BACKGROUND: Sepsis is a life-threatening response to infection with a high mortality rate. In order to explore the prognostic value of dynamic monitoring of cellular immunity during late severe sepsis, we assessed levels of Tlymphocyte subsets, the human leukocyte antigen D-related (HLA-DR), and the high mobility group box-1 (HMGB1) protein. METHODS: Study participants included 247 consecutive severe sepsis patients who were admitted to Beijing ChaoYang Hospital's Emergency Intensive Care Unit. Patients were divided into survivors and non-survivors based on 90-day survival rates, and clinical data were collected. T-lymphocyte subsets on days 1 and 7, HLA-DR on days 1 and 12, and HMGB1 on days 1, 3, 5, 7, and 12 were analyzed. RESULTS: Counts of CD3+, CD3+CD4+, and CD3+CD8+ T cells on day 1 in non-survivors were lower than those in survivors. By day 7, counts of all three types of T cells had increased in both survivors and non-survivors, but CD3+ and CD3+CD8+ T cells remained lower in non-survivors than in survivors. There was no significant difference in HLA-DR levels between survivors and non-survivors on day 1, but HLA-DR levels increased in survivors and decreased in non-survivors by day 12. In contrast, over days 1 - 12, HMGB1 levels increased in non-survivors and decreased in survivors. CONCLUSIONS: Patients with severe sepsis present with cellular immune dysfunction and persistent chronic inflammation, both of which may lead to death in the late phase of severe sepsis. Dynamic monitoring of indicators of cellular immunity and HMGB1 is useful for evaluating the immune status, chronic inflammation processes, and prognoses of patients with severe sepsis.