Keratinocyte Growth Factor Increases Thymic Output of Naïve T-Cells after Total Body Irradiation and Autologous Peripheral Blood Progenitor Cell Transplantation in Rhesus Macaques.

Opportunistic infections have an major impact on morbidity and mortality after peripheral blood progenitor cell transplantation, and are caused by deficient T cell numbers and activities, which correlate with thymic dysfunction. Keratinocyte growth factor (KGF) has been shown to protect thymic epithelial cells from injury induced by chemotherapy and radiation in mice, associated with improved thymopoiesis. We for the first time evaluated the effect of KGF on immune reconstitution after myeloablative total body irradiation (TBI) and autologous transplantation in non-human primates, a clinically relevant large animal model. Four animals received KGF 250mg/kg body weight given once (day −5) before TBI (low dose KGF) and CD34+ purified PBPC transplantation, and two animals received the same dose given 3 times (day −5, −4, −3) before and 3 times (day +1, +2, +3) after TBI (day −2, −1) and transplantation (day 0) (high-dose KGF). These KGF-treated animals were compared to an age and CD34⁺ cell dose-matched control group of five monkeys transplanted with purified CD34⁺ cells but without KGF treatment. We evaluated the reconstitution of T and B cells in blood and lymph nodes (LN) for a year post transplantation. All animals engrafted (neutrophils >500/ml) day by day 11 post transplantation. The animals treated with KGF had higher frequencies of naïve T cells in blood and in peripheral LN post transplantation as compared to the control animals, for instance at one month after transplantation the percentage of LN naïve CD4⁺ T-cells was 35±19% in the high dose KGF group, 14±2% in the low dose KGF group and 15±4% in the control group. At 3 months after transplantation the percentage of naïve CD4⁺ in LN was 56±5% in the high dose and 59±9% in the low dose KGF groups versus 27±7% in the control group. We observed similar findings in the CD8⁺ subset. All KGF treated animals had higher peripheral blood TREC levels, broader TCR repertoires as determined by spectratyping of the CDR3 region, and lower frequencies of Ki-67⁺ proliferating T cells, presumably due to a lower drive for peripheral expansion in animals with better thymic output of naïve T cells. The recovery of circulating B-cells was not altered with KGF treatment compared to the controls. At 12 months after transplantation there was uniform preservation of thymic architecture with proliferating thymocytes in the animals treated with KGF, in comparison to the control group of animals, with thymic atrophy seen in the majority. Thus, peri-TBI treatment with KGF resulted in protection of thymic epithelial cells, improved thymic repopulation, and increased naïve T-cell numbers in secondary lymphatic tissues, and correlated with better immune responses to newly induced (HIV envelope) as well as recall antigens including measles and CMV. KGF-mediated protection and preservation of thymic epithelial cells from TBI-mediated damage, with improved output of naïve T cells post-transplantation may improve immune reconstitution and thus outcomes in patients undergoing autologous or allogeneic transplantation.