News and Publications

Hematopoietic Regulation and HIV Type-1--Induced Dysfunction

B.E. Torbett, B. Buehler, K.A. Smith, D.R. Salomon,* H. Perkin, B. Griffin,* L.J.W. van der Lann,* L. Crisa,* K. Anderson,** R.A. Maki**

* Division of Experimental Hemostasis and Thrombosis, TSRI
** The Burnham Institute, La Jolla, CA

Our research interests are (1) hematopoietic disruption induced by HIV type 1 (HIV-1), (2) the use of human-mouse chimeras as a model of human hematopoiesis, and (3) the role of the ets-family transcription factor PU.1 in regulating the development of myeloid cells

HIV-1 DISRUPTION OF HEMATOPOIESIS

Anemia, neutropenia, and thrombocytopenia occur in patients with AIDS. Disruption of thymopoiesis is also a consequence of HIV-1 infection. We are investigating whether HIV-1 dysregulates hematopoiesis by infecting bone marrow stromal cells and disrupting their function or by infecting hematopoietic stem or progenitor cells and disrupting their development. The infection and disruption of bone marrow or thymic stromal cells would be detrimental for cellular development.

We found that human primary bone marrow or thymic stromal cells, depleted of microvascular or hematopoietic cells, do not express detectable levels of CXCR4, CCR2, CCR3, or CCR5, members of the CXC and CC chemokine families of receptors, and cannot be infected with HIV-1. These receptors, in conjunction with CD4, are used for HIV-1 entry into cells. Thus, we conclude that stromal cells might not normally be made dysfunctional by direct HIV-1 infection.

HEMATOPOIETIC STUDIES IN HUMAN-MOUSE CHIMERAS

We have developed a human-mouse model to study human hematopoiesis. Purified human cord blood cells are transplanted into nonobese diabetic mice that have severe combined immunodeficiency. Hematopoiesis of human cells is maintained in these mice for 6 months, with expansion of CD34⁺/CD38^--/lo cells and production of B cells and myeloid cells. Primitive human progenitor cells egress from the mouse bone marrow space to the periphery when induced with human growth factors. We are using this model to study (1) the mechanisms responsible for cytokine-mediated migration of bone marrow cells and (2) in collaboration with I. Verma and colleagues at the Salk Institute, the potential of lentivirus as a way to target human "stem cells."

THE PU.1 TRANSCRIPTION FACTOR IN HEMATOPOIETIC DEVELOPMENT

PU.1 is a hematopoietic-specific transcription factor critical for the development of myeloid and lymphoid cells. Mice that lack PU.1 have multiple hematopoietic abnormalities. These mice are devoid of B lymphocytes, monocytes/macrophages, dendritic cells, and mature neutrophils but not T cells or immature neutrophils. We showed that disruption of the PU.1 gene results in loss of cell-surface receptors for granulocyte, granulocyte-macrophage, and macrophage colony-stimulating factors and loss of gene expression required for the development and function of myeloid cells. For example, neutrophils do not terminally differentiate or become functionally competent.

To distinguish between gene programs responsible for survival and those responsible for differentiation in myeloid cells that lack PU.1, we are using retroviral delivery to replace either growth factor receptors or PU.1. These studies will enable us to determine at what point in development PU.1-regulated genes dictate specific commitment to myeloid cell lineage and should enable us to identify novel genes required for the development of myeloid cells.

PUBLICATIONS

Anderson, K.A., Conners, K., Smith, K.A., McKercher, S., Maki, R.A., Torbett, B.E. Myeloid development is selectively disrupted in PU.1 null mice. Blood 91:3702, 1998.

Anderson, K.A, Smith, K.A., Pio, F., Torbett, B.E., Maki, R.A. PU.1 null neutrophils are functionally deficient and fail to terminally differentiate. Blood, in press.

Lee, T., Laco, G.S., Torbett, B.E., Fox, H.S., Lerner, D.L., Elder, J.H., Wong, C.-H. Analysis of the S3 and S3´ subsite specificities of the FIV protease: Development of a broad-based protease inhibitor efficacious against FIV, SIV, and HIV in vitro and ex vivo. Proc. Natl. Acad. Sci. U.S.A. 95:939, 1998.

Pedroza-Martins, L., Gurney, K., Torbett, B.E., Uittenbogaart, C.H. Differential tropism and replication kinetics of HIV-1 isolates in thymocytes: Coreceptor expression allows viral entry, but productive infection of distinct subsets is determined at the post-entry level. J. Virol., in press.