Human palatine tonsil: a new potential tissue source of multipotent mesenchymal progenitor cells

INTRODUCTION: Mesenchymal progenitor cells (MPCs) are multipotent progenitor cells in adult tissues, for example, bone marrow (BM). Current challenges of clinical application of BM-derived MPCs include donor site morbidity and pain as well as low cell yields associated with an age-related decrease in cell number and differentiation potential, underscoring the need to identify alternative sources of MPCs. Recently, MPC sources have diversified; examples include adipose, placenta, umbilicus, trabecular bone, cartilage, and synovial tissue. In the present work, we report the presence of MPCs in human tonsillar tissue. METHODS: We performed comparative and quantitative analyses of BM-MPCs with a subpopulation of adherent cells isolated from this lymphoid tissue, termed tonsil-derived MPCs (T-MPCs). The expression of surface markers was assessed by fluorescent-activated cell sorting analysis. Differentiation potential of T-MPCs was analyzed histochemically and by reverse transcription-polymerase chain reaction for the expression of lineage-related marker genes. The immunosuppressive properties of MPCs were determined in vitro in mixed lymphocyte reactions. RESULTS: Surface epitope analysis revealed that T-MPCs were negative for CD14, CD31, CD34, and CD45 expression and positive for CD29, CD44, CD90, and CD105 expression, a characteristic phenotype of BM-MPCs. Similar to BM-MPCs, T-MPCs could be induced to undergo adipogenic differentiation and, to a lesser extent, osteogenic and chondrogenic differentiation. T-MPCs did not express class II major histocompatibility (MHC) antigens, and in a similar but less pronounced manner compared with BM-MPCs, T-MPCs were immunosuppressive, inhibiting the proliferation of T cells stimulated by allogeneic T cells or by non-specific mitogenic stimuli via an indoleamine 2,3-dioxygenase-dependent mechanism. CONCLUSION: Human palatine T-MPCs represent a new source of progenitor cells, potentially applicable for cell-based therapies.