The COVID-19 epidemic is currently a global threat that has affected many parts of the world. Some patients require intensive care unit admission due to severe symptoms in the course of the disease. The severity of symptoms in this disease varies from person to person. The effectiveness of the immune response against viral infections depends on the number and activity of T-cells, which play an important role in eliminating virus-infected cells. In this study, we report two patients with COVID-19 pneumonia, one with moderate symptoms and the other with severe symptoms. Although a decrease of absolute lymphocyte count was seen in both patients, a more significant decline reported in the ICU-admitted patient. Expression of activated markers, HLA-DR, CD38, on CD8-positive T-cells was shown in a patient with more severe disease. On the other hand, partial loss of CD7 in the severe case was also observed. Hence, besides of the above parameters that already mentioned in other studies, loss of pan T-markers could be considered as a potentially valuable test for predicting disease severity. We suggest evaluating the predictability of these tests in COVID-19 in larger studies. This study was approved by the Ethics Committee of Isfahan University of Medical Sciences (IR.MUI.MED.REC.1399.238).