Long term maintenance of myeloid leukemic stem cells cultured with unrelated human mesenchymal stromal cells

Abstract

Mesenchymal stromal cells (MSCs) support the growth and differentiation of normal hematopoietic stem cells (HSCs). Here we studied the ability of MSCs to support the growth and survival of leukemic stem cells (LSCs) in vitro. Primary leukemic blasts isolated from the peripheral blood of 8 patients with acute myeloid leukemia (AML) were co-cultured with equal numbers of irradiated MSCs derived from unrelated donor bone marrow, with or without cytokines for up to 6 weeks. Four samples showed CD34+CD38− predominance, and four were predominantly CD34+CD38+. CD34+ CD38− predominant leukemia cells maintained the CD34+ CD38− phenotype and were viable for 6 weeks when co-cultured with MSCs compared to co-cultures with cytokines or medium only, which showed rapid differentiation and loss of the LSC phenotype. In contrast, CD34+ CD38+ predominant leukemic cells maintained the CD34+CD38+ phenotype when co-cultured with MSCs alone, but no culture conditions supported survival beyond 4 weeks. Cell cycle analysis showed that MSCs maintained a higher proportion of CD34+ blasts in G0 than leukemic cells cultured with cytokines. AML blasts maintained in culture with MSCs for up to 6 weeks engrafted NSG mice with the same efficiency as their non-cultured counterparts, and the original karyotype persisted after co-culture. Chemosensitivity and transwell assays suggest MSCs provide pro-survival benefits to leukemic blasts through cell-cell contact. We conclude that MSCs support long-term maintenance of LSCs in vitro. This simple and inexpensive approach will facilitate basic investigation of LSCs and enable screening of novel therapeutic agents targeting LSCs.

Mesenchymal stromal cells contribute to quiescence of therapy‐resistant leukemic cells in acute myeloid leukemia

“…Interestingly, these protective effects have also been shown for stromal‐derived medium when cultured with BCR‐ABL + lymphoblastic leukemia and various other cell lines . In AML, it has recently been demonstrated that direct contact of leukemic cells to hMSC can inhibit drug‐induced apoptosis . In addition, this study also demonstrated that hMSC preserve leukemia stem cell potential of primary AML cells during long‐term coculture with the retained ability to engraft immune‐incompetent mice after up to 6 weeks .…”

“…In AML, it has recently been demonstrated that direct contact of leukemic cells to hMSC can inhibit drug‐induced apoptosis . In addition, this study also demonstrated that hMSC preserve leukemia stem cell potential of primary AML cells during long‐term coculture with the retained ability to engraft immune‐incompetent mice after up to 6 weeks . Standard AML chemotherapy regimens include substances mainly targeting cycling cells .…”

“…hMSCs were harvested from BM of healthy donors that were collected at our center. AML cells were either treated in direct contact to hMSC or indirectly using a transwell system which has been described previously . Both coculture systems effectively protected leukemic blasts from apoptosis upon AraC treatment in comparison with AML cells treated in media alone.…”

“…It has been shown that the BM‐niche is made up from different cell types, including human mesenchymal stromal cell (hMSC). These cells have been shown to sustain a quiescent state of various hematological cancers which is hypothesized to play a vital role in therapy resistance and relapse initiation . In the human context, many studies have focused on the influence of BM stromal cells as it represents an important and easily accessible component of the BM‐niche .…”

Small molecule regulation of normal and leukemic stem cells

“…These include the use of cytokine combinations [9], improved bioreactor-based methodologies [10], mesenchymal stromal cell cocultures [11][12][13] and immobilized biologicals such as delta 1 notch ligand [14]. New methodologies to identify potent small molecules active on human HSPCs were pioneered by Boitano et al [15].…”