Impact of Immunosuppression on Immune Cell Dynamics in COVID-19: A Serial Comparison of Leukocyte Data in Healthy and Immunocompromised Patients Before and After Infection

<b>Background</b>: The significance of cell population data (CPD) and leukocyte scattergrams in COVID-19 has not been fully established, partly due to the absence of serial leukocyte monitoring before and after SARS-CoV-2 infection. This study first examined changes in these parameters in non-immunosuppressed subjects over the course of infection. Subsequently, these findings were compared with those observed in patients who were immunosuppressed to assess the impact of immunosuppression. <b>Methods</b>: In total, 48 patients with COVID-19 were analyzed. Complete blood count (CBC) results and CPD were assessed using a Sysmex XN-9000 hematological analyzer. <b>Results</b>: The control and IST groups had similar clinical characteristics regarding COVID-19 severity and baseline CBC and CPD. WBC and neutrophil counts showed no significant changes immediately post onset; however, they decreased in the control group and increased in the IST group. Platelet counts decreased transiently on days 3-5 in both groups. The control group's lymphocyte counts significantly dropped, but their lymphocyte-related CPD remained unchanged. The IST group experienced delayed lymphocyte recovery and showed reduced DNA/RNA content and cell size diversity. Scattergrams immediately after onset showed an increase in lymphocyte clusters, particularly juvenile lymphocytes, in the control group, while they decreased in the IST group. In the control group, mature neutrophils decreased while immature neutrophils increased. Conversely, the percentage of mature neutrophils increased in the IST group. Both groups showed minimal plasmacytoid lymphocyte clusters after onset. <b>Conclusions</b>: Immunosuppression impairs juvenile cell mobilization, which may increase susceptibility to viral impacts and potentially worsen prognosis by increasing the risk of infection.