Reviewer response for version 1
Reviewer comments:
In the current study, authors examined the human memory B cell IgG recall responses to H3N2 influenza virus in the presence of CpG 2006 ODN activation with IL-15 co-stimulation in vitro . 
They demonstrated that stalk reactive IgG antibodies induced by B cell exposure to H3 viruses in vitro , in the presence of CpG2006 ODN, are enhanced by IL-15 co-administration. 
In addition, IgG antibodies elicited by H3 viruses and/or IL-15 broadly bound to influenza HAs from both group 1 and group 2 influenza strains, which suggests potential use of CpG adjuvants and/or IL-15 agonists in influenza vaccination strategies. 
The use of IL-15 to enhance responses to immunization has been studied previously (see for example, PMID:24706798 which the authors could cite). 
However in that study, it was T-cell rather than antibody responses that were found to be protective. 
In this context, it would be important in a future study to examine whether the induced, cross-reactive antibodies show any protective activity in an appropriate assay. 
Overall, the manuscript is clearly written and interesting to read. 
However, the authors could consider the following additional points to improve clarity.
- Please include list of abbreviations used in the manuscript.
- Page No. 4. 
What are the concentration of whole HA or the head segments of influenza group 1, group 2, B strain and chimeric HA used for the mplex-Flu assay? 
What is the concentration of PE conjugated goat anti-human IgG (mplex-Flu assay) used in the current study?
- Page No. 5. 
On what basis was the concentration of IL-15 (50 ng/mL) fixed for the study? 
Did the authors check effects of different concentrations? 
If yes, what was the effect? 
(It is important to screen the IL-15 concentration because, in a previous NHP study antibody responses were sensitive to IL-15 dose with a slight increase at lower doses, but a decrease at higher doses ( Yin et al., High dose of plasmid IL-15 inhibits immune responses in an influenza non-human primates immunogenicity model. Virology; 393(1), 2009, 49-55.).
- In the result section, authors mention “As shown in Figure 1B, H3 stalk-reactive IgG was detected in plasma (dilution of 1:5,000) from 11 donors, with 4 to 11-fold lower than H3 strain-specific antibodies. For 4 of them, MFI values were greater than 3,000”. 
However, the maximum MFI values given in data set is 1250. 
Also there is no caption for Figure 1C.a
- Page No. 9. 
H2N2 should be changed to H3N2.
- Use A/Vic11 abbreviation consistently throughout the manuscript.
- References should be uniform.
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