Anti-CD74 Antibody hLL1 Is Associated with Lymphoma and Chronic Lymphocytic Leukemia Cell Effects In Vivo (2011)

Abstract Abstract 1796 Background: CD74 is the invariant chain of the MHCII complex and has an established role as a chaperone protein, which also prevents premature loading of antigenic peptides to the MHC. More recently, CD74 has been implicated as having a role in cancer development by its mediating the prosurvival signaling of the ligand macrophage migration inhibitory factor (MIF) stimulation and it's associated higher level expression in chemoresistant cancers. Blocking of CD74, the receptor for MIF, or its downstream target, a4b1 integrin has been reported to block the homing of CLL cells to bone marrow. The hLL1 antibody (Milatuzumab; Immunomedics, Inc, Morris Plains, NJ) shows promising anti-cancer activity, with eradiation of lymphoma and myeloma xenografts in mice through an undefined mechanism of action. Because of this apparent central role in cancer development, we examined CLL cells of patients (pts) treated with humanized anti-CD74 antibody hLL1. Study Design: Adults with relapsed non-Hodgkin's lymphoma or CLL, who had at least one prior therapy, were enrolled on this phase I-II trial. Patient criteria; ANC 1000, hemoglobin 9, platelets 50,000, adequate organ function, ECOG performance of 1–2, provided informed consent. The hLL1 antibody, in 4 or 8 mg/kg dosages, was administered intravenously over 4 hours, two or three times per wk for 4 wks. Results: Seven pts (4 male) with a median age 65 (range 57–72) with a median 2 (range 1–4) prior chemotherapy treatments were enrolled. Histologies included showed 1 pts with large B cell lymphoma, 5 with pts with SLL/CLL (5) and 1 with marginal zone lymphoma. All pts completed therapy except one who received 5 of 8 doses of planned therapy; 2 pts received dose escalated hLL1 at 8 mg/kg. The hLL1 was well-tolerated with some infusion related side effects, which responded to medications. All other patients maintained adequate hematologic indices, which did not prevent completing the initial therapy plan. Tumor responses were: one partial response, 1 progression, 1 non-evaluable, and 4 with stable disease. Pts' tumor cells were analyzed by reverse-phase protein analysis for activation status of 120 signaling proteins. In 4 of 4 pts with CLL, hLL1 therapy was associated with consistently lower phosphorylated levels of Akt T308 and Notch3; but whether this effect was caused by other concurrent medications could not be ruled out. All the pts who had elevated lymphocyte counts (with bone marrow involvement) showed a rise in lymphocyte counts (Figure) during treatment with hLL1 therapy and then returned to baseline or below baseline after completing infusion. Interestingly, the blocking of CD74 has been shown to interfere with the homing of CLL cells to bone marrow through the binding of CD74-dependent a4b1 integrin. The binding of CLL a4b1 integrin to stroma is a potent cell survival stimulus. To ascertain this mechanisms of CD74 hLL1 antibody induced release of lymphocytes, we analyzed migration of CLL cells in transwell towards MIF. CLL cells without hLL1 exposure had a 2–3 fold cell number migration towards MIF indicating these cells have an intact CD74 receptor mechanism. This analysis suggests that hLL1 targets CLL cells in vivo and interferes with homing of CLL. Follow up analyses will examine whether CLL cells of hLL1-treated pts downregulate a4b1 integrin mediate binding and alter binding to bone marrow stroma. Uncovering such actions are important steps in the elucidation of hLL1's mechanisms of action and for the development of targeted therapies for hematopoietic cancers. Disclosures: Fanale: Novartis Corporation: Honoraria, Research Funding; Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; MedImmune: Research Funding; Millenium: Research Funding. Goldenberg:Immunomedics, Inc.: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties.