In a multicenter, randomized, open-label trial across 6 intensive care units, 361 patients with severe sepsis were randomized to receive standard therapy or standard therapy plus subcutaneous thymosin alpha 1 (1.6 mg every 12 hours for 7 days). The primary endpoint was 28-day all-cause mortality. 28-day mortality was significantly lower in the thymosin alpha 1 group (26.0% vs. 35.0%, P=0.04), accompanied by accelerated recovery of mHLA-DR expression.