Hematopoietic Chimerism LEVELS ARE RELATED to RELAPSE and GRAFT VERSUS Host DISEASE IN REDUCED INTENSITY Allogeneic STEM CELL Transplantion

The allogeneic hematopoietic stem cell transplantation remains the only curative option for certain hematological malignancies. The use of reduced intensity conditioning (RIC) has diminished the transplant-related mortality, making it possible to consider this therapeutic option in elderly patients with associated morbidity. The graft versus host disease (GVHD) is a late-onset complication in this type of transplant which still remains one of the major causes of morbidity and mortality.

Hematopoietic chimerism (HQ) levels related to relapse or GVHD in RIC allogeneic transplantation (allo-RIC) have not been established. We have studied the relationship between HQ and the incidence of GVHD and relapse, using real time-PCR for chimerism quantification.

We evaluated 16 patients with hematological malignancies (11 AML, 3 ALL, 1 CLL, 1 plasma cell leukemia) undergoing allo-RIC in the last three years. The median follow up of this series was 310 days (range 86–958 days), with a median age of 53 years (range 26–64). A sibling donor was found in 11 cases (69%) and fourteen donors (88%) were HLA identical. Bone marrow was the source of progenitors in 12 cases, peripheral blood in 3 and umbilical cord in one.

The conditioning regimen was: fludarabine + busulphan (44%), fludarabine + busulphan + timoglobulin (23%), fludarabine + melphalan (13%) and others (21%).

GVHD prophylaxis was performed with cyclosporine A (CsA) + methotrexate (44%), CsA + mycophenolate (31%) and tacrolimus + syrolimus (19%).

The HQ was studied in peripheral blood DNA at the time of granulocyte engraftment, and later 30, 45 and 60 days after stem cells infusion. Chimerism was expressed as a percentage of residual host cells. Quantitative real-time PCR amplification of null alleles or insertion/deletion polymorphisms was used for HQ analysis (Jimenez et al, 2005; Leukemia 2005; 19:336-43). Chimerism was expressed as a percentage of residual host cells.

Chi-square test was employed to evaluate qLas variables cualitativas se analizaron mediante chi-cuadrado y se usaron test no paramétricos para las cuantitativas. ualitative variables and non-parametric tests for quantitative variables. El análisis multivariante fue realizado mediante regresión de Cox. The Kaplan-Meier model with log-rank test comparisons were applied for survival analysis.

The median time of engraftment was 16 days (12-27) for granulocytes and 18 days (10-69) for platelets.

Ten patients (63%) developed acute GVHD (aGVHD), eight of them Grade II-IV. The incidence of late-onset aGVHD was 38%, with a mean time to appearance of 117 days (90-190). Six patients (38%) developed chronic GVHD (cGVHD), and in four cases a previous late-onset aGVHD had been recorded.

In our series, disease relapse was observed in 6 patients (37.5%), whereas 7 patients died (3 infections, 2 progressive disease, 1 aGVHD and one bleeding).

No relapse was found in the group of patient who developed cGVHD compared with 60% relapses in those without cGVHD (Fisher's exact test, p = 0.026). However, overall survival did not differ significantly in both groups.

Median HQ at the time of granulocyte engraftment was 2,65% (0.07 to 55), on day +30 was 1.4% (0.01-12), on day +45 was 1.0% (0.01-9) and on day +60 1.7% (0.01-15). HQ showed significantly lower levels in those patients who did not relapsed either on day +30 (0.4% vs 4.0%, p= 0.016), on day +45 (0.35% vs 5.5%, p= 0.04), and on day +60 (0.4% vs 4.5%, p= 0.04). With respect to cGVHD, we observed a trend to lower HQ levels in those patients who developed cGVHD compared with those who did not develop it on day +30 (0.25% vs 1.9%, p= 0.056) and +45 (0.26% vs 1.7%, p= 0.066), but these results were at the limit of statistical significance.

Our data show that HQ levels may help us to identify a group of patients whith higher risk of relapse also in allo-RIC. The monitoring of HQ may also be useful to predict patients who will develop cGVHD after SCT.

No relevant conflicts of interest to declare.