Alanine-based spacer sequences between neoantigen peptides significantly improved immune cell recognition compared to the commonly used GGGS linker in cancer vaccine design.
Spacer > position or flankingThe choice of spacer between neoantigen peptides had the largest impact on immune presentation efficiency — more important than peptide position or surrounding sequences
What the researchers found
Using an in vitro MHC-I antigen presentation assay with the SIINFEKL peptide (H-2 Kb-restricted OVA epitope), the study found:
- Spacer type had the largest impact on neoantigen processing and MHC-I presentation efficiency
- Alanine-based linkers promoted more efficient peptide presentation than the commonly used GGGS linker
- Peptide position within the concatenated chain had minimal impact on presentation
- Flanking regions had minimal impact on presentation
These findings suggest that spacer selection — often treated as an afterthought in vaccine design — is actually a critical determinant of vaccine immunogenicity.
Why it matters
Personalized cancer vaccines are one of the most promising frontiers in oncology, but their effectiveness depends on how well the immune system can process the vaccine's peptide components. This seemingly simple finding — that alanine spacers work better than standard linkers — could immediately improve the design of cancer vaccines already in clinical development.
How the study worked
In vitro assay evaluating MHC-I-dependent antigen presentation of SIINFEKL (a well-characterized model epitope). Various linker sequences were tested between concatenated neoantigen peptides. The impact of spacer type, peptide position, and flanking regions on presentation efficiency was systematically evaluated.
What this study cannot tell us
The study used an in vitro assay with a single model epitope (SIINFEKL), which may not represent all neoantigen peptides. Results need validation with diverse tumor neoantigens and in vivo immune responses. The study assessed MHC-I presentation but not the resulting T cell responses. Clinical relevance in actual cancer patients remains to be demonstrated.
How to read the evidence
This is an in vitro study using a model antigen system. While the experimental design is well-controlled and the findings are clearly demonstrated, clinical relevance requires in vivo validation with diverse patient neoantigens.
When this study was published
Published in 2023, this study provides timely guidance for the rapidly growing field of personalized neoantigen cancer vaccines, many of which are currently in clinical trials.
The bigger picture
Neoantigen-based cancer vaccines are being tested in clinical trials for melanoma, lung cancer, and other cancers. This study addresses a fundamental design question that affects all such vaccines: how to connect multiple peptide fragments for optimal immune recognition. Better design principles could improve response rates for this entire class of immunotherapy.
Questions still open
- Do alanine spacers also improve MHC-II presentation and CD4+ T cell responses?
- Would switching to alanine spacers improve outcomes in ongoing neoantigen vaccine clinical trials?
- Is there an optimal alanine spacer length for different types of neoantigen epitopes?
Common questions
What are neoantigen cancer vaccines?
Why do spacers between peptides matter so much?
Read the original research
Alanine-based spacers promote an efficient antigen processing and presentation in neoantigen polypeptide vaccines.
Cancer immunology, immunotherapy : CII, 72(7), 2113-2125
Citation
Aguilar-Gurrieri, Carmen; Barajas, Ana; Rovirosa, Carla; Ortiz, Raquel; Urrea, Victor; de la Iglesia, Nuria; Clotet, Bonaventura; Blanco, Julià; Carrillo, Jorge. (2023). Alanine-based spacers promote an efficient antigen processing and presentation in neoantigen polypeptide vaccines.. Cancer immunology, immunotherapy : CII, 72(7), 2113-2125. https://doi.org/10.1007/s00262-023-03409-3