In vitro and in vivo stability a Cryptococcus neoformans glucuronoxylomannan epitope that elicits protective antibodies

The monoclonal antibody (MAb) 2H1 defines an epitope in Cryptococcus neofor mans capsular glucuronoxylomannan (GXM) that can elicit protective antibodi es. In murine models of cryptococcosis, MAb 2H1 administration prolongs sur vival and reduces fungal burden but seldom clears the infection, The mechan ism by which C. neoformans persists and escape antibody-mediated clearance is not understood. One possibility is that variants that do not bind MAb 2H 1 emerge in the course of infection. Using an agglutination-sedimentation p rotocol, we recovered a variant of strain 24067 that did mt agglutinate, co uld not be serotyped, and had marked reduction in GXM O-acetyl groups. Bind ing of MAb 2H1 to 24067 variant cells produced a different immunofluorescen ce pattern and lower fluorescence intensity relative to the parent 24067 ce lls. Addition of MAb 2H1 to 24067 variant cells had no effect on cell charg e. Phagocytic assays demonstrated that MAb 2H1 was not an effective opsonin for the 24067 variant. The 24067 variant was less virulent than the 24067 parent strain in mice, and MAb 2H1 administration did not prolong survival in animals infected with the variant strain. To investigate whether variant s which do not bind MAb 2H1 are selected in experimental infection, three C . neoformans strains mere serially passaged in mice given either MAb 2H1 or no antibody. Analysis of passaged isolates by agglutination assay, Bow cyt ometry, and indirect immunofluorescence revealed changes in MAb 2H1 epitope expression but no clear trend with regards to gain or loss of MAb 2H1 epit ope. C. neoformans variants with reduced MAb 2H1 epitope content can be iso lated in vitro, but persistence of infection in mice given MAb 2H1 does not appear to be a result of selection of escape variants that lack the MAb 2H 1 epitope.