Human T Lymphocyte Differentiation Antigens as Target for Immunotoxins or Complement‐Mediated Cytotoxicity

Abstract

Graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT) is initiated 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 CD8 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 as 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 CD8-positive cells is effectively obtained by MoAb with complement.

Blocked and non-blocked ricin immunotoxins against the CD4 antigen exhibit higher cytotoxic potency than a ricin A chain immunotoxin potentiated with ricin B chain or with a ricin B chain immunotoxin

“…Similarly, a ricin A chain immunotoxin against the L3T4 antigen inhibited the ability of lymph hode cells from primed mice to induce antigen-specific B cells to proliferate and secrete IgM in vitro with an ICs0 ~> 1 nM [16]. Recently, Preijers et al reported that ricin A chain linked to the OKT4 antibody against the human CD4 antigen showed only low toxicity to human peripheral blood lymphocytes in vitro [13]. We have also found that a ricin A chain immunotoxin made with the monoclonal antibody M-T310, which binds to an epitope on the CD4 antigen distinct from that recognised by M-T151 [15], was also weakly toxic to the CEM cell line with an IC50 >5 nM (unpublished results).…”

Characterization of the increased cytotoxicity of gelonin anti-T cell immunoconjugates compared with ricin A chain immunoconjugates

“…MoAb-RTA and MoAb-Gel conjugates are also Correspondence: Dr Dianne Fishwild, GenPharm Intemational, 297 North Bernardo Avenue, Mountain View, CA 94043, LTSA. cytotoxic for murine and human lymphoid cells in vitro [3,7,[18][19][20][21][22].…”

“…When PBMC from one donor were tested on three separate occasions, a reproducible susceptibility pattern emerged with the rGelc247 and RTA30 conjugates. Specifically, the median IC50 values (range) for H65-RTA30, cH65-rGelc247, cH65 F(ab')2-rGelc247 and cH65 Fab'-rGelc247 were 300 pM RIP (240-410), 54 (51-78), 25 (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37) and 59 (59-61), respectively. Furthermore, the relative potencies of the immunoconjugates were the same as when PBMC from multiple donors were tested.…”

“…For example, conjugates made with anti-tumour MoAbs kill target cells in vitro [3][4][5][6][7][8][9][10][11][12][13][14] and deplete tumour cells in animals [3,13,[15][16][17]. MoAb-RTA and MoAb-Gel conjugates are also cytotoxic for murine and human lymphoid cells in vitro [3,7,[18][19][20][21][22].…”