Objectives: The OX-40 receptor (OX-40R/CD134) is expressed primarily on activated CD4⁺ (“helper”) T cells. We have previously reported the presence of OX-40⁺ T cells in head and neck cancer and melanoma, where they appear to be restricted to tumor compartments (primary tumor infiltrating lymphocytes [TILs] and draining lymph node cells) and therefore may represent the tumor antigen-specific CD4⁺ T cells.

Methods: In order to determine the degree of OX-40R expression, and any relationship with the presence of tumor cells (lobular and/or infiltrating ductal carcinoma), 45 archived paraffin-embedded breast primary tumors and their associated draining (axillary) lymph nodes were retrospectively analyzed using standard immunohistochemical techniques.

Results: Seven of 45 primary tumors (16%) and 7 of 29 with lympocytic infiltrates (24%) were noted to have elevated levels of OX-40R⁺ lymphocytes within the tumor specimens, including 2 of 4 specimens thought to have only “pure” ductal carcinoma in situ (DCIS). No OX-40R⁺ lymphocytes were noted in normal breast tissue. Twenty-one (43%) patients had axillary metastases at the time of resection. High levels of OX-40R expression was seen in 9 (45%) of these 21 axillary node specimens, whereas no such staining was seen in the node-negative specimens (P <0.001). Furthermore, in a patient thought to be without axillary disease, several subcapsular single-cell metastases were retrospectively discovered near a lone cluster of OX-40R⁺ lymphocytes. In general, visual inspection showed OX-40R⁺ T cells to be in close proximity to tumor and often in direct contact with metastatic cells.

Conclusions: The OX-40R is upregulated on lymphocytes within tumor draining lymph nodes, and these lymphocytes are specifically localized around tumor deposits. These data imply that OX-40R immunostaining may be useful for both determination of occult involvement of lymph nodes by tumor and for identification of potential candidates for future OX-40 based immunotherapy.