Targeted therapies for non-Hodgkin lymphoma: rationally designed combinations

Successful construction and massive expression of a novel Anti-CD19 human-mouse chimeric antibody Hm2E8b

CD19 antigen is a major target for human B cell malignancies. Many studies have shown that the antibodies recognizing this antigen hold clinical therapeutic potential, while CD19 antibody of mouse origin requires genetic engineering to reduce the potential side effects of the antibody for their clinical use. There are many clones of CD19 antibodies available with different subclasses of immunoglobulin. IgM type antibody holds a high affinity and high complement activating capacities facilitating the targeting efficacy when it is used in targeting therapy. However, engineering the murine IgM antibody into a functional humanized antibody remains a challenge. The aim of this study was to construct a chimeric antibody composed of a CD19 specific murine IgM antibody 2E8 single-chain antibody fragment (scFv) and human IgG1 Fc region, which was named 2E8scFv-Fc or Hm2E8b. The function and the biological activities of this engineered antibody were characterized using a variety of approaches including cellular, immunological, flow cytometric, and molecular biological approaches. After switching from IgM- to IgG-like type antibody, Hm2E8b retained full antigen-binding activity to membrane CD19 antigen as its parental antibody 2E8, and the immune effector function analysis revealed that it could mediate complement-dependent cytotoxicity (CDC) to kill the target cells via IgG1 Fc domain. The yield of the engineered antibody Hm2E8b in the supernatant was 13.3 μg/mL expressed and secreted in the CHO cell system, which reached the secretory quantity of a regular mouse hybridoma cells. Our conclusion is that the IgM type of CD19 mouse antibody can be successfully engineered into an IgG1 type human-mouse chimeric antibody with similar affinity and biological activity. The yield of the Hm2E8b expression and secretion in CHO cell system was adequate to facilitate further development for therapeutic purpose.

CD19 targeting of chronic lymphocytic leukemia with a novel Fc-domain-engineered monoclonal antibody

CD19 is a B cell-specific antigen expressed on chronic lymphocytic leukemia (CLL) cells but to date has not been effectively targeted with therapeutic monoclonal antibodies. XmAb5574 is a novel engineered anti-CD19 monoclonal antibody with a modified constant fragment (Fc)-domain designed to enhance binding of FcgammaRIIIa. Herein, we demonstrate that XmAb5574 mediates potent antibody-dependent cellular cytotoxicity (ADCC), modest direct cytotoxicity, and antibody-dependent cellular phagocytosis but not complement-mediated cytotoxicity against CLL cells. Interestingly, XmAb5574 mediates significantly higher ADCC compared with both the humanized anti-CD19 nonengineered antibody it is derived from and also rituximab, a therapeutic antibody widely used in the treatment of CLL. The XmAb5574-dependent ADCC is mediated by natural killer (NK) cells through a granzyme B-dependent mechanism. The NK cell-mediated cytolytic and secretory function with XmAb5574 compared with the nonengineered antibody is associated with enhanced NK-cell activation, interferon production, extracellular signal-regulated kinase phosphorylation downstream of Fcgamma receptor, and no increased NK-cell apoptosis. Notably, enhanced NK cell-mediated ADCC with XmAb5574 was enhanced further by lenalidomide. These findings provide strong support for further clinical development of XmAb5574 as both a monotherapy and in combination with lenalidomide for the therapy of CLL and related CD19(+) B-cell malignancies.

Improved therapeutic results by pretargeted radioimmunotherapy of non-Hodgkin's lymphoma with a new recombinant, trivalent, anti-CD20, bispecific antibody

We examined whether a pretargeting method using a new recombinant anti-CD20 bispecific antibody (bsMAb) followed by (90)Y-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid ((90)Y-DOTA)-peptide could reduce hematologic toxicity yet improve therapeutic responses compared with conventional (90)Y-anti-CD20 IgG and a chemically conjugated bsMAb. TF4, a humanized, tri-Fab bsMAb with two Fabs binding CD20 and one Fab binding histamine-succinyl-glycine (HSG), developed by the dock and lock (DNL) method, was tested in nude mice with Ramos B-cell lymphomas. Optimal pretargeting required a 29-h interval between TF4 and (90)Y-DOTA-HSG, and 20-fold more moles of TF4. TF4 cleared more rapidly from the blood than anti-CD20 IgG, with early processing in the liver, spleen, and kidney. At 24 h, TF4 improved tumor uptake of (111)In-HSG-peptide 2.6-fold [13% versus 5% injected dose per gram (ID/g)] and enhanced tumor to blood ratios >45-fold (770 versus 17), compared with an anti-CD20 Fab x anti-HSG Fab chemical conjugate, and by 1.6-fold (9.0% versus 5.6% ID/g) and 1,600-fold (522 versus 0.32), respectively, compared with radiolabeled anti-CD20 IgG. A severe (>or=90%) and prolonged reduction of WBCs was observed at the maximum dose of (90)Y-anti-CD20 IgG, whereas pretargeting resulted in a <or=60% transient drop. TF4 pretargeting resulted in highly significant improvement in survival, curing 33% to 90% of the animals, even at relatively low doses, whereas most tumors progressed quickly without cures with (90)Y-anti-CD20 IgG. These results indicate an improved therapeutic index with pretargeted radioimmunotherapy (RAIT) using a DNL-constructed tri-Fab, bsMAb, compared with conventional therapy with directly radiolabeled antibody or with a chemically conjugated bsMAb. These encouraging results prompt testing these constructs for pretargeting RAIT in patients.