Transient expression of human papillomavirus type 16 virus-like particles in tobacco and tomato using a tobacco rattle virus expression vector

Abstract

The major capsid protein L1 of human papillomavirus type 16 (HPV16) was transiently expressed in tobacco (Nicotiana benthamiana and Nicotiana tabacum) and tomato (Lycopersicon esculentum) leaves using Agrobacterium tumefaciens. The expression vector pTV00 was derived from tobacco rattle virus (TRV). The highest L1 expression 15 μg g-1(f.m.) was achieved when the coding sequence of L1 was optimized for expression in humans that caused an increase of the guanine and cytosine (GC) content from 38.2 % in wild type HPV16 to 64.1 % in optimized sequence. L1 monomers readily self-assembled into capsomeres and further into virus like particles (VLPs). Immunological characterization and electron microscopy showed that 89 % of L1 retained VLP structure also in extracts prepared from freeze-dried leaves. Plant expressed L1 in crude extracts was highly immunogenic without any additional adjuvant as vaccinated mice developed strong humoral and cellular immune response, comparable to that elicited by purified VLPs derived from insect cells. Further, the induced antibodies effectively neutralized infection of 293TT cells with pseudovirions. This finding demonstrates that the TRV expression system is comparable to other plant expression systems and due to the broad host range of TRV is particularly attractive when expression in plants with low content of toxic alkaloids is desired. Moreover, a monoclonal anti-L1 antibody E2 raised in the course of immunization with crude extract from freeze-dried leaves expressing L1 is specific preferentially against HPV VLPs and could be used in direct ELISA for monitoring of VLPs assembly and VLP purification protocols.