Cell-type-specific cytotoxicity of anti-CD4 and anti-CD8 ricin immunotoxins against human alloreactive T-cell clones

F. M. Uckun, D. E. Myers, J. A. Ledbetter, S. L. Wee, D. A. Vallera

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11 Scopus citations


Potent T-cell subset-directed immunotoxins (ITs) were generated by conjugating the anti-CD4 monoclonal antibody (MoAb) G17-2 and the anti-CD8 MoAb G10.1 to the ribosome-inhibitory protein, ricin. The cell-type-specific cytotoxicities of the generated ITs were evaluated at the clonal level using human alloreactive T-cell clones. The kinetics of anti-CD4 ricin-induced inactivation of protein synthesis in target CD4+ cloned T-cells was first order with no detectable lag period and a maximum rate of 0.07 logs per hour (t10 = 13.6 hours; first-order rate constant/K = 0.17 hr-1). The alloantigen specific lytic function of the CD4+ cytolytic T-cell clone JMAC28 was acutely sensitive to anti-CD4 ricin, and no residual lytic activity against allogeneic targets was detectable 24 hours after treatment with as little as 0.5 nmol/L anti-CD4 ricin. Notably, both anti-CD4 ricin and anti-CD8 ricin elicited a selective and dose-dependent inhibition of clonal proliferation of target T-cell clones with a maximum kill of >3 logs at 5 nmol/L. No significant 'bystander effects' were observed for non-target cells. Bone marrow progenitor cells CFU-GM, BFU-E, and CFU-GEMM were only minimally affected by either IT. We conclude that these ITs show considerable potential for effective depletion of T-cell subpopulations from allogeneic donor marrow grafts for clinical graft-versus-host disease (GVHD) prophylaxis.

Original languageEnglish (US)
Pages (from-to)2445-2454
Number of pages10
Issue number7
StatePublished - 1989


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