PDCD1 and lymphoma: Based on these and other observations, the 2016 WHO classification requires that Tfh lymphomas be diagnosed by positive immunostaining for at least 2 (ideally 3) of the following 7 antigens: CD10, BCL6, PD1, CXCL13, C-X-C motif chemokine receptor 5 (CXCR5), ICOS, and signaling lymphocytic activation molecule-associated protein (SAP) [15].