Preprint Club
A cross-institutional Journal Club Initiative

Keywords

• NK cells

• Congenital CMV

• CD56neg NK cells

Main Findings​

Cytomegalovirus (CMV) infection is the most common congenital infection in the world affecting between 1-5%of all new-borns. Despite the well-established role of NK cells in CMV infection in children and adults, an illustration of how NK cells work in utero in response to infection has yet to be elucidated. The aim of this pre-print by Vaaben, Levan and colleagues (2022) was to elucidate frequency, phenotype and functional profile of NK cells in Utero in response to congenital CMV infection (cCMV).  A secondary aim was to elucidate and compare the function of a special subset of NK cells; CD56negCD16+ NK cells, to its CD56bright/dim counterparts. CD56negCD16+ NK cell subset, although less described than its CD56+ counterparts, has been implicated during chronic viral infections (Bjorkstrom, Ljunggren, & Sandberg, 2010).

In short, the authors found that regarding frequency; there was no observable difference in the amount and percentage of total NK cells, between cCMV+ and cCMV- new-borns. However, there was a significantly higher proportion of the more mature/differentiated CD56neg NK cell in cCMV+ new-borns, compared to their CMV- counterparts. Functionally wise, this paper established that NK cells in cCMV+ new-borns had an increased expression of cytotoxic mediators, both singularly (had more expression of at least one cytotoxic mediator) and in conjunction (were more likely to express more than one cytotoxic mediator). However, when measuring the expression of transcription factors T-bet and eomesodermin, and the proliferation marker Ki67, there were no difference between cCMV+ and cCMV- patients.

In regards to phenotype/receptor expression; the authors found that NK cells for cCMV+ neonates show altered expression of activating and inhibitory NK receptors. Most importantly there was no elevated NKG2C expansion, the hallmark for CMV infection, in the CMV infected new-borns, and an effect was only found in new-borns with symptomatic CMV (i.e., low gestational weight and/or microencephaly). In contrast, much like the expression found in adults, CMV+ neonates had reduced level of NKG2A, the inhibitory complement to NKG2C. The authors further showed that most activation and expansion was present in CD16+ cells in all subsets regardless of CD56 expression.

The authors thus concluded that during foetal life, human NK cells can expand, differentiate and are functionally active in response to viral infection such as CMV. The study was also able to observe there are some significant differences in foetal NK cell response when compared to that found in children or adults. Regarding their secondary aim, Vaaben et al., showed that in contrast to healthy adult peripheral blood, cord blood contains a sizeable population of CD56neg, which expands and is functionally mature subset in response to congenital CMV infection.

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Limitations

• One of the major limitations for this study is that no rationale was given  behind the choice of receptors/markers. Common markers such as CD94, NKG2D or KIR2DS were not included (Béziat et al., 2013).

• Since NK cells are very involved in bidirectional cytokine and interferon signalling, there is a large gap that that would be nice to see addressed in future publication regarding cytokines, type 1 interferons (Martinez, Huang, & Yang, 2008) and IFNγ profiles between CMV+ and CMV- neonates.

• This cohort had Congenital Malaria, which could confound immune response to CMV infection perhaps controlling for those individuals might be of benefit.

• The study presented at the end of the results about the Fcγ receptor CD16, suggesting a role for antibody-mediated immunity against CMV in uterobut is interesting, but no serology profiles for new-borns or mothers was presented.

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Significance/Novelty

This preprint shows for the first time a preliminary characterization of NK cells in utero. They are able to distinguish foetal NK  response to the response seen in adults. It is important to understand how CMV can have lasting consequences on new-borns and for optimizing CMV treatment or prevention strategies. The focus on CD56neg cells as a mature subset is also relatively novel and is useful to have this profile described for a better understanding of NK development and maturation starting from foetal development. Moreover, the results allude to an important role of the Fcγ receptor CD16, in which NK cells could possibly use CD16 to maternal-origin IgG. This has implications regarding vaccine deployment for CMV and would be great research niche to fill in the future.

References

• Béziat, V., Liu, L. L., Malmberg, J.-A., Ivarsson, M. A., Sohlberg, E., Björklund, A. T., . . . Malmberg, K.-J. (2013). NK cell responses to cytomegalovirus infection lead to stable imprints in the human KIR repertoire and involve activating KIRs. Blood, 121(14), 2678-2688. doi:10.1182/blood-2012-10-459545

• Bjorkstrom, N. K., Ljunggren, H. G., & Sandberg, J. K. (2010). CD56 negative NK cells: origin, function, and role in chronic viral disease. Trends Immunol, 31(11), 401-406. doi:10.1016/j.it.2010.08.003

• Martinez, J., Huang, X., & Yang, Y. (2008). Direct Action of Type I IFN on NK Cells Is Required for Their Activation in Response to Vaccinia Viral Infection In Vivo. The Journal of Immunology, 180(3), 1592-1597. doi:10.4049/jimmunol.180.3.1592

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Credit

Reviewed by Matilde Oviedo Querejazu as part of the cross-institutional journal club of the Immunology Institute of the Icahn School of Medicine, Mount Sinai, the Kennedy Institute of Rheumatology and the Oxford Centre for Immuno-Oncology  (OXCIO) (University of Oxford, GB) and Karolinska Institute’s Center for Infectious Medicine (CIM) & Center for Molecular Medicine (CMM).