Rituximab Administration before Allogeneic HSCT Is Associated with Accelerated T Cell Reconstitution after Transplantation: Kinetic Evidence for a Graft-Versus-Leukemia Effect
Authors: Hosoba Sakura , Flowers Christopher R. , Wu Catherine J , Wrammert Jens R. , Waller Edmund K. 
Published: October 2019

Abstract
Introduction: Rituximab (R) administration results in depletion of blood B cells and suppression of B cell reconstitution for several months after, with suggestions that T cell reconstitution may also be impaired. We hypothesized that pre-transplant R would be associated with delayed B and T cell reconstitution after allo-HSCT compared with non-R-treated allo-HSCT recipients.
Methods: We conducted a retrospective analysis of 360 patients who underwent allo-HSCT using BM or G-CSF mobilized PB. Recipients of cord blood, T cell depleted grafts and 2nd allo-HSCT were excluded. Analysis of lymphocyte subsets in at least one blood at 1, 3, 6, 12, and 24 months post-allo-HSCT was available for 255 eligible patients. Data on lymphocyte recovery was censored after DLI or post-transplant R therapy. Post-HSCT lymphocyte recovery in 217 patients who never received R (no-R) was compared to 38 patients who had received R before allo-HSCT (+R) including 12 CLL, 19 NHL, and 7 B-cell ALL patients. +R patients received a median of 9 doses of R with the last dose of R at a median of 45 days pre-transplant.
Results: Mean lymphocyte numbers in the blood at 1, 3, 6, 12, and 24 months were B-cells: 55 ± 465/µL, 82 ± 159/µL, 150 ± 243/µL, 255 ± 345/µL, and 384 ± 369/µL (normal range 79-835); and T-cells: 65 ± 987/µL, 831 ± 667/µL, 1058 ± 788/µL, 1291 ± 985/µL, and 1477 ± 1222/µL (normal range 675-3085). Lymphocyte reconstitution kinetics did not vary significantly based upon the intensity of the conditioning regimen or related vs. unrelated donors allowing aggregation of patients in the +R and no-R groups (Figure). B cell reconstitution in the +R patients was higher at 1 month post-allo-HSCT (relative value of 143% p=0.008) and lower at 3 months post-transplant (19.2%, p=0.069) compared to no-R patients. Blood B cells in the +R group rebounded by the 6th month post-allo-HSCT and remained higher than the no-R group through the 24th month post-HSCT (197% at the 6th month, p=0.037). Higher levels of B-cells at 1 month in the +R group was due to higher blood B-cells at 1 month post-HSCT among 12 CLL patients compared with no-R patients (423%, p<0.001; Figure), while B-cell counts in the remaining +R patients (B-cell NHL and B-cell ALL) were lower than the no-R patients at both 1 and 3 months. Reconstitution of CD4+ and CD8+ T cells among +R patients were similar to no-R patients in the first month post-allo-HSCT and then rebounded to higher levels than the no-R group of patients (relative value 194%, p=0.077 at the 24th month for CD4+ T cell subset, and 224%, p=0.020 for CD8+ T cell subset; Figure). CLL patients had a striking increase in blood levels of donor-derived CD4+ and CD8+ T cells at 3 months post-transplant concomitant with the disappearance of blood B cells compared with no-R patients (relative value of 178% and 372%, p=0.018 and p=0.003, respectively; Figure). Long term T cell reconstitution remained higher for +R patients compared with no-R patients, even when CLL patients were excluded (relative value of 203%, p=0.005 at 24 months post-HSCT; Figure).
Conclusions: We observed higher levels of blood B cells and T cells ³ 6 months post-allo-HSCT in +R patients compared with no-R patients. B cell recovery at 6 months post-transplant is consistent with clearance of residual plasma R given the 1-2 months half-life of R, and the median of 1.5 months between the last dose of R and allo-HSCT. The increased blood CD8+ T cells in the blood of CLL patients at 3 months post-allo-HSCT associated with clearance of the B-cells seen 1 month post-HSCT is consistent with a donor T cell-mediated GVL effect. Pre-transplant R therapy does not appear to have any long-term deleterious effect on immune reconstitution, indicating that post-allo-HSCT vaccination at ≥6 months may be efficacious.
Figure: Kinetics of lymphocyte reconstitution after allo-HSCT varied by history of pre-transplant R administration and primary disease. Panels show mean counts of each lymphocyte subset at 1, 3, 6, 12 and 24 months post-allo-HSCT for: (1) B cell, (2) T cell, (3) CD4+ and (4) CD8+ T cells. Solid lines with triangle show no-R group; dashed lines with circles shows subgroups of CLL and NHL/ALL +R patients. Asterisks show p values from t-test of the comparison between CLL +R or the NHL/ALL +R patients with no-R patients. *p<0.05; ** p<0.01; *** p<0.001. Figure:. Kinetics of lymphocyte reconstitution after allo-HSCT varied by history of pre-transplant R administration and primary disease. Panels show mean counts of each lymphocyte subset at 1, 3, 6, 12 and 24 months post-allo-HSCT for: (1) B cell, (2) T cell, (3) CD4+ and (4) CD8+ T cells. Solid lines with triangle show no-R group; dashed lines with circles shows subgroups of CLL and NHL/ALL +R patients. Asterisks show p values from t-test of the comparison between CLL +R or the NHL/ALL +R patients with no-R patients. *p<0.05; ** p<0.01; *** p<0.001.

Disclosures
No relevant conflicts of interest to declare.