Receptor-Mediated Antigen Delivery by &Alpha;<Sub>2</Sub>-Macroglobulin: Effect on Cytotoxic T Lymphocyte Immunity and Implications for Vaccine Development

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The receptor-recognized form of α2-macroglobulin (α2M*) targets antigens (Ag) to professional Ag-presenting cells (APCs) for rapid internalization, processing, and presentation. When employed as an Ag delivery vehicle, α2M* amplifies major histocompatibility complex (MHC) class II presentation as demonstrated by increased antibody (Ab) titers. Recent evidence, however, suggests that α2M*-encapsulation may also enhance Ag-specific cytotoxic T lymphocyte (CTL) immunity. In these studies, we demonstrate that α2M*-delivered Ag (ovalbumin, OVA) enhances the production of specific in vitro and in vivo CTL responses.

Murine splenocytes expressing a transgenic T cell receptor (TCR) specific for CTL peptide OVA257-264 (SIINFEKL) demonstrated up to 25-fold greater IFN-γ and IL-2 secretion when treated in vitro with α2M*-OVA compared to soluble OVA. The frequency of IFN-γ -producing cells was increased ~15-fold as measured by ELISPOT. Expansion of the OVA-specific CD8+ T cells, as assayed by tetramer binding and [3H]thymidine incorporation, and cell-mediated cytotoxicity, as determined by a flow cytometric assay, were also significantly enhanced by α2M*-OVA. Furthermore, CTL responses were observed at Ag doses tenfold lower than those required with OVA alone.

We also observed enhanced humoral and CTL responses by naïve mice following intradermal immunization with α2M*-OVA. These α2M*-OVA-immunized mice displayed increased protection against a subcutaneously implanted OVA-expressing tumor, as demonstrated by delayed tumor growth and prolonged animal survival. The anti-tumor response observed with α2M*-mediated Ag delivery was comparable to that of an accepted vaccine adjuvant (CpG 1826) and appeared superior to a cell-based vaccine technique.

To further understand the mechanism underlying this enhanced CTL immunity, the subsets of professional APCs capable of cross-presenting α2M*-encapsulated Ag were investigated. Although both dendritic cells (DCs) and macrophages appear to stimulate some degree of cross-priming in response to α2M*-encapsulated Ag, CD8+CD4- and CD8-CD4+ DCs appear to do so with the greatest efficiency. The implications of this finding to the ongoing debate regarding the relative contributions of APC subsets to Ag cross-presentation and the determinants of which cells cross-present with high efficiency are discussed.

These observations demonstrate that α2M*-mediated Ag delivery promotes cross-presentation resulting in enhanced Ag-specific CTL immunity. Considered in the context of previous work, these results support α2M* as an effective Ag delivery system that may be particularly useful for vaccines based on weakly immunogenic subunits or requiring dose sparing.






Bowers, Edith Villette (2009). Receptor-Mediated Antigen Delivery by Α2-Macroglobulin: Effect on Cytotoxic T Lymphocyte Immunity and Implications for Vaccine Development. Dissertation, Duke University. Retrieved from


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