This also relates to methods for production thereof, to pharmaceutical compositions containing such Antibodies and Uses Thereof (Cancer Therapy).Claim 1: a Protein that binds a monovalent Antigen and is formed by: a) a Long Chain modified an Antibody that specifically binds to an antigen, in which the domain has been replaced by the VH VL domain of the Antibody； and (b) a Long Chain modified d Said Antibody and the CH1 Domain, which has been replaced by the cl domain of the Antibody.Claim 2: monovalent Protein that binds to the Antigen according to claim 1, wherein the CH3 domain of Long Chain modified Antibody to the CH3 Domain) and the long chain modified Antibody (b) together in one interface.It is formed by the interface between the CH3 domains of the Antibody； this interface is altered to encourage the formation of monovalent Protein that binds to the antigen, the disturbance is characterized in that: (i) a Long Chain of the CH3 domain is altered, M Odo to the original interface within the CH3 domain of a Long ChainThe original interface that binds to the CH3 domain of other Long Chain within the Protein that binds a monovalent Antigen amino acid by replacing a rest, a rest that has a Greater volume of amino acid side chainResulting in a Bulge in the interface of the CH3 domain of a Long Chain that can live inside a Cavity of the interface of the CH3 domain of other long chain and (ii) The CH3 domain of other long chain is altered, so that originates within the interface L the second Domain CH3That binds to the interface of the Original First of the CH3 Domain Protein that binds a monovalent Antigen amino acid by replacing a rest, a rest that has a Lower volume of amino acid side chain, which generates a Second Cavity at the interface of the CH3 Domain within d And which can stay a protuberance of the first Interface of the CH3 domain.La presente también se refiere a métodos para su producción, a composiciones farmacéuticas que contienen dichos anticuerpos y a
