Anti-CD3 Antibody Decreases Inflammation and Improves Outcome in a Murine Model of Pneumocystis Pneumonia

The T cell–mediated immune response elicited by Pneumocystis plays a key role in pulmonary damage and dysfunction during Pneumocystis carinii pneumonia (PcP). Mice depleted of CD4+ and CD8+ T cells prior to infection are markedly protected from PcP-related respiratory deficit and death, despite progressive lung infection. However, the therapeutic effectiveness of Ab-mediated disruption of T cell function in mice already displaying clinical symptoms of disease has not been determined. Therefore, a murine model of PcP-related immune reconstitution inflammatory syndrome was used to assess whether Ab to the pan-T cell molecule CD3 is effective for reducing the severity of PcP when administered after the onset of disease. Mice that received anti-CD3 Ab exhibited a rapid and dramatic halt in the PcP-associated pulmonary function decline within 1 week after treatment, and a striking enhancement of survival rate compared with mice receiving the control Ab. Physiologic improvement in anti-CD3 treated mice was associated with a significant reduction in the number of CD4+ and CD8+ T cells recovered in lung lavage fluid. This effectiveness of anti-CD3 was noted whether the mice also received antibiotic therapy with trimethoprim-sulfamethoxazole. These data suggest that monoclonal Ab-mediated disruption of T cell function may represent a specific and effective adjunctive therapy to rapidly reverse the ongoing pathologic immune response occurring during active PcP. Thus, the anti-human CD3 monoclonal Ab OKT3, which is already in clinical use, has the potential to be developed as an adjunctive therapy for PcP.