V-set and transmembrane domain containing 1 (VSTM1) is a protein containing the V-set domains. V-set domains are immunoglobulin-like domains resembling the antibody variable region. V-set domains are found in many kinds of protein families, including immunoglobulin light and heavy chains, several T-cells such as CD2, CD4, CD80, and CD86, myelin membrane adhesion molecules, junction adhesion molecules (JAM), tyrosine-protein kinase receptors, and the programmed cell death protein1.