Combination immunotherapy with two attenuated Listeria strains carrying shuffled HPV-16 E6E7 protein causes tumor regression in a mouse tumor model

Abstract

Cervical cancer continues to impose a heavy burden worldwide, and human papilloma virus (HPV) infection, especially persistent infection with type 16 (HPV-16), is known to be the primary etiological factor. Therapeutic vaccines are urgently needed because prophylactic vaccines are ineffective at clearing pre-existing HPV infection. Here, two recombinant Listeria strains (LMΔ-E6E7 & LIΔ-E6E7) with deletions of the actA and plcB genes, expressing the shuffled HPV-16 E6E7 protein were constructed. The strains were delivered into the spleen and liver by intravenous inoculation, induced antigen-specific cellular immunity and were eliminated completely from the internal organs several days later. Intravenously treating with single strain for three times, or with both strains alternately for three times significantly reduced the tumor size and prolonged the survival time of model mice. Combination immunotherapy with two strains seemed more effective than immunotherapy with single strain in that it enhanced the survival of the mice, and the LMΔ-E6E7-prime-LIΔ-E6E7-boost strategy showed significant stronger efficacy than single treatment with the LIΔ-E6E7 strain. The antitumor effect of this treatment might due to its ability to increase the proportion of CD8+ T cells and reduce the proportion of T regulatory cells (Tregs) in the intratumoral milieu. This is the first report regarding Listeria ivanovii-based therapeutic vaccine candidate against cervical cancer. Most importantly we are the first to confirm that combination therapy with two different recombinant Listeria strains has a more satisfactory antitumor effect than administration of a single strain. Thus, we propose a novel prime-boost treatment strategy.

A Listeria ivanovii balanced‐lethal system may be a promising antigen carrier for vaccine construction

“…We confirmed that combination therapy with two different recombinant Listeria strains (LM and LI) has a more satisfactory anti‐tumour effect than the administration of a single strain (Su et al, 2021 ). This suggests that both LI and LM hold strong potential for the development of Listeria ‐vectored vaccines.…”

“…In future applications, to maximize the protective efficacy of LIΔdd:dal vectored vaccines, the immunization strategy may need to be optimized and can be optimized by double boost immunization (Pownall et al, 2021) or co-immunization with other type of vaccine. Besides, our previous research had confirmed that the sequential immunization with different Listeria strains vectored vaccine candidates will significantly enhance the immunotherapeutic effect (Su et al, 2021). So the protective efficacy could also be enhanced by co-immunization with other vectored vaccine such as LMΔdd:dal vectored vaccine.…”

“…Immunization with Listeria ‐based recombinant strains (LM and LI) can boost the protective effects of Bacillus Calmette‐Guerin (BCG) against pulmonary mycobacterial infection (Liu, Liu, et al, 2020a ; Liu, Tian, et al, 2020b ). Additionally, an LI strain carrying the human papillomavirus (HPV)‐E6E7 antigen (LIΔ‐E6E7) as a booster for LMΔ‐E6E7 was found to significantly enhance the anti‐tumour effects of a single‐dose LMΔ‐E6E7 therapy (Su et al, 2021 ). These studies suggest that both LI and LM hold strong potential as Listeria ‐vectored vaccines.…”

Human papillomavirus associated cervical lesion: pathogenesis and therapeutic interventions

“…Bacterial vectors‐based vaccines : Listeria and Lactobacillus are the most widely studied vectors 308–310 . Listeria‐based vaccines ADXS11‐001 have undergone phase I/II clinical to assess their efficacy and safety in HPV+ cervical cancer (NCT02164461 and NCT01266460).…”

Preimmunization with Listeria-vectored cervical cancer vaccine candidate strains can establish specific T-cell immune memory and prevent tumorigenesis

“…Therefore, there are still gaps in the research on the immune regulation mechanism of cervical cancer tumor vaccines in tumor prevention. We have successfully constructed two Listeria -vector cervical cancer vaccine candidate strains, LM∆E6E7 and LI∆E6E7, and confirmed that combined immunotherapy with these two vaccine candidate strains could effectively inhibit tumor progression [ 19 ]. Therefore, in this study we aimed to investigate the role of TAAs-specific Tm-cell responses induced by preimmunizing with LM∆E6E7 and LI∆E6E7 in the tumor prevention and the potential antitumor mechanism.…”