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Division of Immunology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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100-fold less Ag to induce
NP-specific lysis than primary T cells, consistent with the observation
that memory T cells have an increased avidity due to affinity
maturation. Finally, during an NP-specific memory response, substantial
numbers of low-avidity NP-specific T cells can be recovered from s.c.
growing tumors. Together, these findings indicate that, when only a
low-avidity repertoire is available to generate antitumor immunity, the
best strategy may be to enhance memory responses. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Despite these multiple mechanisms of peripheral tolerance induction, immunological self-tolerance is far from absolute, as is underscored by the occurrence of T cell-mediated autoimmune diseases (20, 21, 24). However, self-specific T cells can also have beneficial effects, because many of the Ags identified in human tumors are normal self-Ags inappropriately expressed or overexpressed (25, 26, 27, 28). These self-Ags represent potential targets for T cell-based immunotherapy and vaccine design, and it has been demonstrated that self-specific T cells can mediate the rejection of tumors (29, 30, 31, 32, 33, 34, 35). Most of these studies (31, 32, 33, 35) concerned self-epitopes with a restricted expression pattern.
To define the conditions for self-specific antitumor immunity against a ubiquitously expressed self-epitope, we here investigate whether self-specific T cells that have escaped intrathymic deletion can be exploited to generate antitumor immunity. A mouse model is used in which a fragment of the influenza nucleoprotein (NP)3 is expressed as a transgene under control of the H-2K promoter in C57BL/10 mice (B10NP mice). In these mice, an oligoclonal population of self-specific CD8+ T cells which has undergone neither thymic nor peripheral deletion can be activated upon strong immunization (36). This population of cells can persist for prolonged periods of time, has strikingly low avidity for NP/MHC complexes (36), and has severely impaired induction of IL-2 production and clonal expansion (37). Yet these low-avidity self-specific T cells maintain their ability to differentiate into cytolytic effector cells and memory cells (36). In this study, we investigate the in vivo antitumor reactivity of low-avidity self-specific T cells.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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C57BL/10 (H-2b; B10) mice were obtained from the experimental animal department of The Netherlands Cancer Institute (Amsterdam, The Netherlands). To obtain CD8-depleted mice, B10 mice were injected i.p. with 250 µg/ml anti-CD8 mAb (clone 2.43) 3 days in a row, followed by three times a week during the entire experiment. B10 mice transgenic for a fragment of the influenza NP (from which amino acids 3–327 are deleted) under control of the widely expressed class I MHC promoter H-2Kb (B10NP mice) were previously described (38). All mice were kept under specific pathogen-free conditions and used when they were 6–10 wk of age.
Cells and tissue culture conditions
All cell lines were cultured in IMDM (Life Technologies, Glasgow, U.K.) supplemented with 5% heat-inactivated FCS (PAA Laboratories, Linz, Austria), 100 IU/ml penicillin, 100 µg/ml streptomycin (both from Roche, Mannheim, Germany) and 5 x 10-5 M 2-ME (Merck, Hohenbrunn, Germany) (complete medium) at 37°C in humidified air containing 5% CO2.
The melanoma cell line B16 (H-2b) and the murine thymoma EL4 (H-2b) (39) were transduced with a cDNA encoding for fragment amino acids 1, 2, and 328–498 of influenza A/NT/60/68 virus NP together with enhanced green fluorescence protein (eGFP; B16-NP and EL4-NP) or only with eGFP (B16 and EL4) (40, 41). In all experiments cells sorted for comparable levels of eGFP expression were used. In some experiments the NK-sensitive murine T cell lymphoma cell line YAC was used (42) to block NK cell activity.
Viruses, peptides, and tetramers
Purified influenza A/NT/60/68 virus was provided by Dr. R. Consalves (National Institute for Medical Research, London, U.K.). Influenza B/Lee/40 virus was acquired from the American Type Culture Collection (Manassas, VA). Virus was grown and titrated at the Department of Virology, Erasmus University (Rotterdam, The Netherlands). Virus was stored at -70°C in 50% sucrose and was thawed immediately before use.
The NP366–374 peptide (sequence: ASNENMDAM) was produced in the peptide synthesis facility at our institute. Tetramers of soluble MHC class I molecules complexed with the NP366–374 peptide were synthesized according to the original protocol developed by Altman et al. (43) and modified as previously described (44) to block NK cell activity.
Virus infection
For live virus infections, anesthetized mice were infected by intranasal administration of 50 µl of HBSS (Life Technologies) containing 25 hemagglutinin units (HAU) of A/NT/60/68 virus or 125 HAU of B/Lee/40 virus. For a secondary infection mice were infected with 250 HAU of A/NT/60/68 virus.
Enriching NP-specific T cells in culture
Fifteen days after primary or secondary influenza infection,
spleens were isolated from B10 and B10NP mice, homogenized over a nylon
filter (NPBI, Emmer Compascuum, The Netherlands) and treated
with NH4Cl to remove RBC. Splenocytes were seeded
into 24-well culture plates at 5 x 106
cells/well in 2 ml of complete medium supplemented with 5 x
10-4 µg/ml NP366–374
peptide for B10 mice or 0.05 µg/ml NP366–374
peptide for B10NP mice and 20 U/ml IL-2 (Cetus, Emeryville, CA).
Cultures were tested on day 7 for their levels of NP tetramer positive
cells, cytokine production capacity, and cytolytic activity (see
below). At this time point the percentage of NP tetramer positive cells
of the CD8 population is 70–80% for B10 mice and 15–30% for
B10NP mice.
Flow cytometry
To follow the fate of NP366–374-specific T cells in B10 and B10NP mice over time, analysis by flow cytometry was performed on cells isolated from spleen, lungs, and blood. Spleen and lungs were isolated and homogenized over a nylon filter (NPBI). Blood was drawn from the tail vein. RBC were lysed by NH4Cl treatment. A total of 5 x 105 cells were washed twice with PBS containing 0.5% BSA and 0.02% NaN3 (PBS/BSA) and incubated at 4°C for 20 min with 20 µl of the appropriate dilutions of allophycocyanin-conjugated anti-CD8 (BD PharMingen, San Diego, CA) and PE-conjugated tetrameric class I-NP366–374-peptide complexes. Cells were washed twice and resuspended in PBS/BSA. Propidium iodide was used to discriminate between viable and dead cells. Data acquisition and analysis were performed on a FACSCalibur using CellQuest software (BD Biosciences, Mountain View, CA).
To determine the percentage of tumor-infiltrating NP-specific T cells, tumors were excised and transferred to a 24-well plate filled with 1 ml of PBS containing 1 mg/ml collagenase (Sigma, Zwÿndrecht, The Netherlands) and 10 µg/ml DNase (Sigma). Tumors were cut into pieces using a scalpel and incubated for 30 min at 37°C. After the incubation, tumors were homogenized over a nylon filter (NPBI) and treated with NH4Cl to remove RBC. The cells were stained as described above.
To determine NP366–374-specific IL-2 and IFN-
production, intracellular cytokine staining was performed as previously
described (45). Splenocytes from vaccinated B10 and B10NP
mice were cultured as described above in bulk cultures. On day 7 cells
were purified over a Lympholyte-M (Cedarlane Laboratories, Hornby,
Ontario, Canada) gradient. Such purified splenocytes were then
stimulated in 96-well flat-bottom tissue culture plates (Costar,
Corning, NY) at a concentration of 1 x 106
cells/well in 200 µl of complete medium supplemented with 1 µl/ml
brefeldin A (Golgiplug; BD PharMingen) and 50 U/ml human rIL-2 either
with the indicated concentration of NP366–374 or
without the peptide. After 5 h of culture cells were washed with
FACS buffer and surface-stained with allophycocyanin-conjugated
anti-CD8 (BD PharMingen) for 20 min. Cells were washed twice and
stained intracellularly with FITC-conjugated anti-mouse IL-2 or
IFN- and isotype control IgG2b or IgG1, respectively. The staining
was performed using the Cytofix/Cytoperm kit according to the
manufacturer’s protocol (BD PharMingen).
Tumor protection assay
B16 tumor model. Four days after infection, B10NP mice were injected i.v. via the tail vein with 1 x 105 B16-NP tumor cells. After 4 wk, lungs were removed and the pulmonary nodules were enumerated using a microscope.
EL4 tumor model. Three (memory) or 7 (primary) days after infection (anticipating the upcoming peak of the NP-specific T cells), B10 and B10NP mice were inoculated s.c. with 1 x 106 EL-NP tumor cells. The tumor diameter was measured three times a week along two perpendicular axes (x and y) in millimeters using calipers. The mean tumor diameter for each mouse was calculated [(diameter x) + (diameter y)/2]. Mice were sacrificed when the tumors reached diameters >20 mm or if the mice became overtly ill or the tumor became ulcerated.
51Cr release assay
For analysis of cytolytic activity, bulk cultures were prepared as described above. After 7 days of culture cells were purified over a Lympholyte-M gradient and used as effectors in a 51Cr release assay. Splenocytes were serially diluted in triplicate in round-bottom tissue culture plates (Costar). As targets wild-type EL4 and EL4 cells pulsed with various concentrations of NP366–374 peptide and EL4-NP were used. Target cells were labeled with 100 µCi of 51Cr (Amersham Pharmacia Biotech, Little Chalfont, U.K.) for 1 h at 37°C. The labeled cells were washed, and 2 x 103 cells were added per well. To block NK cell activity, a 50-fold excess of unlabeled YAC cells was added to the wells. Per target, spontaneous release was measured by incubating the labeled cells in medium alone. Maximum release was measured by incubating the labeled cells in 2% Triton X-100. After a 5-h incubation at 37°C, 25 µl of supernatant from triplicate cultures was harvested in Luma plates (Packard Instrument, Meriden, CT) and counted in a TopCount Microplate Scintillation Counter (Packard Instrument). The percentage of specific 51Cr release was calculated as a ratio of 100 x (cpm experimental release - cpm spontaneous release)/(cpm 2% Triton X-100 release - cpm spontaneous release).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Previous studies from our laboratory have demonstrated that an
oligoclonal population of self-specific,
NP366–374-specific CD8+ T
cells (referred to as NP-specific T cells) persisted in mice expressing
NP as a self-Ag on all MHC class I-positive cells (B10NP mice) and
could be activated and expanded by a localized infection with an
NP-containing influenza virus (36). This NP-specific T
cell population, which has escaped central tolerance, had diminished
avidity for tetrameric MHC/NP-peptide complexes (36) but
could generate Ag-specific IFN- and CTL responses. Nevertheless,
high Ag doses were required to perform those effector functions.
However, these low-avidity NP-specific T cells were severely limited in
producing IL-2 and had a dramatic defect in expansion upon Ag exposure
(37). This raised the question of whether such a
"crippled" T cell population could perform antitumor effector
function in vivo, and B10NP mice provided an excellent model to study
this issue. Only a low-avidity T cell repertoire will be available for
ubiquitously expressed tumor Ags (such as telomerase, p53, and
Her-2/neu) for which central tolerance exists, and it is important to
define which conditions, if any, must be employed to exploit this
repertoire.
As most NP-specific T cells could be detected in the lungs after
intranasal infection with an NP-containing influenza virus, we first
tested whether tumor growth could be prevented in the lungs of B10NP
mice. Therefore, B10NP mice were infected intranasally with
NP-containing influenza A/NT/60/68 virus or with control influenza
B/Lee/40 virus, before i.v. inoculation of NP-expressing B16 melanoma
cells. i.v. inoculation of B16 melanoma cells resulted in the formation
of numerous pulmonary microtumors in the lungs in control mice (Fig. 1
, left). However, mice
infected with influenza A/NT/60/68 virus showed a dramatic reduction in
the number of NP-expressing pulmonary tumors (Fig. 1, middle), and this was correlated with abundant infiltration
of low-avidity NP-specific CD8+ T cells into the
lungs (36, 37). This antitumor response was Ag specific,
as infection of B10NP mice with a control influenza virus did not
result in reduced numbers of pulmonary tumors (Fig. 1, right). In addition, no effect of influenza A/NT/60/68 virus
infection could be observed on the number of pulmonary B16 tumors only
expressing eGFP and not NP (data not shown). Together, these results
demonstrated that an intranasal challenge with influenza virus that
expresses NP generated infiltration of NP-specific T cells and
clearance of multiple tumors in the lung that expressed that same
influenza epitope. These data prove that low-avidity, NP-specific
CD8+ T cells in B10NP mice can perform effector
functions in vivo.
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Having demonstrated that self-specific T cells, despite their low avidity, can indeed have effector function in vivo in the lung tumor model, we next asked whether these low-avidity, NP-specific T cells could also reject s.c. growing tumors. Importantly, we found that the growth of s.c. growing B16-NP tumors was not affected by an NP-specific response induced by A/NT/60/68 virus infection in B10NP mice (data not shown), while in B10 mice s.c. growth of B16-NP tumors can be dramatically reduced by A/NT/60/80 infection. However, because it was difficult to study the infiltration of T cells into s.c. growing B16 melanoma cells (it grows in a somewhat diffuse pattern and is difficult to process), the EL4 thymoma was used in all subsequent experiments.
An s.c. growing NP-expressing EL4 tumor (EL4-NP) could easily be kept
under control in B10 mice (Fig. 2A). This antitumor response
was correlated with the activation and expansion of NP-specific
CD8+ T cells that could easily be detected in
peripheral blood (Fig. 2B) and secondary lymphoid organs
(data not shown). The antitumor response was CD8 mediated, since no
tumor rejection was observed in CD8 depleted EL4-NP tumor-bearing B10
mice (Fig. 2A). The activated NP-specific T cells also
exhibited ex vivo NP-specific cytolytic activity, as EL4 targets pulsed
with NP366–374-peptide and NP-transduced EL4
cells could be lysed by such tumor-induced activated NP-specific T
cells (data not shown). Therefore, the EL4-NP tumor effectively
triggered activation, expansion, and differentiation of NP-specific T
cells in B10 mice.
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C). Furthermore, the EL4-NP
tumor failed to induce a CD8+ T cell response in
B10NP mice (Fig. 2D) despite the fact that an NP-specific T
cell repertoire did exist in these mice (see below) (36).
Thus, a tumor expressing NP as a foreign Ag can induce a
CD8+ T cell-mediated rejection response, while a
tumor expressing NP as a self-Ag cannot.
To study whether NP-expressing tumors could be rejected in the presence
of activated low-avidity NP-specific T cells, B10NP mice were infected
with A/NT/60/68 influenza virus. After 7 days, before the peak of the
NP-specific T cell response, EL4-NP tumor cells were inoculated s.c.
The EL4-NP tumor grew undisturbed in such A/NT/60/68 virus-infected
B10NP mice (Fig. 2C) despite the presence of activated
NP-specific T cells (Fig. 2D). Thus, while intranasal
A/NT/60/68 virus infection in B10NP mice results in reduced growth of
NP-expressing tumors locally (in the lung), it is ineffective s.c.
Presumably, this is because the lung tumor model represents an ideal
setting for tumor rejection by low-avidity T cells: small tumors and
massive in situ inflammatory conditions.
Memory NP-specific low-avidity T cells can delay tumor growth in B10NP mice
Memory responses can be both qualitatively and quantitatively more
robust than primary responses (46, 47, 48). Therefore, we
investigated whether a memory T cell response might cause tumor
rejection in this tumor model. Previous studies from our laboratory
have demonstrated that infection of B10NP mice with influenza
A/NT/60/68 virus resulted in the induction of an NP-specific T cell
memory population, as defined by rapid and massive expansion of
NP-specific T cells upon rechallenge (36). To study the in
vivo antitumor capacity of NP-specific memory T cells in B10NP mice, a
tumor protection assay was performed during this memory response. B10NP
mice were infected intranasally with NP-containing influenza virus 5 wk
after primary exposure to influenza. Three days later, these mice were
inoculated s.c. with EL4-NP tumor cells. At various time points after
tumor inoculation, the percentages of NP-specific T cells in lungs,
spleen, and blood were determined, and the tumor diameter was measured.
In the lungs, spleen, and blood, the NP-specific T cell memory response
was 3- to 4-fold higher than the response in mice undergoing a
primary infection (Fig. 3A),
and the peak of the response occurred more rapidly after viral
infection in memory mice than in naive mice. This NP-specific T cell
memory response was correlated with delay of growth of the EL4-NP tumor
(Fig. 3B), although it clearly had only a partial effect.
Nevertheless, such a protective effect was never observed during the
primary response (Figs. 2C and 3B). The
response was Ag specific, since mice re-exposed to the antigenically
unrelated B/Lee/40 virus did not show this retardation in tumor growth
(Fig. 3B). Furthermore, the memory NP-specific T cells did
maintain their low-avidity phenotype, although selection for cells at
the high affinity end of the low affinity spectrum did occur (Fig. 3C). Together, these findings suggested that NP-specific
memory T cells in the self-specific T cell repertoire cause a modest
delay of tumor growth. Histological analysis revealed no overt signs of
autoimmune pathology in these mice despite the presence of activated
NP-specific memory T cells (data not shown).
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production, cytolytic
activity, and migration behavior of primary and memory NP-specific
T cells
Why is a self-specific memory T cell population more efficient in
protection against tumors? First, the observed antitumor immunity may
simply be due to higher numbers of memory NP-specific T cells compared
to the numbers of primary NP-specific T cells (Fig. 3A). Second, selection for cells at the
high affinity end of the low affinity spectrum does occur (Fig. 3C). It should be noted that TCR levels of NP-tetramer
binding cells from B10 and B10NP mice are equal in both the primary and
the memory response (36, 37) (data not shown). In
addition, memory cells may produce more or different cytokines, may be
more effective in killing NP-expressing targets, or may have a
different migration behavior.
To investigate these possibilities, we assessed whether primary and
memory T cells differed with respect to their cytokine production
profile, cytolytic capacity, and migration behavior. Splenocytes of
mice undergoing a primary or a secondary infection with A/NT/60/68
influenza virus were cultured with
NP366–374-peptide and IL-2, and after 7 days
these splenocytes were compared with respect to IL-2 and IFN-
production and CTL activity. On the average, 70–80% of the
CD8+ T cells from primary and secondary B10
cultures stained with NP tetramers. For B10NP primary and secondary
cultures, 15–30% of the CD8+ T cells were NP
tetramer positive. Restimulated splenocytes from memory B10NP mice did
maintain a higher avidity phenotype than restimulated splenocytes from
mice undergoing a primary infection (data not shown), just as in the
primary responses (Fig. 3C).
As shown in Fig. 4A, primary
and memory NP-specific T cells from B10NP mice both produced IL-2 and
IFN-. However, compared with IFN- production, the production of
IL-2 was very limited. In addition, high Ag doses were required to
perform those effector functions. To determine whether the Ag
sensitivity for cytokine production of memory T cells differed from
that of primary T cells, in vitro cultured primary and memory
splenocytes were stimulated with decreasing concentrations of
NP366–374 peptide. No difference in the IL-2
response could be observed after stimulation of primary or memory T
cells from B10NP mice with decreasing concentrations of
NP366–374 peptide (Fig. 4A). Thus,
memory T cells from B10NP mice in this tumor model were not more
sensitive than primary T cells with respect to IL-2 production.
However, memory T cells did display a 10-fold higher Ag sensitivity for
IFN- production compared with primary T cells. Nevertheless, the
level of intracellular IL-2 (Fig. 4B, upper
panel) and IFN- (Fig. 4B, lower panel)
produced per cell did not differ between primary and memory T cells
from B10NP mice.
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A), providing an explanation
for their ability to perform antitumor effector function in vivo (see
Figs. 1 and 3B). We then compared the Ag sensitivity of
cultured primary and memory cells at a fixed E:T cell ratio. It should
be emphasized that the percentage of NP-tetramer binding cells in
cultures from spleens of primary and memory B10NP mice is overall
comparable (see Fig. 5). Nevertheless, memory T cells from B10NP mice
were 100-fold more potent than primary T cells in executing
NP-peptide specific lysis (Fig. 5B). However, it is worth
noting that the memory cells from B10NP cells still exhibit somewhat
reduced Ag sensitivity compared with primary and memory cells from B10
mice (Fig. 5B).
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). No differences
among the expression patterns of CD44, CD62L, CD11b, and CD49d, all
molecules involved in migration, could be observed in mice undergoing a
primary or a secondary infection (data not shown).
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Taken together, these data imply that the enhanced antitumor effect of
the memory response is caused by the higher numbers of NP-specific T
cells present in B10NP memory mice (Fig. 3A). Overall, the
numbers of NP-specific T cells present in B10NP memory mice are 3-
to 4-fold higher than those in B10NP mice undergoing a primary
infection. In addition, the observed higher affinity of the TCRs of
memory T cells for MHC/peptide complexes (Fig. 3C)
translates into higher functional sensitivity (Figs. 4A and
5B). Collectively, these findings may explain the tumor
growth delay caused by memory self-specific T cells in mice
ubiquitously expressing a self-Ag.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Why might a memory T cell response be more efficient in tumor
rejection? Are the greater speed and efficacy of a memory response
simply due to increased precursor frequency or are they influenced by
qualitative differences between naive and memory T cells? In a
different model, Zimmermann and colleagues (47) also found
that memory cells were far more efficient in tumor eradication. The
kinetics of the responses of naive and memory cells were compared in
that model, and the main difference between CD8+
memory T cells and naive T cells was the ability of the former to
rapidly acquire effector cell functions. Memory T cells could be more
rapidly induced to become cytolytic and to secrete high levels of IL-2
and IFN- than naive cells, enabling them to perform more efficiently
in the early phase of an immune response (47). It has also
been shown that naive and memory T cells have distinct recirculation
pathways, with naive T cells selectively trafficking from blood to
lymph nodes while memory T cells selectively traffic from blood to
peripheral tissues (46). This broader immune surveillance
by memory cells could contribute to more rapid responses. Another study
showed that memory T cells enter cell division more rapidly than naive
cells and have a shortened lag phase (48). In addition,
memory T cells often exhibit cytotoxic activity directly ex vivo and
disappear more slowly after expansion. In contrast to these studies, we
are studying a memory population of low-avidity self-specific T cells.
We could not detect differences in Ag sensitivity for production of
IL-2 between NP-specific CD8+ T cells
during the primary and the memory response. Yet memory NP-specific T
cells were 10-fold more sensitive with respect to IFN-
production. In addition, memory NP-specific T cells exhibited increased
ligand sensitivity in the cytolytic response and also displayed a
higher avidity phenotype than the primary T cells. In addition, we
found that only during an NP-specific memory response, substantial
numbers of low-avidity NP-specific T cells could be recovered from an
s.c. growing tumor. This does not appear to be a consequence of altered
migratory patterns. Therefore, the greater efficacy of the memory
response is a consequence of the fact that memory T cells are somewhat
more efficient in effector functions than primary cells and of the
magnitude of the response. Nevertheless, the potential of the memory
response is limited, because only a delay in tumor growth can be
achieved. Therefore, efforts directed at exploiting the low-avidity,
tumor-specific T cell response should be focused at increasing the
magnitude of a memory response.
An efficient immune response against tumor Ags that also represent self-Ags can potentially be harmful, because immunity against self-Ags may cause autoimmunity. Efficient tumor control in patients may be associated with autoimmune phenomena, and anti-melanoma immunity sometimes correlates with vitiligo (49, 50). Despite the presence of activated NP-specific T cells in the B10NP mice, no overt signs of autoimmune pathology were observed in the present model. Long-term follow-up did not reveal any abnormalities, and immunohistologic analysis of several organs did not show any tissue destruction or abnormal T cell infiltration. Nevertheless, this same low-avidity NP-specific T cell population could kill tumor cells expressing NP endogenously. From these data, it can be concluded that it is possible to exploit the low-avidity T cell repertoire for tumor rejection without causing autoimmune pathology, even for a ubiquitously expressed self-Ag. This window of opportunity for tumor rejection most likely depends on quantitative differences in the expression of Ag between tumor cells and normal cells. Earlier studies already showed that self-specific T cells directed against self-Ags with restricted tissue expression could be exploited for tumor rejection without causing autoimmune pathology (31, 32, 33, 35).
Induction of anti-self-immunity to cure cancer cannot always be
achieved without causing autoimmune pathology. Antitumor treatment with
tumor Ag-loaded DCs causes severe autoimmune disease when the tumor Ags
are not tumor specific, but are also expressed in peripheral
nonlymphoid organs (51). In certain transgenic mouse
models where Ags are exclusively expressed in pancreatic 
islets or
solely in cells of the cardiovascular system, such Ags may be
completely ignored (51). In these mice tumors that also
express these Ags can be successfully controlled by specific DC
vaccination. However, this antitumor vaccination was accompanied by
fatal autoimmune disease, i.e., autoimmune diabetes, or by
severe arthritis, myocarditis, and eventually dilated cardiomyopathy
(51). Whether self-specific tumor rejection can occur
without undesirable autoimmune disease is thus also dependent on the
type of tissue in which these self-Ags are expressed.
Tumor immunotherapy directed against Ags that are also self-Ags might be most promising when Ag-specific T cells of high avidity are recruited. Usually, when the self-Ag is presented in thymus, these high-avidity Ag-specific T cells are deleted in the thymus. Therefore, it has been suggested that it might be preferred to direct immunotherapy against Ags that do not reach the thymus and for which high-avidity T cells persist. However, when such high-avidity self- and tumor-specific T cells are recruited, the risk of autoimmune diseases also increases. Our study shows that even low-avidity self-specific T cells can be activated upon vaccination to generate memory responses and antitumor immunity. The low-affinity interactions between TCR and peptide are associated with selective loss of critical T cell functions. Still, we show in this study that this crippled population can delay tumor growth without causing autoimmune pathology. The magnitude of the response is an important parameter for accomplishing this antitumor effect, as is increased Ag sensitivity, and these are most easily achieved in the memory response. Therefore, future efforts directed at exploiting the low-avidity tumor-specific response should be focused at increasing the magnitude of the memory response.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Ada M. Kruisbeek, Division of Immunology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands. E-mail address: akru{at}nki.nl
3 Abbreviations used in this paper: NP, nucleoprotein; eGFP, enhanced green fluorescence protein; HAU, hemagglutinin unit.
Received for publication July 5, 2001. Accepted for publication November 12, 2001.
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References |
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 S. Yang, K.-Y. Tsang, and J. Schlom Induction of Higher-Avidity Human CTLs by Vector-Mediated Enhanced Costimulation of Antigen-Presenting Cells Clin. Cancer Res., August 1, 2005; 11(15): 5603 - 5615. [Abstract] [Full Text] [PDF]
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M. A. Lyman, C. T. Nugent, K. L. Marquardt, J. A. Biggs, E. G. Pamer, and L. A. Sherman The Fate of Low Affinity Tumor-Specific CD8+ T Cells in Tumor-Bearing Mice J. Immunol., March 1, 2005; 174(5): 2563 - 2572. [Abstract] [Full Text] [PDF]
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E. Quaglino, M. Iezzi, C. Mastini, A. Amici, F. Pericle, E. Di Carlo, S. M. Pupa, C. De Giovanni, M. Spadaro, C. Curcio, et al. Electroporated DNA Vaccine Clears Away Multifocal Mammary Carcinomas in Her-2/neu Transgenic Mice Cancer Res., April 15, 2004; 64(8): 2858 - 2864. [Abstract] [Full Text] [PDF]
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S. Oh, J. W. Hodge, J. D. Ahlers, D. S. Burke, J. Schlom, and J. A. Berzofsky Selective Induction of High Avidity CTL by Altering the Balance of Signals from APC J. Immunol., March 1, 2003; 170(5): 2523 - 2530. [Abstract] [Full Text] [PDF]
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T. N. J. Bullock, D. W. Mullins, and V. H. Engelhard Antigen Density Presented By Dendritic Cells In Vivo Differentially Affects the Number and Avidity of Primary, Memory, and Recall CD8+ T Cells J. Immunol., February 15, 2003; 170(4): 1822 - 1829. [Abstract] [Full Text] [PDF]
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J. Rice, S. Buchan, and F. K. Stevenson Critical Components of a DNA Fusion Vaccine Able to Induce Protective Cytotoxic T Cells Against a Single Epitope of a Tumor Antigen J. Immunol., October 1, 2002; 169(7): 3908 - 3913. [Abstract] [Full Text] [PDF]
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L.-X. Wang, B.-G. Chen, and G. E. Plautz Adoptive Immunotherapy of Advanced Tumors with CD62 L-Selectinlow Tumor-Sensitized T Lymphocytes Following Ex Vivo Hyperexpansion J. Immunol., September 15, 2002; 169(6): 3314 - 3320. [Abstract] [Full Text] [PDF]
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