THE EFFECTS OF ANTI-CD20 THERAPY ON SUSCEPTIBILITY TO PNEUMOCYSTIS INFECTION AND THE CD4+ T-CELL SIGNALS THAT MEDIATE CLEARANCE

Pneumocystis is an opportunistic fungal pathogen that presents as a pulmonary pneumonia. Originally characterized as an AIDs-defining illness, Pneumocystis has now reemerged in non-HIV immunocompromised patients. It has been shown that Pneumocystis prophylaxis of can reduce the incidence of infection, severity of disease, and mortality rate in immunocompromised patients. However, prophylaxis is relatively toxic, and only prescribed to defined at risk populations. Anti-CD20 was originally a therapy for B-cell non-Hodgkin lymphomas, but now it’s also used to treat hematological malignancies, autoimmune diseases, and post-transplant lymphoproliferative disease. Studies have shown that up to 30% of patients receiving anti-CD20 antibodies developed Pneumocystis pneumonia, however, many of these patients were also on concomitant immunosuppressive drugs which complicates any analyses of clinical studies. Thus, we generated a murine model of anti-CD20 therapy, and demonstrated treatment does induce susceptibility to Pneumocystis infection. This correlated to an overall decrease in immune response, but more specifically a loss in CD4+ T-cell mediated protection. \ud The predominant factor required for immunity against Pneumocystis infection is the presence of CD4+ T-cells. This has been validated several times over by clinical data and experimental animal models. Early on, studies have examined the role of T helper 1 (Th1), T helper 2 (Th2), and T helper 17 (Th17) cells. To briefly summarize these studies, Th1, Th2, and Th17 cells can all be detected in the lung during infection, however, removal of their classically defined effector molecules only delayed clearance or had no effect. We examined the importance of each subset of T helper cells by deleting the Stat transcription factors that mediated differentiation. We found that specifically Stat3 was required, however, it was independent of IL-17 and IL-23 signals. We also identified IL-21 as a key cytokine required to mediate clearance. Using a variety of approaches, we determined that GM-CSF and IL-22 play important roles during Pneumocystis infection. GM-CSF+ CD4+ T-cells are critical for T-cell mediated clearance, however, it alone is not sufficient. While IL-22, although not required, was sufficient to reduce burden in IL-21 receptor knockout mice. These data suggest a model of clearance, requiring non-classical T helper cell function. \u