IRX-2 and Thymosin  1 (Zadaxin) Increase T Lymphocytes in T Lymphocytopenic Mice and Humans J. W. HADDEN, E. VERASTEGUI, AND E. HADDEN IRX Therapeutics Inc., Farmingdale, New York, USA ABSTRACT: Mouse studies showed a synergy of thymosin  1 (T 1) and a natural cytokine mixture (IRX-2) in increasing T lymphocyte number and responses. Clinical studies with IRX-2 showed increases of T lym- phocytes in lymphocytopenic cancer patients but relatively little effect on irradiated, lymphocytopenic patients. The present phase 1 and 2 study shows that T 1 enhances the effect of IRX-2 in these lymphocytopenic patients. Patients (seven) were treated with subcutaneously injected IRX- 2 (200 units IL-2 equivalence), T 1 (1.6 mg/day) (four patients), or the combination of IRX-2 and T 1 (seven patients) daily for 10 days. Pe- ripheral blood lymphocytes (T, B, NK) and subsets (CD4, CD8) were measured at the start of treatment and on day 11. IRX-2 and T 1 had little or no significant effect. The combination markedly increased vari- ous lymphocyte populations (>350 cells/L). Four patients followed for 6 weeks displayed sustained increases involving both na¨ ıve and memory T cells. Responses to persistent infections were observed in three of the four patients and no significant toxicity was observed. T 1 and IRX-2 synergize to increase safely T cells in lymphocytopenic patients. KEYWORDS: IRX-2; thymosin  1; NCM; thymalfasin; zadaxin; thymus; T lymphocytes; lymphocytopenia; head and neck cancer; radiotherapy INTRODUCTION The thymus gland is well established as the major organ for T lympho- cytopoiesis. While it is most active in youth to generate T lymphocytes, its age-related involution can be reversed and it can replenish the T cell pool. 1 The alternative source for replenishment lies in the periphery and can, through homeostatic expansion, restore both na¨ ıve and memory T cells. The mechanisms for T cell replenishment by the thymus have been intensively studied 2,3 ; however, those associated with homeostatic expansion are less well Address for correspondence: J.W. Hadden, IRX Therapeutics Inc., Administration, 1 Bioscience Park Drive Suite 101, Farmingdale, NY 11735. Voice: 631-370-8830; fax: 631-370-8856. jwhadden@optonline.net Ann. N.Y. Acad. Sci. 1112: 245–255 (2007). C  2007 New York Academy of Sciences. doi: 10.1196/annals.1415.032 245