Inclusion Criteria:  Clinical diagnosis of FECD3 with:  confirmed presence of trinucleotide repeat (TNR) expansion in the TCF4 gene (50 TNRs or more as determined by PCR), symmetrical disease progression in the opinion of the Investigator, a clinical indication for DMEK in both eyes. BCVA worse than +0.3 logMAR (approximate Snellen equivalent 20/40) in both eyes. BCVA impairment should not be caused by other ophthalmic disease.  Exclusion Criteria:  Presence of any significant ocular or non-ocular disease/disorder which may either put the subject at risk because of participation in the study, may influence the results of the study, or the subject's ability to participate in the study. History of any form of keratoplasty in either eye. Prior lens replacement in either eye. History or presence of ocular herpetic diseases (including herpes simplex virus, varicella zoster or cytomegalovirus) in either eye. Presence of any active ocular infection in either eye. Glaucoma, pseudoexfoliation syndrome, pigment dispersion syndrome or ocular hypertension in either eye. History of amblyopia in either eye. Receipt within 3 months prior to Screening of any intraocular or periocular surgery (including refractive surgery), or an IVT injection, any drugs that cause ocular disease or have ocular side effects including, or planned intraocular surgery or procedure (other than lens replacement or DMEK) during the course of the study in either eye. Current treatment or treatment within the past 12 months with therapies known to influence the immune system (including but not limited to cytostatics, interferons, TNF-binding proteins, drugs acting on immunophilins, or antibodies with known impact on the immune system). Use of any investigational drug or device within 90 days or 5 half-lives of Day 1, whichever is longer, or plans to participate in another study of a drug or device during the study period. Any prior receipt of genetic or stem-cell therapy for ocular or non-ocular disease. History of malignancy within 5 years prior to screening, except adequately treated squamous or basal cell carcinoma of the skin or carcinoma in situ of the cervix that has been successfully treated. Pregnant or breastfeeding subjects. Female subjects of childbearing potential and male subjects must be sexually inactive by abstinence, which is consistent with the preferred and usual lifestyle of the subject, or agree to use highly effective methods of birth control, as defined in the study protocol. Women of non-childbearing potential may be included without the use of adequate birth control, provided the participant meets the criteria.