FDA recognizes the substantial public interest in medicines that are being studied for the prevention or treatment of COVID-19, especially those medicines that may provide a benefit to patients with the most severe forms of disease that can result in respiratory failure and death. Leronlimab, a monoclonal antibody investigational drug under development by CytoDyn, Inc. (CytoDyn), is one of the potential medicines that has been studied to determine whether it is safe and effective in treating patients with COVID-19, including those with severe outcomes from COVID-19.
CytoDyn has conducted two separate clinical trials investigating leronlimab for the treatment of COVID-19. A smaller trial, titled CD10, which included 86 patients, studied leronlimab’s effect on mild-to-moderate COVID-19 disease. A larger trial, titled CD12, which included 394 patients, studied leronlimab’s effect on severe symptoms of respiratory illness associated with COVID-19. CytoDyn has communicated information to the public about the results of these trials. Although FDA generally cannot disclose confidential information about unapproved products, we have concluded that given the significant public interest in leronlimab, it is important to provide summary information about the status of the CytoDyn development program.
First, we underscore the significance of a well-designed clinical trial when evaluating whether a medicine is safe and effective for a particular use. Well-designed trials have specific objectives, referred to as “endpoints”, that are documented (i.e., pre-specified) in the study protocol before the initiation of the investigation. Data obtained from the clinical trial are later analyzed using pre-specified statistical methodologies. If the analyses of the primary and secondary endpoints do not support conclusions of the medicine’s benefit, then FDA considers subgroup analyses to be exploratory, meaning they may inform the design of future trials, but do not support reliable conclusions about the medicine’s benefit. Focusing on only the most favorable of many subgroup analyses, even if the sub-groups are pre-specified, can lead to overestimating the evidence of benefit, because regardless of a drug’s true efficacy, some analyses are likely to appear favorable by chance when a large number of analyses are conducted.
With the conclusion of both the CD10 and CD12 clinical trials, it has become clear that the data currently available do not support the clinical benefit of leronlimab for the treatment of COVID-19. In the smaller study that CytoDyn conducted in patients with mild-to-moderate COVID-19 disease (CD10), there was no observed effect of the drug on the study’s primary endpoint or on any of the secondary endpoints. The primary endpoint for the CD10 trial relied on a measure of participants’ COVID-19 symptoms called a “total clinical symptom score”, which was assigned based on the severity of each participant’s fever, muscle aches, shortness of breath, and cough. This score ranged from 0 (no symptoms) to 12 (all 4 symptoms present and severe). The CD10 trial results showed no clinically meaningful differences in average change in “total clinical symptom score” from baseline to Day 14 between study arms (-3.5 in the leronlimab group versus -3.4 in the placebo group). Additionally, none of the secondary endpoints were met in this study, including mortality, time to symptom resolution, and time to return to normal activity. Taken together, the CD10 results indicate that most study participants experienced resolution in COVID-19 symptoms regardless of whether they received leronlimab or placebo.
The larger trial that CytoDyn conducted in patients with severe COVID-19 disease (CD12) also failed to find any effect of the drug on the primary study endpoint, with no difference seen in mortality (20.5% in the leronlimab treatment group and 21.6% in the placebo treatment group); or on any of the secondary endpoints, for example, with no difference on the average length of hospitalization (21.4 days in both the leronlimab and the placebo treatment groups).
CytoDyn has publicly communicated differences in small subgroups from the CD12 trial (e.g., a sub-group analysis of 62 of the 394 patients studied) suggesting that the data demonstrated a mortality benefit in certain patients who had received leronlimab. Subgroup analyses have well-established limitations, especially in the context of a clinical trial that has failed to show a benefit in the overall study population. For example, subgroups are often small, and therefore imbalances are common. Here, the data from CD12 illustrated imbalances in mortality among subgroups, some favoring leronlimab and some favoring placebo. None of these analyses met statistical significance when using established and reliable analytical methods that correct for multiple comparisons. However, as noted above, such analyses may inform the design of future clinical trials investigating leronlimab for the treatment of COVID-19.
If CytoDyn plans further studies of leronlimab to determine whether the drug can provide clinical benefit to individuals with COVID-19, FDA will continue to provide advice to the company on their development program.
FDA recognizes the critical unmet medical need for new, effective treatments for COVID-19, especially for severe forms of the disease. We are committed to working with sponsors of novel therapies to facilitate development and approval of new treatments.