marked inhibition of cell-mediated lysis is not found with other monoclonal antibodies also reactive with cell surface antigens of human T cells (OKT1, OKT4, OKT5, OKT6, OKT8, and OKT11). OKT3 antibody is mitogenic and this effect appears to require receptor activation in that it occurs at low concentrations (10(-12) M range) of OKT3 antibody, requires intact OKT3 IgG, and is inhibited by a factor(s) in human plasma. By contrast, the inhibition of allogeneic cell-mediated lysis by OKT3 antibody appears to be due to steric hindrance in that it requires higher concentrations of OKT3 antibody (10(-8) M range), Fab fragments retain approximately 10% activity, and inhibition is demonstrable in the presence of human plasma. These findings are consistent with the suggestion that OKT3 antibody reacts with the human T-cell antigen-recognition structure.

Three human lymphocyte antigens recognized by monoclonal antibodies OKIa1, OKT9, and OKT10 were found to be minimally represented on resting peripheral T cells (all three) and thymocytes (OKIa1 and OKT9). These antigens, which are present on "activated" T cells, were promptly displayed on "resting" T cells or thymocytes following cross-linking of surface-bound monoclonal antibody by horse alpha-mouse IgG. These experiments suggested that membrane perturbations may induce the expression of certain antigens that are normally present in an unexpressed form in resting cells.

Sera from 13 patients with mycosis fungoides and 2 with Sezary syndrome were tested for activity that induces lymphocyte differentiation. Induction of Thy-1.2 antigen and surface immunoglobulin were used, respectively, to measure T- and B-cell differentiation. The indicator cells were null lymphocytes from the spleens of congenitally athymic nude mice. Normal serum induced some T-cell but no B-cell differentiation. The T-cell-inducing activity was ascribed to thymic hormone and declined with advancing age. A totally different pattern emerged with patient serum. T-cell-inducing activity was significantly more active than in normal serum (p less than 0.001). This activity did not decline with advancing age and was not inhibited by a concentration of ubiquitin, which blocks nonspecific beta-adrenergic induction. B-cell-inducing activity was also present. This novel serum factor (or factors) is a potent inducer of T- and B-lymphocyte differentiation and is associated with neoplastic lymphoproliferation of the T-cell series.

Terminal deoxynucleotidyl transferase is an enzyme which has the unique property of polymerizing polydeoxynucleotides onto a primer in the absence of a template (1,2). This enzyme is found both in the thymus and the bone marrow of birds, rodents, and humans (3-7). Whether the marrow cells that contain terminal transferase are related to thymocytes, or are on a separate pathway of differentiation, is not yet known (7,8). To determine the lineage of the murine bone marrow cells that have terminal transferase, we have investigated whether these cells have the antigen Thy-1 induced on the cells by treatment with thymopoietin (9). Thymopoietin is known to induce a set of characteristic T-cell markers including the Thy-1 alloantigen on the surface of a subpopulation of bone marrow cells committed to T-cell differentiation (prothymocytes) (10). Destruction of Thy- 1-positive cells after exposure to thymopoietin allows elimination of a substantial fraction of those bone marrow cells that can repopulate an irradiated thymus (11). We find that such an elimination after induction with the thymic polypeptide removes a substantial amount of terminal transferase from the bone marrow cell population, suggesting that at least one-half of the marrow cells bearing this enzyme are related to those found in the thymus.

Peripheral blood helper-inducer and cytotoxic-suppressor T-cell subpopulations in patients receiving marrow transplants for the treatment of acute leukemia or severe aplastic anemia were quantitated on the fluorescence-activated cell sorter (FACS) using the monoclonal antibodies OKT4 and OKT8, respectively. The relative (percent) and absolute number of OKT4+ cells were severely and persistently depleted for up to 2.7 yr posttransplant. In contrast, the percent and absolute number of OKT8+ cells began to recover within the first 60 days of transplant and subsequently remained at normal or high levels for periods of up to 7.3 yr. There was no significant difference in percent or absolute numbers of OKT8+ cells for patients with or without acute graft-versus-host disease (GVHD). The reversal of the normal OKT4:OKT8 ratio (2:1) occurred regardless of whether the recipient was given an allogeneic, syngeneic, or autologous transplant and regardless of whether or not acute or chronic GVHD developed. The reversed ratio was due in the first 3 mo posttransplant to low numbers of OKT4+ cells and later to a combination of low numbers of OKT4+ and high numbers of OKT8+ cells. Normalization and then an increase in the number of OKT8+ cells correlated with increasing time posttransplant and not with resolution of acute GVHD.

OKT10 and OKT20 are monoclonal antibodies that recognize cell surface antigen(s) on resting thymocytes, plasma cells, null cells, monocytes, and some bone marrow cells. The respective antigens, poorly expressed on resting peripheral T cells, are strongly expressed on T cells activated either in vitro or in vivo. Double-staining experiments using either OKT10 or OKT20, in combination with OKT3, provided paradoxical results. If indirect staining with OKT3 plus horse alpha-mouse IgG preceded staining with OKT10 or OKT20, most cells showed double staining; all other staining sequences yielded the expected result that OKT3+ cells expressed very little OKT10 or OKT20. Analysis of the experiments revealed that perturbation of the cell membrane with a monoclonal antibody reactive with a cell surface antigen (for example, OKT3) followed by a crosslinking second antibody caused the expression of these antigens. This suggests that these antigens, normally expressed on activated T cells, are actually present in an unexpressed form within the membrane of resting T cells.

Cells bearing the T-cell differentiation alloantigens TL and Thy-1 were enumerated in preparations of spleen and lymph node cells of nu/nu mice. Healthy nu/nu mice had few or no demonstrable TL+ or Thy-1+ cells whereas mice with viral hepatitis, including some born of nu/nu X nu/nu matings, had many. Healthy nu/nu mice were treated daily with the thymic hormone thymopoietin or with ubiquitin, polypeptides that induce the differentiation of TL+Thy-1" cells from TL-Thy-1- precursors in vitro. After 14 days, 20 to 40 percent of their spleen cells were of the TL+Thy-1+ phenotype typical of thymocytes and 10 to 25 percent of their lymph node cells were TL-Thy-1+, typical of later T-cell differentiation. Similar frequencies of such cells were found in untreated nu/nu mice suffering from severe viral hepatitis. These data conform to the current view that prothymocytes are preprogrammed cells whose maturation to thymocytes, normally induced in the thymus by thymopoietin, can be triggered by other agents under abnormal circumstances. Tests of T-cell function were not included in this study.

Three cell surface antigens that are structurally related to the human major histocompatibility antigens (called HLA antigens) have been characterized from the leukemic T cell line MOLT-4. One antigen is a glycoprotein of Mr 49,000 recognized by two monoclonal antibodies. OKT6 and NA1/34, and is associated with a Mr 12,000 subunit that crossreacts serologically with beta 2-microglobulin but can be distinguished from it by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A second antigen, defined by the monoclonal antibody OKT10, is a Mr 46,000 protein associated with a small subunit distinct from beta 2-microglobulin. The OKT10 antigen is not restricted to T cells and is found on all T and B lymphoblastoid cell lines tested. The third protein is a beta 2-microglobulin-associated glycoprotein of Mr 43,000 that is serologically distinct from the OKT6 (NA1/34), OKT10, and HLA antigens. It is found on some, but not all, T cell lines but is absent from any other hematopoietic cell lines tested.

A hybridoma-secreting monoclonal antibody was produced from the spleen cells of a mouse immunized with human thymocytes. This hybridoma antibody, termed OKT5, was reactive by indirect immunofluorescence with 80% of human thymocytes but only 20% of peripheral blood T cells. Moreover, OKT5 was unreactive with normal B cells, null cells, and macrophages at any dilution tested. A similar pattern of reactivity was seen with an equine antiserum to human thymocytes termed anti-TH2. Fluorescence-activated cell sorting demonstrated that the OKT5 antibody reactivity on peripheral T cells was restricted to the majority of the previously defined TH2+ subpopulation. In functional studies, the OKT5+ subset, like the TH2+ subset, proliferated well to the mitogen Con A and to alloantigens, and contained cytotoxic effector cells after sensitization in MLC, and suppressor effector cells after activation with Con A. In addition, like the TH2+ T cell, the OKT+ T cell was virtually unresponsive to soluble antigen. Thus, the OKT5 monoclonal antibody is reactive with the cytotoxic/suppressor T cell subset. OKT5 should provide an important probe to assess the status of suppressor cells in human disease.

A panel of monoclonal antibodies and other markers (e.g., terminal deoxynucleotidyl transferase, sheep erythrocyte rosettes, peanut agglutinin) have been used in conjunction with flow cytometry and biochemical analysis to monitor the induction of maturation in human thymic (T) leukaemic cell lines by phorbol ester (TPA). Seven cell lines underwent multiple phenotypic alterations in response to TPA but were unresponsive to synthetic thymic hormones (TP5, FTS) or to other compounds (e.g. DMSO, retinoic acid) which induce maturation in other types of leukaemia. The changes parallel those observed in normal T-cell differentiation and partly reflect alterations in glycosyl transferase activity, altered synthesis of proteins and regulation of cell surface receptors (for transferrin) associated with rapid growth and metabolism. These studies further illustrate the reversibility of maturation arrest in human leukaemia and provide support for the view that leukaemia may involve regulatory defects in the coupling of proliferation and maturation. Induction of promotion of terminal differentiation in leukaemic equivalents of T-cell precursors may provide a convenient system for the study of biochemical and molecular events involved in T-cell development and diversification.

Sequential monitoring of peripheral blood T cell populations was performed in normal control individuals and in 55 renal allograft recipients. In addition, 66 patients exhibiting prolonged renal allograft survival were each evaluated at least once with the same monoclonal antibodies. A normal or elevated OKT4:OKT8 ratio, especially in the presence of rising numbers of OKT4+ cells was predictive of possible future graft rejection. This observation, when followed by rising serum creatinine values coupled with biopsy evidence of glomerulopathy, was found in at least 15% of graft recipients. In a small number of patients, graft rejection episodes were successfully suppressed by administration of therapeutic doses of OKT3 antibody. However, production of anti-OKT3 antibodies was observed and may be expected to limit administration of this agent to a single short course in each patient.

Ten established human cell lines were tested for their responsiveness to thymopoietin by measuring their intracellular cyclic nucleotide levels. Three T cell lines (CCRF-CEM, MOLT-4 and CCRF-HSB-2) responded to thymopoietin with elevations of intracellular cGMP but not cAMP; seven other human cell lines did not respond to thymopoietin (three T cell lines, three B cell lines and one erythropoietic stem cell line). Interestingly, only one cell line (MOLT-4) was also responsive to the closely related polypeptide splenin, and this reactivity was restricted to human and not bovine splenin. The detection of human cell lines with distinctive patterns of response to immunoregulatory peptides should provide support for understanding the immunopharmacological mechanisms by which these molecules act.

The availability of highly specific and homogeneous antibodies to human T cells by the hybridoma technique has elicited new interest in the clinical use of antibodies to lymphocytes as immunosuppressive agents. OKT3 is the murine monoclonal antibody that has been the most widely used in clinical transplantation to induce immunosuppression. This antibody recognizes a membrane molecular complex, exclusively present on mature human T lymphocytes, which is tightly linked to the T-cell antigen receptor. The long-term therapeutic use of murine monoclonal antibodies in vivo is hampered by the intense antibody response that occurs in most human patients. Thus, when administered alone, OKT3 manifests its immunosuppressive activity only during the 10 to 15 days that precede the onset of sensitization. The results presented here show, by use of isoelectrofocusing, that the antibody response to OKT3, already reported to be restricted in its specificity (only anti-isotypic and anti-idiotypic antibodies are produced), is in addition oligoclonal. This restriction of the anti-monoclonal response may suggest that an efficient way to circumvent the sensitization problem would be to administer consecutively different monoclonal antibodies presenting the same specificity but distinct idiotypes.

It was established previously that committed precursors of T cells, which reside in bone marrow and spleen and lack T cell surface differentiation antigens, can be induced by thymopoietin and certain other agents to differentiate rapidly in vitro into T cells bearing typical surface antigens, including Thy-1 and TL (Komuro-Boyse assay). To relate this differentiative step observed in vitro to physiologic events in vivo, a system was devised to trace the migration of precursor cells to the thymus, and their maturation to T cells. Lethally irradiated mice of a TL- strain received spleen cells from TL+ hybrids i.v., and the TL+ population of the thymus was enumerated 13 to 20 days later. Donor TL+ cells first became detectable at 13 days and increased thereafter. Preliminary tests showed that cells capable of migrating to the thymus have a similar density to the cells that are inducible in the Komuro-Boyse assay, this being lower than that of mature of T cells. The thymus-repopulating properties of the donor spleen population were not affected by: 1) pre-treatment in vitro with thymus extract or thymopoietin, which initiates differentiation of T cells precursors, nor b) pre-treatment with anti Thy-1 serum plus complement, which eliminates differentiated T cells. But pre-treatment a) and b) applied in sequence markedly reduced the capacity of spleen cells to repopulate the thymus. These results can be interpreted as follows: induction of Thy-1-TL- precursor cells (pro-thymocyte) in vitro yields Thy-1+TL+ cells (early thymocytes) which have not yet lost their property of repopulating the thymus; therefore, thymus-repopulation was not depleted by treatment a) alone, which induced Thy-1 +TL+ cells, nor by treatment b) alone, which did not affect thymus-repopulation by Thy-1-TL- cells, although treatments a) plus b) did eliminate the newly induced Thy-1+TL+ cells and thus impaired repopulation of the thymus. We conclude that the cell which responds to thymopoietin in the Komuro-Boyse assay by expressing the T cell surface phenotype is the same cell (pro-thymocyte) that normally migrates in vivo from hemopoietic tissues to the thymus and is there induced by thymopoietin to express the phenotype of an early T cell.

In the present study, we investigated the immunoregulatory potential of OKT8+ cells after in vitro activation. Initial studies had demonstrated that the T cell marker OKT4 identifies T cell sets containing helper cells, whereas OKT8 reacts with the suppressor and cytotoxic T cell effectors. More detailed analysis of the OKT4+ subset, however, demonstrated that there is functional heterogeneity in the OKT4+ population. The evidence for this heterogeneity arose from studies on (1) the relative radiosensitivities of the distinct immunoregulatory functions of cells contained within this set, and, (2) the effects of the state of activation of this population on immune function. For example, OKT4+ cells included radiosensitive helper cells, radioresistant helper cells, and radiosensitive inducers of suppressor cells. Furthermore, after activation, the OKT4+ population also contained cells capable of suppressing B cell differentiation. Since activation of the OKT4+ population results in the emergence of cells with counterbalancing immunoregulatory properties, it was of interest to determine whether the state of activation of the OKT8+ population influences the immunoregulatory potential of this subset. In the experiments reported here E+ cells were cultured with pokeweed mitogen (PWM) for 60-70 h and then thoroughly depleted of OKT4+ cells, leaving OKT8+ cells. The ability of the PWM-activated OKT8+ cells (first culture) to exert suppressive activity was determined by adding graded numbers of these cells to fresh autologous OKT4+ cells and B cells. The cell mixtures were cultured in the presence of PWM for 5 days and then assayed for plaque-forming-cell (PFC) activity by the reverse hemolytic plaque assay. Our studies demonstrate that activation of OKT8+ cells results in the emergence of cells with apparently counterbalancing immunoregulatory properties. Activated nonirradiated OKT8+ cells consistently suppressed B cell immunoglobulin production. However, the immunoregulatory function mediated by irradiated activated OKT8+ cells is highly dependent on the magnitude of the helper activity obtained with fresh OKT4+ cells. Thus, irradiated activated OKT8+ cells suppressed the generation of PFC only when the level of helper activity was optimal. However, when the level of help was not optimal, no suppressor activity was observed; rather, under these conditions, irradiated activated OKT8+ cells amplify the PFC response. We would emphasize that the amplification function of irradiated OKT8+ cells depends strictly on the presence of fresh OKT4+ cells. Irradiated activated OKT8+ cells alone are not helper cells, since addition of these cells to B cells thoroughly dep

The extent and diversity of T cell differentiation in nude athymic mice are matters of dispute. In this study, we examined the splenic T cell population of pathogen-free and germ-free nu/nu mice, treated or not treated with the pentapeptide analogue of thymopoietin (TP-5), in terms of TL, Qa-1, and Lyt phenotypes. At all ages, 50-60% of nu/nu splenocytes, enriched for T lymphocytes by removal of sIg+ cells, expressed T markers, as compared with greater than 85% in normal mice. At 2 mo of age, all nu/nu splenic T cells expressed the surface phenotype TL+:Thy-1+:Ly-123. This is abnormal in two respects: first, because expression of TL is normally confined to thymocytes; and second, because there was no evidence of the usual diversification into the subsets Ly-1 and Ly-23. From 10 wk of age onwards, diversification into Ly subsets was evident in nu/nu spleen, although the usual predominance of Ly-1 over Ly-123 cells was not attained, and some TL+ cells persisted. Also, the ratio of Qa-1+ to Qa-1- cells rose progressively to as high as 4:1 at 4-6 mo, in contrast to the usual ratio of approximately 1:1, regardless of age. In the spleens of nu/nu mice treated with TP-5 from 5-8 weeks of age and tested 1 wk later, the proportion of T cells was raised, though not to normal levels, the number of TL+ cells was reduced, and there was diversification into Ly sets.

Two monoclonal antibodies (OKT27 and OKT27b) have been produced that react with distinct epitopes of a 95-kDa peptide. The T27 antigen is widely distributed, being expressed on B lymphocytes, monocytes, and adult T-leukemic cells but not on polymorphonuclear leukocytes or platelets. There was a low level of T27 expression on resting T cells that increased on T-cell activation. In preliminary studies, the OKT27b antibody coprecipitated a 55-kDa peptide, as well as the 95-kDa peptide, from the radiolabeled cells of the HuT 102B2 cell line. Preclearance with anti-Tac, a monoclonal antibody to the 55-kDa peptide of the multichain interleukin 2 receptor, removed the 55-kDa but not the 95-kDa peptide from subsequent OKT27b immunoprecipitates of HuT 102B2 extracts, suggesting the possibility that the T27 peptide was associated with the Tac peptide. However, the precipitation of the p55 Tac peptide by OKT27b was quite inconsistent. Thus, additional information was sought using a flow cytometric energy transfer technique to provide a physical estimation of the proximity between the Tac and the T27 peptides. The flow cytometric version of the fluorescence resonance energy transfer technique permits the determination of inter- and intramolecular distances at 2- to 10-nm levels on a cell-by-cell basis. Using this approach, there was a mean energy transfer of 7.3% with HuT 102B2 cells when fluorescein isothiocyanate anti-Tac served as the donor and tetramethylrhodamine isothiocyanate OKT27 served as the acceptor. In contrast, there was no energy transfer in comparable studies observed when fluorescein anti-Tac and rhodamine anti-transferrin receptor antibodies were used. These observations support the conclusion that there is a close nonrandom proximity in HuT 102B2 cells between the 95-kDa peptide identified by the OKT27 monoclonal antibody and the p55 Tac peptide of the multichain interleukin 2 receptor.

The authors review a large body of contemporary immunohistologic findings on the tissue distribution of T lymphocytes in normal and pathological conditions. The suggestions for technological advances in this field are: signal amplification using mixtures of monoclonal antibodies directed against different epitopes on the same antigen (e.g. OKT4A+B+D), triple layer amplification systems using hapten-labelled antibodies, and informative double staining methods with combinations of antibodies labelled with different fluorochromes or enzymes. Review of histological observations in a series of human diseases suggests that imbalances of OKT4+ and OKT8+ subsets of T lymphocytes may represent different types of immunoregulatory disorders. Rheumatoid arthritis and sarcoidosis appear to involve a high level of OKT4+ subpopulation response coupled with an associated appearance of a special type of HLA-DR+ macrophages. It remains to be seen whether normal or self-limited immunological responses (early stages of bacterial infection or delayed-type hypersensitivity reactions) produce OKT4+ and macrophage responses that are characteristically different. Meanwhile, excessive levels of OKT8+ cells have been found in a wide range of recognized or presumed immunoregulatory disorders including: graft-vs.-host reaction and viral infections. These disorders, as well as primary biliary cirrhosis and lichen planus, appear to possess both overlapping and disparate clinical characteristics, and the immunohistological observations may reflect the functional heterogeneity of OKT8+ populations in these diseases. These studies show that histologically meaningful heterogeneity can already be demonstrated for the OKT8+ lymphocyte group.

Immunofluorescence studies were carried out in cutaneous T cell lymphoma (mycosis fungoides) in order to analyse the microanatomical relationship of the different T lymphocyte subsets (inducer and suppressor/cytotoxic cell populations) to large nonlymphoid Langerhans-type and so-called "indeterminate" or interdigitating cells. The conventional and mouse (monoclonal) antibodies were used in various combinations using fluorescein and rhodamine labeled second layers. In 5 of the 7 cases studied the dermal infiltrate consisted of numerous T (HuTLA+) lymphocytes, 80-90% of which expressed the inducer phenotype (HuTLA+,OKT4+). Most of these cells formed close contact with large cells exhibiting large amounts of Ia-like antigens. These cells corresponded to the interdigitating and indeterminate cells in the sections. By contrast, only small numbers (10-20%) of T cells of suppressor/cytotoxic type (HuTLA+,OKT8+) were seen. These did not show a close affinity to the Ia-like antigen positive nonlymphoid component but appeared to have a predilection for the epidermis. Epidermal Langerhans cells, also strongly Ia-like antigen positive, were further defined by 2 monoclonal antibodies reacting with a cortical thymocyte antigen HTA-1. Although Langerhans cells are probably related to the Ia-like antigen positive dermal cells only a few of the abundant latter population were HTA-1+. In the remaining 2 cases, larger populations of OKT8+ (suppressor/cytotoxic) cells were seen and could be heralding a particularly benign course. These observations indicate a close functional relationship between the lymphoid and Ia-like antigen positive dermal cells during the pre-malignant phase of cutaneous T cell lymphoma.