Response relationship of VAS and Likert scales in osteoarthritis efficacy measurement.

OBJECTIVE/BACKGROUND: Efficacy in osteoarthritis (OA) is principally measured using subjective visual analogue (VAS) and/or Likert scale responses. The relationship between these two scales and their relative precision in discriminating active from placebo treatment in OA patients was determined. DESIGN/METHODS: Patient overall pain assessment, and patient and investigator global assessments were each measured on a 100mm VAS and on a 0 to 4 point Likert scale in a 6-week OA study of rofecoxib vs placebo. The relationship between the VAS and Likert responses was examined graphically and via summary statistics. Analysis of variance was used to assess consistency of the VAS/Likert relationship over time and across the different endpoints. Precision was compared using effect size, and normality of VAS scale of measurement was assessed using the Shapiro-Wilk test. RESULTS: Mean VAS scores and changes from baseline at individual time points were generally highly correlated with corresponding Likert responses (r-values generally approximately 0.7-0.8). The magnitude of VAS values and changes varied depending on endpoint, on the associated magnitude of increment of Likert score, and on the Likert baseline value (i.e., where on the Likert scale the change was occurring). Precision of VAS and Likert responses to detect difference between treatments was generally similar with effect sizes approximately 1. Normality and homogeneity of variance of VAS scores was most closely approximated by actual changes in comparison to percent change or log-transformed measures. CONCLUSIONS: VAS and Likert responses are highly correlated and yield similar precision for discriminating treatments in OA patients. Since Likert responses are easier to administer and interpret, they may be preferable to measure OA response.

Rofecoxib shows consistent efficacy in osteoarthritis clinical trials, regardless of specific patient demographic and disease factors.

OBJECTIVE: To evaluate the efficacy of rofecoxib (Vioxx) in subpopulations of patients with osteoarthritis (OA) identified by demographic or baseline disease characteristics, or varied OA involvement. METHODS: Data were combined from three 6-week double blind trials in patients with OA of the knee or hip. All trials contained placebo, 12.5 mg rofecoxib, and 25 mg rofecoxib arms (the only trials to date containing all 3 treatments). Analyses were performed on subgroups categorized according to the following baseline demographics and disease characteristics [age, sex, height, weight, body mass index, American Rheumatism Association (ARA) functional class, joint tenderness, joint stiffness, Western Ontario-McMaster University OA Index (WOMAC) functional subscale, unilateral/bilateral joint involvement, number of joint groups involved]. Three primary endpoints--Pain Walking on Flat Surface (WOMAC), Patient Global Assessment of Response to Therapy, and Investigator Global Assessment of Disease Status--were analyzed. The global assessments, which provided data on overall aspects of OA, regardless of affected joint, were used to assess effects among patients with one, 2, 3, or 4 joint groups affected (from among the following: interphalangeal/first carpal-metacarpal joint, spine, hip, or knee). RESULTS: Data from 1501 patients were included. No consistent treatment-by-subgroup interaction was observed with all 3 primary endpoints for patients taking placebo or 12.5 or 25 mg rofecoxib. Rofecoxib showed generally consistent efficacy across subgroups of patients identified by sex, race, age, OA location(s), prior OA therapy, baseline study joint tenderness or swelling (patients with knee OA only), and ARA functional class level. CONCLUSION: In this combined analysis, no specific factor predicted a differential treatment effect to rofecoxib.

Effect of rofecoxib therapy on measures of health-related quality of life in patients with osteoarthritis.

BACKGROUND: Bodily pain and physical disability can negatively impact health-related quality of life (HRQL) in patients with osteoarthritis (OA). OBJECTIVE: To assess the effects of treatment with a new agent, rofecoxib, on HRQL in patients with OA. STUDY DESIGN: Randomized, double-blind, 6-week clinical trial comparing treatment with rofecoxib, 5 to 50 mg, with placebo in 672 patients with OA of the hip or knee. MAIN OUTCOME MEASURE: Patient HRQL was assessed at baseline and at the end of treatment using the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). RESULTS: At 6 weeks, mean change from baseline in all SF-36 mental and physical health domain scores demonstrated significant improvement with rofecoxib use (P < .05 for all doses for all SF-36 domains), with evidence of a dose-response relation. Improvements in mental and physical HRQL domains with rofecoxib treatment were significantly greater than those with placebo treatment (P < .05 for each dose of rofecoxib vs placebo for all domains except general health) and highly correlated with improvements observed using disease-specific OA outcome measures such as the Western Ontario and McMaster Universities Osteoarthritis Index-visual Analog 3.0 OA index pain and physical function subscales. The effect of rofecoxib vs placebo treatment on mental health largely disappeared after adjustment for improvement in OA disease-specific measures. CONCLUSIONS: Rofecoxib treatment increased physical and mental HRQL domain scores on the SF-36. Improvements in mental health with rofecoxib use primarily resulted from effective treatment of OA (i.e., reduction in pain and improvement in physical function).

A multicenter, randomized, controlled trial to evaluate the safety profile, tolerability, and efficacy of rofecoxib in advanced elderly patients with osteoarthritis.

This 6-week study was conducted to test the efficacy, safety, and tolerability of rofecoxib (a selective COX-2 inhibitor) compared to nabumetone (a non-selective NSAID) and placebo in osteoarthritis (OA) patients aged 80 and older. Three hundred forty-one patients, mean age 83 years, were randomized. Allocations were made in an approximately 1:2:1:2 ratio (placebo: 12.5 mg rofecoxib: 25 mg rofecoxib: 1500 mg nabumetone). Least square mean changes from baseline in the primary efficacy endpoint, Patient Global Assessment of Disease Status, were as follows (with negative numbers indicating improvement): -14.85 mm for placebo; -25.34 mm for 12.5 mg rofecoxib; -25.40 mm for 25 mg of rofecoxib; and -25.95 mm for nabumetone (p<0.001 for all active treatments vs placebo.) Results from secondary endpoints, including the 3 WOMAC sub-scales (pain, stiffness, and disability) and the Investigator Global Assessment of Disease Status, were consistent with those for the primary endpoint. No significant between-group differences were observed in the proportions of patients who discontinued treatment due to either clinical or laboratory adverse experiences. Renal safety (edema and hypertension adverse experiences) was similar for rofecoxib and nabumetone. No gastroduodenal ulcers occurred; however, the demonstration of gastrointestinal risk with rofecoxib or nabumetone was beyond the scope of this trial. We conclude that in patients 80 years and older, rofecoxib, 12.5 mg and 25 mg once daily, demonstrated clinical efficacy for the treatment for OA as did 1500 mg of nabumetone. Rofecoxib and nabumetone were generally well tolerated in this elderly population.

Precision of composite measures of osteoarthritis efficacy in comparison to that of individual endpoints.

OBJECTIVE: Osteoarthritis (OA) clinical studies generally employ various endpoints to evaluate a spectrum of disease manifestations. Compared with individual endpoints, a composite measure might (1) provide a uniform outcome measure of OA efficacy with greater face validity, (2) address multiplicity, and (3) enhance precision. Combinations of endpoints were analyzed to investigate precision of composite measures of OA efficacy. METHODS: We reanalyzed three 6 week, placebo controlled, double blind, parallel group studies (2 by the same protocol) of the cyclooxygenase-2 (COX-2) specific inhibitor rofecoxib. The average change from baseline at study weeks 2, 4, and 6 was assessed for 10 individual response variables, including patient and investigator global assessments, WOMAC 3.0V OA Index pain, stiffness and physical function subscales, graded study joint tenderness, and rescue analgesic use. Relationships among variables were evaluated using pairwise correlations and principal components analysis. The precision of variables to differentiate rofecoxib from placebo was evaluated using effect size (i.e., mean difference between rofecoxib versus placebo divided by pooled SD). RESULTS: Correlations among all pairs of response variables ranged from 0.5 to 0.9, except those with tenderness (0.4 to 0.6) and those with analgesic use (0.2 to 0.4). The first principal component explained about 70% of the total variability, with weights generally similar (0.17 for rescue analgesic use, 0.25 for tenderness, and 0.30 to 0.37 for the others). These results indicate that nearly all measures are closely related. Based on these results, various linear combinations of the 9 endpoints were formed and their precision to discriminate active treatment from placebo was compared to that of the individual endpoints. Effect sizes of the individual endpoints ranged from 0.6 to 1.1; those of the composites from 0.7 to 0.9. The results were very consistent between study protocols. CONCLUSION: In comparison to individual endpoints, composite analyses of OA clinical endpoints do not increase precision to discriminate active treatment from placebo.

Minimal perceptible clinical improvement with the Western Ontario and McMaster Universities osteoarthritis index questionnaire and global assessments in patients with osteoarthritis.

OBJECTIVE: To determine the minimal perceptible clinical improvement (MPCI) in patients with osteoarthritis (OA) with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire, and patient and investigator global assessment of disease status in randomized clinical trials for treatment of OA. METHODS: Subjects with OA of the knee or hip were randomized to receive either rofecoxib 12.5 or 25 mg once daily, ibuprofen 800 mg 3 times daily, or placebo for 6 weeks. The WOMAC and global assessments were completed at baseline and Weeks 2, 4, and 6. A patient global assessment of response to therapy (0 to 4 scale) was used to "anchor" the WOMAC scores. MPCI was defined as the difference in mean change from baseline in WOMAC (100 mm normalized visual analog scale, VAS) between patients with 0 = "None" global response to therapy and patients with 1 = "Poor" global response to therapy. RESULTS: MPCI was determined to be 9.7, 9.3, and 10.0 mm for the WOMAC pain, physical function and stiffness subscales, respectively, and 11.1 mm for WOMAC question 1: Pain walking on a flat surface. The MPCI for the investigator was 0.4 with investigator assessment of disease status reported on a 0 to 4 Likert scale. Of note, the estimated MPCI for the WOMAC and investigator globals were similar irrespective of treatment, sex, age, or geographic region. CONCLUSION: In this analysis, mean changes of roughly 9 to 12 mm (100 mm normalized VAS) on WOMAC scales were perceptible changes to patients with hip and knee OA. A mean decrease of 0.4 in global disease status (0 to 4 Likert scale) as assessed by the investigator corresponded to the patients' MPCI. Understanding the minimal perceptible differences may permit a better assessment of the clinical relevance of therapeutic interventions in OA.

Pharmacokinetics, COX-2 specificity, and tolerability of supratherapeutic doses of rofecoxib in humans.

OBJECTIVE: Prostaglandin synthesis is catalyzed by a constitutive cyclo-oxygenase isoform (COX-1) and an inducible isoform (COX-2). It is hypothesized that the analgesic and anti-inflammatory effects of nonsteroidal anti-inflammatory drugs (nonspecific COX-1/COX-2 inhibitors) such as ibuprofen principally derive from COX-2 inhibition. The purpose of this study was to evaluate steady-state pharmacokinetics, biochemical selectivity and tolerability of rofecoxib (Vioxx), characterized in vitro as a COX-2 inhibitor. METHODS: Four panels of healthy men (n = 8 per panel) were administered rofecoxib (n = 6) (25, 100, 250, 375 mg) or placebo (n = 2) once daily on day 1 and days 3-14. Blood samples for assays of rofecoxib plasma concentration and COX isoform activity were obtained pre-dose and at specified time points post-dose. RESULTS: Rofecoxib pharmacokinetics were found to be complex and nonlinear. Elimination half-life ranged from 9.9 h to 17.5 h after multiple dosing with an accumulation ratio close to 2 for all doses. COX-2 inhibitory activity as assessed by average inhibition of whole blood lipopolysaccharide-stimulated prostaglandin E2 over the 8-h post-dose period on day 14 was 0.3, 67, 96, 92 and 96% for the placebo and the 25-, 100-, 250- and 375-mg treatment groups, respectively. No treatment group showed significant inhibition of COX-1 as assessed by thromboxane B2 generation in clotting whole blood. Side effects were mild and transient. CONCLUSION: The results indicate that rofecoxib is a potent and specific inhibitor of COX-2 in humans even at doses more than tenfold higher than those associated with efficacy in patients with osteoarthritis.

A randomized trial of the efficacy and tolerability of the COX-2 inhibitor rofecoxib vs ibuprofen in patients with osteoarthritis. Rofecoxib/Ibuprofen Comparator Study Group.

BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). It is not known whether a specific inhibitor of COX-2 will provide efficacy in osteoarthritis (OA) comparable with NSAIDs. Therefore, we compared the efficacy and safety of the rofecoxib, which specifically inhibits COX-2, with those of the NSAID ibuprofen in patients with OA. OBJECTIVE: To compare the clinical efficacy and tolerability of rofecoxib (12.5 and 25 mg once daily) with ibuprofen (800 mg 3 times daily). METHODS: A randomized, double-blind trial of 809 adults with OA was conducted. Patients with OA in whom the knee or hip was the primary source of pain were randomized to 1 of 4 treatment groups on demonstration of disease activity: placebo; rofecoxib, 12.5 or 25 mg once daily; or ibuprofen, 800 mg 3 times daily. Clinical efficacy and safety were monitored during a 6-week treatment period. RESULTS: Both doses of rofecoxib demonstrated efficacy clinically comparable with ibuprofen as assessed by 3 primary end points (pain walking on a flat surface [Western Ontario and McMaster Universities Osteoarthritis Index], patient global assessment of response to therapy, and investigator global assessment of disease status) according to predefined comparability criteria. Both rofecoxib doses and the ibuprofen dose provided significantly (P<.001) greater efficacy than placebo on all primary end points. Results from secondary end points were consistent with those of the primary end points. All treatments were well tolerated; the overall incidence rates of clinical adverse experiences were not significantly different (P>.05) among the treatment groups. CONCLUSION: Rofecoxib was well tolerated and provided clinical efficacy comparable with a high dose of the NSAID ibuprofen.

Rofecoxib, a specific inhibitor of cyclooxygenase 2, with clinical efficacy comparable with that of diclofenac sodium: results of a one-year, randomized, clinical trial in patients with osteoarthritis of the knee and hip. Rofecoxib Phase III Protocol 035 Study Group.

OBJECTIVE: To compare the clinical efficacy of rofecoxib, a specific inhibitor of cyclooxygenase 2 (COX-2), with that of diclofenac in patients with osteoarthritis (OA) and to evaluate the safety and tolerability of rofecoxib. METHODS: We performed a randomized, double-blind, active comparator-controlled trial in 784 adults with OA of the knee or hip. Patients were randomized to 1 of 3 treatment groups: 12.5 mg of rofecoxib once daily, 25 mg of rofecoxib once daily, and 50 mg of diclofenac 3 times daily. Clinical efficacy and safety were evaluated over a 1-year continuous treatment period. RESULTS: Rofecoxib at dosages of 12.5 and 25 mg demonstrated efficacy that was clinically comparable to that of diclofenac, as assessed by all 3 primary end points according to predefined comparability criteria. Results from secondary end points were consistent with those of the primary end points. There were small statistical differences favoring diclofenac for 2 of the end points. All treatments were well tolerated. CONCLUSION: Rofecoxib was well tolerated and provided efficacy that was clinically comparable, according to predefined statistical criteria, to that of 150 mg of diclofenac per day in this 1-year study. Specific inhibition of COX-2 provided therapeutic efficacy in OA.

Effect of specific COX-2 inhibition in osteoarthritis of the knee: a 6 week double blind, placebo controlled pilot study of rofecoxib. Rofecoxib Osteoarthritis Pilot Study Group.

OBJECTIVE: To determine the efficacy and safety of the cyclooxygenase 2 (COX-2) specific inhibitor, rofecoxib in patients with osteoarthritis (OA) of the knee. METHODS: Rofecoxib, 25 mg or 125 mg once daily, was compared with placebo in a 6 week, double blind, parallel group, randomized, multicenter study of 219 patients with knee OA. RESULTS: Both doses of rofecoxib produced clinically significant improvement as assessed by primary (e.g., WOMAC Pain Subscale 0-100 mm, decrease from baseline: placebo: 7.1 mm; rofecoxib 25 mg: 28.1 mm, rofecoxib 125 mg: 28.0 mm; p < 0.001 rofecoxib vs placebo) and secondary efficacy (p < 0.05) criteria compared with placebo. Clinical improvement with the 25 mg dose was similar to that with the 125 mg dose. Both rofecoxib doses were generally well tolerated. CONCLUSION: Specific inhibition of COX-2 by 25 and 125 mg rofecoxib, administered once daily, resulted in clinically meaningful improvements in patients with OA. This study confirms that COX-2 derived prostanoids are important clinical mediators of pain and other symptoms of knee OA and that inhibition of COX-1 is not required to provide clinical benefit.

The safety profile, tolerability, and effective dose range of rofecoxib in the treatment of rheumatoid arthritis. Phase II Rofecoxib Rheumatoid Arthritis Study Group.

Nonsteroidal anti-inflammatory drugs. (NSAIDs) inhibit both cyclooxygenase (COX)-1 and COX-2 isoenzymes and are effective in the treatment of inflammatory disorders. This 8-week, double-masked, placebo-controlled trial was undertaken to assess the safety profile, tolerability, and effective dose range of once-daily rofecoxib, a COX-2-specific inhibitor, in the treatment of rheumatoid arthritis (RA). After a 3- to 15-day washout of prior NSAID therapy, 658 patients were randomly allocated to receive placebo or rofecoxib 5 mg, 25 mg, or 50 mg once daily. Safety profile, tolerability, and efficacy were evaluated after 2, 4, and 8 weeks of therapy. Six hundred fifty-eight patients (168, 158, 171, and 161 in the placebo and 5-mg, 25-mg, and 50-mg rofecoxib groups, respectively) were enrolled at 79 clinical centers in the United States. Mean age was 55 years, mean duration of RA was 10 years, and 506 (77%) of the 658 patients were female. All groups had similar baseline demographic characteristics. Patients taking rofecoxib 25 and 50 mg showed significant clinical improvement compared with those taking placebo; 43.9% in the rofecoxib 25-mg group and 49.7% in the rofecoxib 50-mg group completed the treatment period and achieved an American College of Rheumatology 20 response (P = 0.025 and 0.001 vs. placebo, respectively). The 5-mg dose of rofecoxib did not differ significantly from placebo. Patients in the rofecoxib 25- and 50-mg groups showed significant improvement in key individual efficacy measurements, including patient global assessment of pain, patient and investigator global assessment of disease activity, and Stanford Health Assessment Questionnaire Disability Index (P<0.05 vs placebo). Compared with placebo, significantly fewer patients in the 25-mg and 50-mg rofecoxib groups discontinued therapy because of lack of efficacy (P = 0.02 and P = 0.032, respectively). Our results show that rofecoxib 25 and 50 mg once daily was effective and generally well-tolerated in patients with RA.

Interpreting the clinical significance of the differential inhibition of cyclooxygenase-1 and cyclooxygenase-2.

The International Consensus Meeting on the Mode of Action of COX-2 Inhibition (ICMMAC) brought together 17 international experts in arthritis, gastroenterology and pharmacology on 5 6 December 1997. The meeting was convened to provide a definition of COX-2 specificity and to consider the clinical relevance of COX-2-specific agents. These compounds are a new class of drugs that specifically inhibit the enzyme COX-2 while having no effect on COX-1 across the whole therapeutic dose range. The objectives of the meeting were to review the currently available data regarding the roles and biology of COX-1 and COX-2, and to foster a consensus definition on COX-2 specificity. At the present time, no guidelines exist for the in vitro and in vivo assessment of COX specificity, and it was felt that consensus discussion might clarify some of these issues. The meeting also reviewed recent clinical data on COX-2-specific inhibitors. The following article reflects discussion at this meeting and provides a consensus definition of COX-2-specific inhibitors.

Characterization of rofecoxib as a cyclooxygenase-2 isoform inhibitor and demonstration of analgesia in the dental pain model.

BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, and indomethacin (INN, indometacin) inhibit both the constitutive (COX-1) and inducible (COX-2) isoforms of cyclooxygenase. The induction of COX-2 after inflammatory stimuli has led to the hypothesis that COX-2 inhibition primarily accounts for the therapeutic properties of NSAIDs. METHODS: Chinese hamster ovary (CHO) cell lines that express each COX isoform were used to characterize the in vitro selectivity of rofecoxib. Single oral doses of rofecoxib and indomethacin were then assessed in subjects with use of ex vivo COX-isoform specific assays (serum thromboxane B2 [TXB2] and lipopolysaccharide [LPS]-stimulated whole blood prostaglandin E2 and assays of COX-1 and COX-2 activity, respectively). A double-blind, parallel-group study compared the analgesic efficacy of rofecoxib to placebo and ibuprofen in 102 patients with dental pain. RESULTS: Rofecoxib showed a >800-fold COX-2 selectivity with use of CHO cells that express human COX-1 and COX-2. In subjects, dose- and concentration-dependent inhibition of LPS-stimulated prostaglandin E2 was observed with both rofecoxib (IC50 [the concentration estimated to produce 50% inhibition], 0.77 micromol/L) and indomethacin (IC50, 0.33 micromol/L). Whereas indomethacin inhibited TXB2, (IC50, 0.14 micromol/L), no inhibition was observed with rofecoxib even at doses of up to 1000 mg. In the dental pain study, total pain relief (TOTPAR) over the 6 hours after dosing was similar between 50 mg and 500 mg rofecoxib and 400 mg ibuprofen (P > .20). All active treatments showed greater improvement than placebo (P < .001) CONCLUSIONS: Rofecoxib inhibited COX-2 without evidence of COX-1 inhibition, even at oral doses of up to 1000 mg. Nonetheless, rofecoxib showed analgesic activity indistinguishable from that observed with ibuprofen, a nonisoform-selective COX inhibitor. These results support the hypothesis that the analgesic effects of NSAIDs primarily derive from inhibition of COX-2.

A human whole blood assay for clinical evaluation of biochemical efficacy of cyclooxygenase inhibitors.

In this study, PGE2 levels in lipopolysaccharide (LPS)-challenged human whole blood and TxB2 levels following blood coagulation were measured as biochemical index for cyclooxygenase (Cox)-2 and Cox-1 activity respectively. Incubation of human mononuclear cells isolated from whole blood with LPS (100 mu g/mL) induced a time-dependent increase in the expression of Cox-2 protein (>100 fold at 24 hr). This is associated with increases in PGE2 production and free arachidonate release in the plasma. Cox-1 protein was detected in the human mononuclear cells at time zero but was not induced by either LPS or PBS. Most non-steroidal anti-inflammatory drugs (NSAIDs) are more potent at inhibiting Cox-1 than Cox-2. Five experimental compounds CGP-28238, Dup-697, NS-398, SC-58125 and L-745,337, have a greater selectivity for Cox-2. Indomethacin at a single oral dose (25 mg) inhibited approximately 90% the whole blood Cox-2 and Cox-1 activities ex vivo in healthy subjects. These results support the use of this assay to assess the biochemical efficacy of selective Cox-2 inhibitors in clinical trials.

The nature of major histocompatibility complex recognition by gamma delta T cells.

Despite intensive efforts, the general rules for gamma delta T cell recognition remain undefined. Here, we take advantage of the detailed knowledge of the molecular structure and biosynthetic pathways of major histocompatibility complex (MHC) molecules to analyze the recognition properties of the gamma delta T cell clones LBK5 (specific for the class II MHC, IEk) and G8 (specific for the nonclassical class I MHC, TL10b). We find that the activation of these clones requires neither class I nor class II antigen-processing and that peptides do not confer specificity. Epitope mapping also shows that the topology of gamma delta T cell receptor interaction with the MHC is distinct from that of alpha beta T cells. These results suggest that the molecular nature of gamma delta T cell recognition is fundamentally different than that of alpha beta T cells.

T cell receptor interaction with peptide/major histocompatibility complex (MHC) and superantigen/MHC ligands is dominated by antigen.

While recent evidence strongly suggests that the third complementarity determining regions (CDR3s) of T cell receptors (TCRs) directly contact antigenic peptides bound to major histocompatibility complex (MHC) molecules, the nature of other TCR contact(s) is less clear. Here we probe the extent to which different antigens can affect this interaction by comparing the responses of T cells bearing structurally related TCRs to cytochrome c peptides and staphylococcal enterotoxin A (SEA) presented by 13 mutant antigen-presenting cell (APC) lines. Each APC expresses a class II MHC molecule (I-Ek) with a single substitution of an amino acid residue predicted to be located on the MHC alpha helices and to point "up" towards the TCR. We find that very limited changes (even a single amino acid) in either a CDR3 loop of the TCR or in a contact residue of the antigenic peptide can have a profound effect on relatively distant TCR/MHC interactions. The extent of these effects can be as great as that observed between T cells bearing entirely different TCRs and recognizing different peptides. We also find that superantigen presentation entails a distinct mode of TCR/MHC interaction compared with peptide presentation. These data suggest that TCR/MHC contacts can be made in a variety of ways between the same TCR and MHC, with the final configuration apparently dominated by the antigen. These observations suggest a molecular basis for recent reports in which either peptide analogues or superantigens trigger distinct pathways of T cell activation.

Molecular components of T-cell recognition.

We review recent data that increase our understanding of the ternary complex of the T cell receptor (TCR), antigenic peptides, and molecules of the major histocompatibility complex (MHC). Studies using synthetic peptide analogs for T-cell antigens have identified peptide residues that appear to interact with the MHC molecule and/or the TCR. The logical extension of these studies, using a complete replacement set of peptide analogues for a model peptide antigen, has more precisely defined the biochemical character of putative MHC and TCR contact residues, and indicated that the TCR is highly sensitive to subtle changes in peptide conformation. Insight into the binding site for peptide on the TCR has recently come from variant peptide immunization of TCR single-chain transgenic mice. These experiments indicate that residues encoded by the V(D)J junctions of both TCR chains contact peptide directly. TCR-MHC contacts have also been studied, using in vitro-mutagenized MHC molecules, particularly those altered at residues predicted to point "up," toward the TCR. These studies reveal that TCR-MHC contacts appear to be quite flexible, and vary between even closely related TCRs. A measure of the affinity of TCR for peptide/MHC complexes has come from competition experiments using soluble MHC complexed with specific peptides. This affinity, with a KD of 5 x 10(-5) M, is several orders of magnitude lower than that of most antibodies for their protein antigens and suggests that the sequence of events leading to T-cell activation begins with antigen-independent adhesion.