**6. Conclusions**

NK cells have a crucial role in immunosurveillance against tumor development. However, when both the innate and adaptive immune systems fail and tumors develop, NK cells and their receptors can still be targeted in many therapeutic approaches. NK cells are more effective in treating hematologic malignancies than in treating solid tumors. This might result from inefficient homing of NK cells to the site of tumor. Therefore, NK cell-based immunotherapy can be successfully exploited in the hematopoietic stem cell transplantation for the treatment of hematological malignancies, but efforts have to be made to improve the homing and in vivo persistence of NK cells. Targeting CSCs with NK cell-based immunotherapy represents an attractive strategy for cancer therapy.

NK cells clearly have a role in future immunotherapies of the treatment of cancer and should continue to be evaluated in clinical trials.

## **Author details**

Lynda Addou-Klouche Address all correspondence to: addouklouche.lynda@yahoo.fr University of Sidi-Bel-Abbes, Algeria
