The present invention is a method for inhibiting Treg cell functional activities by blocking Treg cell-mediated mast cell activation. It has been found IL-9 produced by Treg cells activates mast cells, which in turn mediate an amplification loop critical for graft tolerance and immune responses to tumors. Thus, a method for enhancing an immune response to a vaccine, such as a cancer vaccine, is also provided as is a method for increasing cell and humoral immunity in a subject.
