Abstract: An activated affinity ligand is described comprising: a ligand having (a) a region with affinity for binding sites of a lectin; and (b) a reactive group capable of covalently linking the ligand to the lectin to thereby block one or more of the binding sites of the lectin. A blocked lectin is described comprising one or more affinity ligands covalently linked by means of a reactive group present on each of the ligands to a lectin such that one or more binding sites of the lectin is blocked. A cell-binding agent-blocked lectin conjugate is described comprising the above-described blocked lectin and a cell-binding agent covalently linked to: (a) one of the covalently linked affinity ligands; or (b) the lectin. A method of preparing a blocked lectin is described. A method of preparing the cell-binding agent-blocked lectin conjugate is described. An affinity support capable of binding to a lectin to form a blocked lectin is described comprising an activated affinity ligand covalently linked to a solid support.

Abstract: A cytotoxic agent comprising one or more maytansinoids linked to a cell binding agent. A therapeutic agent for killing selected cell populations comprising: (a) a cytotoxic amount of one or more maytansinoids linked to a cell binding agent, and (b) a pharmaceutically acceptable carrier diluent or excipient. A method for killing selected cell populations comprising contacting a cell population or tissue suspected of containing cells from said selected cell population with a cytotoxic amount of a cytotoxic agent comprising one or more maytansinoids linked to a cell binding agent. An N-methyl-alanine-containing ester of maytansinol or an analogue of maytansinol, said N-methyl-alanine-containing ester comprising a linking group capable of linking an N-methyl-alanine-containing maytansinoid ester to a chemical moiety. N-methyl-cysteine-containing ester of maytansinol or an analogue of maytansinol.

Abstract: Immunotoxins having improved toxic activity have the composition ##STR1## wherein Toxin-NH is a ribosome-inactivating protein containing no accessible sulfhydryl groups, n is an integer from 1 to 5, m is an integer from 1 to 5, and NH-Antibody is a monoclonal antibody specific to eucaryotic cells or antigens associated therewith. The immunotoxins are made by reacting the Toxin-NH with an iminothiolester salt to form a first conjugate, reacting the NH-Antibody with N-succinimidyl-3-(2-pyridyldithio) propionate to form a second conjugate, and reacting the two conjugates to form the immunotoxin.

Abstract: Heterobifunctional reagents that are cleavable under mildly acidic conditions are disclosed. The reagents include an acid cleavable cyclohexene-1,2,-dicarboxylic acid monoamide group. Also disclosed are methods of making the cross-linkers, as well as methods of using the cross-linkers, e.g., to deliver a biologically active substance across the membranes of selected cells in a heterogeneous cell population; once inside the cell the active substance is released, intact, by the transient, mild acidity of certain cell structures. Finally, a method of characterizing complex multi-chain protein structures is disclosed.

Abstract: A photo-cleavable compound for delivery and release of a biologically active substance to selected target cells; the compound includes a binding partner for a specific cell-surface receptor of those target cells, the biologically active substance to be delivered, and a photo-cleavable bridge between the binding partner and the biologically active substance. When the compound is exposed to a heterogeneous population of target and non-target cells, it binds selectively to the receptors on the surface of the target cells. Exposing the compound to light of selected wave length cleaves it, yielding the active substance.

Abstract: Amino-sulfhydryl cross-linking reagents that are cleavable under mildly acidic conditions are disclosed. Also disclosed are methods of making the cross-linkers, as well as methods of using the cross-linkers, e.g., to deliver a biologically active substance across the membranes of selected cells in a heterogeneous cell population; once inside the cell the active substance is released, intact, by the transient, mild acidity of certain cell structure. Finally, a method of characterizing complex multi-chain protein structures is disclosed.

Abstract: Amino-sulfhydryl cross-linking reagents that are cleavable under mildly acidic conditions are disclosed. Also disclosed are methods of making the cross-linkers, as well as methods of using the cross-linkers, e.g., to deliver a biologically active substance across the membranes of selected cells in a heterogeneous cell population; once inside the cell the active substance is released, intact, by the transient, mild acidity of certain cell structures. Finally, a method of characterizing complex multi-chain protein structures is disclosed.

Abstract: Amino-sulfhydryl cross-linking reagents that are cleavable under mildly acidic conditions are disclosed. Also disclosed are methods of making the cross-linkers, as well as methods of using the cross-linkers, e.g., to deliver a biologically active substance across the membranes of selected cells in a heterogeneous cell population; once inside the cell the active substance is released, intact, by the transient, mild acidity of certain cell structures. Finally, a method of characterizing complex multi-chain protein structures is disclosed.