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Published on: February 27, 2019
Bispecific antibodies and CAR T cells targeting a TP53 mutation-associated neoantigen show discordant affinity
Sarah R DiNapoli1,2,3, Katharine M Wright2,4,5, Brian J Mog1,2,3,6
1Ludwig Center, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Abstract:
Mutation-associated neoantigens (MANAs) are highly cancer-specific targets for immunotherapy where peptides derived from intracellular mutant proteins are presented on the cell surface via HLA molecules. T cell-engaging bispecific antibodies and CAR T cells can target MANAs to eliminate cancer cells via T cell activation. However, the low antigen density of MANAs on the cell surface can limit therapeutic efficacy. Here, we investigated whether increasing the affinity of the H2 single-chain variable fragment (scFv) targeting the p53 R175H MANA (HMTEVVRHC presented on HLA-A*02:01) improves its therapeutic effect. We identified higher-affinity H2 variants via phage biopanning and a thiocyanate elution method. Increasing bispecific antibody affinity to the low nanomolar range increased cancer cell killing and tumor control in mouse xenograft models without sacrificing antigen specificity. We next asked how increasing scFv affinity impacts CAR T cell function - a matter of debate. We appended each variant scFv to a CD28z CAR, CD3γ, or the T cell receptor. In striking contrast to the bispecific antibody results, increasing CAR affinity decreased function in each CAR format due to lower T cell activation upon interaction with target cancer cells. These results have important implications for the design of future immunotherapeutic approaches targeting low-density antigens.
Insights
Increasing the affinity of targeting molecules for mutation-associated neoantigens (MANAs) enhances bispecific antibody therapy but impairs CAR T cell function. This finding impacts the design of novel cancer immunotherapies.
Area of Science:
- Immunology
- Oncology
- Biotechnology
Background:
- Mutation-associated neoantigens (MANAs) are specific cancer targets for immunotherapy.
- Low MANA density on cancer cells limits therapeutic effectiveness.
- Bispecific antibodies and CAR T cells can target MANAs to activate T cells.
Purpose of the Study:
- To investigate if increasing the affinity of a single-chain variable fragment (scFv) targeting the p53 R175H MANA improves therapeutic efficacy.
- To determine the impact of increased scFv affinity on both bispecific antibody and CAR T cell functionality.
Main Methods:
- Phage biopanning and thiocyanate elution were used to identify higher-affinity H2 scFv variants.
- Higher-affinity scFvs were incorporated into bispecific antibodies and CAR T cell constructs (CD28z, CD3γ, TCR).
- Cancer cell killing and tumor control were assessed in mouse xenograft models.
Main Results:
- Increased bispecific antibody affinity enhanced cancer cell killing and tumor control without compromising specificity.
- Conversely, increased CAR T cell affinity, regardless of CAR format, decreased T cell activation and anti-cancer function.
- A notable contrast was observed between the effects of affinity enhancement on bispecific antibodies versus CAR T cells.
Conclusions:
- Enhanced affinity of targeting molecules has differential effects on bispecific antibodies and CAR T cells.
- Optimizing affinity is crucial for developing effective immunotherapies against low-density MANAs.
- These findings provide critical insights for the rational design of future MANA-targeted cancer therapies.
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