Immunomedics, Inc., a biopharmaceutical company primarily focused on the development of monoclonal antibodybased products, announced that two new classes of bispecific antibodies were created as the DOCK-ANDLOCK (DNL) complexes using the company’s patented platform technology that enables site-specific conjugation of two self-assembling modules. These bispecific antibodies exhibited potent cell killing activity against lymphoma cell lines in vitro.

Antibodies are large Y-shaped proteins, comprising two identical target-binding arms, each referred to as the fragment, antigen binding (Fab) region, and a tail known as the fragment crystalline (Fc) region. When an antibody is bound to its target via the two Fab arms, interaction of the Fc region with the Fc receptors on blood cells may result in eliminating the tagged target.

Other mechanisms of target killing can be achieved with engineered antibodies of various designs, often with enhanced potency compared to the parental antibodies.

One advance that the Company presented at the 2012 ASH Annual Meeting is a novel T-cell redirecting agent made as a DNL complex by tethering a pair of Fabs that recognize CD19 on B cells to a single-chain variable fragment (scFv) that binds to CD3 on T cells. Referred to as (19)-3s, the prototype potently directs T cells to destroy CD19-expressing B cells by linking them together. Specifically, (19)-3s was shown to bind to T cells and non-Hodgkin lymphoma (NHL) cells simultaneously, and induce T-cell-mediated killing of NHL cells at less than 1 picomolar (pM) concentrations in an ex vivo setting, with maximal activity at 10 pM.

“We expect (19)-3s to have an elimination rate longer than that of blinatumomab, which is made of two scFvs to co-ligate CD19 and CD3,” commented Cynthia L Sullivan, president and chief executive officer. Sullivan added, “We are currently evaluating the in vivo activity of (19)-3s, as a prototype, to determine if this novel bsAb offers additional advantages.”

Sullivan informed that the slower clearance and the fact that (19)-3s has two binding arms might allow for less frequent dosing, and possibly subcutaneous administration. The modular nature of DNL will allow the rapid production of a large number of related conjugates for redirected T-cell killing of various malignancies, without the need for additional recombinant engineering and protein production.

Another advance the company presented at  the 2012 ASH Annual Meeting is an improved design of IgG-based DNL complexes that have the AD2-sequence fused at the end of the light chain (the CK-format) instead of at the end of the heavy chain (the CH3-format), resulting in superior pharmacokinetic profiles, increased bioavailability in mice and rabbits, and a higher effector functions, as shown with a bsHexAb, referred to as CK-22-(20)-(20), generated by conjugating IgG-AD2 of epratuzumab (anti-CD22) to Fab-DDD2 of veltuzumab (anti-CD20), or with an immunocytokine, referred to as Ck-20-2b, generated by conjugating IgG-AD2 of veltuzumab to DDD2-IFNa2b.

Importantly, both CK-22-(20)-(20) and Ck-20-2b demonstrated more potent anti-tumor activity than their CH3-format counterparts in an animal model of human NHL. For example, with a single low dose of 0.25 µg, Ck-20-2b cured 7 of 8 animals, with a median survival time (MST) greater than 189 days, which was statistically significant (P=0.035) when compared with CH3-20-2b (3 of 8 survivors; MST of 134.5 days). With Ck-22-(20)-(20), two injections of 1 mg produced a MST greater than 130 days with 100% survival, which was superior to MST of 71 days with  10% survival obtained with the CH3-counterpart (P<0.001).

Furthermore, a low dose treatment of 10 µg x 2 resulted in a MST of 91 days with 2 animals surviving as compared to 50.5 days with no survivors (P=0.001) for the Fc-based construct.

“These new constructs demonstrate further enhancement of two different classes of fusion proteins with already potent anti-lymphoma efficacy,” remarked Sullivan. “The strategy of designing antibody fusion proteins  at the C-terminus of the light chain, instead of at the commonly used Fc, may improve the in vivo efficacy of most immunoconjugates in general, and the DNL conjugates in particular.”

Finally, the Company presented results from a  preclinical study  that shows milatuzumab, the Company’s proprietary humanized anti-CD74 antibody, effectively prevents the onset and manifestations of acute graft-versus-host disease in a humanized-mouse model. Encouraged by results from this study, the Company plans to respond to investigators who have requested to study milatuzumab for this indication by conducting an initial small clinical trial to evaluate the safety and efficacy of milatuzumab for the control of this challenging disease.

This work was supported in part by Award Number R41AI093082 from the National Institute of Allergy and Infectious Diseases.