Direct Intra-Bone Marrow Transplant of Cord Blood Cells: A Way To Overcome Delayed Engraftment.

The major limit of cord blood (CB) transplant in adult patients is represented by the delayed engraftment. Newer approaches have been suggested including double cord blood transplant and infusion of CD34+ selected cells from a relative to achieve a transient engraftment until CB cells generate mature blood cells.

Our initial pre-clinical studies showed that intra-bone injection of hematopoietic cells in the mouse was associated with an engraftment about 10 times more efficient with respect to the usual intravenous injection. Moreover, we had already demonstrated that the defect of cord blood cells in term of delayed engraftment was not related to the lower number of hematopoietic cells infused since the capacity to reconstitute the host stem cell reservoir was higher than adult bone marrow. Therefore, we set-up a pilot study to evaluate whether this type of transplant could shorten the time of engraftment. Five patients [4 male (M) and 1 female (F)] have been enrolled in this study. Clinical characteristics at transplant were: three patients had acute myeloid leukaemia: 2 refractory-relapsing and one in 1^st CR (age 37 M, 50 M, 60 M) and 2 acute lymphoblastic leukaemia: one in 1^st CR and one in 2^nd CR (age 42 F, 18 M). Cord Blood grafts were matched as follows: 3/6 in one patients, 4/6 in three patients, and 5/6 in one patient for HLA-A, B, DRB1 (serology for HLA class I and allelic for class II). Patients were prepared with standard conditioning including TBI. Anti-Thymocyte-Globulin 3.75mg/kg was given on day −3,−2. GVHD Prophylaxis was cyclosporine from day -7 (therapeutic range 200–400 ng /ml) plus mycophenolate-mofetil 15mg/kg b.i.d. from day +1 to +28. The number of cord blood cells infused was 2.4, 1.6, 2.4, 3.0, 2.7 x 10^7/kg b.w. Cells were infused under very short general anaesthesia (propofol) of 5–10 minutes in the posterior iliac crest with a standard bone marrow aspiration needle (gauge n. 14). Before infusion, CB cells were washed to eliminate DMSO.

Sustained engraftment of PMN (more than 3 consecutive days > 500 PMN x10^9/l) was recorded at day: + 20, 25, 18, 20, 23. Platelets sustained engraftment (more than 3 consecutive days > 20.000 Platelets x10^9/l) was recorded at day: +32, 42, 25, 29, 31.Acute GVHD was absent in these five patients.

This is a pilot study with very short follow-up (2 to 5 months). Thus, no conclusive answer can be drawn on the impact of this technique on the final outcome of these patients. However, the time to PMN and Platelets engraftment is much shorter with respect to the available data obtained with intra-venous (IV) injection of the same amount of cells. Seeding efficiency experiments have shown that less than 10% of the injected cells via IV actually seed in the active hematopoietic sites. Cord blood cells, injected directly into the bone marrow, may undergo a better homing without loss, proliferate and finally colonise the rest of the bone marrow; thus, improving considerably the seeding efficiency. Alternatively, CB cells may undergo faster maturation if injected intra-bone marrow and, at the same time, colonise more efficiently the rest of active hematopoietic sites. If confirmed in larger studies, this approach may render cord blood cells transplant suitable for a greater number of adult patients who so far were excluded from this therapeutic option. This work was supported by AIRC, CARIGE; Compagnia di San Paolo.