It should be noticed that taliglucerase alfa (Elelyso
® ), the first plant-made
licensed recombinant pharmaceutical protein, is produced by carrot cell suspension
cultures (Shaaltiel et al. 2007) as well as the veterinary vaccine for poultry against
Newcastle disease approved by the US Department of Agriculture that is produced
in suspension-cultured tobacco cells.
Despite general concerns about a possible genetic instability, plant cell cultures
are fundamentally a reliable system in which medium optimization, process
engineering, experimental/process design and scale-up can be tuned on demand
(reviewed in Santos et al. 2016).
2.1.3 Green Unicellular Microalgae
In the recent past, other systems have been devised, which can easily be contained,
propagated and transformed to produce recombinant proteins. A protein expression
system that is based on the unicellular green alga Chlamydomonas reinhardtii
has been developed (Mayfield et al. 2003). This alga has nuclear, plastidial and
mitochondrial genomes completely sequenced. In this system, chloroplast-targeted
transgenes were used to express different recombinant, health-related proteins.
Like bacteria, the chloroplast lacks the machinery to perform complex posttranslational modifications such as glycosylation (the glycosylated proteins come
from the endoplasmic reticulum), but, unlike E. coli, Chlamydomonas chloroplast
allows the disulphide bond formation and is able to carry out some types of
phosphorylation. Unlike higher plants, C. reinhardtii has a single chloroplast, with
about 80 genome copies. Consequently, conversion of all copies of the chloroplast
genome to recombinant homoplasmy is facilitated. Complex molecules such as
fully functional antibodies, therapeutics (among which a candidate therapeutic
vaccine against human papillomavirus-related tumours based on a soluble, immunogenic form of the E7 viral protein) and other biologics have been produced
with various yields highlighting the potential of microalgae as alternative platforms for the production of biologics for human uses (Mayfield et al. 2003;
Demurtas et al. 2013). This relatively novel platform offers advantages including
short time from transformation to scaling-up, rapid growth (doubling time of
few hours), ease of cultivation, safety (microalgae do not harbour human pathogens
and many are generally regarded as safe (GRAS) organisms) facilitating production
of biopharmaceuticals in GMP conditions and homogeneity of protein production.
Technologies for molecular pharming in C. reinhardtii are still in the infancy,
while efforts are made to bring productivity to levels comparable to those of wellestablished platforms.
2.1.4 The “Hairy Root” Culture System
Together with cell suspensions, organ cultures such as hairy root offer advantages including containment, defined cultivation conditions and product homogeneity (Schillberg et al. 2013). Hairy roots (HR) are particularly attractive for the
72
S. Massa et al.
® ), the first plant-made
licensed recombinant pharmaceutical protein, is produced by carrot cell suspension
cultures (Shaaltiel et al. 2007) as well as the veterinary vaccine for poultry against
Newcastle disease approved by the US Department of Agriculture that is produced
in suspension-cultured tobacco cells.
Despite general concerns about a possible genetic instability, plant cell cultures
are fundamentally a reliable system in which medium optimization, process
engineering, experimental/process design and scale-up can be tuned on demand
(reviewed in Santos et al. 2016).
2.1.3 Green Unicellular Microalgae
In the recent past, other systems have been devised, which can easily be contained,
propagated and transformed to produce recombinant proteins. A protein expression
system that is based on the unicellular green alga Chlamydomonas reinhardtii
has been developed (Mayfield et al. 2003). This alga has nuclear, plastidial and
mitochondrial genomes completely sequenced. In this system, chloroplast-targeted
transgenes were used to express different recombinant, health-related proteins.
Like bacteria, the chloroplast lacks the machinery to perform complex posttranslational modifications such as glycosylation (the glycosylated proteins come
from the endoplasmic reticulum), but, unlike E. coli, Chlamydomonas chloroplast
allows the disulphide bond formation and is able to carry out some types of
phosphorylation. Unlike higher plants, C. reinhardtii has a single chloroplast, with
about 80 genome copies. Consequently, conversion of all copies of the chloroplast
genome to recombinant homoplasmy is facilitated. Complex molecules such as
fully functional antibodies, therapeutics (among which a candidate therapeutic
vaccine against human papillomavirus-related tumours based on a soluble, immunogenic form of the E7 viral protein) and other biologics have been produced
with various yields highlighting the potential of microalgae as alternative platforms for the production of biologics for human uses (Mayfield et al. 2003;
Demurtas et al. 2013). This relatively novel platform offers advantages including
short time from transformation to scaling-up, rapid growth (doubling time of
few hours), ease of cultivation, safety (microalgae do not harbour human pathogens
and many are generally regarded as safe (GRAS) organisms) facilitating production
of biopharmaceuticals in GMP conditions and homogeneity of protein production.
Technologies for molecular pharming in C. reinhardtii are still in the infancy,
while efforts are made to bring productivity to levels comparable to those of wellestablished platforms.
2.1.4 The “Hairy Root” Culture System
Together with cell suspensions, organ cultures such as hairy root offer advantages including containment, defined cultivation conditions and product homogeneity (Schillberg et al. 2013). Hairy roots (HR) are particularly attractive for the
72
S. Massa et al.