PROJECT SUMMARY
Several members of the orthopoxvirus (OPXV) genus, including variola (the cause of smallpox), monkeypox
virus (MPXV) and camelpox virus (CMPV) pose serious threats to human health, while the ultimate impact of
emerging OPXVs of concern such as Alaskapox virus (AKPV) is unknown. Other OPXVs are highly pathogenic
in their natural hosts, including ectromelia (ECTV), the cause of mousepox - a disease with many similarities to
smallpox. It is concerning, then, that the extreme virulence typical of the OPXVs remains poorly understood.
Central to OPXV virulence are the virus-encoded proteins that impede host defenses. This proposal focuses
on members of the B22 family of OPXV immunoevasins due to their potency, complexity and limited
characterization. With respect to potency, MPXV197 significantly enhances mortality in a nonhuman primate
model, and ECTV C15 alone determines whether ECTV is 100% lethal or 100% survivable in a BALB/c mouse
infection model. With respect to complexity, B22 family members are exceedingly large (~1900 aa), highly
homologous multimembrane-spanning glycoproteins. We have observed that C15 is novel in targeting both
adaptive and innate host responses, preventing activation of CD4+ and CD8+ T cells (TCD4 and TCD8), and
interfering with the ability of natural killer (NK) cells to engage infected cells. Other B22 members have been
implicated in hindering only TCD4 and/or TCD8 function; however, given the high degrees of homology, we suspect
common functionalities, including targeting of NK cells. With respect to limited characterization, essentially no
structure/function studies have been done with any B22 member. Through application of such studies to B22
members, key insights into OPXV virulence will be gained, potentially leading to novel therapeutic strategies and
enhanced general principles of viral virulence.
Guided by published and preliminary data, we propose a model in which topologically complex B22 members
contain two functional subunits created by posttranslational cleavage: 1) an upstream (N-terminal) subunit that
interferes with NK cell recognition via an MHC class I-like structure. 2) a C-terminal subunit that inhibits
conjugation of TCD4 and TCD8 with their cognate targets. This model will be tested by pursuing three
complementary aims that: 1) reveal the structural properties of B22 members, 2) identify and map the functional
activities of B22 members, and 3) elucidate the viral and cellular binding partners of B22 proteins.
The value of these studies derives from: a) the significance of many OPXV members as human pathogens,
b) the potency of B22 members as virulence factors, c) the enigmatic immunoevasion activities of B22 members,
and d) the potential for the proposed work to lead to new insights into virus:host interplay, the development of
novel antiviral strategies and many future lines of investigation, including elucidation of the advantage to
aggregating innate and adaptive immunoevasion activities into a single protein.
