Prophylactic Rituximab after Reduced Intensity Conditioning Transplantation Results in Low Chronic Gvhd

Background: B cells are implicated in the pathophysiology of chronic GVHD. We hypothesize that prophylactic anti-B cell therapy delivered two months after reduced intensity conditioning (RIC) transplantation would prevent or reduce chronic GVHD incidence from the historical 50%. Chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) were the target diseases as they are B cell malignancies with clear allogeneic GVL benefit.

Methods: CLL and MCL patients were conditioned with total lymphoid irradiation (TLI) 80 cGy in 10 fractions, d-11 to d-1 and anti-thymocyte globulin (ATG) 1.5mg/kg/day, d-11 to d-7 (total 7.5mg/kg). PBPC were infused on day 0. Primary GVHD prophylaxis was cyclosporine (CSA) on d-3 with taper by 6 months, and MMF from day 0 until d28 for related donors, d100 for unrelated donors. Rituximab (375 mg/m²/week ×4) was infused on days 56, 63, 70, and 77 post-transplant.

Results: 36 patients accrued to the study (median age 57, range 31–66 yrs), with 34 patients completing the 4 rituximab infusions. All 22 CLL patients were high risk (fludarabinerefractory, unmutated VH-IgG, or P53 deletion). The 14 MCL patients included 4 patients in PR and 10 patients in CR status at transplant. Median follow-up is 20 months. Twenty patients had sibling donors; 16, unrelated donors. Median CD34 cell dose was 7.5 CD34/kg. All patients had donor cell engraftment except for one patient who had graft failure with stable autologous recovery. Full donor chimerism (PB CD3>95%) was achieved in 14 out of 31 patients (45%) by day 90. However, all but 5 patients had achieved full donor chimerism at 1 year. The incidence of grade 2–4 acute GVHD was 6%. The incidence of chronic GVHD was 18%. Day 100 NRM was 0% and 1-year NRM was 3%. Ten relapses have occurred (5 CLL, 5 MCL). Estimated FFP and OS at 2 years for CLL patients is 82%(CI +/−16%) and 73% (CI +/−33%), respectively; for MCL patients, 64% and 68%, respectively Full donor chimerism was associated with persistent disease remission. Twelve of 19 VHIg mutated CLL patients have achieved minimal residual disease (MRD) by quantitative allele-specific oligonucleotide-IgH PCR (ASO-Q-PCR). DLI was given to 5 CLL patients and 1 MCL who had relapsed and had not achieved full donor chimerism.. There were no infusional toxicities with rituximab. Transient rituximab related neutropenia occurred in 10 patients d100–150. Post-transplant infections included influenza B, RSV, fungal sinusitis, pseudomonas, klebsiella infection, VZV reactivation, and one PTLD before day 56 rituximab. All recovered Of 22 patients at risk for CMV reactivation, 10 reactivated ( range 4 to 56 days post-HCT). Therefore, rituximab did not contribute to the CMV reactivation or increase infection incidence.

Conclusion: Prophylactic rituximab infusion post RIC transplantation is well tolerated, provides safe donor B cell depletion without detrimental effect on engraftment or infection incidence, and is associated with a low incidence of chronic GVHD while maintaining GVL. A randomized trial of rituximab prophylaxis after allogeneic HCT is warranted.