Allogeneic stem cell transplantation is curative for certain cancers, but the high doses of chemotherapy/radiotherapy lead to toxicity. Here, we treat patients with refractory cancer with 100 cGy total body irradiation (TBI) followed by infusion of nonmobilized pheresed allogeneic peripheral blood cells. Twenty-five patients, with a median age of 47 years, with refractory cancers were enrolled. Eighteen patients received sibling and 7 received unrelated cord blood cells. Donor chimerism was assessed at weeks 1, 2, 3, 4, and 8 after transplantation. Seven patients with solid tumors received a sibling transplant and 6 received a cord blood transplant; none achieved donor chimerism, but 1 treated at the higher dose level of 1 ؋ 10 8 CD3 ؉ cells/kg had a transient nodal response. Twelve patients with hematologic malignancies were treated; 1 received a cord blood transplant and 11 received sibling donor cells. Nine of these 11 patients achieved donor chimerism, ranging from 5% to 100%. Four patients had sustained complete remission of their cancers, including one patient with transient 5% donor chimerism. The development of chimerism correlated with hematologic malignancy (P < .001), total previous myelotoxic chemotherapy (P < .001), T-cell dose (P ‫؍‬ .03), and graft-versus-host disease (P ‫؍‬ .01). Tumor response correlated with donor chimerism (P ‫؍‬ .01). Engraftment was achieved in patients with hematologic malignancies who had been heavily pretreated, suggesting the degree of immunosuppression may be a determinant of engraftment. Low-dose TBI and allogeneic lymphocyte infusion may induce remission in patients with refractory hematologic malignancy. (Blood. 2002; 100:442-450)

The donor stem cell phenotype and host microenvironment determine the outcome of a stem cell transplant. In a series of transplant studies in syngeneic male to female or congenic Ly5.1/Ly5.2 models in which hosts have received no or minimal irradiation (100 cGy), evidence overwhelmingly supports the concept that syngeneic engraftment is determined by stem cell competition. These approaches can be extended to H-2 mismatched allogeneic mouse combination when antigen pre-exposure and CD40-CD40 ligand antibody blockage are employed. A human trial in patients with resistant neoplasia infusing pheresed blood with 10 8 CD3 cells/kg showed that tumor responses and complete chimerism occur with very low levels of CD34 + cells/kg and that the extent of previous treatment is a critical factor in determining chimerism. A major feature of transplants is the phenotype of the donor stem cell. This phenotype shows dramatic reversible plasticity involving differentiation, adhesion protein expression, and engraftment with cytokine-induced cell-cycle transit. Homing is probably also plastic. Marked fluctuations in engraftment capacity are also seen at different points in marrow circadian rhythm.