Dendritic cells (DCs) serve as sentries for the immune system. DCs recognize foreign compounds (antigens) in the body, which they internalize and process. When DCs uptake foreign antigens, they migrate to secondary lymphoid organs, where the processed antigens are presented to T cells.

Various DC subsets with unique cell lineages, surface protein markers, and tissue localization determinants have been identified. For example, Langerhans cells (LCs) and interstitial dendritic cells (intDCs) are DCs found in stratified epithelia, such as the skin. Though both are expressed in the skin, they differ with respect to their origin and surface protein content and can activate distinct types of immune responses. They may also have different specificities for the capture of antigens and presentation to circulating T cells.

To date, it is unknown what role, if any, the different DC populations that reside or repopulate in the skin play in the development and progression of skin graft-versus-host disease (GVHD) following bone marrow transplant.

Inclusion Criteria:

• At least 18 years of age at enrollment
• Willing and able to sign the informed consent
• Current diagnosis/suspected diagnosis of acute skin GVHD OR Current diagnosis/suspected diagnosis of chronic skin GVHD

Exclusion Criteria:

• Known infection with Hepatitis B or C, HTLV, or HIV
• Pregnant females

Patients with current or suspected acute or chronic GVHD of the skin