Killer immunoglobulin-like receptor 2DS5 is associated with recovery from coronavirus disease 2019

BACKGROUND: Despite numerous advances in the identification of risk factors for the development of severe coronavirus disease 2019 (COVID-19), factors that promote recovery from COVID-19 remain unknown. Natural killer (NK) cells provide innate immune defense against viral infections and are known to be activated during moderate and severe COVID-19. Killer immunoglobulin-like receptors (KIR) mediate NK cell cytotoxicity through recognition of an altered MHC-I expression on infected target cells. However, the influence of KIR genotype on outcome of patients with COVID-19 has not been investigated so far. We retrospectively analyzed the outcome associations of NK cell count and KIR genotype of patients with COVID-19 related severe ARDS treated on our tertiary intensive care unit (ICU) between February and June 2020 and validated our findings in an independent validation cohort of patients with moderate COVID-19 admitted to our tertiary medical center. RESULTS: Median age of all patients in the discovery cohort (n = 16) was 61 years (range 50-71 years). All patients received invasive mechanical ventilation;11 patients (68%) required extracorporeal membrane oxygenation (ECMO). Patients who recovered from COVID-19 had significantly higher median NK cell counts during the whole observational period compared to patients who died (121 cells/microL, range 16-602 cells/microL vs 81 cells/microL, range 6-227 cells/microL, p-value = 0.01). KIR2DS5 positivity was significantly associated with shorter time to recovery (21.6 +/- 2.8 days vs. 44.6 +/- 2.2 days, p-value = 0.01). KIR2DS5 positivity was significantly associated with freedom from transfer to ICU (0% vs 9%, p-value = 0.04) in the validation cohort which consisted of 65 patients with moderate COVID-19. CONCLUSION: NK cells and KIR genotype might have an impact on recovery from COVID-19.