Howard Petrie, PhD

Department of Immunology and Microbiology
Florida Campus

Scripps Research Joint Appointments

Head, Flow Cytometry Core

Research Focus

Like all cells of hematopoietic origin, new T lymphocytes must be generated throughout life, a task that is the primary function of the thymus. Unlike other tissues that undergo steady-state differentiation, however, the thymus contains no self-renewing progenitor cells. Instead, new progenitors are specifically recruited from a pool of multi-potent progenitors that circulate within the blood. Once inside the thymus, these progenitors undergo a series of cell divisions to generate a large pool of T-lineage restricted cells that undergo selection based on the specificity of their antigen receptors, and are ultimately exported to the peripheral immune system. Our laboratory focuses on the early aspects of the intrathymic differentiation process, particularly on those aspects that relate to thymic homing, proliferative expansion, and T lineage commitment. In recent years, we have shown that different phases of these processes take place in specific tissue regions within the thymus, indicating the presence of different signaling microenvironments in the thymus, and obligating the existence of a system for moving progenitors between them.

Currently, we are focusing on the following goals:

  • defining novel stromal signals that induce T lineage specification and/or support proliferative expansion of immature T cell progenitors;
  • defining signals that facilitate progenitor migration between different microenvironments within the thymus;
  • characterizing functionally-defined stromal microenvironments in the thymus, and how they differentially signal to lymphocytes in a stage-specific manner;
  • understanding the global biology of the thymus, including the biology of stromal cells;
  • understanding the changes in T cell production efficiency that accompany aging of the thymus.


Ph.D. (Medical Sciences), University of Nebraska Medical Center, 1988
M.S. (Microbiology), The Pennsylvania State University, 1981
B.S. (Microbiology), The Pennsylvania State University, 1978

Professional Experience

2005-2017 Professor, Cancer Biology, Scripps Research
1993-2004 Assistant / Associate Member, Sloan-Kettering Institute
1991-1992 Postdoctoral Fellow, Section of Immunology, School of Medicine, Yale University
1988-1991 Postdoctoral Fellow, Lymphocyte Differentiation Unit, Walter and Eliza Hall Institute of Medical Research, The University of Melbourne

Selected References

All Publications

Griffith AV, Fallahi M, Venables T, and Petrie HT. 2012. Persistent degenerative changes in thymic organ function revealed by an inducible model of organ regrowth. Aging Cell: in press.

Shi J, Fallahi M, Luo JL, and Petrie HT. 2011. Non-overlapping functions for Notch1 and Notch3 during murine steady-state thymic lymphopoiesis.  Blood 118:2511-2519.

Griffith AV, Fallahi M, Nakase H, Gosink M, Young B, and Petrie HT. 2009. Spatial mapping of thymic stromal microenvironments reveals unique features influencing T lymphoid differentiation. Immunity: 31:999-1009.

Umland O, Mwangi WN, Anderson B, Walker J, and Petrie HT. 2007. The blood contains multiple distinct progenitor populations with clonogenic B and T lineage potential. J Immunol 178:4147-4152.

Petrie HT and Zúñiga-Pflücker JC. 2007. Zoned out: functional mapping of stromal signaling microenvironments in the thymus. Ann Rev Immunol 25:6649-6679.

Porritt HE, Rumfelt LL, Tabrizifard S, Schmitt TM, Zúñiga-Pflücker JC, Petrie HT. 2004. Heterogeneity among DN1 prothymocytes reveals multiple progenitors with different capacities to generate T cell and non-T cell lineages. Immunity 20:735-745.


Acclaimed Immunologist Howard T. Petrie Named Professor at Scripps Florida