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.

Monoclonal antibody against a "Pan-T-cell" antigen expressed by thymocytes, peripheral T-lymphocytes and T-cell leukemias

A monoclonal antibody, LAU-A1, which selectively reacts with all cells of the T-lineage, was derived from a fusion between spleen cells of a mouse immunized with paediatric thymocytes and mouse myeloma P X 63/Ag8 cells. As shown by an antibody-binding radioimmunoassay and analysis by flow microfluorometry of cells labelled by indirect immunofluorescence, the LAU-A1 antibody reacted with all six T-cell lines but not with any of the B-cell lines or myeloid cell lines tested from a panel of 17 human hematopoietic cell lines. The LAU-A1 antibody was also shown to react with the majority of thymocytes and E-rosette-enriched peripheral blood lymphocytes. Among the malignant cell populations tested, the blasts from all 20 patients with acute T-cell lymphoblastic leukemia (T-ALL) were found to react with the LAU-A1 antibody, whereas blasts from 85 patients with common ALL and 63 patients with acute myeloid leukemias were entirely negative. Examination of frozen tissue sections from fetal and adult thymuses stained by an indirect immunoperoxidase method revealed that cells expressing the LAU-A1 antigen were localized in both the cortex and the medulla. From the very broad reactivity spectrum of LAU-A1 antibody, we conclude that this antibody is directed against a T-cell antigen expressed throughout the T-cell differentiation lineage. SDS-PAGE analysis of immunoprecipitates formed by LAU-A1 antibody with detergent lysates of radiolabeled T-cells showed that the LAU-A1 antigen had an apparent mol. wt of 76,000 under non-reducing conditions. Under reducing conditions a single band with an apparent mol. wt of 40,000 was observed. Two-dimensional SDS-PAGE analysis confirmed that the 76,000 mol. wt component consisted of an S-S-linked dimeric complex. The surface membrane expression of LAU-A1 antigen on HSB-2 T-cells was modulated when these cells were cultured in the presence of LAU-A1 antibody. Re-expression of LAU-A1 antigen occurred within 24 hr after transfer of the modulated cells into antibody-free medium.

Target cell susceptibility to immune lysis and expression of MHC antigens are independent of position in the cell cycle

We have investigated the effects of progression through the mitotic cell cycle upon the tumor (P815) cell line's expression of H-2 antigens and susceptibility to immune cytolysis. By using a combination of DNA quantitation by Hoechst 33342 staining and fluorescence-activated cell sorter analysis we were able to obtain pure populations of G1, S, and G2+M cells for study. Furthermore, by employing a fluorescence quenching technique utilizing bromodeoxyuridine substitution we were able to monitor the times required for the P815 cells to transit each of the various phases. By using mAb and cloned CTL populations with well-defined specificities we observed that neither H-2 antigen expression nor lytic susceptibility to mAb plus complement or CTL fluctuated with cell cycle progression. Each of the three major MHC loci (H-2Kd, -Dd, and -Ld) was analyzed. These results demonstrated that expression of H-2 antigens and susceptibility to immune lysis were independent of a cell's position in the cell cycle.

Target cell susceptibility to immune lysis and expression of MHC antigens are independent of position in the cell cycle

We have investigated the effects of progression through the mitotic cell cycle upon the tumor (P815) cell line's expression of H-2 antigens and susceptibility to immune cytolysis. By using a combination of DNA quantitation by Hoechst 33342 staining and fluorescence-activated cell sorter analysis we were able to obtain pure populations of G1, S, and G2+M cells for study. Furthermore, by employing a fluorescence quenching technique utilizing bromodeoxyuridine substitution we were able to monitor the times required for the P815 cells to transit each of the various phases. By using mAb and cloned CTL populations with well-defined specificities we observed that neither H-2 antigen expression nor lytic susceptibility to mAb plus complement or CTL fluctuated with cell cycle progression. Each of the three major MHC loci (H-2Kd, -Dd, and -Ld) was analyzed. These results demonstrated that expression of H-2 antigens and susceptibility to immune lysis were independent of a cell's position in the cell cycle.

Differentiation in vitro of Lyt 2+ thymocytes from embryonic Lyt 2- precursors

In mice, the thymus is regarded as being the primary anatomical site for the generation of immunologically competent T lymphocytes. Such cells comprise approximately 20% of the cells in the thymus and share with T lymphocytes from peripheral lymphoid tissues certain phenotypic properties defined by anti-Lyt antibodies. Thus, most immunocompetent T cells are either Lyt 1+2+ or Lyt 1+2- with the former cells being restricted to recognizing antigen in association with class I (H-2K, D) major histocompatability complex (MHC) products and the latter to class II (H-21) MHC products. Although evidence suggests that Lyt 1+2+ cells are generated from Lyt 1+2- precursor the independent development of two separate Lyt-defined lineages of thymocytes could not be ruled out. Here, the acquisition of Lyt 2 antigen by Lyt 2- cells from late embryonic and early postnatal thymuses is directly demonstrated. Furthermore, by combining cell cycle and Lyt phenotype analysis on a flow microfluorometer, the role of cell division in this differentiation process has been investigated.

Characterization of a monoclonal antibody (A12) that defines a human acute lymphoblastic leukemia-associated differentiation antigen

A human leukemia-associated differentiation antigen has been identified by a monoclonal antibody (A12) raised to the lymphoblastoid cell line NALM-1. The A12 antigen was expressed on the surface of leukemic cells from patients with common acute lymphoblastic leukemia (c-ALL) as well as on cells of the hematopoietic cell lines NALM-1, Reh-6, Raji, Daudi, CEM, and 8402 as determined by an antibody-binding radioimmunoassay, as well as by indirect immunofluorescence and FACS analysis. This antigen was not detected on normal blood lymphocytes, normal bone-marrow cells or leukemic cells from patients with acute myeloid leukemia (AML). The A12 antigen had an apparent molecular weight of 100 kD as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and appeared to be related to if not identical with the acute lymphoblastic leukemia antigen CALLA described by others. Cross-blocking experiments indicated that preincubation of NALM-1 cells with antibody A12 or J5 (anti-CALLA) could block subsequent binding of 125I-labeled A12 and J5 antibody. These results suggest that the two monoclonal antibodies recognize identical or closely located antigenic sites. The surface membrane expression of A12 antigen in NALM-1 cells was modulated when the cells were cultured in the presence of A12 antibody. Under these conditions, the expression of Ia antigens was unaffected. Re-expression of A12 antigen occurred within 24 h after transfer of the modulated cells into medium devoid of monoclonal antibody.

Correlated expression of T cell growth factor dependence, sensitivity to Vicia villosa lectin, and cytolytic activity in hybrids between cytolytic T cells and T lymphomas

Somatic cell fusion between cytolytically active, T cell growth factor- (TCGF) dependent murine T cell lines (CTL lines) and noncytolytic, TCGF-independent murine T lymphoma lines has yielded two types of somatic cell hybrids (5): cytolytic hybrids, growth of which is dependent on TCGF, and hybrids with very weak or undetectable cytolytic activity which grow at the same rate with or without TCGF. Here we report that the former can produce stable variants that resemble the latter type. Some of these TCGF-independent variants still have TCGF receptors. High susceptibility to the cytotoxic effects of Vicia villosa lectin, a marker distinguishing the parental CTL lines from T lymphomas, is expressed by the TCGF-dependent hybrids but not by the TCGF-independent variants. The two types of hybrids also differ in the expression of surface glycoproteins. We propose that there exists a genetic element in the CTL line that represses the TCGF-independent replication mechanism of the T lymphoma parent in the TCGF-dependent hybrids and that this genetic element is lost or switched off in the TCGF-independent variants.

Cell cycle regulation of cloned cytolytic T cells by T cell growth factor: analysis by flow microfluorometry

In an attempt to better define the mode of action of TCGF we have investigated the effect of complete removal of TCGF on the cell cycle kinetics of a TCGF-dependent murine CTL cloned line (B6.1). Cells that had been cultured in the presence or absence of TCGF were stained with propidium iodide, a DNA binding dye, and the distribution of DNA content was analyzed by flow cytometry. Results indicated that the proportion of cells entering the S phase of the cell cycle started to decrease 6 hr after removal of TCGF from the culture medium. This fraction continued to decrease as a function of time, and after 30 hr without TCGF 93% of the cells were in the G1 phase of the cell cycle in comparison to 38% in control cultures containing TCGF. Direct evidence that B6.1 cells completed one cell cycle after removal of TCGF before they accumulated in the G1 phase was obtained with a technique combining the use of BUdR, a thymidine analog, and the DNA binding dye Hoechst 33342. When TCGF was added again to cultures of B6.1 cells that were arrested in the G1 phase, the majority of cells entered the S phase in a synchronous fashion after a lag phase of 10 to 12 hr. The duration of this lag phase was independent of the concentration of TCGF used to restimulate quiescent B6.1 cells. However, the number of cells entering S phase 10 hr after re-addition of TCGF was concentration dependent. Additional experiments indicated that the cytolytic activity was not dependent on TCGF, since no decrease in the activity of B6.1 cells was noted after these cells had been deprived of TCGF for up to 30 hr.

Cell cycle regulation of cloned cytolytic T cells by T cell growth factor: analysis by flow microfluorometry

In an attempt to better define the mode of action of TCGF we have investigated the effect of complete removal of TCGF on the cell cycle kinetics of a TCGF-dependent murine CTL cloned line (B6.1). Cells that had been cultured in the presence or absence of TCGF were stained with propidium iodide, a DNA binding dye, and the distribution of DNA content was analyzed by flow cytometry. Results indicated that the proportion of cells entering the S phase of the cell cycle started to decrease 6 hr after removal of TCGF from the culture medium. This fraction continued to decrease as a function of time, and after 30 hr without TCGF 93% of the cells were in the G1 phase of the cell cycle in comparison to 38% in control cultures containing TCGF. Direct evidence that B6.1 cells completed one cell cycle after removal of TCGF before they accumulated in the G1 phase was obtained with a technique combining the use of BUdR, a thymidine analog, and the DNA binding dye Hoechst 33342. When TCGF was added again to cultures of B6.1 cells that were arrested in the G1 phase, the majority of cells entered the S phase in a synchronous fashion after a lag phase of 10 to 12 hr. The duration of this lag phase was independent of the concentration of TCGF used to restimulate quiescent B6.1 cells. However, the number of cells entering S phase 10 hr after re-addition of TCGF was concentration dependent. Additional experiments indicated that the cytolytic activity was not dependent on TCGF, since no decrease in the activity of B6.1 cells was noted after these cells had been deprived of TCGF for up to 30 hr.

Demonstration at the single-cell level of the existence of distinct clusters of epitopes in two predefined human Ia molecular subsets

The expression at the cell surface level of two previously defined human Ia antigen subsets, NG1 and NG2, was studied. Two monoclonal hybridoma antibodies, D1-12 (anti-NG1) and D4-22 (anti-NG2), labeled with distinct fluorochromes, were used as probes. The results indicate that NG1 and NG2 molecules are simultaneously expressed on the same cell, and moreover, that they are identifiable as spatially separate structures. In addition, when a series of 6 other anti-Ia monoclonal antibodies previously described were analyzed in a checkerboard test of binding inhibition at the cell surface level, they were found to closely mimic the reactivity pattern of either D1-12 or D4-22 antibody, suggesting that NG1 and NG2 Ia subsets express independent clusters of highly immunogenic epitopes.

Cytolytic T lymphocyte function is independent of growth phase and position in the mitotic cycle

We have investigated mitotic cell cycle and growth phase regulation of homogeneous cytolytic T lymphocytes (CTL). Two independently derived CTL clones were stained with the DNA-binding dye Hoechst 33342, sorted in a fluorescence-activated cell sorter according to their position in the cell cycle, and then assayed for specific lytic activity using a short-term (30 min) (51)Cr release assay. Results show that lytic activity remained unchanged throughout the cell cycle. Furthermore, there was no significant difference in the lytic activity of CTL clones growing exponentially or arrested in a plateau phase. These results demonstrate that T cell-mediated cytolysis is independent of growth phase and position in the cell cycle.

Phenotypic characterization of human cytolytic T lymphocytes in mixed lymphocyte culture

Mixed lymphocyte reaction (MLR)-activated T cells were analyzed according to the expression of various cell surface markers by the specific cytotoxic T lymphocytes (CTL) generated in the MLR. CTL were found exclusively in a population of MLR-activated T cells that lacked detectable Fc gamma R but that expressed a surface antigen recognized by the 4F2 monoclonal antibody. In contrast, CTL were found in both the Ia-positive and Ia-negative cells after MLR activation. Thus, the specific CTL generated in the allogeneic MLR can be identified and isolated by virtue of the expression of a particular cell surface marker.