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VAV1, also known as Vav guanine nucleotide exchange factor 1, is a member of the Vav family of proteins. It is a dual-function guanine nucleotide exchange factor （GEF） that plays a crucial role in the regulation of T and B cell receptor signaling, T cell activation, T helper cell differentiation, and cytokine production. VAV1 is primarily expressed in hematopoietic cells, including T cells, B cells, monocytes, natural killer （NK） cells, granulocytes, and dendritic cells.