Key Inclusion Criteria: Participants eligible for inclusion in this study must meet all the following criteria: 1. Informed consent in writing from parent(s) or legal guardian(s) must be provided 2. 2 to 5 years of age (including 5 years and 364 days old) at Screening 3. Weight-for-stature is ≥ the third percentile, and is ≥ 10 kg 4. Oral cysteamine therapy for at least 6 months 5. Historic clinical diagnosis of nephropathic cystinosis 6. Laboratory evidence of of renal fanconi syndrome (RFS) 7. Relatively preserved kidney function (eGFR ≥ 60mL/min/1.73m2) 8. Received all age-appropriate vaccinations Key exclusion Criteria for Cohort 1 and 0 1. A history of kidney transplantation 2. A prior or planned bone marrow or stem cell transplantation or prior treatment with gene therapy 3. History of malignancy 4. A severe or uncontrolled medical disorder 5. Major surgery within 90 days Additional Key exclusion criteria for Cohort 1 - The following exclusion criterion applies to Cohort 1 only as it is related to DFT383 treatment: 1\. Indomethacin within 2 weeks prior to Screening Other protocol-defined inclusion/exclusion criteria may apply.