AML Relapse after Rituximab Treatment for Graft-Versus-Host Disease: Crucial Role for B Cells in Graft-Versus-Host and Graft-Versus-Leukemia

Patients with hematologic malignancies that develop graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (HSCT) have a reduced risk of disease relapse compared to patients that do not develop GvHD, suggesting that GvHD and graft-versus-leukemia (GvL) responses are co-dependent. T cells are important in these processes, as T cell depletion from the graft reduces the risk of GvHD at the expense of disease relapse. Much less is known about the effect of B cell depletion on GvHD and GvL responses. Small patient series have demonstrated variable efficacy of Rituximab in the treatment of steroid-refractory chronic GvHD but the effect of depleting allo-reactive B cells on disease relapse remains to be determined. We here report on a patient with steroid-refractory GvHD whose AML relapsed after Rituximab treatment.

This 39-year old male received an allogeneic HSCT for chemotherapy-related AML (AML-t) that however relapsed 8 weeks after the transplantation. Upon rapid cessation of immunosuppressive therapy (cyclosporine, mycophenolic acid) and without additional chemotherapy he obtained full remission, at the expense of severe GvHD of the skin, liver and intestine that was corticosteroid-refractory. B cell depletion with Rituximab was successful as second-line treatment for GvHD but eliminated the GvL response and the patient died of AML relapse several months after.

To evaluate the B cell repertoire of this patient at the moment of maximal GvH and GvL responses, we isolated peripheral blood B lymphocytes that were transduced with Bcl-xL and Bcl-6 to create clonal B cell lines. These B cells were screened for binding to AML and host tissues. One clone was retrieved that specifically bound to AML cell lines and AML blasts freshly isolated from newly diagnosed AML patients. Antibodies from this clone induced antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity of AML cells in vitro. Several other clones were retrieved that were specific for host tissues such as liver (HepG2 and H69 cell lines), skin (primary fibroblasts) and/or colon (CaCo cell line).

These data demonstrate the pivotal role of B lymphocytes in anti-leukemia and anti-host immune responses in an allogeneic HSCT recipient with relapsed AML-t.