Three different signals are required for the induction of cytolytic T lymphocytes from resting precursors

The requirement for the signals in induction of cytolytic T lymphocytes (CTL) has been investigated. C57BL/6 X CBA/T6 F1 spleen cells stimulated with the lectin leukoagglutinin (L-A) failed to show CTL activity in a PHA-facilitated assay, although L-A-activated splenic T cells were able to respond to T cell growth factor (TCGF). Concanavalin A (Con A) on the other hand was able to induce cytolytic activity from CTL-P, as well as to render splenic T cells responsive to TCGF. Furthermore, L-A-activated splenic T cells could generate cytolytic activity upon subsequent culture in secondary mixed leukocyte culture supernatant (2 degrees MLC SN). In contrast, EL-4-derived SN (EL-4 SN) was unable to induce cytolytic activity from L-A-activated spleen cells. In addition, proliferation of L-A-activated spleen cells cultured in EL-4 SN was similar to those cultured in 2 degrees MLC SN. Nonactivated spleen cells were totally unresponsive to both SN in proliferation and generation of CTL. Analysis of T cell clones for the production of a factor necessary for induction of cytolytic activity revealed that both cytolytic and noncytolytic T cell clones were able to produce a factor(s) for the generation of cytolytic activity from L-A-activated T cells. On the other hand, SN from certain antigen-stimulated T cell clones produced factors capable of inducing cytocytic activity by L-A-activated T cells only in the presence of EL-4 SN. Neither EL-4 SN nor cloned T cell SN alone had such a capacity. The nature of the necessary lymphokines in the SN from the clone cells or from the EL-4 is unknown. In the case of the EL-4 SN, it is not known whether the presence of TCGF plays a role or whether that role is perhaps more differentiative than proliferative. This study provides evidence that the induction of CTL from CTL-P can be dissociated into activation, which is required to render T cells responsive to second signals, and differentiation, which is mediated by two different factors.     

Disparate functional properties of two interleukin 1-responsive Ly-1+2- T cell clones: distinction of T cell growth factor and T cell-replacing factor activities

We describe the properties of two Ly-1+2- T cell clones (Ly-1.14 and Ly-1.21), which are maintained in long-term culture in the absence of other cell types. The clones require media containing a source of interleukin 1 as well as interleukin 2. They retain physiologic responses to interleukin 1, which is required for optimal production of T cell lymphokines by these clones in response to concanavalin A (Con A). The two Ly-1+2- T cell clones differ in their production of lymphokines after stimulation by Con A. The supernatant of clone Ly-1.21 promotes the proliferation of T cells maintained in long-term culture, induces antibody synthesis in cultures of B cells and antigen, and induces the differentiation of cytolytic cells in cultures of thymocytes and antigen; these assays define the properties of T cell growth factor (TCGF), T cell-replacing factor for B cells (TRF-B), and T cell-replacing factor for cytolytic cells (TRF-C), respectively. In contrast, the supernatant of clone Ly-1.14 contains only TCGF activity and does not promote antibody synthesis by B cells or differentiation of cytolytic cells from thymocytes. The results indicates that TCGF and TRF activities reside on independent, although perhaps related, molecules.     

Cytolytically active murine T-lymphocyte/polyoma virus-transformed fibroblast hybrids

It would be of great interest to obtain permanent T-cell lines retaining specific activity without either allogeneic or xenogeneic stimulation. Functionally active hybrids between cytolytic T cells and thymoma were previously reported, but they had to be selected in a TCGF-containing medium. This study contains new results and reports the preparation of a hybrid cell from a cytolytic T cell and a polyoma virus-infected fibroblast, in which the T-cell characteristics dominate over the polyoma-transformed characteristics. A differentiated T-cell function (i.e., cytolysis) persists and the differentiated line does not require TCGF. The loss of cytolytic activity during in vitro evolution may be due to a selection favouring transformed cells, as suggested by concomitant enhancement of the transformed phenotype and chromosome loss.     

The generation of cytolytic activity in mixed leukocyte cultures: cortisone-resistant thymocytes are deficient in helper T lymphocytes

Cortisone-resistant (CR) thymocytes did not generate cytolytic activity toward H-2 K or D alloantigen unless they were also stimulated by H-2 I or non-H-2 alloantigens, even though spleen cells generated brisk cytolytic activity toward H-2 K or D alone. Backstimulation by stimulating strain T lymphocytes accounted for neither the response of spleen cells toward H-2 K or D alloantigen nor the response of CR thymocytes to a full set of alloantigens. In addition, lack of non-T accessory cells did not account for the CR thymocyte pattern of reactivity. Rather, CR thymocytes appeared to be relatively deficient in helper T lymphocytes (HTL). CR thymocytes generated specific cytolytic activity toward H-2 D alloantigen when T cell growth factors (TCGF) or cloned alloreactive helper T lymphocytes were added to culture. CR thymocytes contained fewer HTL precursors detected at limit dilution than spleen cells did. Thus spleen cells generated cytolytic activity toward class I alloantigens alone, but under the same culture conditions CR thymocytes had to be stimulated by both class I and class II alloantigens. Class II alloantigens may be required to stimulate cytolytic activity only under culture conditions in which class I-reactive HTL are not sufficient to provide a minimal threshold of help.     

Dominant manifestation of pluripotency in embryonic stem cell hybrids with various numbers of somatic chromosomes

Developmental potential was assessed in 8 intra-specific and 20 inter-specific hybrid clones obtained by fusion of embryonic stem (ES) cells with either splenocytes or fetal fibroblasts. Number of chromosomes derived from ES cells in these hybrid clones was stable while contribution of somatic partner varied from single chromosomes to complete complement. This allowed us to compare pluripotency of the hybrid cells with various numbers of somatic chromosomes. Three criteria were used for the assessment: (i) expression of Oct-4 and Nanog genes; (ii) analyses of teratomas generated by subcutaneous injections of the tested cells into immunodeficient mice; (iii) contribution of the hybrid cells in chimeras generated by injection of the tested cells into C57BL blastocysts. All tested hybrid clones showed expression of Oct-4 and Nanog at level comparable to ES cells. Histological and immunofluorescent analyses demonstrated that most teratomas formed from the hybrid cells with different number of somatic chromosomes contained derivatives of three embryonic layers. Tested hybrid clones make similar contribution in various tissues of chimeras in spite of significant differences in the number of somatic chromosomes they contained. The data indicate that pluripotency is manifested as a dominant trait in the ES hybrid cells and does not depend substantially on the number of somatic chromosomes. The latter suggests that the developmental potential derived from ES cells is maintained in ES-somatic cell hybrids by cis-manner and is rather resistant to trans-acting factors emitted from the somatic one.     

Allo-Ia reactive murine T-cell lines. II. Mechanisms of clonal expansion of T cells explored by use of the allo-Ia reactive T cell clones

Murine T cell clones, which were retrieved from an A.TH anti-A.TL(lak) T cell line and had been long-term cultured in the medium supplemented with T cell growth factor (TCGF) and mitomycin C(MMC)-treated feeder cells of either Is or Ik haplotype, were found to survive in TCGF-free medium for a long time, quite in contrast to so far reported TCGF-dependent T cell clones. When T cells of these clones at the full growth in the TCGF-medium were transferred to TCGF-free medium, they survived at resting state for a long time, and half-life, i.e., the time when 50% of the transferred cells were still viable, of some clones reached 20 days. The cloned T cells at the resting state retained full responsiveness to the specific lak antigen but lost the responsiveness to TCGF as determined by [3H]thymidine uptake, whereas the same T cells harvested from TCGF-medium did not show the antigen-specific responsiveness. The cloned T cells at the resting state showed marked DNA synthesis in response to the specific antigen but never entered the phase of the cell division. Addition of TCGF to the antigen-activated cloned T cells at their peak DNA synthesis triggered the cell division without time lag. Thus, it was confirmed at a single clone level that two sequential signals, one via the antigen-receptor reacting with specific antigen and another via the TCGF-receptor accepting TCGF, are required for clonal expansion of T cells reacting with antigen. The mitogen-responsiveness among five clones was examined at their resting state; two clones responded to Con A and PHA only in the presence of accessory cells (MMC-treated, T cell-depleted syngeneic spleen cells), and one clone responded well to Con A and PHA in the absence of accessory cells. Thus, most of our clones retained physiologic characteristics of T cells directly collected from mice even after long-term culture in TCGF-medium.     

Unequal segregation of parental chromosomes in embryonic stem cell hybrids

Chromosome segregation was studied in 14 intra- and 20 inter-specific hybrid clones generated by fusion of Mus musculus embryonic stem (ES) cells with fibroblasts or splenocytes of DD/c mice or Mus caroli. As a control for in vitro evolution of tetraploid karyotype we used a set of hybrid clones obtained by fusion of ES cells (D3) with ES cells (TgTP6.3). Identification of the parental chromosomes in the clones was performed by microsatellite analysis and in situ hybridization with labeled species-specific probes. Both analyses have revealed three types of clones: (i) stable tetraploid, observed only for ES x ES cell hybrids; (ii) bilateral loss of chromosomes of both ES and somatic partners; (iii) unilateral segregation of chromosomes of the somatic partner. Observed unilateral segregation was extensive in ES-splenocyte cell hybrids, but lower in ES-fibroblast hybrid clones. Developmental state of the somatic partner is presumably responsible for directional chromosome loss. Nonrandom segregation implies that initial differences in the parental homologous chromosomes were not immediately equalized implying at least transient persistence of the differentiated epigenotype.     

The effect of T cell growth factor on the generation of cytolytic T cells.

The development of cytotoxic effector cells through primary allogeneic mixed tumor-lymphocyte culture (MTLC) was found to be accompanied by the production of T cell growth factor (TCGF). Addition of supplemental TCGF to MTLC resulted in the generation of significantly greater quantities of effector cells, and these effector cells displayed augmented cytotoxic activity. The TCGF-induced effect could not by duplicated by the addition of fresh medium or a mitogenic concentration of concananvalin A. Although TCGF augmented the proliferation of antigen-nonreactive cells, antigen-reactive cells appeared to be preferentially stimulated by TCGF. Finally, it was shown that depletion of TCGF from MTLC resulted in an impairment of proliferation and differentiation of cytotoxic effector cells. These findings demonstrate that soluble factors are involved in the regulation of in vitro cell-mediated immune responses in an analogous manner to similar factors that have been shown to regulate humoral immune responses. Therefore, the forces affecting TCGF production may modulate the amplitude of a T cell-mediated cytolytic response.     

Expression of the tumor necrosis factor locus is not necessary for the cytolytic activity of T lymphocytes

In order to test whether tumor necrosis factors alpha (TNF-alpha) or beta (TNF-beta, also known as lymphotoxin) are involved in the lysis of target cells by cytolytic T lymphocytes, we probed for the presence of the TNF mRNAs in several quiescent and activated CTL clones. No TNF mRNA could be found in constitutively cytolytic Lyt-2+ clones, and only two out of three clones tested accumulated TNF mRNA after stimulation with phorbol myristate acetate and ionomycin. Of two L3T4+ clones that can be induced to become cytolytic by a combination of antigen and IL-1, only one accumulated TNF-beta mRNA in the process. The PC60 rat X mouse T cell hybrid, which becomes cytolytic in response to a combination of IL-1 and IL-2, also failed to accumulate TNF mRNA after stimulation with these agents. Our results strongly suggest that TNF-alpha or -beta are not necessary agents of the cytolytic activity exhibited by antigen-specific T lymphocytes.     

Preferential generation of human T cell hybrids with a tetraploid fusion partner

The factors determining successful derivation of human T lymphocyte hybrids are largely unknown. This report describes diploid and tetraploid clones of the T cell line CEM which were fused with either a human T cell line (Jurkat) or with peripheral blood lymphocytes (PBL). Fusions of all CEMR clones with the Jurkat cell line yielded hybrids at a very high frequency (1 X 10(-4)). Fusion of diploid clones of CEM with PBL yielded no hybrids, whereas fusion of tetraploid clones of CEM with PBL resulted in growth frequencies of 1 to 3 X 10(-6). Enumeration of hybrids immediately after fusion indicated that in all cases, fused cells represented 5 to 10% of the population. That the ability to yield viable hybrids after fusion was a characteristic of tetraploid cells was indicated by the finding that tetraploid variants of a diploid clone could also yield viable hybrids after fusion. Possible mechanisms for the difference in results generated with diploid and tetraploid cells, and characteristics of the hybrid cells generated, are also discussed.     

Embryonic stem cell/fibroblast hybrid cells with near-tetraploid karyotype provide high yield of chimeras

Ten primary clones of hybrid cells were produced by the fusion of diploid embryonic stem (ES) cells, viz., line E14Tg2aSc4TP6.3 marked by green fluorescent protein (GFP), with diploid embryonic or adult fibroblasts derived from DD/c mice. All the hybrid clones had many characteristics similar to those of ES cells and were positive for GFP. Five hybrid clones having ploidy close to tetraploidy (over 80% of cells had 76–80 chromosomes) were chosen for the generation of chimeras via injection into C57BL blastocysts. These hybrid clones also contained microsatellites marking all ES cell and fibroblast chromosomes judging from microsatellite analysis. Twenty chimeric embryos at 11–13 days post-conception were obtained after injection of hybrid cells derived from two of three clones. Many embryos showed a high content of GFP-positive descendents of the tested hybrid cells. Twenty one adult chimeras were generated by the injection of hybrid cells derived from three clones. The contribution of GFP-labeled hybrid cells was significant and comparable with that of diploid E14Tg2aSc4TP6.3 cells. Cytogenetic and microsatellite analyses of cell cultures derived from chimeric embryos or adults indicated that the initial karyotype of the tested hybrid cells remained stable during the development of the chimeras, i.e., the hybrid cells were mainly responsible for the generation of the chimeras. Thus, ES cell/fibroblast hybrid cells with near-tetraploid karyotype are able to generate chimeras at a high rate, and many adult chimeras contain a high percentage of descendants of the hybrid cells. A. A. Kruglova and E. A. Kizilova contributed equally to this work. This study was financially supported by grants from the Russian Academy of Sciences, Siberian Branch 5.2 and 14.0.     

Cloned "anomalous" killer cells derived from allogeneic mixed leukocyte culture

In addition to allospecific cytotoxic lymphocytes, cytolytic effector cells capable of killing a broad range of targets are generated during mixed leukocyte culture (MLC). These cells, which have been previously called anomalous killer cells, are a distinct functional subset separate from natural killer cells or allospecific cytotoxic lymphocytes but display many characteristics of lymphokine-activated killers. In order to isolate anomalous killer cells for detailed analysis, we generated the cytolytic effectors from an allogeneic MLC using heat-inactivated stimulators. This treatment of the stimulator population abrogated the generation of classical allospecific cytotoxic lymphocytes but allowed the generation of anomalous killer cells which were subsequently cloned via limiting dilution. The clones derived by this method displayed the functional properties of anomalous killers seen in bulk MLCs. The clones demonstrated potent cytolytic activity against both NK-sensitive and NK-resistant tumor targets in vitro and also suppressed tumor growth in vivo. Ultrastructural studies revealed features similar to those of cloned antigen-specific cytolytic cells and clones with NK-like function. The cells expressed surface glycoproteins associated with both NK and T lymphocytes including Thy-1, Ly-2, T200, Qa-5, asialo GM1, and the antigens defined by the NK alloantisera NK-2.1 and NK-3.1. These cells may play an important role during early phases of the immune response, since cytolytic cells of broad specificity may protect the host until classical cytotoxic lymphocytes with restricted specificity are generated.     

IL-4 and IFN (alpha and gamma) exert opposite regulatory effects on the development of cytolytic potential by Th1 or Th2 human T cell clones.

The cytolytic potential of a total number of 118 CD4+ human T cell clones specific for purified protein derivative (PPD) from Mycobacterium tuberculosis, tetanus toxoid, Lolium perenne group I allergen (Lol p I), Poa pratensis group IX allergen (Poa p IX), or Toxocara canis excretory/secretory antigen(s) (TES) was assessed by both a lectin (PHA)-dependent and a MHC-restricted lytic assay and compared with their profile of cytokine secretion. The majority of clones with Th1 or Th0 cytokine profile exhibited cytolytic activity in both assays, whereas Th2 clones usually did not. There was an association between the cytolytic potential of T cell clones and their ability to produce IFN-gamma, even though IFN-gamma produced by T cell clones was not responsible for their cytolytic activity. IL-4 added in bulk culture before cloning inhibited not only the differentiation of PPD-specific T cells into Th1-like cell lines and clones, but also the development of their cytolytic potential. The depressive effect of IL-4 on the development of PPD-specific T cell lines with both Th1 cytokine profile and cytolytic potential was dependent on early addition of IL-4 in bulk cultures. In contrast, the addition in bulk culture of IFN-gamma enhanced both the cytolytic activity of PPD-specific T cell lines, as well as the proportion of PPD-specific T cell clones with cytolytic activity. The addition in bulk cultures before cloning of IFN-gamma or IFN-alpha favored the development of TES-specific and Poa p IX-specific T cells into T cell clones showing a Th0 or even a Th1, rather than a Th2, cytokine profile. Accordingly, most of TES- and Poa p IX-specific T cell clones derived from cultures containing IFN-gamma or IFN-alpha displayed strong cytolytic activity. These data indicate that the majority of human T cell clones that produce IFN-gamma, but not IL-4 (Th1-like), as well as of T cell clones that produce IFN-gamma in combination with IL-4 (Th0-like) are cytolytic. More importantly, they demonstrate that the addition of IFN (alpha and gamma) or IL-4 in bulk cultures before cloning may influence not only the cytokine profile of human CD4+ T cell clones but also their cytolytic potential.     

Measles virus-specific murine T cell clones: characterization of fine specificity and function

Measles virus (MV)-specific murine helper T cell clones (Thy-1.2+, CD4+, CD8-) were generated from mice immunized with MV-infected mouse brain homogenate by limiting dilution and in vitro stimulation of spleen cells with UV-inactivated MV Ag. The protein specificity of 7 out of 37 stable T cell clones, which displayed MHC-restricted MV Ag recognition, could be assessed by using purified MV proteins. Two fusion (F) protein-specific, two hemagglutinin-specific, and three nucleoprotein- or matrix protein-specific clones were shown to be established. The F protein-specific T cell clones together with a panel of previously generated F protein-specific T cell clones were characterized for their fine specificity by using beta-galactosidase fusion products, which contained different parts of the F protein. It was shown that at least two epitopes on the major part of the F protein (amino acid 2-513) can be recognized by mouse T cells. Functional characterization of three T cell clones showed that they were able to assist MV-specific B cells and bystander B cells for antibody production. Furthermore, they were shown to produce the lymphokines IL-2 and IFN-gamma. It was also shown that these T cell clones induced a MV-specific delayed type hypersensitivity response. These observations suggest that all of the T cell clones characterized belong to the TH1 helper subset.     

Somatic hybrids <Emphasis Type="Italic">Solanum nigrum</Emphasis> (+) <Emphasis Type="Italic">S. tuberosum</Emphasis>: morphological assessment and verification of hybridity

Somatic hybrids between the cultivated potato diploid hybrid clone, ZEL-1136, and hexaploid non-tuber-bearing wild species Solanum nigrum L. exhibiting resistance to Phytophthora infestans were regenerated after PEG-mediated fusion of mesophyll protoplasts. The objective was to transfer the late-blight resistance genes from the wild species into plants of the cultivated potato clone. From a total of 59 regenerants, 40 clones survived and have been maintained in vitro on hormone-free MS/2 medium. Thirty-two somatic hybrids were identified by their intermediate morphology (leaves of nigrum type and flowers of tuberosum type) and verified by flow cytometry and random amplified polymorphic DNA (RAPD) patterns. The RAPD analysis of nuclear DNA confirmed the hybrid nature of 29 clones. Flow cytometry revealed a wide range of ploidy in the generated hybrids, from nearly the tetra- to decaploid level. Most of the hybrid clones were stable in vitro, grew vigorously in soil, and set flowers and parthenocarpic berries. However, all of the flowering hybrids were male-sterile. Nine hybrid clones produced tuber-like structures in soil. The most vigorous flowering somatic hybrids were selected for assessment of the late-blight resistance.     

Response against single minor histocompatibility antigens. I. Functional and immunogenetic analysis of cloned cytolytic T cells

A clonal approach was used to investigate the cellular basis of a T cell response to single minor histocompatibility antigens (miHA). This analysis was performed by functional and immunogenetic characterization of a large number of clones derived from short-term mixed leukocyte culture (MLC) populations generated against the miHA, H-1.3. Forty-nine clones isolated from such MLC were specifically cytolytic for H-1.3-bearing, H-2Db-compatible target cells. Thirty-seven of the 49 cytolytic clones were driven to proliferate when stimulated by spleen cells bearing the H-1.3 alloantigen in the absence of added T cell-derived growth factor(s) (GF). The remaining 12 clones proliferated only when GF was added. A strong positive correlation was observed between antigen-induced proliferation and the production of interleukin 2 (IL 2) activity. A similar correlation was observed when comparing the ability of both antigen and concanavalin A to induce IL 2 activity from the clones. These data suggest that i) antigen-driven or helper T cell-independent cytolytic T cells (HITc) are frequent components of an MLC response to a single miHA, and ii) the ability of HITc to undergo antigen-driven proliferation is related to their ability to produce antigen-induced GF.     

Regulation of the rate of cell cycle progression in quiescent cytolytic T cells by T cell growth factor: analysis by flow microfluorometry

We have previously shown that greater than 90% of B6.1 cells, a murine cytolytic T lymphocyte (CTL) cloned line which is solely dependent on T cell growth factor (TCGF) for continuous growth in vitro, accumulates in the G1 phase of the cell cycle after transfer into culture medium containing no TCGF. Moreover, when such quiescent cells are exposed again to TCGF, greater than 85% reenter the S phase and subsequently divide in a relatively synchronous fashion. In this study, the regulation of the rate of cell cycle progression of quiescent B6.1 cells after exposure to TCGF was analyzed using two complementary DNA staining techniques, namely, the propodium iodide method (to enumerate cells entering the S phase) and the Hoechst 33342-bromodeoxyuridine substitution technique (to enumerate cells which have gone through mitosis). After TCGF addition, quiescent B6.1 cells resumed DNA synthesis and divided after a lag phase of 10 and 20 h, respectively. The duration of the lag phase was found to be dependent on the length of time during which quiescent B6.1 cells had been deprived of TCGF, but was independent of the concentration of TCGF used for restimulation. In contrast, the proportion of cells responding to TCGF as well as the rate of their first passage through mitosis was dependent on TCGF concentration. The presence of TCGF for at least 6 h was required for a maximal response. Moreover, direct evidence was obtained that TCGF by itself was able to stimulate proliferation of quiescent B6.1 cells in the absence of other growth factors and serum constituents other than bovine serum albumin, transferrin, and lipids.     

Class I MHC antigens in the generation and expression of promiscuous cytotoxic cell function

In recent years investigators from a number of laboratories have described antigen nonspecific, lymphocyte-mediated cytotoxicity generated by TCGF alone, in the absence of antigen or mitogen. The exact origin of the cells mediating this cytotoxicity, in either mouse or humans, is unknown. We found that when mouse spleen cells are incubated with higher than normal concentrations of TCGF, good levels of cytotoxicity toward allogeneic, NK, and untransformed self target cells are generated by day 5 or 6 in culture. We were unable to block the lysis of any of these target cells with antibodies to target cell class I antigens. However, generation of this cytotoxicity from naive spleen cells was very strongly blocked by anti-class I MHC antibodies. When T cells from spleen were extensively purified, they did not respond to TCGF at any concentration unless adherent cells were added back. Generation of cytotoxicity under these conditions was also blocked by class I antibodies. Generation of promiscuous killing activity by PMA and ionomycin, on the other hand, was class I independent. Our data suggest that pre-CTL, under the influence of TCGF, can be activated to CTL and that under the continued influence of TCGF can be driven into a so-called "promiscuous" state of cytotoxicity. Possible roles for class I antigens in this process are discussed.