The potential of Physcomitrella patens as a platform for the production of plant-based vaccines Expert Rev. Vaccines 13(2), 203–212 (2014) Sergio Rosales- Mendoza* 1 , Lucı ´a Orellana- Escobedo 1 , Andrea Romero- Maldonado 1 , Eva L Decker 2 and Ralf Reski 2–4 1 Laboratorio de Biofarmace ´ uticos Recombinantes, Facultad de Ciencias Quı ´micas, Universidad Auto ´ noma de San Luis Potosı´, Av. Dr. Manuel Nava 6, SLP, 78210, Me ´ xico 2 Plant Biotechnology, Faculty of Biology, University of Freiburg, Schaenzlestr. 1, 79104 Freiburg, Germany 3 BIOSS – Centre for Biological Signalling Research, Freiburg, Germany 4 FRIAS – Freiburg Institute for Advanced Studies, Freiburg, Germany *Author for correspondence: Tel.: +52 444 826 2440 Fax: +52 444 826 2440 osales.s@fcq.uaslp.mx The moss Physcomitrella patens has a number of advantages for the production of biopharmaceuticals, including: i) availability of standardized conditions for cultivation in bioreactors; ii) not being part of the food chain; iii) high biosafety; iv) availability of highly efficient transformation methods; v) a haploid, fully sequenced genome providing genetic stability and uniform expression; vi) efficient gene targeting at the nuclear level allows for the generation of mutants with specific post-translational modifications (e.g., glycosylation patterns); and vii) oral formulations are a viable approach as no toxic effects are attributed to ingestion of this moss. In the light of this panorama, this opinion paper analyzes the possibilities of using P. patens for the production of oral vaccines and presents some specific cases where its use may represent significant progress in the field of plant-based vaccine development. The advantages represented by putative adjuvant effects of endogenous secondary metabolites and producing specific glycosylation patterns are highlighted. KEYWORDS: bioreactor . glycosylation . low cost vaccines . molecular farming . moss . oral immunization After two decades of research, extensive proofs of the concept for plant-based vaccination have been provided, but these approaches have also faced different maturation steps. Improv- ing expression levels and increasing biosafety were priorities. Expression levels have been improved substantially through platforms based on transplastomic technologies or transi- ent expression mediated by viral elements [1,2]. Other relevant aspects were biosafety concerns, especially those related to the risk of undesired gene flow. Therefore, exploring in detail new plant expression platforms compatible with full containment are of special importance [3]. Although some plant species have been assessed in bioreactor-based biomass produc- tion, some disadvantages are identified. Dedif- ferentiated plant cells cultured in suspensions tend to be sensitive to shearing due to their tough cell wall and large size, which limits operating conditions [4]. In addition, these sus- pension cultures require the presence of plant growth regulators, being prone to induce genetic instability known as somaclonal variation [5]. Another trend in the field was changing the concept of ‘eating transgenic fruits as vaccine’ to the concept of using formulations obtained by processing the plant biomass. Therefore, new platforms would provide possibilities to expand the alternatives for the production of vaccines at low cost and under an environment-friendly process. The moss life cycle is characterized by an alternation of two stages: a haploid gameto- phyte and a diploid sporophyte. Gametes are generated from the gametophyte by mitosis. Their fusion results in diploid zygotes, which give rise to embryos that develop into the sporophyte. Subsequently, sporophytes can produce spores through meiosis, which germi- nate to produce further gametophytes [6]. Fol- lowing spore germination, most of the moss species develop a filamentous stage called pro- tonema. In the case of Physcomitrella patens, this stage can be long-lived under lab culture and comprises only two distinct cell types, chloronema and caulonema. Chloronema filaments are produced right after spore germination and possess densely www.expert-reviews.com 10.1586/14760584.2014.872987 Ó 2014 Informa UK Ltd ISSN 1476-0584 203 Perspective Expert Review of Vaccines Downloaded from informahealthcare.com by IBI Circulation - Ashley Publications Ltd on 01/20/14 For personal use only.