Identification of epitopes in ovalbumin that provide insights for cancer neoepitopes
Sukrut Hemant Karandikar, John Sidney, Alessandro Sette, Mark Joseph Selby, Alan Jerry Korman, Pramod Kumar Srivastava
Sukrut Hemant Karandikar, John Sidney, Alessandro Sette, Mark Joseph Selby, Alan Jerry Korman, Pramod Kumar Srivastava
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Research Article Immunology

Identification of epitopes in ovalbumin that provide insights for cancer neoepitopes

Abstract

MHC I–restricted epitopes of chicken ovalbumin (OVA) were originally identified using CD8+ T cells as probes. Here, using bioinformatics tools, we identify 4 additional epitopes in OVA in addition to a cryptic epitope. Each additional epitope is presented in vivo, as deduced from the lack of CD8+ T cell response to it in OVA-transgenic mice. In addition, CD8 responses to the previously known epitopes and those identified in this study are examined in C57BL/6J mice exposed to the OVA-expressing tumor E.G7 in several ways. No responses to any epitope, including SIINFEKL, are detected in mice with growing E.G7 or mice immunized with the tumor. Only in E.G7-bearing mice treated with an anti–CTLA-4 antibody, which depletes tumor-infiltrating regulatory T cells, are CD8 responses to SIINFEKL and the epitope EKYNLTSVL identified in this study detected. Finally, all epitopes fail to treat mice with preexisting tumors. These observations force an important reconsideration of the common assumptions about the therapeutic value of neoepitopes detected by CD8 responses in tumor-bearing hosts.

Authors

Sukrut Hemant Karandikar, John Sidney, Alessandro Sette, Mark Joseph Selby, Alan Jerry Korman, Pramod Kumar Srivastava

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Figure 4

CD8+ T cell responses in E.G7-bearing mice.

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CD8+ T cell responses in E.G7-bearing mice. (A) Lack of CD8+ responses a...
(A) Lack of CD8+ responses against E.G7 or OVA in E.G7-bearing mice. CD8+ cells from tumor-bearing mice were stimulated with peptide-pulsed splenocytes, unpulsed splenocytes (NS), E.G7 cells, or PMA and ionomycin (P+I) (n = 3; experiment performed 3 times). (B) Treatment with antibody 9D9 IgG2a (α-CTLA-4) causes complete regression of E.G7. E.G7-bearing mice were treated with 9D9 or PBS on the days indicated with arrows (n = 5; experiment performed 3 times). (C) CD8+ responses to 257–264 and 289–297 are primed in mice rejecting E.G7. E.G7-bearing or naive mice were treated with 9D9. CD8+ cells were enriched after tumors regressed and stimulated with peptide-pulsed splenocytes or unpulsed splenocytes (NS; n = 4 for both panels; experiment performed 3 times; Welch’s t test). (D) CD8+ cells from mice rejecting E.G7 were stimulated with splenocytes (Spl), EL4 cells, or E.G7 cells (n = 5; experiment performed 2 times, Welch’s t test). (E) Splenocytes pulsed with 289–297 or SIINFEKL were cocultured with B3Z (n = 3; experiment performed 1 time; Welch’s t test). (F) Peptide 289–297 does not elicit protective immunity, while SIINFEKL does. Mice were immunized with SIINFEKL or 289–297 and challenged with E.G7 seven days later (n = 5 for each panel; experiment performed 2 times). **P ≤ 0.01, ***P ≤ 0.001.