Administration Of Anti-CD20 Mab Is Highly Effective In Preventing But Ineffective In Treating Chronic GVHD While Preserving A Strong GVL Effect

Donor T cell-mediated graft versus leukemia/lymphoma (GVL) effect plays a critical role in preventing tumor relapse in leukemia/lymphoma patients treated with allogeneic hematopoietic cell transplantation (HCT). However, these same donor T cells also induce acute and chronic graft versus host disease (GVHD), which remains a major obstacle for allogeneic HCT as a curative therapy for hematological malignancies. Chronic GVHD is a systemic lupus- and scleroderma-like autoimmune syndrome. We and others reported that donor B cells play important roles in augmenting pathogenesis of chronic GVHD in mouse models and humans. Rituxan (an anti-CD20 mAb) has been used in the clinic for the treatment of ongoing chronic GVHD, but the effect is variable and minimum in some reports, and the mechanisms for this ineffectiveness remains unclear. In the current studies, we evaluated the effect of in vivo administration of a depleting anti-CD20 mAb in preventing and treating autoimmune-like chronic GVHD as well as the impact on GVL effect. With the mouse chronic GVHD model of DBA/2 donor to MHC-matched BALB/c recipient established in our lab (Blood, 2006, J. Immunol 2012), we found that one intravenous injection of anti-CD20 (50mg/kg) immediately after HCT effectively prevented induction of autoimmune-like chronic GVHD. While all (12/12) recipients treated with control IgG developed chronic GVHD with proteinuria and hair-loss and died by 30 days, none (0/12) of the anti-CD20-treated recipients developed proteinuria or hair-loss and all survived for more than 50 days after HCT without signs of chronic GVHD. In addition, the anti-CD20-treated recipients eliminated BCL1 leukemia/lymphoma cells without signs of chronic GVHD. The preventative anti-CD20 treatment had little impact on donor CD8⁺ T cell activation and expansion in the periphery and allowed for the strong CD8⁺ T cell-mediated GVL effect. The effective prevention of chronic GVHD by anti-CD20 was associated with significant changes in donor B and CD4⁺ T cells as well as associated with protection of host thymus. Preventive anti-CD20 treatment depleted IL-6-producing donor B cells and increased IL-10-producing B cells. In addition, the treatment also significantly reduced donor CD4⁺ T cell expansion, the percentage of IFN-g-producing CD4⁺ T as well as CD4⁺ T cells expressing CD8αα, the latter of which has recently been reported to represent over-activated pathogenic CD4⁺ T cells, such that the host thymus was protected from donor T-cell-mediated damage. Anti-CD20 or control IgG treatment of recipients with ongoing chronic GVHD 15-20 days after HCT did not show any difference in disease progress, and all (8/8) in each group died within 30 days after HCT. The ineffectiveness of anti-CD20 therapy was associated with little reduction of CD19⁺ B or CD4⁺ T cells, as the majority of CD19⁺ B cells became CD20^- in the recipients with ongoing chronic GVHD. These results indication that anti-CD20 can effectively prevent induction of autoimmune-like chronic GVHD while preserving the GVL effect, but anti-CD20 is ineffective in treating ongoing chronic GVHD. (This study is supported by the Nesvig Lymphoma Foundation).