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Targeted immune depletion prior to reduced-intensity allogeneic stem cell transplantation results in rapid and complete donor chimerism with low treatment-related mortality.

6540 Background: Significant variation in host immune status may influence outcomes after reduced-intensity (RI) allogeneic stem cell transplantation (alloSCT). We have investigated a strategy of targeted immune depletion (TID) with conventional chemotherapy to deplete host T cells and achieve a minimal disease state prior to RI alloSCT. The aim of TID is to rapidly establish complete donor chimerism after RI alloSCT in order to potentiate a graft-versus-tumor (GVT) effect. In a prospective phase II trial (NIH 03-C-0077), we evaluated the effect of TID on donor chimerism, acute graft-versus-host disease (GVHD), and clinical outcome.


METHODS
Thirty-one patients (pts) with relapsed and refractory hematologic malignancies (NHL = 16; HL = 4; CLL/PLL = 4; MDS/AML = 3; other = 4) were enrolled. Median age was 57 years (range: 31-71). All pts received EPOCH-F (etoposide, prednisone, vincristine, cyclophosphamide, adriamycin, fludarabine) ± rituximab (R) as TID to deplete host CD4+ cells <100/μL. All pts then received a RI conditioning regimen consisting of fludarabine and cyclophosphamide followed by a T-cell replete allograft from HLA-matched siblings. GVHD prophylaxis consisted of cyclosporine plus short-course mini-methotrexate.


RESULTS
EPOCH-F(R) achieved the target host T-cell level in 74% of pts. All 31 pts engrafted after RI alloSCT. Complete donor chimerism (> 95%) was observed in 74% and 81% of pts at day +14 and +28 post-transplant, respectively. The incidence of grade II-III acute GVHD was 42% with no cases of grade IV acute GVHD. The median potential follow-up from transplant is 25 months. Actuarial treatment-related mortality at 1 and 2 years was 3% and 8%, respectively. Event-free survival probabilities at 1 and 2 years post-transplant are 65% and 49%, respectively. Ten pts are alive and event-free >24 months post-transplant. The overall survival probabilities at 1 and 2 years are 84% and 64%, respectively.


CONCLUSIONS
TID prior to RI alloSCT results in rapid, complete donor engraftment and may potentiate GVT effects. This treatment strategy was associated with very low TRM and favorable outcomes in an older patient population with advanced hematologic malignancies. No significant financial relationships to disclose.