Long-term maintenance in vitro of human T cells by repeated exposure to the same stimulator cells. Differences when using repeated stimulation in allogeneic mixed leukocyte culture and when using stimulation with autologous lymphoblastoid cells

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.

Fibroblasts mediate T cell survival: a proposed mechanism for retention of primed T cells

This report describes a salvage pathway whereby activated T lymphocytes revert to nonproliferating cells in the absence of antigen or mitogenic signals. After the removal of mitogenic cytokines, cultured T lymphocytes cease dividing and rapidly begin to undergo cell death. However, the addition of fibroblasts to interleukin 2 (IL-2)-propagated T cells results in prolonged survival of the previously activated T lymphocytes in the absence of proliferation. The prevention of cell death is also achieved by conditioned medium from the fibroblasts. T lymphocytes cultured with fibroblasts or the conditioned medium retain the ability to be restimulated if mitogenic stimuli are added to the culture. The activity is not accounted for by IL-1-7. The studies suggest a stromal cell-mediated, nonspecific mechanism for survival of primed T lymphocytes in a nonproliferating state.

The use of supernatants from neuraminidase and galactose oxidase (NAGO)-treated lymphocytes as a source of T cell growth factor

Human peripheral blood or tonsil lymphocytes produce T cell growth factor (TCGF), when activated with neuraminidase (NA) and galactose oxidase (GO). Partial purification of NAGO-TCGF on Sepharose G-100 columns gave a TCGF-active fraction within the same molecular weight range as the conventional lectin-induced TCGF (approximately 15,000 Da). Human T cells, activated in mixed lymphocyte culture (MLC) with irradiated allogeneic EB-virus transformed B-cells (LCL) could be maintained in continuous culture for several months with retained functional activities. The cells showed similar growth patterns when cultured in the presence of either NAGO-TCGF or PHA-TCGF. The growing cells were characterized by means of monoclonal antibodies. After 4 weeks of culture 98% of these were OKT3+ and 87% were also OKT8+. The cytolytic activities of the cultures were tested in cell-mediated lympholysis (CML) against allogeneic LCL as target cells, in natural cytotoxicity (NK) against K562 cells and in antibody dependent cytotoxicity (ADCC) against bovine erythrocytes. Cultures displaying one or several of these functions were obtained. The results indicate, that TCGF obtained from supernatants of NAGO-activated lymphocytes is as potent as the T cell growth promoting factor obtained by lectin stimulation. One major advantage of using NAGO-generated TCGF is that contamination with lectin is avoided.

Establishment of human cytotoxic T-cell lines specific for Epstein-Barr virus-transformed autologous cells

EBV-specific cytotoxic T cells (Tc) induced in vitro have continuously proliferated in vitro for over 9 months. The long-term maintenance of the Tc growth was dependent on periodic supplementation of both irrediated EBV-transformed autologous lymphoblastoid cell line (LCL) cels and conditioned medium. The latter was derived from supernatants of human spleen-cell cultures stimulated with phytohemagglutinin. The cultured Tc maintained significant cytotoxic activity to autologous LCL cells but not to EBV-unrelated target cells, including K-562, B-, T-, null-cell lines and mitogen-stimulated antologous peripheral blood lymphocytes. Thus, established EBV-specific Tc lines from five different individuals always exhibited highly significant cytotoxicity against exhibited highly significant cytotoxicity against autologous LCL cells but not always against allogeneic LCL cells. Furthermore, restriction of the Tc to the autologous LCL was more pronounced after long-term culture than it was initially. This suggests that certain clones of Tc which arignificant cytotoxicity against exhibited highly significant cytotoxicity against autologous LCL cells but not always against allogeneic LCL cells. Furthermore, restriction of the Tc to the autologous LCL was more pronounced after long-term culture than it was initially. This suggests that certain clones of Tc which arignificant cytotoxicity against exhibited highly significant cytotoxicity against autologous LCL cells but not always against allogeneic LCL cells. Furthermore, restriction of the Tc to the autologous LCL was more pronounced after long-term culture than it was initially. This suggests that certain clones of Tc which are probably restricted to HLA are selectively established during long-term cultivation.

Technical aspects of the primed lymphocyte typing (PLT) technique

The influence of different culture conditions in the primary and secondary cultures of the primed lymphocyte typing (PLT) technique was investigated with special reference to the discriminatory capacity of the PLT-cells generated. In the primary cultures, the maximal yield of PLT-cells was observed early (about day 7) and decreased thereafter, while the maximal specificity was obtained considerably later (about day 14). In the secondary cultures, the optimal culture time was in the interval 42 h - 72 h, and up to this culture length, gamma-irradiation (2,200-8,800 rad) of the secondary stimulators had no effect on the 14C-thymidine uptake of the cultures. In U-form microtiterplates, the number of PLT-cells per well should not be less than 2.5 X 10(4), and higher PLT-cell numbers (e.g. 5.0 X 10(4) per well) may confer further robustness upon the technique. The PLT-cell response and the discrimination was only slightly influenced by the number of secondary stimulator cells in the interval 5 X 10(4) to 2 X 10(5) cells per well. Freezing of the PLT-cells under controlled conditions resulted in a minor loss of viable eosin-excluding cells, while the specificity of the PLT-cells was unaffected. Even when the culture conditions are standardized, it is necessary to perform a normalization of the data in order to obtain reproducible results. The normalization procedure should include a compensation for the variation in (i) the general responding capacity of each PLT-cell and in (ii) the general stimulatory capacity of each secondary stimulator.

Continuous in vitro culture of human T lymphocytes

A method for continuous culture of human T lymphocytes by stimulation with irradiated lymphocytes, lymphoblastoid cells, and phytohaemagglutinin is described. Cultures can be maintained for at least 9 months. Growth appears to be dependent on a soluble factor released by lymphocytes when they are stimulated with lymphoblastoid cells and phytohaemagglutinin.

Proliferative and cytolytic reactivities of human lymphocytes fractionated on wheat germ agglutinin-Sepharose columns before or after alloactivation in mixed lymphocyte culture

Human T-lymphocyte preparations from peripheral blood with either high- or low-avidity receptors for wheat germ agglutinin (WGA) were obtained by fractioned on WGA--Sepharose columns. Both fractions contained progenitors of alloreactive T cells, proliferating in mixed lymphocyte culture (MLC) and acting as effector cells in cell-mediated lympholysis (CML). Proliferation and CML activity of the two fractions were equal and similar to those of the unfractionated cells. However, when the lymphocytes were fractionated after 5 days' MLC, most of the proliferating and cytolytic cells were found in the lymphocyte fraction enriched in cells with high-avidity receptors for WGA. The reactivity of the fractions was correlated to their content of blast-transformed cells. The binding of MLC-activated lymphocytes to WGA was specific, since it was inhibited by the competitive hapten D-GlcNAc and no cells were retained on control columns charged with human serum albumin-Sepharose. B cells and monocytic cells were enriched in the fraction with low-avidity receptors for WGA. As indicated by experiments in which cells were mixed in different proportions, the low MLC-CML activity of the lymphocytes in the fraction with low-avidity WGA receptors was not caused by suppressor cells present in that fraction.

Lymphoblastoid cell lines are polyclonal activators of human T lymphocytes

Following stimulation with autologous or allogeneic lymphoblastoid cell lines (LCL) human T lymphocytes acquire two properties which suggest that LCL act as polyclonal activators. Cytotoxic activity, which has an antigen-specific component, is produced towards normal lymphocytes and LCL, and the cells become capable of mounting proliferative responses to antigens on human B lymphocytes which have accelerated secondary-type kinetics. Only weak responses to autologous cells occur. In addition, repeated restimulation with the original LCL leads to a progressive increase in the number of cells in the culture for a period of about 4 weeks. This approach may prove a useful way to grow large numbers of human T lymphocytes for further study.

Lymphoblastoid cell lines of homozygous typing cells used for sensitization in PLT

Lymphoblastoid cell lines of homozygous typing cells were used as the sensitizing cells in MLC to prepare PLT cells. Results obtained using such cells against a panel of restimulating cells were compared to those obtained using regular PLT cells in which priming had been accomplished with normal peripheral blood lymphocytes. It appears that lymphoblastoid cell lines can be used for this purpose; the advantages of such an approach are given.

In vitro induction of cell-mediated immunity to murine leukemia cells. I. Optimization of tissue culture conditions for the generation of cytotoxic lymphocytes

Cytotoxic lymphocytes (CTL) to allogeneic and syngeneic murine leukemia cells were generated in vitro in "one way" mixed lymphocyte-tumor cell cultures carried out under a variety of conditions. In an attempt to define the optimal culture conditions for sensitization, the following parameters were analyzed: culture vessel, culture volume, responder: stimulator (R:S) cell ratio, lymphoid cell density, source of lymphoid cells, duration of culture, fetal calf serum (FCS) concentration, 2-mercaptoethanol (2-ME) concentration, concentration of amino acids, and buffering system. Of the many variables examined, of particular importance were the R:S cell ratio, the cell density, the FCS concentration, the presence of 2-ME, and the time of harvesting. These factors exerted various effects, both quantitatively and qualitatively, on the magnitude and kinetics of the responses induced in microcultures (5 X 10(6) lymphocytes) and macrocultures (25 X 10(6) lymphocytes). Moreover, optimal sensitization in syngeneic cultures required different conditions than those for allogeneic cultures. Cytotoxic activity was assessed in vitro by a quantitative 51Cr-release assay. The sensitized lymphocytes demonstrated the characteristics ofT lymphocytes and reacted specifically with the sensitizing leukemia cells.

Selective in vitro growth of T lymphocytes from normal human bone marrows

Selective growth of T lymphocytes occurred when unfractionated normal human bone marrow cells were cultured with conditioned medium obtained from phytohemagglutinin-stimulated normal human lymphocytes (Ly-CM). Cultures of up to 90 percent T cells have been maintained for more than 9 months. The T cells exhibited a strict growth dependence upon Ly-CM and were consistently negative for Epstein-Barr viral information.

Stimulation of normal lymphocytes with autologous lymphoid cell lines: properties of derived killer cells

Lymphocytes from normal adults, with or without serological signs of previous Epstein-Barr virus (EBV) infection, could be stimulated to proliferate and produce killer cells by incubation with autologous EBV-genome-positive lymphoid cell lines (LCLs). The stimulated cells were most probably of T-cell origin, although at the peak of stimulation many of them lacked the sheep erythrocyte marker. Direct effector-target cell contact was necessary for lysis to occur. The cytotoxicity of autologously stimulated (AS) lymphocytes was not restricted to EBV-genome-positive LCLs, nor to cell lines of hematopoietic origin. It was equally broad if cells carrying complement receptor had been removed before stimulation. Fresh lymphocytes, blasts induced by phytohemagglutinin or concanavalin A, and Burkitt's lymphoma biopsy cells were resistant or considerably less sensitive. Mouse cells--even cell lines--were resistant. The sensitivity of target cells to lysis correlated positively with their capacity to block AS lymphocyte lysis of autologous LCLs in competition experiments. The cytotoxicity of AS lymphocytes was blocked by EBV-genome-positive and -negative cell lines, whereas the EBV-related cytotoxicity of T cells from acute cases of infectious mononucleosis was blocked by EBV-genome-positive LCL only.