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Can Promote Tumor Evasion of the Immune System In Vivo by Down-Regulating Cellular Levels of an Endogenous Tumor Antigen1
Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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has been generally thought to enhance antitumor
immune responses, we found that IFN- can promote tumor escape in the
CT26 colon carcinoma by down-regulating the protein expression of an
endogenous tumor Ag. gp70, the env product of the endogenous ecotropic
murine leukemia virus, has been reported to be the immunodominant Ag of
CT26. We show that IFN- down-regulates intracellular and surface
levels of gp70 protein resulting in a reduced lysis by CTL, which is
restored by pulsing IFN--treated CT26 with the
Ld-restricted immunodominant AH1 epitope derived from gp70.
To investigate the role of CT26 sensitivity to IFN- in vivo, we
constructed two variants of CT26, CT26.mugR and CT26.IFN, that are
unresponsive to IFN- or express IFN-, respectively. We
demonstrate using these variants that tumor responsiveness to IFN-
promotes a reduction in tumor immunogenicity in vivo that is correlated
with an increased tumor incidence in immune mice. Analysis of the
tumors from mice challenged with CT26 or CT26.mugR revealed
infiltration of CD8 T cells secreting IFN-. We conclude that IFN-
secreted by tumor-infiltrating T cells promotes tumor escape through
the down-regulation of the endogenous tumor Ag gp70. These findings
have impact on the design of effective antitumor vaccine
strategies. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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, or PGE2) (4, 5),
up-regulation of antiapoptotic molecules (e.g., Bcl-2 or
Bcl-xL) (6, 7, 8), or expression of Fas ligand
(9, 10). Thus, a challenge for immunotherapeutic
approaches to cancer is the generation of an immune response effective
in countering these strategies of immune evasion.
IFN- has been recognized as a critical cytokine involved in
effective antitumor immune responses. Depletion of IFN- in several
tumor models eliminates the effectiveness of a particular therapeutic
strategy (11, 12). The effectiveness of IFN- in these
therapies has been attributed to its ability to up-regulate MHC class I
expression and other Ag presentation components (1),
induce chemokines that inhibit angiogenesis (e.g., monokine induced by
IFN- and IFN-inducible protein 10) (13, 14), and
down-regulate the expression of immunosuppressive molecules secreted by
tumors (15, 16). Recently, several investigators have
identified the importance of tumor cell responsiveness to IFN- for
the effectiveness of tumor-based vaccine strategies and IL-12 therapy.
Tumor cell unresponsiveness to IFN- reduces the immunogenicity of
such tumor cells in vivo (17). In addition, tumor cell
responsiveness to IFN- is critical for the effectiveness of IL-12 to
inhibit angiogenesis within the tumor (18).
We chose to analyze the role of tumor cell responsiveness to IFN- in
the murine CT26 colon carcinoma model where the immunodominant tumor Ag
is reported to be gp70, an envelope glycoprotein of an endogenous
ecotropic murine leukemia virus (19). Surprisingly, we
found that IFN- promotes tumorigenicity despite its ability to
up-regulate MHC class I expression. We found that this increase in
tumorigenicity correlated with a down-regulation of gp70 protein levels
promoted by IFN-. We demonstrate here the first report where IFN-
secreted by tumor-infiltrating T cells promotes tumor escape through
the down-regulation of an immunodominant endogenous tumor Ag.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Female BALB/c mice, 6–8 wk of age, were purchased from Charles River Laboratories (Wilmington, MA). CT26 is an N-nitroso-N-methylurethane-induced colon carcinoma (20) that is syngeneic to BALB/c. EL4 is a carcinogen-induced lymphoma syngeneic with C57BL/6. Both cell lines were cultured in RPMI 1640 containing 10% FCS and penicillin/streptomycin. In addition, 0.05 mM 2-ME was added to EL4 cultures.
Transfections and retroviral infections
The plasmids pEF2.mugR and pL(mIFN-KDEL)SN were contributed
by William Lee (University of Pennsylvania, Philadelphia, PA). The
expression plasmid pEF2.mugR contains a truncated murine IFN-R
cDNA under the control of the eukaryotic translation elongation factor
1 promoter (18, 21). To create CT26 cells expressing
this mutant IFN-R, parental cell lines were transfected with
pEF2.mugR using Lipofectin reagent (Life Technologies, Grand Island,
NY). G418-resistant cells were sorted by flow cytometry for cells
overexpressing IFN-R and subsequently maintained in medium
containing G418. The retroviral vector pL(mIFN-KDEL)SN contains a
mutant mIFN- containing the carboxyl-terminal endoplasmic reticulum
retention signal Lys-Asp-Glu-Leu (KDEL) inserted into the retroviral
vector LXSN (22, 23). The pL(mIFN-KDEL)SN vector was
transfected into the BOSC-23 packaging cell line by standard calcium
phosphate coprecipitation, and the 24-h culture supernatant was used to
infect CT26 cells for 4 h in the presence of polybrene (4
µg/ml). G418-resistant clones were then analyzed for reduced
expression of cell surface gp70 by flow cytometry.
Detection of gp70 protein by Western blot
Lysates were generated by resuspension of cells in lysis buffer (50 mM Tris-HCl (pH 8.0), 150 mM NaCl, 0.1% SDS, 1% Triton X-100, and 20 µg/ml PMSF). The total protein levels of cleared lysates were determined using the Bio-Rad Dc Protein Assay (Bio-Rad, Richmond, CA). Samples (25 µg of total protein) were boiled for 3 min at 95°C in reducing buffer (0.125 M Tris-HCl (pH 6.8), 4% SDS, 0.005% bromophenol blue, 20% glycerol, and 0.7 M 2-ME) before being analyzed by electrophoresis in 4–12% Tris-glycine precast gels (NOVEX, San Diego, CA). After electrophoresis, proteins were transferred to PolyScreen polyvinylidene difluoride transfer membranes (NEN Life Science Products, Boston, MA) using a Bio-Rad semidry transfer cell. Probing of blots was conducted using Vectastain ABC Rat IgG peroxidase kit (Vector Laboratories, Burlingame, CA). Probed blots were developed using enhanced chemiluminescence Western blotting detection reagents (Amersham Pharmacia Biotech, Arlington Heights, IL) and were analyzed by autoradiography.
Cell-mediated cytotoxicity assay
For the generation of CT26-specific CTLs, mice were immunized
with 2 x 106 irradiated (15,000 rad) CT26
cells on day 0 and challenged with 5 x 105
CT26 on day 21. Single-cell suspensions of splenocytes from mice
remaining tumor free for 60 days were prepared, and RBC were removed by
NH4Cl treatment. Splenocytes were cultured at
4 x 106/ml with 2 µM AH1 peptide in RPMI
1640 containing 10% FCS, penicillin/streptomycin, and 2-ME (0.05 mM).
After 6 days, responder cells were harvested, washed twice, and
incubated with 51Cr (1 mCi/ml; NEN)-labeled CT26,
CT26 treated with mIFN- for 3 days at 1000 U/ml, or MHC class
I-mismatched EL4 cells at different E:T cell ratios. Where indicated,
target cells were incubated for 30 min at 37°C with AH1 peptide and
washed with medium before addition of responders. Following an
incubation period of 4 h, supernatants were assayed for
radioactivity using a Wallac 1450 MicroBeta liquid scintillation
counter (Wallac, Gaithersburg, MD). The percentage of specific lysis
was calculated as [(sample cpm - spontaneous cpm)/(maximal
cpm - spontaneous cpm)] x 100%. All assays were performed in
quadruplicate. Spontaneous release was <15%.
Ags, mAbs, and cytokines
The AH1 peptide (SPSYVYHQF) is the class I
Ld immunodominant epitope recognized within gp70
(19) and was provided by Drew Pardoll (Johns Hopkins
University, Baltimore, MD). The E7 peptide (RAHYNIVTF) is a class I
Db epitope from the human papilloma virus E7
protein (24). Abs against CD62 ligand
(CD62L;3 clone
MEL-14), CD8.2 (clone 53-5.8), CD45 (clone 30-F11), IFN-R
(clone GR.20), and murine IFN- (clone XMG1.2) were purchased from
PharMingen (San Diego, CA). Secondary goat anti-rat FITC IgG and
goat anti-mouse IgG FITC Abs were purchased from Sigma (St. Louis,
MO). The 28-14-8S hybridoma (anti-Ld) was
obtained from American Type Culture Collection (Manassas, VA)
(2). The 35/299 hybridoma (-gp70) was a gift from Drew
Pardoll (Johns Hopkins University) and expresses a rat IgG2a mAb
specific for gp70 (25). 35/299 and 28-14-8S hybridoma
supernatants were purified over a protein G column (Amersham Pharmacia
Biotech). Recombinant murine IFN- was purchased from Genzyme
(Cambridge, MA).
Flow cytometry
To determine surface expression of murine IFN-R, cells
were stained with primary monoclonal rat anti-IFN-R Ab and
secondary goat anti-rat IgG FITC-conjugated Ab. Surface expression
of MHC class I Ld was determined using purified
28-18-8S (anti-Ld) Ab and secondary goat
anti-mouse IgG FITC Ab.
Intracellular cytokine expression
For assessment of tumor immunogenicity, irradiated (15,000 rad)
tumor cells (5 x 106) were s.c. inoculated
into BALB/c mice. Ten days later, single-cell suspensions of
splenocytes from immunized mice were prepared, and RBC were removed by
NH4Cl treatment. Splenocytes were cultured at
4 x 106/ml with 2 µM AH1 peptide in RPMI
1640 containing 10% FCS, penicillin/streptomycin, and 2-ME (0.05 mM).
After 6 days, responder cells were harvested, washed, and restimulated
with 2 µM AH1 or 2 µM E7 control peptide for 5 h in the
presence of brefeldin A. For detection of cytoplasmic cytokine
expression, cells were stained with PE-anti-CD8 mAb and
APC-anti-CD62L mAb, fixed and permeabilized with Cytofix/CytoPerm
solution (PharMingen), and stained with FITC-conjugated
anti-IFN- mAb for 30 min on ice. The percentage of cells
expressing cytoplasmic IFN- was determined by flow cytometry
(FACScalibur; Becton Dickinson, Mountain View, CA).
Vaccinations and tumor growth
Irradiated (15,000 rad) CT26 (2 x 106) cells were inoculated s.c. into the right flank of BALB/c mice. After 21 days, mice were challenged with 5 x 105 CT26 or CT26.mugR cells s.c. in the left flank. Alternatively, mice were immunized i.p. with a recombinant vaccinia construct containing the full-length gp70 gene that was a gift from Drew Pardoll (Johns Hopkins University). After 28 days immunized mice were challenged with 5 x 104 CT26 or CT26.mugR cells s.c. in the left flank. Mice were monitored three times per week for the development of tumor nodules. In each experiment, eight mice were used per group.
Processing of tumors for ex vivo analysis
Tumors of 10 mm in diameter were excised, processed in PBS containing 1 mg/ml DNase I (Life Technologies), 2 mg/ml collagenase P (Roche, Indianapolis, IN), and penicillin/streptomycin for 1 h at 37°C as previously described (26). For analysis of intracellular cytokine expression, 2 x 106 cells were cultured per well in a 96-well round-bottom plate for 7 h in the presence of brefeldin A. Tumor cells were analyzed for gp70 expression by gating on CD45-negative cells.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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reduces tumor lysis by CTL
We undertook this study to determine whether IFN- would enhance
the susceptibility of CT26 to recognition and lysis by tumor-specific
CD8+ CTL. The dominant tumor Ag recognized on
CT26 is gp70, an envelope protein of the endogenous murine leukemia
virus. Previous work has demonstrated that the immunodominant epitope
recognized within gp70 is AH1, a peptide nonamer presented in the
context of MHC class I Ld (19). As
shown in Fig. 1
A, IFN-
enhances the expression of the MHC class I molecule
Ld. Nevertheless, treatment of CT26 cells with
IFN- for 3 days markedly reduced the level of CT26 lysis by
AH1-specific CTL (Fig. 1B). Recognition and lysis of
IFN--treated CT26 were restored by addition of the AH1 peptide,
indicating that loss of recognition was due to lack of AH1
presentation.
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down-regulates gp70 expression
We investigated the loss of AH1 presentation on CT26 cells
following treatment with IFN- by analyzing the ability of IFN- to
down-regulate gp70 protein levels. The gp70 envelope protein is
normally expressed at modest levels on the cell surface of CT26. As
shown in Fig. 2A, treatment of
CT26 with IFN- results in the loss of gp70 expression from the cell
surface. Analysis of cell supernatants by Western blot demonstrated
that this loss in gp70 surface expression is not due to shedding of the
protein into the surrounding medium (data not shown). Rather, loss of
surface expression is a result of reduced total gp70 protein levels, as
shown in Fig. 2B. Analysis of gp70 protein levels by Western
blot revealed two molecular species, with the more slowly migrating
product representing the gp70 protein. The other molecular species that
migrates faster in the gel has previously been observed
(27). This product, which probably represents
nontranslocated, cytoplasmic gp70 polypeptides, lacks
N-linked oligosaccharides as well as inter- or
intramolecular disulfide bonds and is rapidly degraded in vivo
(27). Our results indicate that this molecular species is
not processed for presentation to CTL (Fig. 1
B).
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promotes tumor escape in vivo
Since CT26 responsiveness to IFN- reduces the level of
recognition by AH1-specific CTL, we hypothesized that CT26 cells
rendered unresponsive to IFN- may be rejected more efficiently than
IFN--responsive CT26 cells in immune mice. To test this hypothesis,
we took advantage of a dominant negative mutant of IFN-R that has
been described previously (17, 18). By overexpressing this
mutant in CT26 we generated cells designated CT26.mugR that present
high levels of a truncated form of the IFN-R -chain at the cell
surface (Fig. 3A). These cells
are unresponsive to IFN-, as shown by the inability of IFN- to
down-regulate gp70 surface expression (Fig. 3B). We next
compared the levels of tumorigenicity of CT26 and CT26.mugR in immune
mice. BALB/c mice were immunized with 2 x
106 irradiated CT26 cells s.c. in the right flank
and 3 wk later were challenged with 5 x 105
cells of either CT26 or CT26.mugR. As shown in Fig. 4A, the onset of tumor growth
for naive animals challenged with either CT26 or CT26.mugR was the
same. However, CT26 immune animals were found to reject CT26.mugR more
efficiently than CT26. We also observed this same finding in mice
vaccinated with a recombinant vaccinia construct only expressing the
gp70 gene (Fig. 4B). These observations support our
hypothesis that tumor responsiveness to IFN- favors tumor outgrowth
in the CT26 model.
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reduces tumor immunogenicity in
vivo
Previous studies using tumor cells unresponsive to IFN-
demonstrated that these tumor cells display a decreased level of
immunogenicity in vivo. However, our findings would suggest that
unresponsiveness to IFN- might increase immunogenicity. To test the
role of tumor responsiveness to IFN- on tumor immunogenicity in
vivo, we constructed an additional variant of CT26 that overexpresses
IFN- (CT26.IFN). This variant was constructed by transducing CT26
with a retroviral vector coding for a mutant IFN- containing the
carboxyl-terminal endoplasmic reticulum retention signal
Lys-Asp-Glu-Leu (KDEL). Inclusion of the KDEL signal sequence anchors
IFN- in the endoplasmic reticulum (22, 23). Therefore,
IFN- signaling occurs only in the tumor cell, and no IFN- is
secreted from the cell. CT26.IFN displays a loss of gp70 expression at
both the surface and total protein levels, while exhibiting enhanced
expression of MHC class I Ld as shown in Fig. 5. We compared the level of
immunogenicity of CT26, CT26.mugR, and CT26.IFN in vivo by immunizing
mice with 5 x 106 irradiated tumor cells.
As shown in Fig. 6A, CT26.mugR
induced the highest level of AH1-specific CD8+
cells to secrete IFN- in a 5-h intracellular cytokine assay, while
CT26.IFN induced the fewest number of AH1-specific
CD8+ cells. These findings demonstrate that CT26
responsiveness to IFN- decreases the level of tumor immunogenicity
in vivo. A similar trend was observed using live tumor cells injected
s.c. (Fig. 6B). Although live tumor cells are less
immunogenic than irradiated tumor cells, their level of immunogenicity
is still inversely dependent on responsiveness to IFN-. In agreement
with this finding, we have also observed that immunization of mice with
irradiated CT26.IFN is less effective in protecting against challenge
with CT26 (Fig. 4A). Therefore, tumor responsiveness to
IFN- reduces immunogenicity in the CT26 model.
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by T lymphocytes infiltrating tumor
We hypothesized that if IFN- is the dominant factor regulating
gp70 expression in vivo, then ex vivo analysis of CT26 and CT26.mugR
tumors should reveal differential levels of gp70. To test this
hypothesis, BALB/c mice were challenged with 5 x
105 tumor cells s.c. and harvested when they
reached 10 mm in diameter. By flow cytometric analysis, gating on tumor
cells revealed that CT26 tumors had lost gp70 surface expression,
whereas gp70 surface expression was retained in CT26.mugR tumors (Fig. 7A). Further, preparation of
ex vivo tumor lysates revealed a marked down-regulation of total gp70
levels in CT26 compared with CT26.mugR tumors (Fig. 7B). We
sought to determine the source of the IFN- responsible for the loss
of gp70 expression in CT26 by analyzing ex vivo tumor homogenates. We
found by flow cytometry that mice challenged with CT26 and CT26.mugR
display a vast tumor infiltration of CD45-positive cells containing
CD8+, CD4+, and
MAC-1+ cells. We show here in Fig. 8 that tumor-infiltrating
CD8+ T cells secrete IFN- in both CT26 and
CT26.mugR. We have also observed secretion of IFN- by
tumor-infiltrating CD4+ cells, but not
MAC-1+ cells (data not shown). These findings
indicate that CT26 has evolved to evade an immune response by
down-regulating expression of the gp70 tumor Ag in response to tumor
infiltrating T lymphocytes secreting IFN-.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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increases MHC class I expression at the expense of reduced
tumor recognition and lysis by CTL. We demonstrate here that this loss
of recognition and lysis is explained by the ability of IFN- to
down-regulate the protein levels of the immunodominant tumor Ag gp70.
We investigated the significance of this observation in vivo by using
IFN--insensitive CT26 tumors to evaluate the role of tumor
responsiveness to IFN- for rejection in immune mice. Perhaps the
most significant observation of this study is the demonstration that
tumor responsiveness to IFN- reduces tumor immunogenicity in vivo.
This loss of immunogenicity is shown to be the result of a reduction in
gp70 expression in vivo in response to IFN- secretion by
tumor-infiltrating lymphocytes. As a result, immune mice display an
enhanced rejection of IFN--insensitive compared with
IFN--responsive CT26 tumors.
The findings reported in this study are the first to demonstrate a role
for tumor responsiveness to IFN- in promoting tumor escape in vivo.
Other tumor models have demonstrated the requirement of tumor
responsiveness to IFN- for therapeutic effectiveness. Dighe et al.
(17) demonstrated that sensitivity to IFN- in the MethA
tumor increases tumor immunogenicity in vivo. The authors explained
that MethA tumor cells are not inherently very immunogenic, but acquire
immunogenicity when exposed to host-derived IFN- in vivo. As a
result, established IFN--insensitive MethA tumors remain
unresponsive to treatment with LPS, whereas IFN--responsive tumors
are rejected. Similarly, Coughlin et al. (18) have shown
that tumor insensitivity to IFN- enhances tumorigenicity in vivo. In
this study tumor responsiveness to IFN- was required for the
effectiveness of IL-12 to slow tumor growth through inhibition of
angiogenesis. However, tumor responsiveness to IFN- was recently
shown not to be required for the ability of adoptively transferred
CD4+ T cells to induce tumor rejection
(28). Therefore, it is likely that both the form of immune
therapy adopted and the characteristics of the tumor targeted will be
important in determining the requirement for tumor responsiveness to
IFN-.
The gp70 protein was identified as a tumor Ag on CT26 by a method
involving the fractionation of tumor cell antigenic content and the
assaying of each fraction for recognition by tumor-specific CTL. This
method, using in vitro cultured CT26 cells as a source of Ag, led to
the identification of the AH1 antigenic epitope of gp70
(19). However, we have found that gp70 is differentially
expressed on freshly ex vivo isolated and in vitro cultured CT26 cells.
Our results demonstrating loss of Ag expression in vivo urge the use of
freshly isolated autologous tumor cells rather than cultured tumor cell
lines for identification of potential tumor rejection Ags. Indeed,
distinct CTL can often display differential activity against fresh and
cultured autologous tumor cells (29). In addition,
although previous work has described gp70 as the immunodominant tumor
Ag of CT26, our finding that vaccinia virus-expressing gp70 is
ineffective in providing protection against challenge with the parental
tumor suggests that gp70 may not be a good target for tumor
immunotherapy. These results further suggest the existence of other
potential CT26-specific rejection Ags, as enhanced protection is
provided with whole irradiated tumor cells. Nevertheless, the ability
of vaccinia-expressing gp70 to protect against challenge with an
IFN--resistant variant of CT26 implies that gp70 can act as a tumor
rejection Ag under these conditions. These results provide support for
IFN--dependent loss of endogenous tumor Ag expression as a mechanism
of tumor escape that is associated with decreased tumor
immunogenicity.
The ability of IFN- to regulate tumor immunogenicity in vivo has
previously been investigated in the MethA tumor model. In this system,
it was proposed that IFN- may induce a subset of proteasomes that
contains latent membrane protein-2 and -7, called the immunoproteasome,
which may be critical in enhancing immunogenicity (17).
However, recent work by Morel et al. (30) has demonstrated
that induction of the immunoproteasome by IFN- results in less
efficient processing of some tumor Ags, allowing for evasion of
recognition by CTL. In this study, in agreement with our results,
IFN- was found to decrease tumor immunogenicity. However, in
contrast to our findings, the majority of tumor Ags examined were not
significantly regulated by IFN- (30). Although we
cannot dismiss the possibility in the CT26 tumor model that induction
of the immunoproteasome by IFN- reduces efficient processing of the
AH1 epitope of gp70, we have shown that IFN- significantly
down-regulates gp70 to levels that would result in reduced CTL
recognition and lysis.
Loss of tumor Ag expression is recognized as a mechanism by which
tumors may escape immune recognition. In murine models, elimination or
down-regulation of entire genes encoding tumor Ags has been correlated
with decreased immunogenicity and increased tumorigenicity of Ag loss
variants (31, 32). In humans, several reports have
documented the loss of immunogenic tumor Ags during tumor progression
or following therapy. Mai et al. (33) reported two cases
of advanced prostatic adenocarcinoma following hormonal therapy,
showing complete loss of three tissue immunoreactive prostatic markers,
including prostate-specific Ag. In melanoma, loss of the targeted Ags
tyrosinase and MART-1/Melan-A is often observed in patients undergoing
peptide-based immunization (3). These reports suggest that
selective pressure facilitates the emergence of Ag-negative tumors.
Indeed, the observation that tumor Ag expression can be down-modulated
by IFN- may help explain the emergence of tumor Ag loss variants
following immunotherapy. In fact, the ability of IFN- to decrease
the levels of human papilloma virus E6 and E7 transcripts in several
cervical cancer cell lines (34) may explain the
ineffectiveness of E7 peptide-based vaccine therapies (35, 36) and the limited correlation between intratumoral expression
of IFN- and clinical outcome (37). In addition, in
melanoma IFN- down-regulation of the tissue-specific tumor Ag
MART-1/Melan-A (30) as well as several other
tumor-associated Ags has been reported (38). Certainly,
IFN- down-regulation of MART-1/Melan-A expression may explain the
frequently observed loss of MART-1/Melan-A in patients receiving
peptide-based therapy. Therefore, although our study addresses the
regulation of a retrovirally derived murine endogenous tumor Ag, it is
likely that the findings presented here may be extended to human tumor
viral Ags as well as to human tissue-specific tumor Ags.
If loss of tumor Ag expression following immunotherapy targeting the induction of type I cell-mediated immunity is a frequent event, development of strategies to counteract this phenomenon must be explored. Recent reports have demonstrated that type I and type II therapies are equally effective in inducing tumor regression (39, 40). However, our findings suggest that tumor Ag-based therapies exploiting type I immune responses may in some cases be ineffective due to the down-regulation of tumor Ags by type I cytokine-secreting tumor-infiltrating lymphocytes. In such cases, therapies promoting type II immune responses may be worthy of investigation and prove more successful.
Finally, our results emphasize the importance of understanding the
regulation of tumor Ag expression in vivo for enhancing the
effectiveness of tumor-Ag based immunotherapies. Although tumor
exposure to IFN- has previously been recognized to enhance tumor
immunogenicity, it is clear that down-regulation of tumor Ag expression
or reduced Ag processing by immunoproteasomes can reduce tumor
immunogenicity. These findings may provide an explanation for the lack
of correlation between induction of antitumor CTL capable of secreting
IFN- and tumor regression as well as account for some observations
demonstrating increased tumor progression following systemic IFN-
treatment (41, 42). In addition, our results support a
need for investigating the effectiveness of type II compared with type
I immunotherapy as an alternative therapeutic approach for targeting
endogenous tumor Ags that may be otherwise lost during type I immune
responses.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Yvonne Paterson, University of Pennsylvania, 323 Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104-6076.
3 Abbreviation used in this paper: CD62L, CD62 ligand.
Received for publication May 18, 2000. Accepted for publication August 21, 2000.
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K. Dredge, J. B. Marriott, S. M. Todryk, G. W. Muller, R. Chen, D. I. Stirling, and A. G. Dalgleish Protective Antitumor Immunity Induced by a Costimulatory Thalidomide Analog in Conjunction with Whole Tumor Cell Vaccination Is Mediated by Increased Th1-Type Immunity J. Immunol., May 15, 2002; 168(10): 4914 - 4919. [Abstract] [Full Text] [PDF]
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 I. C. Le Poole, A. I. Riker, M. E. Quevedo, L. S. Stennett, E. Wang, F. M. Marincola, W. M. Kast, J. K. Robinson, and B. J. Nickoloff Interferon-{gamma} Reduces Melanosomal Antigen Expression and Recognition of Melanoma Cells by Cytotoxic T Cells Am. J. Pathol., February 1, 2002; 160(2): 521 - 528. [Abstract] [Full Text] [PDF]
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 P. Nanni, G. Nicoletti, C. De Giovanni, L. Landuzzi, E. Di Carlo, F. Cavallo, S. M. Pupa, I. Rossi, M. P. Colombo, C. Ricci, et al. Combined Allogeneic Tumor Cell Vaccination and Systemic Interleukin 12 Prevents Mammary Carcinogenesis in HER-2/neu Transgenic Mice J. Exp. Med., October 29, 2001; 194(9): 1195 - 1206. [Abstract] [Full Text] [PDF]
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G. L. Beatty and Y. Paterson IFN-{{gamma}}-Dependent Inhibition of Tumor Angiogenesis by Tumor-Infiltrating CD4+ T Cells Requires Tumor Responsiveness to IFN-{{gamma}} J. Immunol., February 15, 2001; 166(4): 2276 - 2282. [Abstract] [Full Text] [PDF]
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), 2 x 106 irradiated CT26 s.c. (
and
), or 2 x 106 irradiated CT26.IFN s.c. (
and
) on day -21. On day 0, mice were challenged with 5 x
105 CT26 (
