Characterization of plasmablasts expansion and antibodies derived therefrom after 17DD vaccination and natural infection with wild-type yellow fever virus

Yellow fever (YF) is an arboviral disease that remains a public health problem in Brazil, where a recent outbreak occurred with 1376 confirmed cases 35% of lethality rate. The yellow fever vaccine is highly effective conferring protective immunity against yellow fever virus (YFV) probably by induction of neutralizing antibodies (Abs). Despite the effectiveness of the well-established vaccine, vaccination coverage is poor and there is no specific treatment for YF yet, which has a high mortality rate. Faced with the constant challenges in the fight against YFV and considering the relevance of neutralizing Abs in prevention, the therapeutic use of these molecules may represent a promising strategy. Thus, the aim of this project is to characterize kinetics expansion of circulating plasmablasts (PBs) and the PBs-derived repertoire of monoclonal Abs present in the peripheral blood of patients with yellow fever (n=70) or vaccinated with 17DD (n=7), as well as the YFV binding and neutralization capability . The multiparametric flow cytometric analysis revealed the frequency of PBs (CD27high CD38high) did not show a significant increase in the vaccinated group; in contrast in YFV infected patients the magnitude of PBs response was significantly high (P < 0.001), reaching peaking number on the 6th day after the onset of symptoms. Circulating PBs derived from the two groups were isolated and subjected to amplification and sequencing reactions of the variable regions of heavy and light chains from the immunoglobulin (Ig). A total of 668 Ig pairs from both groups were obtained and they presented a high identity rate with germline sequences and elevated level of somatic hypermutation. The IgHV3 family was frequently seen among the isolated Ig from both groups followed by IgHV4 in infected individuals and IgHV1 in vaccinees. Abs were isolated from the infected group after cloning and transfection, though the binding affinity was modest and none of them were able to neutralize the 17D strain in vitro. Our data suggest that YFV infection stimulates a significant PBs expansion of low affinity and poor neutralizing capability Abs during the acute phase of the disease (AU)