TARGETED AND UNTARGETED FUSION PROTEINS: CURRENT APPROACHES TO CANCER IMMUNOTHERAPY - Fusion Protein Technologies for Biopharmaceuticals: Applications and Challenges - page 300

models of immunocompetent mice. Cell deletion experi-
ments have identified the importance of NK þ and CD8 þ
effector T cells for tumor immunotherapy and the negative
influence of CD25

5. Bitonti AJ, Dumont JA, Low SC, Peters RT, Kropp KE,
Palombella VJ, et al. (2004) Pulmonary delivery of an
erythropoietin Fc fusion protein in non-human primates
through an immunoglobulin transport pathway. Proc. Natl.
Acad. Sci. U S A 10, 9763-9768.
6. Waldmann TA. (2003) Immunotherapy: past, present, and
future. Nat. Med. 9, 269-277.
7. Blattman JN, Greenberg PD. (2004) Cancer immunotherapy:
a treatment for the masses. Science 305, 200-205.
8. Aluvaihare VR, Kallikourdis M, Betz AG. (2004) Regulatory
T-cells mediate maternal tolerance to the fetus. Nat. Immunol.
5, 266-271.
9. Marshall NA, Christie LE, Munro LR, Culligan DJ, Johnston
PW, Barker RN, et al. (2004) Immunosuppressive regulatory
T-cells are abundant in the reactive lymphocytes of Hodgkin's
lymphoma. Blood 103, 1755-1762.
10. Leach DR, Krummel MF, Allison JP. (1996) Enhancement of
antitumor immunity by CTLA-4 blockade. Science 271,
1734-1736.
11. North RJ, Awwad M. (1990) Elimination of cycling CD4 þ
suppressor T cells with an anti-mitotic drug releases non-
cycling CD8 þ T cells to cause regression of an advanced
lymphoma. Immunology 71, 90-95.
12. Tanaka H, Tanaka J, Kjaergaard J, Shu S. (2002) Depletion of
CD4 þ CD25 þ regulatory cells augments the generation of
specific immune T cells in tumor-draining lymph nodes.
J. Immunother. 25, 207-217.
13. Pardoll D. (2003) Does the immune system see tumors as
foreign or self? Annu. Rev. Immunol. 21, 807-839.
14. Li J, Hu P, Khawli LA, Epstein AL. (2003) LEC/chTNT-3
fusion protein for the immunotherapy of experimental solid
tumors. J. Immunother. 26, 320-331.
15. Li J, Hu P, Khawli LA, Epstein AL. (2003) Complete
regression of experimental solid tumors by combination
LEC/chTNT-3 immunotherapy and CD25 þ T-cell depletion.
Cancer Res. 63, 8384-8392.
16. Liu A, Hu P, Khawli LA, Epstein AL. (2005) B7-Fc fusion
protein treatment induces tumor regressions with long-term
memory and is enhanced by Treg cell depletion. Clin. Cancer
Res. 11, 8492-8502.
17. Liu A, Hu P, Khawli LA, Epstein AL. (2006) B7.1/NHS76: A
new co-stimulator fusion protein for the immunotherapy of
solid tumors. J. Immunother. 29, 425-435.
18. Sturmhoefel K, Lee K, Gray GS, Jenifer Thomas J, Zollner R,
O'Toole M, et al. (1999) Potent activity of soluble B7-IgG
fusion proteins in therapy of established tumors and as
vaccine adjuvant. Cancer Res. 59, 4964-4972.
19. Runyon K, Lee K, Zuberek K, Collins M, Leonard JP,
Dunussi-Joannopoulos K. (2001) The combination of chemo-
therapy and systemic immunotherapy with soluble B7-immu-
noglobulin G leads to cure of murine leukemia and lymphoma
and demonstration of tumor-specific memory responses.
Blood 97, 2420-2426.
20. Chen L. (2004) Co-Inhibitory molecules of the B7-CD28
family in the control of T-cell immunity. Nat. Rev. Immunol.
4, 336-347.

T reg cells. Both nontargeted soluble Fc
and targeted antibody fusion proteins have been found to be
effective agents for the delivery of immunoregulatory mol-
ecules that can induce significant tumor regression or cure.
In particular, the chemokine LEC and several different co-
stimulatory molecules including B7.1, OX40L, GITRL, and
CD137L were found to be especially effective in the induc-
tion of effective cancer treatment. These co-stimulatory
molecules are not the only protein-based conjugates that
have been investigated as fusion proteins. We have also
demonstrated that treatment with H60/TNT-3, a new immu-
notherapeutic fusion protein drug, could dramatically
enhance antitumor effect of experimental murine tumors
[111]. Interestingly, these results proved that injection of
H60/TNT-3 could stimulate innate antitumor immunity via
NK cell activation and thereby suppress tumor growth.
Additional antibody conjugates such as those with CpG
and other toll-like receptor agonists may also prove to be
highly effective in stimulating innate immunity in the tumor
microenvironment. In general, our work demonstrates that
several fusion proteins may have clinical potential for the
immunotherapy of cancer. Although several challenges in
optimizing the development of fusion proteins remain,
advances in protein engineering should provide ready solu-
tions to enable these promising immunomodulatory reagents
to reach the clinic.

þ

ACKNOWLEDGMENTS

We would like to thank all our past and present students for
their dedication and commitment during the long hours of
experimental studies. We also would like to express appre-
ciation to the many colleagues and peers who have con-
tributed to expanding our knowledge of fusion proteins and
regret the absence herein of many valuable reference cita-
tions due to space limitations.

REFERENCES

1. Beck A, Wurch T, Bailly C, Corvaia N. (2010) Strategies and
challenges for the next generation of therapeutic antibodies.
Nat. Rev. Immunol. 10, 345-352.
2. Roopenian DC, Akilesh S. (2007) FcRn: the neonatal Fc
receptor comes of age. Nat. Rev. Immunol. 7, 715-725.
3. Sidhu SS. (2007) Full-length antibodies on display. Nat.
Biotechnol. 25, 537-538.
4. Mocellin S, Rossi CR, LiseM,Marincola FM. (2002) Adjuvant
immunotherapy for solid tumors: from promise to clinical
application. Cancer Immunol. Immunother. 5, 1583-1595.