Expression of ED-B Fibronectin in Tissues from Human Hematologic Malignancies.

Newly formed blood vessels in tissues infiltrated by hematologic malignancies or solid cancers are strikingly different from normal healthy counterparts. Notoriously, they are characterized by vascular shunts, uneven vessel diameters, and endothelial fenestrations. In addition, for the vast majority of solid cancers the extracellular matrix of such vessels was found to contain a type of fibronectin that has an extra-domain B (ED-B), which is expressed during embryonic development and during major tissue remodeling, but not in normal adult organs. The unique expression pattern attributed to ED-B suggests that it may be well suited for vascular targeting. Preliminary data has shown that ED-B expression may also be detected in hematologic malignancies. We have analyzed a large series of human samples of different hematological malignancies, non-malignant or reactive lymphatic conditions, and normal lymphatic and hematopoietic tissues for ED-B expression, using immunohistochemistry (IHC; mAbs BC1, L19, and the newly created MX1) on paraffin sections after steam pressure-based epitope recovery. Consistent with the data from solid tumors, ED-B expression was not detected in normal lymph nodes and lymphatic tissues. However, considerable but variable vessel-associated ED-B expression was detected in the following tissue samples of hematologic malignancies: 56/59 (95%) of Hodgkin lymphomas, 33/36 (91.7%) of DLBCLs, 32/33 (97%) of follicular lymphomas, 17/18 (94.4%) of mantle cell lymphomas, 14/15 (93.3%) of anaplastic large T cell lymphomas, 16/16 (100%) of multiple myelomas,13/14 (92.8%) of B-CLL samples, and in 5/6 (83.3%) samples from chronic myeloproliferative bone marrow, and in 3/3 (100%) from acute leukemia. Reactive lymph nodes (9/10; 90%) showed a faint ED-B expression in the vascular walls, whereas in hypertrophic tonsils (n=5) and healthy or reactive bone marrow (n=12) ED-B expression was rarely detected. Consistent with the literature, ED-B expression was not detected in tissue samples from normal lymph nodes (n=5). Immunofluorescence was used to identify co-localization of ED-B fibronectin and blood vessel-associated epitopes (eg CD34). Also, results will be presented from experiments in which lymphoma and leukemia animal models were treated with a novel IL2 immunocytokine specifically targeted to the ED-B fibronectin (L19-IL2). Preliminary results from these models suggest that hematopoietic malignancies contain ED-B+ vessels. Our study indicates the presence of vessel-associated ED-B in the vast majority of tissue samples from patients with varied hematologic malignancies, suggesting a potential approach for clinical investigation with targeted immunocytokines.