Voie d'immunisation et séquence d'administration de l ... - TEL

tel-00827710, version 1 - 29 May 2013
5
Abstract
Most successful vaccines currently in use are based on the generation of protective antibodies.
However, CD8 + T cell responses are crucial in the defense against several infectious agents,
including HIV or plasmodium, as well as for the treatment of cancer or chronic diseases.
Thus, the development of vaccine strategies capable of eliciting robust CD8 + T cell responses
is absolutely needed. Antigen cross-presentation is known to be an important mechanism for
the activation of antigen-specific CD8 + T cells, and it has been shown that multiple
parameters contribute to the efficiency of cross-priming. We examined two of them in detail:
the route of immunization and the timing of adjuvant delivery.
Our first priority was to develop and optimize the tetramer-based enrichment strategy and
combined its advantages with additional approaches, which allowed us to perform an in-depth
study of the kinetics, phenotype and functionality of the endogenous CD8 + T cell response.
These approaches permitted us to work within a model reflecting “physiologic” conditions in
terms of initial precursor T cell frequency.
We applied these methods to investigate the impact of the route of immunization on CD8 + T
cell cross-priming. By comparing different strategies of immunization, we report that local
delivery of cell-associated antigen results in delayed cross-priming due to the increased time
required for antigen capture and presentation. In comparison, delivery of systemically
disseminated antigen resulted in rapid T cell priming. Surprisingly, local injection of cellassociated
antigen, while slower to mount a functional response, resulted in the differentiation
of a more robust, polyfunctional effector T cell population and an enhanced secondary
response. However, the overall diversity and avidity of the responding antigen-specific T cells
did not appear to be affected by the route of immunization. Factors such as inflammation
induced at the site of injection, dendritic cell (DC) subsets involved in antigen uptake and
presentation, or the persistence of antigen may all contribute to the differences observed.
We were next interested in evaluating the combination of cell-associated antigen with the
delivery of poly I:C, an adjuvant known to induce the production of type I interferons (IFN).
We observed an immunization-route-specific effect regarding the timing of innate immune
stimulation and identified the optimal time window for adjuvant administration in order to
maximize the boosting effects on CD8 + T cell cross-priming. We characterized in detail
several effects of poly I:C, as well as type I IFN, exerted on immune cells, such as the
induction of DC maturation and recruitment in lymphoid organs, but also disappearance of the
CD8α + DC subset, providing the basis for our hypotheses as to why adjuvant treatment may
lead to either the inhibition or enhancement of cross-priming depending on the timing of
delivery.
Together, these studies highlight the importance of working within conditions that reflect the
“physiologic” conditions of human vaccination. We demonstrated in a fundamental model,
that it is crucial to consider the timing and persistence of antigen presentation, and to
coordinate this kinetic with the timing for adjuvant delivery in order to elicit a potent cellmediated
immune response. Similar approaches to those used here in an established
experimental model of cross-presentation may also be applied to assess the efficiency of
combinatorial therapies and sequence of administration of several treatments in complex
human diseases such as cancer or chronic viral diseases.
Keywords: cross-priming, cell-associated antigen, CD8 + T cell, route of immunization, timing
of adjuvant delivery, pleiotropic roles of type I interferons, vaccination