This study will test the safety and effects of SBT777101 when given as a single dose to subjects with hidradenitis suppurativa. Increasing dose levels will be given after the safety at lower dose levels is shown.

The study evaluates the safety and effects of a novel regulatory CARTreg cell-based autoimmune and inflammatory disease therapy for the treatment of hidradenitis suppurativa. The therapy is an autologous (using the patient's own cells) Treg cell therapy that targets proteins in the inflamed, disease-associated tissue, with the aim to dampen inflammation and restore balance to the immune system.

Inclusion Criteria:

• Body mass index (BMI) ≤50 kg/m2, inclusive
• Diagnosis of clinically active moderate-to-severe HS (Hurley Stage 2 or 3)
• Total abscess or inflammatory nodule (AN) count of ≥5, affecting at least 2 distinct anatomic regions, with at least 1 accessible AN of adequate size for biopsy (diameter > 1 cm)
• Total draining tunnel (dT) count of ≤20
• Documented history of inadequate response or intolerance to at least a 3-month course of 1 conventional systemic therapy (e.g., antibiotic) and 1 biologic drug (e.g., adalimumab or secukinumab)
• Doses of medications for HS must be stable for at least 5 weeks prior to study drug administration
• Must agree to use highly effective method of contraception for at least 1 year post SBT777101 administration

Exclusion Criteria:

• Major surgery within 12 weeks prior to screening or planned within 12 months after dosing
• History of or current inflammatory or other autoimmune disease
• Complex presentations of HS
• Skin disease other than HS that may confound clinical assessments or increase subject risk in the study
• Uncontrolled concomitant cardiovascular, nervous system, pulmonary, renal, hepatic, endocrine, or gastrointestinal disease
• Active current infection or history of recurrent infections
• Active or untreated latent tuberculosis
• Primary or secondary immunodeficiency