Targeting Interleukin-2 to the Neovasculature Potentiates Rituximab‘s Activity Against Mantle Cell Lymphoma in Mice

Antibody-based tumor targeting strategies promise to specifically target anti-neoplastic agents (e.g. radionuclides, drugs, cytokines) to the tumor site while sparing healthy tissues. In this context, the selective delivery of bioactive molecules to the vasculature seems particularly attractive, considering the fact that antigens expressed in blood vessels are the most accessible structures within a tumor mass and that a vigorous neo-vasculature development is a common feature of virtually all solid and hematologic malignancies. Vascular targeting antibodies functionalized with different payloads are currently being investigated in patients with solid tumors and are increasingly being considered also for the treatment of hematological malignancies. In the present work, we evaluated the efficacy of the fusion protein L19-IL2, comprising the human monoclonal antibody fragment scFv(L19) linked to the cytokine Interleukin-2 (IL-2), against Mantle Cell Lymphoma (MCL), a disease for which existing therapeutic approaches still remain highly unsatisfactory.

Expression of the extra-domain B of fibronectin (EDB-Fn), a well-characterized marker of angiogenic blood vessels, was analyzed in Granta-519 and HBL-2 MCL xenografts and human MCL specimens using immunohistochemistry and dual-color immunofluorescence. The in vivo targeting performance of the EDB-Fn targeting immunocytokine L19-IL2 was investigated using ex vivo immunofluorescence analyses. SCID mice xenografted subcutaneously with Granta-519 or intravenously with HBL-2 MCL cells were used for mono- and combination therapy experiments, featuring i.v. injections of L19-IL2 (30 μg, corresponding to 9.9 μg or 177000 IU rIL-2 equivalents), unconjugated rIL-2 (9.9 μg), the anti-CD20 antibody rituximab (200 μg), rituximab plus IL-2, rituximab plus L19-IL2 or saline.

In vivo, L19-IL2 selectively homed to EDB-Fn expressing angiogenic blood vessels, thereby mediating the accumulation of IL-2 in MCL lesions. In mono-therapy experiments, L19-IL2 showed a superior anti-lymphoma activity compared to equimolar amounts of non-targeted recombinant IL-2. In combination with rituximab, L19-IL2 induced complete remissions (CR) of established subcutaneous Granta-519 tumors in 75 % (6/8) of the cases, whereas rituximab alone or in combination with free IL-2 only delayed lymphoma progression. Mice that experienced lymphoma relapse after having achieved a CR responded a second time to L19-IL2 and rituximab treatment. In the systemic HBL-2 MCL model, the combination of L19-IL2 and rituximab almost doubled survival of mice as compared to IL-2 and rituximab (median survival 63 vs. 33 days).

In summary, we show that the vascular targeting immunocytokine L19-IL2 promotes a potent anti-lymphoma response in combination with anti-CD20 immunotherapy. The clinical evaluation of this combination is facilitated by the fact that L19-IL2 is entirely human and already being studied in Phase II clinical trials in patients with solid tumors.

Menssen:Philogen: Employment. Neri:Philogen: Dario Neri is a co-founder and shareholder of Philogen, the biotech company which has licensed the L19 antibody from the ETH Zurich Other, Equity Ownership.