Toxoids of Streptococcal Pyrogenic Exotoxin A Are Protective in Rabbit Models of Streptococcal Toxic Shock Syndrome

Abstract

Streptococcal pyrogenic exotoxins (SPEs) are superantigens that have been implicated in causing streptococcal toxic shock syndrome (STSS). Most notably, SPE serotype A is made by nearly all M-protein serotype 1 and 3 streptococci, the M types most associated with the illness (these strains contain one or more other SPEs, and those proteins are likely also to contribute to disease). We have prepared double-, triple-, and hexa-amino-acid mutants of SPE A by PCR and other mutagenesis procedures. The sites chosen for mutation were solvent-exposed residues thought to be important for T-cell receptor (TCR) or major histocompatibility complex (MHC) class II interaction. These mutants were nonsuperantigenic for human peripheral blood mononuclear cells and rabbit and mouse splenocytes and were nonlethal in two rabbit models of STSS. In addition, these mutants stimulated protective antibody responses. Interestingly, mutants that altered toxin binding to MHC class II were more immunogenic than mutants altering TCR binding. Collectively, these studies indicate that multiple-site mutants of SPE A are toxoids that may have use in protecting against the toxin's effects in STSS.

Functional Characterization of Streptococcal Pyrogenic Exotoxin J, a Novel Superantigen

“…Serial 10-fold dilutions of rSPE J (beginning at 10 g/well) were added to the wells, and each dilution was assayed in quadruplicate; control wells received lymphocytes only. Equivalent concentrations of purified SPE A or SPE C prepared as previously described (38,50) were added to the wells for comparison. Plates were incubated at 37°C for 72 h in 7% CO 2 , and then 1 Ci of [ 3 H]thymidine (Amersham Corp., Arlington Heights, Ill.) was added to each well.…”

T-cell proliferation and antitumour activities of a truncated mutant of staphylococcal enterotoxin C2 with decreased cytokine secretion

“…The massive release of inflammatory cytokines is one of the reasons for immune-mediated fever by SEs (Roggiani et al, 1997). Our results indicated that SEC(14-128) minimally induced mouse T-cells to secrete IL-2 and IFN-c in vitro.…”

Mutational effects on protein folding stability and antigenicity: the case of streptococcal pyrogenic exotoxin A

“…To decrease the chances that this protein will have any superantigenicity in vivo, the binding sites for all three factors known to bind SPEA have been mutated: TCR (N20D), MHC (L42A), and Zn 2ϩ (D77A). Other combinations of mutations in SPEA were also found by Roggiani et al [5] to provide good protection, using a rabbit model and potentiation with endotoxin.…”

“…The naturally occurring substitution V76I, known as the SPEA3 allele [13], has been shown to possess an eightfold higher affinity for HLA-DQ than SPEA1 [7,8]-even though it is not located at the predicted MHC-binding surface. Residues N20 [5,14] and L24 have been predicted to be at or near the TCR interaction surface, while residue L42 is believed to be located in the SPEA contact site for MHC class II molecules [7,8]. Residue N20 is observed to contact the TCR ␤ chain in the structure of Sundberg et al (2002) [9].…”

“…Subsequent physiological consequences include rash, hypotension, and, in severe cases, multiple organ failure. The continuing public health threat posed by streptococcal infections and the emergence of antibiotic-resistant strains of this species of bacteria indicate the need for a protective vaccine [5]. In accordance with this goal, efforts to develop a vaccine against SPEA from a recombinant, mutationally inactivated toxin mandate a bet- …”