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.