Molecular imaging is a family of techniques that visualizes biological processes in living subjects by using probes that bind to specific molecular targets. In nuclear medicine, PET (positron emission tomography) and SPECT (single-photon emission computed tomography) are workhorse modalities because they can detect tiny (trace) amounts of radiolabeled compounds and quantify target-related signals in vivo. Within PET/SPECT, targeted peptides have become a major probe class: short amino-acid sequences engineered to recognize receptors or other biomarkers (often overexpressed in tumors or diseased tissue), then “tagged” with a radionuclide so the binding event becomes imageable. 1) What Makes Peptide Targeting So Useful in PET and SPECT? Peptides sit in a sweet spot between small molecules and antibodies: High affinity and specificity (when well-designed): peptides can be tuned to fit receptor binding pockets or interaction surfaces, producing strong target-to-background contrast. Fast pharmacokinetics: many peptides clear from blood relatively quickly, which can reduce background signal and enable same-day imaging workflows (depending on isotope half-life and probe design). Chemically modular: it’s typically straightforward to add linkers, chelators, or stabilizing modifications without destroying binding—if the chemistry is placed away from the binding “hot spots.” In practice, peptide probes often target cell-surface receptors…
Vaccine development increasingly relies on precision antigen selection: instead of using a whole pathogen or a full-length protein, researchers can focus immune responses on carefully chosen antigen epitopes—the specific parts of an antigen that B cells and T cells recognize. This strategy underpins peptide vaccines (and multi-epitope constructs), where short synthetic sequences are selected, optimized, and formulated to drive protective immunity while reducing unnecessary or reactogenic components. In modern pipelines, epitope screening acts as the bridge between basic immunology and engineering-style vaccine design. 1) What “Epitope Screening” Means in Vaccine Development An epitope is a minimal molecular “handle” from an antigen that immune receptors can recognize. Epitope screening aims to identify epitopes that are: Immunogenic (able to elicit a measurable immune response) Relevant to protection (correlated with neutralization, clearance, or T cell control) Conserved (less likely to mutate and escape) Safe (low risk of off-target reactivity or adverse immunopathology) Broadly coverable across populations (especially for T-cell epitopes that depend on HLA/MHC diversity) As vaccine programs move from exploratory research into preclinical assessment, selecting the right antigen targets—including epitope-level targets—becomes a foundational decision that influences downstream formulation, assay development, and clinical strategy. 2) Why Peptide Vaccines Depend on…