"NS3 protease Teleprevir and Boceprevir are the first generation protease inhibitors that are FDA approved. NS3 protease inhibitors work on the fact that NS3 protease undergoes end product cleavageand the P side product remain attached to the protease active site inhibiting the binding of the 10, 11 other substrates . NS3 protease inhibitors have low genetic barrier hence these are usedoften in combinations. Simeprevir is a second generation protease inhibitor effective againstgenotype 1 but taken in combinations due to low genetic barrier. The other approaches toinhibit the NS3 protease Include12 1. Inhibiting the binding site for the Zinc atom leading to misfolding of the protein 13 2. Blocking the interaction of NS3 protease with its cofactor NS4A eg. ACH-806halted developmentNS5A protein A membrane associated phosphoprotein, involved in membrane web formation andreplication. The research by Gao and colleagues lead to the discovery of the antiviral14 compound Daclatasvir . This is known to inhibit the membrane web formation and thusinhibiting RNA replication ( C.Berger and R. Bartenschlager, unpublished). Daclatasvir hashigh antiviral activity against Genotypes 1 to 4. Daclatasvir also has low resistance barrier.Ledipasvir is another NS5A inhibitor effective against genotype 1, 4 and 6. It is availableonly in combination with sofosbuvir known as HARVONI produced by Gilead Sciences.NS5B proteinNS5B is an RNA dependent RNA polymerase that carries HCV replication. The GDD motifin the palm subdomain constitutes the active site of the polymerase which along with the2+ Mg ions is involved in binding the nucleotide substrates and nucleotide polymerisation.There are 2 classes of NS5B inhibitors- the Nucleotide Inhibitors (NIs) and the Nonnucleotide Inhibitors (NNIs). The NI resembles the natural substrate and gets incorporated inthe growing chain leading to termination of elongation. On the other hand the NNI bind to theenzyme as allosteric inhibitors and induce conformational change thus inhibiting thepolymerase activity. On uptake they need to be converted to di- and triphosphate. The NI(s)have pangenotypic activity and have high genetic barrier. Sofosbuvir is a NI that resembles5’- monophosphate, has pangenotypic activity and showed high SVR in patients.The non nucleotide inhibitors exhibit four allosteric binding sites- two sites located in thethumb domain(thumb 1 and thumb 2) and two reside in the palm domain (palm 1 and palm 2)15 close to the active site . NNI work by inducing a conformational change like the hyperclosedactive site or can limit the mobility of the enzyme.Table 1- Treatment recommendation for patients with HCV ? Prophylactic and Therapeutic VaccinesDifferent preclinical studies have been carried out in the development of prophylactic andtherapeutic vaccines within the last two decades using different strategies and targetingdifferent regions of the HCV polyprotein. The different vaccine strategies employed forclinical trial include the recombinant proteins, synthetic peptides, DNA vaccines and Vectorbased vaccines (Listed in table 2) some of which are discussed below.Recombinant proteins The genes encoding the viral proteins are cloned into yeast and the recombinant proteins arepurified and used in vaccine development. The advantage of this strategy is that it offers apathogen free candidate and it do not require cultivation of the organism. Using this approachHCV envelop proteins have been immunised in rodents, chimpanzees and healthy human16, 17 volunteers . These studies showed high neutralising antibody response. Aphase I clinicaltrial (NCT00500747)addressing the safety and efficacy of the vaccine in healthy humans18 showed that the vaccine induce strong humoral and CD4+ T cell response .This study didnot complete the phase II due to technical difficulties in protein production.Many studieswere carried out using recombinant proteins for vaccine development but they had withdrawsdue to technical difficulties, low titres of nAb elicited and HCV evasion mechanisms.Synthetic PeptidesThese are viral peptides coupled with adjutants that can induce strong humoral and cellmediated immune response.Strong cellular immune response was showed in mice 19 immunised with peptides of the core and nonstructural proteins (NS5A and NS4B) . Acomparative analysis between the DNA and peptide approaches showed that immunization with peptides of nonstructural regions showed efficient viral clearance, long lasting immune20 response and increased antibody in comparison with DNA based immunisation . DNA vaccinesIn DNA vaccine, the plasmid encoding the antigenic HCV protein(s) is injected, this resultsin protein expression in vivo which generate humoral and cell mediated immune response21. 22(strong Cytotoxic T lymphocytes response) .The host cells take up the DNA vaccine,transcribe and translate it to yield proteins. These viral proteins are processed via theendogenous pathway. The productions in inexpensive and they are safe in animals and23 humans . Using this strategy a therapeutic vaccine ChronVac C encoding HCV NS3/4A has24 been proposed for chronic HCV cases and currently it is in Phase II clinical trial(ClinicalTrials.gov Identifier: NCT01335711).Virus vector Based VaccinesThe main idea behind the use of virus vector based vaccines is to manipulate the virus todeliver foreign genetic material into the mammalian cells. They can induce T cell immunityand humoral immune response. The advantages of these vector vaccines are that they canaccommodate large foreign genes and they remain outside the host cells. The most commonlyused vectors are Adenovirus, Modified vaccinia Ankara (MVA), alphavirus or paramyxovirusvectors. Adenovirus expressing HCV nonstructural proteins shoed protective T cell responses25 in chimpanzees and were immunogenic in healthy volunteers . However the disadvantages with adenovirus are the pre-existing immunity that results in itsclearance before inducing immune response. This issue was overcome by the use of Modified 26, 27. vaccinia Ankara virus due to its minimal pre-existing immunity Using MVA, a vaccine called TG4040 was developed. This encodes the HCV NS3, NS4 andNS5B genes and the results in phase I clinical trial on 15 chronically infected HCV patients28 showed decline in the viral load and significant T cell response . A phase II clinical trial iscompleted but no results have been posted yet (ClinicalTrials.gov Identifier: NCT01055821). Different strategies for vaccine are in phase I and Phase II clinical trial and research isstill continuing in terms of development of a safe and efficient vaccine for HCV.Proposalsto improve the design, selection of immunogens, safety and administration are in progress."