QUANTITATIVE STUDIES ON THE BEHAVIOR OF SENSITIZED LYMPHOCYTES IN VITRO. II. INHIBITORY INFLUENCE OF THE IMMUNE SUPPRESSOR, IMURAN, ON THE DESTRUCTIVE REACTION OF SENSITIZED LYMPHOID CELLS AGAINST HOMOLOGOUS TARGET CELLS

Effects of extracellular adhesion molecules on immune cell mediated solid tumor cell killing

Adoptive cell therapy (ACT) using ex vivo engineered/expanded immune cells demonstrated poor efficacy against solid tumors, despite its great success in treating various hematopoietic malignancies. To improve ACT for solid tumors, it is crucial to comprehend how the numerous components of the tumor microenvironment (TME) surrounding solid tumor cells influence killing ability of immune cells. In this study, we sought to determine the effects of extracellular adhesion provided by extracellular matrix (ECM) of TME on immune cell cytotoxicity by devising microwell arrays coated with proteins either preventing or promoting cell adhesion. Solid tumor cells in bovine serum albumin (BSA)-coated microwells did not attach to the surfaces and exhibited a round morphology, but solid tumor cells in fibronectin (FN)-coated microwells adhered firmed to the substrates with a flat shape. The seeding densities of solid tumor cells and immune cells were tuned to maximize one-to-one pairing within a single microwell, and live cell imaging was performed to examine dynamic cell-cell interactions and immune cell cytotoxicity at a single cell level. Both natural killer (NK) cells and T cells showed higher cytotoxicity against round tumor cells in BSA-coated microwells compared to flat tumor cells in FN-coated microwells, suggesting that extracellular adhesion-mediated firm adhesion of tumor cells made them more resistant to immune cell-mediated killing. Additionally, NK cells and T cells in FN-coated microwells exhibited divergent dynamic behaviors, indicating that two distinct subsets of cytotoxic lymphocytes respond differentially to extracellular adhesion cues during target cell recognition.

A cell culture assay for the detection of cardiotoxicity

An important step in minimizing the number of animal experiments in medical research is the study of in vitro model systems. We propose the use of "shock protein" formation, which is a cellular response to cell-damaging stress as an assay to monitor cardiotoxicity. Isolated and cultured cardiac myocytes were prepared by a trypsin digestion method from 18-day-old fetal mice. These cells respond to typical substances inducing "shock protein" formation in other cellular systems as well as to known cardiotoxins with the de novo synthesis of "shock proteins." Pharmaceuticals relevant in transplant medicine were tested for possible cardiotoxic effects: Cyclosporine A evokes "shock protein" formation at subtherapeutic concentrations. Azathioprine and methyl-prednisolone exert the same effect but at concentration ranges highly above the therapeutic level. The ability to induce "shock protein" synthesis obviously seems to be restricted to toxic drugs. The data presented demonstrate that the proposed in vitro model system for cardiotoxicity is animal saving and sensitive.

Immunosuppression in the treatment of inflammatory bowel disease. II. The effects of azathioprine on lymphoid cell populations in a double blind trial in ulcerative colitis

Blood lymphocytes and rectal plasma cells have been studied in patients with ulcerative colitis taking part in a double-blind trial of treatment with azathioprine. Treatment for 1 year resulted in a modest fall in blood lymphocyte count, with little change in neutrophils or platelets. There was no major change in the proportions of circulating T and B lymphocytes, suggesting that the number of such cells per millilitre of blood fell in proportion to the change in lymphocyte count. The number of plasma cells in the rectal lamina propria was reduced to a mean less than half that of the control patient group. Blood K-cell cytotoxic activity fell at least 25-fold after 1 year's treatment. PHA-induced cytotoxicity was also reduced, but less consistently. Reduced K-cell activity is interpreted as reflecting depletion of effector cells from the circulation. The fall in lymphocyte count, K-cell activity and gut plasma cells was slow, indicating continuous inhibition of lymphopoiesis or differentiation throughout the trial period. Thus, azathioprine has some immunosuppressive effects which develop only after prolonged treatment. The clinical results of the trial did not show a major beneficial effect of azathioprine in the treatment of ulcerative colitis, nor were there clear correlations between the results of lymphocyte assays and clinical response in individual patients.

The immunology of experimental Chagas' disease. 3. Rejection of allogeneic heart cells in vitro

Experiments that consisted of incubation of Trypanosoma cruzi-sensitized lymphocytes derived from chronically infected rabbits and from rabbits repeatedly immunized with a small particle or membrane fraction derived from homogenates of T. cruzi forms, showed destruction of allogeneic, parasitized and nonparasitized heart cells in vitro. Mononuclear cells collected from peripheral blood were incubated for 1 h at 37 degrees C to isolate the lymphocytes. Following incubation, over 99% of the cells in the supernate were lymphocytes, which were utilized in these experiments. At the start of these experiments, 70-80% of the sensitized lymphocytes were unattached, small and round, with sparse filipodia. In the ensuing hours, marked heart cell destruction, similar to that seen in an active lesion when lymphocytes invade heart tissue, were observed. After 18 h incubation, about 65-70% of the lymphocytes were attached, larger, and rough surfaced. Inhibition of monocyte migration tests, each in the presence of the antigens of subcellular fractions of T. cruzi organisms and of allogeneic heart myofibers, indicated the presence of a cross-reacting antigen common to both the parasite and the heart in the small particle or membrane fractions. The particulate antigens of the 30,000 g, 35-min fraction of heart muscle gave rise to inhibition of monocyte migration as did the counterpart fraction derived from T. cruzi organisms. The destruction of nonparasitized target heart cells by T. cruzi-sensitized lymphocytes is an in vitro model of the chronic myocarditis of Chagas' disease, and the recognition of cross-reactive antigens of the host cell by T. cruzi-sensitized lymphocytes is believed to be the pathogenic basis for subsequent tissue injury in the chronic phase of this disease.

Interaction of human melanoma cell lines with autochthonous lymphoid cells

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In vitro studies of the cell-bound and antibody-mediated immunity evoked by murine renal allotransplants. Influence of presensitization, total body irradiation and immunosuppressive agents

The influence of presensitization, total body irradiation and several immunosuppressive drugs on the immune response evoked by allogeneic rat kidneys was studied in vitro and in vivo. The cytotoxic effect of recipient thoracic duct lymphoid cells and fresh or heat-inactivated recipient serum against donor target cells was measured with ⁵¹Cr assay.

Rats that had undergone two consecutive allogeneic transplantations from isogenous donors had thoracic duct lymphoid cells and serum with an increased cytotoxic effect against donor strain target cells as compared to control rats transplanted only once. Heat-inactivated recipient serum from such animals also had an increased blocking effect on cell-mediated cytotoxicity.

ALS had the strongest depressive effect on the cell-bound immunological responses evoked by the transplants in the recipient rats, decreasing both the number of lymphoid cells in the thoracic duct lymph and the cytotoxic activity of the remaining cells. Methylprednisolone and methotrexate also strongly suppressed the cellular immunological events in the way just mentioned. Actinomycin-C and total body irradiation depressed cell-bound immune response only by causing a decrease in the number of cells in the thoracic duct lymph. Azathioprine did not influence cell-bound immunological responses to allogeneic kidney transplants.

Total body irradiation, methotrexate and methylprednisolone treatment markedly diminished the cytotoxic effect of fresh recipient serum against target cells and reduced the blocking effect of heat-inactivated recipient serum on lymphoid cell-mediated cytotoxicity. The other tested agents all caused a moderate depression of the cytotoxic and blocking effect of fresh and heat-inactivated recipient serum, respectively.

When folinic acid was given regularly between consecutive methotrexate injections, the depression of the lymphoid cell amount in the thoracic duct lymph was markedly less. The results of the cytotoxicity tests were similar to those obtained with methotrexate treatment alone.

Cell-mediated cytotoxicity during rejection and enhancement of allogeneic skin grafts in rats

Cell-mediated cytotoxicity (CMC) in spleens and lymph nodes of allografted rats was determined by release of (51)Cr from labeled target cells incubated with aggressor lymphoid cells. CMC was first detected in grafted adult rats on day 5, peaked on days 7 and 8, and declined rapidly to background levels by days 9 to 11. In allografted neonates and in cyclophosphamide-treated or neonatally thymectomized adults CMC was a fraction of that observed in normal adult rats. Enhancing antibodies deferred in vivo peak activity of CMC in allografted neonates for 3-4 days, and blocked in vitro the action of aggressor lymphocytes by binding to target cells. Enhancing antibodies had no effect on the cytotoxicity of aggressor cells, but horse antibodies to rat thoracic duct cells inhibited in vitro CMC of aggressor cells.

Suppression of the immune response

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In vitro cytotoxicity by human lymphocytes from individuals immunized against histocompatibility antigens. I. Kinetics and specificity of the reaction. Influence of metabolic inhibitors and anti-lymphocyte serum

Lymphocytes from humans that had rejected allogeneic skin grafts acquired a cytotoxic potential, which was expressed in vitro upon contact with fibroblast monolayer cultures of the skin donor genotype. No cytotoxic effect was obtained on autochthonous fibroblasts, but did occur on other allogeneic fibroblasts, non-related to the skin donor, suggesting shared histocompatibility antigens. The damage to the target cells developed at the area of lymphocyte application and was detected after 48 hr. The cytotoxic effect of the immune lymphocytes on the specific target cells was suppressed by treatment with actinomycin-C, Mitomycin-C and prednisolone, indicating that cellular synthetic processes and cell divisions are required for cytotoxicity to be expressed. Anti-lymphocyte serum also inhibited the cytotoxic reaction, probably by coating the lymphocyte surface.

In view of previous investigations, concerning cytotoxicity exerted by non-immunized lymphocytes stimulated by non-specific agents, the present results suggest that the specificity of the cytotoxic damage by immunized lymphocytes is confined to the initial immunological recognition of the antigen(s) on the target cells. This reaction triggers the lymphocytes to a cytotoxic state which can be non-specifically expressed. The need for synthetic processes within the lymphocytes may be required for magnifying the process by increasing the number of cytotoxically activated cells and probably also for the continuous synthesis of the antigen-specific receptors.

Studies of allograft immunity in mice. II. Mechanism of target cell inactivation in vitro by sensitized lymphocytes

The mechanisms of the in vitro interaction of sensitized lymphocytes and allogeneic target cells has been studied in a tumour allograft system in inbred mice. The cytotoxic effect of sensitized lymphocytes is shown to require the presence of Ca^{+ +} and Mg^{+ +}. Pretreatment of the lymphocytes with trypsin led to inhibition of cytotoxicity, followed by spontaneous reversal after 1–3 hours incubation. Reactivation was found to be blocked by an inhibitor of protein synthesis (cycloheximide). Cortisone was not found to inhibit the lytic interaction significantly; an occasional effect is thought to be due to toxicity of cortisone for lymphocytes as revealed by dye exclusion test. Inhibition of DNA-synthesis with FUdR (an inhibitor of the enzyme thymidine synthetase) did not reduce the lytic activity of sensitized lymphocytes.

Isologous anti-target cell sera induced in various strains of inbred mice were found to be ineffective in blocking the cellular immune reaction in vitro when directed against a minor part of the antigenic complex, but strongly inhibitory when reactive against a major part or the whole complex. Similarly, target cells lacking several of the sensitizing H-2 antigens were not lysed. An isologous anti-lymphocytic serum induced in the graft donor strain and directed against the recipient strain (lymphocyte donor) did not inhibit the cytotoxic reaction. In a heterologous system on the other hand, the lytic effect of guinea-pig lymphocytes sensitized against mouse target cells was effectively blocked by an anti-lymphocytic serum induced in mice of the graft donor strain by injection of recipient (guinea-pig) spleen cells.

Renal homotransplantation in rats. II. Tolerant recipients

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Quantitative assay of the lytic action of immune lymphoid cells on 51-Cr-labelled allogeneic target cells in vitro; inhibition by isoantibody and by drugs

The in vitro cytotoxic effect of spleen cells of mice immunized by tumour allografts was studied by measuring target cell inactivation as a function of release of radioactive label (⁵¹Cr) or loss of cloning efficiency. When sensitized lymphoid cells were incubated with target cells at a ratio of 100:1, up to 90 per cent of the incorporated label was released within 6–9 hours, while the number of clone-forming cells was reduced by up to 99 per cent in the same time period. Isoantiserum from the graft recipients, as well as its 19S and 7S fractions, protected target cells against the toxic effect of the spleen cells, but a lipoprotein antigen isolated from the tumour cells failed to inhibit the cytotoxic reaction. Target cell lysis as measured by specific release of ⁵¹Cr was partially inhibited by actinomycin-D and by cycloheximide at concentrations which effectively blocked DNA-dependent RNA and protein synthesis.

Local recognition of histocompatibility differences in skin grafts

Studies in rabbits of skin grafts tagged with tritiated thymidine indicate a greater proliferation of endothelial cells and fibroblasts at the site of an allograft than at that of an autograft as early as the first day after grafting. It appears, therefore, that allogeneic differences can be recognized and responded to locally almost at once. Labeled nuclear material is found to be transferred from the epithelial cells of skin grafts to host cells of the adjacent tissues. A mechanism therefore exists which might effect a local transfer of information on histocompatibility differences.

Quantitative studies on tissue transplantation immunity. VII. The normal lymphocyte transfer reaction

The normal lymphocyte transfer reaction (NLT reaction) is a cutaneous inflammatory episode of delayed onset that is aroused when living lymphocytes from one guinea-pig are injected into the skin of another, and it occurs only in those genetic situations that show it to be an immunological response of the transferred lymphocytes to antigens of the animals into which they are injected (§4). When the recipient guinea-pig is exposed to 600 r whole-body irradiation before transfer, to delay the onset of an immunological counter-attack on the transferred cells, the NLT reaction evolves in three phases spread over about 6 days (§3). These are: ( a ) the first inflammatory episode, of moderate intensity, which reaches its peak at 24 h and remains stationary for 2 further days; ( b ) the flare-up , starting between the third and fourth days and rising to a peak of violent intensity at about the sixth day; and ( c ) the fade-out , which is mainly due to an immunological recovery of the host. The same three components may be discerned when the transferred lymphocytes have been presensitized against the tissues of their future recipients, but the pitch of the reaction is much higher throughout and presensitized cells perform as strongly at 24 h as normal cells do when they reach the peak of their activity at 5 to 6 days (figure 2). In general, lymphocyte transfer reactions vary in intensity rather than in tempo: the weak reactions that occur where antigenic disparity is slight, or when relatively few cells are injected, differ from strong reactions—even the very strong reactions caused by presensitized cells—in their general pitch of intensity but not in the relative timing of the various episodes of the response. In terms of the power of a given number of cells to excite an NLT reaction, blood lymphocytes were two to five times more active, and thymocytes ten to twenty times less active, than lymph node cells (§5). Cells from lymph nodes caused to enlarge greatly by stimulation with human gamma globulin emulsified in Freund’s complete adjuvant were not more effective than normal cells in exciting an NLT reaction. Lymphoid cells from foetal or newborn mesenteric nodes gave bold and clear NLT reactions rising to a peak not lower than that achieved by the same number of adult lymphoid cells (§5). The NLT reaction lent itself very well to a study of inhibitorsof the immunological response. Immunosuppressive agents (§6) were applied, as appropriate, to the cell donor before transfer, to the lymphoid cells in transit, or to the recipient before, during or after transfer. Immunosuppressive agents did not in general affect the first inflammatory episode; with varying degrees of effectiveness they did, however, eliminate the flare-up. The two most effective agents in this respect (Methotrexate and cyclophosphamide) did not, however, oppose the immunological performance of pre sensitized cells at concentrations more than sufficient to eliminate the flare-up. It is therefore reasoned that conventional immunosuppressive agents do not affect any distinctively immunological activity of lymphoid cells: they merely prevent the multiplication of the cells activated in the first episode of the NLT reaction, and therefore the transformation of a ‘normal’ into a sensitized population. Reasons are given for thinking that the antigens which excite the NLT reaction belong to the homograft system and that the reaction as a whole can be construed as a homograft reaction in reverse (§7). The first inflammatory episode is interpreted as the outward design of a ‘recognition’ event, i.e. of a distinctively immunological process, unaccompanied by cell division and in no way dependent on it, that occurs when a lymphocyte is first engaged by an antigen of the homograft system and is committed to the evolution revealed outwardly by the flare-up. A quantal theory of the reaction is proposed, according to which the violent response given by normal lymphoid cells at the peak of their flare-up, and by presensitized cells from the outset, is simply an arithmetic multiple of the recognition process, i.e. it simply consists in more cells doing what a relatively small number does in the first inflammatory episode. Immunosuppressive agents act by preventing this multiplication. This interpretation implies that any 'true’ immunosuppressive agent which weakens or abolishes the first inflammatory episode must weaken the performance of a presensitized population to an exactly similar degree.