(464f) Colloidal Materials for Modulating the Immune Response

Polymeric nanoparticles hold tremendous potential in medicine, especially if modes of biofunctionality can be incorporated into them.  Here we consider different kinds of biofunctionality, focused on applications in antigen presenting cell-targeted immunotherapeutics.  We consider functionality in pathways for degradation, in physiological routes of penetration of biological barriers for delivery, and in activation of dendritic cells for induction of adaptive immune responses.

Our laboratory has recently described a novel family of AB and ABA block copolymeric amphiphiles that are capable of forming micelles and vesicles ^{1, 2}, as well as inverse emulsion-polymerized nanoparticles based on the B block using Pluronic emulsifiers ^{3, 4}.  As a hydrophilic block A, we employ polyethylene glycol (PEG), because of its well known toxicological profile and its well-defined and low polydispersity.  As a hydrophobic block, we have selected polypropylene sulfide (PPS), a low Tg polymer that can be synthesized by a ring opening living polymerization also with low polydispersity ⁵.  We have demonstrated that these polymers form mesoscopic aggregates that are sensitive to oxidative environments by conversion of the hydrophobic PPS to the hydrophilic polypropylene sulfone ²; this provides a route of degradation of the micelle-forming amphiphile into a fully soluble low molecular weight polymer, sufficiently small for clearance by renal filtration.   We have also sought to render these same structures sensitive to reduction, to allow destabilization of vesicles within the early endosome after endocytosis by linking the two blocks with a reduction-sensitive disulfide ⁶, for use in intracellular delivery, for example of adjuvant molecules targeting intracellular receptors (such as CpG DNA), antigens for targeted MHC 1 presentation, or antigen-encoding DNA.  Thus, the redox sensitivity of these materials can be used to enable release of incorporated agents and ultimate elimination of the micelle-forming polymer.

With the micelle-forming AB and ABA block copolymers as well as the analogous materials formed by inverse emulsion polymerization of propylene sulfide using Pluronics as emulsifier, we are seeking nanoparticle forms that are sufficiently small as to pass barriers to efficiently access the targeted antigen-presenting cells.  Of particular interest to us, is targeting dendritic cells resident in the lymph nodes after intradermal or subcutaneous injection ⁷.  We have shown that ultrasmall particles, ca. 25 nm, can target lymph node-resident dendritic cells very efficiently, being swept through the tissue interstitium by the slow flows that exist between the blood and lymphatic capillaries in the skin.  Also with such small nanoparticles, we see very effective penetration of mucosal barriers in the nasal sinus⁸ and very efficient uptake by antigen presenting cells in the lung after instillation in the mouse. We show that when antigen is reversibly coupled to these nanoparticle surfaces by a disulfide link, very potent cellular immune responses can be induced^{9, 10}.

We seek to be able to incorporate biofunctionality into these nanoparticles for activation of antigen presenting cells.  In a first approach, we designed the nanoparticle surface for activation of complement by the alternative pathway, and we demonstrated that complement activation could serve as a very potent, particle-mediated danger signal for dendritic cell activation in situ ^{11, 12}.   Current work also addresses incorporation of additional danger signal molecules into the nanoparticle formulation, including engineered flagellin truncation variants⁸, and CpG DNA sequences incorporated into the nanoparticle surfaces and cores.

References:

1.  Cerritelli, S. et al. Thermodynamic and kinetic effects in the aggregation behavior of a poly(ethylene glycol-b-propylene sulfide-b-ethylene glycol) ABA triblock copolymer. Macromolecules 38, 7845-7851 (2005).

2.  Napoli, A., Valentini, M., Tirelli, N., Muller, M. & Hubbell, J.A. Oxidation-responsive polymeric vesicles. Nature Materials 3, 183-189 (2004).

3.  Rehor, A., Botterhuis, N.E., Hubbell, J.A., Sommerdijk, N.A.J.M. & Tirelli, N. Glucose sensitivity through oxidation responsiveness. An example of cascade-responsive nano-sensors. J. Mater. Chem. 15, 4006-4009 (2005).

4.  Rehor, A., Tirelli, N. & Hubbell, J.A. A new living emulsion polymerization mechanism: Episulfide anionic polymerization. Macromolecules 35, 8688-8693 (2002).

5.  Napoli, A., Tirelli, N., Kilcher, G. & Hubbell, J.A. New synthetic methodologies for amphiphilic multiblock copolymers of ethylene glycol and propylene sulfide. Macromolecules 34, 8913-8917 (2001).

6.  Cerritelli, S., Velluto, D. & Hubbell, J.A. PEG-SS-PPS: Reduction-sensitive disulfide block copolymer vesicles for intracellular drug delivery. Biomacromolecules 8, 1966-1972 (2007).

7.  Reddy, S.T., Rehor, A., Schmoekel, H.G., Hubbell, J.A. & Swartz, M.A. In vivo targeting of dendritic cells in lymph nodes with poly(propylene sulfide) nanoparticles. Journal of Controlled Release 112, 26-34 (2006).

8.  Stano, A. et al. PPS nanoparticles as versatile delivery system to induce systemic and broad mucosal immunity after intranasal administration. Vaccine 29, 804-812 (2011).

9.  van der Vlies, A.J., O'Neil, C.P., Hasegawa, U., Hammond, N. & Hubbell, J.A. Synthesis of pyridyl disulfide-functionalized nanoparticles for conjugating thiol-containing small molecules, peptides, and proteins. Bioconjugate Chemistry 21, 653-662 (2010).

10.  Hirosue, S., Kourtis, I.C., van der Vlies, A.J., Hubbell, J.A. & Swartz, M.A. Antigen delivery to dendritic cells by poly(propylene sulfide) nanoparticles with disulfide conjugated peptides: Cross-presentation and T cell activation. Vaccine 28, 7897-7906 (2010).

11.  Reddy, S.T. et al. Exploiting lymphatic transport and complement activation in nanoparticle vaccines. Nature Biotechnology 25, 1159-1164 (2007).

12.  Thomas, S.N. et al. Engineering complement activation on polypropylene sulfide vaccine nanoparticles. Biomaterials 32, 2194-2203 (2011).