Clinical Pharmacology for Zevaskyn
Mechanism Of Action
In patients with recessive dystrophic epidermolysis bullosa (RDEB), both copies of the COL7A1 gene are mutated, resulting in the absence or low levels of biologically active C7 protein which form anchoring fibrils (AFs). The lack of AFs disrupts the connection between the epidermis and the dermis and causes skin fragility and other signs and symptoms of RDEB. ZEVASKYN consists of a patient's own cells that have been gene-modified through RVV transduction to express the COL7A1 gene to produce the C7 protein. These cells are formed into cellular sheets for topical application onto wounds.
Pharmacodynamics
In a single-arm, clinical study (n=7), C7 was assessed by both immunofluorescence and the presence of AFs at Months 3, 6, and 12. The NC2 domain of C7 was assessed using the LH24 antibody, and the presence of AFs was assessed by immunoelectron microscopy. The NC2 domain of C7 and AFs were detected in 6 patients at 3 months and in 5 patients at 6 months. One year after treatment with ZEVASKYN, 3 patients were positive for NC2 or AFs. At Year 2, 2 out of 3 patients with biopsies were positive for NC2 or AFs (1 patient was positive for both AFs and NC2; the second patient was positive only for NC2, as an additional biopsy for AF assessment was not obtained).
Pharmacokinetics
No clinical studies have been conducted to evaluate the pharmacokinetics of ZEVASKYN.
Immunogenicity
The observed incidence of anti-drug antibodies is highly dependent on the sensitivity and specificity of the assay. Differences in assay methods preclude meaningful comparisons of the incidence of anti-drug antibodies in the studies described below with the incidence of anti-drug antibodies in studies with other products.
In a single-arm, clinical study, anti-C7 antibodies against Type VII collagen were assessed in 7 patients at baseline, 1, 3, and 6 months and then annually for 5 years at physician’s discretion after treatment with ZEVASKYN. Out of 7 patients, circulating anti-C7 antibodies were detected in 2 patients which resolved at 1 year follow-up. Tissue-bound anti-C7 antibodies were detected in 4 patients which resolved in 3 patients at 1 year follow-up. In 1 patient with positive baseline anti-C7 antibodies, localized immunoreactants were observed at treated sites for up to 2 years after treatment.
In the VIITAL study, anti-C7 antibodies were assessed at baseline and at physician’s discretion at Months 3 and 6. Eight patients were biopsied at either Month 3 or 6, and none of those patients tested positive for C7 immune complexes [see Clinical Studies].
Because of the small sample size, there is limited data to determine the effect of anti-C7 antibodies on the pharmacodynamics, safety, and/or effectiveness of ZEVASKYN.
Clinical Studies
The efficacy of ZEVASKYN was evaluated in a multi-center, randomized, intrapatient-controlled study (VIITAL; NCT04227106). The study compared the application of ZEVASKYN to the standard of care treatment in patients with wounds associated with recessive dystrophic epidermolysis bullosa (RDEB). For enrollment, the patients were required to have at least one pair of matched, large (at least one wound ≥20 cm² for treatment and at least one wound ≥20 cm² for control) and chronic wounds (open for ≥6 months) associated with RDEB. Patients with current or history of squamous cell carcinoma (SCC) at the treatment site were excluded. Matched wound pairs were randomized in a 1:1 ratio to receive either ZEVASKYN (up to 6 sheets) or control treatment (standard of care wound dressings).
A total of 86 wounds in 11 patients were enrolled and treated with ZEVASKYN or standard of care in the study. The demographic characteristics of the population were as follows: the mean age was 23 years (range 6 to 40 years) including 2 pediatric patients (aged 6 and 16 years), 7 patients (64%) were female, 10 patients (91%) were White, 1 patient (9%) was of unknown race, and 2 patients (18%) were Hispanic or Latino. The wounds assessed in the study at baseline had been open for a median of 5 years (range 0.5-21 years).
The co-primary efficacy outcome measures were 1) proportion of randomized wound pairs with at least 50% healing at Month 6 with confirmation of wound healing two weeks later as assessed using baseline digital photography by the Investigator, and 2) pain reduction as assessed by the mean differences in patient-reported pain scores using the Wong-Baker FACES scale between randomized wound pairs at Month 6.1 Secondary outcome measures were proportion of randomized wound pairs with complete wound healing defined as reepithelialization with no drainage or erosion and presence of only minor crusting from baseline at Month 3 and at Month 6 with confirmation of wound healing two weeks later.
The efficacy results are summarized in Table 2.
Table 2: Efficacy results for VIITAL Study (N=86 wounds)
| Efficacy endpoint |
ZEVASKYN
(N=43 wounds) |
Control
(N=43 wounds) |
P value |
| Proportion of randomized wound pairs healed ≥50% from baseline at Month 6a n (%) |
35 (81%) |
7 (16%) |
<0.0001 |
| Mean pain reduction from baseline at Month 6b Mean (SD) |
-3.07 (3.19) |
-0.90 (2.73) |
0.0002 |
| Proportion of randomized wound pairs completely healed from baseline at Month 3 n (%) |
6 (14%) |
0 (0%) |
0.0316 |
| Proportion of randomized wound pairs completely healed from baseline at Month 6a n (%) |
7 (16%) |
0 (0%) |
0.0160 |
N=total number of observations; SD=Standard deviation; %=percentage
Complete wound healing is defined as re-epithelialization with no drainage or erosion and presence of only minor crusting.
a The proportion of wounds achieving success criteria at Month 6 must have been confirmed at least 2 weeks later.
b One wound was excluded from the control group due to missing baseline value. |
REFERENCES
1. Wong-Baker FACES Foundation. Wong-Baker FACES Pain Rating Scale. Retrieved 24 July 2023 with permission from https://www.WongBakerFACES.org. Originally published in Whaley & Wong’s Nursing Care of Infants and Children. Elsevier Inc. 2022.