Deletion of C7L and K1L Genes Leads to Significantly Decreased Virulence of Recombinant Vaccinia Virus TianTan

Abstract

The vaccinia virus TianTan (VTT) has been modified as an HIV vaccine vector in China and has shown excellent performance in immunogenicity and safety. However, its adverse effects in immunosuppressed individuals warrant the search for a safer vector in the following clinic trails. In this study, we deleted the C7L and K1L genes of VTT and constructed six recombinant vaccinia strains VTT△C7L, VTT△K1L, VTT△C7LK1L, VTKgpe△C7L, VTKgpe△K1L and VTT△C7LK1L-gag. The pathogenicity and immunogenicity of these recombinants were evaluated in mouse and rabbit models. Comparing to parental VTT, VTT△C7L and VTT△K1L showed significantly decreased replication capability in CEF, Vero, BHK-21 and HeLa cell lines. In particular, replication of VTT△C7LK1L decreased more than 10-fold in all four cell lines. The virulence of all these mutants were decreased in BALB/c mouse and rabbit models; VTT△C7LK1L once again showed the greatest attenuation, having resulted in no evident damage in mice and erythema of only 0.4 cm diameter in rabbits, compared to 1.48 cm for VTT. VTKgpe△C7L, VTKgpe△K1L and VTT△C7LK1L-gag elicited as strong cellular and humoral responses against HIV genes as did VTKgpe, while humoral immune response against the vaccinia itself was reduced by 4-8-fold. These data show that deletion of C7L and K1L genes leads to significantly decreased virulence without compromising animal host immunogenicity, and may thus be key to creating a more safe and effective HIV vaccine vector.

Deletion of the K1L Gene Results in a Vaccinia Virus That Is Less Pathogenic Due to Muted Innate Immune Responses, yet Still Elicits Protective Immunity

“…Liu et al also observed that humoral responses were decreased when K1L was absent (19). Humoral responses for vΔK1L were not measured here.…”

“…Humoral responses for vΔK1L were not measured here. It is difficult to accurately predict if vΔK1L would give results similar to those of vTTΔK1L because the parental vector (vTT) lacks several genes other than K1L (19,72). Nevertheless, we chose to examine only CD8 ϩ T cell responses because others have reported that CD8 ϩ T cells provide protection against VACV intranasal infection even in the absence of CD4 ϩ T cells and B cells (71).…”

“…Despite this vast knowledge of K1, only one publication has examined the role of K1 in pathogenesis (19). Liu et al showed that deletion of the K1L gene attenuates VACV strain TianTan, as measured by weight loss and neurovirulence in intradermal and intracranial routes of infection (19).…”

“…Liu et al showed that deletion of the K1L gene attenuates VACV strain TianTan, as measured by weight loss and neurovirulence in intradermal and intracranial routes of infection (19). Unfortunately, the parental strain used by Liu et al lacked additional genes involved in vaccinia virus immune evasion (A53R and C12L) or morphogenesis (A33L) (19), making it difficult to assess the specific contributions of K1 to VACV pathogenesis.…”

Unique safety issues associated with virus-vectored vaccines: Potential for and theoretical consequences of recombination with wild type virus strains

“…Two examples are provided. Attenuated vaccinia Tiantan [65,66] used in China for smallpox eradication is being assessed as a replication-competent vector for both HIV-1 [67] and H5N1 [68] vaccines and in its replication-defective form for hepatitis C vaccine [69]. Similarly, replication-competent adenovirus serotype 4 (Ad4) has been tested in humans as a vector for H5N1 [70] HIV and anthrax.…”