Systems and methods for identifying HLA-associated tumor peptides
Systems and methods for determining amino acid sequences of peptides that bind to MHC-I or HLA-I complex or MHC-II or HLA-II complex are provided. One embodiment includes isolating peptides from MHC or HLA class I or class II-peptide complexes and adding one or more known labeled peptides of interest to form a sample containing labeled peptides and unlabeled isolated peptides. The method also includes analyzing the sample with an LC-MS/MS system to obtain sequence data of the peptides, and increasing the sensitivity of the LC-MS/MS system when the labeled peptide is detected by the LC-MS/MS system. The method then concludes with determining the amino acid sequence of the unlabeled peptides in an m/z range that includes the m/z of the labeled peptide. The system can be triggered to increase the sensitivity in or near the m/z of the labeled peptide using an algorithm or computer program.
1. A mass spectrometry method, the method comprising:
obtaining a sample comprising unlabeled isolated peptides from an MHC-I or HLA-I complex or an MHC-II or HLA-II complex;
adding one or more labeled peptides to the sample to form a single mixed sample comprising the labeled peptides and the unlabeled isolated peptides;
processing the single mixed sample with an LC-MS/MS system, comprising:
i) processing the single mixed sample in discovery mode to detect and identify one or more of the unlabeled isolated peptides and the one or more labeled peptides in the single mixed sample;
ii) wherein, when the one or more labeled peptides are detected, processing the same mixed sample with the LC-MS/MS system in targeted mode, thereby detecting and identifying the one or more labeled peptides; and
iii) wherein the LC-MS/MS system toggles between processing the mixed sample in discovery mode and processing the mixed sample in targeted mode in the same LC-MS/MS run,
thereby detecting both labeled and unlabeled peptides in the single mixed sample.
2. The method of claim 1 , further comprising:
iv) wherein, when the one or more labeled peptides is no longer detected, processing the mixed sample with the LC-MS/MS system in discovery mode to detect and identify one or more of the unlabeled isolated peptides and the one or more labeled peptides in the mixed sample.
3. The method of claim 2 , further comprising:
v) wherein, when the one or more labeled peptides are detected, processing the mixed sample with the LC-MS/MS system in targeted mode, thereby detecting and identifying the one or more labeled peptides.
4. The method of claim 3 , wherein steps iii) and iv) and v) are repeated 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, or 10 times.
5. The method of claim 1 , wherein the obtaining step comprises isolating the unlabeled peptides from an MHC-I or HLA-I complex or an MHC-II or HLA-II complex.
6. The method of claim 5 , wherein the isolating comprises affinity chromatography and/or column chromatography.
7. The method of claim 5 , wherein the isolating comprises
isolating by affinity chromatography the MHC-I or HLA-I complex or the MHC-II or HLA-II complex obtained from a tissue lysate; and
separating peptides from the complexes by column chromatography to produce the unlabeled isolated peptides.
8. The method of claim 5 , wherein the isolating comprises
passing a tissue lysate through an affinity chromatography column to produce a flow-through;
eluting the column to produce a first eluate, wherein the first eluate comprises MHC-peptide complexes and beta2M associated peptides;
passing the flow-through through a second affinity chromatography column to obtain a second eluate comprising MHC-peptide complexes and beta2M associated peptides; and
independently eluting the peptides from the first and second eluates to produce unlabeled isolated peptides.
9. The method of claim 6 , wherein the affinity chromatography comprises an anti-HLA I column.
10. The method of claim 6 , wherein the second affinity column comprises a pan HLA II column.
11. The method of claim 6 , wherein the column chromatography comprises use of a C18 reverse phase chromatography column.
12. The method of claim 1 , wherein the sample comprising unlabeled isolated peptides is a tissue lysate.
13. The method of claim 12 , wherein the tissue lysate is produced using chemical and/or physical techniques.
14. The method of claim 13 , wherein the tissue lysate is produced from a tissue using a detergent.
15. The method of claim 13 , wherein the tissue lysate is produced from prostate tissue, breast tissue, testicular tissue, thyroid, colon tissue, ovarian tissue, pancreatic tissue, nervous tissue, bone, bone marrow, peripheral blood mononuclear cells, metastatic tissue, cancer cell lines, biopsies, or ocular tissue.
16. The method of claim 1 , further comprising determining an amino acid sequence of the unlabeled isolated peptides detected.
17. The method of claim 1 , wherein a sequence of the unlabeled isolated peptides is determined in an m/z range that includes the m/z of the one or more labeled peptides.
18. The method of claim 1 , wherein the labeled peptides are peptides labeled with heavy leucine, isoleucine, valine, threonine, lysine, tyrosine, phenylalanine, glycine, alanine, arginine, aspartic acid, or proline.
19. The method of claim 17 , wherein the heavy leucine is (L)( 13 C 6 15 N 1 ).
20. The method of claim 1 , wherein the method quantifies peptides present at a level of 30, 40, or 50 copies per cell or more.