INFECriON AND IMMUNITY, Mar. 1994, p. 1079-1088 Vol. 62, No. 3 0019-9567/94/$04.00+0 Copyright © 1994, American Society for Microbiology Monoclonal Antibodies to Cryptococcus neoformans Capsular Polysaccharide Modify the Course of Intravenous Infection in Mice SUSHOVITA MUKHERJEE,' SUNHEE LEE,2 JEAN MUKHERJEE,3 MATTHEW D. SCHARFF,3 AND ARTURO CASADEVALLl 4* Departments of Microbiology and Immunology," Pathology, 2 and Cell Biology,3 and Division of Infectious Diseases of the Department of Medicine,4 Albert Einstein College of Medicine, Bronx, New York 10461 Received 1 October 1993/Returned for modification 22 November 1993/Accepted 10 December 1993 Immunoglobulin Gl (IgGl) monoclonal antibodies (MAbs) to the capsular glucuronoxylomannan (GXM) were studied for their ability to modify the course of intravenous Cryptococcus neoformans infection in mice. A/J mice were given intraperitoneal injection of 1.0 mg of either a GXM-binding IgGl MAb (2H1 or 2DlOyl) or the irrelevant isotype-matched control MAb 36-65 prior to intravenous infection. Parameters used to study antibody efficacy were lung and brain tissue fungal burden, lung and brain weights, serum GXM levels, and histopathological examination of lung, brain, heart, kidney, and spleen tissues. Mice given GXM-binding MAb had significantly reduced lung tissue fungal burden as measured by CFU. In contrast to the reduction in lung tissue burden, the reduction in brain tissue burden was small and did not achieve statistical significance. Serum GXM levels were reduced in mice receiving GXM-binding MAb. Histopathological examination revealed reduced numbers of granulomas and C. neofornans organisms in the lungs, brains, and kidneys of MAb 2H1-treated mice relative to control mice. The lungs and brains of mice receiving GXM-binding MAb weighed significantly less than those of control animals, consistent with the reduced inflammation noted histologically. Subendocardial inflammation and kidney cortical infarctions were present in control infected mice but not in MAb 2H1-treated mice. Immunocytochemical staining for polysaccharide antigen revealed a marked reduction in the amount of tissue polysaccharide in mice treated with MAb 2H1 relative to control mice. The results support an useful role for passive antibody administration in C. neoformans infections. Cryptococcus neoformans causes life-threatening meningo- encephalitis in approximately 10% of patients with AIDS (77). In the setting of AIDS, cryptococcal infections are usually incurable because antifungal therapy does not eradicate the infection (73) despite in vitro susceptibility of the organism to antifungal drugs (6). This has renewed interest in the potential of vaccines (9) and passive antibody therapy (15, 45, 58, 59, 67) to prevent infection. Passive antibody is an attractive option because it could enhance residual immunity in immunosup- pressed patients (2). Precedent for the use of antibody in therapy of human cryptococcosis exists: in 1925, Shapiro and Neal used rabbit immune sera in an unsuccessful attempt to treat a boy with meningitis (71); in 1959, Littman used human gamma globulin and amphotericin B in a small number of patients with encouraging results (48); and in 1963, Gordon and Vedder used rabbit immune globulin and amphotericin B to successfully treat two patients with cryptococcosis (23, 25). Specific antibody can potentiate the effect of amphotericin B against C. neoformans in mouse models (14, 24, 59a), suggest- ing a rationale for combined therapy. It is generally accepted that cellular immunity is the primary line of defense against C. neoformans (1, 29, 31, 42, 45, 47, 54, 60) and that complement provides opsonins for phagocytosis (1, 13, 43). In contrast, the importance of natural antibody immunity has remained uncertain. Passive immunization with polyclonal sera has produced evidence for (22, 28) and against (49) a role for antibody in protection. Casting doubt on the importance of antibody immunity are the observations that an * Corresponding author. Mailing address: Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. Phone: (718) 430-4260. Fax: (718) 597-5814. immunogenic vaccine failed to protect mice (26), B-cell defi- cient mice are not at increased risk (55), and antibody is not an absolute requirement for phagocytosis (1, 13) or killing of C. neoformans (27, 52). However, the observation that antibodies are potent opsonins (40, 41, 69) which are required for NK cell (53, 61) and leukocyte (10, 11, 51) antifungal activity in vitro suggests a role for antibody immunity. Other observations supporting an important role for antibody are as follows: the appearance of antibody in cerebrospinal fluid of rabbits is temporally correlated with decreased colony counts in brain tissue (36); mice succumb to infection when their serum antibody titers decline (70); serum antibody is a good prognos- tic indicator in humans (12); recovery from cryptococcal meningitis is accompanied by the production of specific anti- body in cerebrospinal fluid (44); and cryptococcosis in the setting of hypogammaglobulinemia is occasionally reported (30, 68). Three groups have shown that administration of monoclonal antibody (MAb) to the capsular polysaccharide can mediate protection in murine models of C. neoformans infection (14-17, 57-59, 67). Antibody efficacy is dependent on the quantity (15, 16), the isotype (58, 67), and the fine specificity (58) of the MAb used, findings that could explain the discordant results obtained in earlier experiments with polyclonal sera. In 1981, Graybill showed that the choice of animal model was crucial for demonstrating efficacy with polyclonal sera (28). The best animal model for identifying potential antibody reagents against C. neoformans for human use is not known and will not be known until human efficacy data are correlated with data from animal studies. We have previously evaluated the efficacy of some of our MAbs in intraperitoneal (i.p.) (57, 58) and intracerebral (i.c.) (59) murine models of C. neofor- 1079 on July 24, 2020 by guest http://iai.asm.org/ Downloaded from