Autoreactive T cells, responsible for the destruction of pancreatic b cells in type 1 diabetes, are known to have a skewed TCR repertoire in the NOD mouse. To define the autoreactive T cell repertoire in human diabetes, we searched for intraislet monoclonal expansions from a recent onset in human pancreas to then trace them down to the patient's peripheral blood and spleen. Islet infiltration was diverse, but five monoclonal TCR β-chain variable expansions were detected for Vβ1, Vβ7, Vβ11, Vβ17, and Vβ22 families. To identify any sequence bias in the TCRs from intrapancreatic T cells, we analyzed 139 different CDR3 sequences. We observed amino acid preferences in the NDN region that suggested a skewed TCR repertoire within infiltrating T cells. The monoclonal expanded TCR sequences contained amino acid combinations that fit the observed bias. Using these CDR3 sequences as a marker, we traced some of these expansions in the spleen. There, we identified a Vβ22 monoclonal expansion with identical CDR3 sequence to that found in the islets within a polyclonal TCR β-chain variable repertoire. The same Vβ22 TCR was detected in the patient's PBMCs, making a cross talk between the pancreas and spleen that was reflected in peripheral blood evident. No other pancreatic monoclonal expansions were found in peripheral blood or the spleen, suggesting that the Vβ22 clone may have expanded or accumulated in situ by an autoantigen present in both the spleen and pancreas. Thus, the patient's spleen might be contributing to disease perpetuation by expanding or retaining some autoreactive T cells. Copyright © 2011 by The American Association of Immunologists, Inc.