CTLA4 and type 1 diabetes mellitus: In humans, in addition to the full-length form of CTLA-4 (flCTLA-4), a soluble form of CTLA-4 exists (sCTLA-4) that lacks the transmembrane domain encoded by exon 3.74,75 Interestingly, sCTLA-4 has been associated with type 1 diabetes (T1D).