By Klaus D. Linse
Can synthetic peptides be used for the development of vaccines against cancer cells?
Many medical scientists think the answer is yes. In a study published by Schwartzentruber et al. in the “New England Journal of Medicine” in June 2011 a group of researchers report that the treatment of patients with advanced metastatic melanomas when treated with the gp100:209-217(210M) peptide vaccine in combination with interleukin-2 showed promising results to do just that. The scientists report that “in patients with advanced melanoma, the response rate was higher and progression-free survival longer” when treated” with “the” vaccine” compared to the treatment with interleukin-2 alone. Furthermore they report that the median overall survival rate was also longer in the vaccine–interleukin-2 group in comparison to the interleukin-2–only group. However, the study was critically reviewed in the same journal in August 2011 by Dr. David M. Minor, M.D. because, according to him, the study was not a double-blind study. He argued that this type of study may bias the results because the physicians administering the drug knew what they were giving the patients. However I believe after reviewing the published study that this type of vaccination has a very high chance to become an effective treatment in the future. On the other hand, many scientists caution that more studies will be needed to rule out potential side effects.
Recent research in the fields of molecular immunology and molecular medicine has increased our understanding of antigen recognition at the molecular level. This understanding allows scientist now to rationally design and develop peptide based vaccines. B-cell and T-cell epitopes which are immunodominant and can induce specific immune responses have been and can be identified employing molecular biology/biochemical approaches such as the use of synthetic peptide libraries to screen for bioactive peptides. This is just one example and many other approaches are possible. A B-cell epitope of a target molecule can be coupled to a promiscuous T-cell epitope to make it immunogenic. Since peptides can now be synthesized with relative ease they have become attractive candidates for vaccine development. However, to make peptides more useful for this purpose several obstacles need to be addressed. Some of these include their low immunogenicity, the need for better adjuvants and carriers, as well as the existence of reliable and simple assays to measure T-cell response. Nonetheless, current efforts to circumvent these limitations are in progress and a few peptide based vaccines against cancer are undergoing phase I and phase II clinical trials, some with a positive outcome. In addition, vaccination approaches using synthetic peptides are also investigated for their use to treat or moderate pain and for prophylactic immunotherapies.
Generally applicable screening approaches to identify new HLA-DRB1*0301-restricted CD4+ T cell epitopes derived from melanoma antigens have been developed. The employed strategy is applicable to screen for antigens of other tumor entities or even other pathogenic entities and to different HLA class II molecules without prior characterization of their peptide binding motives. T cells isolated from the peripheral blood and tumor tissue of melanoma patients are known to recognize epitopes derived from melanoma antigens. Melanoma cells stimulate endogenic immune responses that can play a critical role in combating the disease in some individual patients. The use of adoptive T-cell transfer showed that these melanoma differentiation antigen–specific T-cells exhibit cytolytic activitis against autologous tumor cells in vitro and in vivo. Identified antigens that belong to the melanoma differentiation antigen group include gp100, MelanA/MART-1, tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2. Several recent studies revealed the protective antitumor capacity of TRP-2-specific murine cytotoxic T cell suggesting that TRP-2 might function as an autologous tumor rejection antigen also in humans.
Kawakami, Robbins and Rosenberg published a review paper in 1995 reviewing human melanoma antigens that are recognized by T lymphocytes. Classical techniques that were developed to identify the antigens as well as the classification of the antigens were discussed.
According to Kawakami et al. isolated human melanoma antigens can be classified as:
1) melanocyte specific melanosomal proteins (MART-1, gp100, tyrosinase and TRP-1),
2) testis specific proteins which are also expressed in a variety of cancers (MAGE-1, MAGE-3, BAGE and GAGE),
3) tumor specific mutated proteins (β-catenin, MUM-1 and CDK4), and
4) others (p15).
The researchers stated in their review that “Peptides may be used for immunization in conjunction with adjuvants or lipids” and that “Clinical trials using MART-1 or gp100 peptides along with incomplete Freund’s adjuvant are being conducted in melanoma patients in the NCI Surgery Branch.”
More recently Buonaguro et al. in 2011 published a minireview in which the uses of tumor antigens to design and develop cancer vaccines useful for cancer immunotherapies are described. The overall goal is to find specific and selective tumor antigens that are promising targets for the development of tumor-specific cancer vaccines. Furthermore, the scientists argue that optimal delivery systems, adjuvants and strategies are needed to overcome immune tolerance and regulatory T (Treg) cell responses. The following graphic illustrates the reported approach called “DC-based vaccine preparation.”
Schematic representation of a DC-based vaccine preparation.
(Source: Buonaguro et al. in 2011)
In this dentritic cell (DC) based approach CD14+ monocytes or CD34+ hematopoietic progenitor cells are isolated from patients. Different specialized DC subsets are generated in vitro. The DC subsets drive the adaptive immunity to the Th1 or Th2 response. Next, mature DCs are loaded with one of the indicated sources of tumor antigens and reinfused in the patient. Relevant cell markers characterizing the different activation stages of DCs are indicated in the graphic.
How does vaccination with pg 100 peptides against cancer cells work?
A peptide vaccine for cancer vaccination can be developed by isolating proteins from cancer cells. Bioactive synthetic peptides selected from the isolated proteins and screened for their ability to induce an immune response are used to immunize cancer patients against these proteins. The hope is to stimulate an immune reaction that will kill the cancer cells. Many researchers and companies are now working feverishly to develop therapeutic cancer vaccines with the hope to treat breast, lung, colon, skin, kidney, prostate, and other cancers.
The Gp100:209-217(210M) peptide based vaccine is a synthetic cancer vaccine consisting of a peptide with the amino acid residues 209 through 217 of the glycoprotein 100 (gp100) melanoma antigen, with a methionine substitution at position 210 often referred to as the gp100 cancer vaccine that can also include other peptides based on the sequence of the gp100 protein. The replacement of threonine with methionine in position two in the peptide sequence has been reported to induce melanoma reactive cytotoxic T lymphocytes more efficiently than the unmodified native peptide.
The following structures of gp100 and gp100 complexes have been published and can be retrieves for investigation and used as models to guide targeted vaccine development from the NIH website: http://www.ncbi.nlm.nih.gov/structure?term=gp100. A list of the structures as well as some additional structural information that can be retrieved from the NIH protein database is shown below.
Solved 3D structures for the gp100 protein
1. H-2db Complex With Human Gp100[Immune System]. Taxonomy: Mus musculus, synthetic construct. MMDB ID: 69928, PDB ID: 3CC5.
2. Crystal Structure Of Modified Melanoma Antigen Gp100(209-T2m) Bound To Human Class I Mhc Hla-A2[Immune System], Taxonomy: Homo sapiens, synthetic construct. MMDB ID: 32748 PDB ID: 1TVH
3. Crystal Structure Of Melanoma Antigen Gp100(209-217) Bound To Human Class I Mhc Hla-A2[Immune System], Taxonomy: Homo sapiens, synthetic construct. MMDB ID: 32747 PDB ID: 1TVB
4. Crystal Structure Of H-2db In Complex With Chimeric Gp100[Immune System], axonomy: Mus musculus, synthetic construct. MMDB ID: 70519 PDB ID: 3CH1
5. H-2db Complex With Murine Gp100[Immune System], Taxonomy: Mus musculus, synthetic construct. MMDB ID: 70080 PDB ID: 3CCH
More info for two of these structures is shown below as well.
PDB ID: 3CC5.
Nonameric peptide bound to gp100 protein 3CC5: kvprnqdwl
PDB ID: 1TVH
Nonameric peptide bound to gp100 protein 1TVH; imdqvpfsv
The following table shows the peptides bound to the gp100 protein derived from the 3D structures of the gp100-peptide complexes.
Peptide bound to gp100 protein
In conclusion, peptide libraries as well as other molecular biological approaches are useful tools to identify antigenic peptides as useful candidates for the development of peptide based immunotherapies. Available 3D structures of representative protein-peptide complexes allow for structure guided design of peptide drugs. Further developments of these approaches may allow scientist to design needed vaccines in the near future.
Luigi Buonaguro, Annacarmen Petrizzo, Maria Lina Tornesello, and Franco M. Buonaguro; Translating Tumor Antigens into Cancer Vaccines. CLINICAL AND VACCINE IMMUNOLOGY, Jan. 2011, p. 23–34.
Yutaka Kawakami, Paul F Robbins and Steven A Rosenberg. REVIEW: Human Melanoma Antigens Recognized by T Lymphocytes. Keio J Med 45 (2): 100-108, June 1996.
Kawakami Y.; New cancer therapy by immunomanipulation: development of immunotherapy for human melanoma as a model system. Cornea. 2000 May;19(3 Suppl):S2-6.
Naz RK, Dabir P.; Peptide vaccines against cancer, infectious diseases, and conception. Front Biosci. 2007 Jan 1;12:1833-44.
Osen W, Soltek S, Song M, Leuchs B, Steitz J, et al.; (2010) Screening of Human Tumor Antigens for CD4+ T Cell Epitopes by Combination of HLATransgenic Mice, Recombinant Adenovirus and Antigen Peptide Libraries. PLoS ONE 5(11): e14137. doi:10.1371/journal.pone.0014137
Annette Paschen, Mingxia Song, Wolfram Osen, Xuan Duc Nguyen, Jan Mueller-Berghaus, Daniela Fink, Nadine Daniel, Mariel Donzeau, Wolfgang Nagel, Harald Kropshofer, and Dirk Schadendorf; Detection of Spontaneous CD4+ T-Cell Responses in Melanoma Patients against a Tyrosinase-Related Protein-2–Derived Epitope Identified in HLA-DRB1*0301 Transgenic Mice Clin Cancer Res July 15, 2005 11; 5241.
Douglas J. Schwartzentruber, M.D., David H. Lawson, M.D., Jon M. Richards, M.D., Ph.D., Robert M. Conry, M.D., Donald M. Miller, M.D., Ph.D., Jonathan Treisman, M.D., Fawaz Gailani, M.D., Lee Riley, M.D., Ph.D., Kevin Conlon, M.D., Barbara Pockaj, M.D., Kari L. Kendra, M.D., Ph.D., Richard L. White, M.D., Rene Gonzalez, M.D., Timothy M. Kuzel, M.D., Brendan Curti, M.D., Phillip D. Leming, M.D., Eric D. Whitman, M.D., Jai Balkissoon, M.D., Douglas S. Reintgen, M.D., Howard Kaufman, M.D., Francesco M. Marincola, M.D., Maria J. Merino, M.D., Steven A. Rosenberg, M.D., Ph.D., Peter Choyke, M.D., Don Vena, B.S., and Patrick Hwu, M.D. gp100 Peptide Vaccine and Interleukin-2
in Patients with Advanced Melanoma. The new England journa l o f medicine 364;22 nejm.org june 2, 2011.
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