CK0802 Tregs will be administered intravenously at a fixed dose of 100 million Treg cells.

Subjects will receive seven planned doses of CK0802 on study day +1, +3 (+/-1 day), +5 (+/-1 day), +7 (+/- 2 day), +14 (+/- 3 days), +21 (+/-3 days) and +28 (+/-3 days). A total of 7 doses will be administered.

If Day 29 assessment shows PR or MR, then 4 additional weekly infusion of CK0802 Tregs can be administered (study days: 35 (+/- 2 day), 42 (+/- 2 day), 49 (+/- 2 day), and 55(+/- 2 day)), for a total of 11 infusions

Dose limiting toxicities of CK0802 in SR GVHD as assessed by the incidence and severity of AE and SAEs determined by the NCI-CTCAE Version 6.0.

Non-Hematologic: Any ≥ Grade 3 non-hematologic AE as per CTCAE v6.0 Hematologic: Any new or worsened Grade 4 neutropenia, thrombocytopenia, or anemia compared with baseline that persists for >7 days despite supportive care and is not clearly and incontrovertibly attributable to the underlying disease or another extraneous cause.

Death: Death within 28 days that is not clearly and incontrovertibly attributable to the underlying disease or another extraneous cause

Overall Response (OR) at day +29. Overall response (OR) will include complete response (CR) and partial response (PR). Response to be determined from the maximum acute GVHD stage and grade in each organ.

Complete Response (CR): Stage 0 in all organs (skin, liver, and GI tract) and no intervening additional therapy Partial Response (PR): Improvement of at least 1 stage in 1 or more organs without progression in other organs, and no intervening additional therapy Overall Response (OR): Includes both CR and PR Very Good PR (VGPR): Improvement by at least one stage in one or more organs and

• Skin: No rash, or bullae, and residual erythematous rash involving <25% of the body surface
• Liver: Total serum bilirubin concentration of <2 mg/dL or <25% of baseline at enrollment
• Gut: Tolerating food or enteral feeding, predominantly formed stools, no overt GI bleeding or abdominal cramping, no more than occasional nausea or vomiting
• No intervening additional therapy