Cystemustine induces redifferentiation of primary tumors and confers protection against secondary tumor growth in a melanoma murine model.

N'-(2-Chloroethyl)-N-(2-(methylsulfonyl)-ethyl)-N'-nitrosourea (cystemustine) is a chloroethylnitrosourea that has been used in the treatment of human melanoma. Its main antitumor effect is DNA damage to malignant melanocytes. Although unreported at present, other effects may also account for its cytotoxicity, some of them could be more or less delayed with respect to its administration. In this report, we have developed a model of secondary tumor with B16 melanoma in syngeneic C57B16 recipients to investigate the impact of cystemustine treatment of primary B16 melanoma tumors on the fate of secondary implanted untreated tumors. The data presented in this report indicate that cystemustine-treated cells or the administration of cystemustine provoke an important growth delay of primary melanoma tumors, together with an increase in cell pigmentation and cell morphology changes. Data also show that prime treatment induces a dramatic decrease in tumor weight of secondary untreated tumors accompanied by an increase in melanin content and an alteration of cell morphology. Finally, 1H-NMR spectroscopy was performed on treated B16 cells, showing an alteration in the phospholipid derivatives of melanocytes, suggesting subsequent modifications of membrane phospholipid composition. In conclusion, the data highlight two important findings: (a) cystemustine produces modifications other than DNA damage, i.e., cell morphology changes, pigmentation, and phospholipid metabolism alterations, indicating an interference with cell cycle, cell redifferentiation, and proliferation programs; and (b) cystemustine-treated tumors appear to confer a protective effect against the development of secondary untreated tumors that may be mediated by cytokines or an immune response.

Aberrant expression of CD27 and soluble CD27 (sCD27) in HIV infection and in AIDS-associated lymphoma.

CD27 is a member of the tumor necrosis factor receptor superfamily that is expressed primarily on T cells, as well as on subsets of B cells and NK cells. CD70, which is expressed on activated B and T cells, but not on resting lymphocytes, is a ligand for CD27. Cell surface CD27 can be proteolytically cleaved to produce a 32-kDa soluble CD27 (sCD27) molecule. Elevated levels of sCD27 are seen in a number of disease states and malignancies. Although it has been reported that cerebrospinal fluid sCD27 levels were elevated in people who had AIDS dementia, little is known about CD27 expression in HIV disease. To determine if sCD27 levels were elevated in those with HIV infection, and/or in those with AIDS-associated non-Hodgkin's lymphoma (AIDS-NHL), sCD27 levels were measured in HIV-negative and HIV-positive subjects as well as in people who developed AIDS-NHL. Serum sCD27 levels were seen to be elevated in HIV+ subjects. Furthermore, sCD27 levels were particularly elevated in those subjects who went on to develop AIDS-NHL, with serum sCD27 levels in AIDS-NHL subjects being significantly higher than those in HIV+ subjects who did not develop lymphoma. Most AIDS-NHL cell lines and primary AIDS-NHL tumor specimens expressed both CD27 and its ligand, CD70. The proportion of circulating B cells that expressed cell surface CD27 was substantially reduced in those with HIV infection, and B cells from HIV-infected subjects produced decreased levels of sCD27 in culture. Together, these results indicate that CD27/sCD27 expression is abnormal in HIV infection and suggest that this molecule merits further examination as a potential marker for AIDS-NHL.

Chimeric anti-CD20 (IDEC-C2B8) monoclonal antibody sensitizes a B cell lymphoma cell line to cell killing by cytotoxic drugs.

More than 50% of patients with aggressive B lymphomas and the majority of patients with low grade lymphomas are not cured by current therapeutic strategies. The lymphomas express the B cell antigen CD20 on the cell surface and this antigen serves as target for antibody-directed therapies. Clinical studies with encouraging results have been underway with the use of a chimeric anti-CD20 antibody (IDEC-C2B8), consisting of human IgG1-6 constant regions and variable regions from the murine monoclonal anti-CD20 antibody IDEC-2B8. This study investigated the potential anti-tumor therapeutic value of combination treatment with anti-C2B8 and cytotoxic drugs. The in vitro study examined the sensitizing effect of C2B8 antibody on the DHL-4 B lymphoma line to various cytotoxic agents. Cytotoxicity was determined by the MTT assay. Surface and cytoplasmic proteins were determined by flow cytometry. Pretreatment of DHL-4 with C2B8 resulted in inhibition of cell proliferation and cell death and a fraction of the cells underwent apoptosis. While the DHL-4 tumor cells were relatively resistant to several cytotoxic drugs, pretreatment with C2B8 rendered the cells sensitive to TNF-alpha, ricin, diphtheria toxin (DTX), adriamycin and cisplatin but not to VP-16. Chemosensitization of DHL-4 tumor cells was not due to downmodulation of either the MDR-1 or bcl-2 gene products. However, treatment of DHL-4 with C2B8 inhibited TNF-alpha secretion. These findings demonstrate that C2B8 antibody potentiates the sensitivity of DHL-4 tumor cells to several cytotoxic agents. Further, the findings suggest that combination treatments with C2B8 antibody and drugs may be of clinical benefit in the treatment of patients with resistant aggressive B lymphomas.

Sensitization of AIDS related non-Hodgkin's B lymphoma cell lines to cytotoxic drugs toxins by interferon-gamma.

AIDS-related lymphomas (ARL) progressively become resistant to conventional chemotherapy. We have developed three B cell lines from tumor biopsies of AIDS patients with non-Hodgkin's lymphoma (NHL). The ARL cell lines were shown to be resistant to a panel of cytotoxic cytokines, toxins and drugs such as tumor necrosis factor, diphteria toxin, ricin, adriamycin, cis-platinum and anti-Fas antibody. However, when these cell lines were pretreated with low concentrations of interferon-gamma (IFN-gamma), (50 U/ml or 150 U/ml) for 24 to 48 h, the tumor cells became sensitive to these cytotoxic agents. Pretreatment of ARL with IFN-gamma stimulated proliferation while IFN-gamma inhibited the growth of ovarian tumor cell lines. Further, following treatment with IFN-gamma, the secretion of TNF-alpha by ARL lines was significantly decreased and TNF-alpha surface receptor expression was downregulated. The expression of several surface antigens on ARL was upregulated by IFN-gamma. These findings demonstrate that treatment of ARL with IFN-gamma stimulated cell proliferation, modulated several surface antigens, inhibited TNF-alpha secretion and sensitized the tumor cells to cytotoxicity by various drugs/toxins. These findings may be clinically relevant in the treatment of drug-refractory ARL.

In vitro T cell response to staphylococcal enterotoxin B superantigen in chronic plaque type psoriasis.

Recent studies have demonstrated the important role of CD4+ T cells in the pathophysiology of psoriasis. One of the current hypotheses is that triggering of the psoriatic inflammatory process could be secondary to CD4+ T cell activation by bacterial superantigens in the skin. In this study, IL-2-derived T cell lines were recovered from the blood and the skin of 4 patients with chronic plaque type psoriasis and of 2 patients with allergic contact dermatitis (ACD). Blood and skin T cell lines were tested for their ability to proliferate in vitro to staphylococcal enterotoxin B (SEB) presented by MHC class II expressing antigen-presenting cells. The results showed a significantly higher SEB-induced T cell proliferation in skin T cell lines as compared to blood T cell lines in 3 out of 4 psoriatic patients and in one of the 2 ACD patients. No difference between the skin and blood T cells for their response to phytohemagglutinin was observed. Furthermore the blood T cell lines from both patients and control individuals responded equally well to SEB. Thus psoriatic skin T cell lines were characterized by an enrichment in SEB-responding T cells. Since similar enhancement of SEB-responsive T cells was occasionally found in ACD patients, we propose that SEB could be an environmental factor associated with rather than responsible for psoriatic inflammation.

Establishment of nickel-specific T cell lines from patients with allergic contact dermatitis: comparison of different protocols.

Allergic contact dermatitis is a delayed-type hypersensitivity reaction, secondary to hapten-specific T lymphocyte activation in sensitized individuals. The present study reports on the establishment of T cell lines from peripheral blood mononuclear cells (PBMC) of nickel-allergic patients, initially cultured with nickel, IL-2, or PHA and IL-2. It was possible to derive hapten-specific T cell lines from the three protocols, and the best proliferative responses to nickel were observed when PBMC were cultured in the presence of nickel in vitro. T cell lines initially cultured with IL-2 always gave better specific proliferative responses to nickel than those derived with PHA and IL-2. Phenotypical analysis of the nickel-specific T cell lines showed that they were mainly composed of activated CD8+ TcR alpha beta + T lymphocytes. These results emphasize the importance of initial culture conditions for the generation of hapten-specific T cell lines and suggest that CD8+ lymphocytes could play an important role in the pathogenesis of allergic contact dermatitis.

[Bias of index of T-lymphocytes and chronic inflammatory dermatoses]. / Biais du répertoire des lymphocytes T et dermatoses inflammatoires chroniques.

The pathogenesis of chronic inflammatory and autoimmune diseases is still not understood. The hypothesis that a bias in the T cell receptor repertoire could explain the susceptibility of some individuals to a particular disease was recently proposed on the basis of results obtained in animal models of human diseases. In this review, we focus on the structure of the T cell receptor and on the new insights in the study of the T cell repertoire in human inflammatory diseases, with special emphasis to skin disorders.

The effect of anti-CD4 monoclonal antibody treatment on immunopathological changes in psoriatic skin.

Recent clinical studies which showed the therapeutic effect of cyclosporin A and of anti-CD4 MoAb emphasized the role of activated CD4+ T cells infiltrating the lesional skin in the pathogenesis of psoriasis. The aim of the present study was to analyze the mode of action of anti-CD4 MoAb in 3 psoriatic patients who experienced an anti-CD4 MoAb-induced clinical improvement maximal 3-4 weeks after the onset of an 8-day therapy. We evaluated the effect of anti-CD4 MoAb treatment on the phenotype of resident and passenger inflammatory skin cells in lesional skin samples. We observed a gradual improvement of 3 out of 4 histopathologic features including parakeratosis, papillomatosis and acanthosis. In the dermis there was no modification in the density of the dermal mononuclear cell infiltrate, which consisted mainly of CD3+, CD45RO+, TCR alpha beta+, CD11a+, HLA-DR+T cells with a CD4/CD8 cell ratio of 1.5/1. Therefore as previously observed for peripheral blood mononuclear cells, the number of CD4+ T cells infiltrating the dermis remained unaffected by the treatment. In contrast, CD4 MoAb treatment was associated with drastic changes in the epidermis. These included a decrease in both CD4+ and CD8+ epidermal T cell infiltrate, diminished numbers of ICAM-1+ and HLA-DR+ keratinocytes and restored numbers of CD1a+ epidermal Langerhans cells. We conclude from this study that clinical improvement of psoriasis by anti-CD4 MoAb therapy paralleled: (1) a decrease in epidermal T cells, and (2) a down-regulation of keratinocyte activation markers (ICAM-1 and HLA-DR). These results suggest that the observed changes are secondary to down-regulation of inflammatory cytokine production by T cells in situ.

Sensitivity of drug-resistant B-cell lines from AIDS-related non-hodgkins-lymphoma to newly synthesized podophyllotoxin derivatives and aza-alkyllysophospholipids - enhanced sensitization by pretreatment with interferon-gamma.

Non-Hodgkin's lymphoma B cells (NHL-B) often become refractory to conventional chemotherapeutic drugs. The present study investigated the sensitivity of three AIDS-derived NHL-B cell lines to newly synthesized azaalkyllysophospholipids (AALP) and podophyllotoxin derivatives. All three cell lines were sensitive to 5 AALP derivatives and toxicity was detectable at 24 h of culture and was increased at 48 and 72 h of incubation. Toxicity was concentration-dependent and die extent of cytotoxicity varied slightly from one cell line to another. These cell lines were less sensitive to the podophyllotoxin derivatives VP-16, BDPTN and BEPT than to die AALP. This was shown by the extent of cytotoxicity calculated on a molar basis and by the delayed kinetics of lysis. Pretreatment of the tumor cells with IFN-gamma stimulated cell proliferation. IFN-gamma treated tumor cells were also tested for their sensitivity to the various cytotoxic agents. In all cases, the sensitivity of the IFN-gamma pretreated cell lines to the podophyllotoxin derivatives and AALP was significantly enhanced. These findings demonstrate that drug resistant NHL-B cells are sensitive to a new family of AALP and podophyllotoxin derivatives. Further, the sensitivity of the tumor cells was enhanced by treatment with IFN-gamma. The potential clinical use of these new cytotoxic agents to overcome resistance of AIDS-related cell lymphomas is discussed.

Contact sensitivity in mice: differential effect of vitamin D3 derivative (calcipotriol) and corticosteroids.

Vitamin D3 derivatives are new compounds used topically for the treatment of psoriasis. To get better insights into the mechanisms of action of these compounds, we studied the effect of local treatment with calcipotriol (vitamin D3 synthetic analogue) and compared it to that of betamethasone dipropionate in a murine contact sensitivity (CS) test, the Mouse Ear Swelling Test. Two haptens were used: oxazolone and paraphenylenediamine. Betamethasone and calcipotriol exerted a differential effect on the delayed-type hypersensitivity response. When drugs were applied to the abdomen (sensitization site) before sensitization, no effect was observed. When betamethasone was applied to the abdomen for 4 consecutive days after epicutaneous sensitization, a diminution of the CS response to the relevant hapten was observed, whereas calcipotriol given in the same conditions did not affect the reaction. Ointments were then administered to the ear (elicitation site) either for 4 consecutive days prior to the challenge, or for 4 days before and 2 days after the challenge. In both conditions, calcipotriol and betamethasone exerted a differential effect on elicitation, the latter inhibiting and the former increasing the CS response to oxazolone and paraphenylenediamine. From these results we conclude: (1) that vitamin D3 derivatives are devoided of immunosuppressive effects when applied topically, and (2) that clinical improvement of chronic inflammatory dermatoses observed with topical vitamin D3 derivatives and corticosteroids is due to different mechanisms.

Effects of chloroquine on antigen-presenting functions of epidermal cells from normal and psoriatic skin.

The lysosomotropic drug chloroquine has been added to cultures containing peripheral blood mononuclear cells (PBMC) and allogeneic antigen-presenting cells obtained from the epidermis of normal human skin or from skin of patients with psoriasis. We found that in the presence of chloroquine, the allostimulatory properties of freshly obtained, normal epidermal antigen-presenting cells (EAPC) were profoundly impaired. By contrast, normal EAPC (cultured for 72 h prior to exposure to alloreactive T cells), as well as fresh EAPC from psoriatic skin were not impaired by chloroquine. In fact, in some experiments, cultured EAPC and psoriatic EAPC in the presence of chloroquine displayed significantly enhanced abilities to activate allogeneic T cells. Moreover, chloroquine partially reversed the inhibitory effect of transforming growth factor-beta (TGF beta) on T-cell activation induced by cultured normal EAPC. Fresh normal EAPC, which are normally impervious to the effects of TGF beta, were not protected by TGF beta from chloroquine inhibition. We conclude that the addition of chloroquine to tissue culture medium unmasks important differences in antigen processing and presenting properties of fresh, normal EAPC, on the one hand, and cultured normal EAPC and psoriatic EAPC on the other. The ability of chloroquine to exaggerate the accessory cell function of the latter cells may relate to the capacity of this drug to cause the secretion of acid hydrolases into their immediate microenvironment. Moreover, the capacity of chloroquine to enhance the accessory cell functions of freshly obtained psoriatic EAPC emphasizes an abnormality that psoriatic cells in the epidermis constitutively express. We postulate that this abnormality may be related to the clinical observations that psoriatic skin lesions may be induced or aggravated by chloroquine therapy.

T-lymphocyte-activating properties of epidermal antigen-presenting cells from normal and psoriatic skin: evidence that psoriatic epidermal antigen-presenting cells resemble cultured normal Langerhans cells.

Fresh and cultured human Langerhans cells display disparate functional programs, based on their capacities to activate autologous and allogeneic T cells, and with respect to their susceptibility to inhibition by transforming growth factor-beta (TGF beta). We have compared the functional properties of epidermal antigen-presenting cells (APC) procured from uninvolved and involved skin of patients with psoriasis with fresh and cultured normal epidermal cells. Freshly obtained psoriatic epidermal APC resembled cultured normal epidermal cells in their superior capacity to activate syngeneic and allogeneic T cells; fresh normal epidermal cells failed to activate syngeneic T cells, and induced only modest proliferation among allogeneic T cells. The modest T-cell--activating properties of fresh, normal epidermal cells were not suppressed by TGF beta, whereas the T-cell--activating potential of psoriatic epidermal cells, cultured normal epidermal cells, and blood APC was inhibited approximately 50% by TGF beta. Thus, fresh psoriatic epidermal APC resemble cultured normal epidermal cells functionally. Because these properties are already evident in cells obtained from uninvolved psoriatic skin, the "cultured" functional phenotype of epidermal APC in this disease may precede the appearance of active psoriatic skin lesions. Surface marker analysis of normal and psoriatic epidermal cell suspensions revealed that virtually all of the bone marrow--derived cells in normal epidermal cell suspensions were conventional (CD1+) Langerhans cells, whereas CD1+ cells comprised only a minority of bone marrow--derived (CD45+) cells in psoriatic epidermis. It is speculated that some of the CD1-, CD45+ cells in psoriatic epidermis may be Langerhans cells that have lost their "fresh" phenotype. These data indicate that an abnormality in epidermal APC function exists in psoriatic skin--even before clinical lesions develop, and we speculate that the abnormal capacity of psoriatic epidermal APC to activate syngeneic T cells may be important in the expression of keratinocyte pathology. Because psoriatic epidermal APC functions were profoundly inhibited in vitro by treatment with cyclosporin A, the effectiveness of this drug in psoriasis may be due in part to its ability to inhibit epidermal antigen-presenting cell function in vivo.

Comparison of effects of transforming growth factor-beta and cyclosporin A on antigen-presenting cells of blood and epidermis.

The antigen-processing and -presenting functions of freshly obtained epidermal Langerhans cells (fresh LC) and 72-h cultured Langerhans cells (cultured LC) differ remarkably. It has been proposed that the disparate functional programs revealed in vitro may correspond directly with distinct in vivo physiologic functions--fresh LC are the in vitro equivalent of intraepidermal LC and cultured LC are equivalent to LC that have migrated from skin to the draining lymph node. As an approach to studying this proposal, we have compared the effects of two immunosuppressive agents, cyclosporin A (CsA) and transforming growth factor-beta (TGF beta), on the alloantigen-presenting capabilities of fresh LC, cultured LC, and peripheral blood mononuclear cells (PBMC). CsA pretreatment (1 and 10 mu/ml x 2 h) profoundly inhibited alloantigen presentation by fresh LC, cultured LC, and PBMC. By contrast, TGF beta pretreatment (1 and 10 ng/ml x 2 h) inhibited presentation by PBMC and cultured LC, but not by fresh LC. The resistance of fresh LC to the deleterious effects of TGF beta is discussed in terms of the possibility that TGF beta may inhibit antigen processing following conventional endocytosis. We suggest that fresh, but not cultured, LC escape TGF beta effects because they possess an "alternative" endocytic pathway, marked by the presence of Birbeck granules.

Functional dichotomy between Langerhans cells that present antigen to naive and to memory/effector T lymphocytes.

The general thrust of this volume is to review the roles of accessory cells in regulating T and B lymphocytes. To that end, we have summarized the evidence that indicates the crucial role that Langerhans cells play in the induction and expression of immunity to antigens that gain access to, or arise within, skin. Langerhans cells accomplish this important goal by their abilities to (a) activate naive T cells to antigens not previously encountered by the host, and (b) activate memory/effector T cells specific for previously encountered antigens. Arguments have been advanced to support the view that the functional properties of Langerhans cells used to present antigens to naive T cells differ substantially from the properties that equip Langerhans cells to activate effector T cells. The arguments are based in part on the fact that Langerhans cells carry out these functions in two very different environments: in the epidermis, and in the draining lymph node. The arguments are also based on results of in vitro experiments that reveal distinct differences in antigen processing and presenting properties of Langerhans cells freshly obtained from mouse and human skin as compared to Langerhans cells that have been cultured in vitro for 2-3 days. We propose that freshly explanted Langerhans cells faithfully reflect the functional program of intraepidermal Langerhans cells, and are able to present antigen to memory/effector T cells that enter the epidermal compartment. To accomplish this task, epidermal LC pick up environmental antigens, process them with great efficiency, and then present them in situ, without further upregulation of "accessory" signals (cell-adhesion molecules, secretion of additional cytokines). They can carry out this function, even in the presence of TGFB--a a cytokine which is constitutively made by keratinocytes, and which we have found to profoundly inhibit antigen presentation by most other types of "professional" antigen-presenting cells. Intraepidermal Langerhans cells are also capable of carrying cutaneous antigens through the dermal epidermal junction and migrating to the draining lymph node. We further propose that cultured Langerhans cells are fated to present antigens to unprimed/naive T cells, and thereby to initiate immune responses to new cutaneous antigens. Cultured LC process antigens less efficiently than fresh cells, but their unique capacity to present antigen effectively to unprimed T cells rests chiefly on the fact that they have significantly upregulated cell surface adhesion molecules, expression of MHC molecules, and secretion of activating cytokines--the "accessory" signals that are required for arousing naive T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Dissociation of antigenicity and immunogenicity of neonatal epidermal allografts in the mouse.

Cultured neonatal epidermal cells or sheets have been grafted successfully onto allogeneic recipients across an MHC barrier, while genetically identical skin allografts were rejected. Induction of specific allosensitization by prior priming with allogeneic spleen cells or allogeneic skin grafts did not prejudice the survival of subsequent cultured epidermal allografts. When cultured epidermis and adult skin of the same genotype were grafted simultaneously, as double grafts, cultured epidermis survived despite the presence of an ongoing allograft rejection reaction in the host. Furthermore, pretreatment of the recipients with cultured epidermis failed to protect against rejection of subsequent allogeneic adult skin grafts of the same genetic origin. These data indicate that cultured epidermis is neither immunogenic nor antigenic in allogeneic host. In companion experiments it was determined that neonatal (noncultured) epidermal allografts also survived indefinitely, implying that neonatal epidermis lacks antigenicity. However, in contrast to cultured epidermis, neonatal epidermal allografts evoked specific systemic immunity in their recipients, since they rejected a subsequent allogeneic adult skin grafts in accelerated fashion. These data demonstrate that in neonatal epidermis antigenicity can be dissociated from immunogenicity.

Influence of microenvironmental factors on human Langerhans cell function in vitro.

When murine epidermal cells are placed in tissue culture for 48-72 hr, the Langerhans cell subpopulation acquires a markedly enhanced capacity to activate autologous as well as allogeneic T cells. This change is mediated largely, if not exclusively, by GM-CSF derived from keratinocytes present in the same cultures. When human epidermal cells are cultured under similar conditions, Langerhans cells display much more limited functional changes. We have investigated whether the relative failure of human Langerhans cells to change their functional program in vitro is due to (a) production of prostaglandins by keratinocytes during functional assays (which would inhibit T cell proliferation), and/or (b) relative deficiency of GM-CSF in the 72-hr epidermal cell culture. Freshly procured and cultured (72 hr) human epidermal cells were used as stimulators for allogeneic T cells in cultures to which indomethacin was added to block prostaglandin production. Under these circumstances, the allostimulatory capacity of cultured cells was enhanced, although there was no significant increase in the stimulatory properties of fresh cells, implying that prostaglandins may account in part for the relatively poor antigen presenting properties of cultured human cells. In addition, human epidermal cells were cultured with or without exogenous GM-CSF prior to being used as stimulators for autologous and allogeneic T cells. Following exposure to GM-CSF, cultured human epidermal cells acquired markedly enhanced T cell-activating properties, rivaling those reported for cultured murine epidermal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure, function, and immunogenicity of human insulinoma cells.

Dissociated human insulinoma cells were plated onto plastic multiwell dishes. Cells were maintained for 1 mo on plastic with three passages. Cultures consisted of small colonies with some areas of stratification and few intercellular spaces. Ultrastructural studies indicated that cultured cells had epithelial features with desmosomes at cell-to-cell contacts and intermediate filaments in addition to secretory granules in the cytoplasm. Insulin and C-peptide were released in equimolar amounts in culture media. When challenged for 30 min with 16.7 mM glucose, 1 mM 3-isobutyl-1-methylxanthine, 4 mM tolbutamide, or 10(-6) M glucagon, insulinoma cells responded by a 1.5-, 1.5-, 2-, or 3-fold increase, respectively, in insulin release above baseline levels. A 15-min challenge with 10(-5) M isoproterenol increased insulin secretion by 1.85-fold. By indirect immunofluorescence, an anti-insulin antibody reacted positively with cell cytoplasm, whereas anti-somatostatin and anti-glucagon antibodies did not. Insulinoma cell surface expressed class I MHC molecules but not class II molecules. Immediately after isolation, crude insulinoma cells were contaminated by 2% of DR+ cells from nonislet components that disappeared after several weeks in culture. The ability of insulinoma cells to stimulate allogenic T-lymphocyte proliferation was assessed by [3H]thymidine incorporation in mixed culture combinations. Crude insulinoma cells elicited a strong lymphoproliferative response with a stimulation index ranging between 3.5 and 7, whereas no stimulation was found after 1 mo in culture. It is postulated that absence of class II-positive cells in the stimulatory cell preparation conditioned this immune tolerance across the major histocompatibility barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Absence of allogeneic T cell response to human insulin-secreting cells following long-term culture.

Lymphocyte proliferative responses (3H-Thymidine uptake) were studied in mixed culture combinations of peripheral blood lymphocytes as responder cells and human insulinoma cells as stimulator cells (MILR). Influence of culture time on the ability of insulinoma cells to stimulate allogeneic T cell proliferation was examined. Crude cell suspensions initiated a strong lymphoproliferative response with a stimulation index (SI) that ranged between 3 and 7, whereas insulinoma cells did not stimulate allogeneic T cells after one month of culture. Expression of cell surface determinants coded by the major histocompatibility complex (MHC) was evaluated simultaneously by indirect immunofluorescence using monoclonal antibodies to class I shared-determinant or class II molecules. Human insulinoma cells expressed class I but not class II molecules. Crude insulinoma cell suspensions were found to be contaminated by 2% of DR+ cells from nonislet components. It is postulated that loss of these DR+ lymphoreticular cells with culture time resulted in absence of immune recognition and lymphoproliferative response. These results emphasize the need of culturing human islet cells prior to transplantation in order to reduce cell immunogenicity.