Expression of T cell receptor delta chains in benign and malignant T lineage lymphoproliferations

Recent studies in both human and murine systems have demonstrated the existence of a second CD3-associated T cell receptor (the γ δ-TCR) distinct from the αβ heterodimer associated with antigen recognition by classical T cells. Using a monoclonal antibody specific for the δ component of the human γδ-TCR, the expression of this antigen in both benign, reactive lymphoid tissues and T lineage lymphomas was studied with immunohistologic techniques. In the normal thymus, TCR-δ⁺ cells constituted less than 5% of the CD3⁺ thymocytes and were located primarily in the medulla or juxtamedullary cortex. Within the T zones of 16 histologically varied reactive peripheral lymphoid tissues, including four patients with marked predominantly paracortical hyperplasia, the authors identified from less than 1% to a maximum of 5% TCR-δ⁺ cells. While these results are consistent with the hypothesis that TCR-γδ⁺ cells comprise a small distinct subpopulation of peripheral T cells in humans, selective localization or recruitment of these cells could not be demonstrated in any of a number of tissues or reactive situations. Among 62 T lineage lymphomas, including 14 CD3⁺/TCR-β^- cases, only two TCR-δ⁺ neoplasms were identified, both lymphoblastic lymphomas displaying the CD3⁺/CD4^-/CD8^- phenotype known to be associated with normal TCR-γδ⁺ T cells. Because the majority of CD3A+/TCR-β^- lymphomas did not display TCR-δ, these results argue against the hypothesis that the high incidence of CD3/TCR-β discordance noted in T lineage lymphomas represents preferential transformation of the TCR-δ-expressing subset.