Biomedical Engineering Reference
In-Depth Information
FIGURE 19.3 Targeted human B7.1/NHS76 and untargeted B7.1-Fc immunotherapy in COLON
26-bearing BALB/c mice. Control studies showed that pretreatment with NHS76 antibody alone does
not show any effect.
targeted molecule, mice treated with B7.1/NHS76 alone
showed a 35% reduction in the COLON 26 tumor volume
(Figure 19.3). These observations fit with other solid tumors
that produced a 55% tumor growth reduction in the
MAD109 and RENCA tumor models [16]. Identical treat-
ment studies performed with the soluble B7.1-Fc fusion
protein showed complete regression of COLON 26 tumors
after a 5-day treatment regimen (Figure 19.3). This was true
even in mice with established MAD109 tumors, which are
known to be poorly immunogenic.
TNT-3/CD137L per gram of tumor was significantly higher
than the uptake in normal organs at 24 h (3.1% ID/g) and
showed even higher retention at 48 h postinjection (4.5%
ID/g). As expected, Fc-CD137L demonstrated low tumor
retention over time (0.6% ID/g at 48 h postinjection). Exami-
nation of the tumor draining lymph nodes, an important site
for tumor immunotherapy, revealed that TNT-3/CD137L
(1.2%ID/g) had slightly better uptake than Fc-CD137L
(0.5% ID/g) at 48 h postinjection. However, the average
tumor draining lymph node retention of TNT-3/CD137L
was still much lower than that measured in tumor.
A dosing study was also performed in COLON 26-
bearing BALB/c mice with different doses ranging from 1
to 100 ug/dose of TNT-3/CD137L, Fc-CD137L, and the
anti-CD137 agonist antibody 2A (Figure 19.4). Higher doses
of TNT-3/CD137L and Fc-CD137L treatment resulted in
30-40% tumor reduction. At the highest doses, however, the
TNT-3/CD137L group showed 70% tumor reduction,
whereas the Fc-CD137L-treated mice achieved only 30%
tumor reduction. This difference indicates that at this par-
ticular dosage, localization of CD137L in tumor is critical
and therefore more effective. All 2A treated groups showed
95% tumor reduction; eventually became tumor free and
were free of signs of toxicity throughout the 140-day
observation period. Additional studies are underway to
improve the potency of antibody/CD137L fusion proteins
since biological activity of CD137 depends on functional
homotrimer structures.
19.3.3.2 CD137L Fusion Proteins Besides its relation-
ship with conventional T cells, CD137 signaling on
CD4
T reg cells, although presumed, has been
controversial. For example, Zheng et al. [66] have verified
the expression of CD137 on T reg cells isolated from mice,
and demonstrated that CD137L ligation augmented the
proliferation of functional T reg cells. Choi et al. [67], how-
ever, using the agonist 2A antibody, showed that CD137
signaling resulted in negligible enhancement of proliferation
of T reg cells and actually inhibited T reg cell function in vitro
and in vivo.
Taking into account the importance of the extracellular
C-terminus of CD137L for its bioactivity, the N-terminus of
the extracellular CD137L gene was fused to the C-terminus
of the mTNT-3 HC gene to construct both TNT-3/CD137L
and Fc-CD137L fusion genes [68]. Whole-body clearance
studies were performed in healthy BALB/c mice to establish
the in vivo half-life of TNT-3/CD137L and Fc-CD137L,
which was found to be 18 and 24 h, respectively. Tissue
biodistribution studies in COLON 26 tumor-bearing BALB/c
mice were performed to determine the relative tumor
uptake of each fusion protein. The uptake of radioiodinated
þ
CD25
þ
19.3.3.3 GITRL Fusion Proteins Recently, there have
been a number of studies that have attempted to characterize
the cell surface of T reg cells to evaluate whether individual
proteins play a role in the activation or inhibition of
Search WWH ::




Custom Search