INTRODUCTION: Anti-CD19 chimeric antigen receptor (CAR) -T cells, which recognize and kill both B lymphoblasts and normal B cells, result in B cell aplasia and humoral immunodeficiency. However, there were only a few detailed reports on the profile of immune reconstitution after anti-CD19 CAR-T cell therapy. METHODS: Thirty nine patients with relapsed or refractory (R/R) B cell acute lymphoblastic leukemia (ALL) receiving anti-CD19 CAR-T cell therapy were enrolled. Subjects died, relapsed, received other treatment, or lost to follow-up within 60 days post-infusion were excluded. 21 patients were finally selected. Laboratory and clinical data were collected for analysis of immune reconstitution. RESULTS: CD8+ cells were the first to recover with a median time on day 21(7-87), followed by CD16/CD56+ cells on day 28(14-87), and finally CD4+ cells with only 5(23.81%) patients recovered within 60 days post-infusion. CD4/CD8 ratio was inverted, sustaining for at least 1 year. B cell aplasia occurred in all patients and CD19+ cells returned to normal on a median time of day 79(41-118). All patients developed hypogammaglobulinemia with a median onset time of 2 weeks post-infusion. IgG recovered in 6 patients with a median time on day 184(89-346). IgM recovered on days 212, 242, and 346 in 3 patients. IgA recovered most slowly and remained low >1 year postinfusion. A total of 9 infections occurred in 6(28.57%) patients. CONCLUSIONS: Our data showed prolonged reconstitution of immune function, especially humoral immunity, in R/R B cell ALL patients receiving anti-CD19 CAR-T cell therapy.