INS and type 1 diabetes mellitus: Building on this experience, two parallel first-in-human studies aimed to optimize the cell dose and perforation configuration of PEC-Direct subcutaneous implants in small numbers of T1D recipients (n = 1732; n = 1533) demonstrated that C-peptide, a marker produced by insulin-secreting cells, could be newly detected in some individuals at 6 months post-transplant and could persist until 24 months.