CD4 and neoplasm: A lower number of αβ CD4 + and CD8 + T cells was also observed in the lungs of antibiotic-treated animals, although no further characterisation of T-cell subtypes and their contributions to tumour immunity was performed.18 Given the increasing evidence that the host microbiota and IL-9-producing T cells modulate tumour progression,16–18,29,33,39 we sought to evaluate whether Th9 and Tc9 cells would be among the players of microbiota-mediated protection against tumour development.