DETAILED DESCRIPTION What is claimed is: 1.
In a process for preparing a composition comprising a conjugate of the chain A of ricin coupled by means of a disulfide bridge with an antibody directed against human T cells, the improvement comprises adding to said conjugate an amount of ammonium chloride effective to increase the cytotoxic activity of said conjugate.
Description:
In U.
S.
Pat.
No.
4 340 535, there is described the preparation of anticancer products, called conjugates, obtained by coupling the A chain of ricin, by means of a covalent bond, with a protein structure, such as an antibody, an immunoglobulin or an immunoglobulin fragment, capable of selectively recognizing a given antigen on the surface of the target carrier cells, such as cancer cells.
The principal property of these conjugates, which are also called immunotoxins, is that they are specific cytotoxic agents for the intended target cells.
The use of antibodies directed against cancer cell differentiation antigens had already made it possible to obtain conjugates exhibiting a considerable specificity towards the target cells.
The present invention relates to a process for potentiating the activity of these conjugates, which consists in adding an effective quantity of ammonium chloride to the said conjugates.
Conjugates are understood to mean artificial mixed molecules in which the A chain of ricin is associated, by a covalent bond of the disulfide type, with an antibody or an antibody fragment directed against human T cells, capable of selectively recognizing an antigen associated with target cells.
The preparation of the pure A chain of ricin has been described in our earlier patents.
The preparation of monoclonal antibodies directed against human T leukemia cells has been mentioned in the scientific literature.
(Reference may be made in particular to Journal of Immunology 125 (2), 725-731, (1980).
) To prepare the conjugates, the proteins to be coupled must each carry at least one sulfur atom which is naturally capable or has been artificially rendered capable of creating the desired disulfide bond
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Molecular Biology 
