DQ8/InsB:R3 was identified as an antigen by functional analysis of reactive T cells from peripheral blood, but direct evidence of antigenicity in islets is missing. The hypothesis is that the endogenous DQ8/InsB:R3 appear at the core organs of T1D in a disease stage-related timing. CODEX is a highly multiplexed tissue imaging platform enabling >50 markers to be simultaneously analyzed in single cells. We will use the CODEX platform to measure the expression of DQ8/InsB:R3 in different antigen-presenting cells, analyze the association of antigen with HLA-DQ and islet beta cells in the pancreas and pancreatic lymph nodes. Expression of DQ8/InsB:R3 only in patients and AAI+ individuals strongly support its pathogenic role in the development of T1D.