T cells fail to develop in the human skin-cell explants system; an inconvenient truth

Area of Science:

• Immunology
• Cell Biology
• Transplantation Science

Background:

• Haplo-identical hematopoietic stem cell (HSC) transplantation effectively treats hematological tumors.
• A significant challenge post-transplant is the prolonged T-cell lymphopenic phase, leading to high morbidity and mortality.
• A previously described skin-explant system aimed to produce donor-HSC-derived T-cells to address this deficiency.

Purpose of the Study:

• To validate the reproducibility of the described skin-explant system for generating T-cells.
• To assess the feasibility of T-cell production from HSCs using this ex vivo platform.

Main Methods:

• Attempted to replicate the skin-explant culture conditions as per published procedures.
• Evaluated keratinocyte maturation and delta-like ligand (DLL) expression.
• Assessed HSC differentiation and T-cell lineage commitment in culture.
• Utilized cell lines over-expressing DLL for antibody validation.

Main Results:

• The skin-explant system's conditions for HSC differentiation into mature T-cells were not reproducible.
• Keratinocyte maturation yielded fragile cells with minimal DLL expression, hindering HSC adherence and differentiation.
• Antibodies used in the original study likely detected non-specific staining (7AAD+) rather than native DLL.
• Jagged-1 expression by keratinocytes was confirmed, but its role in T-cell development was not established.

Conclusions:

• The mechanism behind the T-cell development reported by Clark et al. remains unexplained and unreproducible.
• Understanding and replicating this co-culture system is critical for managing post-transplant lymphopenia.
• Alternative strategies for accelerating T-cell reconstitution are under development and may offer future therapeutic options.