Keratinocyte growth factor impairs human thymic recovery from lymphopenia.

BACKGROUND. The lymphocyte-depleting antibody alemtuzumab is a highly effective treatment for relapsing-remitting multiple sclerosis (RRMS); however, 50% of patients develop novel autoimmunity after treatment. Most at risk are individuals who reconstitute their T cell pool by proliferating residual cells, rather than producing new T cells in the thymus, raising the possibility that autoimmunity might be prevented by increasing thymopoiesis. Keratinocyte growth factor (palifermin) promotes thymopoiesis in nonhuman primates. METHODS. Following a dose tolerability substudy, individuals with RRMS (duration <= 10 years; expanded disability status scale <= 5.0, with >= 2 relapses in the previous 2 years) were randomized to placebo or 180 mu g/kg/d palifermin, given for 3 days immediately before and after each cycle of alemtuzumab, with repeat doses at month 1 (M1) and M3. The interim primary endpoint was naive CD4(+) T cell count at M6. Exploratory endpoints included number of recent thymic emigrants (RTEs) and signal joint T cell receptor excision circles/ml (sjTRECs/ml) of blood. The trial's primary endpoint was incidence of autoimmunity at M30. RESULTS. At M6, individuals receiving palifermin had fewer naive CD4(+) T cells (2.229 x 10(7)/l vs. 7.733 x 10(7)/l; P = 0.007), RTEs (16% vs. 34%), and sjTRECs/ml (1100 vs. 3396), leading to protocol-defined termination of recruitment. No difference was observed in the rate of autoimmunity between the 2 groups. CONCLUSION. In contrast with animal studies, palifermin reduced thymopoiesis in our patients. These results offer a note of caution to those using palifermin to promote thymopoiesis in other settings, particularly in the oncology/hematology setting, where alemtuzumab is often used as part of the conditioning regime.