Development of a diphtheria toxin mutant conjugate directed against antigen-specific B cells expressing high affinity surface Ig.

Modification of a mutant diphtheria toxin, possessing reduced binding capacity, with TNP groups resulted in an Ag-toxin conjugate capable of eliminating TNP-specific B cells. Previous experimental approaches to the elimination of Ag-specific B cells have involved the conjugation of Ag to holoricin molecules or ricin A chain. Holoricin conjugates possess efficacy, but display high nonspecific toxicity. A chain conjugates, which appear specific, lack high potency. In developing the diphtheria toxin-based conjugate, we found high potency for target anti-TNP hybridoma cells and for spleen cells isolated from TNP-immunized mice. The similar intoxication of nontarget cells required concentrations approximately three orders of magnitude higher. Additionally, it was found that the TNP-specific agent may have selectively depleted B cells producing high affinity IgG anti-TNP antibodies.