Clinical Outcomes in Patients with FLT3-ITD-Mutated Relapsed/Refractory Acute Myelogenous Leukemia Undergoing Hematopoietic Stem Cell Transplantation after Quizartinib or Salvage Chemotherapy in the QuANTUM-R Trial

Despite the substantial clinical activity of fms-related tyrosine kinase 3 (FLT3) inhibitors in relapsed or refractory (R/R) FLT3-ITD‒positive acute myelogenous leukemia (AML), durable remissions and prolonged survival in this population require allogeneic hematopoietic stem cell transplantation (allo-HSCT). Quizartinib, a once-daily oral, highly potent, and selective FLT3 inhibitor, significantly prolonged overall survival (OS) and improved clinical benefit compared with salvage chemotherapy (median OS, 6.2 months versus 4.7 months; hazard ratio [HR], .76; 95% confidence interval [CI], .58 to .98; P = .018; composite complete remission [CRc] rate, 48% versus 27%; median duration of CRc, 2.8 months versus 1.2 months; mortality rate, .8% versus 14% by day 30, 7% versus 24% by day 60) in patients with R/R FLT3-ITD AML in the phase 3 QuANTUM-R trial. In this post hoc analysis, we described the characteristics of and clinical outcomes in patients who underwent on-study HSCT in QuANTUM-R at the investigator's discretion and institutional practices. Of 367 randomized patients, 78 (32%) in the quizartinib arm and 14 (11%) in the salvage chemotherapy arm underwent on-study allo-HSCT without any intervening therapy for AML after quizartinib or study-specified salvage chemotherapy. Pooled data of patients from both treatment arms showed a longer median overall survival (OS) in transplant recipients versus those treated without allo-HSCT (12.2 months versus 4.4 months; HR, .315; 95% CI, .233 to .427). Pooled data also showed a longer median OS in patients with a last recorded response of CRc before allo-HSCT versus patients without a CRc (20.1 months versus 8.8 months; HR, .506; 95% CI, .296 to .864). By treatment arm, the median OS was 25.1 months with quizartinib and 20.1 months with salvage chemotherapy in patients with a last recorded response of CRc before allo-HSCT. Forty-eight patients in the quizartinib arm continued quizartinib treatment after allo-HSCT. In the 31 patients with a last recorded response of CRc before allo-HSCT who continued quizartinib after allo-HSCT, the median OS was 27.1 months. Continuation of quizartinib after allo-HSCT was tolerable, and no new safety signals were identified. These results suggest that post-transplantation survival following salvage chemotherapy and quizartinib treatment are similar. However, quizartinib response occurs more frequently than with salvage chemotherapy, potentially allowing more patients to undergo transplantation and achieve durable clinical benefit. In addition, post-transplant quizartinib was found to be tolerable and may be associated with prolonged survival in some patients, highlighting its potential value in the management of patients with FLT3-ITD R/R AML.

Effect of Food on the Pharmacokinetics of Quizartinib

Quizartinib is an oral, highly potent, and selective type II FMS‐like tyrosine kinase 3 inhibitor in development for acute myeloid leukemia. This parallel‐group study evaluated potential food effects on quizartinib absorption in healthy subjects who received a single 30‐mg dose after overnight fasting (n = 34) or a high‐fat, high‐calorie meal (n = 30). Blood samples were collected through 504 hours after dosing, and pharmacokinetic parameters calculated were maximum observed concentration (C_max) and area under plasma concentration–time curve from time 0 to last quantifiable concentration (AUC_last) and from time 0 to infinity (AUC_inf). Mean quizartinib pharmacokinetic profiles were similar under fasted and fed conditions. The geometric least squares means ratios (%) for fed/fasted and associated 90% confidence intervals (CIs) for C_max, AUC_last, and AUC_inf were 91.58 (82.15‐102.08), 105.39 (90.79‐122.35), and 108.39 (91.54‐128.34), respectively. The 90%CI for the ratio fell within the 80% to 125% limits for C_max and AUC_last, with 90%CI for AUC_inf slightly outside the limits (ie, 128%). Food delayed quizartinib time to C_max by 2 hours. All adverse events were either mild or moderate; no discontinuations due to adverse events occurred. Based on these results, quizartinib can be administered without regard to food.

Effects of CYP3A inhibitors on the pharmacokinetics of quizartinib, a potent and selective FLT3 inhibitor, and its active metabolite

Aims

Quizartinib is an oral, highly potent and selective next‐generation FMS‐like tyrosine kinase 3 (FLT3) inhibitor under investigation in patients with FLT3‐internal tandem duplication‐mutated acute myeloid leukaemia. This drug–drug interaction study assessed the pharmacokinetics (PK) of quizartinib when coadministered with strong or moderate cytochrome P450 3A (CYP3A) inhibitors.

Methods

In this parallel‐group study, subjects were randomised to receive: (i) quizartinib + ketoconazole; (ii) quizartinib + fluconazole; or (iii) quizartinib alone. On Days 1–28, subjects received ketoconazole 200 mg or fluconazole 200 mg twice daily, and on Day 8, all subjects received a single 30‐mg quizartinib dose. Blood samples were collected for PK analyses, steady‐state PK parameters were simulated by superpositioning, and safety was assessed.

Results

Ninety‐three healthy subjects were randomised; 86 completed the study. When administered with ketoconazole, geometric mean ratios (90% confidence interval) for quizartinib maximum observed plasma concentration (C_max) and area under the plasma concentration–time curve (AUC) from time 0 extrapolated to infinity were 117% (105%, 130%) and 194% (169%, 223%), respectively, vs quizartinib alone. Steady‐state PK simulation demonstrated ~2‐fold increase of both steady–state C_max and AUC from time 0 to the end of the dosing interval when quizartinib was administered with ketoconazole due to accumulation of quizartinib at steady state. When administered with fluconazole, geometric mean ratios (90% confidence interval) for quizartinib C_max and AUC from time 0 extrapolated to infinity were 111% (100%, 124%) and 120% (104%, 138%), respectively, vs quizartinib alone. Overall, 5.4% of subjects experienced quizartinib‐related adverse events; no serious adverse events or deaths occurred.

Conclusions

These results suggest reducing the dose of quizartinib when coadministered with a strong CYP3A inhibitor, but not with a moderate or weak CYP3A inhibitor. This dose reduction was implemented in phase 3 evaluation of quizartinib.

Quizartinib, an FLT3 inhibitor, as monotherapy in patients with relapsed or refractory acute myeloid leukaemia: an open-label, multicentre, single-arm, phase 2 trial

BACKGROUND

Old age and FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutations in patients with acute myeloid leukaemia are associated with early relapse and poor survival. Quizartinib is an oral, highly potent, and selective next-generation FLT3 inhibitor with clinical antileukaemic activity in relapsed or refractory acute myeloid leukaemia. We aimed to assess the efficacy and safety of single-agent quizartinib in patients with relapsed or refractory acute myeloid leukaemia.

METHODS

We did an open-label, multicentre, single-arm, phase 2 trial at 76 hospitals and cancer centres in the USA, Europe, and Canada. We enrolled patients with morphologically documented primary acute myeloid leukaemia or acute myeloid leukaemia secondary to myelodysplastic syndromes and an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 into two predefined, independent cohorts: patients who were aged 60 years or older with relapsed or refractory acute myeloid leukaemia within 1 year after first-line therapy (cohort 1), and those who were 18 years or older with relapsed or refractory disease following salvage chemotherapy or haemopoietic stem cell transplantation (cohort 2). Patients with an FLT3-ITD allelic frequency of more than 10% were considered as FLT3-ITD positive, whereas all other patients were considered as FLT3-ITD negative. Patients received quizartinib once daily as an oral solution; the initial 17 patients received 200 mg per day but the QTcF interval was prolonged for more than 60 ms above baseline in some of these patients. Subsequently, doses were amended for all patients to 135 mg per day for men and 90 mg per day for women. The co-primary endpoints were the proportion of patients who achieved a composite complete remission (defined as complete remission + complete remission with incomplete platelet recovery + complete remission with incomplete haematological recovery) and the proportion of patients who achieved a complete remission. Efficacy and safety analyses included all patients who received at least one dose of quizartinib (ie, the intention-to-treat population). Patients with a locally assessed post-treatment bone marrow aspirate or biopsy were included in efficacy analyses by response; all other patients were considered to have an unknown response. This study is registered with ClinicalTrials.gov, number NCT00989261, and with the European Clinical Trials Database, EudraCT 2009-013093-41, and is completed.

FINDINGS

Between Nov 19, 2009, and Oct 31, 2011, a total of 333 patients were enrolled (157 in cohort 1 and 176 in cohort 2). In cohort 1, 63 (56%) of 112 FLT3-ITD-positive patients and 16 (36%) of 44 FLT3-ITD-negative patients achieved composite complete remission, with three (3%) FLT3-ITD-positive patients and two (5%) FLT3-ITD-negative patients achieving complete remission. In cohort 2, 62 (46%) of 136 FLT3-ITD-positive patients achieved composite complete remission with five (4%) achieving complete remission, whereas 12 (30%) of 40 FLT3-ITD-negative patients achieved composite complete remission with one (3%) achieving complete remission. Across both cohorts (ie, the intention-to-treat population of 333 patients), grade 3 or worse treatment-related treatment-emergent adverse events in 5% or more of patients were febrile neutropenia (76 [23%] of 333), anaemia (75 [23%]), thrombocytopenia (39 [12%]), QT interval corrected using Fridericia's formula (QTcF) prolongation (33 [10%]), neutropenia (31 [9%]), leucopenia (22 [7%]), decreased platelet count (20 [6%]), and pneumonia (17 [5%]). Serious adverse events occurring in 5% or more of patients were febrile neutropenia (126 [38%] of 333; 76 treatment related), acute myeloid leukaemia progression (73 [22%]), pneumonia (40 [12%]; 14 treatment related), QTcF prolongation (33 [10%]; 32 treatment related), sepsis (25 [8%]; eight treatment related), and pyrexia (18 [5%]; nine treatment related). Notable serious adverse events occurring in less than 5% of patients were torsades de pointes (one [<1%]) and hepatic failure (two [1%]). In total, 125 (38%) of 333 patients died within the study treatment period, including the 30-day follow-up. 18 (5%) patients died because of an adverse event considered by the investigator to be treatment related (ten [6%] of 157 patients in cohort 1 and eight [5%] of 176 in cohort 2.

INTERPRETATION

Single-agent quizartinib was shown to be highly active and generally well tolerated in patients with relapsed or refractory acute myeloid leukaemia, particularly those with FLT3-ITD mutations. These findings confirm that targeting the FLT3-ITD driver mutation with a highly potent and selective FLT3 inhibitor is a promising clinical strategy to help improve clinical outcomes in patients with very few options. Phase 3 studies (NCT02039726; NCT02668653) will examine quizartinib at lower starting doses.

FUNDING

Ambit Biosciences/Daiichi Sankyo.

Results of a phase 1 study of quizartinib as maintenance therapy in subjects with acute myeloid leukemia in remission following allogeneic hematopoietic stem cell transplant

FLT3-ITD-mutated acute myeloid leukemia (AML) has very high risk of relapse and is associated with poor outcome following allogeneic hematopoietic-cell transplant (allo-HCT). This two-part, phase 1, multicenter, open-label, sequential-group, dose-escalation study aimed to determine dose-limiting toxicities (DLTs), maximum tolerated dose (MTD), and safety/tolerability of quizartinib, a selective and highly potent FLT3 inhibitor, when administered as maintenance therapy after allo-HCT. Thirteen subjects with documented FLT3-ITD-mutated AML in morphological remission following allo-HCT received one of two quizartinib dihydrochloride dose levels (DL): 40 mg/d (DL1; n = 7) and 60 mg/d (DL2; n = 6), administered orally in 28-day cycles for up to 24 cycles. Median age of participants was 43 years. All subjects received human leukocyte antigen (HLA)-matched allo-HCT. One subject treated at DL1 and 1 treated at DL2 had DLTs that required drug interruption (grade 3 gastric hemorrhage and grade 3 anemia, respectively). Ten subjects (77%) received quizartinib for >1 year; 5 (38%) completed 24 cycles. Four subjects (31%) discontinued quizartinib due to adverse events. One subject (8%) experienced relapse during cycle 1 and discontinued treatment. Most common grade 3/4 adverse events were neutropenia (23%), anemia (15%), leukopenia (15%), lymphopenia (15%), and thrombocytopenia (15%). This study demonstrated acceptable tolerability and early evidence of reduced relapse rate following allo-HCT with quizartinib maintenance compared to historical cohorts. No MTD was identified, but 60 mg daily was selected as highest dose for continuous daily administration based on randomized comparison of daily 30 and 60 mg doses in relapsed/refractory AML.

An open-label, single-dose, phase 1 study of the absorption, metabolism and excretion of quizartinib, a highly selective and potent FLT3 tyrosine kinase inhibitor, in healthy male subjects, for the treatment of acute myeloid leukemia

1. Quizartinib absorption, metabolism and excretion were characterized in six healthy men receiving a single oral dose of 60 mg (≈100 μCi) of [¹⁴C]-quizartinib. Blood, plasma, urine and faeces were collected ≤336 h postdose. 2. Four hours postdose, maximum mean ± SD blood radioactivity concentrations were 296 ± 67.4 ng equivalents/g. A mean ± SD of 1.64 ± 0.482% and 76.3 ± 6.23% of the dose was recovered in urine and faeces, respectively, within 336 h postdose. 3. Radio-detector high-performance liquid chromatography (radio-HPLC) and liquid chromatography-mass spectrometry (LC-MS) showed two main radioactive peaks in plasma, unchanged quizartinib and mono-oxidative metabolite, AC886. Five additional metabolites in plasma were identified by LC-MS, but low levels prevented radio-HPLC detection. Although unchanged quizartinib was the main radioactive component in faeces (mean, 4.0% of administered dose), 15 metabolites representing a mean of 1.0-3.5% of administered dose were found. Quizartinib was predominantly metabolized by phase I biotransformations (oxidation, reduction, dealkylation, deamination, hydrolysis and combinations thereof). 4. This study indicated that quizartinib was rapidly and orally bioavailable, extensively metabolized, with AC886 as the major circulating metabolite, and predominantly eliminated in faeces. Quizartinib was well tolerated in the subjects.

A Phase I Study of Quizartinib Combined with Chemotherapy in Relapsed Childhood Leukemia: A Therapeutic Advances in Childhood Leukemia & Lymphoma (TACL) Study

PURPOSE

To determine a safe and biologically active dose of quizartinib (AC220), a potent and selective class III receptor tyrosine kinase (RTK) FLT3 inhibitor, in combination with salvage chemotherapy in children with relapsed acute leukemia.

EXPERIMENTAL DESIGN

Quizartinib was administered orally to children with relapsed AML or MLL-rearranged ALL following 5 days of high-dose cytarabine and etoposide (AE). A 3+3 dose escalation design was used to identify a safe and biologically active dose. Plasma inhibitory assay (PIA) testing was performed weekly to determine biologic activity.

RESULTS

Toxicities were consistent with intensive relapsed leukemia regimens. One of 6 patients experienced a dose-limiting toxicity (DLT) at 40 mg/m(2)/day (elevated lipase) and 1 of 9 had a DLT (hyperbilirubinemia) at the highest tested dose of 60 mg/m(2)/day. Of 17 response evaluable patients, 2 had complete response (CR), 1 complete response without platelet recovery (CRp), 1 complete response with incomplete neutrophil and platelet recovery (CRi), 10 stable disease (SD), and 3 progressive disease (PD). Of 7 FLT3-ITD patients, 1 achieved CR, 1 CRp, 1 Cri, and 4 SD. FLT3-ITD patients, but not FLT3 wild-type (WT) patients, had significantly lower blast counts post-quizartinib. FLT3 phosphorylation was completely inhibited in all patients.

CONCLUSIONS

Quizartinib plus intensive chemotherapy is well tolerated at 60 mg/m(2)/day with near complete inhibition of FLT3 phosphorylation in all patients. The favorable toxicity profile, pharmacodynamic activity, and encouraging response rates warrant further testing of quizartinib in children with FLT3-ITD AML. Clin Cancer Res; 22(16); 4014-22. ©2016 AACR.

Phase I study of quizartinib administered daily to patients with relapsed or refractory acute myeloid leukemia irrespective of FMS-like tyrosine kinase 3-internal tandem duplication status

PURPOSE

FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) mutations in acute myeloid leukemia (AML) are associated with early relapse and poor survival. Quizartinib potently and selectively inhibits FLT3 kinase activity in preclinical AML models.

PATIENTS AND METHODS

Quizartinib was administered orally at escalating doses of 12 to 450 mg/day to 76 patients (median age, 60 years; range, 23 to 86 years; with a median of three prior therapies [range, 0 to 12 therapies]), enrolled irrespective of FLT3-ITD mutation status in a phase I, first-in-human study in relapsed or refractory AML.

RESULTS

Responses occurred in 23 (30%) of 76 patients, including 10 (13%) complete remissions (CR) of any type (two CRs, three CRs with incomplete platelet recovery [CRp], five CRs with incomplete hematologic recovery [CRi]) and 13 (17%) with partial remissions (PRs). Of 17 FLT3-ITD-positive patients, nine responded (53%; one CR, one CRp, two CRis, five PRs); of 37 FLT3-ITD-negative patients, five responded (14%; two CRps, three PRs); of 22 with FLT3-ITD-indeterminate/not tested status, nine responded (41%; one CR, three CRis, five PRs). Median duration of response was 13.3 weeks; median survival was 14.0 weeks. The most common drug-related adverse events (> 10% incidence) were nausea (16%), prolonged QT interval (12%), vomiting (11%), and dysgeusia (11%); most were ≤ grade 2. The maximum-tolerated dose was 200 mg/day, and the dose-limiting toxicity was grade 3 QT prolongation. FLT3-ITD phosphorylation was completely inhibited in an in vitro plasma inhibitory assay.

CONCLUSION

Quizartinib has clinical activity in patients with relapsed/refractory AML, particularly those with FLT3-ITD, and is associated with an acceptable toxicity profile.

Response rate and bridging to hematopoietic stem cell transplantation (HSCT) with quizartinib (AC220) in patients with FLT3-ITD positive or negative relapsed/refractory AML after second-line chemotherapy or previous bone marrow transplant

7012

Background: FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) in acute myeloid leukemia (AML) is associated with early relapse after chemotherapy and poor survival. Relapse after HSCT or failure of salvage chemotherapy in FLT3-ITD AML is rarely associated with subsequent HSCT or durable survival. Quizartinib, an oral FLT3 inhibitor, shows promising activity; a Ph 2 study (n=333) of quizartinib monotherapy (Levis et al, ASH 2012) reported that quizartinib often bridged patients (pts) to HSCT. Methods: 136 FLT3-ITD(+) and 40 FLT3-ITD(-) pts, relapsed/refractory after HSCT or 1-second line regimen, were included. The response category of composite complete remission (CRc) comprised complete remission [CR] + complete remission with incomplete platelet recovery [CRp] + complete remission with incomplete hematologic recovery [CRi]. Results: Quizartinib was discontinued for HSCT in 47/136 FLT3-ITD(+) pts (35%), with 44/47 having at least a PR (2 CRp, 24 CRi, 18 PR). Median overall survival (OS) was 41.5 wks for pts with CRc prior to HSCT and 29 wks for pts with PR. The 1y survival rate was 39% for both response groups. Pts with a CRc (n=36) or PR (n=20) but no HSCT, respectively, had a median OS of 24.5 and 20.9 wks and 1y survival rates of 25% and 5%. Of 27 pts with OS >52 wks, 17 (63%) had HSCT. Quizartinib was discontinued for HSCT in 14/40 FLT3-ITD(-) pts (35%), with 13/14 having at least a PR (1 CR, 1 CRp, 7 CRi, 4 PR). Median OS was not yet reached for pts with CRc, and was 40.7 wks for pts with PR. The 1y survival rate was 78% for pts with CRc and 50% for pts with PR. 8 of these 14 pts had detectable ITD mutation but the level was below the prespecified 10% cutoff. Conclusions: Of clinical significance in these heavily pretreated pts who had failed salvage chemotherapy or HSCT, approximately 1/3 were successfully bridged to potentially curative HSCT, with encouraging 1y survival rates. To extend the potential benefits of FLT3 inhibitor therapy in combination with allogeneic HSCT, studies of maintenance quizartinib to prevent relapse post HSCT are ongoing. Clinical trial information: NCT00989261.

Efficacy and safety of quizartinib (AC220) in patients age ≥ 70 years with FLT3-ITD positive or negative relapsed/refractory acute myeloid leukemia (AML)

7023

Background: Advanced age and FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) in AML are each associated with early relapse after standard chemotherapy and poor survival. Quizartinib, an oral FLT3 inhibitor active against ITD mutant and wild type FLT3, has shown promising activity in Ph 1 and 2 studies. Methods: We provide detailed analysis from a Ph 2 study (N = 333) of quizartinib monotherapy, focusing on patients (pts) aged ≥ 70 y with AML that relapsed and/or was refractory to prior therapy. Results: A total of 83 pts age ≥70 y included 60 (72%) FLT3-ITD(+) and 23 (28%) FLT3-ITD(-). Median duration of treatment was 14.6 wks for FLT3-ITD(+) pts and 5.9 wks for FLT3-ITD(-) pts. Composite complete remission (CRc) rate included complete remission (CR), complete remission with incomplete platelet recovery (CRp), and complete remission with incomplete hematologic recovery (CRi). Of 60 FLT3-ITD(+) pts, 32 (53%) had a CRc (1 CR, 3 CRp, 28 CRi). Of 23 FLT3-ITD(-) pts, 10 (43%) had a CRc (2 CR, 1 CRp, 7 CRi). 12/27 FLT3-ITD(+) pts (44%) and 5/10 FLT3-ITD(-) pts (50%) refractory to prior therapy responded to quizartinib, and 12/83 (14%) survived >1 y. The most common (≥10%) Grade 3 or 4 treatment-related adverse events (TRAEs) were febrile neutropenia (22%), anemia (20%), transient QT interval prolongation (17%; no Grade 4), and thrombocytopenia (12%). 15 pts (18%) had TRAEs resulting in discontinuation. Conclusions: Because AML in the elderly, particularly in those aged ≥70 y, is genetically heterogeneous and often follows a myelodysplastic syndrome, there is a wide assumption that it may be less amenable to FLT3-targeted therapy than AML in younger pts. Our data argue against these conclusions and show that pts aged ≥70 y with chemotherapy-resistant AML have preserved high response rates, and promising survival to quizartinib. Clinical trial information: NCT00989261. [Table: see text]

Effect of quizartinib (AC220) on response rates and long-term survival in elderly patients with FLT3-ITD positive or negative relapsed/refractory acute myeloid leukemia

7021

Background: Advanced age and FMS-like tyrosine kinase 3 internal tandem duplications (FLT3-ITD) in acute myeloid leukemia (AML) are associated with early relapse after standard chemotherapy and poor survival. Quizartinib (AC220), an oral FLT3 inhibitor active against ITD mutant and wild type FLT3, has shown promising activity in Ph 1 and 2 studies. Methods: Patients (pts) in a Ph 2 open label study (N = 333) of quizartinib monotherapy included 154 aged ≥60 y with known FLT3-ITD status and AML relapsed in <1 y or refractory to 1st line chemotherapy. Median duration of treatment was 14.2 wks (range 0.1–70.6 wks) for FLT3-ITD(+) pts and 9.5 wks (range 1.1–77.0 wks) for FLT3-ITD(-) pts. The composite complete remission (CRc) rate included complete remission (CR), complete remission with incomplete platelet recovery (CRp), and complete remission with incomplete hematologic recovery (CRi). Results: Of 110 FLT3-ITD(+) pts, 63 (57%) had a CRc (3 CR, 4 CRp, 56 CRi). Of 44 FLT3-ITD(-) pts, 16 (36%) had a CRc (2 CR, 1 CRp, 13 CRi). Median overall survival (OS) in FLT3-ITD(+) pts was 25.3 wks and 16/110 (15%) survived >52 wks. The median age of these pts surviving >52 wks was 69.5 y (range 66–80 y) and median OS was 76.3 wks (range 56.9–96.0 wks). All of these pts responded to quizartinib (2 CR, 2 CRp, 8 CRi, 4 partial remission [PR]). 2 pts were still alive >1 ½ y (OS 93.0 and 96.0 wks). Median OS in FLT3-ITD(-) pts was 19.1 wks and 6/44 FLT3-ITD(-) pts (14%) survived >52 wks. The median age of these pts was 70.0 y (range 65–77 y) and their median survival was 76.6 wks (range 54.9–98.4 wks). 5 of these pts responded to quizartinib (1 CR, 3 CRi, 1 PR). Conclusions: These data for an FLT3-targeted agent show encouraging survival in a subset of elderly pts with relapsed/refractory FLT3-ITD(+) AML. Clinical trial information: NCT00989261. [Table: see text]

An international, randomized, phase III trial of bacillus Calmette-Guerin (BCG) plus allogeneic melanoma vaccine (MCV) or placebo after complete resection of melanoma metastatic to regional or distant sites

8508

Background: Active specific immunotherapy with BCG and an allogeneic, melanoma cell vaccine can induce antibody and T-lymphocyte immune responses to numerous antigens expressed by melanoma cells. This study compared overall and disease-free survival in patients receiving BCG plus placebo versus BCG plus MCV. Methods: Between June 1998 and November 2005, 1,656 patients without evidence of residual disease after resection of stage III (n = 1,160) or stage IV (n = 496) melanoma were randomly assigned to the two treatment arms (1:1). BCG was given as an immunologic adjuvant for the first two injections of both MCV and placebo, which thereafter were administered by intradermal injection every two weeks for the next three injections, every month for the remainder of the first year, every two months for the second year and every three months for years three, four and five. Results: Based on the recommendation of the independent Data and Safety Monitoring Board (DSMB), both studies were terminated after the interim analysis. The recommendation was based on a low probability of demonstrating significant improvement in survival of the BCG plus MCV arm if the study had continued to completion of follow-up and final analysis. Conclusions: This is the largest multicenter clinical trial of postoperative adjuvant immunotherapy after resection of melanoma metastatic to regional lymph nodes or distant sites. It is a landmark study not only because it represents the first randomized multicenter trial to use surgical resection as initial therapy for stage IV melanoma patients with up to five metastatic sites, but also because its results demonstrate excellent survival for the entire study population with 42.3% of stage IV and 63.4% of stage III patients projected to be alive at five years. Updated data for survival and immunologic endpoints which show a significant correlation between immune responses and survival will be provided at the meeting.

[Table: see text]

Prolonged survival after complete resection of disseminated melanoma and active immunotherapy with a therapeutic cancer vaccine

PURPOSE

The curative effect of surgery in certain patients with metastatic melanoma suggests the presence of endogenous antitumor responses. Because melanoma is immunogenic, we investigated whether a therapeutic cancer vaccine called Canvaxin (CancerVax Corporation, Carlsbad, CA) could enhance antitumor immune responses and thereby prolong survival.

PATIENTS AND METHODS

Of 263 patients who underwent complete resection of American Joint Committee on Cancer stage IV melanoma, 150 received postoperative adjuvant vaccine therapy and 113 did not. The overall survival (OS) for the two groups was compared by Cox regression. Further survival analysis was performed by matched-pair analysis according to three prognostic variables: sex, metastatic site, and number of tumor-involved organ sites.

RESULTS

Five-year OS rates were 39% for vaccine and 19% for nonvaccine patients. On multivariate analysis, vaccine therapy was the most significant prognostic variable in this cohort (P =.0001). Analysis of 107 matched pairs of vaccine and nonvaccine patients revealed a significant OS advantage for vaccine therapy (P =.0009): 5-year OS was 39% for vaccine patients versus 20% for nonvaccine patients. There was a significant delayed-type hypersensitivity (DTH) response to adjuvant vaccine therapy (P =.0001), and OS was significantly correlated with DTH to vaccine (P =.0001) but not with DTH to purified protein derivative (PPD), a control antigen.

CONCLUSION

Prolonged survival was observed in patients who received postoperative active immunotherapy with Canvaxin therapeutic cancer vaccine. The correlation of survival with vaccine-DTH responses but not PPD-DTH indicates a treatment-specific effect. These findings suggest that adjuvant active specific immunotherapy should be considered after cytoreductive surgery for advanced melanoma.

Prolonged survival of patients receiving active immunotherapy with Canvaxin therapeutic polyvalent vaccine after complete resection of melanoma metastatic to regional lymph nodes

OBJECTIVE

To determine whether adjuvant postoperative active specific immunotherapy with a therapeutic polyvalent vaccine (PV) called Canvaxin can prolong survival following complete resection of melanoma metastatic to regional nodes (American Joint Committee on Cancer [AJCC] stage III melanoma).

SUMMARY BACKGROUND DATA

Despite complete lymphadenectomy, 5-year overall survival (OS) for patients with melanoma metastatic to regional lymph nodes is only 20% to 50%, depending on the number of tumor-involved nodes. In 1984, the authors began phase II trials of Canvaxin PV as postsurgical adjuvant therapy for AJCC stage III melanoma.

METHODS

Patients who received PV between 1984 and 1998 were compared with patients who did not receive PV postsurgical therapy between 1971 and 1998. The seven covariates recently defined by the AJCC Melanoma Staging Committee (number of metastatic nodes, palpable status, ulceration, age, primary site, pT stage, and gender) were included by Cox regression in a multivariate model of OS. A computerized program matched PV and non-PV patients by these covariates.

RESULTS

Of 2,602 patients who underwent complete lymphadenectomy for AJCC stage III melanoma with regional nodal metastases and were followed up by the same team of oncologists between 1971 and 1998, 935 received PV and 1,667 did not. Median OS and 5-year OS were significantly higher in PV than non-PV patients (56.4 vs. 31.9 months and 49% vs. 37%, respectively; P =.0001). When the non-PV patients were matched by the four most significant covariates, 447 matched pairs were formed between patients seen before or after January 1, 1985, and the OS was not different between the two time periods ( P=.789). However, when the PV patients were matched with non-PV patients by six covariates forming 739 pairs, the PV patients survived longer ( P=.0001). Detailed analysis of the 1,505 patients who were seen or who began vaccine therapy within 4 months after lymphadenectomy, and who had more complete data on the seven prognostic covariates showed that median OS and 5-year OS were higher in 445 PV patients than in 1,060 non-PV patients: 70.4 versus 31 months and 52% versus 37%, respectively (P =.0001). Multivariate Cox regression analysis identified six significant prognostic factors: number of metastatic nodes, size of metastatic nodes, pT stage, ulceration, age, and PV therapy. PV therapy reduced the relative risk of death to 0.64 (95% confidence interval, 0.55-0.76) ( P=.0001); sex and site of primary were of borderline significance.

CONCLUSIONS

This large single-institution study independently confirmed the significance of prognostic covariates in the new AJCC staging system. By using modern statistical methods that controlled for all known prognostic factors, it also demonstrated PV's ability to significantly enhance OS. A multicenter phase III randomized trial is underway to validate the efficacy of PV as a postsurgical adjuvant.

Maintenance biotherapy for metastatic melanoma with interleukin-2 and granulocyte macrophage-colony stimulating factor improves survival for patients responding to induction concurrent biochemotherapy

PURPOSE

A prospective Phase II study of a novel maintenance biotherapy regimen after induction biochemotherapy was conducted in patients with metastatic melanoma in efforts to maintain responses and improve survival.

EXPERIMENTAL DESIGN

Thirty-three patients with poor prognosis metastatic melanoma who achieved a partial response (PR) or stable disease (SD) to induction concurrent biochemotherapy were treated with chronic low-dose interleukin (IL)-2 and granulocyte macrophage-colony stimulating factor, and intermittent pulses of intermediate/high-dose decrescendo IL-2 over a 12-month period. The outcome of these patients was compared with a control group of patients at our institution who were treated recently with induction biochemotherapy and achieved a PR or SD.

RESULTS

Five patients (15%) achieved a complete response, and 4 patients (12%) maintained SD for at least 6 months on maintenance biotherapy. The median progression-free survival (PFS) and overall survival (OS) were 8.1 months and 18.5 months, respectively, compared with historical controls, which were PFS 5.9 months (P = 0.0015) and OS 9.3 months (P = 0.0004). Administration of maintenance biotherapy was a significant predictor of PFS (P = 0.0008) and OS (P = 0.0001) in multivariate and matched-pair analyses (P = 0.002). The maintenance biotherapy regimen was well tolerated with no dose-limiting acute or cumulative toxicities.

CONCLUSION

In this single institution study, maintenance biotherapy with IL-2 and granulocyte macrophage colony-stimulating factor in patients achieving PR or SD to induction biochemotherapy improved PFS and OS compared with historical controls. A larger multicenter Phase II trial has been initiated in an effort to confirm these results.

High-dose tamoxifen added to concurrent biochemotherapy with decrescendo interleukin-2 in patients with metastatic melanoma

BACKGROUND

In vitro cell culture data and preclinical models suggest that tamoxifen modulates tumor cell sensitivity to a wide range of therapeutic agents. In the current study, the authors examined whether high-dose tamoxifen (HDT) improved the overall and complete response in patients with metastatic melanoma who were treated with concurrent biochemotherapy.

METHODS

Forty-nine patients were treated with a biochemotherapy regimen of dacarbazine, vinblastine, cisplatin, decrescendo interleukin-2, interferon-alpha-2b, and tamoxifen. The study had a 2-step design, beginning with a tamoxifen dose escalation from 40 mg to 320 mg (17 subjects) to evaluate safety and tolerability, followed by Phase II accrual of 32 patients to HDT (320 mg) to assess clinical efficacy. Efficacy was compared with a similar modified biochemotherapy regimen with low-dose tamoxifen (LDT). Pharmacokinetic studies were performed to determine in vivo tamoxifen levels.

RESULTS

Tamoxifen dose escalation was completed without any reported dose-limiting toxicity. The overall response rate in the HDT group was 50% (95% confidence interval, 33.2%-66.8%), with a complete response rate of 6% and a median survival of 9.5 months. The overall response rate was not improved and the complete response and survival appeared inferior compared with that of patients recently treated with concurrent biochemotherapy and LDT. Serum tamoxifen levels were found to correlate with the dose administered, with a mean of 0.9 microM at the 40-mg dose to 4.6 microM at the 320-mg dose. Ultrafiltered protein-free sera demonstrated low (< 0.01 microM) concentrations of tamoxifen.

CONCLUSIONS

The addition of HDT to a regimen of concurrent biochemotherapy did not appear to improve response rates or overall survival, despite reaching the targeted plasma concentration. Unknown drug interactions or high protein binding of tamoxifen may account for the lack of clinical effectiveness.

Inhibition of endotoxin-induced TNF-alpha production in macrophages by 5Z-7-oxo-zeaenol and other fungal resorcylic acid lactones

Resorcylic acid lactones are fungal metabolites that exhibit a wide range of biological properties which includes oestrogenic, antifungal, phytotoxic and anti-inflammatory activity. The capacity of 5Z-7-oxo-zeaenol, a resorcylic lactone of fungal origin and six naturally occurring analogues to inhibit lipopolysaccharide (LPS)-induced cytokine production in phorbol 12-myristate-13-acetate (PMA)-treated cultured myelomonocytic cells (U937) was compared. The activity of the natural analogues in the U937 assay varied over 10(4)-fold, with 5Z-7-oxo-zeaenol the most potent of those tested inhibiting tumour necrosis factor-alpha (TNF alpha) production in these cells with IC50 of 6 nM. The isomeric 7-oxo-zeaenol and structurally more distant monorden (radicicol) were the next most active compounds with IC50 approximately 500 nM, and zearalenone, the least active with IC50 > 400 microM. 5Z-7-oxo-zeaenol retained activity in LPS-stimulated peripheral blood mononuclear cells with an IC50 of 10-25 nM. This compound also inhibited LPS-induced TNF alpha production in whole blood experiments (IC50 100-1000 nM) and lowered serum levels of TNF alpha in mice when administered prior to LPS. 5Z-7-oxo-zeaenol was shown to inhibit the phosphorylation and activation of mitogen-activated protein kinase (MAPK) induced by LPS. These data are consistent with a mechanism of action at or upstream of MAPK with resultant downstream effects. This series of naturally occurring analogues represents an interesting group of compounds with diverse biological properties. Of this series, 5Z-7-oxo-zeanenol has exceptionally potent anti-inflammatory properties exhibited by its strong inhibition of cytokine production.

Vaccine therapy for patients with melanoma

Investigation into the therapeutic use of vaccines in patients with metastatic melanoma is critically important because of the lack of effective conventional modalities. The most extensively studied melanoma vaccines in clinical trials are whole-cell preparations or cell lysates that contain multiple antigens capable of stimulating an immune response. Unfortunately, in the majority of studies, immune responses to these vaccines have not translated into a survival advantage. Advances in tumor cell immunology have led to the identification of candidate tumor cell antigens that can stimulate an immune response; this, in turn, has allowed for refinements in vaccine design. However, the exact tumor antigens that should be targeted with a specific vaccine are unknown. The univalent antigen vaccines, which have greater purity, ease of manufacturing, and reproducibility compared with polyvalent vaccines, may suffer from poorer efficacy due to immunoselection and appearance of antigen-negative clones within the tumor. Novel approaches to vaccine design using gene transfection with cytokines and dendritic cells are all promising. However, the induction of immune responses does not necessarily confer a therapeutic benefit. Therefore, these elegant newer strategies need to be studied in carefully designed clinical trials so that outcomes can be compared objectively with standard therapy. If survival is improved with these vaccine approaches, their ease of administration and lack of toxicity will firmly entrench active specific vaccine immunotherapy as a standard modality in the treatment of the melanoma patient.

Advantages of concurrent biochemotherapy modified by decrescendo interleukin-2, granulocyte colony-stimulating factor, and tamoxifen for patients with metastatic melanoma

PURPOSE

Concurrent biochemotherapy results in high response rates but also significant toxicity in patients with metastatic melanoma. We attempted to improve its efficacy and decrease its toxicity by using decrescendo dosing of interleukin-2 (IL-2), posttreatment granulocyte colony-stimulating factor (G-CSF), and low-dose tamoxifen.

PATIENTS AND METHODS

Forty-five patients with poor prognosis metastatic melanoma were treated at a community hospital inpatient oncology unit affiliated with the John Wayne Cancer Institute (Santa Monica, CA) between July 1995 and September 1997. A 5-day modified concurrent biochemotherapy regimen of dacarbazine, vinblastine, cisplatin, decrescendo IL-2, interferon alfa-2b, and tamoxifen was repeated at 21-day intervals. G-CSF was administered beginning on day 6 for 7 to 10 days.

RESULTS

The overall response rate was 57% (95% confidence interval, 42% to 72%), the complete response rate was 23%, and the partial response rate was 34%. Complete remissions were achieved in an additional 11% of patients by surgical resection of residual disease after biochemotherapy. The median time to progression was 6.3 months and the median duration of survival was 11.4 months. At a maximum follow-up of 36 months (range, 10 to 36 months), 32% of patients are alive and 14% remain free of disease. Decrescendo IL-2 dosing and administration of G-CSF seemed to reduce toxicity, length of hospital stay, and readmission rates. No patient required intensive care unit monitoring, and there were no treatment-related deaths.

CONCLUSION

The data from this study indicate that the modified concurrent biochemotherapy regimen reduces the toxicity of concurrent biochemotherapy with no apparent decrease in response rate in patients with poor prognosis metastatic melanoma.

Overview of melanoma vaccines: active specific immunotherapy for melanoma patients

Although a phase III trial has yet to show a statistically significant improvement in the disease-free or overall survival of melanoma patients receiving vaccine therapy, several phase II trials have shown enhanced disease-free and overall survival of patients who develop a humoral and/or cellular response to a melanoma vaccine. The challenge of active specific immunotherapy research is to determine which combination of humoral and cellular immune responses optimizes clinical outcome and how to monitor the immune response effectively. This review identifies key components of a successful melanoma vaccine, discusses new ways to modulate and stimulate the immune system, and summarizes some of the important clinical trials of active specific immunotherapy for patients with melanoma.

Is the survival of melanoma patients receiving polyvalent melanoma cell vaccine linked to the human leukocyte antigen phenotype of patients?

PURPOSE

An allogeneic polyvalent melanoma cell vaccine (PMCV) has been shown to be efficacious in improving overall survival of patients with malignant melanoma in a phase II clinical setting. The PMCV consists of three allogeneic melanoma cell lines. The objectives of the study were to determine (1) whether the survival of melanoma patients who received PMCV was related to the patient's human leukocyte antigen (HLA) class I phenotype matching the HLA class I phenotype of the PMCV, and (2) whether PMCV clinical efficacy was correlated to melanoma patients with a particular HLA phenotype(s).

MATERIALS AND METHODS

PMCV was given to 69 melanoma patients with American Joint Committee on Cancer (AJCC) stage I to IV disease status. The PMCV and patients lymphocytes were typed for HLA-A and -B. A correlation was made between the HLA expression of PMCV lines and the HLA of patients to their survival status. A second correlation was made between the HLA of patients and survival independent of the PMCV HLA phenotype.

RESULTS

Patients whose HLA phenotype (A3/11 and B7/44) matched the PMCV lines had a better overall survival (P < .029). Analysis of HLA expression of patients independent of PMCV HLA to survival showed that HLA-A25 phenotype patients had a significantly better overall survival (P = .006). HLA-B35 patients had a poorer survival outcome (P = .019).

CONCLUSION

The studies indicate that overall survival following PMCV treatment in melanoma patients significantly correlates with their HLA phenotypes. These correlations may be related to the host immune response to the PMCV or due to differences in the clinical course of melanoma in patients with different HLA types.

Update on active specific immunotherapy with melanoma vaccines

Although a randomized clinical trial has yet to show a statistically significant improvement in the survival of patients receiving vaccine therapy for malignant melanoma, several studies have shown enhanced survival of patients developing an immune response to a melanoma vaccine. The knowledge and techniques of modern molecular biology and immunology suggest multiple strategies to augment this response. The challenge of immunotherapy research is to determine which combination of approaches leads to a favorable clinical response and how to monitor that response effectively. This review identifies components of a successful vaccine, discusses new ways to modulate and stimulate the immune system, and summarizes some of the more interesting clinical trials of melanoma vaccine immunotherapy.

Differential effects on TNF alpha production by pharmacological agents with varying molecular sites of action

This study describes the activation conditions for tumor necrosis factor-alpha (TNF alpha) production in myelomonocytic U937 cells and human primary peripheral blood monocytes in response to lipopolysaccharide (LPS) and/or phorbol 12-myristate 13-acetate (PMA). PMA itself induced only low levels of TNF alpha production with delayed kinetics (e.g. 0.758 +/- 0.128 ng/ml from U937 cells after 48 h) while LPS induced greater levels of TNF alpha production in less time (e.g. 2.083 +/- 0.96 ng/ml from monocytes in 24 h). Pharmacological agents with various molecular sites of action were used to validate the two systems, with the protein serine-threonine kinase inhibitors staurosporine and Ro-31-8220, the protein tyrosine kinase inhibitor herbimycin A (HBA) and dexamethasone exhibiting the greatest potency (IC50S 5-350 nM). In contrast to the effect on TNF alpha production, PMA induced strong phosphorylation/activation of p42/p44mapk in monocytes by 10 min determined in a mobility shift assay, while LPS was a weaker inducer. Additionally, staurosporine (to LPS and PMA) and HBA (to LPS only) inhibited the activation of these mitogen-activated protein kinase (MAPK) isoforms at doses 10-100 fold higher than those required to inhibit maximal TNF alpha production. These data indicate the involvement of the p42/p44mapk signalling pathway in LPS-induced pro-inflammatory cytokine production but suggest that other signalling pathways are also implicated in this phenomenon.

Detection of interleukin-1 signal transduction inhibitors: action of protein kinase inhibitors

The dysregulated production of IL-1 has been shown to play an important role in many pathological processes. Despite the apparent value of compounds able to inhibit either the secretion of IL-1 or its signal transduction pathway in a specific manner, there are no such compounds suitable for clinical use. A major problem in identifying novel and specific inhibitors of signal transduction is the lack of knowledge of the intracellular events which mediate the cellular actions of IL-1. In this study a simple cellular assay has been established to screen natural product and synthetic compound libraries for low molecular weight inhibitors of the cytokine signalling pathways of potential therapeutic value. In addition, we have studied the action of several known modulators of signal transduction on the actions of IL-1.

A fungal metabolite which inhibits the interaction of CD4 with major histocompatibility complex-encoded class II molecules

CD4, a cell-surface glycoprotein expressed on a subpopulation of T cells, is the receptor for class II molecules of the major histocompatibility complex (MHC II) and a receptor for the envelope glycoprotein (gp 120) of human immunodeficiency virus-1 (HIV-1). Screening of microbial metabolites for CD4-binding activity using an enzyme-linked immunosorbent assay based on the binding of the CD4-specific monoclonal antibody (mAb), anti-Leu3a, identified a family of compounds comprising several novel polyketides. The parent compound (411F, Vinaxanthone) is a C28 molecule probably arising from a dimerization of two C14 polyketide units. It strongly inhibited the interaction of anti-Leu 3a and that of several other D1/D2 epitope-specific mAb with CD4, but only weakly inhibited the binding of HIV-1 gp120. Binding of a representative MHC class II molecule, HLA-DRB*0401, was also inhibited by 411F with a comparable inhibitory concentration (IC50 = 1 microM). In functional assays 411F inhibited antigen-induced CD4-dependent T cell proliferative responses of peripheral blood mononuclear cells. At the clonal level 411F exhibited selectivity in that the compound inhibited peptide-induced CD4+ T cell proliferative responses but not alloantigen-induced CD8+ T cell proliferation. It is hypothesized that 411F, a polyanionic compound in aqueous solution at neutral pH, inhibits CD4-dependent functions by binding over a broad area of the positively charged amino-terminal D1 and D2 domains implicated in the interaction with MHC II molecules. 411F has the potential for development as an immunosuppressive agent with a novel mechanism of action.

Complications in the functional analysis of transfected MHC genes

Analysis of the relationship between the structure of a protein molecule and its function often exploits the techniques of gene mutation and expression in transfected cell lines. This approach has been used extensively in the study of MHC molecules for testing predictions derived from structural models. Comparison of the functional properties of mutant molecules is difficult because MHC molecules interact with both peptides and T cell receptors. Functionality is commonly determined in biological assays which are dependent on T cell recognition of specific peptide/MHC complexes and measure secondary events triggered by T cell activation. In this study four L cell lines transfected with different combinations of alpha and beta chains from I-Ak and I-Au were used as antigen-presenting cells to activate two hen egg-white lysozyme-specific T cell clones. We compared several biological assays, namely, T cell proliferation, cytokine production, and cytotoxicity. Different assays indicated varying degrees of functionality for the same MHC molecule and thus demonstrated the difficulty in unambiguous interpretation of data from complex assays. Furthermore, we detected differences among the transfected lines which appeared unrelated to the expression of the introduced MHC genes.

Determinant spreading and the dynamics of the autoimmune T-cell repertoire

In this article the authors propose a dynamic model of autoimmunity with T-cell recruitment and selection leading to changes in the specificity of the anti-self response during the course of disease. They argue that these changes are due to alterations in self-antigen presentation that lead to the display of previously cryptic self-determinants. Mechanisms that could underlie this differential self-presentation are proposed.

CD4-binding compounds: an assay to detect new classes of immunopharmacological agents

The interaction of antibodies with protein antigens is accepted as a paradigm of protein-protein interactions. In searching for a new generation of immunomodulatory compounds based on the interaction of the T-cell surface glycoprotein CD4 with MHC class II antigens, a model assay has been developed in which MHC molecules have been substituted by a monoclonal antibody (anti-Leu3a) to the CD4 amino-terminal domain-specific epitope, Leu3a. This assay can detect diverse classes of molecules including proteins such as HIV envelope glycoprotein gp120 and low molecular weight compounds such as aurin tricarboxylic acid, dextran sulphate and Evans blue. The interaction of these molecules with CD4 in the assay appears to be identical to their interaction with native CD4 on intact cells. Other protein-antibody pairs could be substituted for CD4-anti-Leu3a enabling this assay format to be used for the detection of proteins or small organic compounds which interfere with a wide range of therapeutically-relevant macromolecular interactions.

The dominant self and the cryptic self: shaping the autoreactive T-cell repertoire

Deletion of autoreactive T cells during the induction of self tolerance has been directly demonstrated. However, it is still relatively easy to detect self reactivity in normal healthy animals. In this article, Guy Gammon, Eli Sercarz and Gilles Benichou speculate on which T cells may escape tolerance induction and discuss how these cells could subsequently be involved in autoimmunity.

Induction of self-tolerance in T cells but not B cells of transgenic mice expressing little self antigen

Self-tolerance to a transgene-encoded protein, hen egg lysozyme, was examined in the T and B cell repertoires of a series of lines of transgenic mice that expressed different serum concentrations of soluble lysozyme. T cells were tolerant in all lines in which lysozyme was expressed irrespective of the antigen concentration, whereas B cell tolerance did not occur when the serum lysozyme concentration was less than 1.5 nanograms per milliliter (0.1 nM). Induction of elevated transgene expression could restore B cell tolerance. These findings support the hypothesis that autoimmune disease may in some instances arise through a bypass of T cell tolerance.

T cell determinant structure: cores and determinant envelopes in three mouse major histocompatibility complex haplotypes

T lymphocytes recognize discrete regions on an antigen. The specificity of the T cell responses in three mouse strains of differing major histocompatibility complex (MHC) haplotype to a protein antigen, lysozyme, was analyzed using a series of peptides that walk the antigen in single amino acid steps. These peptide series were synthesized using the pin synthesis system, which was modified to allow the peptides to be cleaved from the pins into a physiological buffer free of toxic compounds. This methodology overcomes many of the problems associated with the production of peptides for screening proteins for antigenic determinants. The T cell determinants for the three strains were markedly different. This result points out the limitations of algorithms predicting determinants without reference to the MHC, and the importance of the empirical methodology. This analysis of the T cell response to lysozyme constitutes the most complete study of reactivity to a foreign protein to date and illustrates many important features of antigen recognition by T cells, e.g., presence of major and minor determinant regions. The outer boundaries of each immunogenic region, the determinant envelope, are difficult to define from recently immunized lymph nodes because of the heterogeneity in T cell recognition. However, core sequences common to all the immunogenic peptides in a continuous sequence can be easily defined.

T cell dominance and the vaccine problem: modifying effects on immunogenicity by residues at a distance from the site of T cell recognition

The design of the optimal T cell-inducing component of a vaccine requires consideration of events both at, and distant from, the T cell recognition site. This area is approached here by analysis of T cell immunodominance. After describing the unpredictability of defining dominant T cell-inducing determinants and the preference of empirical methods, the question of designing a solely T determinant vaccine is explored. In this regard, evidence is presented that T helper cell-inducing and T proliferation-inducing determinants are not necessarily identical. With regard to the influence of other determinants on the molecule, three issues are discussed with relevance to vaccine design: (1) 'preferential partnerships' between T and B cells of certain specificities (2) the existence of suppressor T cells, reactive against non-overlapping determinants (3) competitive antigenic determinants, restricted to the same or to a different MHC molecule.

Does the presence of self-reactive T cells indicate the breakdown of tolerance?

There are many experimental systems in which autoreactive T cells can easily be demonstrated but where the host does not normally develop autoimmune disease. How do these animals avoid autoimmunity? Does the presence of these self-reactive cells indicate the failure of self-tolerance? To answer these questions it is necessary to consider how some T cells might escape tolerance induction and why they are not activated in the host. There are several different explanations which can be broadly placed into one of two categories. First, although autoreactive cells may be easily stimulated under experimental conditions, the requirements for activation and likewise deletion may not be met under physiological conditions. The self-antigen may be poorly presented by APC or sequestered in a particular body compartment; alternatively, these T cells may have low affinity receptors needing high levels of antigen. The second category is characterized by the need for immunoregulation. A random selection of T cells may escape clonal inactivation in the thymus but may be kept under constant suppression, which provides a fail-safe mechanism for deletional tolerance. In this review we will discuss these mechanisms and their possible importance in the prevention of autoimmunity.

The T cell repertoire to a multideterminant antigen. Clonal heterogeneity of the T cell response, variation between syngeneic individuals, and in vitro selection of T cell specificities

The specificity of lysozyme-induced T cell proliferative responses by individual B10.A mice was compared by using a panel of three peptides. A surprising degree of variation in the focus of the responses was observed among individual animals, both in the newly isolated lymph node cell populations and in long term T cell lines. The responses to each determinant after hen egg-white lysozyme immunization were not equal and in examining the mice as a group some determinants tended to be dominant. However, despite each animal favoring a restricted number of determinants, the responding T cell populations were still highly heterogeneous. The data suggest that many determinants are involved in the response to the whole Ag. The role of one or more dominant determinants can be overestimated because the degree of heterogeneity in long term T cell lines appears to be less than in freshly obtained lymph node cells, indicating that a process of in vitro selection occurs. We observed that the T cells responsive to one peptide, 46-61, appeared to have a selective advantage in vitro culture.

The T cell repertoire to a multideterminant antigen. Clonal heterogeneity of the T cell response, variation between syngeneic individuals, and in vitro selection of T cell specificities

The specificity of lysozyme-induced T cell proliferative responses by individual B10.A mice was compared by using a panel of three peptides. A surprising degree of variation in the focus of the responses was observed among individual animals, both in the newly isolated lymph node cell populations and in long term T cell lines. The responses to each determinant after hen egg-white lysozyme immunization were not equal and in examining the mice as a group some determinants tended to be dominant. However, despite each animal favoring a restricted number of determinants, the responding T cell populations were still highly heterogeneous. The data suggest that many determinants are involved in the response to the whole Ag. The role of one or more dominant determinants can be overestimated because the degree of heterogeneity in long term T cell lines appears to be less than in freshly obtained lymph node cells, indicating that a process of in vitro selection occurs. We observed that the T cells responsive to one peptide, 46-61, appeared to have a selective advantage in vitro culture.

How some T cells escape tolerance induction

A feature common to many animal models of autoimmune disease, for example, experimental allergic encephalomyelitis, experimental autoimmune myasthenia gravis and collagen-induced arthritis, is the presence of self-reactive T cells in healthy animals, which are activated to produce disease by immunization with exogenous antigen. It is unclear why these T cells are not deleted during ontogeny in the thymus and, having escaped tolerance induction, why they are not spontaneously activated by self-antigen. To investigate these questions, we have examined an experimental model in which mice are tolerant to an antigen despite the presence of antigen-reactive T cells. We find that the T cells that escape tolerance induction are specific for minor determinants on the antigen. We propose that these T cells evade tolerance induction because some minor determinants are only available in relatively low amounts after in vivo processing of the whole antigen. For the same reason, these T cells are not normally activated but can be stimulated under special circumstances to circumvent tolerance.

Ia molecule-associated selectivity in T cell recognition of a 23-amino-acid peptide of lysozyme

Ak- or Ek-restricted T cells, generated by immunization with a 23-amino-acid peptide of hen egg-white lysozyme (amino acid 74-96), showed a strict correlation between the minimal peptide determinant recognized and the Ia molecule restricting recognition. All Ak-restricted clones obtained from six independently derived lines recognized determinants contained within peptides 74-86, while Ek-restricted clones recognized determinants within 85-96. This correlation was true whether B10.A mice (Ak, Ek) were immunized with peptide 74-96 or with each of the two smaller peptides (74-86 or 85-96). Furthermore, a T cell response could be obtained to peptide 74-86, but not to peptide 85-96 in B10.A (4R) mice, which express only the Ak molecule. Thus, an Ia molecule-associated selectivity exists in the choice of T cell determinants even within this small 23-amino-acid peptide antigen. Significant differences were noted, however, in the boundaries of the minimal peptide determinants recognized within peptide 74-96 by Ak- or Ek-restricted T cells, in comparison to those recognized by Ab-restricted T cells. These results indicate that interaction of the same peptide with distinct Ia molecules results in recognition of unique aspects of the antigenic determinants by the T cell receptor.

The choice between two distinct T cell determinants within a 23-amino acid region of lysozyme depends on their structural context

The specificity of C57BL/6 T cells reactive to peptide aa 74-96 of hen egg-white lysozyme (HEL) was analyzed by using a panel of synthetic peptides of varying lengths from this region. It was found that peptide 74-96-reactive T cells induced by native HEL (aa 1-129) or its denatured fragment L2 (aa 13-105) recognized two distinct but overlapping determinants contained within aa 74-90 or aa 81-96, respectively. Peptide 74-96 itself induced both peptide 74-90-and peptide 81-96-specific T cells. Thus, a choice was made between these two potential T cell determinants on peptide 74-96, depending on which immunogen was used. Interestingly, the ability of both peptide determinants aa 74-90 and aa 81-96 to stimulate peptide 74-96-reactive T cells was partly dependent on the presence of residues within the overlap region (aa 81-90), suggesting that this region may play an important role in Iab-restricted T cell activation. This was further supported by the poor immunogenicity of shorter peptides 74-86 or 85-96, lacking residues from the overlap region in B6 mice. These two short peptides were nevertheless capable of eliciting T cell responses in B10.A mice, suggesting that the importance of this overlap region in obtaining a response to peptide 74-96 is related to the MHC haplotype.

The choice between two distinct T cell determinants within a 23-amino acid region of lysozyme depends on their structural context

The specificity of C57BL/6 T cells reactive to peptide aa 74-96 of hen egg-white lysozyme (HEL) was analyzed by using a panel of synthetic peptides of varying lengths from this region. It was found that peptide 74-96-reactive T cells induced by native HEL (aa 1-129) or its denatured fragment L2 (aa 13-105) recognized two distinct but overlapping determinants contained within aa 74-90 or aa 81-96, respectively. Peptide 74-96 itself induced both peptide 74-90-and peptide 81-96-specific T cells. Thus, a choice was made between these two potential T cell determinants on peptide 74-96, depending on which immunogen was used. Interestingly, the ability of both peptide determinants aa 74-90 and aa 81-96 to stimulate peptide 74-96-reactive T cells was partly dependent on the presence of residues within the overlap region (aa 81-90), suggesting that this region may play an important role in Iab-restricted T cell activation. This was further supported by the poor immunogenicity of shorter peptides 74-86 or 85-96, lacking residues from the overlap region in B6 mice. These two short peptides were nevertheless capable of eliciting T cell responses in B10.A mice, suggesting that the importance of this overlap region in obtaining a response to peptide 74-96 is related to the MHC haplotype.