ICOS and neoplasm: A similar population of PD1+ CXCR5+ ICOS+ CD69+ cells is found in 1‐year‐old Vav1ΔC/ΔC mice (Fig. 4H–O), suggesting that the faster development of tumours found in Trp53ER/ER;Vav1ΔC/ΔC mice is probably due to the shortening in approximately 6 months of the time required for the expansion of the population of chronically activated TFH cells found in 1‐year‐old Vav1ΔC/ΔC animals.