We evaluated an ex-vivo photodepletion technique to selectively deplete graft-versus-host disease (GVHD) alloreacting T cells given to 24 HLA-identical sibling stem cell transplant (SCT) recipients. Donor lymphocytes were activated by 72 hr exposure to irradiated in-vitro expanded recipient T lymphocytes and pulsed with TH9402 photosensitizer. Alloactivated T cells preferentially retaining the photosensitizer were eliminated by light exposure. The photodepletion product showed an inverted CD4+/CD8+ ratio with greatest depletion occurring in the CD4+naïve and central memory populations. In contrast, the CD8+ naive and effector cells were relatively conserved, reflecting the differential extrusion of TH9402 by T cell subsets. CMV reactive T cells were reduced in the photodepletion product and in recipient blood 100 days after SCT when compared with contemporaneous HLA-identical sibling donor T cell depleted SCT recipients. Although PD SCT recipients experienced similar absolute lymphocyte counts during the first 100 days after SCT, they achieved 100% donor T cell chimerism more rapidly and had higher CD8+ naive T cell counts early after SCT. SCT recipients of photodepleted products with the lowest CD4 central memory content had the highest risk of developing chronic GVHD (p = 0.04), and a poorer survival (p = 0.03). While the persistence of CD8+ naive T cells may have contributed to important anti-leukemia responses resulting in a relatively low relapse rate, our findings emphasize the role of donor memory T cells and CD4 cells in establishing immune competence post SCT. Although photodepletion is associated with excellent outcomes in the haploidentical setting, the low frequency of alloactivations in HLA-matched pairs makes the PD approach used by our group for allodepletion in HLA-matched sibling transplantations an inefficient technique.

The monoclonal anti CD20 antibody Rituximab (RTX) is increasingly used in allogeneic stem cell transplantation (SCT) to treat lymphoproliferative disorders and chronic graft-versus-host disease (GVHD). RTX administration can be complicated by delayed and prolonged neutropenia, but the mechanism is unclear. We report the occurrence of profound cytopenias following RTX given in the conditioning regimen or early after T cell deplete-SCT to treat B cell lymphoproliferative disorders or c-GVHD. Between 2006–2009, 102 patients (median age 43, range 13–68 years), received a myeloablative matched-sibling T cell-deplete SCT for lymphoid or myeloid hematological disorders. Neutropenia occurring within 4 weeks of treatment developed in 16 of 17 patients given RTX within the first 190 days after SCT. Fourteen patients developed severe neutropenia (count < 0.5K/μL) lasting up to 10 months and 12 required hospitalization to treat severe neutropenic infections. Six of the 14 patients died of infection complicating GVHD treatment. Recovery of lymphocytes and immunoglobulins was also delayed, with a significantly lower ALC at 9 months and 12 months post SCT compared to patients with c-GvHD not treated with early RTX (p < 0.02). In contrast, patients receiving RTX one year after SCT experienced only moderate neutropenia 3–5 months after treatment lasting 10–20 days while maintaining ANC > 1.0 × 109/L. Although RTX rapidly controlled c-GVHD, we conclude that its administration early after T cell deplete-SCT is associated with prolonged profound and life-threatening cytopenias, and should be avoided.

Blood Institute institutional review board-approved protocols. Patients and donors provided written informed consent before enrolling in the transplantation protocols. The clinical characteristics of these 220 patients and their respective donors are presented in Table 1.