RESURGENCE OF BISPECIFIC ANTIBODIES - Fusion Protein Technologies for Biopharmaceuticals: Applications and Challenges - page 515

FIGURE 35.6 Bispecific antibody constructs based on diabodies or single-chain antibodies. Red
and green colors highlight variable antibody domains of distinct specificity. Disclosed binding
specificities and particular structural features are labeled. Single-chain antibodies (scFvs) show a
peptide linker between variable domains.

induction of effector T-cell proliferation. It appears that for
efficient and safe T-cell engagement BiTE antibodies all of
these properties have to be combined. Prolonged infusion of
the rather short-lived BiTE antibodies to patients allows for a
sustained T-cell engagement against cancer cells as well as for
an exquisite control of safety parameters by swift clearance of
drug on discontinued infusion. Currently, three BiTE anti-
bodies are in clinical development. TheCD19/CD3-bispecific
BiTE antibody blinatumomab is in a pivotal study in patients
with acute lymphocytic leukemia (ALL). It has shown out-
standing efficacy in patients with ALL [65], and non-Hodgkin
lymphoma (NHL) [66]. An EpCAM/CD3-bispecific BiTE
antibody called MT110 is in a Phase I study in cancer
patients with EpCAM-expressing solid tumors, and a CEA-
CD3-bispecific BiTE, developed in collaboration with
MedImmune/Astra Zeneca, has just commenced a Phase I
study in a similar cancer patient population. Three other
BiTE antibodies are in preclinical development together
with Sanofi-aventis, Boehringer

“triplebody” and covalently aligns three scFvs to achieve
targeting of two kinds of malignant cells. A third class of
tandem scFv constructs is unique in that it specifically
engages neutrophils via Fc alpha receptor I (CD89) against
lymphoma cells expressing HLA class II molecules [69].
Tandem diabodies called “Tandabs” are developed by
Affimed and use extra linkers to join two diabodies
(Figure 35.6B) with the goal of increasing binding affinities
and, eventually, potency and serum half-life [70]. Two
Tandabs have been advanced into formal drug development.
One is for engaging T cells via CD3 for lysis of
CD19-expressing lymphoma and leukemia cells [71], and
one for engaging NK cells via Fc g receptor IIIa (CD16A) to
CD30-expressing Hodgkin lymphoma cells [72]. The
CD30/CD16-bispecific Tandab, called AMF13, has just
commenced a Phase I clinical trial in Hodgkin's lymphoma
patients, while the CD19/CD3-bispecific TandAb AMF11 is
in formal preclinical development. One of their hallmarks is
bivalent binding to effector as well as target cells. Bivalent
target binding may promote potency through higher affinity
binding but must be evaluated with great care. For instance,
bivalent binding to CD3 on T cells—as also done by the anti-
CD3 mAb OKT-3—may after initial, nonconditional T-cell
activation cause down modulation of the TCR with impedi-
ment of further efficacy. On the other hand, bivalent binding
to target antigens may down-modulate their surface expres-
sion with an additional negative impact on efficacy.

Ingelheim, and Bayer

Schering Pharma.
Fey and colleagues have developed a number of tandem
scFv-based bi- and trispecific constructs for engagement of
immune cells. Two are designed to redirect natural killer
(NK) cells via CD16 to either CD123-expressing acute
myeloid leukemia (AML) cells [67] or to both CD19-
expressing leukemia and lymphoma, and to CD33-express-
ing AML cells [68]. The latter construct is called a