Programmed death 1 is a marker of angioimmunoblastic T-cell lymphoma and B-cell small lymphocytic lymphoma/chronic lymphocytic leukemia.

Programmed death 1 (PD-1) is a lymphoid receptor that negatively regulates immune responses. PD-1 expression was recently reported in some T-cell non-Hodgkin lymphoma (NHL) subtypes, but the expression profile of PD-1 and its ligands (PD-L1 and PD-L2) in B-NHLs remains largely to be characterized. To investigate this issue, monoclonal antibodies against PD-1, PD-L1, and PD-L2 were generated by immunization of balb-c mice. A series of 161 lymphoma tissue and 11 blood samples was analyzed using either immunohistochemistry or flow cytometry. In reactive lymph nodes, PD-1 was mainly expressed in follicular T cells. In B-NHLs, PD-1 was mainly expressed in reactive T cells; but expression was also noted in neoplastic B cells from small lymphocytic lymphoma (SLL, 12/13), grade III follicular lymphoma (3/3), and diffuse large cell lymphoma (2/25). In contrast, neoplastic B cells from mantle cell lymphoma (0/11), marginal zone lymphoma (0/12), Burkitt lymphoma (0/3), and grade 1 to 2 follicular lymphoma (0/40) were PD-1 negative. PD-L1 and PD-L2 were negative in small B-cell lymphomas, including B-SLL. Flow cytometry showed that blood cells from chronic lymphocytic leukemia (B-CLL) also displayed PD-1 expression, which could be increased by CD40 stimulation. PD-1 expression in T-NHLs was restricted to the angioimmunoblastic subtype (8/8). These results show that PD-1 expression among B-NHLs is mainly associated with SLL/CLL and is influenced by activation of the CD40/CD40L pathway. Because the anti-PD-1.6.4 antibody works on paraffin sections, it represents a useful tool to differentiate SLL/CLL from other small B-cell lymphomas.