Second Exorcist Program

The Second Exorcists is the name given to artificial exorcists created through the Second Exorcist program, which took place around two decades before the start of the events in manga D. Gray Man.

Purpose
The program was an attempt to create human beings who could join with the Innocence. It is not made clear what was done to prepare these artificial to bond with the Innocence but a powerful regeneration ability - which is a secret skill created by the Chang clan. - was included in their making so they could recover and survive from the stresses caused by the innocence during the bonding process.

It's revealed that to the artificially created body the brain of fallen in battle is transferred during the process the hosts memories are erased in order to prevent the new being from falling into madness - when that happens the person is either destroyed or permanently sealed in comatose-like state.

History
Second Exorcist program was a joint operation between the Epstein Family of the American branch and the Chang family of the Asian Branch. The two families pooled their resources to create the program, which would make exorcists to bond with the innocence since finding innocence hosts was quite time consuming and slow compared to the Millennium Earl's speedy production of Akuma. The humans created in the program were then bought before innocence fragments and then forced to bond with the innocence, an incredibly painful process that caused massive injuries to the created humans, which their deaths were only prevented due to a regeneration ability added in their make-up.

Black Order's Dark Legacy
The Program created Yu Kanda and his friend Alma Karma, the former seeming to be the first of the subjects to awaken. Others were shown in their own "pools" awaiting to awaken but they were all annihilated by Alma Karma (along with scientists and members of CROW. who were in the room in that time).

Healing and Regenerating
The fast regenerating - the ability created by Chang's clan - which appears as the tattoo on hosts body (in reality is a ball with said marking) allows to quickly heal the wounds, regenerate lost limbs(or even the whole body) and even rise from death - the power of blood of the Second exorcist was so strong that it even could heal other peaople in contact with their wounds.

Yu Kanda
the only 'active' Second Exorcist and the only Second Exorcist to successfully bond with an Innocence fragment - Mugen.

Alma Karma
Currently the 'womb' of the Third Exorcists program, the reason being it was noted that ordinary humans could not survive and contain the Akuma cells. It is Alma's regeneration abilities that allow him to play such role.

Trivia

 * It is perhaps the first cross branch experiment to occur in the Black Order, or at least that is what is currently known. The Third Exorcist program would follow in it's wake.
 * It's been shown that the second exorcists are actually reincarnations of dead exorcists..
 * Noise Marie offered his body for the Second Exorcist program but he was accidentally revived by Yu Kanda