J.P. Chute

The vascular niche: home for normal and malignant hematopoietic stem cells

Hematopoietic stem cells (HSCs) are uniquely capable of self-renewal and provision of all of the mature elements of the blood and immune system throughout the lifetime of an individual. HSC self-renewal is regulated by both intrinsic mechanisms and extrinsic signals mediated via specialized microenvironments or ‘niches’ wherein HSCs reside. HSCs have been shown to reside in close association with bone marrow (BM) osteoblasts in the endosteal niche and also in proximity to BM sinusoidal vessels. An unresolved question surrounds whether the endosteal and vascular niches provide synchronous or redundant regulation of HSC fate or whether these niches provide wholly unique regulatory functions. Furthermore, while some aspects of the mechanisms through which osteoblasts regulate HSC fate have been defined, the mechanisms through which the vascular niche regulates HSC fate remain obscure. Here, we summarize the anatomic and functional basis supporting the concept of an HSC vascular niche as well as the precise function of endothelial cells, perivascular cells and stromal cells within the niche in regulating HSC fate. Lastly, we will highlight the role of the vascular niche in regulating leukemic stem cell fate in vivo.

Outcomes of a second non-myeloablative allogeneic stem cell transplantation following graft rejection

Following initial graft rejection, a second attempt at allogeneic immunotherapy is often contemplated, but data on the success is limited. We therefore report on 11 patients with hematologic malignancies, renal cell cancer or marrow failure who underwent a second reduced-intensity regimen for primary or secondary graft failure. Nine of the 11 patients initially engrafted with the second attempt including two of four who used the same donor. One of the patients engrafted after the third attempt using a different donor and conditioning regimen. There were two treatment-related deaths. Four patients died from progressive disease 1–9 months after the second transplant. Two patients are still in recovery phase less than 1 year from the second transplant. Long-term remission is possible and three patients are alive in complete remission.

Overcoming drug resistance in mantle cell lymphoma using a combination of dose-dense and intense therapy.

ABSTRACT We present a study of the prevalence of genetic polymorphisms and expression of genes encoding the drug-resistance proteins glutathione S-transferases (GSTs) in order to gain insights into the pattern of failure evident in mantle cell lymphoma. We note a high preponderance of genetic alterations conferring resistance to standard chemotherapy in this illness. Concurrent with this investigation, we present a series of patients who were provided dose-dense and intense chemotherapy to circumvent these drug-resistance mechanisms. High responses were noted, though durable remissions were few, indicating non-traditional chemotherapy options are important to investigate in this illness.