INTERFERENCE OF CORONAVIRUS INFECTION BY EXPRESSION OF IMMUNOGLOBULIN-G (IGG) OR IGA VIRUS-NEUTRALIZING ANTIBODIES

Immunoglobulin gene fragments encoding the variable modules of the hea vy and light chains of a transmissible gastroenteritis coronavirus (TG EV)-neutralizing monoclonal antibody (MAb) have been cloned and sequen ced, The selected MAb recognizes a highly conserved viral epitope and does not lead to the selection of neutralization escape mutants, The s equences of MAb 6A.C3 kappa and gamma 1 modules were identified as sub group V and subgroup IIIC, respectively. The chimeric immunoglobulin g enes encoding the variable modules from the murine MAb and constant mo dules of human gamma 1 and kappa chains were constructed by reverse tr anscriptase PCR, Chimeric immunoglobulins were stably or transiently e xpressed in murine myelomas or COS cells, respectively, The secreted r ecombinant antibodies had radioimmunoassay titers (i.e., the highest d ilution giving a threefold increase over the background) higher than 1 0(3) and reduced the infectious virus more than 10(4)-fold, Recombinan t dimeric immunoglobulin A (IgA) showed a 50-fold enhanced neutralizat ion of TGEV relative to a recombinant monomeric IgG1 which contained t he identical antigen binding site, Stably transformed epithelial cell lines which expressed either recombinant IgG or IgA TGEV-neutralizing antibodies reduced virus production by > 10(5)-fold after infection wi th homologous virus, although a residual level of virus production (<1 0(2) PFU/ml) remained in less than 0.1% of the cells, This low-level p ersistent infection was shown not to be due to the selection of neutra lization escape mutants, The implications of these findings for somati c gene therapy with recombinant antibodies are discussed.