The present invention provides compositions, methods, and assays for treating an inflammatory and/or autoimmune disease, and/or transplanted tissue rejection using anti-αβ TCR antibodies and antibody fragments. Anti-αβ TCR antibodies are antibodies which bind to a αβ TCR. Anti-αβ TCR antibodies produced by the hybridoma TOL101 MCB are also provided. Methods for treatment of an inflammatory disease, an autoimmune disease and for tissue transplant rejection using therapeutic dosing regimen of anti-αβ TCR antibodies and antibody fragments and for upregulating the numbers of Treg T-cells are also provided.