Travis Sims and Molly El Alam et al. show that diversity of gut microbiota is associated with a favorable response to chemoradiation for cervical cancer and use flow cytometry to show that patients with high microbiome diversity had increased tumor infiltration of CD4+ lymphocytes as well as activated subsets of CD4 cells expressing ki67+ and CD69+ throughout radiation therapy. Here, CD4 is linked to cervical carcinoma.