Starting in 1969, he worked on his doctoral thesis in the laboratory of Prof. René Thomas, Département de Biologie Moléculaire, on the interactions between a prokaryote (Escherichia coli) and a virus (bacteriophage lambda).

Lecocq identified new bacterial genes influencing the decision between the lysogenic cycle and lysis and he analyzed mutants of RNA polymerase.

In 1980, he was appointed Scientific Director of Transgène, one of the first biotechnology companies in France, that was founded in Strasbourg in 1979 at the initiative of Prof. Pierre Chambon and Dr. Philippe Kourilsky, the goal being to develop new technologies in biomedical research for industrial applications.

These technologies have been applied, among others, to the following projects: a new concept based on vaccinia virus for a rabies vaccine in the wild (Raboral, in November 1991 awarded with the Rhone Poulenc Prize for Innovation and used in several countries for the vaccination of foxes, and raccoons), recombinant versions of Factor VIII and Factor IX for the treatment of hemophilia A on behalf of the French blood transfusion service CNTS; vaccine candidates for schistosomiasis, toxoplasmosis and babesia canis; recombinant hirudin, α-1-antitrypsin, gamma-interferon and interleukins, and variants thereof, construction of virtually all recombinant proteins of HIV-1, HIV-2 and SIV for mechanistic studies and applications in diagnosis, and immunization; characterization of α-thrombin receptor, mechanisms of cystic fibrosis.

The following is a selection of representative publications: Lococq was on the editorial boards of the following journals: Lecocq was a member of the following organizations: "Jean-Pierre has left us, victim of the Strasbourg airplane accident.