Activation of cytotoxic T cells by nonstimulating tumor cells and spleen cell factor(s)

Kevin Lafferty and the lymphocyte costimulator: theory and practice in Canberra

Between 1969 and 1983 the lab of Kevin Lafferty in Canberra developed the concept of the T-cell "costimulator," an essential second signal for activation. A great deal of the work appeared in this journal before it was known as Immunology & Cell Biology (ICB). As part of the 100-year anniversary of the journal, I offer a personal reflection on Kevin's legacy and impact.

Immunobiology of Cellular Transplantation

The goal of cellular transplantation is to allow long-term function of the grafted cells using minimal host immunosuppression. To this end, the major strategies to implant cells and tissues are through: (i) the pretreatment of the graft to reduce tissue immunogenicity; (ii) the application of immunoisolation technologies to prevent host sensitization to implanted cells; and (iii) the induction of immunological tolerance to the donor tissues. Further, a major dilemma facing clinical tissue grafting is the shortage of donor tissue for transplantation. This problem requires the consideration of tissues from other species (xenografts) as a potential source of donor material. In light of these issues, the focus of this discussion is on the T cell-dependent response to allogeneic and xenogeneic transplants and the implications of this reactivity on the field of cellular replacement therapy.

Cancer immunotherapy via nucleic acid aptamers

Over the past decade, immune therapy has become a standard treatment for a variety of cancers. Monoclonal antibodies, immune adjuvants and vaccines against oncogenic viruses are now well-established cancer therapies. Immune modulation is a principal element of supportive care for many high-dose chemotherapy regimens. Aptamers are short nucleic acids that bind to defined targets with high affinity and specificity. The first aptamers have been selected around two decades ago by an in vitro process named SELEX (systematic evolution of ligands by exponential enrichment). Since then, numerous aptamers with specificities for a variety of targets from small molecules to proteins or even whole cells have been selected. Targeting immunomodulatory ligands in the progressive tumor lesions of the patients would be prophylactic or therapeutic and may reduce drug-associated toxicities. A new class of inhibitory and agonistic ligands composed of short oligonucleotide (ODN) aptamers was developed recently that exhibited bioactivities comparable or superior to that of antibodies. This paper addressed progress in cancer immunotherapy with nucleic acid aptamers and highlighted recent developments either in immune system targeting or in immunotherapy methods involved aptamers. We discussed aptamer limitations when used as therapeutic agents for cancer treatment and suggested ways to overcome those limitations.

T-cell alloimmunity and chronic allograft dysfunction

Solid organ transplantation is the standard treatment to improve both the quality of life and survival in patients with various end-stage organ diseases. The primary barrier against successful transplantation is recipient alloimmunity and the need to be maintained on immunosuppressive therapies with associated side effects. Despite such treatments in renal transplantation, after death with a functioning graft, chronic allograft dysfunction (CAD) is the most common cause of late allograft loss. Recipient recognition of donor histocompatibility antigens, via direct, indirect, and semidirect pathways, is critically dependent on the antigen-presenting cell (APC) and elicits effector responses dominated by recipient T cells. In allograft rejection, the engagement of recipient and donor cells results in recruitment of T-helper (Th) cells of the Th1 and Th17 lineage to the graft. In cases in which the alloresponse is dominated by regulatory T cells (Tregs), rejection can be prevented and the allograft tolerated with minimum or no immunosuppression. Here, we review the pathways of allorecognition that underlie CAD and the T-cell effector phenotypes elicited as part of the alloresponse. Future therapies including depletion of donor-reactive lymphocytes, costimulation blockade, negative vaccination using dendritic cell subtypes, and Treg therapy are inferred from an understanding of these mechanisms of allograft rejection.

Assembling OX40 aptamers on a molecular scaffold to create a receptor-activating aptamer

We show that a molecular scaffold can be utilized to convert a receptor binding aptamer into a receptor agonist. Many receptors (including tumor necrosis receptor family members) are activated when they are multimerized on the cell surface. Molecular scaffolds have been utilized to assemble multiple receptor binding peptide ligands to generate activators of such receptors. We demonstrate that an RNA aptamer that recognizes OX40, a member of the tumor necrosis factor receptor superfamily, can be converted into a receptor-activating aptamer by assembling two copies on an olignucleotide-based scaffold. The OX40 receptor-activating aptamer is able to induce nuclear localization of nuclear factor-kappaB, cytokine production, and cell proliferation, as well as enhance the potency of dendritic cell-based tumor vaccines when systemically delivered to mice.

Transplantation immunology 2003: simplified approach

Transplantation has been performed clinically for four decades and has become the standard of care for end-stage organ failure. Understanding of the immunobiology of transplantation has made tremendous advances, but knowledge still lags behind the clinical use. As a result, nonspecific immunosuppression remains the standard therapy. This article presents an overview of current knowledge of the immunobiology of solid organ transplantation, with emphasis on T-cell activation (antigen presentation, CoS) and cellular allograft (transplantation) immunity. The molecular events of T-cell activation, with some emphasis on the sites of action of modern immunosuppression, are reviewed. A simplified approach to understanding the immunobiology and strategy of maintenance immunosuppression is discussed. Key early and late steps in T-cell activation and the sites of action of immunosuppressive agents are reviewed. The required cellular interactions for the alloresponse and the targets of biologic agents used in transplants are reviewed. Special considerations for the immunology in neonates, infants, and children as recipients are provided. Understanding the immunobiology of transplantation is key to making decisions about children with transplants, developing better protocols, and creating tolerance in the future.

Involvement of the direct and indirect pathways of allorecognition in tolerance induction

It is generally accepted that there are two pathways of allorecognition, direct and indirect, that together contribute to allograft rejection. Although it has been suggested that the direct pathway predominates during early acute rejection and that the indirect pathway provides a continuous supply of alloantigen responsible for chronic rejection, the true relative contribution of each pathway to the overall rejection process is still not entirely known. It is clear, however, that any strategies designed to achieve the ultimate goal in transplantation, the induction of tolerance, will need to take into account both pathways. This review seeks to explore the involvement of the direct and indirect pathways of allorecognition on a mechanistic level as it relates to the induction of tolerance. A brief historical perspective is included for each pathway as well as a comprehensive review of the mechanisms felt to be active during tolerance induction.

Gene transfer of the Co-stimulatory molecules B7-1 and B7-2 enhances the immunogenicity of human renal cell carcinoma to a different extent

Stimulation of a specific antitumour immune response with recruitment and induction of T-cell effector functions represents an attractive concept in human cancer therapy. Different cytokines and the B7 co-stimulatory molecules are both able to provide proliferation and activation signals for T cells. In the present study, we first demonstrated the absence of both B7-1 and B7-2 expression in human renal cell carcinoma (RCC) cell lines. The lack of B7 expression was associated with a low or absent proliferative response of allogeneic and autologous T cells upon stimulation with tumour cells. In order to investigate the role of B7-1 and B7-2, the human RCC cell line, MZ1257RC, which expresses normal levels of adhesion molecules and major histocompatibility complex (MHC) class I surface antigens, was transfected with B7-1 and B7-2 expression vectors, respectively. The B7-1- and B7-2-transduced MZ1257RC cells were potent stimulators of allogeneic and autologous T-cell proliferation. B7-2 transfectants were approximately two- to threefold more effective in the induction of primary T-cell activation than B7-1-transduced cells. Interleukin (IL)-12 synergized with the B7/CD28 interaction to enhance allogeneic T-cell proliferation, independently of the B7 molecule transduced. In contrast, IL-2 only co-operatively increased T-cell activation in the presence of B7-2. Our results suggest the following: first, that co-stimulatory molecules are required for efficient T-cell responses directed against RCC; second, that B7-2 appears to be a more potent stimulator of tumour immunity as compared to B7-1; and third, that B7 molecules selectively co-operate with different T-cell stimulatory cytokines. The different activity of B7-1 and B7-2 molecules on the immunogenicity of RCC will have implications for the development and optimization of RCC-specific cancer vaccines.

T cell-mediated eradication of murine metastatic melanoma induced by targeted interleukin 2 therapy

Induction of a T-cell mediated antitumor response is the ultimate goal for tumor immunotherapy. We demonstrate here that antibody-targeted IL2 therapy is effective against established pulmonary and hepatic melanoma metastases in a syngeneic murine tumor model. The effector mechanisms involved in this tumor eradication are not dependent on NK cells, since the therapeutic effect of antibody-IL2 fusion protein was not altered in NK cell-deficient mice. In contrast, T cells are essential for the observed antitumor effect, since therapy with antibody IL2 fusion proteins is unable to induce tumor eradication in T cell-deficient SCID mice. In vivo depletion studies characterized the essential effector cell population further as CD8 + T cells. Such CD8 + T cells, isolated from tumor bearing mice after antibody-directed IL2 therapy, exerted a MHC class I-restricted cytotoxicity against the same tumor in vitro. These data demonstrate the ability of antibody-targeted IL2 delivery to induce a T cell-dependent host immune response that is capable of eradicating established melanoma metastases in clinically relevant organs.

Pancreatic islet allograft immunity and tolerance: the two-signal hypothesis revisited

The principle assumption of this discussion is that costimulation (CoS) forms the primary stimulus that compels T cells to mount a response to their specific antigen. However, this response can be either positive or negative, depending on the developmental stage of the T cell and the microenvironment in which the antigen and CoS are received. Thus, both immunity and tolerance may represent different outcomes of a two-signal process. We would emphasize that CoS is a functional term and not a strict molecular definition. While many molecular interactions have been described as providing CoS activity, notably those involving the B-7 family of cell surface molecules, it is not yet clear what combination(s) of non-antigen-specific signals may fulfil this function. This point is important because many studies have achieved tolerance through strategies designed to inhibit specific CoS molecules. However, it may be that differential signaling through distinct CoS molecules, rather than a global inhibition of CoS per se, plays a role in the generation of active tolerance in such studies (Bluestone 1995). A corollary of this notion is that antigen (signal 1) delivery to T cells is a null event and so is not an inherently paralysing signal. Of course, if signal 1 is not itself a tolerogenic signal, then other mechanisms are necessary to explain many empirical observations of tolerance to allogeneic or self antigens. This is best illustrated by those forms of functional tolerance to either alloantigens or self antigens that do not appear to be the result of clonal deletion/inactivation. It would be relatively simple to invoke a model of tolerance whereby the relevant tissue-destructive cell is eliminated or inactivated; such a model would preclude the necessity to suggest active regulatory mechanisms of tolerance. However, in several model systems, including our own observations concerning tolerance induction to APC-depleted islet allografts, tissue-destructive T cells can persist in recipients tolerant to allogeneic or self antigens. Furthermore, there are key examples in which tolerance demonstrates a dominant phenotype; that is, tolerant cells can regulate the activity of naive, non-tolerant cells. This latter observation points to the function of an active, regulatory form of tolerance. As such, we would emphasize that tolerance should not be defined as unresponsiveness since the tolerant state is the consequence of very active immune reactions.

T cell costimulation by B7/BB1 induces CD8 T cell-dependent tumor rejection: an important role of B7/BB1 in the induction, recruitment, and effector function of antitumor T cells

A successful antitumor T cell immune response involves induction, recruitment, and effector function of T cells. While B7/BB1 is known as a major costimulatory molecule in the induction of T cell responses, its role in T cell recruitment and effector function is still unclear. In this study, we show that introducing a major costimulatory molecule B7/BB1 into a major histocompatibility complex class II-negative tumor cell line, J558, results in a drastic reduction of its tumorigenicity. The tumor rejection depends on CD8 T cells but not CD4 T cells. However, unlike the previous reports on melanoma cell lines, B7/BB1-transfected J558 cells fail to induce cross-protection against parental J558 cells. The B7/BB1-transfected (J558-B7), but not untransfected J558 cells (J558-Neo) induce a CD8 T cell-dominant inflammatory response, and the T cells isolated from the tumor infiltrating lymphocytes (TIL) are polyclonal in terms of their T cell receptor V beta usage. Most surprisingly, the freshly prepared TIL have a potent, CD8 T cell-mediated cytotoxicity on tumor cells without any in vitro stimulation. The cytotoxic T lymphocyte (CTL) activity can be blocked by anti-CD8 monoclonal antibody (mAb). Interestingly, the CTL lyse J558-B7 about 10- to 80-fold more efficiently than untransfected J558-Neo cells. This preferential lysis cannot be attributed to recognition of B7/BB1-derived antigen by the T cells. This finding, together with the lack of the cross-protection between the J558-B7 and J558-Neo, suggests that B7/BB1 can also function at the effector phase of CTL responses. This notion is confirmed by our findings that the lysis of J558-B7 can be blocked by anti-B7 mAbs. Taken together, our results indicate that not only can the B7/BB1 molecule function as a costimulatory molecule at the initiation of immune response, it can also play a major role in T cell recruitment and effector function. This conclusion has significant implications for immunotherapy of tumors.

IL-2 and IL-4 can co-modulate the generation of cytotoxic T cells through CD8- CD4- splenic lymphocytes

Following activation with concanavalin A (Con A), murine T cells are able to suppress the generation of allospecific cytotoxic T lymphocytes (CTL). We have analysed the phenotype, tissue distribution, and mode of action of these cells in an effort to understand further the regulation of CTL-mediated immunity. The precursors of such cells are rare (1 cell per 70,000 spleen cells being able to suppress the generation of a particular allospecific response), but are much more abundant in the spleen than in the thymus. By the use of cytotoxic antibodies, we have been able to demonstrate that the splenic precursors of such cells are Thy-1.2+, CD4-, CD8- but, following activation with Con A, these cells acquire the CD8 marker. Cellular suppression by these lymphocytes is dramatically increased in the presence of the Th2-derived lymphokine, IL-4, whereas IL-2, the Th1-derived lymphokine, significantly augments the generation of CTL in a mixed lymphocyte culture even though relative suppression is still evident in the presence of Con A-activated lymphocytes. Suppression is not due to overcrowding of a cell culture since adding Con A-activated cells to an A anti-B + C culture often resulted in the suppression of the A anti-B response but not the A anti-C response, or vice versa. Suppression appears to require cellular interaction since supernatants from Con A-activated lymphocytes are unable to mediate suppression. Such cells may play an important intermediate role in homeostasis.

Identification of a 24-kDa cytokine that is required for development of cytolytic T lymphocytes

It is known that the production of cytolytic T lymphocytes requires growth factors such as interleukins 2 and 4 (IL-2 and IL-4). Elsewhere we have described bioassays that detect a cytokine that operates in concert with growth factor to generate cytolytic T lymphocytes. The factor that is termed cytolytic T-lymphocyte differentiation factor (CDF), together with IL-2 and lectin, mediates the formation of CD8+ killer cells in 2 days from thymocyte or peripheral lymphoid precursors. CDF is not mimicked by natural or recombinant sources of interferons, colony-stimulating factors, and IL-1 to IL-4. Here we use these bioassays to isolate and further characterize a single 24-kDa CDF protein from the conditioned medium of stimulated human blood mononuclear cells. CDF is first enriched by three successive chromatographic procedures that utilize anion exchange, hydroxyapatite, and phenyl-Superose. A single 24-kDa band with CDF activity is then isolated on 12% NaDodSO4/PAGE and clearly distinguished from the 17-kDa band of IL-2. The apparent molecular mass is similar under reducing and nonreducing conditions. After elution from NaDodSO4/PAGE the cytokine is maximally active at 0.25 nM in the CDF assay and has no growth factor activity for T lymphoblasts. To generate cytolytic CD8+, CD4- cells from spleen and lymph node T lymphocytes, IL-2 and small numbers of accessory dendritic cells must be applied together with CDF.

The immunogenicity of tumour cells

Immunological mechanisms are demonstrably of central importance in preventing the development of certain virus-associated cancers in animals and man; however, they do not appear to fulfill this role in the majority of 'spontaneous' tumours. This does not, however, necessarily indicate that spontaneous tumours lack potential target antigens for immunologically mediated destruction. Work in the field of transplantation immunology has clearly shown that certain cell types fail to elicit rejection reactions despite their possession of alloantigens. Similarly, some tumour cell types are poorly immunogenic to the point that they can grow in and kill animals despite a major histocompatibility barrier. These tumours are, however, susceptible to destruction in vivo in appropriately allo-sensitized animals. Thus, some tumours may be able to grow in autologous or syngeneic hosts because of their poor immunogenicity, despite the fact that they express potential (tumour-associated) rejection antigens. It may be possible to manipulate this situation for therapeutic purposes.

Cellular interactions in the lysis of varicella-zoster virus infected human fibroblasts

The in vitro lysis of varicella-zoster virus (VZV) infected human fibroblasts by blood mononuclear cells (MNC) is inhibited by cyclosporin A, whether or not the effector and target cells chare HLA A or B antigens. Interleukin 2 (IL-2) reversed the inhibition by cyclosporin A (CyA) and also induced a further increase in target cell lysis by MNC in the absence of CyA. MNC depleted of OKM-1+ or Leu-11+ cells showed reduced lysis of VZV infected fibroblasts and this reduction was not overcome by adding IL-2. Depletion of monocytes from the MNC effectors reduced target cell lysis and this effect was reversed by adding Interleukin 1 (IL-1). The results indicate that NK cells contribute to the lysis of VZV infected cells and suggest that IL-2 release by T cells, as a result of HLA matching or antigen representation, may amplify this mechanism.

Studies on clonal heterogeneity in two spontaneously metastasizing mammary carcinomas of recent origin

We have studied the clonal heterogeneity of 2 spontaneously metastasizing mammary carcinomas which recently arose spontaneously in C3H/He female retired breeders. Cells of early (2nd to 5th) transplant generations of these tumors were cloned by a combination of semi-solid agarose colony formation and limiting dilution techniques. Growth characteristics of the various clones in vitro and their tumorigenicity in vivo were evaluated. Subsequently, the role of host immunity and of interclonal interactions in regulating growth of the different clones in vivo were analyzed. We found that, whereas all 16 clones isolated from one tumor (T-58) grew rapidly in vivo and in vitro, 10 clones isolated from the second tumor (MT-2) showed a wide disparity in their growth rates in vivo. Taken together, these clones could generally be divided into 3 categories: (1) rapidly growing lines which grew in vivo at rates similar to or higher than those of the parental line; (2) slow-growing lines which grew more slowly than the parental line; and (3) non-growers which failed to produce tumors in vivo with doses of up to 5 X 10(6) cells injected either s.c. or i.v. but grew in vitro at rates comparable to the parental line. No correlation could be established between the various growth potentials exhibited by these tumor lines and tumor cell morphology in vitro and in vivo, as determined by light and electron microscopy. Sublethal irradiation (550-650 R) of young animals prior to tumor inoculation, or before inoculation of tumor cells into old, low NK syngeneic mice, failed to modify the growth of slow-or non-growing lines in vivo, indicating that host cellular defense mechanisms against the clones, if existent, were not mediated by NK or radiosensitive B or T cells. When clonal interactions were studied by the simultaneous injection of different clones in vivo at different s.c. sites, we found that a slow-growing line failed to modify the growth rate of a rapidly growing line, but accelerated the growth of a second slow-growing line injected simultaneously on the contralateral side, and that this enhancement of tumor growth was radioresistant. A mixture of these 2 lines also grew more rapidly than the individual lines alone. Our findings suggest that phenotypic variations in tumorigenicity can be found in clonal lines derived from spontaneous primary tumors and that these variations are not related to cell cycle properties as measured in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Clonal analysis of helper and effector T-cell function in neonatal transplantation tolerance: clonal deletion of helper cells determines lack of in vitro responsiveness

Mice rendered tolerant at birth of H-2 alloantigens display concordant in vivo and in vitro phenotypes: they fail to reject skin grafts bearing the tolerated antigens, and their lymphoid cells fail to participate in tolerogenspecific mixed lymphocyte reactions (MLRs) and cell-mediated lympholysis (CML). Tolerant animals normally reject third-party skin allografts and develop positive MLRs and CML to third-party antigens. It has been suggested that clonal deletion of antigen reactive cells is the basis for this spectrum of responses. To investigate further the basis for the lack of in vitro alloreactivity, we conducted limiting dilution studies with lymph node cells from adult mice tolerant of various H-2 disparities. When the frequencies of (a) cells responding to the tolerogen in MLR and (b) interleukin-2-producing cells against the tolerogen were determined, it appeared that both types of cells were functionally deleted, that is, the frequency of cells responding to tolerogen-bearing stimulator cells was identical with that of cells stimulated with syngeneic cells. On the assumption that cells from H-2 tolerant mice are deficient in helper cell activity toward the tolerogen, we performed CML cultures under conditions in which exogenous help was provided in the form of supernatants derived from concanavalin A stimulated rat spleen cell cultures. Lymphoid cells from H-2 tolerant mice generated significant cytotoxicity toward the tolerogen under these conditions, although the absolute level of killing was reduced compared with that of cells from normal mice. Limiting dilution assays confirmed that Tc precursors were present in tolerant mice, and that they were reduced to less than 10% of normal numbers; however, tolerogen-specific Tc precursors were present in frequencies significantly greater than self-reactive Tc precursors. These data indicate that a deletion mechanism operates in neonatal transplantation tolerance to reduce the clone size of all three categories of functional T cells assayed, but that its efficiency is greatest among cells destined to provide specific T-cell help. The absolute functional deletion of helper cells determines the in vitro CML unresponsiveness of lymphoid cells from tolerant mice, and may be a crucial factor in promoting the in vivo phenotype of skin allograft tolerance.

Clones of cytotoxic T lymphocytes reactive to haptenated allogeneic cells: precursor frequency and characteristics as determined by a split-culture approach

CBA (H-2k) responder spleen cells have been cultured at limit dilution with trinitrophenyl (TNP)-modified BALB/c (H-2d) stimulator cells and a source of T-cell growth factor in order to generate cytotoxic effector clones. After culture, such clones were split into two to four replicates and each was assayed against a different target. This allowed identification of clones capable of lysing TNP-modified P815 (H-2d) targets but not unmodified P815 targets. Thus, clones specific for TNP and allogeneic restriction elements were detected without the need to use techniques that deplete the responder population of alloreactive cells. Cytotoxic T lymphocyte precursors (CTL-P) specific for TNP-modified P815 (major histocompatibility complex-nonidentical) targets were identified, at a low frequency (28.2 x 10(-6)) compared to CTL-P for TNP-modified C1.18 (H-2k) (identical) targets (224 x 10(-6)). The hapten specificity, H-2 restriction specificity, and Thy-1 status of these clones have been examined. Fourteen percent of CBA CTL-P reactive to TNP-modified P815 targets also showed reactivity to NIP-modified P815 targets, and 86% of CBA clones reactive to TNP-modified P815 targets ("allo-TNP-reactive" clones) failed to show reactivity to TNP-modified C1.18 targets--i.e., showed a restriction preference for allo rather than self. All such H-2d-restricted, TNP-specific clones were uniformly sensitive to anti-Thy-1 antibody and complement. Among the H-2k responders studied, we have not demonstrated CTL-P reactive to TNP-modified syngeneic cells which also react with H-2d cells or NIP-modified H-2d cells among 168 clones analyzed. This suggests that such clones, if present, are relatively rare.

Variation in accessory cell requirements in human mixed lymphocyte response to leukaemic cell lines

Human leukaemia and lymphoma cell lines were investigated as stimulating cells in an allogeneic mixed lymphocyte response. Purified T cells and unfractionated mononuclear cells from normal donors were used as responders. The cell lines fell into three groups: (i) those which stimulated allogeneic responder T cells in the presence or absence of accessory (non-T) cells; (ii) those which stimulated T cells only in the presence of accessory cells; and (iii) those which failed to stimulate in either case. The accessory function was provided by adherent cells and non-adherent, non-T cells. There was no correlation between the stimulatory capacity of these cell lines and the presence of serologically defined HLA-DR determinants. These results are discussed in the context of the current two-signal hypothesis for T-cell activation.

Lethal effect of the intravenous injection of H-2 alloantigen activated T cells

T cells of C57BL/6J (B6) mice activated in vitro against the K and D determinants of the H-2d haplotype, and expanded in tissue culture in the presence of interleukin 2, were capable of rapidly killing lethally irradiated BALB/c recipients when injected intravenously. Mice given 10(6), 10(7) and 10(8) such T cells survived 10.5, 8.5 and 0.5 days respectively. Mice given irradiation only survived 10.5 days. Mice given 10(8) B6 T cells activated against all determinants of a third party haplotype (H-2k) survived 8.5 days. Respiratory distress developed within 3 hr of injection in mice given 10(8) T cells activated against the H-2 alloantigens of the recipient haplotype, and at autopsy their lungs showed pulmonary congestion, focal obliteration of the alveolar space and thickening of alveolar interstitial tissue with fibrin, red cell and a mononuclear cell infiltrate. These findings may have relevance to the use of cellular immunotherapy.

Purification of murine T cell growth factor. A lymphocyte mitogen with helper activity

Mouse T cell growth factor was purified from the serum-free conditioned medium of lectin-stimulated spleen cells. A 3,000-fold purification was achieved with a final yield of 12%. The purified protein, with an apparent Mr of 23,000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis, was active at concentrations of 4 x 10(-11) M, both in the T cell growth factor and T cell replacing factor assays. In addition, purified T cell growth factor alone was mitogenic for spleen cells from both nude and normal mice.

Interleukin 2 production by both Ly2+ and Ly2- T-cell subsets

Homogeneous T-cell populations produced by activating lymphocytes to I-, K-, or K+ D- region-encoded determinants of the mouse H-2 complex release interleukin 2 when restimulated by concanavalin A. Contrary to earlier reports on the cellular origin of the lymphokine, we find that interleukin 2 production can be either Ly2+ or Ly2- T-cell-dependent.

Enhancement of spontaneous killer cytotoxicity by soluble factor

Two-stage stimulation of SK activity of normal human peripheral blood lymphocytes by soluble factors was demonstrated. The first stage was initiated by factors present in supernatant derived from normal B-LCL cultures. Only cell lines which could induce SK activity in culture in an MLR-type reaction had the capacity to produce the active factor. Supernatant factor required adherent cells to cause SK augmentation. The interaction of adherent cells plus supernatant factor resulted in the production of a second soluble factor which stimulated an increase in SK activity in responding lymphocyte populations. This second stage involved a different soluble factor which acted directly on the non-SK, Fc-negative lymphocyte population, and within 3 hr. Data obtained using antisera to interferon (IF) indicated that IF is a component of the second soluble factor, and not of the supernatant factor derived from the B-LCL.

A two-signal mechanism for the induction of cytotoxic T lymphocytes

Depletion of adherent cells from stimulator and responder lymphocytes by a single filtration through nylon wool columns led to complete abrogation of the cytotoxic response to the stimulating alloantigen. Cytotoxic responses were restored by adding anti-Thy-1 + complement-greated normal peritoneal exudate cells (PEC) syngeneic or allogeneic to the responding population. Alternatively, the response could be reconstituted with costimulator, a lymphokine obtained by stimulation of spleen cells with concanavalin A. Costimulator was not itself cytotoxic and induced few or no cytotoxic T lymphocytes (CL) in the absence of stimulator cells. Costimulator was also more efficient than allogeneic PEC, which in turn were more efficient than syngeneic PEC, in reconstituting the cytotoxic response. The number of CL produced to the activating alloantigen was shown to increase with increasing concentration of costimulator. More interestingly, in the presence of a relatively high concentration of costimulator, CL were also activated to target cells that differ in H-2 haplotype from the stimulating alloantigen. Lysis of the third-party target cells could not be inhibited by cold targets syngeneic to the activating alloantigen. A clonal assay for cytotoxic precursors was used to confirm that CL for the activating alloantigen and CL for the third-party H-2 antigens were derived from different progenitors. Only about 37% of the cytotoxic clones produced were specific for the activating alloantigen. These observations are explained in terms of a two-signal model of CL activation.

Direct evidence for a two-signal mechanism of cytotoxic T-lymphocyte activation

The cellular requirements for the activation of cytotoxic T lymphocytes to alloantigens are complex. In addition to cytotoxic precursors (CLPs), metabolically active stimulator cells, adherent accessory (A) cells and antigen-specific helper T cells are also required. However, the requirement for A cells, metabolically active stimulator cells or helper T cells can be replaced by soluble factors or co-stimulator (CoS), a lymphokine obtained by stimulation of murine spleen cells with concanavalin A (Con A). We show here that in the presence of CoS, cultures containing on average one lymph node lymphocyte (LNL) and Con A can be activated to produce single cytotoxic clones. This observation strongly suggests that one of the target cells of CoS is the CLP and provides more direct evidence for a two-signal mechanism for cytotoxic T lymphocyte activation.

Interleukin 2 in cell-mediated immune responses

The lymphokine Interleukin 2(IL2) restores T cell responses in a number of in vitro systems where immunogenicity has been compromised. UV irradiation of the stimulating allogeneic cells in a mixed leukocyte culture eliminates the production of cytotoxic T lymphocytes and greatly reduces the DNA synthesis response. IL2 restores both parameters. UV-irradiated stimulators are also unable to induce the normal production of IL2 which is observed in a mixed leukocyte culture. The cytotoxic activity of allogeneically stimulated thymocytes is almost completely lost within 24 hours after removal of IL2 at 5 days, indicating that the lymphokine is continuously required to maintain CTL. Thymocytes in 4-day cultures do not adsorb IL2 unless they are simultaneously activated with a mitogen. Finally, IL2 does not adequately restore a secondary response to the purified protein derivative of tuberculin (PPD) in adherent-cell-depleted cultures, indicating that macrophages, in addition to being required for IL2 production, have other functions. These probably include the presentation of soluble antigens to responding cells.

Quantitative studies on the precursors of cytotoxic lymphocytes. VI. Second signal requirements of specifically activated precursors isolated 12 h after stimulation

It is shown that, in a mixed lymphocyte reaction, the production of cytotoxic T lymphocytes (CL) from cytotoxic T lymphocyte precursors (CLP) requires two signals which are separated time. Using a flow cytometer-cell sorter and a vital, fluorescent DNA stain, Hoechst 3342, CLP specific for the stimulator cells can be separated from other CLP and from stimulator cells 12 h after initiation of mixed lymphocyte cultures. These CLP are in a state of partial activation and can produce CL in the absence of stimulator cells if a second signal in the form of a concanavalin A-induced spleen cell supernate factor is added. Specific CL are also generated when the partially activated CLP are cultured with both nude spleen cells and stimulator cells. In this case it appears that an interaction between the stimulator cells and the nude spleen cells leads to production of the second signal.

Suppression of T cell-mediated immunity by tumor cells: immunogenicity versus immunosuppression and preliminary characterization of the suppressive factors

In studying the immunogenicity of spleen cells and tumor cells in the generation, of cytotoxic T lymphocyte (CTL) in the allogeneic mixed lymphocyte culture (MLC) or mixed lymphocyte tumor cell culture (MLTC) reactions, we have found that the tumor cells not only appear to be poorly immunogenic, but are also immunosuppressive. This was shown by the ability of the tumor cells or their cell-free extracts to suppress standard MLC reactions. This suppression was acting mainly at the induction phase of the cytotoxic response. It could not interfere with the killing activity of the fully generated CTLs. In a Friend virus-induced leukemia FBL-3 system, at least two major components could be attributed to the cause of immunosuppression; one was of viral origin and the other was of non-viral origin. The viral component was sensitive to UV-irradiation and could be pelleted after ultracentrifugation at 100,000 g. The non-viral component was UV-resistant and was retained in the supernatant fraction after ultracentrifugation. Friend virus and 12 commonly found murine viruses have been excluded as the possible candidates causing the immunosuppression. The immunosuppressive viruses are very likely of endogenous origin and are defective in replication as shown by electromicroscopy, and by the virus focus-inducing and reverse transcriptase assays. These findings indicate that probably all tumor cells possess the immunosuppressive factor(s) which may account for their apparent lack of immunogenicity and the lack of proper immune responses in the tumor-bearing hosts.

A high frequency of cytotoxic precursor cells for a syngeneic tumour

The average frequency of cytotoxic precursor cells in DBA/2 lymph node cell preparations reactive to the syngeneic tumour P815 has been determined as 1 in 2000. This frequency is similar to the precursor frequency for an allogeneic tumour EL-4. The normal lack of response of DBA/2 lymph node cells to the syngeneic tumour P815 in vitro cannot be attributed to a lack of cytotoxic precursor cells. We conclude that in this tumour-host system non-immunogenicity reflects a defect at the inductive step.

Studies on T lymphocyte activation. I. Requirements for the mitogen-dependent production of T cell growth factors

Conditioned media (CM) obtained from concanavalin A (Con A)-stimulated spleen cell cultures maintain mitogen-derived T cell blasts in exponential growth for indefinite periods of time. Such purified T cell blasts do not respond to Con A, and the growth-promoting activity in CM is independent of the mitogenic lectin used for its production. However, the appearance of activity in CM is Con A dose-dependent. Furthermore, the production of these T cell growth factors is independent of B cells, while it requires both T cells and nontheta-bearing, probably Ia-positive cells present in normal and nude spleens. On the other hand, the T cell blasts which are reactive to the growth factors, neither produce CM by themselves nor can they cooperate with nude spleen cells for its production, in the presence of a mitogenic lectin. Since the concentration of growth factors in CM determines the extent of T cell growth, we propose that the growth of some T cells is necessarily dependent upon the activity in CM described here and, consequently, that the basis for T cell activation is the induction of such growth factors.

Immunosuppression by a mouse tumor resembles antigenic competition

The intraperitoneal injection of gamma-radiated, UV-radiated, or unradiated P-815 tumor cells into syngeneic or allogeneic mice suppressed the immune response to a subsequent intraperitoneal injection of sheep erythrocytes in a manner similar to the suppression caused by the injection of manner similar to the suppression caused by the injection of horse erythrocytes and termed antigenic competition. In both cases, the greatest suppression occurred when the sheep erythrocytes were injected at the same site (intraperitoneal) as the tumor or antigen several days after the tumor or antigen and in a dose of 10(8) erythrocytes or less.

Enhancement of the primary cytotoxic response to membrane by a lymphokine costimulator

The primary and secondary cytotoxic T cell responses of C57Bl/6 (H-2b) mouse spleen cells to P-815 membrane fragments (H-2d) were examined. The primary response required the addition of a supernatant from mitogen-stimulated spleen cells, or costimulator, to the culture medium. Costimulator had little effect on the secondary response unless the spleen cells were first passed through a nylon wool column. Our data suggested that secondary cultures produced their own costimulator and that adherent cells were required for its production. The possibility that adherent cells are needed to activate helper cells is discussed.

In vitro maturation of immature thymocytes into immunocompetent T cells in the absence of direct thymic influence

Peanut lectin (PNL) binds to a majority of mouse thymocytes (Thc) in suspension. By using cell affinity chromatography on a column of anti-PNL antibody, Thc populations at least 96 percent pure in PNL + or - cells, as judged by immunofluorescence, were obtained. PNL(+) cells are rich in Thy 1 and poor in H(2) antigens, cortisone sensitive, unresponsive to phytohemagglutinin (PHA), and immunologically incompetent, as judged by mixed lymphocyte reaction, popliteal lymph node graft-versus-host assay, and by testing helper activity in a primary in vitro antibody response to sheep erythrocytes; the converse is true of PNL(-) cells. Thus, PNL(+) and (-) cells appear to correspond to cortical and medullary Thc, respectively, as previously suggested. In culture, PNL(+) Thc show poor viability and a weak proliferative response to concanavalin A (Con A), except when supernate (SUP) of 24 h Con A stimulated lymph node lymphocyte cultures, or irradiated lymph node cells, are added, in which cases a strong proliferative response to the mitogen is observed. A variety of control experiments showed that the proliferating cells did not result from preferential stimulation of a few contaminating PNL(-) Thc present in the PNL(+) Thc cultures. The blasts resulting from PNL(+) Thc proliferation display mitogen-induced cytotoxicity, and give rise to a population of medium-sized lymphocytes, mostly PNL(-), poor in Thy 1 and rich in H(2) antigens, PHA responsive, and immunologically competent in the above-mentioned assays. Fresh PNL(+) Thc responded in mixed lymphocyte reaction in the presence of SUP (lectin depleted) and since incubation in SUP alone did not confer reactivity on PNL(+) Thc, it appears therefore that (a) immature Thc possess alloantigen and mitogen-specific surface receptors but lack the capacity to respond by proliferation to receptor triggering without the help of extracellular factor(s) released by mature lymphoid cells stimulated by mitogens (b) cell division is associated with the acquisition of immunological responsiveness, characteristic of mature T lymphocytes. The implications of these findings for the ontogenesis of thymus-derived lymphocytes, and for the possible traffic of Thc within and from the thymus, are discussed.