Residual clonable host cell detection for predicting engraftment of T cell depleted BMTs

Rejection of T-depleted BMTs is predominantly mediated by alloreactive host T cells. A low but significant number of radiochemoresistant clonable T cells can be detected following a conventional cytoreductive protocol given prior to T-depleted BMT. Elimination of these cells increases the engraftment rate. We found no clonable T cells at the end of the conditioning regimen in 100 ml of peripheral blood from 47 patients who received an HLA-identical T-depleted BMT. None rejected the graft and none displayed mixed chimerism. In addition, although no clonable T cells were detected in nine patients who received a mismatched BMT, two rejected their graft. However, in three mismatched patients, who for clinical reasons received a modified pre-BMT schedule, the presence of host clonable T cells was associated with immunological rejection. These findings suggest that the detection of clonable T cells should prove a valuable indicator for optimising immunosuppression prior to T-depleted BMT.

Antibodies to adhesion molecules inhibit the lytic function of MHC-unrestricted cytotoxic cells by preventing their activation

We evaluated the effect of the antibodies to adhesion molecules CD2, CD11a/CD18 (LFA-1), and CD56 (N-CAM) on MHC-unrestricted cytotoxicity mediated by polyclonal NK cells and LAK cells or by CD3+ or CD3- cytolytic cell clones against a panel of tumor cell targets selected according to expression or absence of the corresponding ligands. We show that (i) antibodies to CD11a/CD18 and, to a lesser extent, antibodies to CD2 inhibit target cell lysis, whereas anti-CD56 antibodies exert little if any effect; (ii) in a model system using polyclonal NK/LAK cells as effectors and K562 or HL60-R (NK-resistant) cells as targets, inhibition of cytotoxicity occurs without a significant impairment of effector to target cell binding; (iii) the cytotoxic function of CD3+ or CD3- cytotoxic cell clones is inhibited differentially by antibodies to adhesion molecules; (iv) conjugates formed in the presence of antibodies which inhibit target cell lysis display a significant reduction of target to effector cell contact surface; and (v) this may lead to defective activation of effector cells, as indicated by lack of redistribution of the microtubular apparatus. We conclude that (i) MHC-unrestricted cytotoxicity is regulated by a number of molecular interactions that span far beyond our present knowledge and that it is strictly dependent on the surface phenotype of the effector cell and of the target cell; (ii) in certain types of effector/target cell interactions, antibodies to adhesion molecules do not prevent conjugate formation but reduce the extent of cell-to-cell surface contact which, in turn, leads to defective activation of the effector cell and, therefore, to inhibition of target cell lysis.

Adhesion molecule-mediated signals regulate major histocompatibility complex-unrestricted and CD3/T cell receptor-triggered cytotoxicity

Appropriate experimental conditions were devised to demonstrate that CD58 (LFA-3), CD54 (ICAM-1) and CD11a/CD18 (LFA-1) adhesion molecules are the source of signals that regulate nonspecific major histocompatibility complex-unrestricted and CD3/T cell receptor (TcR)-triggered cytotoxicity. Using anti-LFA-3 monoclonal antibody (mAb)-treated, interleukin-2 (IL-2)-cultured peripheral blood lymphocytes (PBL) or cloned CD3+/CD8+ cells as lymphocyte-activated killer (LAK) effectors, and ligand (CD2)-negative tumor cell lines as targets, a down-regulation of CD3- and CD3+ cell-mediated LAK activity was consistently observed. Anti-LFA-3 mAb also down-regulated tumor cell lysis when T cell clones were triggered to kill P815 cells through stimulation of the CD3/TcR complex by an anti-CD3 mAb. The inhibitory effect of anti-LFA-3 mAb was not prevented by stimulatory anti-CD2 mAb. Anti-ICAM-1 mAb treatment of IL-2-cultured PBL consistently up-regulated LAK cytotoxicity against tumor target cells. However, this effect was only exerted on CD3- LAK effectors. Anti-LFA-1 mAb blocked conjugate formation between effector cells and tumor target cells, thus rendering this model unsuitable to evaluate the regulatory role of LFA-1. Therefore, a cytotoxicity model system was applied in which a hybrid anti-CD3/anti-human red blood cell (HuRBC) mAb triggers cytolytic T cells to lyse HuRBC. In these experiments, anti-LFA-1 mAb markedly up-regulated the lytic ability of IL-2-cultured PBL. We conclude that mAb against LFA-3, ICAM-1 and LFA-1 molecules deliver regulatory signals for LAK cells and cytotoxic T lymphocytes. As these stimuli may be delivered by ligands expressed on tumor targets as well as on other immune competent and inflammatory cells, the present observations are relevant in the context of both the host's immune response against tumors and the general functioning of the immune system.

Human T-helper clones induce IgG production in a subclass-specific fashion

The mechanisms governing the induction of IgG subclasses by T-helper cells in humans were investigated. As preliminary bulk-culture experiments had indicated that a direct B cell contact with viable T cells was an essential requirement for optimal IgG subclass production, 256 CD4+ human T cell clones were preactivated with PHA and cultured in direct contact with autologous B cells. These clones induced IgG production in a strikingly subclass-specific fashion. Moreover, the distribution of subclass-specific helper clones was very similar to the IgG subclass profile observed in serum and peripheral lymphoid tissue plasma cells (IgG1 approximately 60%, IgG2 approximately 30%, IgG3 approximately 5-10%, IgG4 less than or equal to 5%) and unlike that observed in resting B cells (which is IgG1 approximately 40% and IgG2 approximately 50%). It would, therefore, seem that a predominance of T cells capable of delivering IgG1-specific, as opposed to IgG2-specific, help is an essential factor for the preferential induction of IgG1 antibodies during B cell proliferation and differentiation. There was no relationship between IL2, IL4, IL6, and IFN-gamma secreted by the T-helper clones and their IgG subclass induction patterns. In addition, only a few supernatants were able to reproduce the helper effects of the clones themselves. Therefore, direct contact of B cells with helper clones is crucial for IgG-subclass production in humans.

Interleukin-6 is constitutively produced by human CTL clones and is required to maintain their cytolytic function

Maturation of cytolytic T lymphocytes from nonlytic precursors requires cytokines in addition to IL2. Interleukin-6 is the principal cytokine that cooperates with IL2 in the induction of CTL differentiation from murine and human thymocyte precursors. However, a cytotoxic differentiation factor (CDF) role of IL6 for mature T cells is challenged by data indicating that IL2 alone is sufficient for CTL generation. The aim of this study was to identify a model system in which IL6 acted as a CDF for human peripheral T cells. We noted that IL6 was endogenously produced by CTL clones in the course of their expansion with APC, lectin, and IL2. The majority of several hundred T-cell clones, both CD4+ and CD8+, produced IL6 in response to relatively high doses of IL2. Other experiments that compared the cytolytic function of CTL clones cultured in the presence of IL6 with that of the same clones cultured in the absence of IL6 demonstrated that IL6 contributes to the cytolytic ability of the majority of human CTL clones. Our data suggest that IL6 acts in an autocrine fashion to support CTL differentiation in human T-cell clones.

[Pathogenetic and clinical significance of the adhesion molecule expression on T cells of the lung in sarcoid alveolitis]

A double immunofluorescence analysis of CD4+ cell population from bronchoalveolar lavage (BAL) fluid samples of patients with active pulmonary sarcoidosis was carried out. The results showed that, unlike BAL and peripheral blood CD4+ cells of healthy subjects, almost all BAL CD4+ cells of the patients highly express, besides CDw29 antigen, LFA-1 and ICAM-1 adhesion molecules. The co-expression of these molecules on BAL CD4+ cells during high intensity sarcoid alveolitis could represent a marker of immunological memory. The relevant pathogenetic and clinical implications of this observation are discussed.

Anti-CD3 and anti-CD2-induced T-cell activation in primary Sjögren's syndrome

Because T-cell dysfunctions have been reported in patients with primary Sjögren's syndrome (SS), peripheral blood mononuclear cell (PBMC) proliferation obtained with anti-CD3 and anti-CD2 monoclonal antibodies was evaluated in these patients. Anti-CD3-induced mitogenesis, which varied widely among the patients, was lower in subjects with evidence of anti-SSA and anti-SSB antibodies than in controls. Moreover, the anti-CD2-induced response was depressed in about half the patients and the nonresponders were mainly those with anti-SSA and anti-SSB antibodies. Phorbol myristate acetate, a protein kinase C activator, used alone or added to anti-CD3, induced greater proliferation in patients than in control PBMC. In contrast, exogenous recombinant interleukin 2 (rIL-2) did not significantly enhance the anti-CD2-induced response of patients' PBMC, as it did in normal PBMC. Peripheral blood and parotid T cells from a patient with well-defined primary SS and parotid enlargement also responded poorly to anti-CD2 stimulation. Exogenous rIL-2 restored T-cell proliferation only in the salivary gland cultures of this patient. The present findings suggest that there is a T-cell activation defect in subjects with primary SS, particularly in those with circulating anti-SSA and anti-SSB antibodies. In addition, the difference in the response to IL-2 of peripheral blood and parotid-infiltrating T cells would seem to indicate that T-cell subsets are differently distributed in the blood and inflammation site.