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

Pizzo, Salvatore V

Bowers, Edith Villette

2010-05-18T05:00:17Z

2009-08-27T18:33:53Z

2009-08-27T18:33:53Z

2009

Pathology

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 OVA_257-264 (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.

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https://hdl.handle.net/10161/1319

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Health Sciences, Pathology

Health Sciences, Immunology

Antigen presentation

Cross

presentation

cytotoxic T cells

dendritic cells

Vaccination

Receptor-Mediated Antigen Delivery by Α₂-Macroglobulin: Effect on Cytotoxic T Lymphocyte Immunity and Implications for Vaccine Development

Dissertation

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