IMMUNOSCINTIGRAPHY OF PNEUMOCYSTIS-CARINII PNEUMONIA IN AIDS PATIENTS

The diagnosis of Pneumocystis carinii pneumonia (PCP) currently relies upon cytological demonstration of the organism in sputum or bronchosc opy specimens, The purpose of this study was to develop a radiolabeled monoclonal antibody (Mab) against Pneumocystis carinii (P. carinii) a nd to evaluate its use for imaging PCP. Methods: We studied 16 HIV-inf ected patients with pneumonia in order to evaluate a new Mab-based ima ging method for diagnosing PCP. Most patients were managed for opportu nistic pneumonia associated with AIDS, including standard cytological tests, and, in all cases, intensive chemotherapy. Prior to the clinica l study, the Mab raised to P. carinii was shown to react with human P. carinii but not with rat P. carinii or human white blood cells. Resul ts: After labeling a 1-mg Mab Fab' fragment with 30 mCi of (TC)-T-99m, the presence or absence of PCP could be confirmed in six of seven or seven of eight assessable patients, respectively, by external photosca nning within 24 hr. This shows a sensitivity of 85.7% and a specificit y of 86.7%. Conclusion: Our findings suggest that PCP can be diagnosed by a noninvasive imaging method employing a small dose of a Tc-99m-la beled Mab showing specificity for the infectious organism, since patie nts with P. carinii-free pneumonia were correctly negative in 87.5% of cases. Rapid diagnosis and organ-locaiization of other infectious les ions with organism-specific, radiolabeled Mabs may be feasible.