C-ImmSim started, in 1995, as the C-language "version" of IMMSIM, the IMMune system SIMulator, a program written back in 1991 in APL-2 (APL2 is a Registered Trademark of IBM Corp.) by the astrophysicist Phil E. Seiden together with the immunologist Franco Celada to implement the Celada-Seiden model.