A Study to Assess Safety, Efficacy, and Pharmacokinetics of INM004 in Pediatric Patients With STEC-HUS

Hemolytic uremic syndrome (HUS) is a form of thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. HUS of infectious origin, associated with infection by Shiga toxin (Stx)-producing Escherichia coli.

This disease can cause sporadic cases or outbreaks. Argentina is the country with the highest incidence of STEC-HUS worldwide. The disease is endemic, representing approximately 95% of all HUS cases.

There is no specific treatment capable of preventing or controlling renal and extrarenal damage caused by Stx. The treatment is mainly symptomatic. Therapy for patients with acute kidney injury is supportive and includes hydric and electrolyte management; thus, most cases require red blood cell transfusions and approximately half of cases require dialysis.

INM004 is a neutralizing serum consisting of the F(ab')2 fragment of equine immunoglobulins with specificity against the B subunits of Stx1 and Stx2. The F(ab')2 fragments are obtained through the processing of serum from horses immunized with Stx1B and Stx2B immunogens, obtained through genetic engineering techniques. A polyclonal therapy based on INM004 offers the advantage that the different subtypes of Stx could be recognized by multiple antibodies simultaneously, even when the toxin circulates bound to neutrophils or microvesicles derived from them.

The objective of this study is to evaluate the efficacy, safety, and pharmacokinetics of INM004 administered in patients between 1 and 12 years of age who are in the early stage of the disease.

The initial hypothesis is that INM004 would reduce the complications associated with STEC-HUS by neutralizing the harmful effect of Stx on the body. Intravenous administration of INM004 is expected to interrupt the Stx-mediated cascade, reducing the occurrence of renal and extrarenal complications (such as the need for and duration of dialysis, number of transfusions, CNS complications, and length of hospitalization).

Two doses of 4 mg/kg of INM004 will be administered as an intravenous infusion over a period of 50 min, with an interval of 24 h (± 2 h) from each other. The selection of the exposure level is based on preclinical in vitro data regarding the affinity of INM004, its neutralizing capacity for both Stx toxins, and clinical data obtained from the previous Phase I study in adult volunteers and the Phase 2/3 study in children with STEC bloody diarrhea.

Study design: A Phase II, multicenter, controlled study, with a prospective open "treatment group" (with INM004 and Standard of Care -SoC-), and a retrospective "control group" (only treated with SoC). Considering that STEC-HUS is an orphan disease currently without treatment, the design with retrospective control has been chosen.

The treatment group will enroll 100 patients hospitalized in 16 healthcare centers in Argentina, between September 2022 and May 2023, time of highest incidence of STEC-HUS. The data of the control group will be obtained retrospectively from 200 cases of STEC-HUS treated in the same centers, in the same seasonal period in the years 2018, 2019 and until March 2020 (COVID-19 pre-pandemic), with the same screening criteria as the subjects in the treatment group.

Primary Objectives: To assess: 1) the efficacy of INM004, plus SoC, in the treatment of STEC-HUS, in terms of improvement of renal involvement; 2) the safety of the administration of INM004; 3) the pharmacokinetics (PK) of INM004.

Secondary Objectives: To assess the efficacy of INM004: 1) in the mortality reduction; 2) in the improvement of the STEC-HUS associated thrombotic microangiopathy, plus SoC; 3) in the treatment of STEC-HUS, in the prevention and reduction of renal involvement in the short term, plus SoC; 4) in the treatment of STEC-HUS, in the prevention and reduction of extrarenal involvement in the short term, plus SoC; 5) the in the prevention and reduction of the complications not associated to thrombotic microangiopathy, plus SoC; 6) in terms of the length of hospital stay; and 7) the evolution of laboratory parameters of interest after the administration of INM004.

Exploratory Objectives: To assess: 1) the immunogenicity of INM004; 2) the presence of circulating Stx before the administration of INM004; 3) the immune response to STEC infection over 4 weeks follow-up; 4) the correlation between serotype/ genotype of isolated STEC strains and disease severity.

Study Procedures:

For the control group: Data will be collected from the medical records of the subjects who have been eligible from the "Potential Subjects Selection List" of the year's corresponding to this population. The data to be collected for this group will be the same as for the treatment group, except for that related to the specific procedure of the intervention: basal ECG and post dose control; 1st dose and 2nd dose, and associated controls (vital signs and AESI evaluation); blood samples for biological and/or pharmacokinetic studies; adverse events.

The inclusion of subjects in the treatment group will be conducted in two stages: Stage 1 (Safety): A safety analysis will be performed by the Data Safety Monitoring Board (DSMB) after the first 12 subjects have been enrolled and 24 h after the administration of the second dose of INM004 have occurred. Stage 2 (Safety and Efficacy): Enrollment will continue until May 2023, and it is estimated that 88 more subjects will enroll in this stage.

Once the participant was included the following data will be collected:

Demographic data, medical history data, data of the current illness (related to the prodromal period of STEC-HUS and to the clinical features compatible with STEC-HUS at the time of diagnosis); Complications associated with STEC-HUS at the time of diagnosis and before: renal, neurological, cardiovascular, gastrointestinal, endocrinological, hematologic, lung involvement, infectious compromise. The follow up will continue to the day 28 after diagnosis.

For statistical analyses, the following populations will be considered:

• Full Analysis Set (FAS): For the treatment group, defined as all subjects who received at least 1 dose of INM004 with available follow-up evaluation on at least one efficacy parameter. This population will be used for all main efficacy analyses. All subjects included in the control group will be part of the FAS for the comparative analyses.
• Population by Correct Protocol (PCP): includes all the subjects in the FAS who did not present major deviations from the protocol that could affect the measures of efficacy. This population will be analyzed as a sensitivity evaluation for the main analyzes of the study.
• Safety Population (SP): For the treatment group, it is defined as all subjects who have received at least one dose of INM004.

Statistical methods:

Statistical analyzes will be mainly descriptive. For continuous variables, mean, median, standard deviation, quartiles, maximum and minimum will be presented. Categorical variables will be described by absolute frequencies and percentages.

Baseline parameters, demographics, clinical history and previous treatments will be described in a cross-sectional manner prior to the start of treatment. The continuous evaluations carried out throughout the study will be described longitudinally by the change from baseline. For categorical variables, shift tables can be generated.

In the treatment group, the last measure performed prior to the administration of the first dose of INM004 will be considered as the baseline measure of efficacy and safety. If a generalized delay in the administration of the INM004 treatment is observed, the closest measurement available to the diagnosis of symptoms compatible with STEC-HUS may be considered as the baseline measurement. For the control group, the baseline assessments will be those at the time of diagnosis of symptoms compatible with STEC-HUS.

Multivariate analyzes will be assessed to identify risk factors related to the evolution and severity of the disease.

Safety will be assessed throughout the study describing subjects with at least one AE, serious adverse events (SAE) and AESI, and subjects with at least one major safety deviation for each of the parameters: ECG, vital signs, clinical laboratory evaluations, including liver function tests.

Efficacy and sensitivity analyzes will be performed to detect possible subjects who could benefit more from treatment in subgroups defined according to levels of severity at admission Comparative multivariate analyzes of the main efficacy variables against the control group will be performed. These comparisons will be duly adjusted using propensity scoring techniques in order to minimize any confusion bias between both groups. Among the potential confounders to consider as adjustment variables in the model will be age, sex and severity levels at admission. Due to the exploratory nature of the comparisons, no adjustments will be made for multiple comparisons.

Due to the exploratory nature of this study, a sample of approximately 100 evaluable subjects in the treatment group would be sufficient to detect any existing trends regarding the efficacy and safety of INM004. In the control group, 200 subjects are expected to be evaluated.

With 100 evaluable subjects we will obtain a precision (distance from the mean to the end of the bilateral confidence interval at 95%) of ±1.2 for the days on dialysis (SD 6.1 days) and ±2.4 for the days of admission (SD 12 days).