Horizontal Transmission of Cytomegalovirus in a Rhesus Model Despite High-Level, Vaccine-Elicited Neutralizing Antibody and T-Cell Responses.

The development of a vaccine to prevent congenital human cytomegalovirus (HCMV) disease is a public health priority. We tested rhesus CMV (RhCMV) prototypes of HCMV vaccine candidates in a seronegative macaque oral challenge model. Immunogens included a recombinant pentameric complex (PC; gH/gL/pUL128/pUL130/pUL131A), a postfusion gB ectodomain, and a DNA plasmid that encodes pp65-2. Immunization with QS21-adjuvanted PC alone or with the other immunogens elicited neutralizing titers comparable to those elicited by RhCMV infection. Similarly, immunization with all 3 immunogens elicited pp65-specific cytotoxic T-cell responses comparable to those elicited by RhCMV infection. RhCMV readily infected immunized animals and was detected in saliva, blood, and urine after challenge in quantities similar to those in placebo-immunized animals. If HCMV evades vaccine-elicited immunity in humans as RhCMV evaded immunity in macaques, a HCMV vaccine must elicit immunity superior to, or different from, that elicited by the prototype RhCMV vaccine to block horizontal transmission.

The pro-sequence domain of streptopain directs the folding of the mature enzyme.

The cysteine endopeptidase streptopain, an extracellular enzyme from pathogenic Streptococcus pyogenes, is synthesized as a precursor containing an NH2-terminal pro-sequence. The pro-sequence of streptopain was expressed in Escherichia coli and subjected to structural and functional investigation. Heat-induced denaturation of the pro-sequence studied using circular dichroism spectroscopy revealed that it forms a compact structure and represents an independently folded domain. The isolated pro-sequence exhibits high affinity towards mature streptopain and associates with its cognate enzyme by forming an equimolar complex. Refolding of denatured streptopain in the presence of pro-sequence in vitro facilitated recovery of active enzyme. Expression of the mature streptopain in E. coli either alone, or in trans with its pro-sequence as an independent polypeptide, led to the formation of insoluble protein aggregates or functionally active enzyme, respectively. These results demonstrate that the pro-sequence domain acts as an intramolecular chaperone that directs the correct folding of the mature streptopain.