An exploratory, non-interventional, single-center study to characterize a set of immune cells in a range of dermatologic diseases

Eligible healthy volunteers must meet all the following inclusion criteria at screening:

1. Signed informed consent prior to any study-mandated procedure.
2. Male or non-pregnant female subjects, >18 years of age at the time of signing informed consent; in general, stable good health as per judgement of the investigator based upon the results of a medical history, physical examination, vital signs, ECG, and laboratory assessments performed at screening. Repeated laboratory testing may be performed at the discretion of the clinical investigator.
3. Body mass index (BMI) > 18.0 and < 30.0 kg/m2. 
4. No clinically significant auto-immune or auto-inflammatory disease as judged by the investigator.
5. Subject has the ability to communicate well with the investigator in the Dutch language and is willing to comply with the study requirements. 

Eligible immune-mediated inflammatory dermatologic disease patients must meet all the following inclusion criteria at screening:

1. Signed informed consent prior to any study-mandated procedure.
2. Male or non-pregnant female patients, 18 to 75 years of age at the time of signing informed consent (inclusive).
3. Body mass index (BMI) > 18.0 and < 40.0 kg/m2.
4. Patient has the ability to appropriately communicate with the investigator in the Dutch language and is willing to comply with the study requirements.
5. Participants must have a diagnosis of one or more of the following and must be eligible and/or receive systemic treatment according to the Dutch guidelines:

• Atopic Dermatitis (AD), Hidradenitis Suppurativa (HS), Palmoplantar Pustulosis (PPP) or Psoriasis (PsO); allowance also exists for Systemic Sclerosis (SSC) and Psoriatic Arthritis (PsA) patients with skin involvement.
• For all diseases, at least one suitable target lesion that is appropriate for protocol-specified skin biopsies at the discretion of the investigator
• For AD patients, eligible patients must meet all of the following criteria:
  1. Diagnosis and history of chronic, moderate-to-severe AD (by the Eichenfield revised criteria of Hanifin and Rajka) for at least 6 months before baseline visit.
  2. Current treatment can include moisturizers, topical treatment and/or systemic treatments with preferable wash-out (see exclusion criterion #9). On-study treatment is at physician and patient discretion but must include eligibility to starting new systemic treatment.
  3. EASI≥7 (moderate-to-severe disease)
• For PsO patients, eligible patients must meet all of the following criteria:

1. Diagnosis with chronic plaque psoriasis at least 6 months prior to study participation
2. PASI≥5 
3. Current treatment can include moisturizers, topical treatment and/or systemic treatments with preferable wash-out. On-study treatment is at physician and patient discretion

• For PPP patients, eligible patients must meet all of the following criteria:
  1. At least  6-month history of PPP as defined by the presence of pustules on palms and/or soles, but without evidence of infection
  2. Moderate or severe PPP as defined by Palmoplantar Pustulosis Psoriasis Area and Score Index (PPPASI) ≥ 8 
• For HS patients, eligible patients must meet all of the following criteria:

1. History of signs and symptoms consistent with moderate-to-severe HS,  IHS4 score >=4 (Zouboulis et al., 2017), for at least 6 months prior to baseline
2. Current treatment can include topical treatment. On-study treatment is at physician and patient discretion

• For SSc patients, eligible patients must meet all of the following criteria:

a) Diagnosis of SSc at least 6 months prior to study participation
b) At least one target lesion present with at least moderate skin thickness as measured with the mRSS

• For PsA patients, eligible patients must meet all of the following criteria: 
  1. Diagnosis of PsA at least 6 months prior to study participation
  2. DAPSA≥14
  3. Have a target plaque (area) suitable for measurements with a severity defined by TSS score ≥ 4, with at least a clinical score of ≥ 2 for either erythema or induration and ≥1 for the symptom scaling.

Eligible healthy volunteers must meet none of the following exclusion criteria at screening:

1. (History of) immunological abnormality (e.g., immune suppression) that may interfere with study objectives, in the opinion of the investigator. Non-active hay fever allergy is acceptable.
2. Surgical operation or significant physician/dentist within one month before Day 1.
3. Positive hepatitis B surface antigen (HbsAg), hepatitis C antibody (HCV ab), or human immunodeficiency virus antibody (HIV ab) at screening. 
4. Participation in an investigational drug study trial within 5 times the expected half-life of the investigated drug.
5. Loss or donation of blood over 500mL within three months prior to screening. 
6. The use of any medication (prescription or OTC including vitamins) within 7 days prior to Day 1 or within 5 half-lives (whichever is longer), if the investigator judges it may interfere with the study objectives. 
7. History of alcohol abuse or consumption exceeding 5 standard drinks per day on average within 3 months of screening. Alcohol consumption will be prohibited from at least 24 hours preceding each study visit. 
8. Positive urine test for drugs at screening (retesting is allowed, at the discretion of the investigator).
9. (A history of) any clinically significant medical condition, factor or abnormality that might interfere with study conduct or interpretation, as judged by the investigator.
10. History of keloid or hypertrophic scarring
11. Any pre-study clinical or laboratory findings that, as judged by the investigator, could significantly confound results from that individual. 

Eligible patients must meet none of the following exclusion criteria at screening:

1. Any active or chronic and/or uncontrolled condition that, in the opinion of the investigator, may influence study conduct or interpretation. For clarity, active disease or disease sequalae related to the patient’s autoimmune disease diagnosis are allowed.
2. Other relevant skin infection/disease in the treatment area other than the investigated skin disease.
3. Received treatment with any non-marketed drug substance (that is, an agent which has not yet been made available for clinical use following registration) within 4 weeks or 5 half-lives (whichever is longer) prior to the baseline visit.
4. Any other condition, disease, pre-study clinical or laboratory findings or any other factors that, as judged by the investigator, could significantly interfere with the study conduct or the study objectives as per judgement of the investigator.