The patent office recently granted an application for application number 7124/CHENP/2010 to Immunogen Inc. The application claims cross-linkers and drug conjugates comprising said linkers. The applicant submitted that cross linkers of the invention lead to several unexpected advantages of the resulting immune-conjugates, such as increased drug loading, enhanced conjugate potency against tumor cells, particularly, against multidrug resistant tumor cells, and enhanced in vivo anti-tumor activity. The applicant also submitted that these advantages would not have been expected or predicated based on the teachings of the documents cited. The Controller considered such linkers and the advantages associated with them as unexpected. Also an opposition was filed by Indian Pharmaceutical Alliance during prosecution of the application, however, the same was withdrawn by the Opponent and the application was allowed.