Reduced intensinty conditioning allows performing allogeneic hematopoietic transplantation in patients with contraindication for a high-dose procedure. Since the introduction of this technique, the upper age limit for allogeneic transplantation has increased from 50 years old in 1995 to 70 years old in 2006. Additionally, patients with co-morbidities may be transplanted after mild preparative regimens. The prognosis of second transplants may also improve by administering attenuated conditioning.
The rationale for performing RIC transplant is double. On one hand, it is now clear that very high doses of chemotherapy and/or radiation are not required for donor cells engraftment. On the other hand, it is well known that graft vs tumor effect mediated by immune-competent cells in the graft is the most important mechanism to eradicate cancer with hematopoietic transplantation.
In RIC transplants there is a transient coexistence of donor and recipient lympho-hematopoiesis, a circumstance called mixed chimera. Spontaneously, or after donor lymphocyte infusions, this situation evolves to a full chimera from donor cells. Is in this status when graft versus host disease and graft versus tumor effect are more manifest. The anti-tumor activity is clinically relevant if graft versus tumor effect sustains during weeks or months as the consequence to the development of chronic graft versus host disease. Many experiences indicate that chronic GVHD decreases the relapse rate and increases survival after RIC transplantation. For this reason, patients transplanted for acute or uncontrolled disease are less likely to benefit from this procedure, since early tumor progression makes unfeasible the chronic antineoplastic effect of the graft. In consequence, the results of RIC transplantation are best in patients with relatively indolent diseases such as low-grade lymphomas, chronic lymphocytic leukemia or multiple myeloma.
Results of RIC transplants in 187 patients from the Hospital de la Santa Creu i Sant Pau, and data from the Spanish, European and International Transplant Groups will be presented.