Innate immune activation profiles are associated with polarization of the T cell response to recombinant arenaviral vectors

Arenavirus-based vectors are uniquely positioned to generate durable T cell responses against tumors, which remains a central challenge in cancer immunotherapy. Two members of the arenavirus family, Lymphocytic choriomeningitis virus and Pichinde virus, were genetically engineered to encode a non-oncogenic fusion protein, originating from human papillomavirus 16 E 6 and E7. Hereafter, these vectors are referred to as HB-201 and HB-202, respectively. HB-201 alone or in combination with HB-202 elicited strong and durable E6/E7-specific CD8+ T cell responses in HPV 16+ cancer patients. Despite their classification within the same virus family, Lymphocytic choriomeningitis virus and Pichinde virus are phylogenetically distant, which may influence virus-host interactions and the pathways leading to antiviral immune responses. Previous studies showed that both vectors infect and activate professional antigen presenting cells. To elaborate on these findings, this study aimed to characterize in depth the innate immune response to HB-201 and HB-202 by single cell sequencing in an in vitro human PBMCs infection model. We confirmed the preferential infection of antigen presenting cells for both vectors, with HB-201 infecting the cross-priming conventional dendritic cell subset cDC1 more efficiently than HB-202. Furthermore, HB-201 induced stronger type I interferon responses than HB-202, as well as quantitative and qualitative differences in inflammatory response associated with a distinct reshaping of monocyte subsets towards intermediate and non-classical monocytes. Antigen presentation and T cell priming cytokines in dendritic cells appeared to favor antiviral CD8+ T cell responses upon HB-201 infection, whereas a more balanced CD4+ and CD8+ priming profile was observed upon HB-202 infection. Immunogenicity data from patients treated with HB-201 and HB-202 confirmed the in vitro findings with functional differences in early T cell response. Thus, despite their shared origins within the arenavirus family, HB- 201 and HB-202 demonstrate distinct differences in early host-virus interaction, potentially resulting in shaping unique T cell responses.