At least five antigenic epitopes on the streptokinase molecule are recognized by human CD4+ TCR alpha beta+ T cells

CD34 expression in native human acute myelogenous leukemia blasts: differences in CD34 membrane molecule expression are associated with different gene expression profiles

BACKGROUND

The stem cell marker CD34 is expressed by leukemia blasts only for a subset of patients with acute myelogenous leukemia (AML). It is still controversial as to whether CD34 expression (defined as at least 10-20% positive cells) has any prognostic effect in patients with AML who receive intensive chemotherapy. The present study investigated whether gene expression profiling could be used to further subclassify CD34(+) AML cell populations.

METHODS

AML blasts derived from 25 patients were examined; these patients were randomly selected from a larger consecutive group of patients. CD34 protein expression was determined by flow cytometry and expressed as the percentage of positive cells. Gene expression profiles were determined by complementary DNA microarrays.

RESULTS

By unsupervised hierarchical clustering our patients could be grouped into two or three major subsets depending on the methodologic approach before clustering analysis (filtering or flooring of data, respectively). However, both approaches identified a cluster characterized by high gene expression and membrane molecule level of CD34. When using the floored expression profiles, the patient cluster characterized by increased CD34 gene expression was also characterized by a high percentage of CD34(+) cells (median 82%, range 56-100%) compared with the two other major clusters (median 19%, range <1-55%), but three of four outpatients also showed a high percentage of CD34(+) cells.

CONCLUSION

A major proportion of patients with AML and high CD34 expression (usually >80% CD34(+) cells; nearly all patients had >50% positive cells) showed similarities in gene expression profile. In contrast, patients with lower CD34 expression often had a profile similar to those of patients regarded as CD34(-) according to conventional criteria. Our results suggest that the possible prognostic effect of CD34 expression should be reevaluated in clinical studies using additional or alternative cutoff values to describe CD34 expression.

T cell recognition pattern of bovine milk alphaS1-casein and its peptides

T cell recognition patterns of CAS1_Bovin, its limited hydrolysis, oxidized, reduced/alkylated, cyanogen bromide cleavage fractions and synthetic peptides were examined. Thirteen overlapping peptides covering the intact molecule, with chain lengths varied between 17 and 20 AA, were prepared by f-moc SPPS. In addition, six CNBr-cleavage fragments were obtained and extensively purified using RP/HPLC. Likewise, chemically modified derivatives and limited pepsin hydrolysate, were performed and the specificities were confirmed. Stimulation of PBMC and TCL cultures by the intact CAS1_Bovin molecule, synthetic peptides and modified derivatives were screened by [methyl-3H] thymidine incorporations. PBMC phenotype was performed by flow cytometry and the mean CD4+/CD8+ ratio of freshly prepared PBMC was compared with the ratio following specific CAS1_Bovin stimulation. CD4+ phenotypes (TH1/, TH2 and TH0) were assigned by assay of four marker cytokines IL-4, IL-6, IL-10 and IFN-gamma. Five CNBr fragments and seven of the thirteen tested peptides were recognized by specific TCL. The most reactive epitopes of CAS1_Bovin comprised seven motifs namely: peptides Cas 1-18, Cas 16-35, Cas 67-85, Cas 91-110, Cas 136-155, Cas 152-169 and Cas 166-183. The stimulation range for the seven peptides was 1058-2383 cpm. Stimulation for the CNBr fragments were, respectively, 8670, 5808, 3324, 5465, 2255 and 321 cpm. Cytokine assay showed that CD4+ TH2 phenotype was dominant for half the number of patients, while TH1 solely or combined TH0 were represented in the other four cell culture filtrates. The T cell reactive epitopes described and their antibodies will be useful tools for methods in progress for the detection of masked casein epitopes encompassed in processed food. In conclusion, T cell recognition pattern of CAS1_Bovin was examined using extensively purified synthetic peptides and CNBr fragments. Five large and seven small peptides were clearly recognized. Peptides of chain length less than six AA were left unrecognised. CD4+ TH2 phenotype was the most dominant TCL subpopulations found in atopic patients while CD4+ TH1 was representative in the non-IgE mediated type IV hypersensitivity.

Profiling the immune responses of human patients treated with recombinant streptokinase after myocardial infarct

The SPOT synthesis of peptide arrays on continuous cellulose membranes should be generally applicable in the analysis of sequential antibody binding sites using the enzyme-substrate or other standard detection protocols. The use of total serum is limited by the occurrence of high background levels. This may be overcome if affinity purified antibodies or sera with high antibody titers are used, which allows work at high dilutions and a consequent reduction of background level. Here we demonstrate the mapping of antigenic regions located on recombinant streptokinase SK-2 (Heberkinase) using cellulose-bound peptide scans and human total sera from patients treated with SK-2 (Heberkinase). Streptokinase (SK) is a 47 kDa protein produced by various strains of hemolytic streptococci and is a potent activator of the fibrinolytic enzyme system in humans. SK is in widespread clinical use to treat acute infarction because of its function as an activator of vascular fibrinolysis. Since streptococcal infections are common, normal individuals are immunized with SK and antibodies (Abs) to SK can be detected in most of them. This therapy generates significant T-cell responses to SK and the neutralizing capacity of the Abs rises significantly. Neutralizing Abs reduces the efficiency of thrombolytic therapy and may cause allergic reactions. The widespread use of SK in humans makes its antigenicity an important clinical problem. In this regard the study of the immunodominant regions of SK becomes an important aspect for the improvement of this thrombolytic agent.

New antigenic regions of streptokinase are identified by affinity-directed mass spectrometry

Streptokinase (SK) is a bacterial protein used for the treatment of myocardial infarction, which is immunogenic in humans. Here we report the use of an affinity-directed MS approach to determine the minimal epitopes involved in the binding between SK and patient antibodies. Using this method we have identified two novel epitopes and mapped these to the minimal recognition regions formed by the amino acids D96-E99 and F323-D328. We have also located three previously identified antigenic regions and have now mapped them and shown that they can be defined more precisely as residues P4-L8, P171-P177 and K334-N338.

A mutant streptokinase lacking the C-terminal 42 amino acids is less reactive with preexisting antibodies in patient sera

Streptokinase (SK) is an efficacious thrombolytic drug for the treatment of myocardial infarction. Because of its immunogenicity, patients receiving SK therapy develop high anti-SK antibody (Ab) titers, which might provoke severe allergic reactions and neutralize SK activity. In this report we studied the reactivity of a synthetic 42-residue peptide resembling SKC-2 C-terminus with patient sera. SKC-2(373-414) peptide was recognized by 39 and 64% of patients, before and after SKC-2 therapy, respectively. An SKC-2 deletion mutant (mut-C42), lacking the same 42 C-terminal residues, was constructed and expressed in Escherichia coli. Recognition of mut-C42 by preexisting Abs from patient sera was 51 and 68% of reactivity to SKC-2, as assessed by direct binding and competition assays, respectively. For most of the patients, mut-C42-neutralizing activity titer (NAT) significantly decreased with respect to SKC-2-NAT. This study opens the possibility of producing a less immunogenic variant of SK, which could constitute a preferred alternative for thrombolytic therapy.

A mutant streptokinase lacking the C-terminal 42 amino acids is less immunogenic

Streptokinase (SK) is the most widely used compound for the treatment of myocardial infarction and the least expensive thrombolytic agent, but a drawback to its use is the widespread presence of anti-SK antibodies (Abs). Clinical failure of the activation of the fibrinolytic system by SK has been reported due to the presence of a high titer of anti-SK neutralizing Abs. Patients receiving SK therapy develop high anti-SK antibody titers, which might provoke severe allergic reactions. These Abs are sufficient to neutralize a standard dose of SK up to four years after initial SK administration. This is a clinical problem because of the increasing number of patients who have been treated once with SK for acute myocardial infarction (AMI) and are likely to require plasminogen activator treatment in the future. In previous in vitro studies, we have shown that a deletion mutant (mut-C42), lacking the 42 C-terminal residues, was significantly less antigenic when compared with the native molecule (SKC-2). In this study, 14 monkeys were subjected to treatment with SKC-2 and mut-C42 in order to compare their humoral response by determining SK neutralizing activity in monkey's sera. All monkeys developed anti-SKC-2 Ab titers, but in the case where treatment induced Abs directed against the C-terminus of SKC-2, neutralizing activity against the native protein was significantly higher than that developed against mutant SK mut-C42.

Mapping of the antigenic regions of streptokinase in humans after streptokinase therapy

Streptokinase (SK) is efficaciously used as a thrombolytic drug for the treatment of myocardial infarction. Being a bacterial protein, SK is immunogenic in humans. Therefore, resulting from SK therapy, patients become immunized and anti-SK antibody (Ab) titers rise post-treatment. High Ab titers might provoke severe immune reactions during SK therapy and neutralize SK activity, preventing effective thrombolysis. Spot synthesis combined with peptide library techniques is a useful tool for studying protein-peptide interactions on continuous cellulose membranes. Here, we report on the mapping of antigenic regions of SK using a spot-synthesized peptide library and human total sera from patients receiving SK therapy. All tested samples have high anti-SK Ab titers and most of them show significant SK neutralizing capacity. Individual variations in peptide recognition were detected. However, patients treated with SK tend, in general, to show a common regional binding pattern, including residues 1-20, 130-149, 170-189, and 390-399. This is the first study reporting the probing of a cellulose-bound set of peptides with total human sera.

Sequences of antigenic epitopes of streptokinase identified via random peptide libraries displayed on phage

Though streptokinase (SK) is widely used to treat humans with thrombotic disease, it is antigenic and anti-SK antibody causes allergic reactions and neutralizes SK's therapeutic effects. To pinpoint the fine structure of two immunodominant, continuous epitopes in SK, we used unconstrained 15 and 6-mer random peptide libraries displayed on phage (theoretical complexity of 3.2 x 10(19) and 0.64 x 10(8) unique sequences). The first epitope, recognized by both human Ab and murine monoclonal (m)Abs, was previously localized to the amino terminus of SK. Repeated panning and selection experiments against a 15-mer peptide phage library, using a representative mAb (A2.5) to this epitope, identified a dominant structural motif (GP[R/L]WL) corresponding to amino acids 3 to 7 of native SK, which was consistent with previous epitope mapping. These findings were further confirmed by: (1) the fact that a synthetic peptide spanning the epitope of A2.5 (AGPEWLL) specifically inhibited the binding of A2.5 to SK and (2) the finding that mAb 9D10, which competes with mAb A2.5 for binding to SK, independently selected, from a different random hexamer library, an epitope sequence spanning residues 4 to 9 that overlaps the A2.5 epitope. Similar studies of the second epitope in SK, which is immunodominant for murine but not human antibodies, identified a consensus sequence KS(K/L)P(F/Y) corresponding to amino acids 59 to 63 of SK; this was confirmed by epitope peptide binding experiments. This epitope is cleaved and destroyed when SK reacts with human but not murine plasminogen. Thus, pinpointing the sequences of antigenic epitopes of SK: (1) provides a potential explanation for species differences in SK's antigenicity, (2) demonstrates the overlapping fine structure of epitopes recognized by competitive mAbs, (3) confirms previous epitope mapping studies and (4) has the potential to identify antigenic sequences that lead to allergic reactions in patients treated with SK.

Structural characterization of immunodominant regions of streptokinase recognized by murine monoclonal antibodies

In order to determine the nature of the antigenic and functional determinants of streptokinase (SK), we produced monoclonal antibodies (MAbs) by immunizing A/J mice with native SK protein. By virtue of their differential binding to a large panel of recombinant SK truncated proteins, and their effect on the formation of functional SK-plasminogen activator complex (SKPAC), these MAbs were found to recognize 6 unique and minimally overlapping epitopes on the SK protein. The fine epitope specificity of the anti-SK MAbs derived from A/J mice was compared with that of MAbs derived from BALB/c mice. A number of MAbs from both inbred strains of mice were directed against the same sequences of SK (1-13, 1-253, 120-352) suggesting that these regions of the molecule contain peptide sequences that are immunodominant. Two of the "immunodominant" sequences of SK protein appeared to be important for SK function, since the formation of SKPAC could be inhibited by MAbs against these sequences.

Mapping the antigenic regions of streptokinase in humans before and after streptokinase therapy

Streptokinase saves lives in patients suffering a myocardial infarction. However, because nearly all humans tested show antibodies against streptokinase, allergic reactions to streptokinase are common and may be severe. In this report we have analysed antibodies purified from normal blood donors and patients, before and after streptokinase therapy, to identify antigenic regions of the streptokinase molecule. Antibody to streptokinase was seen in all subjects, but there were 20-30-fold differences between individuals in the antibody titer. These individual differences in titer persisted after SK treatment, though the titer for all patients rose an average of 7-fold 1 week after streptokinase therapy. To identify the regions of streptokinase to which the antibody bound, we employed a panel of well-characterized murine monoclonal antibodies and recombinant streptokinase truncated fragments. Antibodies to three discrete regions of streptokinase could be detected in all patients. Antibodies to two other regions, at the amino terminal and carboxyl terminus of the molecule, were found in many but not in all patients. However, antibodies to a sixth region of streptokinase were uncommon and of very low titer. Interestingly, individuals receiving streptokinase tended to show the same pattern of immunoreactivity after treatment as they had prior to streptokinase. We conclude that although individual differences exist in the titers of streptokinase antibody, certain regions of streptokinase appear to be more antigenic or immunodominant.