Peptide-bases immunotherapy of atherosclerosis
Final Report Abstract
Immunization or tolerance induction in order to modify atherosclerosis development is still not fully deciphered, new approaches with a gain in efficiency, reduced side effects and the potential for translation into humans are very rare. We utilized apoptotic/necrotic cells as a carrier for Apolipoprotein B100-derived peptides. The antiatherogenic effects of both peptides in a CFA/IFA-vaccination model - the best established approach for anti-atherosclerotic vaccination in animal models at the moment - have been recently published by Tse and colleagues. Though immunization with either only adjuvants or adjuvants in combination with Apolipoprotein-B100 derived epitopes has beneficial effects on the development of atherosclerosis, this intervention is based on the stimulation of mainly Th2, but also Th1 and Th17 responses. Whereas Th1 responses seem undoubtedly to promote the worsening of atherosclerosis, the role for Th17 is unclear. Th2 responses might benefit more than aggravate atherosclerotic burden, but e.g. Th2-associated cytokine IL4 is also highly important for the attachment and immigration of leucocytes in the vessel wall. Peptide-coupled splenocytes have been shown to significantly reduce IFNy production in mouse models of type 1 diabetes mellitus by Niens and co-workers. Hence we expected similar effects in atherosclerosis, where a reduction of Th1 inflammatory properties is supposed to benefit the reduction of atherosclerosis. In our experiments, a stronger Th1 polarization in combination with CD4 T cell activation was observed in spleen, but opposed by reduced proliferative response to antigen recall. Interestingly, also Th17, whose role in atherosclerosis is complex and controversial in several studies, was significantly reduced after immunization with P3/6-SP. The transfer of this model to ApoE-deficient mice however revealed that no significant reduction of atherosclerosis was achieved. We have assessed the inflammatory response with various antigens coupled to spleen cells, which reliably led to Th1 reponses. Interestingly the administration of ECDI-fixed spleen cells without further attachment of antigens had been shown to reduce lymphocyte proliferation. Hence, the induction of Th1 in our experiments might also be due to the chosen antigens, since e.g. P3 and 6 have very high structural affinities to the MHC II complex, which might per se trigger inflammation even without the need for further co-stimulation. Adjuvant-associated effects are highly efficient to control immune responses in vaccination. Though used for decades, the modes-of-action of water-oil emulsions derived from Freund’s adjuvant, or aluminium adjuvants like Alum or MF59, are still not fully understood. The use of adjuvants alone significantly attenuates atherosclerosis in ApoE-deficient mice as e.g. demonstrated by Hansson et al., and is moderately enhanced by the addition of atherosclerosis-associated epitopes. Th2-polarizing Alum, but also Th1 and 17 promoting complete Freund’s adjuvant have this effect on atherosclerosis, though Th1 balanced inflammation has been associated with an aggravation of atherosclerosis. In the study we show evidence, that this phenomenon might be attributed to the rapid expression of pivotal Th2-driving cytokine TSLP within 12 hours after injection. IL1 p is necessary to induce TSLP, but only in male mice, pointing to gender-based differences for the adjuvant-associated effects. The role of proinflammatory IL1 p is puzzling. A recent publication by Shenderov et al. demonstrated inflammasome-dependent IL1 p after CFA-application to be responsible for Th17 responses. Despite its relevance for Th2 balanced immunoresponses, which are in general supposed to benefit atherosclerosis, IL1 p-depletion in ApoE-deficient mice reduces plaques. In our experiments, monocytes and mast cells played a major in the rapid production of TSLP, as demonstrated in monocyte-depleted wildtype mice, or mast cell deficient Cremaster mice, which had a significantly reduced expression of TSLP. Both cell types are known as potential sources for TSLP, but also IL1 p, thus it will be necessary to further dissect their contribution. Eventually, the expression of TSLP relevantly modifies the quality of the subsequent inflammatory response, as TSLPR-deficient mice show a significantly higher production of IFNy in proportion to IL4, which displays a relevant shift towards a Th1 response. In that part of the study, we identified TSLP as a crucial factor for the regulation of CFA-induced inflammation.
