Induction of human antibody responses in vitro with emphasis on allogeneic helper factors

Cellular origin(s) of chronic lymphocytic leukemia: cautionary notes and additional considerations and possibilities

Several cell types have been suggested as giving rise to chronic lymphocytic leukemia (CLL), and these suggestions have reflected the sophistication of technology available at the time. Although there is no consensus as to the normal cellular counterpart(s) in the disease, an antigen-experienced B lymphocyte appears required based on surface membrane phenotypes and gene expression profiles. However, what is still unclear is whether a single or multiple normal precursors were stimulated to evolve into CLL and at what stage(s) this occurred. A unifying, parsimonious theory is that CLL clones with either mutated or unmutated IGHVs derive from marginal zone B cells. However, evidence for remarkably similar B-cell receptor amino acid sequence and striking differences in polyantigen and autoantigen-binding activity, found in some but not all CLL clones, challenge a single-cell derivation for CLL. In this Perspective, we summarize data regarding normal counterparts of CLL cells and suggest that a multistep process of leukemogenesis is important to consider when assigning a cellular origin for this disease. Finally, although available data do not definitively identify the cell(s) of origin, we offer possibilities for single- and multiple-cell origin models as straw men that can be improved on and hopefully lead to final answers to this puzzle.

Recent advances in the molecular biology and immunobiology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) has long been viewed as a relatively homogeneous disease caused by the accumulation of monoclonal immature, immunoincompetent B cells with faulty apoptotic capacities. However, recent evidence, reviewed here, demonstrates that at least two different B-CLL subgroups exist with different clinical courses and outcomes. The malignant cells from both B-CLL subgroups are antigen-experienced cells that have a normal apoptotic apparatus and turnover continually. The leukemic cells of the two B-CLL subgroups have engaged antigen before transformation, although primarily the cells of patients in the poor outcome subgroup can respond to antigens following transformation. The difference in the ability to respond to antigen as a full-fledged B-CLL probably accounts for the different biological features and clinical outcomes of the patients in these subgroups.

B cell chronic lymphocytic leukemia: lessons learned from studies of the B cell antigen receptor

B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5(+) B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

A simple method for the purification of human peripheral blood antigen presenting cells (dendritic cells, monocytes/macrophages, and B lymphocytes)

An adherence method was developed that enriches for antigen presenting cells (dendritic cells, monocytes/macrophages, and B lymphocytes) from peripheral blood mononuclear cell (PBMC) preparations. This method utilizes the cells' natural adherence to polystyrene tissue culture dishes and their subsequent removal with K3EDTA after incubation at 4 degrees, with gentle pipeting. Flow cytometric analysis revealed that on average, the enrichment of CD83+ dendritic cells, CD14+ monocytes/ macrophages, and CD19+ B cells increased by 12.5 to 20, 2, and 4 fold, respectively, compared to their initial numbers present in PBMC preparations. Cell viability, determined by trypan blue exclusion, was between 90 and 98%. After the enrichment procedure, the cells could still be activated by tetanus toxoid and this was shown by flow cytometric analysis, as enhancement of class II major histocompatibility complex (MHC) (31% increase) (after antigen treatment). This is a fast and economical alternative to other established methods for the preparation of pure, functionally competent antigen presenting cells derived from peripheral blood.

Direct helper T cell-induced B cell differentiation involves interaction between T cell antigen CD28 and B cell activation antigen B7

Cognate interactions between major histocompatibility complex class II antigen (Ag)-reactive CD4+ T helper (Th) and Ag-presenting B cells induce first the activation of B cells and their subsequent differentiation into Ig-secreting cells (IgSC). The Th cell-associated homodimeric glycoprotein CD28 has been implicated as an important regulator of Th activation. Recently, B cell-associated early activation Ag B7 has been identified as a ligand for the CD28 molecule. In this study, we have examined using monoclonal antibodies (mAb) the roles of CD28 and B7 molecules during the Th-B cell cognate interactions leading to the differentiation of B7+ B cells. Anti-CD28 mAb 9.3 specifically inhibited proliferative responses of CD4+ T cells to both allogeneic B cells and soluble Ag-presenting autologous non-T cells. In addition, anti-CD28 mAb 9.3 inhibited Th-induced differentiation of alloantigen-presenting B cells into ISC. Similar inhibition of both Ag-induced Th activation and B cell differentiation into ISC was observed using mAb BB1 which recognizes a B cell-associated molecule B7. In contrast, non-cognate Th-independent exogenous interleukin 6-induced differentiation of B7+ B cells into ISC was not inhibited by mAb to either molecule. These results clearly demonstrate the involvement of CD28 on Th and its ligand B7 on B cells during cognate Th-B interactions leading to the differentiation of B cells. Furthermore, these results also suggest the development of new mAb-based therapeutic approaches for exaggerated B cell activation associated with certain autoimmune diseases such as systemic lupus erythematosus.

Production of autoantibodies by CD5-expressing B lymphocytes from patients with chronic lymphocytic leukemia

CD5-expressing B lymphocytes from patients with selected chronic lymphoproliferative disorders were used to determine whether monoclonal populations of CD5+ human B cells produce autoantibodies. CD5+ B cells from 19 patients with chronic lymphocytic leukemia (CLL) and one with diffuse well-differentiated lymphocytic lymphoma (DWDL) were cultured, with and without mitogenic stimulation, to obtain Ig from these cells. 17 of the 20 samples produced Ig in vitro. mAb from nine of the 17 patients were reactive with either IgG, ssDNA, or dsDNA. In every instance, the autoantibodies displayed monotypic L chain usage that correlated precisely with the L chain expressed on the CD5+ leukemic B cell surface. These monoclonal autoantibodies varied in their degree of antigenic specificity; some were quite specific, reacting with only one antigen, whereas others were polyspecific, reacting with two or all three autoantigens tested. Three features distinguish these autoantibodies from those observed in prior studies of CD5+ B cells. First, they are clearly the products of monoclonal populations of CD5+ cells; second, several react with dsDNA, a specificity not previously reported and often seen in association with significant autoimmune disorders; and third, two of the monoclonal autoantibodies secreted by the CD5+ clones were of the IgG class. Although not all of the Ig-producing, CD5-expressing clones elaborated mAbs reactive with the autoantigens tested, greater than 50% did. It is possible that with a broader autoantigenic panel or with larger quantities of CLL/DWDL-derived Ig, even more autoantibody-producing clones might be identified. These studies may have important implications for the antigenic specificity of subsets of human B lymphocytes as well as for lymphoproliferative and autoimmune disorders in general.

Functional property of Ia-positive T cells in peripheral blood from patients with systemic lupus erythematosus

Ia-positive (Ia+) T cells in peripheral blood and their functional property were examined in patients with systemic lupus erythematosus (SLE). Binding of specific monoclonal antibodies was assessed by indirect immunofluorescence. Functional study of Ia+ T cells was carried out in coculture experiments by measuring the IgG secreted into the culture supernatant. We found that the percentage of Ia+ T cells in peripheral blood from patients with SLE was raised and the rise correlated positively with serum gamma globulin and IgG level. The elevation was further increased after stimulation with DNA in vitro, indicating the presence of DNA-sensitive T cells. Functionally, Ia+ T cells acted as helper cells in spontaneous IgG synthesis of SLE B cells, and were enriched in the OKT4 subset. These results indicate that SLE T cells are activated in vivo and that the Ia+ T cells may play a crucial role in the immunoregulatory function. Accordingly, demonstration of Ia antigens on T cells by monoclonal antibody may provide a useful tool for the measurement of immunological activity in patients with SLE.

Regulation of B cell activation and differentiation with factors generated by human T cell hybridomas

Human T cell hybridomas were generated by several techniques and the supernatants generated were screened for activity on human B cells. Three general activities were noted; B cell proliferation factor ( BCPF ), B cell differentiation factor (BCDF), and an IgA isotype-specific helper factor. BCPF acts on B cells to induce proliferation without differentiation and is distinct from conventional BCGF. This was documented by BCPF 's inability to synergize with anti-mu Ab in a standard BCGF assay ( Muraguchi & Fauci 1982, Howard et al. 1982, Sieckman et al. 1981), as well as its differential effect on a leukemic B cell preparation, when compared with BCGF. A possible schema for BCPF activity is depicted in Figures 3 and 4. In Figure 3, BCPF acts like Ag in vivo or like anti-mu in vitro, pre-activating B cells and rendering them responsive to BCGF. Figure 4 represents what our data depict, that is that BCPF bypasses the response to BCGF and induces cells to proliferate without pre-activation. The difference in the 2 mechanisms may be concentration-dependent and this possibility is currently being evaluated. It is interesting to speculate that T cells in vivo are capable of initiating B cell activation and may account for polyclonal responses seen with some Ag-specific reactions. BCDF(s) act on post-activated B cells (Figure 3) to induce differentiation to Ig-secreting cells. They appear to be heterogeneous and, therefore are capable of inducing varied responses depending on the B cell subpopulation affected. Figure 3 is deliberately complex demonstrating some of the possible as well as documented BCDF activities including polyclonal differentiation and isotype specific activity in IgA committed B cells. We cannot be certain of the frequency of these BCDF-secreting T cells, but the studies of cells from patients with common variable immunodeficiency and chronic lymphocytic leukemia have helped to dissect out these activities. These data would suggest that these BCDF subgroups are important, as deficiencies in one or more subgroups may result in disease.

One out of five peripheral blood B lymphocytes is activated to high-rate Ig production by human alloreactive T cell clones

Human alloreactive helper T cell clones were isolated from a secondary mixed lymphocyte reaction by limiting dilution in the presence of irradiated stimulator cells and T cell growth factor (interleukin 2). When cultured with B cells and macrophages possessing the relevant alloantigens, the T cell clones proliferated and induced a strong B cell activation with production of high immunoglobulin levels. Limiting dilution of the B cells from the peripheral blood showed that about one in 5-10 can be activated to produce IgG, one in 10 IgM, one in 20-40 IgA and one in 2000-5000 IgE. Following stimulation by the relevant alloantigen, the clones were able to help also B cells that lacked the alloantigen, indicating that a direct T-B cell interaction is not required. This method is particularly interesting because it is suitable for the clonal analysis of a B cell subset that is triggered in the absence of antigen by an unrestricted T cell help.

Immunoregulatory T cell circuits in man. Alloantigen-primed inducer T cells activate alloantigen-specific suppressor T cells in the absence of the initial antigenic stimulus

Although alloantigen-specific suppressor T cells are generated in MLR, the cellular signals that lead to activation of suppressor T cells as opposed to cytotoxic T cells are unknown. The current study was undertaken to characterize interactions among T cell subsets involved in the generation of suppressor T cells in MLR. Human peripheral blood Leu-2+ (suppressor/cytotoxic) and Leu-3+ (helper/inducer) T cell subsets were activated with allogeneic non-T cells and then examined for their inductive effects on fresh autologous T cells. Fresh Leu-2+ cells proliferated in response to alloantigen-primed Leu-3+ cells and subsequently suppressed the response of fresh autologous Leu-3+ cells to the original, but not third party, allogeneic stimulator non-T cells. Moreover, only Leu-2+ cells that lacked the 9.3 marker, an antigen present on the majority of T cells including precursors of cytotoxic T cells, differentiated into suppressor cells. The alloantigen-specific suppressive effect of Leu-2+,9.3-cells was not mediated by cytolysis of allogeneic stimulator cells, nor could it be explained by alteration of MLR kinetics. Suppression was observed only when activated Leu-2+ cells were added to fresh MLRs within 24 h of initiation of cultures, suggesting that these cells block an early phase of the activation of Leu-3+ cells in MLR. These results indicate that alloantigen-primed inducer T cells can activate alloantigen-specific suppressor T cells in the absence of allogeneic stimulator cells.

T-lymphocyte subpopulations in chronic lymphocytic leukemia: a quantitative and functional study

In the peripheral blood of patients with chronic B-cell lymphocytic leukemia (B-CLL) absolute numbers of E-rosetting lymphocytes were increased. The proportions of TG and TM cell subsets were analyzed, as were their effects on the pokeweed mitogen (PWM)-dependent differentiation of normal allogenic B cells or of autologous leukemic cells. The TG lymphocyte subset was further studied for its cytotoxic activity in antibody-dependent cellular cytotoxicity (ADCC). A marked increase both in percentages and in absolute numbers of TG cells was found. TM lymphocytes percentages were normal, but because of the T lymphocytosis occurring in all patients, the absolute numbers of TM were increased. TM and TG subsets showed helper and suppressor activity, respectively, in PWM-induced B-cell differentiation. TG cells displayed effector cell activity in ADCC. The results provide further evidence that T lymphocytes from patients with B-CLL are functionally normal. However, a noticeable increase of the T-cell subset having suppressor and cytotoxic activity in ADCC was observed. This may be the consequence of a normal immune reaction to the leukemic population.

Generation of immunoglobulin secreting cells in mixed lymphocyte culture

The nature of the cellular interactions and role of the HLA system in the generation of immunoglobulin secreting cells in primary and secondary mixed lymphocyte cultures were investigated. The B lymphocyte response to alloantigen stimulation as measured by a Protein A reverse hemolytic plaque assay, consisted of polyclonal activation with production of IgG, IgM, IgA secreting cells detectable as early as day 4 in a primary and by 24 hr in a secondary mixed lymphocyte culture. B cell activation was shown to be dependent upon collaboration with T helper cells. A disparity at the HLA D/DR region between responding and stimulating cell populations was required for the induction of T helper cells. However, once activated, T helper cells could collaborate with autologous or allogeneic B lymphocytes and, without additional antigen, trigger immunoglobulin production. The mixed lymphocyte culture may now be considered a model of B cell as well as T cell activation.

Stimulation of primary in vitro IgE antibody responses in culture of human peripheral mononuclear cells

Experiments are presented herein that demonstrate the capacity to stimulate human peripheral mononuclear cells to synthesize and secrete significant quantities of IgE molecules in vitro by exposure to appropriate concentrations of 2,4-dinitrophenyl (DNP)-protein conjugates, pokeweed mitogen (PWM), or a combination of DNP-proteins and PWM. Cultures stimulated in this fashion synthesize increased quantities of both total IgE and DNP-specific IgE antibody molecules. This in vitro human IgE antibody system should provide a useful tool for further exploration of regulatory control of IgE responses in both normal humans and those manifesting various forms of IgE-mediated allergic disorders.

Plasmacytic differentiation of circulating Epstein-Barr virus-infected B lymphocytes during acute infectious mononucleosis

During the acute phase (1 wk of symptoms or less) of infectious mononucleosis (IM), 70--80% of circulating Epstein-Barr virus nuclear antigen (EBNA)-positive cells have differentiated toward plasma cells. Thus the characteristics of the infected cells in the majority of IM patients during early disease are indistinguishable from EBNA-positive tumor cells of a previously reported child who developed lymphoma during IM. IgA and IgG were the most frequent and IgM the least frequent immunoglobulin isotypes detected in EBNA-positive cells. In acute disease EBNA was present in 5.5--20% of T cell-depleted blood lymphocytes but in the 2nd or 3rd wk of illness the number of EBNA-positive cells sharply decreased to 0.4--1.4%. At the same time the fraction of antigen-positive cells containing cytoplasmic immunoglobulins also diminished, suggesting either that differentiation of infected cells was altered during the disease or that nondifferentiated antigen-positive cells had a survival advantage. Both the high proportion of plasmacytic EBNA-positive cells seen during acute disease and the apparent loss of differentiation by these cells later in disease may be regulated by host immunologic factors. Immunoglobulin-producing EBNA-positive cells may be the source of heterophile antibodies and other seemingly inappropriate antibodies usually found in serum during IM; however, increased numbers of noninfected plasma cells were present in some patients and may also be a potential source of these unusual antibodies.

Characterization of renal tissue lymphocytes in patients with interstitial nephritis

Five patients with interstitial nephritis who presented with a variety of clinical profiles were studied with particular emphasis on documentation of the cellular types of potentially immunocompetent lymphocytes and mononuclear cells present within interstitial renal infiltrates. Immunohistologic studies coupled with conventional light and electron microscopic observations indicated that most mononuclear cells making up renal interstitial infiltrates were T cells. Some chronic inflammatory cell foci within renal interstitium were characterized by clusters of Ia antigen-positive T cells considered to be markers for activated lymphocytes. B cells were present in very small proportions (5 percent or less). The profile of immunocompetent cells present in lesions of interstitial nephritis suggests a major role for cell-mediated immunity in this disorder. Increase in tissue lymphocytes of the T gamma subclass with receptors for the Fc portion of immunoglobulin G (IgG) also suggests local activation of intrinsic suppressor cell mechanisms.

Depressed primary in vitro antibody response in untreated systemic lupus erythematosus. T helper cell defect and lack of defective suppressor cell function

The in vitro antibody response of peripheral blood lymphocytes (PBL) from 19 patients with untreated systemic lupus erythematosus (SLE) was compared with that of 20 control patients and 44 normal subjects. Trinitrophenyl polyacrylamide beads (TNP-PAA) were used to induce IgM anti-TNP plaque-forming cells. SLE patients displayed a markedly depressed, and in most instances virtually absent, response. This was not due to an unusual kinetics of the response; nor could it be induced by preincubation of SLE patients' PBL. In co-cultures of SLE patients and normal PBL, the former, with few exceptions, did not exert a suppressive effect. In four patients the anti-TNP response of either unfractionated or T-depleted SLE PBL could be restored by T cells from a normal individual. Conversely in three of these patients, SLE T cells could not support the response of normal B cells, suggesting a T helper cell defect in SLE PBL. Concanavalin A (Con A)-induced suppressor cells of the antibody response could be assayed by two approaches: (a) in responder SLE patients, by the direct addition of Con A to TNP-PAA-stimulated cultures; (b) in seven patients by transfer of Con A-activated cells to the responding culture of a normal allogeneic donor. In both cases SLE PBL were able to exert a suppressive effect to the same extent as normal PBL.