Latent cytomegalovirus disrupts NK cell responses to P. falciparum and impairs parasite control

NK cells are major innate and adaptive responders to malaria, with multiple roles in protection. Function of NK cells is heterogeneous, underpinned by expression of a diversity of receptors. One driver of NK cell heterogeneity is latent CMV infection, which drives the expansion of memory-like NK cells. We have recently reported that latent CMV infection can negatively impact the adaptive immune response to malaria, but whether CMV-mediated changes to the NK cell compartment also impact responses to malaria is unknown. Methods: We investigated the impact of latent CMV infection on NK cell response to the malaria parasite Plasmodium falciparum in vitro, and in CMV seronegative and seropositive individuals during controlled human malaria infection. We analysed NK cell activation, cytotoxicity and NK cell receptor expression. Additionally, we investigated the impact of CMV serostatus on cytokine production in response to TLR stimulation in the myeloid cell compartment. The impact of CMV and NK cell responses on malaria symptoms and parasite control and symptoms of malaria was investigated. Results: NK cells from CMV seropositive individuals had reduced responsiveness to P. falciparum parasites in vitro and had reduced activation during controlled human infection. Reduced activation was not restricted to NK subsets modulated by CMV but occurred across the entire NK cell compartment. Consistent with global NK cell attenuation, IL-12 production from myeloid cells, a response that supports NK cell activation on exposure to P. falciparum parasites, was lower in CMV infected individuals. Linking NK cell activation to clinical outcomes, NK cells expressing perforin were strongly associated with parasite control in CMV seronegative individuals. Conclusion: CMV infection modulates NK cell responses during malaria by disruption of IL-12, leading to reduced parasite control. Overall design: PBMCs were co-cultured at 37 °C, 5% CO2 in a 96-well U-bottom plate for 4 hours at a 1:1 cell ratio with 1x106 mature trophozoite stage pRBCs. After incubation NK cells subsets were FACS sorted using the BD FACSAria™ III Cell Sorter. RNA was extracted from isolated cell population lysates using the QIAGEN PicoPureTM RNA isolation kit (Applied Biosystems™, KIT0204), and RNA quality confirmed with the 2200 TapeStation system (G2964AA) by High Sensitivity RNA ScreenTape (5067- 5579). RNA sequencing libraries were constructed using the NEBNext® Single Cell/Low Input RNA Library Prep Kit for Illumina® (E6420S) and NEBNext® Multiplex Oligos for Illumina® (96 Unique Dual Index Primer Pairs) (E6440S). The libraries were sequenced using a NetSeq 550 system