Biomedical Engineering Reference
In-Depth Information
3
chTNT-3
LEC/chTNT 3
2.5
LEC-Fc
2
1.5
1
0.5
0
5
7
9 11
Days after tumor implantation
13
15
17
19
FIGURE 19.2
Immunotherapy in MAD 109-bearing BALB/c mice treated daily for 5 days with
intravenous injection of 0.1mL LEC/chTNT-3 (20
m
g), Fc-LEC (20
m
g), or control chTNT-3 (20
m
g).
several murine tumor cells with B7.1 or B7.2 genes induced
T cell-dependent rejection of B7-expressing tumors in mice
and protected against tumor challenge with parental tumor
cells. These data suggest that the presentation of B7 mol-
ecules on the tumor cell surface in vivo might be a promising
novel approach for cancer immunotherapy. Other forms of
B7.1 and B7.2, namely soluble B7-Igs (now termed B7-Fc),
were studied and found to be very effective for the immu-
notherapy of solid tumors [18], but little work with these
reagents were done past these initial studies.
Co-stimulatory molecules of the TNFSF are also protein-
based conjugates that have been investigated as fusion
protein partners. Members of the TNFSF are type II cell
surface glycoproteins that are normally expressed on APCs.
Their receptors are type I transmembrane proteins, charac-
terized by cysteine-rich motifs in their extracellular
domains, and are transiently expressed on T cells after initial
activation. Several members of the TNFSF family including
CD137L, GITRL, and OX40L, on binding to their receptors,
provide critical signals for T cells to sustain their response
after initial activation (immunological memory). In addition,
CD137 (previously called 4-1BB) is another important co-
stimulatory molecule that has been recently described [60].
Generally, CD137 is found on activated T cells, and its
natural ligand CD137L is found on activated B cells, acti-
vated macrophages and differentiated dendritic cells.
CD137L has been shown to co-stimulate T cell responses
independently of signals through the CD28 molecule [61]
and can stimulate both primary [62] and secondary [63]
responses of both CD4
agonistic anti-CD137 2A antibody eradicates established
subcutaneous tumors in mice [64]. It is not surprising
therefore, that a human 2A antibody is in development
for the treatment of cancer.
19.3.3.1 B7.1 Fusion Proteins
B7.1 is a prototypic co-
stimulatory molecule and has the ability to provide T cells
with the “second signal” that ensures T cell activation
supersedes T cell anergy. To target B7.1, Sharifi et al.
[65] linked the molecule to NHS76, a human TNT mAb
generated by phage display that is capable of binding
intracellular antigens accessible and abundant in necrotic
regions of tumors. These intracellular antigens show prefer-
ential localization in malignant tumors because of the
presence of abnormally permeable, degenerating cells not
found in normal tissues. Because the N-terminus of B7.1
is critical for interaction with its counter-receptors, the
C-terminus of B7.1 was linked to the N-terminus of
NHS76. Studies confirmed that the B7.1/NHS76 fusion
protein retained both the co-stimulatory activity of B7.1
and the tumor-targeting ability of NHS76 antibody [17]. For
comparison, Liu et al. [16] also constructed a B7.1 fusion
protein consisting of human B7.1 and the Fc portion of
human IgG
1
, referred to as B7.1-Fc. Relative tumor uptake
of the fusion protein was determined by tissue biodistribu-
tion studies in COLON 26 tumor-bearing BALB/c mice
using radioiodinated B7.1/NHS76. Despite the rapid clear-
ance of
125
I-B7.1/NHS76, these data demonstrate that
B7.1/NHS76 targets the tumor with good retention as com-
pared to normal organs and blood. Since human B7.1 can
interact functionally with murine B7.1 counter-receptors,
the immunotherapeutic potential of this fusion protein was
tested in different mouse tumor models. In testing the
T cells. Several experi-
ments have shown that enhanced CD137/CD137L interac-
tions amplify T cell-mediated antitumor immunity in several
mouse models and that systemic administration of the
þ
and CD8
þ
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