A promising way of generating cancer vaccines uses dendritic cells — specialized antigen-presenting cells. But to generate an effective vaccine, they must be collected from the patient and then subjected to time-consuming and costly 'customizing' procedures — in which they are expanded and loaded with tumour antigens and/or cytokine-encoding genes — before they can be re-administered to the patient. Could this lengthy ex vivo process be replaced by a simpler procedure?
Langerhans cells (LCs) — dendritic cells that reside in skin — generally stay put unless they are induced to mature. Maturation involves acquiring receptors for chemokines such as macrophage inflammatory protein 3β (MIP-3β), allowing them to move along a chemokine gradient from the epidermis to draining lymph nodes. This response can be triggered by haptens — small molecules that are not antigenic unless they are associated with a larger molecule such as a protein. But what if a 'decoy' lymph node could be produced that diverts LCs away from their real destination to a site where they can easily be pulsed with antigen? To this aim, the authors produced ethylene–vinyl–acetate (EVA) rods that released MIP-3β, and implanted them just under the abdominal skin of mice. Application of fluorescein isothiocyanate (FITC) — a hapten that also doubles up as a fluorescent signal for tracking LC migration — revealed that MIP-3β-expressing rods 'trapped' LCs by attracting them to the rods. By contrast, after 24 hours, a significant number of LCs had migrated from the epidermis to the draining lymph nodes in mice with either no implanted rods or rods expressing a control protein.
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