Hendra and Nipah viruses are pathogenic paramyxoviruses of the Henipavirus genus known to cause highly fatal outbreaks of encephalitis or respiratory illness in humans. Current treatment options for Henipavirus infections are limited to re-purposed antivirals such as Ribavirin and Remdesivir. Investigational mAb therapies for Nipah have been developed but their efficacy in humans has not been tested. We aimed to isolate neutralising mAbs cross-reactive against both Hendra and Nipah virus entry (G) and fusion (F) glycoproteins for development of potential therapeutic and prophylactic agents.
We recruited an individual who recovered from Hendra virus infection in 2008 and obtained PBMC and plasma samples. At 15 years post-infection, the convalescent individual still had high plasma neutralising activity against Hendra pseudovirus (50% inhibitory dilution (ID50) of 1:2632) and cross-neutralising activity against Nipah pseudovirus (ID50 of 1:355). Using recombinant G and F probes, we single cell sorted antigen-specific memory B cells and recovered 107 BCR sequences for G and 165 BCR sequences for F. Memory B cell frequencies were generally low (0.02% and 0.1% of IgD-IgG+ memory B cells for G and F respectively), with clonal expansions observed within both populations. A total of 16 G-specific and 21 F-specific mAbs were isolated and tested for binding and neutralisation. All 16 mAbs that bound to Hendra G neutralised Hendra pseudovirus, with 9 having cross-neutralising activity against Nipah. For F-specific mAbs, 17 of 21 mAbs could neutralise Hendra pseudovirus, with 14 having cross-neutralising activity against Nipah. Neutralising G mAbs that could block receptor binding to Ephrin-B2 and Ephrin-B3 were the most potent, with IC50 values ranging from 0.4-1.1 ng/ml. Neutralising F mAbs were less potent on average, with IC50 values ranging from 28-8700 ng/ml. Competition ELISAs revealed 4 distinct clusters within the head domain of Hendra G, indicating neutralising epitopes beyond the receptor binding site. High resolution structures of 4 G mAbs and 2 F mAbs were solved via cryo-electron microscopy. Future studies will test the prophylactic and therapeutic efficacies of the most potent G and F mAbs in animal challenge models.
Henipaviruses continue to be a serious health threat to the Asia-Pacific region, as emphasised by ongoing Nipah outbreaks and the emergence of Langya virus. Our work in developing therapeutic mAbs against henipaviruses will increase pandemic preparedness against future outbreaks.