Efficacy Study on the Strategy of HSV-Tk Engineering Donor Lymphocytes to Treat Patients With High Risk Acute Leukemia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy Study on the Strategy of HSV-Tk Engineering Donor Lymphocytes to Treat Patients With High Risk Acute Leukemia (NCT00914628), a randomized phase 3 study. The primary outcome is Disease-free Survival (DFS).

2. Clinical Question

The central statistical question is comparative: whether the recorded time to relapse, progression, or death differs between the randomized groups. DFS combines these events into an endpoint, so the comparison concerns the time until the first qualifying event rather than a measure of any one event alone. The registry definition specifies that relapse or progression is determined by the Investigator using disease examinations that may include morphology, chimerism assessment, and cytogenetic, molecular, or other tests according to institutional clinical practice.

The trial is described as a randomized phase III study with parallel arms and no masking. Randomization supports a comparison between assigned strategies, but the posted information does not include the allocation procedure or enough detail to assess how the analysis handled participants after assignment. The clinical question is therefore clear at the level of the stated endpoint and treatment strategies, while the registry record does not provide the result needed to quantify the comparison.

3. Trial Design

TK008 is recorded as a randomized phase III trial with a parallel-group design and no masking. It compares haploidentical HCT with an HSV-Tk donor-lymphocyte add-back strategy against the control strategy, described as T-cell-depleted or T-cell-replete approaches. The record’s brief summary frames the main objective as comparing DFS in high-risk leukemia patients who underwent haploidentical HCT.

The recorded enrollment is 92. The registry lists a start date of 2010-04-12, a primary completion date of 2019-11-30, and a status of terminated. The reason for termination is not reported in the registry record. These administrative details describe the study as registered; they do not, by themselves, explain how many participants were analyzed for the primary outcome or why the study ended.

The arm descriptions identify arm A as HSV-TK engineering donor lymphocytes and arm B as T-cell-depleted or T-cell-replete strategies. The summary describes the experimental approach as an add-back strategy following haploidentical HCT and the control as standard haploidentical HCT. More detailed treatment schedules, the allocation ratio, and specific eligibility criteria are not reported in the registry record.

DFS is the stated primary outcome. The record defines it from randomization until relapse or progression, or death from any cause, whichever occurs first, with assessment up to 12 months. Secondary outcomes include overall survival, immune reconstitution, engraftment, acute and chronic graft-versus-host disease, relapse, and infectious episodes and mortality. The registry lists 12 outcome measures and 26 analyses, but their full analysis procedures are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Planned sample size n.170; Randomized patients n. 92. Discontinued n. 70; Early termination by the Sponsor n. 22;

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The analysis has been performed for all patients in the two treatment arms. The NRM analysis was performed on the "Intention to Treat Population" (ITT) and "Per Protocol" (PP) set populations.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Disease-free Survival (DFS), measured over From the date of randomization, assessed up to 12 months.

The primary endpoint is disease-free survival (DFS), defined as the time from randomization until relapse or progression, or death from any cause, whichever occurs first. The stated timeframe is from randomization, assessed up to 12 months. This is a composite time-to-event outcome: a participant can have an event through relapse, progression, or death, and the endpoint records the first qualifying event.

The registry says relapse or progression was determined by the Investigator. The listed assessments include morphology in bone marrow or peripheral blood, confirmation of mixed or full chimerism, and cytogenetic, molecular, or other tests according to institutional clinical practice. This definition allows disease assessment to draw on more than one type of examination, while also indicating that the procedures may follow local practice.

As a general statistical point, a time-to-event endpoint can retain information about when an event occurs, rather than only whether it occurred by a selected time. A composite endpoint can capture several clinically relevant ways in which disease-free status ends, but its overall result does not distinguish the contribution of each event type unless those components are also reported separately. The registry information does not provide a DFS estimate, uncertainty interval, or component-specific result. It therefore establishes what DFS was intended to measure, but not the size or precision of the observed arm comparison.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized, parallel-group phase III trial with no masking. Those features define the broad comparison structure, but do not by themselves specify the statistical methods used to analyze DFS or the other outcomes. The registry record identifies the endpoint and its timeframe without reporting the model, estimation procedure, treatment-effect measure, or confidence-interval method for the primary comparison.

What does randomization contribute?

As a general statistical principle, random assignment is intended to make the treatment groups comparable at the point of assignment, including with respect to factors that are known or unknown. It provides a basis for comparing assigned strategies, but does not guarantee identical groups in a particular trial. The record does not report the randomization sequence method, allocation concealment, or allocation ratio, so those implementation details cannot be assessed.

The trial is recorded as having no masking. In general, masking can limit the influence of knowledge about assigned treatment on care, outcome assessment, or reporting. Its absence is especially relevant to outcomes involving judgment, although the degree of influence depends on how outcomes are assessed. The registry describes DFS determinations by the Investigator and lists several possible examination types; it does not report whether independent or blinded outcome review was used.

How should DFS be understood statistically?

DFS is defined as time from randomization to relapse or progression, or death from any cause, whichever occurs first. In general, time-to-event methods can account for differences in the observed follow-up time and can use information on when an event occurred. Such methods also need to address participants who have not had an event by the end of observation or whose follow-up is incomplete. The analysis method, censoring rules, and handling of missing or incomplete follow-up are not reported in the registry record here, so it is not possible to describe how those issues were addressed in the trial analysis.

Because DFS combines relapse, progression, and death, an overall DFS comparison would summarize the first occurrence of any of those events. As a general point, the composite result does not show whether one component accounts for more of the observed events than another. The registry lists relapse as a secondary outcome, but the registry entries do not give component-specific counts or estimates that could clarify this. The Investigator’s disease assessment may use morphology, chimerism, and other tests according to institutional clinical practice, as described in the endpoint definition.

What do confidence intervals and p-values convey?

In general, an estimate describes the observed treatment contrast, while a confidence interval describes the precision of that estimate under the chosen method. A narrower interval indicates greater precision than a wider one, but neither interval width nor statistical significance establishes clinical importance on its own. A p-value summarizes how compatible the observed data are with a specified null model under the analysis assumptions; it is not the probability that the null hypothesis is true. No DFS effect estimate, confidence interval, or p-value is reported in the registry information, so these concepts cannot be applied to quantify this trial’s primary comparison.

Why do outcome and analysis counts matter?

The registry lists 12 outcome measures and 26 analyses. In general, examining many outcomes, time points, or comparisons creates a multiplicity issue: when many statistical tests are considered, the chance of at least one apparently notable result can increase. Statistical plans may address this with a hierarchy or adjustment, or may identify some results as exploratory. The registry record does not report whether a multiplicity strategy was specified or used, which outcomes were prioritized beyond identifying DFS as primary, or how the 26 analyses relate to the outcome measures.

The record gives a primary outcome population description stating that the analysis was performed for all patients in the two treatment arms. It also says that the NRM analysis was performed on the Intention to Treat Population (ITT) and Per Protocol (PP) set populations. The relationship between these population statements and the primary DFS analysis is not fully explained in the information. In general, an ITT analysis retains participants according to randomized assignment, whereas a per-protocol analysis uses a defined adherence-based population; the specific definitions and analysis implementation for this trial are not reported in the registry record.

The sample-size planning information is explicitly an illustration based on an observed effect, not the trial’s own design. General planning calculations depend on assumptions about the target effect, significance level, allocation, and statistical method. Such illustrations do not describe the observed evidence and are not observed power. The trial’s own sample-size justification and planning assumptions are not reported in the registry record. No planning figure should be treated as a result from the randomized comparison.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 12 outcome measures and 26 analyses. DFS is identified as the primary outcome, and the listed secondary outcomes include overall survival, immune reconstitution, engraftment, graft-versus-host disease outcomes, relapse, and infectious outcomes. However, the record does not report a multiplicity plan, such as a hierarchy among outcomes, adjustment across analyses, or a distinction between confirmatory and exploratory tests. Without that information, the role of any individual analysis in the overall evidence cannot be judged from the registry summary alone.

Missing-data methods are also not reported in the registry record. The primary outcome is described as assessed up to 12 months, but the available information does not specify how participants without complete follow-up were handled, what censoring rules were used, or whether sensitivity analyses were performed. These details matter generally because incomplete follow-up can affect time-to-event estimates, particularly when the reasons for missingness are related to outcomes or treatment.

The population description says the primary analysis was performed for all patients in the two treatment arms. It separately states that the NRM analysis used ITT and PP set populations. The record does not clarify how that NRM statement relates to the primary DFS analysis, or provide the definitions of the analysis populations. As a general principle, analysis population definitions influence which participants contribute to a comparison and how the result is interpreted.

The registry also does not report interim analyses, stopping rules, or the statistical plan. These items should not be inferred from the phase, study status, or number of analyses. The termination reason is not reported in the registry record.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: moderate acute graft versus host disease (11.1%), life threatening septic shock (7.4%), life threatening leukaemia recurrent (7.4%), severe acute graft versus host disease (5.7%), moderate chronic graft versus host disease (5.7%).

The registry’s safety summary separates the A-Experimental Arm and B - Control Arm. For the experimental arm, it reports 53 participants at risk for serious adverse events and 35 affected; for the control arm, it reports 27 at risk and 17 affected. The summary also reports 53 and 27 participants at risk, respectively, for the additional adverse-event category, with 22 and 0 affected. Death counts are reported as 35 in the experimental arm and 17 in the control arm. These are the registry’s recorded counts; the information does not state the time window or define the additional category in further detail.

The listed serious event terms include Moderate Acute graft versus host disease at 11.1%, Life threatening Septic shock at 7.4%, Life threatening leukaemia recurrent at 7.4%, Severe Acute graft versus host disease at 5.7%, Moderate Chronic graft versus host disease at 5.7%, and Severe Chronic graft versus host disease at 5.7%. The calculation basis for these percentages is not reported in the registry record, so they should be read as the posted percentages rather than converted into participant counts.

These summaries are descriptive. The counts alone do not establish that an event was caused by a treatment, and the death counts do not identify causes or timing. The different numbers at risk also mean the raw counts should not be treated as directly comparable measures of event frequency. The registry information does not provide an adjusted safety comparison or uncertainty estimates.

12. What the Result Does, and Does Not, Mean

This registry record identifies a randomized phase III comparison of haploidentical HCT strategies and defines DFS as its primary outcome. It also records a trial status of terminated, an enrollment of 92, and a range of secondary outcomes. These details establish the intended design and scope of the study. They do not establish the direction, size, or precision of the primary treatment comparison.

The main limit is that the available record does not provide a single DFS comparison estimate, its uncertainty, or a p-value. Without those results, it is not possible to describe how the observed DFS data differed between arms. The record’s definition makes clear what counted as an event, but it does not substitute for the outcome estimates or the underlying number of participants and events.

The safety information is also limited to posted counts and selected percentages. It does not specify the time window, calculation basis for the percentages, or a comparative statistical analysis. Counts can describe what was recorded in the two arm summaries, but they do not by themselves establish causation or a difference in risk. No conclusion about the treatment’s clinical benefit or harm should be drawn from these registry entries alone.

As a general statistical principle, a result is best interpreted using the effect estimate, its precision, the analysis population, and the assumptions behind the analysis together. Here, the analysis method, missing-data approach, multiplicity handling, and detailed population definitions are not reported in the registry record. The sample-size information is a planning illustration based on an observed effect, not the trial’s own design and not observed power. It cannot fill the gap left by the missing comparative outcome results.

The appropriate reading is therefore bounded: the registry describes the research question, trial structure, DFS definition, and selected adverse-event summaries, but the available information does not answer the primary comparative question. The accompanying displays may organize posted results, but no unreported estimate or method should be inferred from the trial description or its status.

13. Why This Trial Matters Statistically

This trial matters statistically because it sets up a randomized comparison of two haploidentical HCT strategies in patients with high-risk acute leukemia, with DFS specified as the primary outcome. The endpoint is defined around time from randomization to relapse or progression, or death from any cause. That definition makes the event rule explicit and identifies the comparison the study was intended to address.

The record also illustrates why a clear endpoint definition is not enough to interpret a clinical trial. Readers need the comparative estimate and its precision, as well as information about who was included in each analysis and how incomplete follow-up was handled. Those primary-result and analysis details are not reported in the information. Without them, the posted trial description cannot establish how the arms compared on DFS.

The trial includes a broad set of secondary outcomes and analyses. As a general statistical issue, multiple outcomes and analyses raise questions about prespecification, prioritization, and multiplicity. The registry lists 12 outcome measures and 26 analyses, but does not report the strategy used to interpret them together. This makes it important to distinguish a registered endpoint from a fully described statistical analysis plan.

The safety summary is another useful example of why denominators, time windows, event definitions, and uncertainty matter. It gives arm-level counts and selected serious event percentages, but does not report their calculation basis or a comparative analysis. The counts are informative as a record of what was posted, while remaining insufficient for causal or comparative conclusions.

More broadly, the record shows the value of separating design information from results. Randomization and the stated primary endpoint describe the intended study structure; they do not replace the observed outcome estimates. Statistical interpretation depends on both.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The available registry information leaves several trial-specific questions unresolved. Although the study is described as randomized and parallel, the randomization method, allocation ratio, and concealment procedures are not reported in the registry record. Masking is listed as none, but the record does not describe whether any outcome review was independent or whether assessment procedures were consistent across sites.

The DFS definition permits disease relapse or progression to be determined by the Investigator using morphology, chimerism, and cytogenetic, molecular, or other tests according to institutional clinical practice. The record does not describe a uniform assessment schedule or central review process. This does not establish that assessments differed, but it limits what can be assessed about measurement consistency from the registry information.

The record does not provide a single DFS comparison estimate or its uncertainty. It also does not report the numbers contributing to the primary analysis, the number of DFS events, censoring rules, missing-data handling, or sensitivity analyses. The population statement refers to all patients in the two arms, while the ITT and PP statement is specifically attached to NRM; the relationship between these statements is not explained.

The registry records 92 participants enrolled, but the adverse-event summary lists different numbers at risk across arms. The reason and timing represented by those denominators are not reported in the registry record. The serious-event percentages are listed without their calculation basis, and the death counts have no cause or timing information in the registry entries. The trial’s termination reason, statistical analysis plan, interim analyses, and sample-size justification are also not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Efficacy Study on the Strategy of HSV-Tk Engineering Donor Lymphocytes to Treat Patients With High Risk Acute Leukemia — NCT00914628.
• Registry record last updated 2021-06-22; status last verified 2021-06.
• Results first posted 2021-06-22.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT00914628 is a randomized phase III, parallel-group trial with no masking, comparing an HSV-Tk donor-lymphocyte add-back strategy following haploidentical HCT with control strategies described as T-cell-depleted or T-cell-replete. The registry reports enrollment of 92, a start date of 2010-04-12, primary completion on 2019-11-30, and terminated status.

The primary outcome is DFS from randomization until relapse or progression, or death from any cause, whichever occurs first, assessed up to 12 months. The registry also lists secondary outcomes involving survival, immune reconstitution, engraftment, graft-versus-host disease, relapse, and infection. It records 12 outcome measures and 26 analyses.

The available information includes selected serious adverse-event terms and arm-level safety counts, but does not report a single comparative DFS estimate or its precision. The reason for termination and detailed analysis methods are not reported in the registry record.