The goal of this observational study is to characterize nasal mucosal immunity to respiratory viruses, such as SARS-CoV-2, in immunocompromised individuals and healthy volunteers.

The study involves adults of any sex, between 18 and 90 years old, including both immunocompromised patients with medical conditions or treatments that can affect immune cell functions and healthy controls with no underlying medical conditions declared, no clinical history of immunodeficiency or use of immunosuppressive medications.

Researchers will compare immunocompromised participants to healthy volunteers to determine how underlying immunodeficiency and related treatments affect immune cell composition and virus-specific responses.

Inclusion Criteria:

• Informed Consent: Participants must have signed an informed consent form.
• Age Range: Participants aged between 18 and 90 years.
• Healthy Immunocompetent Donors: no underlying medical conditions declared, no clinical history of immunodeficiency or use of immunosuppressive medications.
• Immunocompromised Patients: subjects with medical conditions or treatments associated with significant impairment of the immune system. This may include organ or stem cell transplants, ongoing immunosuppressive therapies, documented genetic immunosuppression.

Exclusion Criteria:

• Pregnant or lactating women.
• Individuals unable to provide informed consent

The recruitment will take place at primary care clinic. Immunocompromised participants will be selected based on their regular visits, while healthy donors will be recruited through hospital and research networks.