Synergism between subpopulations of thymus-derived cells mediating the proliferative and effector phases of the mixed lymphocyte reaction

An innovative antibody fusion protein targeting PD-L1, VEGF and TGF-β with enhanced antitumor efficacies

Immunosuppressive pathways in the tumor microenvironment (TME) are inextricably linked to tumor progression. Mono-therapeutics of immune checkpoint inhibitors (ICIs, e.g. antibodies against programmed cell death protein-1/programmed cell death ligand-1, PD-1/PD-L1) is prone to immune escape while combination therapeutics tends to cause high toxicity and side effects. Therefore, using multi-functional molecules to target multiple pathways simultaneously is becoming a new strategy for cancer therapies. Here, we developed a trifunctional fusion protein, DR30206, composed of Bevacizumab (an antibody against VEGF), and a variable domain of heavy chain of heavy chain antibody (VHH) against PD-L1 and the extracellular domain (ECD) protein of TGF-β receptor II (TGF-β RII), which are fused to the N- and C-terminus of Bevacizumab, respectively. The original intention of DR30206 design was to enhance the immune responses pairs by targeting PD-L1 while inhibiting VEGF and TGF-β in the TME. Our data demonstrated that DR30206 exhibits high antigen-binding affinities and efficient blocking capabilities, the principal drivers of efficacy in antibody therapy. Furthermore, the capability of eliciting antibody-dependent cellular cytotoxicity (ADCC) and mixed lymphocyte reaction (MLR) provides a greater possibility to enhance the immune response. Finally, in vivo experiments showed that the antitumor activity of DR30206 was superior to those of monoclonal antibody of PD-L1 or VEGF, PD-L1 and TGF-β bispecific antibody or the combination inhibition of PD-L1 and VEGF. Our findings suggest there is a great potential for DR30206 to become a therapeutic for the treatment of multiple cancer types, especially lung cancer, colon adenocarcinoma and breast carcinoma.

Toward a molecular understanding of adaptive immunity: a chronology, part I

The adaptive immune system has been the core of immunology for the past century, as immunologists have been primarily focused on understanding the basis for adaptive immunity for the better part of this time. Immunological thought has undergone an evolution with regard to our understanding as the complexity of the cells and the molecules of the system became elucidated. The original immunologists performed their experiments with whole animals (or humans), and for the most part they were focused on observing what happens when a foreign substance is introduced into the body. However, since Burnet formulated his clonal selection theory we have witnessed reductionist science focused first on cell populations, then individual cells and finally on molecules, in our quests to learn how the system works. This review is the first part of a chronology of our evolution toward a molecular understanding of adaptive immunity.

The biological effect of three thymosin fraction 5 polypeptides in the murine mixed lymphocyte reaction

The biological effects of three thymosin fraction 5 polypeptides, designated as beta 10, beta 4, and alpha 1 were tested in the MLR of mouse splenocytes, lymph node cells and thymocytes against syngeneic or allogeneic stimulators. It was found that all three polypeptides, after in vivo and in vitro treatment of the responder cell population, could enhance the allogeneic MLR. These polypeptides were also able to induce significant syngeneic MLR in systems where responder cells were used against irradiated syngeneic splenocytes. In addition, while beta 4 was shown to have a weak stimulatory effect on allogeneic MLR utilizing thymocytes as the responder cell type, alpha 1 could strongly induce such responses when syngeneic splenocytes were included into the culture system. Preincubation of purified mature T cells or thymocytes with alpha 1 has shown these cells to be the target of this polypeptide action. Thus, it appears that thymosin fraction 5 polypeptides not only initiate differentiation processes of immature T cells, but also exert their effects on mature T lymphocytes.

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

T cell clones interacting with accessory and T helper cells for a proliferative response

The requirement for cell interactions in T cell activation has been studied with two continuously in vitro growing T cell clones. These clones are specific for minor histocompatibility antigens, are H-2K restricted, and one clone is functionally a cytolytic T lymphocyte. Both can proliferate when interleukin 2 is added to the cultures, but for continuous growth they require irradiated spleen cells carrying the specific minor histocompatibility antigen and the restricting H-2. In this study we show that for proliferation the clones require at least two cell populations in the stimulator spleen, one is a splenic-adherent cell (SAC), the other a T cell. The SAC are plastic adherent, Thy-1-, Ia+. The T cells are nylon wool nonadherent, Thy-1+, Lyt-1+2- and Ia-. Cell mixing experiments of stimulator cells (all were done with H-2-syngeneic cells), depleted of either SAC or T cells confirm the requirement for a specific interaction between these two cell types and the T clone. Neither SAC, syngeneic with the T clone when mixed with T cells of the stimulator type, nor T cells syngeneic with the clone added to stimulator SAC, can induce an optimal proliferative response. Such a response is obtained only if both cell types, SAC and T cells, are of the stimulating genotype. This suggests that, in addition to an interaction of clonal T cells with SAC, a specific recognition at the T cell level between T stimulator and T clone is necessary. The interaction of the T clones with stimulator SAC and T cells leads to an activation, mediated by antigen recognition, of all three cell populations. Since we also show that each of the stimulator cell types are impaired by ultraviolet light irradiation, we conclude that factor production by SAC and T helpers is the final prerequisite for clonal expansion.

Lectin-dependent cell-mediated cytotoxicity following in vitro culture of normal lymphocytes in medium containing 2-mercaptoethanol

Cell-mediated cytotoxic reactivity resulting from the in vitro incubation of normal lymphocytes was assessed using nonspecific lectin-dependent cell-mediated cytotoxicity (LDCC) as a measure of overall reactivity. Spleen cells from non-immune C57BL/6 mice were incubated in vitro in RPM1-1640 supplemented with 10% fetal calf serum and 2-mercaptoethanol (2ME). Cytotoxicity was assayed against syngeneic Cr51-labeled EL-4 cells in the presence of Con A or PHA. Optimal LDCC was observed after 8 days of culture in the presence of 5 X 10(-5) M 2ME. Cytotoxicity was mediated by an activated T-lymphocyte population whose development did not appear to require macrophages. Usually LDCC in the presence of PHA was significantly greater than that obtained in the presence of Con A. The presence of 2ME during the initial phase of culture was crucial for the development of cytotoxicity, since early removal of 2ME after 1 or 3 days of culture did not alter the subsequent development of cytotoxicity, whereas delayed addition of 2ME on day 1 or 3 failed to produce cytotoxic reactivity. This rapid conversion from a 2ME sensitive state to a 2ME insensitive state may be related to a rapid loss of accessory cell viability during the early phase of culture. Together the results indicate that this system may provide a useful model for the investigation of the events leading to the development of CTL in vitro.

The in vitro effects of Bordetella pertussis lymphocytosis-promoting factor on murine lymphocytes. IV. Generation, characterization, and specificity of cytotoxic lymphocytes

Cytotoxic effector lymphocytes were induced in cultures of mouse spleen or lymph node cells by lymphocytosis promoting factor (LPF). The LPF-activated cytotoxic cells: (a) were not generated unless proliferation occurred; (b) sedimented in the lighter density fraction of a bovine serum albumin gradient; (c) were large, blast-like cells; and (d) were lysed by Thy-1.2 antiserum plus complement and, therefore, were T cells. Neither LPF alone nor supernates from stimulated cultures were cytotoxic. Unlike the situation with concanavalin A and phytohemagglutinin P, LPF-stimulated cytotoxic effector lymphocytes required no further addition of mitogen for maximal cytotoxicity. The effector cells displayed specificity, destroying only allogeneic but not syngeneic normal cells; in the case of tumor cells, both allogeneic and syngeneic cells werelysed in the absence of added mitogen. The reason for differentiated cytotoxicity toward syngeneic tumor and normal cells is not clear but may have some relevance to in vivo tumor rejection initiated by Bordetella pertussis.

In vitro generation of antigen-specific helper T cells that collaborate with cytotoxic T-cell precursors

Antigen-specific helper T cells are required in the generation of cytotoxic T cells from thymocyte precursors. We have demonstrated that these alloantigen-specific helper cells can be generated in vitro and that both the quantity and quality of the helpers appear to be superior to the help obtained from unprimed spleen cells. Optimal helper cell activity is produced at day two of culture when CBA splenic helper precursors are stimulated by irradiated allogeneic spleen cells. Helper cell precursors are antigen-specific cells which cannot be instructed to express forbidden receptor specificities and bear theta antigen on their surface. The helper effectors are radioresistant, theta-bearing, and antigen-specific cells.

Amplification of the proliferative response to alloantigen by a factor present in an extract of syngeneic thymic lymphoid cells

A synergistic interaction in the proliferative response to alloantigen has been previously noted when intact thymus cells are cultured with post-thymic (peripheral) lymphoid cells. In the present study, a factor extracted from the thymus has been shown to similarly enhance the reactivity of syngeneic lymph node cells and thus to retain the amplifier activity of intact thymus cells. The factor has no effect on lymphoid cell proliferation in the absence of alloantigen. Cells with amplifier activity are found in highest concentration in the thymus but also may be detected in spleen cells that are nonadherent to nylon wool. The factor is shown in these experiments to be derived from thymic lymphoid cells and to act primarily upon post-thymic (peripheral) lymphoid cells. As such, this factor appears to be distinct from various other thymus factors that have been localized to thymic reticuloepithelial elements and that are thought to effect predominantly the differentiation of T-cell precursors.

Regulation of delayed-type hypersensitivity. I. T suppressor cells for delayed-type hypersensitivity to sheep erythrocytes in mice

Mice injected with 1 X 10(8) sheep red blood cells (SRBC) into the footpad showed high levels of delayed-type hypersensitivity (DTH) to SRBC 4-8 days after the injection. In contrast, mice injected intravenously with 1 X 10(9) SRBC were unresponsive to DTH induction through 1 X 10(8) SRBC injected into the footpad. This suppression of DTH was maintained for at least 6 weeks and was transferable spleen, lymph node and thymus cells to normal syngeneic recipients. Bone marrow cells, on the other hand, did not contain the suppressor cells. The suppression of DTH was antigen-specific in that DTH to chicken red blood cells and contact sensitivity to 2,4-dinitrofluorobenzene was not affected. The suppressor cells were theta-positive and Ig-negative. They appeared in the spleen in optimum number 3-4 days after induction. The suppressor cells affected both the induction and manifestation of DTH. The presence of suppressor and effector cells for DTH inducible by different routes of antigenic presentation reflects the dynamic balance in the regulation of DTH.

Responses of alloantigen-primed lymphocytes in vitro. The contribution of increased frequencies of responding lymphocytes to differences between reactivity of normal and primed lymphocyte populations

Sensitization of lymphocytes against allogeneic cells in vitro results in significant enrichment of alloreactive lymphocytes. Such enrichment was found to profoundly influence the conditions for measuring proliferative responses. Fewer primed lymphocytes than unprimed ones had to be cultured to favor optimal proliferation. Second, proliferative responses could be detected using 10 to 20 times fewer primed responding cells than when using unprimed responders. Finally, although responses of both unprimed and primed lymphocytes were dependent on the number of stimulator cells in culture, the primary mechanism(s) through which this dependence was expressed appeared to differ. The results demonstrate that, under the same conditions, comparisons of responses of two populations that contain different proportions of reactive lymphocytes may not be justified.

A requirement for antigen-specific helper T cells in the generation of cytotoxic T cells from thymocyte precursors

Thymocytes cultured with irradiated, allogeneic stimulator cells yield no cytotoxic effector cells after a period in culture. If, however, a population of irradiated spleen cells syngeneic to the responder cells are added to these cultures, cytotoxicity is generated. The helper activity present in the irradiated syngeneic spleen cells was found to be mediated by a cell bearing theta antigens. Furthermore, it was found to be antigen specific; helper cells which were tolerant of the stimulator cell antigens were unable to help the thymocyte responder cells, although these tolerant cells did contain helpers specific for a third party antigen. These experiments are consistent with a requirement for associative recognition of linked determinants in the induction of killer precursors which is thus strictly analogous to the induction of B-cell precursors via collaboration with helper T cells. In more extensive studies, it was found that histoincompatible helper cells (H-2b, H-2p, H-2q) were able to help a cytotoxic T cell (H-2k) response to a third party stimulator cell antigen (H-2d); that is, the helper T cells which interact with cytotoxic T-cell precursors are not strain specific. It seems likely that the histocompatible helper cells induce killer precursors in an antigen-specific cooperation event similar or identical to normal syngeneic cooperation.

Studies on delayed hypersensitivity in mice. III. Evidence for suppressive regulatory T1-cell population in delayed hypersensitivity

T-T-cell interactions involved in delayed hypersensitivity (DH) response have been studied by employing delayed foot pad assay to methylated human serum albumin in C57BL/6J mice. The DH response, one of the T-cell manifestations of cell-mediated immune response is suppressively regulated by T cells and such observation was based on studies of age-associated kinetics of foot pad reaction and effects of cell transfer and adult thymectomy on developing DH response. These suppressively regulatory T cells in DH have a life span of less than 4 wk and a constant derivation from the thymus is required. Such cells are numerous in the young mouse thymus and few in the spleen and thymus of old mice. On the one hand, the presence of a long-lived effector T-cell population was suggested in DH. These cells are numerous in the spleen and are low responders to phytohemagglutinin in vitro. It is assumed that these suppressive T cells interact with antigen-reactive cells at their proliferating stage by recognition of the iodiotypic difference through surface receptors. As in the case of graft-vs.-host and humoral response in vivo, three different subsets of immune competent cells participate in the DH response. These cells consist of one specifically antigen-reactive T cell, one suppressive regulatory T cell, and one bone marrow-derived cell, a macrophage that responds to a chemical mediator from sensitized effector T cells and that develops a DH skin lesion nonspecifically.

Analysis of the induction phase of contact sensitivity by footpad transfer of regional lymph node cells. Macrophages and radioresistant T-lymphocytes induce immunity

The skin of CBA mice was painted with the contact sensitizing agent 4-ethoxymethylene-2-phenyloxazolone (oxazolone). One day later the regional lymph node cells were injected into the footpads of normal recipients. The recipients were tested 6 days later for contact sensitivity by challenging the ears with oxazolone and measuring the increase of ear thickness at 24 h. T cells and macrophages in the regional lymph nodes each independently gave rise to contact sensitivity in the recipient following injection into the footpad. This activity of T cells and macrophages was found in lymph nodes taken 1, 3 and 4 days after painting the donors. The role of T cells in the injected population was shown by purifying T cells by nylon-wool filtration and rosetting with sheep red cells coated with antibody and complement (EAC rosetting) and by destroyed T cells with anti-0 serum and complement. The activity of purified T cells resisted 2000 rad in vitro. The activity of cells from T-deprived (B) mice showed that a second cell type was important in the footpad transfer. This cell behaved like a macrophage, and not like a B cell, on EAC rosetting in the presence or absence of divalent cations and on treatment with silica and carrageenan--agents which damage macrophages. Our working hypothesis is that the footpad transfer may be caused independently by macrophages or T cells with oxazolone (probably linked to major histocompatibility complex antigens) on their surface and that these cells act by collaborating with T cells in the recipient which give rise to the effector cells for contact sensitivity.

Cell-free media of mixed lymphocyte cultures augmenting sensitization in vitro of mouse T lymphocytes against allogeneic fibroblasts

Using an in vitro mouse lymphocyte anti-fibroblast reaction (AFR), we recently reported that the addition of allogeneic stimulator lymphocytes to the sensitization phase of the AFR enhanced sensitization to fibroblast antigens as evidenced by a marked increase in the cytolytic activity of the sensitized lymphocyte population. In the present report we studied the mechanism of this helper effect by testing the capacity of cell-free media derived from 48-h mixed spleen cultures to enhance anti-fibroblast sensitization. We found that such cell-free media could produce a marked helper effect when applied to the sensitization phase of the AFR, but not when added to the cytolytic effector phase. The stimulator cells in the mixed lymphocyte culture (MLC) did not have to be syngeneic with the sensitizing fibroblasts in the AFR in order for the helper effect to be demonstrated. Lymphocytes sensitized to fibroblast antigens in the presence of MLC medium retained their specificity of the effector phase. Our data suggest that the MLC medium acts by enhancing differentiation processes of antigen-triggered lymphocytes. Generation of helper activity by the MLC was abolished by 1000 r irradiation of the responder cells. By using nu/nu and normal spleens, both from two different strains, as cell sources for the MLC, we found that the generation of helper activity depended on T cells capable of proliferation. Furthermore, stimulator lymphocytes differing from responder lymphocytes by non-H-2 alloantigens as well as by point mutation with the H-2 complex were capable of eliciting helper factor(s). Thus, soluble factor(s) produced in a MLC, which are dependent on T lymphocyte proliferation, have the capacity to enhance the sensitization of mouse lymphocytes against antigens present on allogeneic fibroblasts.

Characterization of dextran-activated T-cell factors

Dextran given to mice caused splenic T cells to elaborate factors in vitro which heightened normal splenic B- and T-cell responses to the mitogens LPS and Con A, respectively. Chromatographic separation of dextran-triggered spleen cell supernatants revealed two T cell-derived enhancing factors which affect T cells (TDEF-TI and TDEF-TII) and two that alter B cells (TDEF-BI and TDEF-BII). All appear to be proteinaceous because exposure to trypsin destroyed their activities. Furthermore, their presence was found to be dependent upon protein synthesis since cycloheximide treatment of the cells inhibited synthesis whereas mitomycin C treatment did not. Based on absorption studies, receptors for TDEF-TI and TII were detected on thymic cells as well as on O-deficient bone marrow cells, whereas receptors for TDEF-BI and BII were on bone marrow cells but not thymic cells.

Dextran-triggered T cells heighten T- and B-cell reactions to mitogens

Dextran administered to mice of six strains has been found to cause enhanced responses of spleen cells to the mitogens Con A and LPS. When added to cultures of spleen cells in vitro in a wide range of concentrations dextran, alone, was neither mitogenic nor toxic. The enhancement is mediated through T cells since it was absent in spleen cells from dextrantreated athymic mice. Furthermore, for the enhanced response to LPS, T cells from dextran-treated mice apparently must be in close association with B cells for longer than 2 h. The enhancement is accomplished through a humoral factor(s) produced by splenic T cells. The T cell-derived enhancing factor(s) has been shown to affect allogeneic as well as isogeneic T and B cells.

The differentiation of cytotoxic T lymphocytes in vitro: an ultrastructural study

T killer cells were identified morphologically in two different culture systems. The first system allowed identification by comparing under identical culture conditions two types of stimulation, one leading to cytotoxic activity levels that were very high (H-2 stimulation) and the other to levels which were practically nil (M-locus stimulation). A second system allowed identification by the use of a collaborative system in which relatively pure precursors of T killer cells were mixed with precursors of T amplifier cells from which they were distinguishable by their Thy-l antigen. In this latter case, surface labelling techniques had to be used. As in the in vivo situation, T killer cells were medium-sized pale cells with evidence of a well-developed secretory and motile apparatus. No evidence of highly active protein synthesis was found. Other T cells were dark and mainly derived from the T amplifier population, again consistent with in vivo findings. There was considerable background proliferation, even in the absence of any added antigen, and this included the formation of some well-developed plasma cells.

Cellular immune response in vitro: I. A requirement for time-dependent T-lymphocyte cell division of cytotoxic cells in the allogeneic response

Immunocompetent lymphoid cells cultured in vitro with allogeneic stimulator cells have been shown to produce T-lymphocyte populations which are specifically cytotoxic in vitro to the stimulatory cells whether normal or malignant. Although the culture requirements as well as the allogeneic requirements are known, the events leading to the production of T-lymphocyte cytotoxic cells is poorly understood. This study examines the role of cell division in the production of allogeneic cytotoxic T-cells in vitro. The elimination of cell division during the first 24 hr of allogeneic culture does not affect the cell-mediated cytotoxic immune response in vitro. Cell division is required, however, from 24 hr through 96 hr in culture and not necessary after 96 hr.

Synergistic and suppressive interactions among mouse T lymphocytes in the response to phytohemagglutinin

A synergistic effect in the proliferative response to phytohemagglutinin (PHA) can be observed in cultures containing a mixture of mouse CBA/Ca lymph node cells (LNC) and syngeneic CBA/T6T6 thymocytes (ThC) when compared to cultures containing only one cell type. This effect was analyzed, at various days of culture and in LNC-ThC mixtures of different ratios, by comparing the origin of the cells in mitosis (detected by caryotypic analysis), the stimulation of DNA synthesis, the number of blasts, and the percentage of blasts labeled after pulses of [3H]thymidine (detected by autoradiography). The following conclusions were reached: (a) ThC are induced to proliferate by the presence of LNC, while they are almost unresponsive to PHA when cultured alone; and (b) the strongest "synergistic" effect is exerted on LNC, whose proliferation is markedly enhanced. Evidence is presented that this last effect is not specific to the presence of ThC, but results from a dilution of LNC which retards the time when the culture reaches a critical concentration of blasts, above which proliferation progressively stops. Thus, conditions of culture allowing the response to PHA of a low concentration of LNC leads to the most prolonged T-cell proliferation. These observations may be relevant to the types of T-cell interactions, "synergistic" or "suppressive," occurring during in vitro or in vivo immune responses.

Cell-mediated immunity: differential maturation of mixed leukocyte reaction and cell-mediated lympholysis

While spleen cells from neonatal B10 (H-2b) are reactive (proliferate) in one-way mixed leukocyte culture, cell-mediated lympholysis reactivity does not arise until 7 days of age. When B10 cells are sensitized to B10.D2 (H-2d), cross-killing of third-party B10.BR (H-2k) target is always lower than the specific killing of B10.D2 targets and is not demonstrable until 27 days after birth.

Immune responses to hapten conjugates in vitro

Several functions of the animal body can take place in cell or tissue cultures with almost unreduced efficiency and precision. Functions, where only one cell type is involved, often do so, but also some differentiation steps where interactions between two or more cell types are clearly needed can take place in tissue culture (Saxén et al. 1968).

Most immune responses require collaboration between two or more cell types (Claman, Chaperon & Triplett, 1966; Miller & Mitchell, 1968; Feldmann & Nossal 1972c). Some of them can be easily induced in vitro but others cannot. Even when antibody responses can be induced in vitro their intensity varies a great deal. With some antigens and under some circumstances a response in vitro can be nearly as strong as one in vivo. A crude comparison can be derived from responses in vitro and in vivo to the same antigen, conjugate of hapten NIP and pneumococcal polysaccharide type III (NIP-SIll, Nakamura, Ray & Mäkelä, 1973).

Functional subclasses of T lymphocytes bearing different Ly antigens. II. Cooperation between subclasses of Ly+ cells in the generation of killer activity

Lymphocytes from BALB/c or C57B6/6 mice that develop killer activity to alloantigens belong to the numerically small Ly-23 subclass of peripheral T cells, distinguished by selective expression of Ly-23 determinants on their surfaces. The maturation of these cells to killer cells can be amplified by Ly-1+ cells, which do not themselves contribute to the killer cell pool. This amplification was abolished by escluding Ia("Beta")+ cells from the stimulator population during mixed lymphocyte culture (MCL), suggesting that amplification is due to selective recognition of I region antigens by L-1+ cells, a conclusion already drawn from our previous evidence that Ia differences activate Ly-1+ cells but not Ly-23+ cells. These and other experiments indicate that amplification of killer cell production in vitro by Ly-1+ cells is not due to their conversion to Ly-23+ cells during MLC, but to their ability to recognize major histocompatibility complex determinants not recognized by Ly-23+ cells.

Transient impaired cell-mediated tumor immunity after acute infection with lymphocytic choriomeningitis virus

Intraperitoneal injection of nononcogenic lymphocytic choriomeningitis (LCM) virus in adult C3H mice causes a symptomless infection but stimulates specific cell-mediated and humoral immune responses. However, median survival time of virus-infected mice inoculated with syngeneic tumor cells was significantly shortened, and growth of semiallogeneic tumors was significantly enhanced. Cell-mediated cytotoxicity measured as chromium-51 release from labeled tumor cells was significantly suppressed but was recovered within 55 days after infection. The suppressed immune responsiveness could be conferreo on a normal spleen cell population when activated in virus-infected recipients. Chronically LCM virus-infected mice showed an unimpaired cell-mediated immune response to tumor allografts.

Thymosin-induced differentiation of murine thymocytes in allogeneic mixed lymphocyte cultures

Calf thymosin is shown to enhance the one-way MLR of CBA thymocytes cultured with allogeneic mitomycin-C- treated C57BL/J6 spleen cells. Thymosin does not enhance the one-way MLR of CBA thymocytes cultured with syngeneic mitomucin-C-treated spleen cells. Based on this finding we present a relatively simple, rapid and quantitative in vitro microculture hioassay for inducers of T-cell differentiation and propose that thymosin treatment, when accompanied by antigen presentation, induces the two-step maturational sequence of pre-T yields T1 yields T2.

Sequential responses of mouse spleen T cells in mixed lymphocyte culture-induced cytolysis

T cells triggered to blast transformation and proliferation by histoincompatible cells have the capacity of reverting "back" to lymphocytes. These "secondary" lymphocytes and their progeny cells are able to respond repeatedly to the same allogeneic stimulus in vitro.

Expression of T-cell differentiation antigens on effector cells in cell-mediated cytotoxicity in vitro. Evidence for functional heterogeneity related to the surface phenotype of T cells

The cell-mediated cytotoxicity (CMC) of nonadherent cells from the peritoneal cavity (NAPC) of alloimmunized mice can be measured by the [3H]proline microassay. The exhibition of thymus-derived (T) cell antigens on these killer cells was studied by incubating them with the relevant T-cell antisera and complement (C), under optimal conditions for lysis, before performance of the CMC assay. Under these conditions, the following T-cell antigens were demonstrable on the killer population in terms of percent reduction in CMC by the respective antisera: (a) Thy-1.1 (83%) and Thy-1.2 (100%), (b) MSLA (86%), (c) NTA-RA (a T-cell antigen recognized by naturally occurring autoantibody of NZB mice) (62%), (d) Ly1.1 )58%, (e) Ly-2.1 (11%; considered a marginal result) and Ly-2.2 (63%), and (f) Ly-3.2 (77%). The following were not demonstrable: (g) TL, and (h) Ly-1.2. (i) The antigen Ly-3.1 was not studied. Omission of C deprived all T-cell antisera tested of their capacity to suppress CMC, indicating that the cell components recognized by such antisera may perform no direct function in CMC. On the assumption that all Ly+ cells are Thy-1+, it is clear that the T-cell members of the immune NAPC population must be heterogenous. This follows from the fact that the proportions of T cells lysed by different Ly antisera did not correspond with ensuing degree of loss of CMC capacity. The extremes were represented by anti-Ly-1.2 (74% Thy-1+ cells lysed, but no reduction in CMC) and Ly-3.2 (54% Thy-1+ cells lysed, with 77% reduction in CMC). From this initial survey it appears that the C57BL/6 mice killer T-cell population active in CMC in vitro is relatively rich in surface antigens of the Ly-2/Ly-3 category and relatively poor in representation of the Ly-1 surface antigens. It remains to be seen whether this killer cell phenotype, poor in Ly-1 and rich in Ly-2/Ly-3, is characteristic of the mouse generally. From these results it appears that subsets of T cells with different immunological functions may exhibit qualitative or quantitative differences in surface antigens specified by different Ly loci; this will be easier to assess in the future when the results of experiments with the same Ly antisera but dealing with T-cell functions other than CMC become available.

Regulatory mechanisms in cell-mediated immune responses. I. Regulation of mixed lymphocyte reactions by alloantigen-activated thymus-derived lymphocytes

Regulatory effects of alloantigen-activated thymus-derived lymphocytes in mixed lymphocyte reactions have been demonstrated. Mice were injected into foot pads with allogeneic spleen cells; 4 days following sensitization spleen or regional lymph node cells from these animals were treated with mitomycin C and incorporated into MLR as regulator populations syngeneic to the responder cell type. Activated spleen cells suppressed MLR responses 60-90% whereas activated lymph node cells from the same animals enhanced MLR responses. Suppression by activated spleen cells was not due to cytotoxic effects nor to altered kinetics of the proliferative response. Studies of splenic suppressor cell generation in vivo revealed peak activity four days after alloantigen stimulation with no activity demonstrable at 7 days or at later times. Suppressor cell activity was abrogated by treatment with anti-thetaC3H serum and complement, and was not alloantigen specific.

Synergy between subpopulations of mouse spleen cells in the in vitro generation of cell-mediated cytotoxicity: evidence for the involvement of a non-T cell

Two subpopulations separated from normal spleen have been shown to synergize as responding cells in the in vitro induction of specific cell-mediated cytotoxicity during the mixed lymphocyte culture (MLC). The synergizing populations are a nylon wool column-adherent and a nylon wool column-nonadherent fraction, enriched for B lymphocytes and T lymphocytes, respectively. When a mixture of these fractions is used as the responding cell population in MLC, greater cytotoxicity is generated than would be expected from the sum of activities generated in the two subpopulations sensitized separately. The synergy appears to occur at the sensitization rather than the effector phase. The synergizing cell which is contained in the nylon-adherent subpopulation is distinct from the cytotoxic effector T lymphocyte, is resistant to lysis by rabbit antimouse brain serum, and is unresponsive to phytohemagglutinin; its synergizing function could not be replaced by either plastic-adherent spleen cells or peritoneal exudate cells. These results suggest a role of a non-T-cell nonmacrophage population in the generation of cytotoxic activity.

Cell-mediated immune responses in vitro. I. Suppression of the generation of cytotoxic lymphocytes by concanavalin A and concanavalin A-activated spleen cells

The effects of soluble concanavalin A (Con A) or Con A-activated spleen cells on the generation of cytotoxic lymphocytes (CL) in mixed leukocyte cultures (MLC) were examined. Mitogenic concentrations of soluble Con A or small numbers of Con A-activated spleen cells substantially inhibited CL responses. The suppression was partial rather than absolute and was critically dependent upon the concentration and time of addition of soluble Con A or Con A-activated spleen cells to the MLC. Suppressive effects of Con-A activated spleen cells were mediated by T cells since suppressor cell activity was abrogated by treatment of spleen cells with anti-theta serum and complement before or after Con A activation. X irradiation of spleen cells before Con A treatment also abrogated generation of suppressor cell activity. After activation by Con A, however, the function of suppressor cells was radioresistant. Although the precise mechanism(s) of suppression is, as yet, unknown, the precursors of CL must be exposed to Con A-activated cells during the early phases of the immune response for suppression to occur. Kinetic studies revealed that suppression of CL responses was not due to a failure to initiate an immune response, but represented a response which developed initially, but subsequently aborted. The relevance of these observations to the concepts of T-cell-T-cell interaction and regulatory control of immune responses by T cells is discussed.

The differentiation pathway of T lymphocytes. Evidence for two differentiated cell types

Two experimental models have been used to study T-cell differentiation. The first, a graft-vs.-host reaction, was induced by injecting thymocytes or cortisone-resistant thymocytes into lethally irradiated allogeneic mice. The second was tumor graft rejection in allogeneic hosts. Ultrastructural studies at various time intervals revealed two differentiated T-cell types. One of these (the "pale" cell) is probably high cytotoxic as measured in the chromium-release assay, the other (the "dark" cell) may be an "amplifier" cell, helping in the differentiation of cytotoxic cells.