No abstract

Objective SARS‐CoV‐2 infection results in severe lung disease in up to 50% of hospitalised patients. The aetiopathogenesis in a subset of such patients, who continue to have progressive pulmonary disease following virus clearance, remains unexplored. Methods We investigated the role of NKG2C+/NKG2A− adaptive natural killer (ANK) cells, KLRC2 genotype and cytomegalovirus (CMV) reactivation in 22 such patients. Results The median duration of virus positivity was 23 days, and the median duration of hospitalisation was 48 days. The overall survival at 60 days in this group was 50%. Older age and comorbidities impacted survival negatively. CMV viraemia was documented in 11 patients, with a survival of 25% vs 80% in those without viraemia with viral load correlating with mortality. Both NK and T cells were markedly depressed in all patients at day 15. However, only persistently low ANK cells at 30 days along with an inversely high NKG2C−/NKG2A+ inhibitory NK cells significantly correlated with high CMV viraemia and mortality, irrespective of KLRC2 genotype. However, day 30 ANK cells were significantly lower in the KLRC2 deletion group. The release of IFN‐γ and perforin was severely compromised in all patients at day +15, with significant improvement in the survivors at day +30, but not in those with adverse outcome. Conclusion Patients with progressive lung disease even after negative SARS‐CoV‐2 status, with persistently reduced and functionally compromised ANK cells, are more likely to have CMV reactivation and an adverse outcome, independent of KLRC2 genotype.

The kinetics of NKG2C+ adaptive natural killer (ANK) cells and NKG2A+inhibitory NK (iNK) cells with respect to the incidence of SARS-CoV-2 infection were studied for 6 months in a cohort of healthcare workers following the administration of the heat-killed Mycobacterium w (Mw group) in comparison to a control group. In both groups, corona virus disease 2019 (COVID-19) correlated with lower NKG2C+ANK cells at baseline. There was a significant upregulation of NKG2C expression and IFN-γ release in the Mw group (p=0.0009), particularly in those with a lower baseline NKG2C expression, along with the downregulation of iNK cells (p<0.0001). This translated to a significant reduction in the incidence and severity of COVID-19 in the Mw group (incidence risk ratio-0.15, p=0.0004). RNA-seq analysis at 6 months showed an upregulation of the ANK pathway genes and an enhanced ANK-mediated antibody-dependent cellular cytotoxicity (ADCC) signature. Thus, Mw was observed to have a salutary impact on the ANK cell profile and a long-term upregulation of ANK-ADCC pathways, which could have provided protection against COVID-19 in a non-immune high-risk population.

To evaluate ability of modulated innate immune response to provide resistance to development of symptomatic RT-PCR confirmed COVID-19, 96 inpatient front line health care workers (HCW) were cohorted in 1:2 ratio to receive TLR2 agonist (heat killed Mycobacterium w, Mw; n=32) as innate immune response modulator or observation (n=64). All were followed up for 100 days. The incidence of COVID-19 was 31 (32.3%) for the entire cohort, with only one developing COVID-19 in Mw group (3.1% vs 46.8%. protective efficacy - 93.33%, p=0.0001; 95% CI 53.3-99.1). Self-limiting local injection site reaction was the only side effect and was seen in 14 HCW. Findings from the study suggest the potential for providing resistance against novel pathogen like SARS-CoV-2 by modulating innate immune response.

Objective: COVID-19 infection results in severe lung disease in a small but significant number of infected patients. The etiopathogenesis in a subset of such patients, who continue to have progressive pulmonary disease following virus clearance remains unexplored. Methods: We investigated the role of NKG2C+/NKG2A- adaptive natural killer (ANK) cells, KLRC2 genotype and cytomegalovirus reactivation in 22 such patients. Results: The median duration of virus positivity was 23 days and the median duration of hospitalisation was 48 days. The overall survival at 60 days in this group was 50%. Older age and comorbidities impacted survival negatively. CMV viremia was documented in 11 patients, with a survival of 25% vs 80% in those without viremia with viral load correlating with mortality. ANK cells were markedly depressed in all patients at day 15. However, persistently low ANK cells at 30 days along with an inversely high NKG2C-/NKG2A+ inhibitory NK cells significantly correlated with high CMV viremia as well as mortality, irrespective of KLRC2 genotype. Day 30 ANK cells were significantly lower in KLRC2 deletion group. IFN-gamma and Perforin release were severely compromised in all patients at day +15, with significant improvement in the survivors at day +30, but not in those with adverse outcome. Conclusion: Patients with severe lung disease even after negative SARS-CoV-2 status, with persistently reduced and functionally compromised ANK cells, are more likely to have CMV reactivation and an adverse outcome, independent of KLRC2 genotype.