Universal and Stemness-RelatedT umorAntigens: Potential
Use in Cancer Immunotherapy
Giorgio Parmiani,1Vincenzo Russo,1Andrea Marrari,2Gianluca Cutolo,2Chiara Casati,2
Lorenzo Pilla,2Cristina Maccalli,1Licia Rivoltini,2and Chiara Castelli2
After a decade of cancer immunotherapy (both active and
adoptive), based on the use of well-defined tumor-associated
antigens (TAA), and despite the large amount of new
information that has been collected both in preclinical and
clinical settings, the clinical outcome of immunotherapy trials
has been altogether disappointing (1, 2). Several reasons have
been put forward to explain such phenomenon like tumor
escape from and alterations of the immune response caused by
the presence of growing tumor cells (3).
Less attention has been paid, however, to the nature of
TAAs to be used in vaccine formulation. In fact, practically all
the trials of immunotherapy of cancer (by and large of
vaccination) conducted during the last 10 years were based on
the use of TAAs encompassing normal proteins or peptides, to
generate antitumor T cells mostly restricted by class I HLA (4).
These TAAs are now known to be weakly immunogenic owing
to different forms of tolerance to them displayed by the
patients’ immune system. Moreover, several of these self-TAAs
have been shown to be heterogeneously expressed within the
tumor mass (5) and selected against by CTLs during tumor
growth allowing an immunologically unrestricted progression
of the neoplasia (6, 7). Thus, the search for new, tumor-
specific and immunogenic TAAs constitutively linked to the
neoplastic state and, therefore, unselectable by the patient
immune reactions, remains an important issue in tumor
Truly tumor-specific TAAs are those expressed only by tumor
cells and not by whatsoever normal cells. Such TAAs may derive
(a) from somatic gene mutations of tumor cells resulting in
new TAA epitopes recognized by the host T lymphocytes, like
the unique TAAs (8, 9), or less frequently, (b) from alterations
in splicing (10–12). Unique TAAs are now being frequently
found in several human tumors, although their use in clinical
trials is difficult for the time required to characterize unique
TAAs at a single patient level (8, 9, 13).
Universaland Cancer Stemness-RelatedTAAs as
Potentially More EffectiveTargets in
Recently, another group of TAAs was described that include
antigens overexpressed by neoplastic and fetal cells, and was
weakly expressed in a phase-specific way in a few normal cells
(14, 15). Such TAAs have the remarkable feature of being
indispensable for tumor growth and progression. Immune
responses targeting these proteins could thus result in a limited
or no generation of antigen-loss variants and, therefore, they
may efficiently control in vivo tumor growth, thus meeting the
requirements for an ideal TAA set forth above. These are the
so-called universal TAAs and include molecules like human
telomerase reverse transcriptase (hTERT) and the inhibitor of
apoptosis proteins (IAP).
An additional group of TAAs, practically unknown at the
moment, includes those that might be expressed by cancer stem
cells (CSC), a minor population of tumor cells which, however,
shows the features of stemness (see ref. 16) and, therefore, may
represent the most important target for eradicating tumor
lesions even in case of immunotherapy. It is, therefore,
mandatory to identify TAAs or other cell surface molecules
(e.g., natural killer cell–activating receptors) of CSCs in order
to assess whether they can represent a new target for the host
immune system. Our prediction is that at least some of the CSC
antigens will match proteins already known to serve as TAAs
and expressed by embryo-fetal tissues (e.g., survivin, telomer-
ase, cancer/testis antigens) reflecting common functions be-
tween embryonic stem cells and CSCs, i.e., multipotent
differentiation, plasticity, and self-renewal. However, because
these TAAs are expressed even by the majority of cancer cells
of a given tumor, while CSCs encompass a small subpopulation
of the tumor mass, CSCc may represent a better target if
specifically enriched in cancer/testis, IAP-derived and/or
mutated (unique) antigens in parallel with stem cell markers
(e.g., CD44, CD133), in comparison with other tumor cells
showing a more disperse concentration of such TAAs (17).
Therefore, immune-mediated tumor regression should reflect
a qualitative rather than a quantitative targeting aimed at
eliminating a specific, minor subpopulation of tumor cells, i.e.,
CSC, rather than the majority of neoplastic cells. If so, this will
represent a new paradigm in the immunotherapy of human
The Universaland CSC-DerivedTAAs:Tissue
Distribution and Immune Functions
The universal TAAs have been well-defined because of their
wide distribution in human tumors of different histology, and
Authors’Affiliations:1Department of Oncology, San Raffaele Scientific Institute
and2Departmentof Experimental Oncology, Istituto NazionaleTumori, Milan, Italy
Received 4/12/07; revised 6/15/07; accepted 7/2/07.
Grant support: Associazione Italiana Ricerche sul Cancro (Milan), the European
Community FP5 (Brussels), the Italian Ministryof Health (Rome).
The costs of publicationof this articlewere defrayedinpart by the paymentof page
charges.This article must therefore be hereby marked advertisement in accordance
with18 U.S.C. Section1734 solely toindicatethis fact.
Requests for reprints: Giorgio Parmiani, Department of Oncology, San Raffaele
Scientific Institute, Milan, Italy. E-mail: email@example.com.
F2007 American Association for Cancer Research.
www.aacrjournals.orgClin Cancer Res 2007;13(19) October1, 2007 5675
due to the general and fundamental functions they exert in
tumor biology, i.e., that of maintaining an effective proliferation
and resistance to apoptosis, thus contributing to cancer cell
progression and survival (Fig. 1). CSCs should also express
universal TAAs together with most cells of the tumor mass, as
suggested by immunohistochemical analysis, which reveals the
presence of hTERT and IAPs (e.g., survivin) in the large majority
of tumor cells (15, 18). However, whether CSCs are endowed
with the ability to mount IAP-derived epitopes on their HLA is
being tested in ongoing studies. Preliminary findings suggest
that CSCs show a variable, but in general, low expression of HLA
on their surface.3Moreover, if the CSC target molecules are also
present in normal stem cells, potential damage to normal tissues
may occur. Therefore, CSC-selective elimination by immune
responses should be based either on new CSC-specific targets
resulting from somatic alterations/mutations of CSC genes that
do not occur in normal stem cells, or in an enrichment of
molecules, like the universal TAAs, that in normal stem cells
cannot represent a valuable target whereas mediating a T cell
cytotoxicity on neoplastic counterparts (14, 15).
Universal TAAs have recently been assessed in preclinical
in vitro studies for their ability to generate T cell–specific
immune responses (see ref. 19). Repeated stimulations of
peripheral blood lymphocytes from both healthy donors and
cancer patients with APCs pulsed with HLA-I restricted epitopes,
entire proteins, or mRNAs encoding the antigens has made it
possible to detect CD8+and CD4+T cell spontaneous and/or
induced responses against survivin, livin, hTERT, and Bcl-2
(19–25). Importantly, these effectors recognize HLA-matched
tumor cells, which endogenously process the antigens, but not
normal cells (e.g., CD34+ hematopoietic precursors, activated
T and B cells; ref. 18). Moreover, ex vivo studies have shown a
significant frequency of functional CTLs directed against
hTERT among peripheral blood lymphocytes of a proportion
of cancer patients as well as the presence of survivin-specific
CTLs in tumor-invaded lymph nodes (26, 27). All these features
make universal TAAs suitable targets for cancer immunother-
apy, although a screening of single patients to analyze their
capacity to mount an anti-hTERT immune response seems
By applying the reverse immunology approach, several
peptides binding different HLA alleles have been recently
identified in survivin, livin, and hTERT proteins. Some of these
peptides have been shown to function as T cell epitopes being
able to induce peptide-specific T cells in patients’ peripheral
blood mononuclear cells (see ref. 19). However, an additional
crucial issue that needs to be addressed in order to consider a
defined peptide as useful for a therapeutic approach is its ability
to elicit T cells that can recognize the naturally processed
peptide on tumor cells expressing the target protein and the
appropriate HLA molecule. Although this requirement has been
met for a majority of the identified peptides, for some, doubts
on the efficiency of their presentation by tumor cells still
remain (28, 29). An example of such a phenomenon has been
reported for the hTERT peptide 540-548, which although being
processed by human cells when transfected with hTERT
encoding cDNA, was only marginally produced by tumor-
derived proteasomes (29). In view of these observations, the
functional properties of T cells elicited by immunogenic
peptides should always be analyzed on a large panel of tumor
cells of different histologies.
Fig.1. Functionsofsurvivin, livin, and telomeraseincancercells.Survivinandlivinare IAPs thatinterferewiththeapoptoticprocess by blockingupstream caspase-9 activity
and/or the final downstream effector step of caspase-3 and caspase-7 as well as by binding the mitochondrialprotein Smac (left). Survivin can also favor tumor cell mitosis
by localizing mostly to centrosomes and microtubules whose regular assembly is also dependent on the presence of this IAP (middle).Telomerase is a RNA-dependent
polymerase that allows the maintenance of chromosome length and stability in tumor cells, whichin turn can divide indefinitely. It includes repeated DNA sequences
(TTAGGG) and associated proteins. RNA antisense and other inhibitors canblock telomerase activity and allows only a limited number or divisions to tumor cells (right).
3Maccalli C, Galli R, Parmiani G, unpublished results.
www.aacrjournals.orgClin Cancer Res 2007;13(19) October1, 2007 5676
ClinicalTrials with UniversalTAAs
Although the central role of universal TAAs in malignant
transformation and cancer progression and their immunoge-
nicity have been established, only a limited number of
vaccination protocols targeting IAPs have been and are being
carried out (Table 1). The following is a brief summary of such
In a pilot study, patients with chemotherapy-resistant
metastatic breast cancer or hormone-resistant prostate cancer
received ex vivo–generated autologous dendritic cells (DC)
pulsed with the HLA-A*0201–restricted hTERT I540 peptide
together with keyhole limpet hemocyanin (28). Among six of
the seven evaluable patients, a mixed clinical response was seen.
In these patients, prevaccination and postvaccination immuno-
histochemical analyses of skin nodules showed a lymphoid
infiltrate predominantly made of CD8+T cells, but no
information on the function of these tumor-infiltrating lym-
phocytes was reported. A specific T cell response against hTERT
was detected in the uncultured peripheral blood mononuclear
cells of three patients. After 1 week of in vitro peptide
sensitization, CD8+tetramer+T cells were seen in four patients.
These CTL populations contained clones that were able to
recognize and lyse hTERT expressing HLA-A*0201 cancer cells.
A peptide-based approach of immunotherapy was carried
out by Parkhurst and coworkers using the same epitope
emulsified in Montanide ISA51 but achieving opposite results
(29). None of the 14 patients with metastatic melanoma
developed a CTL response recognizing endogenously processed
telomerase target cell, even though high-avidity T cell clones
were obtained. Furthermore, no clinical benefits were observed
in these patients.
Other hTERT-derived class I and class II epitopes given
together with different adjuvants have been tested in patients
with progressive and chemotherapy-unresponsive tumors. Both
native and modified peptides have proved to be safe, showing
their ability to induce a specific immune response without
causing any sign of hematological toxicity on the blood stem
cell compartment. For example, Gaudernack and coworkers
treated lung and pancreatic cancer patients with HR2822
(540-548) and GV1001 (611-626) hTERT-derived epitopes
(30, 31). The latter is a promiscuous HLA class II epitope that
has been shown to induce a strong CD4+T cell response able to
generate and sustain a CTL response. The immunologic res-
ponder patients showed a tendency for a prolonged survival as
compared with historical controls. This seems to be important
considering the aggressiveness and the immune-suppressive
activity that characterizes these tumors.
In the effort to overcome the problems of altered antigen
processing, hTERT mRNA was used to transfect metastatic
prostate cancer–derived DCs (22). In a subgroup of patients, a
chimeric transcript made of the lysosomal-associated mem-
brane antigen-1 was fused to the target antigen, thus improving
the generation of CD4+T response. Although no clinical
benefits were achieved in either group, transient and short-
lasting effects on prostate-specific antigen doubling times were
obtained in some patients.
In the attempt to develop a polyvalent vaccine targeting both
patient-specific tumor and stromal targets, total RNA derived
from renal tumor tissue was used to transfect patients’
autologous DCs (32). Although no assessment of the thera-
peutic effect could be made, a strong immunologic response
against hTERT was elicited.
Clinical experience on the use of survivin in tumor
vaccination trials is limited to few studies (19), despite the
development of a spontaneous immune response to such an
antigen, which seems to be quite common in patients with
cancer. A modified HLA-A*0201 epitope of survivin (96-104,
2M) has been used to vaccinate stage IV melanoma patients
with DC as adjuvant (33). Four out of five patients mounted a
specific antisurvivin immune response detected both in the
peripheral blood and in metastatic lesions showing the ability
of the vaccine-induced CD8+T cell population to home into
peripheral tumor tissues. At the same time, these patients
experienced an unexpected long survival.
In a phase I trial, eight patients with hormone-refractory
prostate cancer received autologous DCs pulsed with HLA-
A*0201–restricted epitopes derived from prostate cancer–
associated antigens and survivin (95-104; ref. 34). In this trial,
the strongest reduction of prostate-specific antigen plasma
levels was observed in the four patients (one with partial
remission and three with stable disease) developing specific
CD8+T cell–mediated immune response, only two of whom,
however, directed against the survivin epitope.
In our centers (Istituto Nazionale Tumori, San Raffaele
Scientific Institute), clinical trials involving vaccination with
Table 1. Clinical trials involving the use of universal TAAs
AntigenTumor No. of patientsImmune responders Clinical outcome Reference
hTERT mRNA loaded DCs
2/24 (for 540-548)
13/24 (for 611-626)
1 PR, 3 SD
Abbreviations: ND, not determined; NSCLC, non–small cell lung cancer; CR, complete remission; NE, not evaluable; GM-CSF, granulocyte
macrophage colony-stimulating factor; OS, overall survival; PR, partial remission; SD, stable disease.
*Mixed responses only.
cIncreased long-term survival without statistical assessment.
www.aacrjournals.orgClin Cancer Res 2007;13(19) October1, 2007 5677
peptides derived from survivin are presently ongoing. These
trials are based on the administration of multiple HLA-
A*0201–restricted peptides derived from differentiation anti-
gens and cyclophosphamide aimed at reducing the in vivo effect
of regulatory T cells. This approach is under evaluation in early
stage melanoma, prostate cancer patients with biochemical
failure after conventional treatments (receiving PSMA and
survivin-derived peptides), and in locally recurrent rectal
carcinoma (with carcinoembryonic antigen and survivin-
derived epitopes). Preliminary immunologic analysis shows
that a significant boost of T cells specific for all the adminis-
tered peptides, including survivin, could be detected in both
PBLs and in draining lymph nodes.4
Altogether, these early clinical trials have enrolled a limited
number of patients and are too heterogeneous in terms of
vaccine formulation and tumor targets to allow any meaningful
conclusion on the clinical efficacy of immunizations based on
universal TAAs. Further results of ongoing phase II studies with
a larger number of patients are eagerly awaited in order to
assess the importance of this approach for cancer therapy.
From the studies on universal TAAs, we have learned that
such antigens are, more than any other TAAs, frequently
expressed in many different human tumors and, therefore, they
apparently provide the most common, neoplasia-related and
easily identifiable immune target. Upon closer examination,
however, it remains to be established whether hTERT is more
immunogenic for T cells of cancer patients as compared with
other TAAs obtained from the same tumor as suggested by Su
and coworkers in renal cell carcinoma patients vaccinated with
tumor RNA pulsed DCs (22). In fact, a different study found
that the frequency of HLA-A2–restricted T cell precursors
against hTERT peptide was similar in cancer patients and in
normal donors (35).
As for survivin, cancer patients were shown to have
spontaneous T cell responses against survivin peptides (27)
and we have also shown that anti-survivin T cell precursors are
detectable in cancer patients but not in normal individuals
(24); importantly, such T cells were found to recognize tumor
cells expressing survivin. These findings suggest that survivin
may be strongly immunogenic in at least a fraction of patients.
Whether these antigens might also actually represent a
significant target for CSCs is unknown at the moment.
However, the study of the immunogenic potential of universal
TAAs is worth pursuing because it may pave the way for in vitro
and in vivo characterization of similar, if not identical, TAAs
expressed by CSCs; thus allowing their use as targets in future
trials of cancer immunotherapy. The presence of CSCs in the
tumor mass may change the whole paradigm of cancer
immunotherapy with the need for preparing T and/or natural
killer cell effectors and/or antibodies able to recognize and
preferentially destroy the small CSC subpopulation, rather than
a huge number of lymphocyte effectors aimed at targeting as
many tumor cells as possible. Because the markers (antigens?)
which have thus far been reported to characterize different
types of CSC (e.g., ESA, CD44, CD133; refs. 16, 36–47) seem
to be normal molecules involved in the process of cell adhesion
and migration, it is likely that such molecules may be more
easily targeted by antibodies than by antigen-specific T cells. In
fact, an antibody against CD44 has recently been shown to
eradicate xenografted human acute myelogenous leukemia
stem cells, possibly by interfering with the CSC-supporting
microenvironment (48). The anti-CSC function of T cells,
however, cannot be completely discarded. In fact, one of CSC’s
most common markers, ESA (Ep-CAM; refs. 16, 39), has been
shown to contain epitopes that can be recognized by class I
HLA–restricted T cells (49), and which has been used to
vaccinate colorectal cancer patients, although with limited
success (50). In this context, vaccines containing T cell–defined
universal and CSC TAAs and their combination with antibodies
targeting the cell surface molecules expressed by CSCs (e.g.,
CD44) may be much more effective than those including self-
TAAs previously used in cancer vaccination.
4Rivoltini L, Castelli C, Parmiani G, unpublished results.
www.aacrjournals.org Clin Cancer Res 2007;13(19) October1, 20075678
1. Parmiani G, Castelli C, Dalerba P, et al. Cancerimmu-
notherapy with peptide-based vaccines: what have
we achieved? Where are we going? JNatl CancerInst
2. Rosenberg SA,YangJC, Restifo NP. Cancerimmuno-
therapy: moving beyond current vaccines. Nat Med
and reasons for failure in the interaction between
tumour cells and the immune system: how can we tilt
the balance towards immune-mediated cancer con-
trol? Expert Opin BiolTher 2005;5:463^76.
tumorantigens recognizedbyTcells: March 2004up-
5. Anichini A, Fossati G, Parmiani G. Heterogeneity of
clones from a human metastatic melanoma detected
by autologous cytotoxicT lymphocyte clones. J Exp
6. MaeurerMJ, Gollin SM, Martin D, et al.Tumorescape
from immune recognition: lethal recurrent melanoma
in a patient associated with downregulation of the
peptide transporter proteinTAP-1and loss of expres-
sion of the immunodominant MART-1/Melan-A anti-
gen. JClin Invest1996;98:1633^41.
7. Boon T, Coulie PG, Van den Eynde BJ, van der
Bruggen P. HumanTcellresponses againstmelanoma.
8. Sensi M, Anichini A. Unique tumor antigens: evi-
dence forimmune controlof genomeintegrityandim-
munogenic targets forTcell-mediated patient-specific
immunotherapy. Clin Cancer Res 2006;12:5023^32.
9. Parmiani G, De Filippo A, Novellino L, Castelli C.
Unique human tumor antigens: immunobiology and
usein clinical trials. JImmunol 2007;178:1975^9.
10. GuillouxY, Lucas S, Brichard VG, et al. A peptide
recognized by human cytolytic T lymphocytes on
of the N-acetylglucosaminyltransferaseVgene. JExp
11. Robbins PF, El-Gamil M, Li YF, Fitzgerald EB,
KawakamiY, Rosenberg SA.Theintronic region ofan
incompletely spliced gp100 gene transcript encodes
an epitope recognized by melanoma-reactive tumor-
12. Lupetti R, Pisarra P,Verrecchia A, et al.Translationof
a retained intron in tyrosinase-related protein (TRP)
2 mRNA generates a new cytotoxicT lymphocyte
(CTL)-defined and shared human melanoma antigen
not expressed in normal cells of the melanocytic line-
age. JExp Med1998;188:1005^16.
13. LennerzV, Fatho M, Gentilini C, et al.The response
edby mutatedneoantigens. Proc Natl Acad Sci US A
Altieri DC. Developmentally regulated expression of
the novel cancer anti-apoptosis gene survivin in hu-
man and mouse differentiation. Am J Pathol 1998;
15. Altieri DC, Marchisio PC. Survivin apoptosis: an in-
terloper between cell death and cell proliferation in
cancer. Lab Invest1999;79:1327^33.
16. Dalerba P, Cho RW, Clarke MF. Cancer stem cells:
17. Gedye C, Quirk J, Browning J, et al. Melanoma
stem-like cells can be eliminated by targeting cancer/
testis antigens. Keystone Symposia: Stem Cells and
Universaland Stemness-RelatedTumorAntigens Download full-text
www.aacrjournals.org Clin Cancer Res 2007;13(19) October1, 20075679
18.Vonderheide RH, HahnWC, SchultzeJL, Nadler LM.
Thetelomerasecatalytic subunitis awidelyexpressed
tumor-associated antigen recognized by cytotoxicT
19. Andersen MH, BeckerJC, Straten P. Regulators of
apoptosis: suitable targets forimmune therapyofcan-
cer. Nat Rev Drug Discov 2005;4:399^409.
20. Minev B, Hipp J, Firat H, Schmidt JD, Langlade-
Demoyen P, Zanetti M. Cytotoxic T cell immunity
against telomerase reverse transcriptase in humans.
Proc Natl Acad Sci US A 2000;97:4796^801.
21. Schmitz M, Diestelkoetter P,Weigle B, et al.Genera-
tion of survivin-specific CD8+ Teffector cells by den-
dritic cells pulsed with protein or selected peptides.
Cancer Res 2000;60:4845^9.
of telomerase-specific CD4(+) Tcells using dendritic
cells transfected with RNA encoding a chimeric gene
product. Cancer Res 2002;62:5041^8.
23. Schroers R, Huang XF, HammerJ, Zhang J, Chen
CD4+ T-helper cells. Cancer Res 2002;62:2600^5.
24. Casati C, Dalerba P, Rivoltini L, et al.The apoptosis
inhibitor protein survivin induces tumor-specific
CD8+ and CD4+ Tcells in colorectal cancer patients.
Cancer Res 2003;63:4507^15.
25. SchmidtSM,SchagK,MullerMR,etal.Survivinis a
variety of malignancies and recognized by specific
cytotoxicTcells. Blood 2003;102:571^6.
26. Filaci G, Fravega M, Setti M, et al. Frequency of
telomerase-specific CD8+ T lymphocytes in patients
with cancer. Blood 2006;107:1505^12.
Becker JC, thor Straten P. Spontaneous cytotoxic
T-cell responses against survivin-derived MHC class
I-restrictedT-cell epitopes in situ as well as ex vivo in
cancer patients. Cancer Res 2001 ;61:5964^8.
28.Vonderheide RH, Domchek SM, Schultze JL, et al.
Vaccination of cancer patients against telomerase
induces functional antitumor CD8+ T lymphocytes.
Clin Cancer Res 2004;10:828^39.
29. Parkhurst MR, RileyJP, IgarashiT, LiY, Robbins PF,
Rosenberg SA. Immunization of patients with the
hTERT:540^548 peptide induces peptide-reactiveT
lymphocytes that do not recognize tumors endoge-
nously expressing telomerase. Clin Cancer Res 2004;
30. Brunsvig PF, Aamdal S, Gjertsen MK, et al.Telomer-
ase peptide vaccination: a phase I/II study in patients
with non-small cell lung cancer. Cancer Immunol
31. Bernhardt SL, Gjertsen MK,Trachsel S, et al. Telo-
merase peptide vaccination of patients with non-
resectable pancreatic cancer: a dose escalatingphase
I/IIstudy. BrJCancer 2006;95:1474^82.
32. Su Z, Dannull J,Yang BK, et al.Telomerase mRNA-
transfected dendritic cells stimulate antigen-specific
CD8+ and CD4+ Tcell responses in patients with
metastatic prostate cancer. J Immunol 2005;174:
33. Otto K, Andersen MH, Eggert A, et al. Lack of tox-
icity of therapy-induced Tcell responses against the
universal tumour antigen survivin.Vaccine 2005;23:
34. Fuessel S, MeyeA, Schmitz M, et al.Vaccination of
hormone-refractory prostate cancer patients with
peptide cocktail-loaded dendritic cells: results of a
phase Iclinical trial. Prostate 2006;66:811^21.
35.Vonderheide RH, Schultze JL, Anderson KS, et al.
Equivalent induction of telomerase-specific cytotoxic
T lymphocytes from tumor-bearing patients and
healthy individuals. Cancer Res 2001 ;61:8366^70.
36. LapidotT, Sirard C,VormoorJ, et al. A cell initiating
human acute myeloid leukaemia after transplantation
into SCIDmice. Nature1994;367:645^8.
38. Ponti D, Costa A, Zaffaroni N, et al. Isolation and
invitro propagationof tumorigenic breast cancercells
with stem/progenitor cell properties. Cancer Res
39. Dalerba P, Dylla SJ, Park IK, et al. Phenotypic char-
acterization of human colorectal cancer stem cells.
Proc Natl Acad Sci US A 2007;104:10158^63.
40. Fang D, NguyenTK, LeishearK, et al. Atumorigenic
subpopulation with stem cell properties in melano-
mas. Cancer Res 2005;65:9328^37.
41. Galli R, Binda E,Orfanelli U, et al. Isolationandchar-
acterization of tumorigenic, stem-like neural precur-
sors from human glioblastoma. Cancer Res 2004;64:
42. Patrawala L, CalhounT, Schneider-Broussard R,
xenograft human tumors are enriched in tumorigenic
and metastatic progenitor cells. Oncogene 2006;25:
cell-like characteristics and Mullerian inhibiting sub-
stance responsiveness. Proc Natl Acad Sci U S A
44. Li C, Heidt DG, Dalerba P, et al. Identification of
pancreatic cancer stem cells. Cancer Res 2007;67:
45. O’Brien CA, Pollett A, GallingerS, DickJE.Ahuman
colon cancer cell capable of initiating tumour growth
inimmunodeficient mice. Nature 2007;445:106^10.
tificationofa subpopulationof cells with cancer stem
48. Jin L, Hope KJ, Zhai Q, Smadja-Joffe F, Dick JE.
Targeting of CD44 eradicates human acute myeloid
leukemic stem cells. Nat Med 2006;12:1167^74.
49. Nagorsen D, Keilholz U, Rivoltini L, et al. Natural
T-cell response against MHC class I epitopes of epi-
thelial cell adhesion molecule, her-2/neu, and carci-
noembryonic antigen in patients with colorectal
cancer. Cancer Res 2000;60:4850^4.
virus-derived KSA (Ep-CAM) formulated withmono-
phosphoryl lipid A in liposomal emulsion, with and
without granulocyte-macrophage colony-stimulating