Keratinocyte growth factor facilitates alloengraftment and ameliorates graft-versus-host disease in mice by a mechanism independent of repair of conditioning-induced tissue injury

When the Damage Is Done: Injury and Repair in Thymus Function

Even though the thymus is exquisitely sensitive to acute insults like infection, shock, or common cancer therapies such as cytoreductive chemo- or radiation-therapy, it also has a remarkable capacity for repair. This phenomenon of endogenous thymic regeneration has been known for longer even than its primary function to generate T cells, however, the underlying mechanisms controlling the process have been largely unstudied. Although there is likely continual thymic involution and regeneration in response to stress and infection in otherwise healthy people, acute and profound thymic damage such as that caused by common cancer cytoreductive therapies or the conditioning regimes as part of hematopoietic cell transplantation (HCT), leads to prolonged T cell deficiency; precipitating high morbidity and mortality from opportunistic infections and may even facilitate cancer relapse. Furthermore, this capacity for regeneration declines with age as a function of thymic involution; which even at steady state leads to reduced capacity to respond to new pathogens, vaccines, and immunotherapy. Consequently, there is a real clinical need for strategies that can boost thymic function and enhance T cell immunity. One approach to the development of such therapies is to exploit the processes of endogenous thymic regeneration into novel pharmacologic strategies to boost T cell reconstitution in clinical settings of immune depletion such as HCT. In this review, we will highlight recent work that has revealed the mechanisms by which the thymus is capable of repairing itself and how this knowledge is being used to develop novel therapies to boost immune function.

Sustained thymopoiesis and improvement in functional immunity induced by exogenous KGF administration in murine models of aging

Age-related thymopoietic insufficiency has been proposed to be related to either defects in lymphohematopoietic progenitors or the thymic microenvironment. In this study, we examined whether keratinocyte growth factor (KGF), an epithelial cell-specific growth factor, could increase thymopoietic capacity in aged mice by restoration of the function of thymic epithelial cells (TECs). The thymic cellularity in KGF-treated aged mice increased about 4-fold compared to placebo-treated mice, resulting in an equivalent thymic cellularity to young mice. Enhanced thymopoiesis was maintained for about 2 months after a single course of KGF, and sustained improvement was achieved by administration of monthly courses of KGF. With the enhanced thymopoiesis after KGF treatment, the number of naive CD4 T cells in the periphery and T-cell-dependent antibody production improved in aged mice. KGF induced increased numbers of TECs and intrathymic interleukin-7 (IL-7) production and reorganization of cortical and medullary architecture. Furthermore, KGF enhanced thymopoiesis and normalized TEC organization in klotho (kl/kl) mice, a model of premature degeneration and aging, which displays thymopoietic defects. The result suggests that TEC damage is pathophysiologically important in thymic aging, and KGF therapy may be clinically useful in improving thymopoiesis and immune function in the elderly.

Surfactant protein A is a required mediator of keratinocyte growth factor after experimental marrow transplantation

We reported an association between the ability of recombinant human keratinocyte growth factor (rHuKGF) to upregulate the expression of surfactant protein A (SP-A) and to downregulate pulmonary inflammation that occurs after allogeneic bone marrow transplantation (BMT). To establish a causal relationship, rHuKGF (5 mg/kg) was administered subcutaneously for three consecutive days before irradiation to SP-A-sufficient and -deficient [SP-A(+/+) and SP-A(-/-), respectively] mice given inflammation-inducing allogeneic spleen T cells at the time of BMT. In contrast with SP-A(+/+) mice, rHuKGF failed to suppress the high levels of TNF-alpha, IFN-gamma, and nitric oxide contained in bronchoalveolar lavage fluids collected on day 7 after BMT from SP-A(-/-) mice. Early post-BMT weight loss was attenuated by rHuKGF in both SP-A(+/+) and SP-A(-/-) recipients. In the absence of supportive respiratory care, however, SP-A deficiency eventually abolished the ability of rHuKGF to prevent weight loss and to improve survival monitored for 1 mo after allogeneic BMT. In further experiments, the addition of cyclophosphamide (which is known to cause severe injury to the alveolar epithelium in donor T cell-recipient mice) to the conditioning regimen prevented rHuKGF-induced upregulation of SP-A and suppression of lung inflammation in both SP-A(+/+) and SP-A(-/-) mice. We conclude that endogenous baseline SP-A levels and optimal upregulation of SP-A are required for the anti-inflammatory protective effects of KGF after allogeneic transplantation.