Although IFNγ producing CD4 T cells are key components of the immune response against Mtb, these cells alone are insufficient to provide protection.2,3 A complex array of T cells are implicated in the immune response to TB, but their relative contribution to protection remains undefined;4–6 and the precise characteristics of protective Mtb-specific CD4 T cells remain elusive, hindering the development of new vaccines. The gene discussed is CD4; the disease is tuberculosis.