Direct Intra-Bone Injection of Unrelated Cord Blood Cells Overcomes the Problem of Delayed Engraftment and Improves the Feasibility of Hematopoietic Transplant in Adult Patients.

Background. Cord blood transplants (CBT) are associated with delayed or failed engraftment in a significant proportion of patients (pts). Two of our previous observations suggested (i) that, in the animal model, direct intra-bone (i.b.) injection improves seeding efficiency and (ii) that the delayed engraftment was not related to an insufficient number of hematopoietic stem cells but rather to some difficulties to differentiate and maturate.

Methods. Unrelated CB cells were selected for 29 consecutive pts (18 CB units were 4/6 HLA antigen matched, 10 were 5/6 and one 3/6 antigen matched). Median cell dose infused was 2.3 x10^7/kg (range 1.4 – 4.2). CB cells were concentrated in 4 syringes of 5 ml each and injected in the supero-posterior iliac crest (SPIC) under rapid general anesthesia (10 min. with propofol). Pts’ median age was 38 years (18–63); 25 had acute leukaemia (21 with refractory or relapsed disease and 4 high risk first remission leukemia); 2 chronic myeloid leukemia in advanced phase; 2 refractory Hodgkin’s disease. Most pts (n=24) were prepared with conventional conditioning regimen (TBI-cyclophosphamide).

Results. The infusion of cells i.b. in SPIC (11 pts bilaterally; 18 pts monolaterally) was uneventful. Five pts are not evaluable because they died within 14 days from transplant. All pts surviving more than 14 days engrafted (100%). Median time for PMN (>0.5x10^9/l) and platelets (>20x10^9/l) engraftment was day +23 (14–40) and +38 (range 22–60) respectivelly. Four pts died of infection; one patient died of PTLD on day +140. Four patients relasped and 3 died of relapse. Fifteen out of 16 alive patients are in hematologic or molecular remission at a median follow up of 7.5 months (range 2–17). From day +30 full donor chimerism was documented in CD3, bone marrow cells and progenitor cells from both the injected and in non-injected SPIC; from day +30, CFC progenitors had already reached the lower values of the range of normal individuals in bilateral sites. These findings document the colonization of the hematopoietc system and the recovery of stem cell reservoir possibly due to an improvement of seeding efficiency. Only 3 pts (8%) experienced acute GvHD (2 grade II and 1 grade I); 4 pts. have moderate chronic GVHD. It is known that lymphocyte trafficking is one of the crucial factor in immunity. Two combined factors might contribute to the low incidence of acute GvHD:

• few of the transplanted T cells do not reach/circulate primarily in the lymphatic organs, where they would be immediately confronted with host antigen presenting cells as probably occurs after i.v. injection;

• injected T cells come immediately in contact with mesenchymal stem cells (MSC) and osteoblasts, known to be potent immunosuppressants.

Conclusion. Direct intra-bone transplant of CB cells overcomes the problem of graft failure and is associated with reduced incidence of acute GvHD even when low numbers of HLA mismatched CB cells are transplanted. Nearly all patients searching for a CB unit were able to undergo CBT. This approach may change our policy of hemopoietic cell transplants.