Bach was Director of Inserm Unit 25 (Renal Immunopathology) and CNRS Laboratory 122 (Allograft Immunology), while also directing the Claude Bernard Association's centre on autoimmune diseases.

Among its other activities and functions: Bach published alone or in collaboration, nearly 700 articles as well as several scientific books, including his Traité d'immunologie (six French editions and translated into 3 languages).

[4] His personal work concerned more particularly the study of subpopulations of T lymphocytes related to thymus activity; the characterization of thymic hormones and in particular thymulin, which he synthesized; the action of immunosuppressants (cyclosporin, antilymphocyte sera, monoclonal antibodies against Tlymphocytes).

He played a decisive role in the implementation of treatments for this disease with ciclosporin and, more recently, with anti-CD3 monoclonal antibodies.

Finally, he showed that the decrease in the frequency of infections in developed countries explained the increase in the incidence of autoimmune diseases (hygienist theory).