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Graft-versus-host disease (OVHD) after allogeneic bone marrow transplantation (BMT) is initialed by immunocompetent T cells present in the graft. Selective elimination of distinct T-cell subsets or a sufficient, but not complete T-cell depletion, might abolish severe GVHD without graft rejection and loss of the anti-tumour potential. In this study we analysed the efficacy of different monoclonal antibodies (MoAb) WT32 (CD3). OKT4 (CD4), T101 (CD5), WT1 (CD7), and WT82 (CD8) with respect to their cytotoxicity to T cells either as immunotoxin (IT) or in combination with complement. The cytotoxic potential was assessed by protein synthesis inhibition and clonogenic assays. The ricin A conjugated MoAb exerted only a minor effect on blood or bone marrow T cells, although they were highly inhibitory to T-cell lines. However, in the presence of 20 mM ammonium chloride. IT directed against CD3, CD5, and CD7 were highly cytotoxic. IT directed against CD4 and CDS were less effective, due to a low internalization. The complement-mediated cytotoxicity was efficient for all antigens used. The natural killer (NK) activity, as measured by cytotoxicity to K562, was hardly depressed by anti-CD3, anti-CD4, anti CD5, and anti-CD8, but was eliminated by anti-CD7. All procedures used had only a minimal effect on haematopoietic progenitors us measured by CFU-GM and BFU-E assays. We concluded that, although the T-cell population can be eliminated with the combination of anti-CD3, anti-CD5, and anti-CD7 antibodies plus complement, IT with 20 mM NH4Cl appear to kill higher amounts of T cells. Selective elimination of CD4- and CD5-positive cells is effectively obtained by MoAb with complement. [ABSTRACT FROM AUTHOR]

Anti-Ig antibodies can have two opposing effects on B-cell proliferation, resulting either in stimulation or inhibition. We have examined the proliferative response of 30 B-cell tumours to anti-Ig in the presence and absence of B-cell growth factor. Three reaction patterns were observed. In 12 cases a dose-dependent synergism between anti-Ig and B-cell growth factor was present in the induction of proliferation, in ten cases anti-Ig did not induce any response, and in eight eases anti-Ig suppressed the B-cell growth factor (BCGF)-induced proliferation. Similar responses to anti-Ig were found in the absence of BCGF. When these B-cell tumours were typed for expression of Ig isotypes, HLA class II antigens, several B-cell markers, activation markers, complement receptors, Fc receptors, cell size, and cell cycle phase, no correlation could be found with the proliferative response of these tumour B cells to anti-Ig. T cells or T-cell factors were not involved, because T-cell depletion did not change the tumour B-cell proliferative response to incubation with anti-Ig. The observed inhibition of proliferation did not correlate with the expression of Fc receptors, indicating the involvement of suppressor mechanisms other than the cross-linking of Fc receptors with surface immunoglobulins. Tumour B cells, for which monoclonal anti-idotypic antibodies (MoAb anti-id) were available, responded to MoAb anti-id in the same way as they did to anti-Ig. In view of the treatment of B-cell malignancies with MoAb anti-id, the question of whether these responses in vitro correlate with in vivo clinical outcome of anti-id therapy is of interest. So far our data show that the proliferative response of B-cell tumours to anti-Ig or MoAb anti-id is heterogeneous and cannot be linked to phenotype, is T cell-independent, and is most likely an intrinsic property of the malignant cell. [ABSTRACT FROM AUTHOR]

In the context of ex vivo T cell elimination from bone marrow, the anti-T cell cytotoxic potential of immunotoxins (IT) prepared by conjugation of the monoclonal antibodies (MoAb) WT32 (CD3). T101 (CD5), and WT1 (CD7) to ricin A chain was evaluated. The cytotoxicity of IT was based on protein synthesis inhibition in human T cell lines: CH1, CEM, HPB-ALL, and Jurkat, and appeared closely related to the antigen density and internalization rate of the IT. Normal unstimulated T cells appeared to be rather insensitive to IT not due to a low antigen density or decreased internalization. The cytotoxicity of IT to T cells could be enhanced considerably by NH4Cl. Treatment of T cells with a cocktail of IT (10-8 M) and 20 mM NH4Cl resulted in a 5000-fold cytoreduction as measured by clonogenic assays of limiting T cell dilutions, whereas the haematopoietic progenitor cells remained unaltered. Stimulation of T cells with phytohaemagglutinin (PHA) prior to incubation with IT considerably increased the sensitivity to IT treatment. Thus, normal I cells are less sensitive to anti-T cell IT than T cell lines and activated T cells. This suggests that a low protein synthesis is responsible for the resistance to IT. However, a high specific cytotoxicity of 11 to normal 1 cells can be achieved in the presence of 20 mM ammonium chloride. [ABSTRACT FROM AUTHOR]

We have previously reported a polymorphism in the mitogenic effect of murine (m) IgGI anti-CD3 monoclonal antibodies. This polymorphism was genetically determined and could be attributed to polymorphism of the Fc receptor (FcR) for mIgGl present on human monocytes. We have now extended these studies by quantitating FcR expression on monocytes and cell lines by it recently developed EA rosette assay, using the erythrocyte-associated pseudoperoxidase activity. The data show that the polymorphism of the monocyte FcR for mIg2a-based on a quantitative rather than an absolute difference. Furthermore, this FcR is specific for mIgGI and does not bind mIgG2a nor mIgG2b nor surprisingly, human IgG. The expression of this FcR on cell lines correlates with their accessory function in IgG I anti-CD3-induced T cell proliferation mIgG2a can inhibit the rosetting of monocytes with erythrocytes sensitized with human IgG. The FcR detected by this rosette technique can interact with all four human IgG subclasses but not with mIgG1 or mIgG2b. The expression of this type of FcR in human cell lines correlates well with their ability to support mIgG2a anti-CD3-induced mitogenesis. These direct measurements of FcR expression support the concept that human monocytes have two independent FcR with affinity for mouse IgG: one receptor specific for mIgG2a (which also binds human IgG), and a second specific for mIgG1. [ABSTRACT FROM AUTHOR]

The Raji-cell test is one of the most widely used methods for the detection and quantitation of immune complexes. Immune complexes and not 7 S IgG bind via C3 to complement receptors on the cell membrane of the Raji cell, During sucrose gradient fractionation of human and murine systemic lupus erythematosus sera, with a high Raji cell-binding activity, we could not demonstrate immune complexes in these sera. Subsequent analysis showed that the major part of the Raji cell binding was used by 7 S IgG with an anti-DNA specificity. Blocking experiments with complement-bearing aggregated IgG revealed that complenicni and Fc receptors were not involved in the binding of these anti-DNA antibodies to Raji cells. We conclude that the Raji cell test is not suitable for the detection and quantitation of immune complexes in sera containing anti-DNA antibodies. [ABSTRACT FROM AUTHOR]