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Tolerance to p53 by A2.1-restricted cytotoxic T lymphocytes.

Theobald M, Biggs J, Hernández J, Lustgarten J, Labadie C, Sherman LA - J. Exp. Med. (1997)

Bottom Line: Elevated levels of the p53 protein occur in approximately 50% of human malignancies, which makes it an excellent target for a broad-spectrum T cell immunotherapy of cancer.A major barrier to the design of p53-specific immunotherapeutics and vaccines, however, is the possibility that T cells may be tolerant of antigens derived from wild-type p53 due to its low level of expression in normal thymus and lymphohemopoetic cells.The circumvention of functional tolerance of high avidity CTL may therefore be a necessary prerequisite for optimizing immunotherapy against A2.1-restricted wild-type p53 epitopes in humans.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, Scripps Research Institute, La Jolla, California 92037, USA.

ABSTRACT
Elevated levels of the p53 protein occur in approximately 50% of human malignancies, which makes it an excellent target for a broad-spectrum T cell immunotherapy of cancer. A major barrier to the design of p53-specific immunotherapeutics and vaccines, however, is the possibility that T cells may be tolerant of antigens derived from wild-type p53 due to its low level of expression in normal thymus and lymphohemopoetic cells. The combination of p53 deficient (p53-/-) and p53+/+ HLA-A2.1/Kb transgenic mice was used as a model to explore the possibility that A2.1-restricted cytotoxic T lymphocytes (CTL) are functionally tolerant of self peptides derived from the wild-type p53 tumor suppressor protein. A2.1-restricted CTL specific for a naturally processed p53 self-epitope spanning residues 187-197 were completely aborted in p53+/+ as opposed to p53-/- transgenic mice. In contrast, CTL specific for a second self-epitope spanning residues 261-269 of the murine p53 sequence were detected in both p53-/- and p53+/+ A2.1/Kb transgenic mice. However, the avidity of the CTL effectors obtained from p53+/+ mice was 10-fold lower than that obtained from p53-/- mice, again suggesting elimination of CTL with high avidity for the A2.1-peptide complex. The circumvention of functional tolerance of high avidity CTL may therefore be a necessary prerequisite for optimizing immunotherapy against A2.1-restricted wild-type p53 epitopes in humans.

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Efficiency of peptide recognition by p53-specific CTL derived from p53−/− (closed circle) and p53+/+ (open circle) A2.1/Kb-Tg mice.  Responder spleen cells from peptide-primed p53−/− and p53+/+ A2.1/ Kb-Tg mice were restimulated in vitro with the indicated priming peptide. After 6 d, effector CTL were assayed at an E/T ratio of 30:1 for lytic  activity against T2A2Kb targets and the same cells pulsed with (A) Hu  WT p53.187-197, (B) Hu WT p53.149-157, (C) Mu WT p53.261-269,  and (D) Hu WT p53.264-272 at the indicated concentrations.
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Figure 1: Efficiency of peptide recognition by p53-specific CTL derived from p53−/− (closed circle) and p53+/+ (open circle) A2.1/Kb-Tg mice. Responder spleen cells from peptide-primed p53−/− and p53+/+ A2.1/ Kb-Tg mice were restimulated in vitro with the indicated priming peptide. After 6 d, effector CTL were assayed at an E/T ratio of 30:1 for lytic activity against T2A2Kb targets and the same cells pulsed with (A) Hu WT p53.187-197, (B) Hu WT p53.149-157, (C) Mu WT p53.261-269, and (D) Hu WT p53.264-272 at the indicated concentrations.

Mentions: Spleen cells from mice primed with homologous and nonhomologous A2.1-binding WT p53 peptides were restimulated with peptide in vitro and tested for an A2.1-restricted, peptide-specific CTL response. As reported, p53+/+ A2.1/Kb-Tg mice could mount an A2.1restricted CTL response specific for several nonhomologous Hu WT p53 peptides, including 65-73, 149-157, and 264272, the latter two of which have been shown to represent naturally processed CTL epitopes (Table 1) (23). Also as reported, these mice failed to develop A2.1-restricted CTL specific for the remaining homologous and nonhomologous Hu WT p53 peptides tested, including 129-137, 187-195, 187-197, 210-218, and 255-264 (23). As anticipated, p53−/− A2.1/Kb mice responded to the same three nonhomologous Hu p53 peptides recognized by p53+/+ A2.1/Kb mice, demonstrating a comparable level of lytic activity. A lack of A2.1restricted CTL responses by p53−/− A2.1/Kb-Tg mice was also observed with the remaining nonhomologous peptides, as well as with three out of four of the homologous WT p53 peptides (187-195, 255-264, and 322-330) which are identical in sequence in Hu and Mu p53 (Table 1). In contrast, however, a strong A2.1-restricted, peptide-specific CTL reponse was induced in p53−/− as opposed to p53+/+ A2.1/Kb-Tg mice after priming with the homologous WT p53.187-197 peptide (Table 1 and Fig. 1 A). Also, the amount of lysis obtained with responder spleen cells from p53−/− A2.1/Kb-Tg mice immunized with the Mu WT p53.261-269 peptide was about twofold higher as compared with CTL derived from p53+/+ A2.1/Kb-Tg mice (Table 1). Mu WT p53.261-269 is identical with Hu p53.264-272 at all but one amino acid residue, and has an equivalent high affinity for A2.1 (23). Significantly, the concentration of Mu WT p53.261-269 peptide required to obtain half-maximum lysis of T2A2Kb targets by CTL derived from p53−/− versus p53+/+ A2.1/Kb-Tg mice was ∼10-fold lower (5.2 × 10−8 M versus 4.6 × 10−7 M) (Fig. 1 C). This was in contrast to the comparable avidity demonstrated by p53+/+ and−/− A2.1-restricted CTL specific for the nonhomologous Hu WT p53 epitopes 149-157 and 264-272 (Fig. 1, B and D). As may be anticipated from lack of tolerance against the Hu WT 264-272 peptide, there is no cross-reactive recognition of the Mu 261-269 peptide by the Hu WT 264-272–specific CTL, and vice-versa.


Tolerance to p53 by A2.1-restricted cytotoxic T lymphocytes.

Theobald M, Biggs J, Hernández J, Lustgarten J, Labadie C, Sherman LA - J. Exp. Med. (1997)

Efficiency of peptide recognition by p53-specific CTL derived from p53−/− (closed circle) and p53+/+ (open circle) A2.1/Kb-Tg mice.  Responder spleen cells from peptide-primed p53−/− and p53+/+ A2.1/ Kb-Tg mice were restimulated in vitro with the indicated priming peptide. After 6 d, effector CTL were assayed at an E/T ratio of 30:1 for lytic  activity against T2A2Kb targets and the same cells pulsed with (A) Hu  WT p53.187-197, (B) Hu WT p53.149-157, (C) Mu WT p53.261-269,  and (D) Hu WT p53.264-272 at the indicated concentrations.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196170&req=5

Figure 1: Efficiency of peptide recognition by p53-specific CTL derived from p53−/− (closed circle) and p53+/+ (open circle) A2.1/Kb-Tg mice. Responder spleen cells from peptide-primed p53−/− and p53+/+ A2.1/ Kb-Tg mice were restimulated in vitro with the indicated priming peptide. After 6 d, effector CTL were assayed at an E/T ratio of 30:1 for lytic activity against T2A2Kb targets and the same cells pulsed with (A) Hu WT p53.187-197, (B) Hu WT p53.149-157, (C) Mu WT p53.261-269, and (D) Hu WT p53.264-272 at the indicated concentrations.
Mentions: Spleen cells from mice primed with homologous and nonhomologous A2.1-binding WT p53 peptides were restimulated with peptide in vitro and tested for an A2.1-restricted, peptide-specific CTL response. As reported, p53+/+ A2.1/Kb-Tg mice could mount an A2.1restricted CTL response specific for several nonhomologous Hu WT p53 peptides, including 65-73, 149-157, and 264272, the latter two of which have been shown to represent naturally processed CTL epitopes (Table 1) (23). Also as reported, these mice failed to develop A2.1-restricted CTL specific for the remaining homologous and nonhomologous Hu WT p53 peptides tested, including 129-137, 187-195, 187-197, 210-218, and 255-264 (23). As anticipated, p53−/− A2.1/Kb mice responded to the same three nonhomologous Hu p53 peptides recognized by p53+/+ A2.1/Kb mice, demonstrating a comparable level of lytic activity. A lack of A2.1restricted CTL responses by p53−/− A2.1/Kb-Tg mice was also observed with the remaining nonhomologous peptides, as well as with three out of four of the homologous WT p53 peptides (187-195, 255-264, and 322-330) which are identical in sequence in Hu and Mu p53 (Table 1). In contrast, however, a strong A2.1-restricted, peptide-specific CTL reponse was induced in p53−/− as opposed to p53+/+ A2.1/Kb-Tg mice after priming with the homologous WT p53.187-197 peptide (Table 1 and Fig. 1 A). Also, the amount of lysis obtained with responder spleen cells from p53−/− A2.1/Kb-Tg mice immunized with the Mu WT p53.261-269 peptide was about twofold higher as compared with CTL derived from p53+/+ A2.1/Kb-Tg mice (Table 1). Mu WT p53.261-269 is identical with Hu p53.264-272 at all but one amino acid residue, and has an equivalent high affinity for A2.1 (23). Significantly, the concentration of Mu WT p53.261-269 peptide required to obtain half-maximum lysis of T2A2Kb targets by CTL derived from p53−/− versus p53+/+ A2.1/Kb-Tg mice was ∼10-fold lower (5.2 × 10−8 M versus 4.6 × 10−7 M) (Fig. 1 C). This was in contrast to the comparable avidity demonstrated by p53+/+ and−/− A2.1-restricted CTL specific for the nonhomologous Hu WT p53 epitopes 149-157 and 264-272 (Fig. 1, B and D). As may be anticipated from lack of tolerance against the Hu WT 264-272 peptide, there is no cross-reactive recognition of the Mu 261-269 peptide by the Hu WT 264-272–specific CTL, and vice-versa.

Bottom Line: Elevated levels of the p53 protein occur in approximately 50% of human malignancies, which makes it an excellent target for a broad-spectrum T cell immunotherapy of cancer.A major barrier to the design of p53-specific immunotherapeutics and vaccines, however, is the possibility that T cells may be tolerant of antigens derived from wild-type p53 due to its low level of expression in normal thymus and lymphohemopoetic cells.The circumvention of functional tolerance of high avidity CTL may therefore be a necessary prerequisite for optimizing immunotherapy against A2.1-restricted wild-type p53 epitopes in humans.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology, Scripps Research Institute, La Jolla, California 92037, USA.

ABSTRACT
Elevated levels of the p53 protein occur in approximately 50% of human malignancies, which makes it an excellent target for a broad-spectrum T cell immunotherapy of cancer. A major barrier to the design of p53-specific immunotherapeutics and vaccines, however, is the possibility that T cells may be tolerant of antigens derived from wild-type p53 due to its low level of expression in normal thymus and lymphohemopoetic cells. The combination of p53 deficient (p53-/-) and p53+/+ HLA-A2.1/Kb transgenic mice was used as a model to explore the possibility that A2.1-restricted cytotoxic T lymphocytes (CTL) are functionally tolerant of self peptides derived from the wild-type p53 tumor suppressor protein. A2.1-restricted CTL specific for a naturally processed p53 self-epitope spanning residues 187-197 were completely aborted in p53+/+ as opposed to p53-/- transgenic mice. In contrast, CTL specific for a second self-epitope spanning residues 261-269 of the murine p53 sequence were detected in both p53-/- and p53+/+ A2.1/Kb transgenic mice. However, the avidity of the CTL effectors obtained from p53+/+ mice was 10-fold lower than that obtained from p53-/- mice, again suggesting elimination of CTL with high avidity for the A2.1-peptide complex. The circumvention of functional tolerance of high avidity CTL may therefore be a necessary prerequisite for optimizing immunotherapy against A2.1-restricted wild-type p53 epitopes in humans.

Show MeSH
Related in: MedlinePlus