The present invention relates to a monospecific population of Treg cells, wherein the Treg cells comprise a chimeric receptor, wherein said chimeric receptor recognizes a B cell surface marker on a B cell, and wherein said Treg cells are cytotoxic for B cells. The present invention also relates to methods for obtaining said monospecific Treg cell population and to the use of said monospecific Treg cell population, in particular for treating an autoimmune disease.