Utility of CD279/PD-1 immunohistochemistry in the evaluation of benign and neoplastic T-cell-rich bone marrow infiltrates.

CD279 expression is used to help identify angioimmunoblastic T-cell lymphoma (AITL) or other T-cell lymphomas of T-follicular helper (TFH) cell origin; however, its utility in assessing lymphoid infiltrates in the bone marrow (BM) is not well established. Immunohistochemistry for CD279 was performed on normal staging BM and in BM with benign lymphoid aggregates (LAs), AITLs, and other T-cell lymphomas. Seven of 10 staging BMs demonstrated scattered, usually weakly CD279+ cells. Thirty-four of 38 BMs had scattered weakly/variably intense CD279+ cells within LAs, but only four contained 11% to 25% CD279+ cells. Three of four AITLs were strongly CD279+, but one contained only around 10% CD279+ cells. Eleven of the other 38 T-cell lymphomas were CD279+, including five possible AITLs; four peripheral T-cell lymphomas, not otherwise specified; and two T-cell large granular lymphocytic leukemias. Although useful in assessing selected BM lymphoid infiltrates, CD279 expression may be limited in AITLs, is not specific for TFH lymphomas, and can be seen in benign lymphoid infiltrates, although without extensive strong positivity.